AMS Days @ CERN, 17 th April 2015
M. Heil, MIT
Measurement of the Carbon-‐to-‐Helium Ra9o in Cosmic Rays
with AMS
H He
Li
Be B C
N O
F Ne Na Mg Al Si
Cl Ar K Ca Sc V Cr P S
Fe Ni Ti
Mn
Co
IntroducKon
• Carbon is the nuclei with the 3 rd highest abundance in cosmic rays and is
produced and accelerated by cosmic ray sources, with only a small contribuKon from spallaKon of higher charge nuclei such as oxygen
• With its higher charge and mass than helium, it allows to test producKon and/or
propagaKon mechanism dependence on charge and mass
Key detectors
• Tracker + Magnet:
– determines ParKcle ID with up to nine independent charge measurements:
σ Z (inner) = 0.12 for |Z|=6
– measures Rigidity up to the MDR of 2.5 TV
– background studies with L1
• Time-‐of-‐Flight:
– Trigger
– ParKcle direcKon
– ParKcle ID verificaKon with four independent charge
measurements:
σ Z (uTof) = 0.16 for |Z|=6
TRD!
TOF!
Tr a c k e r!
TOF!
RICH!
ECAL!
L1
L2
L7-L8 L3-L4
L9
L5-L6
Carbon SelecKon
169 GV Carbon nuclei
• Down-‐going parKcle β>0.4
• Full Tracker lever-‐arm à L1 to L9
• Tracker track reconstrucKon quality criteria, e.g.:
• Hits on all “double”-‐planes
• Inner and full-‐span: χ 2 /NDF < 10
• Charge compaKble with carbon in all detectors
• Rigidity > 1.2 * GeomagneKc Cutoff
Background
• Minor background to Carbon flux from charge determinaKon
uncertainty in Tracker L1
• With efficient charge cut on L1 (ε>95%) the
residual background is 0.2% up to 10 GV and
negligible above 50 GV
Charge
5 5.5 6 6.5 7 7.5 8 8.5 9
Entries / bin
10 10
210
310
4Data Fit Result
carbon contribution nitrogen contribution oxygen contribution
Tracker Q L1
Rigidity Bin: 36.1 -‐ 48.5 GV
carbon
nitrogen oxygen
• Data Fit result
L1 charge
Flux measurement
Φ j = N j
T j ε j A
jΔR j
Measurement in rigidity bins (R j , R j +ΔR j ) from 2 GV to 1.8 TV
Exposure Kme T j :
40 months of data taking -‐> 8.5*10 7 seconds
Trigger efficiency ε j determined from data and verified with MC: > 99.9%
A j : EffecKve acceptance determined with MC with all selecKon efficiencies checked between data and MC
N j : Number of carbon
events corrected with
the resoluKon funcKon,
total 1.4 million events
SystemaKc Errors
• ContribuKon to the systemaKcs :
– Background esKmaKon
– Trigger Efficiency esKmaKon
– EffecKve Acceptance esKmaKon
• InteracKon cross-‐secKon uncertainKes
• Data/MC correcKons
– Unfolding and resoluKon funcKon determinaKon
– Rigidity scale uncertainty
Error @ 100 GV:
2.8 % 2.5 % 1.3 %
0.1 %
1.3 % 0.7 %
0.1 %
Carbon interacKon probability
• ElasKc interacKons can be checked by looking at the efficiency of associaKng the Tracker L1 hit to the Inner Tracker
TRD
Z=6 L1
Z=6 L2 L3
L4
Rigidity [GV]
10 102
Efficiency ratio
0.9 0.92 0.94 0.96 0.98 1 1.02 1.04 1.06 1.08 1.1
• Data/MC
§ Systema9c uncertainty
Carbon interacKon probability
• InelasKc interacKons can be checked by looking at the survival probability from Tracker L8 to Tracker L9
ECAL RICH
L7
L8 Z=6
L9 Z=6
Rigidity [GV]
10 102
Survival probability ratio
0.75 0.8 0.85 0.9 0.95 1 1.05
1.1 1.15
1.2
1.25
• Data/MC
§ Systema9c uncertainty
Data/Monte Carlo Agreement
rec. Rigidity [GV]
10 10
2Efficiency ratio
0.7 0.8 0.9 1 1.1 1.2
• We have compared all 1.3
selecKon cut
efficiencies between Data and MC and applied correcKons where necessary (few percent effects)
• The obtained
systemaKc error is 1.3% up to 100 GV and 3.5% @ 1 TV
• Data/MC
§ Systema9c uncertainty
-40 -20 0 20 40
normalized events / bin
10-4
10-3
10-2
§ Data : σ = 10.1 μm
§ MC : σ = 10.2 μm
-1] 1/rL1-1/rL9 [GV
-0.01 -0.005 0 0.005 0.01
normalized entries / bin
10-4
10-3
10-2
Rigidity comparison
Tracker ResoluKon FuncKon
• With the full lever arm of the Tracker, we get an Maximum Detectable
Rigidity (MDR) of 2.5 TV
• Intrinsic check by comparing the rigidity from L1-‐L8 to L2-‐L9 between Data and MC
• ResoluKon funcKon determined from MC à verified by comparing
residuals between Data and MC
• The systemaKc uncertainty due to the Tracker resoluKon funcKon and
unfolding is 3% @ 1 TV
§ Data
§ MC
1/R18-1/R29 [GV-1] normalized events / binnormalized events / bin
Carbon Flux Errors
10 10
210
3Error [%]
0 2 4 6 8
10 Total Error
StaKsKcal Error
Unfolding Error InteracKon X-‐secKon Error Data/MC correcKon Error
Trigger Efficiency Error Background Error
Rigidity Scale Error
Carbon Flux
) [GeV/n]
kinetic Energy (E
1 10 10
210
3] 1.7 (GeV/n) -1 sr -1 s -2 [ m 2.7 k Carbon Flux * E
0 10 20 30 40 50 60
AMS-02
PAMELA (2014) TRACER (2011) ATIC (2009) CREAM II (2009) Buckley et al. (1994) Derrickson et al. (1992) CRN-Spacelab2 (1991) HEAO3-C2 (1990) Simon et al. (1980) Orth et al. (1978)
Lezniak & Webber (1978) Juliusson et al. (1974)
~
Carbon Flux
) [GeV/n]
kinetic Energy (E
1 10 10
210
3] 1.7 (GeV/n) -1 sr -1 s -2 [ m 2.7 k Carbon Flux * E
0 10 20 30 40 50 60
AMS-02
PAMELA (2014) TRACER (2011) ATIC (2009) CREAM II (2009) Buckley et al. (1994) Derrickson et al. (1992) CRN-Spacelab2 (1991) HEAO3-C2 (1990) Simon et al. (1980) Orth et al. (1978)
Lezniak & Webber (1978) Juliusson et al. (1974)
