Cosa tiene assieme il nucleo? E cosa lo fa decadere?

Cosa tiene assieme il nucleo? E cosa lo fa

decadere?

E.P. prova ad andare al nocciolo della faccenda

(terza lezione del corso di Fisica Superiore TFA 2012-2013)

I costituenti del nucleo atomico: il protone

Citation: J. Beringer et al. (Particle Data Group), PR D86, 010001 (2012) (URL: http://pdg.lbl.gov)

p ^{I (JP ) = 1} 2 ( ¹ ₂ +) Status: ∗ ∗∗∗

p MASS (atomic mass units u) p MASS (atomic mass units u) p MASS (atomic mass units u) p MASS (atomic mass units u)

The mass is known much more precisely in u (atomic mass units) than in MeV. See the next data block.

VALUE (u) DOCUMENT ID TECN COMMENT

1.007276466812± 0.000000000090

1.007276466812± 0.000000000090 1.007276466812± 0.000000000090 1.007276466812± 0.000000000090 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.00727646677 ± 0.00000000010 MOHR 08 RVUE 2006 CODATA value 1.00727646688 ± 0.00000000013 MOHR 05 RVUE 2002 CODATA value 1.00727646688 ± 0.00000000013 MOHR 99 RVUE 1998 CODATA value 1.007276470 ± 0.000000012 COHEN 87 RVUE 1986 CODATA value

p MASS (MeV) p MASS (MeV) p MASS (MeV) p MASS (MeV)

The mass is known much more precisely in u (atomic mass units) than in MeV. The conversion from u to MeV, 1 u = 931.494 061(21) MeV/c2 (MOHR 12, the 2010 CODATA value), involves the relatively poorly known electronic charge.

VALUE (MeV) DOCUMENT ID TECN COMMENT

938.272046± 0.000021

938.272046± 0.000021 938.272046± 0.000021 938.272046± 0.000021 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

938.272013± 0.000023 MOHR 08 RVUE 2006 CODATA value 938.272029± 0.000080 MOHR 05 RVUE 2002 CODATA value 938.271998± 0.000038 MOHR 99 RVUE 1998 CODATA value 938.27231 ± 0.00028 COHEN 87 RVUE 1986 CODATA value

938.2796 ± 0.0027 COHEN 73 RVUE 1973 CODATA value

!

! m _p −m p

!

! /m _p

!

! m _p −m p

!

! /m _p

!

! m _p −m p

!

! /m _p

!

! m _p −m p

!

! /m _p

A test of CPT invariance. Note that the comparison of the p and p charge- to-mass ratio, given in the next data block, is much better determined.

VALUE CL% DOCUMENT ID TECN COMMENT

<2 × 10−9

<2 <2 <2 × × × 10−9 10−9 10−9 90 1 HORI 06 SPEC p e−He atom

• • • We do not use the following data for averages, fits, limits, etc. • • •

<1.0 × 10−8 90 1 HORI 03 SPEC p e− 4He, p e− 3He

<6 × 10−8 90 1 HORI 01 SPEC p e−He atom

<5 × 10−7 2 TORII 99 SPEC p e−He atom

1 HORI 01, HORI 03, and HORI 06 use the more-precisely-known constraint on the p charge-to-mass ratio of GABRIELSE 99 (see below) to get their results. Their results are not independent of the HORI 01, HORI 03, and HORI 06 values for !

! qp+qp !

! /e, below.

2 TORII 99 uses the more-precisely-known constraint on the p charge-to-mass ratio of GABRIELSE 95 (see below) to get this result. This is not independent of the TORII 99 value for !

! qp+qp !

!/e, below.

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Citation: J. Beringer et al. (Particle Data Group), PR D86, 010001 (2012) (URL: http://pdg.lbl.gov)

p ^{I (JP ) = 1} 2 ( ¹ ₂ +) Status: ∗ ∗∗∗

p MASS (atomic mass units u) p MASS (atomic mass units u) p MASS (atomic mass units u) p MASS (atomic mass units u)

The mass is known much more precisely in u (atomic mass units) than in MeV. See the next data block.

VALUE (u) DOCUMENT ID TECN COMMENT

1.007276466812± 0.000000000090

1.007276466812± 0.000000000090 1.007276466812± 0.000000000090 1.007276466812± 0.000000000090 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.00727646677 ± 0.00000000010 MOHR 08 RVUE 2006 CODATA value 1.00727646688 ± 0.00000000013 MOHR 05 RVUE 2002 CODATA value 1.00727646688 ± 0.00000000013 MOHR 99 RVUE 1998 CODATA value 1.007276470 ± 0.000000012 COHEN 87 RVUE 1986 CODATA value

p MASS (MeV) p MASS (MeV) p MASS (MeV) p MASS (MeV)

The mass is known much more precisely in u (atomic mass units) than in MeV. The conversion from u to MeV, 1 u = 931.494 061(21) MeV/c2 (MOHR 12, the 2010 CODATA value), involves the relatively poorly known electronic charge.

VALUE (MeV) DOCUMENT ID TECN COMMENT

938.272046± 0.000021

938.272046± 0.000021 938.272046± 0.000021 938.272046± 0.000021 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

938.272013± 0.000023 MOHR 08 RVUE 2006 CODATA value 938.272029± 0.000080 MOHR 05 RVUE 2002 CODATA value 938.271998± 0.000038 MOHR 99 RVUE 1998 CODATA value 938.27231 ± 0.00028 COHEN 87 RVUE 1986 CODATA value

938.2796 ± 0.0027 COHEN 73 RVUE 1973 CODATA value

! !m _p −m p

!

! /m _p

! !m _p −m p

!

! /m _p

! !m _p −m p

!

! /m _p

! !m _p −m p

!

! /m _p

A test of CPT invariance. Note that the comparison of the p and p charge- to-mass ratio, given in the next data block, is much better determined.

VALUE CL% DOCUMENT ID TECN COMMENT

<2 × 10−9

<2 <2 <2 × × × 10−9 10−9 10−9 90 1 HORI 06 SPEC p e−He atom

• • • We do not use the following data for averages, fits, limits, etc. • • •

<1.0 × 10−8 90 1 HORI 03 SPEC p e− 4 He, p e− 3He

<6 × 10−8 90 1 HORI 01 SPEC p e−He atom

<5 × 10−7 2 TORII 99 SPEC p e−He atom

1 HORI 01, HORI 03, and HORI 06 use the more-precisely-known constraint on the p charge-to-mass ratio of GABRIELSE 99 (see below) to get their results. Their results are not independent of the HORI 01, HORI 03, and HORI 06 values for !

! qp+qp !

! /e, below.

2 TORII 99 uses the more-precisely-known constraint on the p charge-to-mass ratio of GABRIELSE 95 (see below) to get this result. This is not independent of the TORII 99 value for !

! qp+qp !

! /e, below.

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Citation: J. Beringer et al. (Particle Data Group), PR D86, 010001 (2012) (URL: http://pdg.lbl.gov)

! !q _p + q _e !

!"e

! !q _p + q _e !

!"e

! !q _p + q _e !

!"e

! !q _p + q _e !

!"e

See BRESSI 11 for a summary of experiments on the neutrality of matter.

See also “n CHARGE” in the neutron Listings.

VALUE DOCUMENT ID COMMENT

<1 × 10−21

<1 <1 <1 × × × 10−21 10−21 10−21 8 BRESSI 11 Neutrality of SF6

• • • We do not use the following data for averages, fits, limits, etc. • • •

<3.2 × 10−20 9 SENGUPTA 00 binary pulsar

<0.8 × 10−21 MARINELLI 84 Magnetic levitation

<1.0 × 10−21 8 DYLLA 73 Neutrality of SF6

8 BRESSI 11 uses the method of DYLLA 73 but finds serious errors in that experiment that greatly reduce its accuracy. The BRESSI 11 limit assumes that n → p e− νe conserves charge. Thus the limit applies equally to the charge of the neutron.

9 SENGUPTA 00 uses the difference between the observed rate of of rotational energy loss by the binary pulsar PSR B1913+16 and the rate predicted by general relativity to set this limit. See the paper for assumptions.

p MAGNETIC MOMENT p MAGNETIC MOMENT p MAGNETIC MOMENT p MAGNETIC MOMENT

See the “Note on Baryon Magnetic Moments” in the Λ Listings.

VALUE (µ _N ) DOCUMENT ID TECN COMMENT

2.792847356± 0.000000023

2.792847356± 0.000000023 2.792847356± 0.000000023 2.792847356± 0.000000023 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

2.792847356± 0.000000023 MOHR 08 RVUE 2006 CODATA value 2.792847351± 0.000000028 MOHR 05 RVUE 2002 CODATA value 2.792847337± 0.000000029 MOHR 99 RVUE 1998 CODATA value 2.792847386± 0.000000063 COHEN 87 RVUE 1986 CODATA value 2.7928456 ± 0.0000011 COHEN 73 RVUE 1973 CODATA value

p MAGNETIC MOMENT p MAGNETIC MOMENT p MAGNETIC MOMENT p MAGNETIC MOMENT

A few early results have been omitted.

VALUE (µ _N ) DOCUMENT ID TECN COMMENT

− 2.793 ± 0.006 OUR AVERAGE

− − − 2.793 ± 0.006 OUR AVERAGE 2.793 ± 0.006 OUR AVERAGE 2.793 ± 0.006 OUR AVERAGE

− 2.7862± 0.0083 PASK 09 CNTR p He+ hyperfine structure

− 2.8005± 0.0090 KREISSL 88 CNTR p 208Pb 11→ 10 X-ray

− 2.817 ± 0.048 ROBERTS 78 CNTR

− 2.791 ± 0.021 HU 75 CNTR Exotic atoms

(µ _p + µ _p ) " µ _p (µ (µ (µ _{p p p} + µ + µ + µ _{p p p} ) ) ) " µ " µ " µ _{p p p}

A test of CPT invariance. Calculated from the p and p magnetic moments, above.

VALUE DOCUMENT ID

(− 0.1± 2.1) × 10−3 OUR EVALUATION (− 0.1± 2.1) × 10−3 OUR EVALUATION (− 0.1± 2.1) × 10−3 OUR EVALUATION (− 0.1± 2.1) × 10−3 OUR EVALUATION

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Citation: J. Beringer et al. (Particle Data Group), PR D86, 010001 (2012) (URL: http://pdg.lbl.gov)

17 BARANOV 01 combines the results of 10 experiments from 1958 through 1995 to get a global average that takes into account both systematic and model errors and does not use the theoretical constraint on the sum αp + βp.

18 FEDERSPIEL 91 obtains for the (static) electric polarizability α p , defined in terms of the induced electric dipole moment by D D D D = 4π$0αpEEEE, the value (7.0±2.2±1.3)×10 − 4 fm3.

p MAGNETIC POLARIZABILITY β _p p MAGNETIC POLARIZABILITY β p MAGNETIC POLARIZABILITY β p MAGNETIC POLARIZABILITY β _{p p p}

The electric and magnetic polarizabilities are subject to a dispersion sum- rule constraint α + β = (14.2 ± 0.5) × 10−4 fm3. Errors here are anticorrelated with those on αp due to this constraint.

VALUE (10−4 fm3) DOCUMENT ID TECN COMMENT

1.9 ± 0.5 OUR AVERAGE 1.9 ± 0.5 OUR AVERAGE 1.9 ± 0.5 OUR AVERAGE 1.9 ± 0.5 OUR AVERAGE

3.4 ± 1.1 ± 0.1 19 BEANE 03 EFT + γ p

1.43± 0.98 + 0.52 −0.98 20 BLANPIED 01 LEGS p(&γ,γ), p(&γ,π0), p(&γ,π+) 1.2 ± 0.7 ± 0.5 21 OLMOSDEL... 01 CNTR γ p Compton scattering 2.1 ± 0.8 ± 0.5 22 MACGIBBON 95 RVUE global average

• • • We do not use the following data for averages, fits, limits, etc. • • • 2.3 ± 0.9 ± 0.7 23 BARANOV 01 RVUE Global average

1.7 ± 0.6 ± 0.9 MACGIBBON 95 CNTR γ p Compton scattering 4.4 ± 0.4 ± 1.1 HALLIN 93 CNTR γ p Compton scattering 3.58+ 1.19 −1.25 + 1.03

−1.07 ZIEGER 92 CNTR γ p Compton scattering 3.3 ± 2.2 ± 1.3 FEDERSPIEL 91 CNTR γ p Compton scattering

19 BEANE 03 uses effective field theory and low-energy γ p and γ d Compton-scattering data. It also gets for the isoscalar polarizabilities (see the erratum) αN = (13.0 ± 1.9+ 3.9 −1.5) × 10−4 fm3 and βN = (−1.8 ± 1.9 + 2.1

− 0.9) × 10−4 fm3.

20 BLANPIED 01 gives α p + βp and αp − βp. The separate αp and βp are provided to us by A. Sandorfi. The first error above is statistics plus systematics; the second is from the model.

21 This OLMOSDELEON 01 result uses the TAPS data alone, and does not use the (re- evaluated) sum-rule constraint that α + β= (13.8 ± 0.4) × 10−4 fm3. See the paper for a discussion.

22 MACGIBBON 95 combine the results of ZIEGER 92, FEDERSPIEL 91, and their own experiment to get a “global average” in which model errors and systematic errors are treated in a consistent way. See MACGIBBON 95 for a discussion.

23 BARANOV 01 combines the results of 10 experiments from 1958 through 1995 to get a global average that takes into account both systematic and model errors and does not use the theoretical constraint on the sum αp + βp.

p CHARGE RADIUS p CHARGE RADIUS p CHARGE RADIUS p CHARGE RADIUS

This is the rms electric charge radius, !

"r2 E #.

Most measurements of the radius of the proton involve electron-proton interactions, and most of the more recent values agree with one another.

The most precise of these is rp = 0.879(8) fm (BERNAUER 10). The CODATA 10 value (MOHR 12), obtained from the electronic results, is 0.8775(51). However, a measurement using muonic hydrogen finds rp

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Citation: J. Beringer et al. (Particle Data Group), PR D86, 010001 (2012) (URL: http://pdg.lbl.gov)

= 0.84184(67) fm (POHL 10), which is eight times more precise and seven standard deviations (using the CODATA 10 error) from the electronic results.

Since POHL 10, there has been a lot of discussion about the disagree- ment, especially concerning the modeling of muonic hydrogen. Here is an incomplete list of papers: DERUJULA 10, CLOET 11, DISTLER 11, DERUJULA 11, ARRINGTON 11, BERNAUER 11, and HILL 11.

Until the difference between the e p and µ p values is understood, it does not make much sense to average all the values together. For the present, we stick with the less precise (and provisionally suspect) CODATA 2010 value (MOHR 12). It is up to workers in this field to solve this puzzle.

VALUE (fm) DOCUMENT ID TECN COMMENT

0.8775 ± 0.0051

0.8775 ± 0.0051 0.8775 ± 0.0051 0.8775 ± 0.0051 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

0.879 ± 0.005 ± 0.006 BERNAUER 10 SPEC e p → e p form factor 0.912 ± 0.009 ± 0.007 BORISYUK 10 reanalyzes old e p data 0.871 ± 0.009 ± 0.003 HILL 10 z-expansion reanalysis 0.84184± 0.00036 ± 0.00056 POHL 10 µ p-atom Lamb shift

0.8768 ± 0.0069 MOHR 08 RVUE 2006 CODATA value

0.844 + 0.008

− 0.004 BELUSHKIN 07 Dispersion analysis

0.897 ± 0.018 BLUNDEN 05 SICK 03 + 2γ correction

0.8750 ± 0.0068 MOHR 05 RVUE 2002 CODATA value

0.895 ± 0.010 ± 0.013 SICK 03 e p → e p reanalysis 0.830 ± 0.040 ± 0.040 24 ESCHRICH 01 e p → e p

0.883 ± 0.014 MELNIKOV 00 1S Lamb Shift in H

0.880 ± 0.015 ROSENFELDR... 00 e p + Coul. corrections

0.847 ± 0.008 MERGELL 96 e p + disp. relations

0.877 ± 0.024 WONG 94 reanalysis of Mainz e p

data

0.865 ± 0.020 MCCORD 91 e p → e p

0.862 ± 0.012 SIMON 80 e p → e p

0.880 ± 0.030 BORKOWSKI 74 e p → e p

0.810 ± 0.020 AKIMOV 72 e p → e p

0.800 ± 0.025 FREREJACQ... 66 e p → e p (CH2 tgt.)

0.805 ± 0.011 HAND 63 e p → e p

24 ESCHRICH 01 actually gives !r2" = (0.69 ± 0.06 ± 0.06) fm2.

p MAGNETIC RADIUS p MAGNETIC RADIUS p MAGNETIC RADIUS p MAGNETIC RADIUS

This is the rms magnetic radius,

# !r2 M ".

VALUE (fm) DOCUMENT ID TECN COMMENT

0.777± 0.013 ± 0.010

0.777± 0.013 ± 0.010 0.777± 0.013 ± 0.010 0.777± 0.013 ± 0.010 BERNAUER 10 SPEC e p → e p form factor

• • • We do not use the following data for averages, fits, limits, etc. • • •

0.876± 0.010 ± 0.016 BORISYUK 10 reanalyzes old e p → e p data

0.854± 0.005 BELUSHKIN 07 Dispersion analysis

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= 0.84184(67) fm (POHL 10), which is eight times more precise and seven standard deviations (using the CODATA 10 error) from the electronic results.

Since POHL 10, there has been a lot of discussion about the disagree- ment, especially concerning the modeling of muonic hydrogen. Here is an incomplete list of papers: DERUJULA 10, CLOET 11, DISTLER 11, DERUJULA 11, ARRINGTON 11, BERNAUER 11, and HILL 11.

Until the difference between the e p and µ p values is understood, it does not make much sense to average all the values together. For the present, we stick with the less precise (and provisionally suspect) CODATA 2010 value (MOHR 12). It is up to workers in this field to solve this puzzle.

VALUE (fm) DOCUMENT ID TECN COMMENT

0.8775 ± 0.0051

0.8775 ± 0.0051 0.8775 ± 0.0051 0.8775 ± 0.0051 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

0.879 ± 0.005 ± 0.006 BERNAUER 10 SPEC e p → e p form factor 0.912 ± 0.009 ± 0.007 BORISYUK 10 reanalyzes old e p data 0.871 ± 0.009 ± 0.003 HILL 10 z-expansion reanalysis 0.84184± 0.00036 ± 0.00056 POHL 10 µ p-atom Lamb shift

0.8768 ± 0.0069 MOHR 08 RVUE 2006 CODATA value

0.844 + 0.008

− 0.004 BELUSHKIN 07 Dispersion analysis

0.897 ± 0.018 BLUNDEN 05 SICK 03 + 2γ correction

0.8750 ± 0.0068 MOHR 05 RVUE 2002 CODATA value

0.895 ± 0.010 ± 0.013 SICK 03 e p → e p reanalysis 0.830 ± 0.040 ± 0.040 24 ESCHRICH 01 e p → e p

0.883 ± 0.014 MELNIKOV 00 1S Lamb Shift in H

0.880 ± 0.015 ROSENFELDR... 00 e p + Coul. corrections

0.847 ± 0.008 MERGELL 96 e p + disp. relations

0.877 ± 0.024 WONG 94 reanalysis of Mainz e p

data

0.865 ± 0.020 MCCORD 91 e p → e p

0.862 ± 0.012 SIMON 80 e p → e p

0.880 ± 0.030 BORKOWSKI 74 e p → e p

0.810 ± 0.020 AKIMOV 72 e p → e p

0.800 ± 0.025 FREREJACQ... 66 e p → e p (CH2 tgt.)

0.805 ± 0.011 HAND 63 e p → e p

24 ESCHRICH 01 actually gives !r2" = (0.69 ± 0.06 ± 0.06) fm2.

p MAGNETIC RADIUS p MAGNETIC RADIUS p MAGNETIC RADIUS p MAGNETIC RADIUS

This is the rms magnetic radius, #

!r2 M ".

VALUE (fm) DOCUMENT ID TECN COMMENT

0.777± 0.013 ± 0.010

0.777± 0.013 ± 0.010 0.777± 0.013 ± 0.010 0.777± 0.013 ± 0.010 BERNAUER 10 SPEC e p → e p form factor

• • • We do not use the following data for averages, fits, limits, etc. • • •

0.876± 0.010 ± 0.016 BORISYUK 10 reanalyzes old e p → e p data

0.854± 0.005 BELUSHKIN 07 Dispersion analysis

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p MEAN LIFE p MEAN LIFE p MEAN LIFE p MEAN LIFE

A test of baryon conservation. See the “p Partial Mean Lives” section below for limits for identified final states. The limits here are to “anything” or are for “disappearance”

modes of a bound proton (p) or (n). See also the 3ν modes in the “Partial Mean Lives” section. Table 1 of BACK 03 is a nice summary.

LIMIT

(years) PARTICLE CL% DOCUMENT ID TECN COMMENT

>5.8 × 1029

>5.8 × 1029 >5.8 × 1029 >5.8 × 1029 n n n n 90 25 ARAKI 06 KLND n → invisible

>2.1 × 1029

>2.1 × 1029 >2.1 × 1029 >2.1 × 1029 p p p p 90 26 AHMED 04 SNO p → invisible

• • • We do not use the following data for averages, fits, limits, etc. • • •

>1.9 × 1029 n 90 26 AHMED 04 SNO n → invisible

>1.8 × 1025 n 90 27 BACK 03 BORX

>1.1 × 1026 p 90 27 BACK 03 BORX

>3.5 × 1028 p 90 28 ZDESENKO 03 p → invisible

>1 × 1028 p 90 29 AHMAD 02 SNO p → invisible

>4 × 1023 p 95 TRETYAK 01 d → n + ?

>1.9 × 1024 p 90 30 BERNABEI 00 B DAMA

>1.6 × 1025 p, n 31,32 EVANS 77

>3 × 1023 p 32 DIX 70 CNTR

>3 × 1023 p, n 32,33 FLEROV 58

25 ARAKI 06 looks for signs of de-excitation of the residual nucleus after disappearance of a neutron from the s shell of 12C.

26 AHMED 04 looks for γ rays from the de-excitation of a residual 15O∗ or 15N∗ following the disappearance of a neutron or proton in 16O.

27 BACK 03 looks for decays of unstable nuclides left after N decays of parent 12C, 13C, 16O nuclei. These are “invisible channel” limits.

28 ZDESENKO 03 gets this limit on proton disappearance in deuterium by analyzing SNO data in AHMAD 02.

29 AHMAD 02 (see its footnote 7) looks for neutrons left behind after the disappearance of the proton in deuterons.

30 BERNABEI 00 B looks for the decay of a 128 53 I nucleus following the disappearance of a proton in the otherwise-stable 129 54 Xe nucleus.

31 EVANS 77 looks for the daughter nuclide 129Xe from possible 130Te decays in ancient Te ore samples.

32 This mean-life limit has been obtained from a half-life limit by dividing the latter by ln(2)

= 0.693.

33 FLEROV 58 looks for the spontaneous fission of a 232Th nucleus after the disappearance of one of its nucleons.

p MEAN LIFE p MEAN LIFE p MEAN LIFE p MEAN LIFE

Of the two astrophysical limits here, that of GEER 00 D involves consider- ably more refinements in its modeling. The other limits come from direct observations of stored antiprotons. See also “p Partial Mean Lives” after

“p Partial Mean Lives,” below, for exclusive-mode limits. The best (life- time/branching fraction) limit there is 7 × 105 years, for p → e− γ. We advance only the exclusive-mode limits to our Summary Tables.

LIMIT

(years) CL% EVTS DOCUMENT ID TECN COMMENT

• • • We do not use the following data for averages, fits, limits, etc. • • •

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1 u = 1.660... 10 ^-27 kg 1 eV = ~ 1.6 10 ^-16 J

1 GeV / c ² = ~ 1.8 10 ^-27 kg

1 fm = 10 ^-15 m

1 µ N = ~ 3.15 10 ^-8 eV/T

I costituenti del nucleo atomico: il neutrone

Citation: J. Beringer et al. (Particle Data Group), PR D86 , 010001 (2012) (URL: http://pdg.lbl.gov)

n ^{I (JP ) = 1 2 ( 1 2 +) Status:} ∗ ∗∗∗

We have omitted some results that have been superseded by later experiments. See our earlier editions.

Anyone interested in the neutron should look at these two new review articles: D. Dubbers and M.G. Schmidt, ”The neutron and its role in cosmology and particle physics,” Reviews of Modern Physics 83 83 83 83 1111 (2011); and F.E. Wietfeldt and G.L. Greene, ”The neutron lifetime,” Reviews of Modern Physics 83 83 83 83 1173 (2011).

n MASS (atomic mass units u) n MASS (atomic mass units u) n MASS (atomic mass units u) n MASS (atomic mass units u)

The mass is known much more precisely in u (atomic mass units) than in MeV. See the next data block.

VALUE (u) DOCUMENT ID TECN COMMENT

1.00866491600± 0.00000000043

1.00866491600± 0.00000000043 1.00866491600± 0.00000000043 1.00866491600± 0.00000000043 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.00866491597± 0.00000000043 MOHR 08 RVUE 2006 CODATA value 1.00866491560± 0.00000000055 MOHR 05 RVUE 2002 CODATA value 1.00866491578± 0.00000000055 MOHR 99 RVUE 1998 CODATA value 1.008665904 ± 0.000000014 COHEN 87 RVUE 1986 CODATA value

n MASS (MeV) n MASS (MeV) n MASS (MeV) n MASS (MeV)

The mass is known much more precisely in u (atomic mass units) than in MeV. The conversion from u to MeV, 1 u = 931.494 061(21) MeV/c2 (MOHR 12, the 2010 CODATA value), involves the relatively poorly known electronic charge.

VALUE (MeV) DOCUMENT ID TECN COMMENT

939.565379± 0.000021

939.565379± 0.000021 939.565379± 0.000021 939.565379± 0.000021 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

939.565346± 0.000023 MOHR 08 RVUE 2006 CODATA value

939.565360± 0.000081 MOHR 05 RVUE 2002 CODATA value

939.565331± 0.000037 1 KESSLER 99 SPEC n p → d γ

939.565330± 0.000038 MOHR 99 RVUE 1998 CODATA value

939.56565 ± 0.00028 2,3 DIFILIPPO 94 TRAP Penning trap

939.56563 ± 0.00028 COHEN 87 RVUE 1986 CODATA value

939.56564 ± 0.00028 3,4 GREENE 86 SPEC n p → d γ

939.5731 ± 0.0027 3 COHEN 73 RVUE 1973 CODATA value

1 We use the 1998 CODATA u-to-MeV conversion factor (see the heading above) to get this mass in MeV from the much more precisely measured KESSLER 99 value of 1.00866491637 ± 0.00000000082 u.

2 The mass is known much more precisely in u: m = 1.0086649235 ± 0.0000000023 u.

We use the 1986 CODATA conversion factor to get the mass in MeV.

3 These determinations are not independent of the m n − mp measurements below.

4 The mass is known much more precisely in u: m = 1.008664919 ± 0.000000014 u.

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n ^{I (JP ) = 1 2 ( 1 2 +) Status:} ∗ ∗∗∗

We have omitted some results that have been superseded by later experiments. See our earlier editions.

Anyone interested in the neutron should look at these two new review articles: D. Dubbers and M.G. Schmidt, ”The neutron and its role in cosmology and particle physics,” Reviews of Modern Physics 83 83 83 83 1111 (2011); and F.E. Wietfeldt and G.L. Greene, ”The neutron lifetime,” Reviews of Modern Physics 83 83 83 83 1173 (2011).

n MASS (atomic mass units u) n MASS (atomic mass units u) n MASS (atomic mass units u) n MASS (atomic mass units u)

The mass is known much more precisely in u (atomic mass units) than in MeV. See the next data block.

VALUE (u) DOCUMENT ID TECN COMMENT

1.00866491600± 0.00000000043

1.00866491600± 0.00000000043 1.00866491600± 0.00000000043 1.00866491600± 0.00000000043 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.00866491597± 0.00000000043 MOHR 08 RVUE 2006 CODATA value 1.00866491560± 0.00000000055 MOHR 05 RVUE 2002 CODATA value 1.00866491578± 0.00000000055 MOHR 99 RVUE 1998 CODATA value 1.008665904 ± 0.000000014 COHEN 87 RVUE 1986 CODATA value

n MASS (MeV) n MASS (MeV) n MASS (MeV) n MASS (MeV)

The mass is known much more precisely in u (atomic mass units) than in MeV. The conversion from u to MeV, 1 u = 931.494 061(21) MeV/c2 (MOHR 12, the 2010 CODATA value), involves the relatively poorly known electronic charge.

VALUE (MeV) DOCUMENT ID TECN COMMENT

939.565379± 0.000021

939.565379± 0.000021 939.565379± 0.000021 939.565379± 0.000021 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

939.565346± 0.000023 MOHR 08 RVUE 2006 CODATA value

939.565360± 0.000081 MOHR 05 RVUE 2002 CODATA value

939.565331± 0.000037 1 KESSLER 99 SPEC n p → d γ

939.565330± 0.000038 MOHR 99 RVUE 1998 CODATA value

939.56565 ± 0.00028 2,3 DIFILIPPO 94 TRAP Penning trap

939.56563 ± 0.00028 COHEN 87 RVUE 1986 CODATA value

939.56564 ± 0.00028 3,4 GREENE 86 SPEC n p → d γ

939.5731 ± 0.0027 3 COHEN 73 RVUE 1973 CODATA value

1 We use the 1998 CODATA u-to-MeV conversion factor (see the heading above) to get this mass in MeV from the much more precisely measured KESSLER 99 value of 1.00866491637 ± 0.00000000082 u.

2 The mass is known much more precisely in u: m = 1.0086649235 ± 0.0000000023 u.

We use the 1986 CODATA conversion factor to get the mass in MeV.

3 These determinations are not independent of the m n − mp measurements below.

4 The mass is known much more precisely in u: m = 1.008664919 ± 0.000000014 u.

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n MASS n MASS n MASS n MASS

VALUE (MeV) EVTS DOCUMENT ID TECN COMMENT

939.485± 0.051

939.485± 0.051 939.485± 0.051 939.485± 0.051 59 5 CRESTI 86 HBC p p → n n

5 This is a corrected result (see the erratum). The error is statistical. The maximum systematic error is 0.029 MeV.

(m _n − m n )/ m _n (m (m (m _{n n n} − m − m − m n n n )/ m )/ m )/ m _{n n n}

A test of CPT invariance. Calculated from the n and n masses, above.

VALUE DOCUMENT ID

(9± 6) × 10−5 OUR EVALUATION (9± 6) × 10−5 OUR EVALUATION (9± 6) × 10−5 OUR EVALUATION (9± 6) × 10−5 OUR EVALUATION

m _n − m p

m m m _{n n n} − m − m − m p p p

VALUE (MeV) DOCUMENT ID TECN COMMENT

1.29333217± 0.00000042

1.29333217± 0.00000042 1.29333217± 0.00000042 1.29333217± 0.00000042 6 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.29333214± 0.00000043 7 MOHR 08 RVUE 2006 CODATA value 1.2933317 ± 0.0000005 8 MOHR 05 RVUE 2002 CODATA value 1.2933318 ± 0.0000005 9 MOHR 99 RVUE 1998 CODATA value 1.293318 ± 0.000009 10 COHEN 87 RVUE 1986 CODATA value 1.2933328 ± 0.0000072 GREENE 86 SPEC n p → d γ

1.293429 ± 0.000036 COHEN 73 RVUE 1973 CODATA value

6 The 2010 CODATA mass difference in u is m n − mp = 1.388 449 19(45) × 10 − 3u.

7 Calculated by us from the MOHR 08 ratio m n/mp = 1.00137841918(46). In u, mn − mp = 1.38844920(46) × 10 − 3 u.

8 Calculated by us from the MOHR 05 ratio m n/mp = 1.00137841870 ± 0.00000000058.

In u, mn − mp = (1.3884487 ± 0.0000006) × 10 − 3 u.

9 Calculated by us from the MOHR 99 ratio m n/mp = 1.00137841887 ± 0.00000000058.

In u, mn − mp = (1.3884489 ± 0.0000006) × 10 − 3 u.

10 Calculated by us from the COHEN 87 ratio m n/mp = 1.001378404 ± 0.000000009. In u, mn − mp = 0.001388434 ± 0.000000009 u.

n MEAN LIFE n MEAN LIFE n MEAN LIFE n MEAN LIFE

Limits on lifetimes for bound neutrons are given in the section“p PARTIAL MEAN LIVES.”

The mean life of the neutron, 878.5 ± 0.8 s, obtained by SEREBROV 05 (for a more detailed account, see SEREBROV 08 A ) was so far from our average of seven other measurements, 885.7 ± 0.8 s, that it made no sense to include it in our average. Thus our 2006, 2008, and 2010 Reviews stayed with 885.7 ± 0.8 s; but we noted that in light of SEREBROV 05 our value should be regarded as suspect until further experiments clarified matters.

However, after our 2010 Review, PICHLMAIER 10 obtained a mean life of 880.7 ± 1.8 s, and we averaged the best seven results to get 881.5 ± 1.5 s

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for our 2011 off-year web update. And since then, ARZUMANOV 12, responding to comments of SEREBROV 10 B , recalculated the systematic corrections to its 2000 measurement (ARZUMANOV 00) and lowered its value from 885.4 ± 0.9 ± 0.4 s to 881.6 ± 0.8 ± 1.9 s. Thus the trend is definitely toward a shorter lifetime.

There seems little better to do than to again average the best seven mea- surements. The result, 880.1 ± 1.1 s (including a scale factor of 1.8), is 5.6 s lower than the value we gave in 2010—a drop of 7.0 old and 5.1 new standard deviations.

For a full review of all matters concerning the neutron lifetime, see F.E.

Wietfeldt and G.L. Greene, “The neutron lifetime,” Reviews of Modern Physics 83 83 83 83 1173 (2011). In particular, there is a full discussion of the experimental methods and results; and an average lifetime is obtained making several different selections of those results. (The revised ARZU- MANOV 12 mean life was not yet available.)

VALUE (s) DOCUMENT ID TECN COMMENT

880.1± 1.1 OUR AVERAGE

880.1± 1.1 OUR AVERAGE 880.1± 1.1 OUR AVERAGE 880.1± 1.1 OUR AVERAGE Error includes scale factor of 1.8. See the ideogram below.

881.6± 0.8± 1.9 11 ARZUMANOV 12 CNTR UCN double bottle 880.7± 1.3± 1.2 PICHLMAIER 10 CNTR UCN material bottle

886.3± 1.2± 3.2 NICO 05 CNTR In-beam n, trapped p

878.5± 0.7± 0.3 SEREBROV 05 CNTR UCN gravitational trap

889.2± 3.0± 3.8 BYRNE 96 CNTR Penning trap

882.6± 2.7 12 MAMPE 93 CNTR UCN material bottle

887.6± 3.0 MAMPE 89 CNTR UCN material bottle

• • • We do not use the following data for averages, fits, limits, etc. • • •

886.8± 1.2± 3.2 DEWEY 03 CNTR See NICO 05

885.4± 0.9± 0.4 ARZUMANOV 00 CNTR See ARZUMANOV 12

888.4± 3.1± 1.1 13 NESVIZHEV... 92 CNTR UCN material bottle

888.4± 2.9 ALFIMENKOV 90 CNTR See NESVIZHEVSKII 92

893.6± 3.8± 3.7 BYRNE 90 CNTR See BYRNE 96

878 ± 27 ± 14 KOSSAKOW... 89 TPC Pulsed beam

877 ± 10 PAUL 89 CNTR Magnetic storage ring

876 ± 10 ± 19 LAST 88 SPEC Pulsed beam

891 ± 9 SPIVAK 88 CNTR Beam

903 ± 13 KOSVINTSEV 86 CNTR UCN material bottle

937 ± 18 14 BYRNE 80 CNTR

875 ± 95 KOSVINTSEV 80 CNTR

881 ± 8 BONDAREN... 78 CNTR See SPIVAK 88

918 ± 14 CHRISTENSEN72 CNTR

11 ARZUMANOV 12 reanalyzes its systematic corrections in ARZUMANOV 00 and obtains this corrected value.

12 IGNATOVICH 95 calls into question some of the corrections and averaging procedures used by MAMPE 93. The response, BONDARENKO 96, denies the validity of the criticisms.

13 The NESVIZHEVSKII 92 measurement has been withdrawn by A. Serebrov.

14 The BYRNE 80 measurement has been withdrawn (J. Byrne, private communication, 1990).

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880.1±1.1 (Error scaled by 1.8)

MAMPE 89 CNTR 6.3

MAMPE 93 CNTR 0.9

BYRNE 96 CNTR 3.6

SEREBROV 05 CNTR 4.2

NICO 05 CNTR 3.3

PICHLMAIER 10 CNTR 0.1 ARZUMANOV 12 CNTR 0.6

! ²

19.0 (Confidence Level = 0.0042)

875 880 885 890 895 900 905

neutron mean life (s)

n MAGNETIC MOMENT n MAGNETIC MOMENT n MAGNETIC MOMENT n MAGNETIC MOMENT

See the “Note on Baryon Magnetic Moments” in the Λ Listings.

VALUE ( µ _{N )} DOCUMENT ID TECN COMMENT

− 1.91304272± 0.00000045

− − − 1.91304272± 0.00000045 1.91304272± 0.00000045 1.91304272± 0.00000045 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

− 1.91304273± 0.00000045 MOHR 08 RVUE 2006 CODATA value

− 1.91304273± 0.00000045 MOHR 05 RVUE 2002 CODATA value

− 1.91304272± 0.00000045 MOHR 99 RVUE 1998 CODATA value

− 1.91304275± 0.00000045 COHEN 87 RVUE 1986 CODATA value

− 1.91304277± 0.00000048 15 GREENE 82 MRS

15 GREENE 82 measures the moment to be (1.04187564 ± 0.00000026) × 10−3 Bohr magnetons. The value above is obtained by multiplying this by mp/me = 1836.152701 ± 0.000037 (the 1986 CODATA value from COHEN 87).

n ELECTRIC DIPOLE MOMENT n ELECTRIC DIPOLE MOMENT n ELECTRIC DIPOLE MOMENT n ELECTRIC DIPOLE MOMENT

A nonzero value is forbidden by both T invariance and P invariance. A number of early results have been omitted. See RAMSEY 90, GOLUB 94, and LAMOREAUX 09 for reviews.

VALUE (10−25 e cm) CL% DOCUMENT ID TECN COMMENT

< 0.29

< < < 0.29 0.29 0.29 90 16 BAKER 06 MRS UCN’s, hν = 2µnB ± 2dnE

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-0.1161±0.0022 (Error scaled by 1.3)

KROHN 73 0.1

ALEKSANDR... 86 3.9

KOESTER 95 0.5

KOPECKY 97 1.8

KOPECKY 97 0.1

! ²

6.5 (Confidence Level = 0.164)

-0.15 -0.14 -0.13 -0.12 -0.11 -0.1 -0.09

n mean-square charge radius

n MAGNETIC RADIUS n MAGNETIC RADIUS n MAGNETIC RADIUS n MAGNETIC RADIUS

This is the rms magnetic radius, !

"r 2 M #.

VALUE (fm) DOCUMENT ID COMMENT

0.862+ 0.009 − 0.008

0.862+ 0.009 0.862+ 0.009 0.862+ 0.009 − − − 0.008 0.008 0.008 BELUSHKIN 07 Dispersion analysis

n ELECTRIC POLARIZABILITY α _n n ELECTRIC POLARIZABILITY α n ELECTRIC POLARIZABILITY α n ELECTRIC POLARIZABILITY α _{n n n}

Following is the electric polarizability αn defined in terms of the induced electric dipole moment by D D D D = 4π#0αnEEEE. For a review, see SCHMIED- MAYER 89.

For a very complete review of the “polarizability of the nucleon and Comp- ton scattering,” see SCHUMACHER 05. His recommended values for the neutron are αn = (12.5 ± 1.7) × 10 − 4 fm3 and β n = (2.7 ∓ 1.8) × 10 −4 fm3, which agree with our averages within errors.

VALUE (10−4 fm3) DOCUMENT ID TECN COMMENT

11.6± 1.5 OUR AVERAGE 11.6± 1.5 OUR AVERAGE 11.6± 1.5 OUR AVERAGE 11.6± 1.5 OUR AVERAGE

12.5± 1.8+ 1.6 − 1.3 19 KOSSERT 03 CNTR γ d → γ p n

8.8± 2.4± 3.0 20 LUNDIN 03 CNTR γ d → γ d

12.0± 1.5± 2.0 SCHMIEDM... 91 CNTR n Pb transmission

10.7+ 3.3 − 10.7 ROSE 90 B CNTR γ d → γ n p

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• • • We do not use the following data for averages, fits, limits, etc. • • •

13.6 21 KOLB 00 CNTR γ d → γ n p

0.0± 5.0 22 KOESTER 95 CNTR n Pb, n Bi transmission

11.7+ 4.3 − 11.7 ROSE 90 CNTR See ROSE 90 B

8 ± 10 KOESTER 88 CNTR n Pb, n Bi transmission

12 ± 10 SCHMIEDM... 88 CNTR n Pb, n C transmission

19 KOSSERT 03 gets α n − βn =(9.8 ± 3.6 + 2.1

− 1.1 ± 2.2) × 10−4 fm3, and uses αn + βn

= (15.2 ± 0.5) × 10−4 fm3 from LEVCHUK 00. Thus the errors on αn and βn are anti-correlated.

20 LUNDIN 03 measures α N − βN = (6.4 ± 2.4) × 10 − 4 fm3 and uses accurate values for αp and αp and a precise sum-rule result for αn + βn. The second error is a model uncertainty, and errors on αn and βn are anticorrelated.

21 KOLB 00 obtains this value with a lower limit of 7.6×10−4 fm3 but no upper limit from this experiment alone. Combined with results of ROSE 90, the 1-σ range is (7.6–14.0) × 10−4 fm3.

22 KOESTER 95 uses natural Pb and the isotopes 208, 207, and 206. See this paper for a discussion of methods used by various groups to extract αn from data.

n MAGNETIC POLARIZABILITY β _n n MAGNETIC POLARIZABILITY β n MAGNETIC POLARIZABILITY β n MAGNETIC POLARIZABILITY β _{n n n}

VALUE (10−4 fm3) DOCUMENT ID TECN COMMENT

3.7± 2.0 OUR AVERAGE 3.7± 2.0 OUR AVERAGE 3.7± 2.0 OUR AVERAGE 3.7± 2.0 OUR AVERAGE

2.7± 1.8+ 1.3 − 1.6 23 KOSSERT 03 CNTR γ d → γ p n

6.5± 2.4± 3.0 24 LUNDIN 03 CNTR γ d → γ d

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.6 25 KOLB 00 CNTR γ d → γ n p

23 KOSSERT 03 gets α n − βn =(9.8 ± 3.6 + 2.1

− 1.1 ± 2.2) × 10−4 fm3, and uses αn + βn

= (15.2 ± 0.5) × 10−4 fm3 from LEVCHUK 00. Thus the errors on αn and βn are anti-correlated.

24 LUNDIN 03 measures α N − βN = (6.4 ± 2.4) × 10 − 4 fm3 and uses accurate values for αp and αp and a precise sum-rule result for αn + βn. The second error is a model uncertainty, and errors on αn and βn are anticorrelated.

25 KOLB 00 obtains this value with an upper limit of 7.6×10−4 fm3 but no lower limit from this experiment alone. Combined with results of ROSE 90, the 1-σ range is (1.2–7.6) × 10−4 fm3.

n CHARGE n CHARGE n CHARGE n CHARGE

See also “ !

! qp + qe !

!/e” in the proton Listings.

VALUE (10−21 e) DOCUMENT ID TECN COMMENT

− 0.2± 0.8 OUR AVERAGE

− − − 0.2± 0.8 OUR AVERAGE 0.2± 0.8 OUR AVERAGE 0.2± 0.8 OUR AVERAGE

− 0.1± 1.1 26 BRESSI 11 Neutrality of SF6

− 0.4± 1.1 27 BAUMANN 88 Cold n deflection

• • • We do not use the following data for averages, fits, limits, etc. • • •

− 15 ± 22 28 GAEHLER 82 CNTR Cold n deflection

26 As a limit, this BRESSI 11 value is < 1 × 10−21 e.

27 The BAUMANN 88 error ±1.1 gives the 68% CL limits about the the value −0.4.

28 The GAEHLER 82 error ±22 gives the 90% CL limits about the the value −15.

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LIMIT ON n n OSCILLATIONS LIMIT ON n n OSCILLATIONS LIMIT ON n n OSCILLATIONS LIMIT ON n n OSCILLATIONS Mean Time for n n Transition in Vacuum

Mean Time for n n Transition in Vacuum Mean Time for n n Transition in Vacuum Mean Time for n n Transition in Vacuum

A test of ∆B=2 baryon number nonconservation. MOHAPATRA 80 and MOHAPA- TRA 89 discuss the theoretical motivations for looking for n n oscillations. DOVER 83 and DOVER 85 give phenomenological analyses. The best limits come from looking for the decay of neutrons bound in nuclei. However, these analyses require model- dependent corrections for nuclear effects. See KABIR 83, DOVER 89, ALBERICO 91, and GAL 00 for discussions. Direct searches for n → n transitions using reactor neu- trons are cleaner but give somewhat poorer limits. We include limits for both free and bound neutrons in the Summary Table. See MOHAPATRA 09 for a recent review.

VALUE (s) CL% DOCUMENT ID TECN COMMENT

>1.3 × 108

>1.3 × 108 >1.3 × 108 >1.3 × 108 90 CHUNG 02 B SOU2 n bound in iron

>8.6 × 107

>8.6 × 107 >8.6 × 107 >8.6 × 107 90 BALDO-... 94 CNTR Reactor (free) neutrons

• • • We do not use the following data for averages, fits, limits, etc. • • •

>1 × 107 90 BALDO-... 90 CNTR See BALDO-

CEOLIN 94

>1.2 × 108 90 BERGER 90 FREJ n bound in iron

>4.9 × 105 90 BRESSI 90 CNTR Reactor neutrons

>4.7 × 105 90 BRESSI 89 CNTR See BRESSI 90

>1.2 × 108 90 TAKITA 86 CNTR n bound in oxygen

>1 × 106 90 FIDECARO 85 CNTR Reactor neutrons

>8.8 × 107 90 PARK 85 B CNTR

>3 × 107 BATTISTONI 84 NUSX

> 2.7 × 107–1.1 × 108 JONES 84 CNTR

>2 × 107 CHERRY 83 CNTR

LIMIT ON n n ^# OSCILLATIONS LIMIT ON n n LIMIT ON n n LIMIT ON n n ^{# # #} OSCILLATIONS OSCILLATIONS OSCILLATIONS

Lee and Yang (LEE 56) proposed the existence of mirror world in an attempt to restore global parity symmetry. See BEREZHIANI 06 for a recent discussion.

VALUE (s) CL% DOCUMENT ID TECN COMMENT

>414

>414 >414 >414 90 SEREBROV 08 CNTR UCN, B field on & off

• • • We do not use the following data for averages, fits, limits, etc. • • •

> 12 95 29 ALTAREV 09 A CNTR UCN, scan 0 ≤ B ≤ 12.5 µT

>103 95 BAN 07 CNTR UCN, B field on & off

29 Losses of neutrons due to oscillations to mirror neutrons would be maximal when the magnetic fields B and B# in the two worlds were equal. Hence the scan over B by ALTAREV 09 A : the limit applies for any B# over the given range. At B# = 0, the limit is 141 s (95% CL).

n DECAY MODES n DECAY MODES n DECAY MODES n DECAY MODES

Mode Fraction (Γi /Γ) Confidence level

Γ ₁ p e ⁻ ν _e 100 %

Γ ₂ p e ⁻ ν _e γ [a] ( 3.09± 0.32) × 10−3

Γ ₃ hydrogen-atom ν _e

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Sir James Chadwick

(20 October 1891 – 24 July 1974)

L’idea che il neutrone fosse un minuscolo atomo neutro di idrogeno era

diffusa e si dimostrò sbagliata, ma era nonostante ciò un’idea fertile.

Le conclusioni di Rutherford sulle proprietà di queste particelle erano

però corrette.

Cosa fa decadere il neutrone?

L’interazione debole (ci torneremo in seguito).

Cosa impedisce al protone di decadere?

Cosa impedisce all’elettrone di decadere?

Conservazione dell’energia, della carica, del numero barionico, del numero leptonico.

Citation: J. Beringer et al. (Particle Data Group), PR D86 , 010001 (2012) (URL: http://pdg.lbl.gov)

n ^{I (JP ) = 1 2 ( 1 2 +) Status:} ∗ ∗∗∗

We have omitted some results that have been superseded by later experiments. See our earlier editions.

Anyone interested in the neutron should look at these two new review articles: D. Dubbers and M.G. Schmidt, ”The neutron and its role in cosmology and particle physics,” Reviews of Modern Physics 83 83 83 83 1111 (2011); and F.E. Wietfeldt and G.L. Greene, ”The neutron lifetime,” Reviews of Modern Physics 83 83 83 83 1173 (2011).

n MASS (atomic mass units u) n MASS (atomic mass units u) n MASS (atomic mass units u) n MASS (atomic mass units u)

The mass is known much more precisely in u (atomic mass units) than in MeV. See the next data block.

VALUE (u) DOCUMENT ID TECN COMMENT

1.00866491600± 0.00000000043

1.00866491600± 0.00000000043 1.00866491600± 0.00000000043 1.00866491600± 0.00000000043 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.00866491597± 0.00000000043 MOHR 08 RVUE 2006 CODATA value 1.00866491560± 0.00000000055 MOHR 05 RVUE 2002 CODATA value 1.00866491578± 0.00000000055 MOHR 99 RVUE 1998 CODATA value 1.008665904 ± 0.000000014 COHEN 87 RVUE 1986 CODATA value

n MASS (MeV) n MASS (MeV) n MASS (MeV) n MASS (MeV)

The mass is known much more precisely in u (atomic mass units) than in MeV. The conversion from u to MeV, 1 u = 931.494 061(21) MeV/c2 (MOHR 12, the 2010 CODATA value), involves the relatively poorly known electronic charge.

VALUE (MeV) DOCUMENT ID TECN COMMENT

939.565379± 0.000021

939.565379± 0.000021 939.565379± 0.000021 939.565379± 0.000021 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

939.565346± 0.000023 MOHR 08 RVUE 2006 CODATA value

939.565360± 0.000081 MOHR 05 RVUE 2002 CODATA value

939.565331± 0.000037 1 KESSLER 99 SPEC n p → d γ

939.565330± 0.000038 MOHR 99 RVUE 1998 CODATA value

939.56565 ± 0.00028 2,3 DIFILIPPO 94 TRAP Penning trap

939.56563 ± 0.00028 COHEN 87 RVUE 1986 CODATA value

939.56564 ± 0.00028 3,4 GREENE 86 SPEC n p → d γ

939.5731 ± 0.0027 3 COHEN 73 RVUE 1973 CODATA value

1 We use the 1998 CODATA u-to-MeV conversion factor (see the heading above) to get this mass in MeV from the much more precisely measured KESSLER 99 value of 1.00866491637 ± 0.00000000082 u.

2 The mass is known much more precisely in u: m = 1.0086649235 ± 0.0000000023 u.

We use the 1986 CODATA conversion factor to get the mass in MeV.

3 These determinations are not independent of the m n − mp measurements below.

4 The mass is known much more precisely in u: m = 1.008664919 ± 0.000000014 u.

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n MASS n MASS n MASS n MASS

VALUE (MeV) EVTS DOCUMENT ID TECN COMMENT

939.485± 0.051

939.485± 0.051 939.485± 0.051 939.485± 0.051 59 5 CRESTI 86 HBC p p → n n

5 This is a corrected result (see the erratum). The error is statistical. The maximum systematic error is 0.029 MeV.

(m _n − m n )/ m _n (m (m (m _{n n n} − m − m − m n n n )/ m )/ m )/ m _{n n n}

A test of CPT invariance. Calculated from the n and n masses, above.

VALUE DOCUMENT ID

(9± 6) × 10−5 OUR EVALUATION (9± 6) × 10−5 OUR EVALUATION (9± 6) × 10−5 OUR EVALUATION (9± 6) × 10−5 OUR EVALUATION

m _n − m p

m m m _{n n n} − m − m − m p p p

VALUE (MeV) DOCUMENT ID TECN COMMENT

1.29333217± 0.00000042

1.29333217± 0.00000042 1.29333217± 0.00000042 1.29333217± 0.00000042 6 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.29333214± 0.00000043 7 MOHR 08 RVUE 2006 CODATA value 1.2933317 ± 0.0000005 8 MOHR 05 RVUE 2002 CODATA value 1.2933318 ± 0.0000005 9 MOHR 99 RVUE 1998 CODATA value 1.293318 ± 0.000009 10 COHEN 87 RVUE 1986 CODATA value 1.2933328 ± 0.0000072 GREENE 86 SPEC n p → d γ

1.293429 ± 0.000036 COHEN 73 RVUE 1973 CODATA value

6 The 2010 CODATA mass difference in u is m n − mp = 1.388 449 19(45) × 10 − 3u.

7 Calculated by us from the MOHR 08 ratio m n/mp = 1.00137841918(46). In u, mn − mp = 1.38844920(46) × 10 − 3 u.

8 Calculated by us from the MOHR 05 ratio m n/mp = 1.00137841870 ± 0.00000000058.

In u, mn − mp = (1.3884487 ± 0.0000006) × 10 − 3 u.

9 Calculated by us from the MOHR 99 ratio m n/mp = 1.00137841887 ± 0.00000000058.

In u, mn − mp = (1.3884489 ± 0.0000006) × 10 − 3 u.

10 Calculated by us from the COHEN 87 ratio m n/mp = 1.001378404 ± 0.000000009. In u, mn − mp = 0.001388434 ± 0.000000009 u.

n MEAN LIFE n MEAN LIFE n MEAN LIFE n MEAN LIFE

Limits on lifetimes for bound neutrons are given in the section“p PARTIAL MEAN LIVES.”

The mean life of the neutron, 878.5 ± 0.8 s, obtained by SEREBROV 05 (for a more detailed account, see SEREBROV 08 A ) was so far from our average of seven other measurements, 885.7 ± 0.8 s, that it made no sense to include it in our average. Thus our 2006, 2008, and 2010 Reviews stayed with 885.7 ± 0.8 s; but we noted that in light of SEREBROV 05 our value should be regarded as suspect until further experiments clarified matters.

However, after our 2010 Review, PICHLMAIER 10 obtained a mean life of 880.7 ± 1.8 s, and we averaged the best seven results to get 881.5 ± 1.5 s

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for our 2011 off-year web update. And since then, ARZUMANOV 12, responding to comments of SEREBROV 10 B , recalculated the systematic corrections to its 2000 measurement (ARZUMANOV 00) and lowered its value from 885.4 ± 0.9 ± 0.4 s to 881.6 ± 0.8 ± 1.9 s. Thus the trend is definitely toward a shorter lifetime.

There seems little better to do than to again average the best seven mea- surements. The result, 880.1 ± 1.1 s (including a scale factor of 1.8), is 5.6 s lower than the value we gave in 2010—a drop of 7.0 old and 5.1 new standard deviations.

For a full review of all matters concerning the neutron lifetime, see F.E.

Wietfeldt and G.L. Greene, “The neutron lifetime,” Reviews of Modern Physics 83 83 83 83 1173 (2011). In particular, there is a full discussion of the experimental methods and results; and an average lifetime is obtained making several different selections of those results. (The revised ARZU- MANOV 12 mean life was not yet available.)

VALUE (s) DOCUMENT ID TECN COMMENT

880.1± 1.1 OUR AVERAGE

880.1± 1.1 OUR AVERAGE 880.1± 1.1 OUR AVERAGE 880.1± 1.1 OUR AVERAGE Error includes scale factor of 1.8. See the ideogram below.

881.6± 0.8± 1.9 11 ARZUMANOV 12 CNTR UCN double bottle 880.7± 1.3± 1.2 PICHLMAIER 10 CNTR UCN material bottle

886.3± 1.2± 3.2 NICO 05 CNTR In-beam n, trapped p

878.5± 0.7± 0.3 SEREBROV 05 CNTR UCN gravitational trap

889.2± 3.0± 3.8 BYRNE 96 CNTR Penning trap

882.6± 2.7 12 MAMPE 93 CNTR UCN material bottle

887.6± 3.0 MAMPE 89 CNTR UCN material bottle

• • • We do not use the following data for averages, fits, limits, etc. • • •

886.8± 1.2± 3.2 DEWEY 03 CNTR See NICO 05

885.4± 0.9± 0.4 ARZUMANOV 00 CNTR See ARZUMANOV 12

888.4± 3.1± 1.1 13 NESVIZHEV... 92 CNTR UCN material bottle

888.4± 2.9 ALFIMENKOV 90 CNTR See NESVIZHEVSKII 92

893.6± 3.8± 3.7 BYRNE 90 CNTR See BYRNE 96

878 ± 27 ± 14 KOSSAKOW... 89 TPC Pulsed beam

877 ± 10 PAUL 89 CNTR Magnetic storage ring

876 ± 10 ± 19 LAST 88 SPEC Pulsed beam

891 ± 9 SPIVAK 88 CNTR Beam

903 ± 13 KOSVINTSEV 86 CNTR UCN material bottle

937 ± 18 14 BYRNE 80 CNTR

875 ± 95 KOSVINTSEV 80 CNTR

881 ± 8 BONDAREN... 78 CNTR See SPIVAK 88

918 ± 14 CHRISTENSEN72 CNTR

11 ARZUMANOV 12 reanalyzes its systematic corrections in ARZUMANOV 00 and obtains this corrected value.

12 IGNATOVICH 95 calls into question some of the corrections and averaging procedures used by MAMPE 93. The response, BONDARENKO 96, denies the validity of the criticisms.

13 The NESVIZHEVSKII 92 measurement has been withdrawn by A. Serebrov.

14 The BYRNE 80 measurement has been withdrawn (J. Byrne, private communication, 1990).

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LIMIT ON n n OSCILLATIONS LIMIT ON n n OSCILLATIONS LIMIT ON n n OSCILLATIONS LIMIT ON n n OSCILLATIONS Mean Time for n n Transition in Vacuum

Mean Time for n n Transition in Vacuum Mean Time for n n Transition in Vacuum Mean Time for n n Transition in Vacuum

A test of ∆B=2 baryon number nonconservation. MOHAPATRA 80 and MOHAPA- TRA 89 discuss the theoretical motivations for looking for n n oscillations. DOVER 83 and DOVER 85 give phenomenological analyses. The best limits come from looking for the decay of neutrons bound in nuclei. However, these analyses require model- dependent corrections for nuclear effects. See KABIR 83, DOVER 89, ALBERICO 91, and GAL 00 for discussions. Direct searches for n → n transitions using reactor neu- trons are cleaner but give somewhat poorer limits. We include limits for both free and bound neutrons in the Summary Table. See MOHAPATRA 09 for a recent review.

VALUE (s) CL% DOCUMENT ID TECN COMMENT

>1.3 × 108

>1.3 × 108 >1.3 × 108 >1.3 × 108 90 CHUNG 02 B SOU2 n bound in iron

>8.6 × 107

>8.6 × 107 >8.6 × 107 >8.6 × 107 90 BALDO-... 94 CNTR Reactor (free) neutrons

• • • We do not use the following data for averages, fits, limits, etc. • • •

>1 × 107 90 BALDO-... 90 CNTR See BALDO-

CEOLIN 94

>1.2 × 108 90 BERGER 90 FREJ n bound in iron

>4.9 × 105 90 BRESSI 90 CNTR Reactor neutrons

>4.7 × 105 90 BRESSI 89 CNTR See BRESSI 90

>1.2 × 108 90 TAKITA 86 CNTR n bound in oxygen

>1 × 106 90 FIDECARO 85 CNTR Reactor neutrons

>8.8 × 107 90 PARK 85 B CNTR

>3 × 107 BATTISTONI 84 NUSX

> 2.7 × 107–1.1 × 108 JONES 84 CNTR

>2 × 107 CHERRY 83 CNTR

LIMIT ON n n ^# OSCILLATIONS LIMIT ON n n LIMIT ON n n LIMIT ON n n ^{# # #} OSCILLATIONS OSCILLATIONS OSCILLATIONS

Lee and Yang (LEE 56) proposed the existence of mirror world in an attempt to restore global parity symmetry. See BEREZHIANI 06 for a recent discussion.

VALUE (s) CL% DOCUMENT ID TECN COMMENT

>414

>414 >414 >414 90 SEREBROV 08 CNTR UCN, B field on & off

• • • We do not use the following data for averages, fits, limits, etc. • • •

> 12 95 29 ALTAREV 09 A CNTR UCN, scan 0 ≤ B ≤ 12.5 µT

>103 95 BAN 07 CNTR UCN, B field on & off

29 Losses of neutrons due to oscillations to mirror neutrons would be maximal when the magnetic fields B and B# in the two worlds were equal. Hence the scan over B by ALTAREV 09 A : the limit applies for any B# over the given range. At B# = 0, the limit is 141 s (95% CL).

n DECAY MODES n DECAY MODES n DECAY MODES n DECAY MODES

Mode Fraction (Γi /Γ) Confidence level

Γ ₁ p e ⁻ ν _e 100 %

Γ ₂ p e ⁻ ν _e γ [a] ( 3.09± 0.32) × 10−3

Γ ₃ hydrogen-atom ν _e

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p ^{I (JP ) = 1} 2 ( ¹ ₂ +) Status: ∗ ∗∗∗

p MASS (atomic mass units u) p MASS (atomic mass units u) p MASS (atomic mass units u) p MASS (atomic mass units u)

The mass is known much more precisely in u (atomic mass units) than in MeV. See the next data block.

VALUE (u) DOCUMENT ID TECN COMMENT

1.007276466812± 0.000000000090

1.007276466812± 0.000000000090 1.007276466812± 0.000000000090 1.007276466812± 0.000000000090 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

1.00727646677 ± 0.00000000010 MOHR 08 RVUE 2006 CODATA value 1.00727646688 ± 0.00000000013 MOHR 05 RVUE 2002 CODATA value 1.00727646688 ± 0.00000000013 MOHR 99 RVUE 1998 CODATA value 1.007276470 ± 0.000000012 COHEN 87 RVUE 1986 CODATA value

p MASS (MeV) p MASS (MeV) p MASS (MeV) p MASS (MeV)

The mass is known much more precisely in u (atomic mass units) than in MeV. The conversion from u to MeV, 1 u = 931.494 061(21) MeV/c2 (MOHR 12, the 2010 CODATA value), involves the relatively poorly known electronic charge.

VALUE (MeV) DOCUMENT ID TECN COMMENT

938.272046± 0.000021

938.272046± 0.000021 938.272046± 0.000021 938.272046± 0.000021 MOHR 12 RVUE 2010 CODATA value

• • • We do not use the following data for averages, fits, limits, etc. • • •

938.272013± 0.000023 MOHR 08 RVUE 2006 CODATA value 938.272029± 0.000080 MOHR 05 RVUE 2002 CODATA value 938.271998± 0.000038 MOHR 99 RVUE 1998 CODATA value 938.27231 ± 0.00028 COHEN 87 RVUE 1986 CODATA value

938.2796 ± 0.0027 COHEN 73 RVUE 1973 CODATA value

! !m _p −m p

!

! /m _p

! !m _p −m p

!

! /m _p

! !m _p −m p

!

! /m _p

! !m _p −m p

!

! /m _p

A test of CPT invariance. Note that the comparison of the p and p charge- to-mass ratio, given in the next data block, is much better determined.

VALUE CL% DOCUMENT ID TECN COMMENT

<2 × 10−9

<2 <2 <2 × × × 10−9 10−9 10−9 90 1 HORI 06 SPEC p e−He atom

• • • We do not use the following data for averages, fits, limits, etc. • • •

<1.0 × 10−8 90 1 HORI 03 SPEC p e− 4 He, p e− 3He

<6 × 10−8 90 1 HORI 01 SPEC p e−He atom

<5 × 10−7 2 TORII 99 SPEC p e−He atom

1 HORI 01, HORI 03, and HORI 06 use the more-precisely-known constraint on the p charge-to-mass ratio of GABRIELSE 99 (see below) to get their results. Their results are not independent of the HORI 01, HORI 03, and HORI 06 values for !

! qp+qp !

! /e, below.

2 TORII 99 uses the more-precisely-known constraint on the p charge-to-mass ratio of GABRIELSE 95 (see below) to get this result. This is not independent of the TORII 99 value for !

! qp+qp !

! /e, below.

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p MEAN LIFE p MEAN LIFE p MEAN LIFE p MEAN LIFE

A test of baryon conservation. See the “p Partial Mean Lives” section below for limits for identified final states. The limits here are to “anything” or are for “disappearance”

modes of a bound proton (p) or (n). See also the 3ν modes in the “Partial Mean Lives” section. Table 1 of BACK 03 is a nice summary.

LIMIT

(years) PARTICLE CL% DOCUMENT ID TECN COMMENT

>5.8 × 1029

>5.8 × 1029 >5.8 × 1029 >5.8 × 1029 n n n n 90 25 ARAKI 06 KLND n → invisible

>2.1 × 1029

>2.1 × 1029 >2.1 × 1029 >2.1 × 1029 p p p p 90 26 AHMED 04 SNO p → invisible

• • • We do not use the following data for averages, fits, limits, etc. • • •

>1.9 × 1029 n 90 26 AHMED 04 SNO n → invisible

>1.8 × 1025 n 90 27 BACK 03 BORX

>1.1 × 1026 p 90 27 BACK 03 BORX

>3.5 × 1028 p 90 28 ZDESENKO 03 p → invisible

>1 × 1028 p 90 29 AHMAD 02 SNO p → invisible

>4 × 1023 p 95 TRETYAK 01 d → n + ?

>1.9 × 1024 p 90 30 BERNABEI 00 B DAMA

>1.6 × 1025 p, n 31,32 EVANS 77

>3 × 1023 p 32 DIX 70 CNTR

>3 × 1023 p, n 32,33 FLEROV 58

25 ARAKI 06 looks for signs of de-excitation of the residual nucleus after disappearance of a neutron from the s shell of 12C.

26 AHMED 04 looks for γ rays from the de-excitation of a residual 15O∗ or 15N∗ following the disappearance of a neutron or proton in 16O.

27 BACK 03 looks for decays of unstable nuclides left after N decays of parent 12C, 13C, 16O nuclei. These are “invisible channel” limits.

28 ZDESENKO 03 gets this limit on proton disappearance in deuterium by analyzing SNO data in AHMAD 02.

29 AHMAD 02 (see its footnote 7) looks for neutrons left behind after the disappearance of the proton in deuterons.

30 BERNABEI 00 B looks for the decay of a 128 53 I nucleus following the disappearance of a proton in the otherwise-stable 129 54 Xe nucleus.

31 EVANS 77 looks for the daughter nuclide 129Xe from possible 130Te decays in ancient Te ore samples.

32 This mean-life limit has been obtained from a half-life limit by dividing the latter by ln(2)

= 0.693.

33 FLEROV 58 looks for the spontaneous fission of a 232Th nucleus after the disappearance of one of its nucleons.

p MEAN LIFE p MEAN LIFE p MEAN LIFE p MEAN LIFE

Of the two astrophysical limits here, that of GEER 00 D involves consider- ably more refinements in its modeling. The other limits come from direct observations of stored antiprotons. See also “p Partial Mean Lives” after

“p Partial Mean Lives,” below, for exclusive-mode limits. The best (life- time/branching fraction) limit there is 7 × 105 years, for p → e− γ. We advance only the exclusive-mode limits to our Summary Tables.

LIMIT

(years) CL% EVTS DOCUMENT ID TECN COMMENT

• • • We do not use the following data for averages, fits, limits, etc. • • •

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Ok… ora conosciamo i mattoni, ma quale legante fa da malta?

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html

Il nucleo di elio ha una massa inferiore a quella delle sue

componenti prese separatamente

http://www.physics.ohio-state.edu/~kagan/phy367/Lectures/P367_lec_14.html

Quanto vale l’ammanco di massa per nucleone?

Quanto vale l’ammanco di massa per nucleone?

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html

H I D E K I Y U K A W A

Meson theory in its developments

Nobel Lecture, December 12, 1949

The meson theory started from the extension of the concept of the field of force so as to include the nuclear forces in addition to the gravitational and electromagnetic forces. The necessity of introduction of specific nuclear forces, which could not be reduced to electromagnetic interactions between charged particles, was realized soon after the discovery of the neutron, which was to be bound strongly to the protons and other neutrons in the atomic nucleus. As pointed out by Wigner ^I , specific nuclear forces between two nucleons, each of which can be either in the neutron state or the proton state,

must have a very short range of the order of 10 ^-13 cm, in order to account for the rapid increase of the binding energy from the deuteron to the alpha- particle. The binding energies of nuclei heavier than the alpha-particle do not increase as rapidly as if they were proportional to the square of the mass number A, i.e. the number of nucleons in each nucleus, but they are in fact approximately proportional to A. This indicates that nuclear forces are sat- urated for some reason. Heisenberg ² suggested that this could be accounted for, if we assumed a force between a neutron and a proton, for instance, due to the exchange of the electron or, more generally, due to the exchange of the electric charge, as in the case of the chemical bond between a hydro- gen atom and a proton. Soon afterwards, Fermi ³ developed a theory of be- ta-decay based on the hypothesis by Pauli, according to which a neutron, for instance, could decay into a proton, an electron, and a neutrino, which was supposed to be a very penetrating neutral particle with a very small mass.

This gave rise, in turn, to the expectation that nuclear forces could be re- duced to the exchange of a pair of an electron and a neutrino between two nucleons, just as electromagnetic forces were regarded as due to the ex- change of photons between charged particles. It turned out, however, that the nuclear forces thus obtained was much too small ⁴ , because the beta- decay was a very slow process compared with the supposed rapid exchange of the electric charge responsible for the actual nuclear forces. The idea of the meson field was introduced in 1935 in order to make up this gaps.

Original assumptions of the meson theory were as follows:

Hideki Yukawa (1907-1981)

(fonte Enciclopedia Britannica)