Measurement of absolute energy scale of ECAL of DAMPE with - - PowerPoint PPT Presentation

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Measurement of absolute energy scale of ECAL of DAMPE with geomagne;c rigidity cutoff Jingjing Zang *(PMO,CAS), Chuan Yue, Xiang Li (On behalf of DAMPE collabora;on) *Speaker, zangjj@pmo.ac.cn 35th ICRC, BUSON KOREA 2017 1 Outline

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SLIDE 1

Measurement of absolute energy scale of ECAL of DAMPE with geomagne;c rigidity cutoff

35th ICRC, BUSON KOREA 2017 1

Jingjing Zang *(PMO,CAS), Chuan Yue, Xiang Li (On behalf of DAMPE collabora;on)

*Speaker, zangjj@pmo.ac.cn

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SLIDE 2

Outline

  • Introduc;on of DAMPE detectors
  • Mo;va;on and method reseach
  • CRE flux measurement

– Pre-selec;on – Background contamina;on

  • 1. hadron background
  • 2. Secondary background
  • CRE flux and cutoff
  • Systema;c Uncertainty
  • Conclusion

35th ICRC, BUSON KOREA 2017 2

Launched on Dec. 17th 2015

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SLIDE 3

DAMPE Detectors

35th ICRC, BUSON KOREA 2017 3 Plas;c Scin;llator Detector(PSD) Ø γ an;coincidence Ø Z-measurement BGO Calorimeter(BGO) Ø Energy measurement(32X0&1.6λI) Ø e/p separa;on Ø Trigger primi;ves Silicon Tungsten Tracker(STK) Ø γ convertor, par;cle track Ø Z-measurement Neutron Detector(NUD) Ø e/p separa;on

More details and performances can be found at arXiv:1706.08453

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SLIDE 4

Mo;va;on and Method research

Mo;va;on:

  • Energy scale of BGO-ECAL is given by on-orbit simulated

energy deposi;on of cosmic ray proton “MIP” events, the real absolute energy scale remains unknown.

  • Absolute energy scale is a systema;c uncertainty on energy

measurement

Method research:

  • Geomagne;c cutoff on cosmic ray electron and positron

spectrum provides a strong spectral feature.

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SLIDE 5

Procedure of absolute energy scale measurement

  • 1. Measure low energy CRE flux with 1<L<1.14

– Primary cosmic ray electron + positron flux from 8GeV to 100GeV – Filng flux in 1<L<1.14 to extract cutoff value

  • 2. Calculate Geomagne;c cutoff

– Trace CRE in the Earth’s magne;c field – Calculate geomagne;c cutoff within L bin range

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Flight Data Sample

  • Jan 2016 – Feb 2017 (425days, 2.15B events in total )
  • Pre-selec;on：
  • 1. High energy Trigger
  • 2. 400MeV<Total deposited Energy<150GeV
  • 3. Reject side and upward events
  • 4. Reject heavy ion events by charge measurement
  • Aqer Pre-selec;on, 40M events leq

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Energy distribu;on First sight on G-cutoff

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SLIDE 7

Acceptance

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  • The pre-selec;on efficiency is evaluated by MC Simula;on and corrected by

flight data.

  • Acceptance is calculated in 30 energy intervals

Due to strict pre-selecCon criteria, acceptance is limited within the absolute energy scale analysis

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SLIDE 8

Hadron Background contamina;on

[14.4, 15.7]GeV [36.4, 39.6]GeV

electron candidates sta;s;c

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Background contaminaCon 20%@8GeV, 1%@12GeV,5%@100GeV

e-candidate

e-candi selec;on criteria are kept at lowest valley between e-peak and H- peak.

electron-hadron discrimina;on

Electron pid efficiency is 90%@8GeV, rapidly increase to 98-99% above 20GeV.

e-candidate

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SLIDE 9

How to es;mate Secondary Background

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  • The selected CRE candidates have two sources
  • 1. Primary electrons originate from interstellar space (primaries)
  • 2. Secondary electrons generated in the atmosphere (secondaries)
  • Primaries and secondaries have different features on azimuth distribu;on
  • Back Tracing for primary template
  • IGRF-12 for geomagne;c field
  • Trace par;cle trajectory in geomagne;c field
  • Data-Driven method of making secondary template

– Geomagne;c field blocks charged par;cles with low rigidity – CREs with energy far less than cutoff should be secondary dominant.

Sub-cutoff events are selected to extract secondary template Secondary Template

Geomagne;c cutoff

1<L<1.14

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Secondary Background Contamina;on

10-11GeV 13-14GeV

Ø Ra;o of Secondary: ü 8-13GeV:56% to 0% ü >13GeV :0%

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Secondary background ra;o change with Energy

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SLIDE 11

( )

1

8 2

/ 1 /

p

y p x x p

−

= ∗ +

CRE Flux & G-cutoff

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Flux = N 1−δh

( ) 1−δs ( )

A⋅ε pid ⋅T ⋅ΔE

Cdata/Ctracer = 1.0125±0.0175(stat)

  • CRE flux in L bin can be calculated by formula
  • Cutoff filng func;on
  • p0: normaliza;on constant, p1: spectrum index, p2: G-cutoff

Flight data G-cutoff have a 1.25% exceeding comparing with back tracing result.

Cutoff energy = 13.20GeV

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SLIDE 12

Systema;c uncertainty (1.29%)

  • Five major systema;c uncertainty sources

I. Binning migra;on

Ø cutoff aqer unfolding = 13.22GeV, varia;on = 0.15%

II. Choice of filng range

Ø change range wider or narrower, uncertainty = 1.1%

III. IGRF-12 model

Ø Difference between DAMPE and Fermi-LAT uncertainty level = 0.5%

IV. e/p Template

Ø change tail longer or shorter, uncertainty = 0.4%

V. Choice of energy interval for secondary template

Ø Change energy interval wider or narrower, closer or farther to the cutoff, uncertainty = 0.15%

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Filng range rms/mean = 1.1% e/p template rms/mean = 0.4%

Fermi-LAT result from Astropar;cle Physics 35(6), 2012, 346-353

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Conclusion

  • We measured absolute energy scale of BGO calorimeter of

DAMPE with geomagne;c cutoff on CRE spectrum using 2.15B events collected from Jan2016 to Feb 2017.

  • By comparing measured geomagne;c cutoff by flight data

with predicted one by back tracing, we found DAMPE’s absolute energy scale is higher by 1.0125±0.0175(stat) ±0.0134(sys) in ~13GeV range.

35th ICRC, BUSON KOREA 2017 13

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SLIDE 14

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We’re very appreciated for your ques;ons and comments!

Thanks for your a}en;on

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SLIDE 15

BACK UP SLIDES

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SLIDE 16

BGO energy scale in the official DAMPESW

  • Energy scale determina;on procedure

in DAMPESW

– “MIP” calibra;on run within la;tude -20° ~ +20°, – Reconstruct proton “MIP” energy spectrum of each BGO crystal, – DAMPESW simulate CR-proton, and give simulated proton “MIP” spectrum, – Simu & flight spectra are in good agreement

  • Energy scale of BGO-ECAL is given by
  • n-orbit simula;on of CR-proton

“MIPs”

  • Same method has been verified with

beam test

35th ICRC, BUSON KOREA 2017 16 verCcal rigidity cutoff @ DAMPE Orbit

Avoid cliffy <2GeV flat

“MIP” calibra;on run range

see PDG chapter 32

“MIP” spectrum is the reference of energy reconstrucCon.

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SLIDE 17

Systema;c uncertainty - Binning

  • G-Cutoff obtained by filng differen;al flux, the migra;on from bin to bin

will change flux and affect filng result.

  • Es;ma;on Method

– Based on MC Reco vs Ekin matrix, do unfolding

  • Results

– cutoff Aqer unfolding = 13.22GeV, varia;on = 0.15%

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SLIDE 18

Systema;c uncertainty – Filng range

  • Choice of filng range will affect filng result.
  • Method

– Modify filng range wider or narrower while keep range cover cutoff energy – Fit elow = Gaus(11,1),Fit ehigh = Gaus(80,10), do 500 ;mes filng – The rms of filng results is systema;c uncertainty

  • Results

– Uncertainty = 0.1464/13.21 = 1.1%

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Systema;c uncertainty – IGRF

  • IGRF-12 model was used to do backtracing and primary template.
  • Method

– It’s difficult to directly es;mate the uncertainty caused by IGRF – We can use Fermi-LAT result to assess uncertainty level, since Fermi-LAT and DAMPE are two independent experiment.

  • Results

– Fermi-LAT, 1<L<1.14, G-cutoff = 13.27GeV – DAMPE, 1<L<1.14, G-cutoff = 13.20GeV – Rela;ve error = 0.5%

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Fermi-LAT result

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SLIDE 20

Systema;c uncertainty – e/p template

  • The Monte Carlo template we used to es;mate hadron background contamina;on

could induce uncertainty on cutoff rigidity.

  • Method

– Background contamina;on is ~1% at 12GeV – Verify leq tail of MC template longer or shorter and calculate background ra;o and flux to perform filng rigidity cutoff.

  • Result

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Filng result changed within ~0.5%

Background contaminaCon 1%@12GeV,13%@100GeV, 20%@8GeV

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SLIDE 21

Systema;c uncertainty – secondary template

  • Secondary template was obtained from low energy flight data sample

(E<<E_cutoff) where the CRE is secondary dominant. Choice of energy interval (2-4GeV) will affect shape of template and thus flux and final value of rigidity cutoff

  • Method

– Change energy interval wider or narrower, closer or farther to the cutoff to extract template – Flux measurement and filng to get final value of rigidity cutoff – The spread of cutoffs reflect systema;c uncertainty caused by secondary template

  • Result

– Max DeviaCon: (13.18-13.20)/13.20=0.15%

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Template change slightly with energy interval.

Energy Width Energy center