S. Schael, RWTH Aachen University on behalf of the AMS Collabora<on
The Electron Spectrum and Positron Spectrum from AMS
2
7. The charge symmetry of 1-‐6
2
The measurements are based on 41 × 109 events collected between May 19, 2011, and November 26, 2013
4
EcalBDT
protons electrons
Analysis Flow
ISS data: 83-‐100 GeV E/p ISS data: 83-‐100 GeV
Frac<on of events Frac<on of events Frac<on of events
electrons
protons electrons
protons
N
1 10 102
/NDF = 1.02 χ2
Positive
26.7
± Proton like 702.0
12.2
± Electron like 135.0
N
1 10 102
/NDF = 1.04 χ2
Negative
5.4
± Proton like 19.1
29.5
± Electron like 863.9
We produce an e± enhanced sample by soZ cuts on:
- the ra<o Energy/|Rigidity|, were the Energy is measured by ECAL and the rigidity by the Tracker.
- the ECAL Es<mator, to separate hadronic showers from electromagne<c showers by their 3D-‐shape
The proton templates are taken from ISS Data, the electron templates from Monte Carlo.
E=132-‐152 GeV
Par<cle Iden<fica<on
Nega<ve Par<cles Posi<ve Par<cles
e
-‐e
+N N
ISS data ISS data
p
-‐p
+χ2/NDF=1.04 χ2/NDF=1.02
Raw Event Rates, sta<s<cal errors only
6
Electrons: 0.5 -‐ 700 GeV Positrons: 0.5 -‐ 500 GeV
Frac<on of charge confused events: fCC
• We use another BDT to derive for each event a classifier (TrkCC) to determine the charge confusion directly from ISS data with a template fit.
e
+χ2/NDF=1.35
E = 56 – 80 GeV
e
-‐ISS data
posi<ve event sample
fCC = 0.0056 ± 0.0006
Frac<on of charge confused events vs Energy
8
Energy [GeV]
10 100 1000
Frac<on of charge confused events
ISS data Monte Carlo
The determina<on of the Flux
In total, 9.23 × 106 events are iden<fied as electrons and 0.58 × 106 as positrons.
Use rare nuclear interac<on events to op<mize the material descrip<on in the Monte Carlo
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side view front view
X-‐Ray of AMS on the ISS from rare nuclear interac<on events The gray scale is propor<onal to the number of ver<ces found.
z [cm]
y [cm]
Number of ver<ces
Control the TRD Geometry at g=0 with an accuracy of 0.1 mm
12
12
0 2 4 6 8 [cm] 10
z [cm]
ISS Data ó MC Data
TRD radiator weight: 60 kg MC: 59.6 kg
ISS
MC
14
|R| = 6 -‐ 18 GV
ISS Data ó MC Data
ISS Data ó MC Data
|R| = 6 -‐ 18 GV
16 16
Efficiency
E [GeV]
1 10 100 1000
ISS data MC data
Efficiency
• ISS tag and probe
• Monte Carlo tag and probe
Efficiency
e
± Iden<fica<on: E/p100 1000 10
Energy [GeV]
1 1000
100 10
Energy [GeV]
log(E/p)
1
log(E/p)
nega<ve event sample posi<ve event sample
FracBon of events
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1 10 100 Energy [GeV] 1000
1+δ A eff [cm2 sr]
1 10 100 Energy [GeV] 1000
Effec<ve Acceptance
Correc<on 1+δ
1 10 100 1000
Determined from ISS data using the unbiased trigger sample.
Data taking <me
• We have analyzed data taken from 19 May 2011 to 26 November 2013 ó 921 days.
• Due to the geomagne<c cutoff the exposure <me is energy dependent.
• The exposure <me is for energies above 30 GeV constant 708 days ó 61 ·∙ 106 seconds
Φe±(E) = Ne±(E)
Aeff (E)⋅εtrig(E)⋅T (E)⋅ ΔE
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87% AMS data taking (ISS orienta<on, TRD gas refills, ...) Live-‐<me: 89%
Geomagne<c cutoff
Energy [GeV]
Time [days]
1 10 100 1000
Φe±(E) = Ne±(E)
Aeff (E)⋅εtrig(E)⋅T (E)⋅ ΔE
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Ø For the positron flux, the sta<s<cal error dominates above ~50 GeV.
Ø For the electron flux above ~200 GeV, the systema<c error and the sta<s<cal error are compa<ble.
[m2 sr s GeV]-‐1 [m2 sr s GeV]-‐1
Time Dependence (to be published)
Electron Flux
<me average
Data from Sep. 2011
(stat. Err. only)
Data from Sep. 2013
(stat. Err. only)
Change/year at 4 GeV: -‐9%
E3 Φ e-‐ [m-‐2 sr-‐1 s-‐1 GeV2 ]
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Electron Flux
24
Electron Flux
26
Positron Flux
26
Positron Flux
28
28
10 100 Energy [GeV]
30
The Positron Flux has no sharp structures and is dominated at high energies by the source term.
Diffuse Term
Source Term
Positron
E3 Φ e+ [m-‐2 sr-‐1 s-‐1 GeV2 ]
E [GeV]
1 10 100 1000
Φe+(E)= E2
Eˆ2 ⎡⎣Ce+Eˆγe+ +CSEˆγS exp(− ˆE / ES)⎤⎦
with ES = 540 GeV from the e+ / (e+ + e−) fit and ˆE as the energy scale of the LIS
Diffuse Term
Source Term
Ø Within this ansatz only one parameter has to be <me dependent:
Positron
Scaled Neutron Monitor
Φe+(E)= E2
Eˆ2 ⎡⎣Ce+Eˆγe+ +CSEˆγS exp(− ˆE / ES)⎤⎦
Eˆ = E +ψe+(t)
E [GeV]
1 10 100 1000
E3 Φ e+ [m-‐2 sr-‐1 s-‐1 GeV2 ]
<me
Jul-‐11 Jan-‐12 Jul-‐12 Dec-‐12 Jul-‐12 Dec-‐13 Jul-‐12 Dec-‐14
ψe+(t), which describes the solar modulation.
ψe+ [GV]
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Diffuse Term
Electron
Source Term
The spectral index of the diffuse term has to become energy dependent:
The source term parameters are constrained from the positron flux fit.
E3 Φ e-‐ [m-‐2 sr-‐1 s-‐1 GeV2 ]
The Electron Flux
Ø has no sharp structures and is dominated by the diffuse term.
Ø is consistent with a charge symmetric source term.
E [GeV]
1 10 100 1000
Φe−(E)= E2
Eˆ2 ⎡⎣Ce−Eˆγe−( ˆE ) +CSEˆγS exp(− ˆE / ES)⎤⎦
• Since September 2014 our publica<on [PRL 113, 121102 (2014)]
has been cited many <mes.
• The models to explain the observed spectral features can be divided into two catergories:
1. New astrophysical processes in cosmic ray accelera<on and/or propaga<on.
2. Dark Mater annihila<on or decay.
• A typical example is shown on the right.
• We are pleased to have the world
leading experts with us during these days to discuss these aspects in detail.
S. Lin, Q. Yuan, and X.-‐J. Bi PHYSICAL REVIEW D 91, 063508 (2015)
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Summary
1. Both the Electron Flux and the Positron Flux are significantly different in their magnitude and energy dependence.
2. Neither the Electron Flux nor the Positron Flux has any sharp structure.
3. Both Fluxes can not be described by a single power law.
4. Both spectra are consistent with a charge symmetric and <me independent source term with a cutoff at Es=540 GeV.
5. AMS will be able to extend these measurements to the TeV scale.
