Antiproton Flux and Antiproton-to-Proton Flux Ratio in Primary Cosmic Rays Measured with AMS on the Space Station

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1 Antiroton Flux and Antiroton-to-Proton Flux Ratio in Primary Cosmic Rays Measured with AMS on the Sace Station Andreas Bachlechner on behalf of the AMS collaboration von TeVPA 017, Columbus

2 Antirotons in cosmic rays The collision of cosmic rays with the interstellar medium (ISM) roduces antirotons, He + ISM è +, He AMS ISM

3 ~85% of the matter in the Universe is dark The collision of cosmic rays with the interstellar medium (ISM) roduces antirotons, He + ISM è +, He χ AMS ISM χ Annihilation of dark matter articles can χ + χ è + roduce additional antirotons 3

4 Antiroton to roton ratio in the cosmic rays Antiroton / roton ratio Donato et al., PRL, (009) Dark matter + collision of cosmic rays with ISM Ratio of ~ -4 requires great background rejection Boost factor= Kinetic energy [GeV] Antiroton excess can be measured by AMS 4

5 AMS: A TeV recision, multiurose sectrometer Transition Radiation Detector Searate, from e ± Time of Flight Z, β 1 Silicon Tracker Z, R TRD TOF 3-4 Magnet ± Z Tracker Ring Imaging Cherenkov Z, β TOF RICH Electromagnetic Calorimeter Searate, from e ± 9 ECAL The charge and energy or rigidity are measured indeendently by several sub-detectors 5

6 Antiroton signal (a) π - 5.4< R <6.5 GV + e π + Events e 4 β RICH Well searated antiroton signal sign(r) Λ TRD (b) (c)

7 Event selection for the / analysis R = 363 GV antiroton 1 TRD ISS data from May 19, 011 to May 6, 015 M. Aguilar et al., Phys. Rev. Lett. 117, 0913 (016) The number of antirotons is determined from temlate fits. To maximize the measurement accuracy, different aroaches are used deending on the backgrounds to challenge. MAGNET ACC Tracker RICH 9 ECAL 7

8 Antiroton identification (low rigidity region) GV 1 Rigidity / GV e - +π - Electron, ion background Mass calculated from TOF β and Tracker rigidity Cut on TRD estimator to suress electrons Temlate events selected from ISS data via the RICH 8

9 Antiroton identification (intermediate rigidity region) GV GV 1 Rigidity / GV # Events < R <5.9 GV Electron and small amount of ion background 00 Utilize RICH information to remove residual Pion contamination 0 e - Temlates from ISS data TRD estimator TRD 9

10 Antiroton identification at high rigidities GV GV GV 1 Rigidity / GV Events may be reconstructed with wrong charge sign, due to: - Finite tracker resolution - Particle interactions with detector material - Leads to charge confused events Probability 1 0< R <450 GV Electron and charge confused roton background 3 Charge confusion estimator CC : - MVA BDT variables based on e.g.: Track fit quality Rigidity algorithms and track attern Charge measurements Charge confusion estimator CC

11 Antiroton identification at high rigidities GV GV GV < R < 11 GV (b) (c) 1 Events 15 Data 15 Events 15 Fit χ /d.f. = 138/154 Rigidity / GV e Charge confused 0 1 Λ TRD Λ CC Λ TRD Λ CC 1 11

12 Antiroton identification GV GV GV 1 Rigidity / GV 1. Low rigidity region: Electron, ion background GV The mass calculated from TOF and Tracker. Intermediate region: Electron and small amount of ion background GV RICH and TRD estimator 3. High rigidity region: Electron and charge confusion roton background GV D temlate in ( TRD - CC ) lane The regions overla, the analysis with the smallest error is taken 3.49 x 5 antirotons and.4 x 9 rotons are selected in the rigidity range 1< R <450 GV 1

13 Antiroton uncertainties Relative error [%] Statistical error dominants below GV and above 0 GV In the intermediate region the systematic uncertainty from the accetance correction dominates 4% σ stat Statistical σ 13% σ syst Total Syst. 1% NCounting 5 % % Rigidity [GV] σ σ A Accetance RRigidity scale 13

14 Antiroton uncertainties Relative error [%] Affecting the accetance, σ Accetance Cross sections MC statistic fluctuations Migration matrix Affecting the antiroton counting σ Counting Geomagnetic cutoff Selection Charge confusion temlates 4% σ stat Statistical σ 13% σ syst Total Syst. 1% NCounting 5 % % Rigidity [GV] σ σ A Accetance RRigidity scale 14

15 Systematic uncertainty from cross section uncertainty The antiroton-to-roton flux ratio is defined as Number of observed antirotons and rotons Accetance ratio of rotons to antirotons Ex. Data comiled by J. Hoffman +C σ abs [mb] The tyical uncertainty is 0% at 1 GV, 15% at GV, and 5% at 0 GV 1 Abrams(1971) Denisov(1973) Carroll(1979) Nakamura(1984) Cork(1957) Aihara(1981) Allaby(1970) +C absortion P(GeV/c) 3 +C inelastic cross section [mb] NA61 (01) Denisov (1973) Bellettini (1965) Carroll (1979) Bowen (1958) Dubna-ex db data IHEP-ex db data Letaw (1983) GEANT Uncertainty is still significant. 1 roton momentum [GeV/c] 3 15

16 Systematic error from charge confusion temlates 6 5 Good agreement between data and MC in 5 orders of magnitude Rigidity resolution function 400 GeV/c Test Beam Data 400 GeV/c Monte Carlo Simulation Events [ GV ] Rigidity The minor difference in charge confusion between MC simulation and data is taken as associated error 16

17 Systematic error from the rigidity scale uncertainty Normalized entries Events Bin e e + - E>30 GeV E>30 GeV, Scaled 1/Δ 0 and σ(1/δ)=1/6 TV Energy Rigidity 17

18 The Sectra of Protons and Antirotons M. Aguilar et al., Phys. Rev. Lett. 117, 0913 (016) ] 1.7 GV -1 4 s -1 sr - [m Φ R.7 ˇ Rigidity [GV] If are secondaries, their sectrum should be different than. Unexectedly and have identical sectra

19 Antiroton-to-Proton Flux Ratio M. Aguilar et al., Phys. Rev. Lett. 117 (016) The fitted value of the sloe Above 60.3 GV: k = (-0.7 ± 0.9)x -7 GV -1 is consistent with zero. The antiroton-to-roton flux ratio reaches its maximum at 0 GV The antiroton-to-roton flux ratio shows no rigidity deendence above 60 GV 19

20 Antiroton-to-Proton Flux Ratio AMS Dark matter Dark Matter Model examle: Donato et al., Phys. Rev. Lett., ( 009 ). Astrohysics Model examles: P. Mertsch and S. Sarkar, Phys. Rev. D 90, (014); K. Kohri, K. Ioka, Y. Fujita, and R. Yamazaki, Prog. Theor. Ex. Phys. 016, 01E01 (016). Momentum [GeV] Different then the ositron fraction excess the antiroton excess cannot be exlained by Pulsars but could be exlained by Dark Matter collisions or by new astrohysics henomena 0

21 Conclusions Antiroton measurement u to 450 GV measured based on 3.49 x 5 antirotons and.4 x 9 rotons extending existing measurements with high recision The antiroton-to-roton flux ratio shows no rigidity deendence above 60 GV - Hint for dark matter or new astrohysical henomena To test these signals a very recise theoretical rediction for the ISM background is needed AMS will continue to collect more data till the end of the ISS lifetime to further exlore the high rigidity region, increase the recision and investigate the time deendent effects 1