thee $+e fluxmeasurement$...
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The e-‐ + e+ flux measurement with the AMS experiment on ISS
The (e++e-‐) flux measurement
�(E,E +�E) =N
obs
(E,E +�E)
�E�Texp
Ae↵
✏trig
F = Absolute differential flux (m-2 sr -1 GeV-1) Nobs = Number of observed events DTexp = Exposure time (s) Aeff = effective acceptance (m2sr) Etrig = trigger efficiency
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 2
�(E,E +�E) =N
obs
(E,E +�E)
�E�Texp
Ae↵
✏trig
F = Absolute differential flux (m-2 sr -1 GeV-1) Nobs = Number of observed events DTexp = Exposure time (s) Aeff = effective acceptance (m2sr) Etrig = trigger efficiency
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 3
The (e++e-‐) flux measurement
Event selecEon 600 GeV electron
- DAQ: efficient data periods (no SAA) - Geomagnetic effects: E>1.25 max cutoff
- TRD : - Minimum 8 hits used for e/p identification - TOF : relativistic down-going particle - ECAL:
- Shower axis within the fiducial volume - Electromagnetic shape of the shower (BDT estimator)
- TRACKER - Z<1.5 from tracker - track/ECAL matching to define fiducial
volume
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 4
TRD-LLe-4 -3.75 -3.5 -3.25 -3 -2.75 -2.5 -2.25 -2
Nor
mal
ized
Ent
ries
-510
-410
-310
-210
TRD-LLe-4 -3.75 -3.5 -3.25 -3 -2.75 -2.5 -2.25 -2
Nor
mal
ized
Ent
ries
0
0.002
0.004
0.006
0.008
0.01
TRD e/p templates Electrons E[50,100]GeV
E[20-22]GeV
E[330-500]GeV
TRD-LLe =
Log10(Pe)
hEle_25__1__1Entries 19229Mean 376.6RMS 369.1
ADC counts500 1000 1500
Nor
mal
ized
Ent
ries
-510
-410
-310
-210
-110hEle_25__1__1Entries 19229Mean 376.6RMS 369.1
Electrons
Protons
TRD - Single tube spectrum
Protons
E[15,35]GeV
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 5
Analysis : 1D fit to measure Ne and Np Reference spectra for the signal and the background are fitted to data
as a function of the TRD estimator for different cuts on the ECAL BDT estimator
Measurement is performed for the BDT cut that minimizes the overall statistical +systematic uncertainty
TRD-LLe-3.6 -3.4 -3.2 -3 -2.8 -2.6 -2.4
Entr
ies
0102030405060708090 Entries: 1249.0
Sig: 1149.7 +/- 34.5
Bkg: 99.3 +/- 12.0
[102.5 - 109.4] GeV - ECAL BDT > +0.20[102.5-109.4] GeV
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 6
The (e++e-‐) flux measurement
�(E,E +�E) =N
obs
(E,E +�E)
�E�Texp
Ae↵
✏trig
F = Absolute differential flux (m-2 sr -1 GeV-1) Nobs = Number of observed events DTexp = Exposure time (s) Aeff = effective acceptance (m2sr) Etrig = trigger efficiency
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 7
Exposure Time
ü Data taking period: 19 May 2011 - 19 May 2013
ü Total exposure time used above 25 GeV: 51.2 x 106 s
ü Average life time fraction Texp/2 years = 81.6 %
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 8
The (e++e-‐) flux measurement
�(E,E +�E) =N
obs
(E,E +�E)
�E�Texp
Ae↵
✏trig
F = Absolute differential flux (m-2 sr -1 GeV-1) Nobs = Number of observed events DTexp = Exposure time (s) Aeff = effective acceptance (m2sr) Etrig = trigger efficiency
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 9
Acceptance • Estimated with MC (Geant 4)
• Agenerated = acceptance of the generation surface • Nselected = events passing the selection criteria
Aeff.(E) = Agenerated ✕ Nselected(E)
Ngenerated(E)
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 10
Acceptance
Preselection Selection
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 11
The (e++e-‐) flux measurement
�(E,E +�E) =N
obs
(E,E +�E)
�E�Texp
Ae↵
✏trig
F = Absolute differential flux (m-2 sr -1 GeV-1) Nobs = Number of observed events DTexp = Exposure time (s) Aeff = effective acceptance (m2sr) Etrig = trigger efficiency
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 12
The trigger efficiency
100% efficiency at E>3 GeV
Determined with ISS data with unbias trigger (pre-scaled by 1/100)
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 13
SystemaEc error Track reconstruction:
σ<1%
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 14
# of electrons with a track # of electrons passing through TRK acceptance
SystemaEc error ≥ 8 TRD hits used in the estimator
σ<1% σ≈2%
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 15
SystemaEc error: stability of the signal vs ECAL BDT cut
In each energy interval the cut on the ECAL BDT has been varied around the working point to verify the stability of the measurement.
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 16 BDT cut efficiency
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
/effi
cien
cy+
+e- eN
1500
1600
1700
1800
1900
2000
2100
2200
2300
0 10 20 30 40 50 60 70 80 90
Mean 1930 RMS 17.34
[102.5,109.4] GeV 0 10 20 30 40 50 60 70 80 90"
Occurrency
The (e-‐ +e+) flux
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 17
Energy (GeV)1 10 210 310
-1 s
sr)
2Fl
ux (G
eV m
-810
-710
-610
-510
-410
-310
-210
-1101
10
210
The (e-‐ +e+) flux
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 18
Energy (GeV)1 10 210 310
-1 s
sr)
2Fl
ux (G
eV m
-810
-710
-610
-510
-410
-310
-210
-1101
10
210 AMS-02ATIC01&02 (2001 & 2003)BETS04 (2004)BETS97&98 (1997 & 1998)CAPRICE94 (1994)Fermi-LAT (2009)HEAT94 (1994)HEAT94&95 (1994 & 1995)HEAT95 (1995)H.E.S.S. (2004 -2007)H.E.S.S. (LE) (2004 & 2005)
The (e-‐ +e+) flux
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 19
Energy (GeV)1 10 210 310
3 E×
-1 s
sr)
2Fl
ux (G
eV m
50
100
150
200
250
300
Energy (GeV)1 10 210 310
3 E× -1
s s
r)2
Flux
(GeV
m
0
50
100
150
200
250
300
AMS-02 : this analysis AMS-02 : sum of e- and e+ fluxes
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 20
The (e-‐ +e+) flux
The (e-‐ +e+) flux
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 21
Energy (GeV)1 10 210 310
3 E×
-1 s
sr)
2Fl
ux (G
eV m
0
50
100
150
200
250
300
350
400AMS-02ATIC01&02 (2001 & 2003)BETS04 (2004)BETS97&98 (1997 & 1998)CAPRICE94 (1994)Fermi-LAT (2009)HEAT94 (1994)HEAT94&95 (1994 & 1995)HEAT95 (1995)H.E.S.S. (2004 -2007)H.E.S.S. (LE) (2004 & 2005)
The (e-‐ +e+) flux
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 22
Energy (GeV)1 10 210 310
3 E×
-1 s
sr)
2Fl
ux (G
eV m
0
50
100
150
200
250
300
350
400AMS-02ATIC01&02 (2001 & 2003)BETS04 (2004)Fermi-LAT (2009)H.E.S.S. (2004 -2007)H.E.S.S. (LE) (2004 & 2005)
Conclusions - 9 million electrons out of ≈ 30 billion triggers have been used to measure the e+ + e- spectrum up to 700 GeV. -This corresponds to ≈ 10% of the expected data sample.
1.03 TeV electron
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 23
BACKUP
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 24
SystemaEcs
• SelecEon MC/Data comparison ≈ 2-‐3% • NormalizaEon Track/No-‐Track analysis ≈ 3% • Energy smearing (< 2 GeV) ≈ 1% • Stability vs BDT cut efficiency ≈ 1% • TRD-‐LLE Reference distribuEon for protons ≈1%
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 25
SystemaEc error: stability of the signal vs ECAL BDT cut
Entries 298Mean 1931RMS 21.02
/ eff+/-fitted e1900 1950 2000
Occ
urre
ncy
0
10
20
30
40
50
60Entries 298Mean 1931RMS 21.02
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 26
In each energy interval the cut on the ECAL BDT has been varied around the working point to verify the stability of the measurement.
BDT cut Efficiency
BDT cut-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4
Fitte
d el
ectr
ons
020040060080010001200140016001800
[102.5 - 109.4] GeV
BDT cut-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4
Effic
ienc
y
0
0.2
0.4
0.6
0.8
1
[102.5 - 109.4] GeV
An enriched sample in electrons is selected by means of negative sign of the charge, E/P matching The same fitting procedure as on the full sample is applied in order to estimate the number of electrons as a function of the BDT cut.
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 27
BDT cut-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6
Effi
cien
cy
0
0.2
0.4
0.6
0.8
1
1.2[202.1 - 226.6] GeV
SystemaEcs on the template
BDT cut-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6
Effi
cien
cy
0
0.2
0.4
0.6
0.8
1
1.2
E/P<1.0E/P<0.9E/P<0.8
E/P<0.75E/P<0.7E/P<0.6E/P<0.5
No BDT cut
BDT < 0
BDT < -0.1
[202.1 - 226.6] GeV
Use different 21 different selections varying (E/p, BDT) to define the proton template and see the effect on the measurement.
ICRC 2013 : e-‐ + e+ measurement with AMS B.Bertucci 28
SystemaEcs: bin-‐to-‐bin migraEon
B.Bertucci ICRC 2013 : e-‐ + e+ measurement with AMS 29
High energy effects • ECAL energy scale for a
single cell is linear from 2 MeV up to 60 GeV
• Thanks to the ECAL granularity the energy is shared among many cells
• This allows to measure the energy of electrons up to the TeV with minor saturaEon effects
B.Bertucci ICRC 2013 : e-‐ + e+ measurement with AMS 30