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

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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 104.

Overview of the AMS Detector

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0.14T trigger

Data Acquisition Since May 2011

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DAQ efficiency reaches 90% (South Atlantic Anomaly excluded) Trigger Rate (Hz) The trigger rates vary from 200 to 2000 Hz per orbit

50 billion events have been collected in the past 3 years.

Electron Identification

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Proton rejection Charge Z Velocity β Charge Z Sign of the charge Momentum P Electron energy E Proton rejection

Electron Selection Electron event @ 1.03TeV

Proton Rejection

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TRD @ 90% e+ efficiency

Electron Number Count

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Positrons 173-206 GeV

TRD estimator fit Positron sample ECAL estimator fit Lepton sample  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

Z.WENG and V.Vagelli @ ICHEP 2014

Charge Confusion

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

Charge Confusion

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

Positron Fraction (2014 @ ICHEP)

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• Energy range extended to 500 GeV
• Improved accuracy compared to PRL result 2013
• ~72 positrons for the last bin: σstat. 0.028, σsyst. 0.019

Positron fraction

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Diffuse power law and source terms are used to describe the behaviour of positron fraction 2014 2013

Es=

𝐹𝑡 = 540+250 −130𝐻𝑓𝑊

Flux Measurement Procedure

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𝜲(𝑭, 𝑭 + ∆𝑭) = 𝑶𝒕𝒋𝒉𝒐𝒃𝒎 𝑩𝒉𝒇𝒑 ∗ 𝜻𝒕𝒇𝒎. ∗ 𝜻𝒖𝒔𝒋𝒉. ∗ 𝑼𝒇𝒚𝒒𝒑(𝑭) ∗ 𝜠𝑭

Isotropic flux:

MC  Acceptance & Selection efficiency

• calculated with MC
• corrected with data

 Systematic uncertainties:

• 2-3% from acceptance
• 2% from energy measurement

MC

Trigger Efficiency

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𝑭𝒎𝒇𝒅𝒖𝒔𝒑𝒐𝒕: 𝛇𝐮𝐬𝐣𝐡. = 𝐎𝐪𝐢𝐳𝐭.𝐮𝐬𝐣𝐡. 𝐎𝐪𝐢𝐳𝐭.𝐮𝐬𝐣𝐡 + 𝐠𝐪𝐬𝐟𝐭𝐝𝐛𝐦𝐟 × 𝐎𝐯𝐨𝐜𝐣𝐛𝐭 Efficiency 100% from 5 GeV

𝐔𝐟𝐲𝐪𝐩(𝐅) = 𝐌𝐣𝐰𝐟𝐔𝐣𝐧𝐟 ∗ 𝐈(𝐅 − 𝐠 ∗ 𝐒𝐍𝐛𝐲𝐝𝐯𝐮𝐩𝐠𝐠)

𝐎 𝟏

Exposure Time

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H(x) is the Heaviside step function Rcutoff is the geomagnetic cutoff value, f the safety factor

Electron Flux (2014 @ ICHEP)

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Positron Flux (2014 @ ICHEP)

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

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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 104.  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

Conclusion

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ECAL Resolution

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17 X0

Charge Confusion: E/P method

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DM origin of positron fraction rise

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Pulsar origin of the positron fraction rise

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