Thee $+e ﬂuxmeasurement$ with$the$AMS$experiment$on$ISS$alpha.sinp.msu.ru/~panov/Lib/Papers/AMS-02/04_ICRC... · EventselecEon$ 600 GeV electron - DAQ: efficient data periods (no

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




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


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


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



�(E,E +�E) =N

obs

(E,E +�E)

�E�Texp

Ae↵

✏trig



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 %



�(E,E +�E) =N

obs

(E,E +�E)

�E�Texp

Ae↵

✏trig



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)


Acceptance

Preselection Selection



�(E,E +�E) =N

obs

(E,E +�E)

�E�Texp

Ae↵

✏trig



The trigger efficiency

100% efficiency at E>3 GeV

Determined with ISS data with unbias trigger (pre-scaled by 1/100)


SystemaEc error Track reconstruction:

σ<1%


# of electrons with a track # of electrons passing through TRK acceptance

SystemaEc error ≥ 8 TRD hits used in the estimator

σ<1% σ≈2%


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


Energy (GeV)1 10 210 310

-1 s

sr)

2Fl

ux (G

eV m

-810

-710

-610

-510

-410

-310

-210

-1101

10

210



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)



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





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)



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


BACKUP


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%


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


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.


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.


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

Documents

Thee $+e ﬂuxmeasurement$ with$the$AMS$experiment$on$ISS$alpha.sinp.msu.ru/~panov/Lib/Papers/AMS-02/04_ICRC... · EventselecEon$ 600 GeV electron - DAQ: efficient data periods (no