Precision Measurement of Positron Fraction and Combined ...€¦ · Precision Measurement of Positron Fraction and Combined Positron Electron Flux by AMS 5m x 4m x 3m 7.5 tons Zuhao

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

9

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



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)


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)


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

– )



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



19

20

AMS (e+ + e–) data with a few non-magnetic detectors

HESS syst. error



21

(e+ + e–) data with AMS and with non-magnetic detectors

HESS syst. error



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.

22

Documents

Precision Measurement of Positron Fraction and Combined ...€¦ · Precision Measurement of Positron Fraction and Combined Positron Electron Flux by AMS 5m x 4m x 3m 7.5 tons Zuhao