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Precision Measurement of Positron Fraction and Combined Positron Electron Flux by AMS
5m x 4m x 3m7.5 tons
Zuhao LI / IHEP, CAS
On behalf of the AMS Collaboration
ICHEP 2018
7, July, 2018
Dark Matter search in space
AMS
p, He
𝒆+𝒆+, 𝒆−
𝒆−
2
• There are particles (protons, electrons) and antiparticles (positrons, antiprotons, anti-deuterons) in the cosmos.
• Particles are produced in many astrophysical sources. • Antiparticles are much less abundant from astrophysical processes. • Both particles and antiparticles can be produced by new physics
sources, like Dark Matter.
Measuring antiparticles are more sensitive to Dark Matter, because the astrophysical background is much smaller.
Tra
cke
r
1
2
7-8
3-4
9
5-6
Transition Radiation Detector (TRD)Identify e+, e-
Silicon TrackerZ, P or R=P/Z
Electromagnetic Calorimeter (ECAL)E of e+, e-
Ring Imaging Cherenkov (RICH)
Z, E
Time of Flight (TOF)Z, E
AMS: A unique TeV precision, multipurpose, magnetic spectrometer
Magnet±Z
Z and P, E or R are
measured independently by Tracker,
ECAL, TOF and RICH
Transition Radiation
3
0 0.5 1 1.5 2 2.5 3
tracker/PE C A LE
0
0.02
0.04
0.06
Norm
alized entries
Protons
Electrons
4Energy/Momentum
No
rmal
ize
d E
ntr
ies
• The synergy of the Energy from ECAL and the Momentum from tracker can be used for proton separation .
• The protons deposit less energy in the calorimeter
Unique feature of AMS
Unique feature of AMS
5
By comparing the ISS data with beam data and MC simulation, the energy scale uncertainty is estimated to be 2% from 10-290GeV, 3% at 2 TeV
1 10 100 1000E nergy[G eV ]
0
2
4
6
Energ
y scale uncertainty [%]
Test beam
3.5%
4%
2%
10 290
Ene
rgy
Scal
e U
nce
rtai
nty
[%
]
Energy [GeV]
• The energy scale is the most important source of systematic errors for non-magnetic cosmic ray experiments.
• AMS determines the energy scale by using the tracker and magnet
6M om entum [G eV /c]
1 10 100 1000
Pro
ton Rejection
1
10
210
310
410
510
pro
ton
Re
ject
ion
• Proton rejection 103 to 104
with TRD
• Proton rejection is above 104 with ECAL and tracker
• TRD and ECAL is separated by the magnet, and have independent proton rejection power.
• The proton rejection power is better than 106
Proton rejection power
Calibration of the AMS Detector
2000 positions
Test beam at CERN SPS: p, e±, π±, 10−400 GeV
Computer simulation:Interactions, Materials, Electronics
12,000 CPU cores at CERN
AMS27 km
7 km
7
In 7 years on ISS, AMS has collected over 120 billion cosmic rays.
Search for Dark Matter is one of the main physics topic of AMS .
8
The measurement of electrons and positrons in AMS
Primary cosmic ray particle:
• E>1.2∙max cutoff
TOF:
• Down-going particle β>0.8
• Charge |Z|=1 particle
TRD:
• Provide proton rejection
tracker and magnet:
• Provide accurate momentum measurement
• Charge |Z|=1 particle
ECAL:
• Provide accurate energy measurement.
• Provide proton rejection with 3D shower
shape
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A 960 GeV positron
1-0.5-
00.5
1
C CL0.5
1
TR DL
0
20
40Events
D ata
1-0.5-
00.5
1
C CL0.5
1
TR DL
0
20
40Events
Fit
signal+e
p background
background-e
Analysis method to determine the number of 𝐞+
10
• ECAL selection to remove bulk of the proton background.
• For each bin, fit templates to positive data sample in (𝚲𝐓𝐑𝐃 − 𝚲𝐂𝐂) plane
• Positron signal template from data using electrons
• Proton background template from proton data
• Charge confusion electron template from electron MC
149 < E < 170 GeV
𝝌𝟐 𝒅𝒇 = 𝟑𝟒𝟐. 𝟖/𝟒𝟗𝟕
p 𝐞+
𝐞−
𝐞+p
2 30
0.1
0.2
Relative error
C harge confusion
E lectron tem plate
P roton tem plate
Tem plate fluctuation
1 10 2103
10
E nergy [G eV ]
0
0.2
0.4
0.6
Relative error
S tatistical error
S ystem atic error
Total error
11
With 28.1 million electrons and 1.9 million positrons,
the study of systematic errors is crucial
1. Charge confusion
2. Template selection
3. Template statistical fluctuation
Statistical errors dominates above 30 GeV for positron flux
Total error
Statistical error
Systematic error
Po
sitr
on
fra
ctio
n r
ela
tive
err
or
1 10 100 1000
E nergy [G eV ]0
0.05
0.1
0.15
0.2
Positro
n fraction
AMS Positron fraction
12
1.9 million 𝐞+28.1 million 𝐞−
𝜱𝒆+
𝜱𝒆+ +𝜱𝒆−
Preliminary Data.Please refer to the AMS
forthcoming publication in PRL.
1 10 210 310E nergy [G eV ]
0
0.1
0.2
0.3
Positro
n fraction
A M S -02
P A M E LA
Ferm i-LA T
M A S S
C A P R IC E
H E A T
13
AMS Positron fraction together with earlier experiments
Preliminary Data.Please refer to the AMS
forthcoming publication in PRL.
A sample of papers on AMS data from more than 2300 publications1) J. Kopp, Phys. Rev. D 88, 076013 (2013); 2) L. Feng, R.Z. Yang, H.N. He, T.K. Dong, Y.Z. Fan and J. Chang Phys.Lett. B728 (2014) 250 3) M. Cirelli, M. Kadastik, M. Raidal and A. Strumia ,Nucl.Phys. B873 (2013) 530 4) M. Ibe, S. Iwamoto, T. Moroi and N. Yokozaki, JHEP 1308 (2013) 029 5) Y. Kajiyama and H. Okada, Eur.Phys.J. C74 (2014) 27226) K.R. Dienes and J. Kumar, Phys.Rev. D88 (2013) 10, 103509 7) L. Bergstrom, T. Bringmann, I. Cholis, D. Hooper and C. Weniger, PRL 111 (2013) 171101 8) K. Kohri and N. Sahu, Phys.Rev. D88 (2013) 10, 1030019) A. Ibarra, A.S. Lamperstorfer and J. Silk, Phys.Rev. D89 (2014) 06353910) Y. Zhao and K.M. Zurek, JHEP 1407 (2014) 01711) C. H. Chen, C. W. Chiang, and T. Nomura, Phys. Lett. B 747, 495 (2015) 12) H. B. Jin, Y. L. Wu, and Y.-F. Zhou, Phys.Rev. D92, 055027 (2015)13) A. Reinert and M. W. Winkler JCAP 01 (2018) 055
and many other excellent papers …
1) R.Cowsik, B.Burch, and T.Madziwa-Nussinov, Ap.J. 786 (2014) 1242) K. Blum, B. Katz and E. Waxman, Phys.Rev.Lett. 111 (2013) 2111013) R. Kappl and M. W. Winkler, J. Cosmol. Astropart. Phys. 09 (2014) 051 4) G.Giesen, M.Boudaud, Y.Gènolini, V.Poulin, M.Cirelli, P.Salati and P.D.Serpico, JCAP09 (2015) 023;5) C.Evoli, D.Gaggero and D.Grasso, JCAP 12 (2015) 039.6) R.Kappl, A.Reinert, and M.W.Winkler, arXiv:1506.04145 (2015)
and many other excellent papers …
1) T. Linden and S. Profumo, Astrophys.J. 772 (2013) 18 2) P. Mertsch and S. Sarkar, Phys.Rev. D 90 (2014) 0613013) I. Cholis and D. Hooper, Phys.Rev. D88 (2013) 0230134) A. Erlykin and A.W. Wolfendale, Astropart.Phys. 49 (2013) 235) P.F. Yin, Z.H. Yu, Q. Yuan and X.J. Bi, Phys.Rev. D88 (2013) 2, 0230016) A.D. Erlykin and A.W. Wolfendale, Astropart.Phys. 50-52 (2013) 477) E. Amato, Int.J.Mod.Phys.Conf.Ser. 28 (2014) 14601608) P. Blasi, Braz.J.Phys. 44 (2014) 4269) D. Gaggero, D. Grasso, L. Maccione, G. DiBernardo and C Evoli, Phys.Rev. D89 (2014) 08300710) M. DiMauro, F. Donato, N. Fornengo, R. Lineros and A. Vittino, JCAP 1404 (2014) 00611) K. Kohri, K. Ioka, Y. Fujita, and R. Yamazaki, Prog. Theor. Exp. Phys. 2016, 021E01 (2016)
and many other excellent papers …
Dark Matter explaining the AMS e+ data
New Astrophysical Sources explaining the AMS e+ data
New Propagation Models explaining the AMS e+ data
14
Models to explain the AMS Positron Fraction Measurements
R. Cowsik et al., Ap. J. 786 (2014) 124, (pink band) explaining that the AMS
positron fraction (gray circles) above 10 GV is due to propagation effects.
However, this requires a specific energy dependence of the B/C ratio
The AMS Boron-to-Carbon (B/C) flux ratio
Cowsik (2014)
11 million nuclei
PRL 117, 231102 (2016)
Some models are constrained by other measurements by AMS.
Examples 1: Modified propagation of cosmic rays
15
Models explain the AMS Positron Fraction Measurements
P. Mertsch and S. Sarkar, Phys.Rev. D 90 (2014) 061301(R)
Subir Sarkar: AMS Days@CERN, April 2015p
osi
tro
n f
ract
ion
B/C
Not able to fit simultaneously the positron and B/C.
Examples 2: Supernova Remnants
16
Some models are constrained by other measurements by AMS.
Subir Sarkar: AMS days@CERN, April 2015
E nergy [TeV ]
3-10 2-10 1-10 1 10
]-1
sr
-1s
-2m
2J(E
) [G
eV
3 E
3-10
2-10
1-10
1
10
210
A M S -02
=0.33(base)d
range(base)s3
17
AMS
HAWC3σ range
17
HAWC rules out that the positron excess is from nearby pulsarsScience 358, 911-914 (2017)
AMS measurement of positron anisotropy (presentation by Jorge Casaus) constrains the pulsar origin of positrons
1 10 100 1000
E nergy [G eV ]0
0.05
0.1
0.15
0.2
Positro
n fraction
⦁ 1.9 million positrons
1.2 TeVDark Matter + Collision of Cosmic Rays
Dark Matter model is based on J. Kopp, Phys. Rev. D 88, 076013 (2013).
Latest AMS Positron fraction results appears to be in
excellent agreement with Dark Matter model
𝜱𝒆+
𝜱𝒆+ +𝜱𝒆−
Po
sitr
on
fra
ctio
n =
e+ /
(e+
+ e
– )
Preliminary Data.Please refer to the AMS
forthcoming publication in PRL.
18
1 10 100 1000E nergy [G eV ]
0
50
100
150
200
250]2
GeV
-1s
-1sr
-2 [m
3 E-
+e
+e
FThe combined (e+ + e–) flux
AMS-02 30 million (𝒆+ + 𝒆−)
The spectrum is smooth, no sharp structure is observed
Preliminary Data.Please refer to the AMS
forthcoming publication in PRL.
19
20
AMS (e+ + e–) data with a few non-magnetic detectors
HESS syst. error
Preliminary Data.Please refer to the AMS
forthcoming publication in PRL.
21
(e+ + e–) data with AMS and with non-magnetic detectors
HESS syst. error
Preliminary Data.Please refer to the AMS
forthcoming publication in PRL.
HESS, DAMPE and AMS all observed a spectral break at ~ 1 TeVMeasuring e+ is the most sensitive way to identify 𝝌 via 𝝌 + 𝝌→ e+, e-, …Measuring (e++e–) is much less sensitive to 𝝌 due to the large e– background
With 1.9 million positrons and 28.1 million electrons, AMS extends the positron fraction measurement to 1 TeV,
and the combined (positron + electron) flux to 2 TeV.
AMS positron fraction by far exceeds the prediction from collisions of cosmic rays and appears to be in excellent
agreement with a Dark Matter model.
By 2024 AMS will collect 4 million positrons, and will be able to determine the origin of the positron excess.
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