De Deeply Virtual Co Compton Scattering at at 10. 10.6 6 GeV - - PowerPoint PPT Presentation

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De Deeply Virtual Co Compton Scattering at at 10. 10.6 6 GeV - - PowerPoint PPT Presentation

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CLAS Collaboration meeting De Deeply Virtual Co Compton Scattering at at 10. 10.6 6 GeV eV wit ith h CLA LAS12 Guillaume CHRISTIAENS (University of Glasgow, CEA Saclay) Thursday, June 20, 2019 Outline 1 - Introduction 2 -

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SLIDE 1

De Deeply Virtual Co Compton Scattering at at 10. 10.6 6 GeV eV wit ith h CLA LAS12

Guillaume CHRISTIAENS (University of Glasgow, CEA Saclay) CLAS Collaboration meeting

Thursday, June 20, 2019

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SLIDE 2

Outline

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

2

  • 1 - Introduction
  • 2 - Previous main analysis steps and results
  • 3 - !" contamination
  • 4 – BH-!" generator
  • 5 – Quick look at the new data
  • Conclusion
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SLIDE 3

Outline

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

3

  • 1 - Introduction
  • 2 - Previous main analysis steps and results
  • 3 - !" contamination
  • 4 – BH-!" generator
  • 5 – Quick look at the new data
  • Conclusion
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SLIDE 4

Deeply Virtual Compton Scattering

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

4

Deeply Virtual Compton Scattering !" → !"$ § GPDs appear in the DVCS amplitude through Compton Form Factors (CFF) such as:

p p γ e− e− FF(t) γ∗

BH at leading order

H = 1

−1

H(x, ξ, t)

  • 1

ξ − x − iϵ − 1 ξ + x − iϵ

  • dx

DVCS at leading order

§ Experimentally we measure photon leptoproduction: interference of DVCS and Bethe-Heitler (BH)

σ(ep → epγ) = |DV CS|2 + |BH|2 + Interference

p(p) p(p′) γ(q′) γ∗(q) e−(k) e−(k′) x + ξ x − ξ H, E, ˜ H, ˜ E(x, ξ, t)

t = (p − p′)2

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SLIDE 5

Beam-spin asymmetry

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

5

§ Extraction of GPDs from DVCS with polarized lepton beam and unpolarized target § Photon leptoproduction beam-spin asymmetry: § At leading order the asymmetry is: known function of kinematical variables combinations of CFF

form factors

ALU = σ+ − σ− σ+ + σ−

ALU ≃ A sin(φtrento) 1 + B cos(φtrento) B = κcBH

1

+ cI

1

κcBH + cI

cI

1, cI 0, sI 1

A = sI

1

κcBH + cI

sI

1 ∝ Im(F1H + ξ(F1 + F2) ˜

H − t 4M 2 F2E) F1, F2

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SLIDE 6

DVCS event in CLAS12

Typical DVCS event: § Electron in the forward detector (torus, DC, ToF, Cherenkov, Calorimeter) § Photon in the forward tagger (calorimeter) § Proton in the central detector (solenoid, Silicon, Micromegas and ToF)

DC Cherenkov ToF Calorimeter Forward Tagger Calorimeter Silicon tracker Micromegas tracker ToF

DVCS at 10.6GeV with CLAS12 at Jefferson Lab

6

Proton Electron Photon

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SLIDE 7

Outlook

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

7

  • 1 - Introduction
  • 2 - Previous main analysis steps and results
  • 3 - !" contamination
  • 4 – BH-!" generator
  • 5 – Quick look at the new data
  • Conclusion
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SLIDE 8

Preliminary selection and exclusivity

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

8

Final state with: § High energy electron > 2GeV § High energy photon > 3 GeV § Proton § § Q2 = −q2 > 1 GeV 2 W 2 = (p + q)2 > 4 GeV 2

Selection of exclusive DVCS events: § Missing mass !" → !"$% § Missing energy !" → !"$% § Cone angle: angle between measured and computed photon (using proton and electron)

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SLIDE 9

First look at beam-spin asymmetry

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

9

Preliminary asymmetry: polarization number of events with helicity + / -

ALU = 1 P N +(φtrento) − N −(φtrento) N +(φtrento) + N −(φtrento)

N + / N −

P

!"#$%"&

'(

Residual background not yet subtracted Only statistical errors Integrated over all kinematic domain About 3% of RG-A statistics

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SLIDE 10

Outlook

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

10

  • 1 - Introduction
  • 2 - Previous main analysis steps and results
  • 3 - !" contamination
  • 4 – BH-#$ generator
  • 5 – Quick look at the new data
  • Conclusion
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SLIDE 11

!" contamination

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

11

Pion electroproduction #$ → #$!" → #$&& If one of these happen:

  • ne photon is not detected
  • ne photon has too low energy
  • the two photons are too close to be distinguished

Then we might take a pion event for a DVCS event à contamination Effect of this contamination

  • () have no or a very low asymmetry
  • nly appear in the denominator

à Contamination reduces the asymmetry ALU = 1 P N +(φtrento) − N −(φtrento) N +(φtrento) + N −(φtrento)

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SLIDE 12

!" contamination – Method 1

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

12

Goal: estimate !" contamination with a !" simulation

  • Simulate #$ with dynamics
  • Compute number of #$ in data

and in the simulation (in a clean region) to find the scaling factor

  • Scale simulation to the data

Preliminary pion contamination (red: total signal, blue contamination)

Missing mass squared %& → %&() (+%,-)

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SLIDE 13

!" contamination – Method 2

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

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Goal: estimate !" contamination with dynamics from the data

  • Identify #$ in the data
  • Simulate decay of these pions

(each pion is randomly decayed multiple times)

  • The events with photons within

exclusivity cuts become DVCS background

Preliminary pion contamination (red: total signal, blue contamination)

Missing mass squared %& → %&() (+%,-)

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SLIDE 14

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

14

Goal: estimate !" contamination using a DVCS + !" simulation

  • Generate both DVCS and #$

with dynamics

  • Background consist of all the

events that are not DVCS

Missing mass squared %& → %&() (+%,-)

Preliminary pion contamination (red: total signal, blue contamination) Warning: Issue with simulation/reconstruction Pid had to be based on MC banks

!" contamination – Method 3

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SLIDE 15

!" contamination – Conclusions

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

15

  • Very preliminary but overall good agreement between all 3 method

– About 30% with the current exclusivity cuts

  • Depends on the kinematics

– # dependence – Q2/xB dependence

#$%&'$( (°) )* 2 4 0.2 0.4 +,

Missing mass squared

  • . → -.01

(3-4*)

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SLIDE 16

Outlook

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

16

  • 1 - Introduction
  • 2 - Previous main analysis steps and results
  • 3 - !" contamination
  • 4 – BH-#$ generator
  • 5 – Quick look at the new data
  • Conclusion
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SLIDE 17

BH- !" Generator – Goals and issues

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

17

Goal of the algorithm

  • Be able to generate DVCS and Pi0 flat or from cross-section

– pure DVCS with cross section – pure Pi0 with cross section – DVCS and Pi0 together with a correct cross-section ratio Issues

  • 1 - BH cross-section is extremely high in some regions

– Accept-reject algorithm is difficult to implement and extremely slow

  • 2- How to generate 2 processes at ‘‘the same time’’ and on a slightly

different 4D phase-space ?

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SLIDE 18

BH- !" Generator – Algorithm

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

18

Issue 1 : Metropolis algorithm … 1 – #$ random starting point (4D: # = ('(, #*, +, ,)) 2 – #./0. new point on a gaussian around #$ 3 – Draw a random number 1 ~ 3[5,6] – if 1 <

9(:;<=;) 9(:>)

, #$?6 = #./0. – else , #$?6 = #$ 4 – Save #$?6, set #$ = #$?6 and restart step 2 Issue 2 : … applied on the sums of the cross sections Use @ # = A*B # + ADE(#)

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SLIDE 19

BH- !" Generator – Example

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

19

Example of sequence of the algorithm (with flat cross section) #$ %& #$ iteration Example of #$evolution for 3000 iterations (with real cross-section)

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SLIDE 20

Outlook

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

20

  • 1 - Introduction
  • 2 - Previous main analysis steps and results
  • 3 - !" contamination
  • 4 – BH-!" generator
  • 5 – Quick look at the new data
  • Conclusion
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SLIDE 21

A quick look at the new cooked data

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

21

Green = spring data train v2 (this winter) Red = fall data train v5 (last week) à Not really comparable (spring vs fall) but great overall improvement

!(#$ → #$&')) (*#+)) , (°)

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SLIDE 22

Outlook

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

22

  • 1 - Introduction
  • 2 - Previous main analysis steps and results
  • 3 - !" contamination
  • 4 – BH-!" generator
  • 5 – Quick look at the new data
  • Conclusion
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SLIDE 23

Conclusion

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

23

  • !" contamination is being analyzed and understood
  • 3 different methods giving consistent results
  • DVCS + !" simulation has been done
  • joint DVCS + !" simulation
  • Metropolis algorithm can be useful
  • Ready to analyze a new set of cooked data
  • We can expect nice improvements by looking at

newly cooked fall data compared to spring DNP data

  • Would like to be able to do some background merging
  • Gemc background merging tool does not seem enough

(example adc from data ≠ adc from simulation for several detectors)

  • Clas12Tools to read HIPO4
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SLIDE 24

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

24

Thanks !!

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SLIDE 25

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

25

Backup

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SLIDE 26

BH- !" Generator

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

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SLIDE 27

BH- !" Generator

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

27

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SLIDE 28

BH- !" Generator

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

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  • Distributions after reconstruction for 1M BH- #$ events

!" BH

%& '( '(

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SLIDE 29

BH- !" Generator

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

29

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SLIDE 30

A quick look at the new cooked data

DVCS at 10.6 GeV with CLAS12 at Jefferson Lab

30

Photon cone angle (°) Photon cone angle (°)

Left = spring data train v2 (this winter) Right = fall data train v5 (last week) Red = photon in FT Green = photon in FD