the AMS on the International Space Station Zuhao LI / IHEP, CAS On - PowerPoint PPT Presentation

Precision Measurement of Positron Fraction by the AMS on the International Space Station Zuhao LI / IHEP, CAS On behalf of the AMS Collaboration ICRC 2017 5m x 4m x 3m 14, July, 2017 7.5 tons

AMS: A TeV precision, multipurpose, magnetic spectrometer Transition Radiation Detector Time of Flight (TRD) (TOF) Identify e + , e - Z, E 1 Magnet ± Z Silicon Tracker 2 Z, P or R=P/Z 3-4 5-6 Tracker 7-8 Ring Imaging Cherenkov Transition Radiation (RICH) Electromagnetic Calorimeter Z, E (ECAL) 9 E of e + , e - Z and P, E or R are measured independently by Tracker, ECAL, TOF and RICH 2

Transition Radiation Detector p e ± 20 layers: fleece radiator and proportional tubes One of 20 layers radiator Measurement with 1 of the 20 TRD Layers Proton rejection at 90% e + efficiency Electrons ISS Data Transition Radiation Protons 70% ISS Data Typically, 1 in 1,000 protons may 80% be misidentified as a positron 90% Rigidity (GV) TRD estimator = -ln( P e /( P e + P p )) 3 3

Silicon Tracker 1 9 planes, 200,000 channels 2 The coordinate resolution is 10 μ m. Maximum Detectable 3 Rigidity (MDR) for Z=1 4 particles is 2.0 TV 5 6 7 8 9 4

Electromagnetic Calorimeter Provides a precision, 17 X 0 , TeV, 3-dimensional measurement of the directions and energies of electrons and positrons, seperate e ± from protons Probability B oosted Decision Tree (BDT): 3D shower shape electrons protons ε e = 90% ECAL estimator Proton rejection at 90% e + efficiency Test beam result Typically, 1 in 10,000 protons may be misidentified as a positron Momentum (GeV/c) 5

In 6 years on ISS, AMS has collected over 100 billion cosmic rays. Search for Dark Matter is one of the main physics topic of AMS . 100 billion events collected 08/05/2017 6

Dark Matter:  Collision of Cosmic Rays with the Interstellar Media will produce e + , p… p, He + ISM  e +, , p + …          p, He AMS ISM e + , p Dark Matter ( ) annihilations  +   e + , p + … The excess of e + , p from Dark Matter ( ) annihilations can be measured by AMS M. Turner and F. Wilczek, Phys. Rev. D42 (1990) 1001; J. Ellis 26 th ICRC (1999) 7

Positron Fraction[e + /(e + +e - )] 4. The energy beyond which it 2. The rate of increase with energy ceases to increase. 3. The existence of sharp structures . e + /(e + + e - ) m  =800 GeV 5. Isotropy. m  =400 GeV 1. The energy at 6. The rate at which it begins which it falls to increase. beyond the turning point. e ± energy [GeV] Dark Matter model based on I. Cholis et al., JCAP 12 (2009) 007. 8

Analysis: 2D fit to measure Ne ± and Np After an efficient ECAL selection to remove the majority of protons, 2D reference spectra for the signal and the background are fitted to data in the [TRD estimator-log(E/|P|)] plane. log(E/|P|) 83.2-100 GeV This method combines information from  TRD  ECAL p  Tracker e ± It provides better statistical accuracy compared to cut-based analysis 9

Fit results: The TRD Estimator shows clear separation between protons and positrons with a small charge confusion background Data (83.2-100 GeV) Fit Positrons Protons Events Charge Confusion(e -  e + ) χ 2 /d.f.=0.60 p e + e −  e + TRD Estimator 10

Fit results: The ECAL energy and Tracker momentum matching (E/P) quantifies the small charge confusion in the signal region. 11

Systematic errors Extensive check for systematic errors on the positron fraction measurement 1. Charge confusion (e -  e + ) is the dominating source of systematic uncertainty at high energies Two sources: 1) large angle scattering and 2) production of secondary tracks along the path of the primary track. Both are well reproduced by the Monte Carlo. The small difference is taken as a systematic error. 12

Systematic errors 2. Selection dependence 173 – 206 GeV Width = 0.006 Positron Fraction Number of Trials Number of Positron Positron Fraction The measurement is stable over wide variations of the cuts in the ECAL shower Shape, E/p matching, etc. For each energy bin, over 1,000 sets of cuts(trials) were analyszed. 13

Systematic errors 3 ) σ acc : Acceptance asymmetry Due to known minute tracker asymmetry (negligible for all energy bin) 4 ) σ mig : Absolute energy scale and bin-to-bin migration negligible above 5 GeV 5 ) σ ref : Reference spectra because definition of the reference spectra is based on pure samples of electrons and protons of finite statistics. PRL113,121101(2014) 14

PRL110 ， 141102(2013) 6.8 million e ± events Selected from 25 billion events collected during the first 18 months of operations: May 19, 2011 to December 10, 2012 Selected by APS as a highlight of the Year 2013 PRL113 ， 121101(2014) 10.9 million e ± events Selected from the sample of 41 billion events Two papers had been cited ~1000 times 15

Positron Fraction PRL113 ， 121101(2014) 16

Positron fraction begin to increase at 7.8 GeV PRL113 ， 121101(2014) 17

The positron fraction rise slope decreases with energy, the maximum is reached at 275 ± 32GeV PRL113 ， 121101(2014) 18

Examples of Theoretical Models for positrons From Dark Matter 1) J. Kopp, Phys. Rev. D 88, 076013 (2013); 2) L. Feng, R.Z. Yang, H.N. He, T.K. Dong, Y.Z. Fan and J. Chang Phys.Lett. B728 (2014) 250 3) M. Cirelli, M. Kadastik, M. Raidal and A. Strumia ,Nucl.Phys. B873 (2013) 530 4) M. Ibe, S. Iwamoto, T. Moroi and N. Yokozaki, JHEP 1308 (2013) 029 5) Y. Kajiyama and H. Okada, Eur.Phys.J. C74 (2014) 2722 6) K.R. Dienes and J. Kumar, Phys.Rev. D88 (2013) 10, 103509 7) L. Bergstrom, T. Bringmann, I. Cholis, D. Hooper and C. Weniger, PRL 111 (2013) 171101 8) K. Kohri and N. Sahu, Phys.Rev. D88 (2013) 10, 103001 9) P. S. Bhupal Dev, D. Kumar Ghosh, N. Okada and I. Saha, Phys.Rev. D89 (2014) 095001 10) A. Ibarra, A.S. Lamperstorfer and J. Silk, Phys.Rev. D89 (2014) 063539 11) Y. Zhao and K.M. Zurek, JHEP 1407 (2014) 017 12) C. H. Chen, C. W. Chiang, and T. Nomura, Phys. Lett. B 747, 495 (2015) 13) H. B. Jin, Y. L. Wu, and Y.-F. Zhou, Phys.Rev. D92, 055027 (2015) 14) M-Y. Cui, Q. Yuan, Y-L.S. Tsai and Y-Z. Fan, arXiv:1610.03840 (2016) 15) A. Cuoco, M. Krämer and M. Korsmeier, arXiv:1610.03071 (2016) ……. From Astrophysical Sources 1) T. Linden and S. Profumo, Astrophys.J. 772 (2013) 18 2) P. Mertsch and S. Sarkar, Phys.Rev. D 90 (2014) 061301 3) I. Cholis and D. Hooper, Phys.Rev. D88 (2013) 023013 4) A. Erlykin and A.W. Wolfendale, Astropart.Phys. 49 (2013) 23 5) P.F. Yin, Z.H. Yu, Q. Yuan and X.J. Bi, Phys.Rev. D88 (2013) 2, 023001 6) A.D. Erlykin and A.W. Wolfendale, Astropart.Phys. 50-52 (2013) 47 7) E. Amato, Int.J.Mod.Phys.Conf.Ser. 28 (2014) 1460160 8) P. Blasi, Braz.J.Phys. 44 (2014) 426 9) D. Gaggero, D. Grasso, L. Maccione, G. DiBernardo and C Evoli, Phys.Rev. D89 (2014) 083007 10) M. DiMauro, F. Donato, N. Fornengo, R. Lineros and A. Vittino, JCAP 1404 (2014) 006 11) K. Kohri, K. Ioka, Y. Fujita, and R. Yamazaki, Prog. Theor. Exp. Phys. 2016, 021E01 (2016) …… From Secondary Production 1) R.Cowsik, B.Burch, and T.Madziwa-Nussinov, Ap.J. 786 (2014) 124 2) K. Blum, B. Katz and E. Waxman, Phys.Rev.Lett. 111 (2013) 211101 3) R. Kappl and M. W. Winkler, J. Cosmol. Astropart. Phys. 09 (2014) 051 4) G.Giesen, M.Boudaud, Y.Gènolini, V.Poulin, M.Cirelli, P.Salati and P.D.Serpico, JCAP09 (2015) 023; 5) C.Evoli, D.Gaggero and D.Grasso, JCAP 12 (2015) 039. 6) R.Kappl, A.Reinertand, and M.W.Winkler, arXiv:1506.04145 (2015) …… 19

Models to explain the AMS Positron Fraction Measurements Some models are constrained by complementary measurement of AMS. Examples 1: Modified propagation of cosmic rays R. Cowsik et al. , Ap. J. 786 (2014) 124, The AMS Boron-to-Carbon (B/C) flux ratio (pink band) explaining that the AMS positron fraction (gray circles) above 10 GV PRL 117, 231102 (2016) is due to propagation effects. However, this requires a specific energy 11 million nuclei dependence of the B/C ratio Cowsik (2014) 20

Models explain the AMS Positron Fraction Measurements Some models are constrained by complementary measurement of AMS. Examples 2: Supernova Remnants positron fraction P. Mertsch and S. Sarkar, Phys.Rev. D 90 (2014) 061301(R) B/C Subir Sarkar: AMS Days@CERN, April 2015 Subir Sarkar: AMS days@CERN, April 2015: Not able to fit simultaneously the positron and B/C. 21

Models to explain the Positron Fraction Measurements Examples: Pulsars • AMS-02 M. DiMauro, F. Donato, N. Fornengo, R. Lineros, A. Vittino, JCAP 1404 (2014) 006 Positron Fraction E(GeV) The rate of falls predicted by pulsars model and dark matter model are different. 22

Models to explain the Positron Fraction Measurements Examples: Dark Matter model with intermediate state M.Cirelli, M.Kadastik, M.Raidal and A.Strumia, Nucl.Phys. B873 (2013) 530 • AMS 2013 PAMELA 2009  The accuracy of the measurement in the last bin is limited by statistics. To understand the origin of the positron excess, we need more data. 23

Comparison of the latest results of positron fraction measurement with a Dark Matter model Preliminary Data. AMS 2016 Please refer to the AMS forthcoming publication in PRL . 17 million events Positron Fraction M  = 1 TeV Model based on e ± energy [GeV] J. Kopp, Phys. Rev. D 88 (2013) 076013 24

To collect data up to 2024, we should be able to understand the origin of the positron excess AMS 2024 Pulsars Positron fraction M  = 1 TeV E(GeV) 25