Measurement of cosmic-ray proton spectrum with the Dark Matter Particle Explorer

Chuan Yue*, Antonio De Benedittis, Mario Nicola Mazziotta, Stefania Vitillo, Zhi-Hui Xu, Yu-Hong Yu

(on behalf of the DAMPE Collaboration)*speaker: yuechuan@pmo.ac.cn

2019.07.30 Madison, USA

“WuKong”

DAMPE Collaboration

for collaboration list see PoS(ICRC2019)1177

• CHINA – Purple Mountain Observatory, CAS – University of Science and Technology of China – Institute of High Energy Physics, CAS – Institute of Modern Physics, CAS – National Space Science Center, CAS

• ITALY – INFN Perugia and University of Perugia – INFN Bari and University of Bari – INFN Lecce and University of Salento – INFN LNGS and Gran Sasso Science Institute

• SWITZERLAND – University of Geneva

2

3

DAMPE Instrument

- Charge measurement (dE/dx in PSD, STK and BGO) - Gamma-ray converting and tracking (STK and BGO) - Precise energy measurement (BGO Crystals) - Hadron rejection (BGO and Neutron Detector)

(Chang et al. Astropart.Phys. 95 (2017) 6–24)

Orbit Information:Sun-synchronous Orbit Altitude: ~ 500 km Inclination: ~ 97 deg Launch Date: Dec.17th, 2015

Main Scientific Goals:Origins and Propagations of Cosmic-Rays Dark Matter Indirected Detection High Energy Gamma-ray Astronomy

(~32X0, ~1.6λI)

Interesting Scientific Issues:

Proton Spectral Hardening at ~400 GeV Other structures beyond TeV Range?

Proton spectrum has been measured with high precision up to TeV

Measurements in high energy range (TeV ~ PeV) have large uncertainties

(Y.S. Yoon et al., CREAM, 2017)

AMS02,ATIC-2,PAMELA,CREAM

DAMPE

Introduction

(E. Atkin et al., NUCLEON, 2018)4

5

Data Sample: Jan. 1st 2016 to Jun. 30th 2018

Total Events: 4.68 Billion Events

Live Time: 5.9670276 * 10^7 s (75.73%)

Data in SAA region are excluded

Dead Time: Instrument Recovery, On-orbit Calibration, etc

Data during Sep2017 Solar Flare (20170908~20170913) are excluded

On-orbit Data Sample

Date01/01/2016 01/07/2016 31/12/2016 02/07/2017 31/12/2017 02/07/2018

Even

ts S

tatis

tic (M

illion

)0

1000

2000

3000

4000

5000DAMPE DAQ Statistic

6

Proton Selections

Cut 0: BgoEnergy > 20 GeV

Cut 1: HE-Trigger

Cut 2: STK Track

Cut 3: Track-PSD Match

Cut 4: Track-BGO Match

Cut 5: PSD pre-selection

Cut 6: BGO pre-selection

Particle Identification

Cut 7: e/p Separation

Cut 8: Charge Selection

Pre-selections Flight-Data Proton (BGO-Energy: 1.2 TeV)

Flight-Data Proton (BGO-Energy: 12.1 TeV)

7

210 310 410

HE

Trig

ger E

ffici

ency

0.2

0.4

0.6

0.8

1MC Proton

Flight Data

BGO Energy [GeV]210 310 410

MC

/Dat

a

0.8

0.9

1

1.1

1.2

Unbias Trigger (G0) MIPs Trigger (G1&G2) High Energy Trigger (G3) Low Energy Trigger (G4)

"trigger =Nhe|unb

Nunb

G3 Trigger Efficiency

2.5%

Uncertainty mainly comes from the threshold calibration and the limited statistics of unbias trigger events

(unbias trigger pre-scaled by 1/512 at low latitudes <20deg and 1/2048 at high latitudes)

High-Energy (G3) trigger efficiency can be obtained by applying all other proton selections (“N-1”) to unbias (G0) sample

HE-Trigger Efficiency

Efficiency Validation (“N-1”):

Preliminary

10 210 310 410

Trac

k R

cons

truct

ion

Effic

ienc

y

0.2

0.4

0.6

0.8

1

MC ProtonFlight Data

BGO Energy [GeV]10 210 310 410

MC

/Dat

a

0.8

0.9

1

1.1

1.2

Preliminary

STK Track Efficiency

8

"track =Ntrack|BGOtrack

NBGOtrack

STK track Efficiency Validation

Selecting a “pure” proton sample by applying BGO shower-axis based proton selections (“N-1”) to estimate STK track reconstruction efficiency

STK Track Efficiency

?

3.5%

∆θx,y(deg)-10 -8 -6 -4 -2 0 2 4 6 8 10

Cou

nts

10

210

310

410

510

610Delta Theta in X-directionDelta Theta in Y-direction

MC Proton

9

BGO Energy (GeV)210 310 410 510

PSD

Cha

rge

1

2

3

4

5

6

7

8

9

10

1

10

210

310

410

Charge selection

PSD Charge1 1.5 2 2.5 3

Num

ber o

f Eve

nts

0

500

1000

1500

2000

2500

3000

3500

4000

4500/TeV < 0.562dep0.447 < E Flight Data

MC ProtonMC HeliumMC Proton+Helium

Layer-yLayer-x

X

ZBethe-Bloch

Zy =qPsdEy/MipE Z

x

=pPsdE

x

/MipE ZPSD

= (Zy

+ Zx

)/2

PreliminaryPSD Charge

(see more in talk CRD7b by Zhang Y.P.)

10

√ Ask the help of the first layer of STK

To Study PSD layer-1 Selection: PSD_L2 && STK_L1

To Study PSD layer-2 Selection: PSD_L1 && STK_L1

PSD Charge Efficiency Validation

10 210 310 410

Cha

rge

Effic

ienc

y0.4

0.6

0.8

1

MC Proton

Flight Data

BGO Energy [GeV]10 210 310 410

MC

/Dat

a

0.9

0.95

1

1.05

1.110 210 310 410

Cha

rge

Effic

ienc

y

0.4

0.6

0.8

1

MC Proton

Flight Data

BGO Energy [GeV]10 210 310 410

MC

/Dat

a

0.9

0.95

1

1.05

1.1

1% 1.5%

PreliminaryPreliminary

Charge selection

PSD layer-y PSD layer-x

11

Bayesian Unfolding Method [Giulio D'Agostini, NIM A362(1995), 487]

Energy Unfolding

Ni =nX

j=1

↵ijMj(1� �j)

↵ij =P (Ed,j |E0,i)N̂i

✏iPn

i=1 P (Ed,j |E0,i)N̂i

Deposited Energy [GeV]210 310 410

Con

tam

inat

ion

[%]

-310

-210

-110

1

10Helium ContaminationElectron Contamination

Background

: Unfolded event numberNi

Mj: Measured event number�j : BackgroundP (Ed,j |E0,i): Response Matrix (MC)

N̂i : Prior (E-2.7)

12

Incident Energy [GeV]210 310 410 510

sr]

2Ef

fect

ive

Acce

ptan

ce [m

0

0.01

0.02

0.03

0.04

0.05

Preliminary

Effective Acceptance

HE Tigger: ~2.5%

Track Reconstruction: ~3.5%Charge Identification: ~1.8%

G4 FTFP_BERT

13

Proton Spectrum

Kinetic Energy [GeV]10 210 310 410 510

]1.

6G

eV-1 s-1

sr-2

[m2.

6 E×

Flux

410

DAMPEATIC-2 (2009)PAMELA (2011)AMS-02 (2015)CREAM-I+III (2017)NUCLEON-KLEM (2018)CALET (2019)

DAMPE Uncertainties (Stat.+Syst.)

Preliminary

14

Proton Spectrum

Kinetic Energy [GeV]10 210 310 410 510

]1.

6G

eV-1 s-1

sr-2

[m2.

6 E×

Flux

410

DAMPEATIC-2 (2009)PAMELA (2011)AMS-02 (2015)CREAM-I+III (2017)NUCLEON-KLEM (2018)CALET (2019)

DAMPE Uncertainties (Stat.+Syst.)

Preliminary

Hardening ~400 GeV

Softening ~10 TeV

15

Conclusions

Since launch on Dec. 17, 2015, DAMPE (“WuKong”) has been operated for more

than three years.

Thirty months of on-orbit data with live time fraction of 75.73% are analysed

for cosmic-ray proton spectrum.

The analysis of proton spectrum for energy range 40GeV-100TeV is reported.

The DAMPE measurement confirms the spectral hardening around 400 GeV and

gives a strong evidence of spectral softening at ~10 TeV

16

Conclusions

Since launch on Dec. 17, 2015, DAMPE (“WuKong”) has been operated for more

than three years.

Thirty months of on-orbit data with live time fraction of 75.73% are analysed

for cosmic-ray proton spectrum.

The analysis of proton spectrum for energy range 40GeV-100TeV is reported.

The DAMPE measurement confirms the spectral hardening around 400 GeV and

gives a strong evidence of spectral softening at ~10 TeV

Thanks for your attentions!