Positron Fraction and Lepton Fluxes in Cosmic Rays with AMS-02 Li - PowerPoint PPT Presentation

Positron Fraction and Lepton Fluxes in Cosmic Rays with AMS-02 Li TAO (LAPP-IN2P3-CNRS) On behalf of AMS collaboration FFP14 @ Marseille in France July 2014

Our goals With AMS, we search for primodial antimatter and evidence of dark matter; we refine the propagation models. Electrons constitute 1% of the cosmic ray particles. Positron identification requires proton rejection power of 10 4 . 2

Overview of the AMS Detector trigger 0.14T 3

Data Acquisition Since May 2011 Trigger Rate (Hz) The trigger rates vary from DAQ efficiency reaches 90% 200 to 2000 Hz per orbit (South Atlantic Anomaly excluded) 50 billion events have been collected in the past 3 years. 4

Electron Identification Electron event @ 1.03TeV Proton rejection Charge Z Velocity β Electron Charge Z Selection Sign of the charge Momentum P Electron energy E Proton rejection 5

Proton Rejection TRD @ 90% e+ efficiency 6

Electron Number Count  Number of leptons and positrons extracted from fitting data with electron and proton templates  Templates obtained from data  Electron and proton templates well separated using ECAL and TRD estimators ECAL estimator fit Lepton sample TRD estimator fit Positron sample Positrons 173-206 GeV 7 Z.WENG and V.Vagelli @ ICHEP 2014

Charge Confusion  Charge confusion estimator developped using tracker information  Other estimators such as E/P  Charge confusion obtained by simultaneously fitting with electron/proton estimator 8

Charge Confusion Good agreement between MC prediction and Data measurement Method BDT Method E/P 9

Positron Fraction (2014 @ ICHEP) • Energy range extended to 500 GeV • Improved accuracy compared to PRL result 2013 • ~72 positrons for the last bin: σ stat. 0.028, σ syst. 0.019 10

Positron fraction E s = 𝐹 𝑡 = 540+250 −130𝐻𝑓𝑊 2013 2014 Diffuse power law and source terms are used to describe the behaviour of positron fraction 11

Flux Measurement Procedure 𝑶 𝒕𝒋𝒉𝒐𝒃𝒎 𝜲(𝑭, 𝑭 + ∆𝑭) = Isotropic flux: 𝑩 𝒉𝒇𝒑 ∗ 𝜻 𝒕𝒇𝒎. ∗ 𝜻 𝒖𝒔𝒋𝒉. ∗ 𝑼 𝒇𝒚𝒒𝒑 (𝑭) ∗ 𝜠𝑭 MC  Acceptance & Selection efficiency MC • calculated with MC • corrected with data  Systematic uncertainties: • 2-3% from acceptance • 2% from energy measurement 12

Trigger Efficiency 𝐎 𝐪𝐢𝐳𝐭.𝐮𝐬𝐣𝐡. 𝑭𝒎𝒇𝒅𝒖𝒔𝒑𝒐𝒕: 𝛇 𝐮𝐬𝐣𝐡. = 𝐎 𝐪𝐢𝐳𝐭.𝐮𝐬𝐣𝐡 + 𝐠 𝐪𝐬𝐟𝐭𝐝𝐛𝐦𝐟 × 𝐎 𝐯𝐨𝐜𝐣𝐛𝐭 Efficiency 100% from 5 GeV 13

Exposure Time 𝐎 𝐔 𝐟𝐲𝐪𝐩 (𝐅) = 𝐌𝐣𝐰𝐟𝐔𝐣𝐧𝐟 ∗ 𝐈(𝐅 − 𝐠 ∗ 𝐒 𝐍𝐛𝐲𝐝𝐯𝐮𝐩𝐠𝐠 ) 𝟏 H(x) is the Heaviside step function R cutoff is the geomagnetic cutoff value, f the safety factor 14

Electron Flux (2014 @ ICHEP) 15

Positron Flux (2014 @ ICHEP) 16

Combined e + +e - Flux (2014@ICHEP) 17

Conclusion  AMS has been performing smoothly for more than 3 years. 30 months of data have been analyzed.  11 million positrons and electrons  The combination of TRD and ECAL achieves a proton rejection power of 10 4 .  Latest AMS results are presented:  Positron fraction up to 500 GeV  Electron flux up to 700 GeV  Positron flux up to 500 GeV  Combined positron and electron flux up to 1 TeV 18

ECAL Resolution 17 X 0 19

Charge Confusion: E/P method 20

DM origin of positron fraction rise 21

Pulsar origin of the positron fraction rise 22

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