Precision Measurement of the Cosmic Boron-to-Carbon Ratio with AMS A. Oliva, CIEMAT, Spain On behalf of the AMS Collaboration 33 rd ICRC 8 Jul 2013 Rio de Janeiro
Multiple Measurements of Charge Carbon (Z=6) Δ Z (cu) Tracker Plane 1 (L1) 0.30 1 0.33 TRD 0.16 Upper TOF (1 counter) 2 3-4 Tracker 5-6 0.12 Inner Tracker (L2-L8) 7-8 0.16 Lower TOF (1 counter) 0.32 RICH 9 Tracker Plane 9 (L9) 0.30 1 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Multiple Measurements of Energy Tracker, R = p/Z 1 MDR (Z=6) ≈ 3TV 2 3-4 Tracker TOF , β 5-6 Δβ ( β =1, Z=6) ≈ 0.01 7-8 9 RICH , β Δβ ( β =1, Z=6) ≈ 5 × 10 -4 2 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Flux and Ratio Determination B/C is a flux ratio . Flux is given by: Number of counts Bin Width Acceptance (m 2 sr) Efficiency Exposure Time K n is the kinetic energy per nucleon , is measured from TOF and RICH (beta) or from Tracker (rigidity) 3 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Nuclei Identification in AMS H He Li Be B C N O F Ne Mg Na Al Si P S Cl Ar K Ca Sc Fe Ti V Cr Mn Ni Co 4 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Nuclei Identification with Inner Tracker Contamination from neightboring charges < 10 -4 , identification efficiency is > 98%. O N C B Be Li He H 5 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Identification of Fragmentation Events Layer 1 = 6.1 TRD = 6.0 UTOF = 7.6 R = 10 GV Inner = 4.8 LTOF = 5.2 RICH = 5.0 6 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Purity Estimation Selection efficiency is >70% for both Boron and Carbon, ratio is ≈ 1. Boron selected with Inner Tracker and TOF. Background estimated down to accuracy of 0.1%. Events Boron Purity = 97% B 3 10 2 10 C B O B 10 4.5 5 5.5 6 6.5 7 7.5 8 8.5 Tracker L1 Charge 7 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Estimation of Fragmentation Acceptance is convolution of geometry and fragmentation effects. Carbon selected with L1 and UTOF. Fragmentation distribution evaluated with LTOF. Data and MC agreement evaluated being at 2% level. Normalized Entries Carbon MonteCarlo -1 10 Data -2 10 -3 10 0 2 4 6 8 10 12 th 4 TOF Layer Charge 8 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Track Efficiency The ratio of Boron and Carbon track efficiencies is calculated and cross-checked with MC up to 100 GV. Is about 2% correction. 1.3 B Track Eff. / C Track Eff. L1 high-Z hit 1.2 TRD track 1.1 1 0.9 Cutoff Rigidity Estimator 0.8 ECAL Rigidity Estimator 0.7 2 10 10 ECAL E Dep Rigidity Estimate (GV) 9 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Trigger Efficiency Trigger efficiency is estimated with an unbiased trigger sample. Efficiency is > 95%, no apparent difference between B and C. ACC UTOF MAGNET LTOF ECAL High-Z particle TOF + ECAL Trigger Horizontal Particle Accepted Accepted Rejected 10 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Top-of-the-Instrument Correction Carbon to Boron conversion on materials above L1. Correction to the ratio has been estimated with MC: e C B = 0.005 ± 0.002. 11 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Isotopic Fraction Evaluation RICH evaluates the isotopic composition of Boron. This fraction is used for the Tracker rigidity kinetic energy conversion. 11 B/( 11 B + 10 B) = 0.7 ± 0.1 ~ 1% systematic error on ratio 0.31 Raw Boron-to-Carbon Ratio 0.3 0.29 0.28 0.27 0.26 10 11 11 B/( B+ B) = 80% 0.25 11 10 11 B/( B+ B) = 70% 11 10 11 0.24 B/( B+ B) = 60% RICH 0.23 4 5 6 7 8 9 10 Kinetic Energy (GeV/n) 12 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Systematics (a) 2% from MC and data comparison of interactions. (b) 1% from isotopic composition evaluation. (c) <2% from TOI correction. (d) bin-to-bin migration error is <1% up to 200 GeV/n, and 2% above. Systematic error will be reduced with more data. 13 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
B/C Ratio 10% of total expected data 14 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
B/C Ratio (year > 2000) 10% of total expected data 15 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
AMS B/C Ratio 10% of total expected data 16 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
Conclusions Measurement of the B/C between 0.5 to 670 GeV/n with AMS has been presented. Sources of differences between Boron and Carbon counting were investigated and corrections applied when needed. Main limitation for the ratio measurement and systematics error evaluation at high energy is the statistics. AMS has collected 10% of the expected statistics. The B/C behavior at high energy will be become more clear with more data. 17 /17 - ICRC 2013 - A. Oliva - AMS Collaboration
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