Measurement of Lithium flux with AMS
L. Derome, LPSC – Grenoble
AMS days, April 2015 1
]
-1s
-1sr
-2m
1.7[GV
2.7R × Flux
110
• Like B and Be, Li is produced by spallaHon processes.
• SensiHve to CR propagaHon parameters (diffusion, convecHon, reacceleraHon…).
Lithium in Cosmic Rays
CNO…Fe + ISM à Li
à B, Be + ISM à Li
à But present data give no valuable constraints to CR propagaHon parameters
Orth et al (1978) Juliusson et al (1974)
Key detectors used in the Lithium analysis:
• Tracker+Magnet: Rigidity measurement, Charge measurement
• TOF: Trigger, Charge measurement
Lithium SelecHon:
• Orbital cuts:
• LiveHme > 0.5 & No SAA
• Zenith < 40°
• Rigidity > 1.2 x MaxCutoff within 25°
• Lithium selecHon:
– Z-‐ selecHon: L1 + TOF U/L + Inner Trk + L9
• Quality cuts:
• All tracker planes fired (L1 & L9 XY)
• Track χ2Y /NDF < 20
3
Lithium : SelecHon and Analysis
L1
TOF
L2-‐L8: Inner Tracker
TOF L9
L2-‐L8: Inner Tracker
• In each rigidity bin the flux is esHmated from:
Key points in the analysis:
à Charge iden+fica+on: Lithium accounts only for
~1/1000 of CRs.
à Acceptance and Migra+on matrix from MC simula+on: both are very sensi+ve to the level of interac+on in the detector: need to validate the MC with data.
[Counts corrected for bin to bin MigraHon]
FLUX =
[Bin Size]x[Exp Time]x[Trig. Eff.] x[Acceptance]
Lithium : SelecHon and Analysis
L1
TOF
TOF L9
Inner traker Charge
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
Normalize entries
10-2
10-1
1 10
Lithium : SelecHon
Main idenHficaHon capability provided by the Inner tracker:
Combined with charge from TOF:
à contaminaHon from Proton and He < 0.02% on the whole rigidity range.
à For heavier nuclei, negligible charge confusion. ContaminaHon from Lithium producHon in the upper part of the detector
Li He
H Be B
ISS Data
SelecHon region
Charge in L1 (c. u.)
2.5 3 3.5 4 4.5 5 5.5 6 6.5 7
Events/bin
10 102
103
104
105
ISS Data Fit to Data Lithium Beryllium Boron Carbon
Charge SelecHon in L1
ISS Data Fit to data Lithium Berylium Boron Carbon
CàLi BàLi
Charge distribuHon in L1 for events selected as Lithium in the inner tracker:
à Layer 1 is used to reject Lithium produced in the upper part of the detector
Lithium
L1
SelecHon
region BeàLi
Lithium SelecHon: Tracker Paserns
• Lithium abundance ~1 per mil in cosmic ray.
Use 2 different tracker paserns to opHmize the measurement:
1. Inner+L1&L9 (Full Span) with largest lever arm to maximize the MDR
(3.2TV)
2. Inner+L1 with 5 Hmes larger the
acceptance to maximize the staHsHc.
• The 2 corresponding set of events are not independent: 1 ⊂ 2
AMS days, April 2015 7
Raw rates for H, He & Li
Rigidity [GV]
1 10 102 103
]-1 [GV s2 R×dN/dR
10-4
10-3
10-2
10-1
1 10 102
Proton
Helium
Lithium
Rates aver Proton, Helium and Lithium selecHon:
[Counts corrected for bin to bin MigraHon]
FLUX =
[Bin Size]x[Exp Time]x[Trig. Eff.]x[Acceptance]
[Counts]
Rate =
[Bin Size] x [Exp Time]
à Acceptance and MigraHon matrix from MC simulaHon
Full Span pasern
• (Quasi)ElasHc cross secHon:
– Affects acceptance and the rigidity reconstruc+on (and thus the migra+on matrix) as it deflects the incoming par+cles.
– Validated with the probability to have a good associa+on between the inner tracker and an hit in L1.
MC validaHon
AMS days, April 2015 9
• (Quasi)ElasHc cross secHon:
– Affects acceptance and the rigidity reconstruc+on (and thus the migra+on matrix) as it deflects the incoming par+cles.
– Validated with the probability to have a good associa+on between the inner tracker and an hit in L1.
• InelasHc cross secHon:
– Mainly affects par+cle survival probability and therefore the acceptance
– Validated by measuring the survival probability of Lithium in the lower part of the detector.
MC validaHon
Z=3
Z=3 Target
Inner Rigidity [GV]
10 102 103
L9 ratio (Data/MC)
0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1
Inner Rigidity [GV]
10 102 103
L1 ratio (Data/MC)
0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1
AMS days, April 2015 11
MC validaHon: External Layer efficiency
• Aver validaHon, MC reproduce well the probability to have a hit in the external layers:
L1
L9
• All Data and MC efficiencies as a funcHon of reconstructed
rigidity are compared: Tracking efficiency, Full Span efficiency, SelecHon cuts and Quality cuts
à Combined Data/MC raHo used to correct the acceptance:
10 Rigidity [GV]
102 103
Data/MC Ratio
0.6 0.8 1 1.2
Acceptance: Data MC correcHons
Data/MC
SystemaHc error CorrecHon
Rigidity [GV]
1 10 102 103
Trigger efficiency
0.85 0.9 0.95 1 1.05
Trigger efficiency
AMS days, April 2015 13
• Obtained directly from data using unbiased trigger events
• Good agreement obtained between MC and Data:
• ε
Trig= 1 for Full Span pasern
• ε
Trig> 0.99 for Inner+L1 pasern
Lithium
Helium
Proton
Full Span Pasern
ISS Data MC
-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02
Events
10-3
10-2
10-1
Bin to Bin MigraHon: ResoluHon
• ValidaHon of the intrinsic rigidity
resoluHon of the tracker. Comparison of residuals between Data and MC:
Rig > 75 GV
R > 75 GV
L2
L5
L8
Data MC
-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02
Events
10-3
10-2
10-1
Events -2
10 10-1
Data MC
Data MC
Rig > 75 GV
Rig > 75 GV
Rigidity [GV]
10 102 103
]
-1s
-1sr
-2m
1.7[GV
2.7R × Flux
110
Lithium flux
• Comparison between the flux obtained for the 2 different paserns:
AMS days, April 2015 15
- Sta+s+cal errors only
Inner+L1
Full Span
Relative Error [%] 1
10
Rigidity [GV]
10 102 103
Relative Error [%] 1
10
Breakdown of errors
• StaHsHcal error
• Acceptance error: Data/MC correcHons -‐ survival prob. -‐
Lithium isotopic abundances.
• Unfolding error, includes
migraHon matrix and unfolding method
• Rigidity Scale error (Alignment
& Mag. Field)
Errors (included systemaHcs) dominated by staHsHcs, will be reduced with more staHsHcs.
Inner+L1 Full Span
Acc.
Acc.
Lithium flux
• Combined result with total errors (Inner+L1 below 800 GV, Full Span above):
AMS days, April 2015 17
Rigidity [GV]
10 102 103
]
-1s
-1sr
-2m
1.7[GV
2.7R × Flux
0 5 10 15 20 25 30
Lithium flux
• Combined result with total errors (Inner+L1 below 800 GV, Full Span above) compared with previous measurements:
AMS02
Orth et al (1978) Juliusson et al (1974)
Rigidity [GV]
10 102 103
]
-1s
-1sr
-2m
1.7[GV
2.7R × Flux
110
AMS days, April 2015 19
Same model as the one used for proton and helium (double power law with smooth transiHon) between 45 GV and 3 TV:
à Change of slope at the same range than for the one found for Proton and Helium.
Fit of Lithium flux
Fit to data Δγ = 0
Summary
• Flux of Lithium measured with AMS02
between 2 GV and 3 TV presented for the first Hme.
• DeviaHon from single power law and
hardening of the Lithium flux above 300 GV.
• This will provides new data to constrain propagaHon models
AMS days, April 2015 21