p-DVCS and n-DVCS experiment status

-Brief overview of the theory

-Experiment setup

-Analysis status

Malek MAZOUZLPSC Grenoble

Hall A Collaboration Meeting June 24th 2005

GPDs properties, link to DIS and elastic form factors

),,(~

,~

, , txEHEH qqqq Generalized Parton distributions

Link to DIS at =t=0

)()()0,0,(~

)()()0,0,(

xqxqxH

xqxqxHq

q

Link to form factors (sum rules)1

1

1

1

2

1

1 1

1 1

( , , ) ( )

( , , ) ( )

( , , ) ( ) , ( , , ) ( )

q q

q q

q q q qA A

dxH x t F t

dxE x t F t

dx H x t g t dx E x t h t

1

1

1 1( , ,0) ( , ,0)

2 2q q

q q qJ L xdx H x E x

Access to quark angular momentum (Ji’s sum rule)Quark correlations !

Brief overview of the theoryDVCS: Simplest hard exclusive process involving GPDs

(DVCS)BHσdσd Im.55 �

Purely real

pQCD factorization theorem (Bjorken regime)

Non perturbative description by

Generalized Parton Distributions

Perturbative description

),,( txGPDix

dxDVCS

225 ).Re(.2 DVCSBHDVCSBHd

0.1 1.34 0.81 0.38 0.04

0.3 0.82 0.56 0.24 0.06

0.5 0.54 0.42 0.17 0.07

0.7 0.38 0.33 0.13 0.07

Proton Target

Proton

2 ( )pF t 1 ( )pF t 1 2( ) ( ) /(2 )p pB BF t F t x x 2

2( / 4 ) ( )pt M F t t

t=-0.3

Target

Proton 1.13 0.70 0.98

H H E

Goeke, Polyakov and Vanderhaeghen

Model:

2 22 GeV

0.3

0.3B

Q

x

t

1 1 2 22( ) ( ) ( ) ( )

2 4B

B

x tA F t F t F t F t

x M

H H E

1 1 2 22( ) ( ) ( ) ( )

2 4

0.34 0.17 + 0.06

B

B

x tA F t F t F t F t

x M

A

H H E

sin(Φ) term

Neutron Target

0.1 -1.46 -0.01 -0.26 -0.04

0.3 -0.91 -0.04 -0.17 -0.06

0.5 -0.6 -0.05 -0.12 -0.08

0.7 -0.43 -0.06 -0.09 -0.08

Neutron

2 ( )pF t 1 ( )pF t 1 2( ) ( ) /(2 )p pB BF t F t x x 2

2( / 4 ) ( )pt M F t t

t=-0.3

Target

Proton 0.81 -0.07 1.73

H H E

Goeke, Polyakov and Vanderhaeghen

Model:

2 22 GeV

0.3

0.3B

Q

x

t

1 1 2 22( ) ( ) ( ) ( )

2 4B

B

x tA F t F t F t F t

x M

H H E

1 2( ) ( ) !!!n nF t F t

1 1 2 22( ) ( ) ( ) ( )

2 4

0.03 0.01 0.12

B

B

x tA F t F t F t F t

x M

A

H H E

neutron

p-DVCS and n-DVCS in Hall A

DVCS on the proton : E00-110

Goal : Measure the absolute cross section of DVCS on proton (3 Q² values: 1.4, 1.9, 2.3 GeV²) and on neutron (Q²=1.9 GeV²)

DVCS on the neutron : E03-106

Simplest access to the least known of GPDs: E First constraint of nucleon orbital angular momentum through model of E

Check Handbag dominance & Test factorization

Deduce Q² dependence and relative importance of leading twist and higher twists in helicity dependent cross-section

Constrain GPD’s

…including Re(DVCS)

Experiment status

s (GeV²)

Q² (GeV²)

Pe (Gev/c)

Θe (deg)

-Θγ* (deg)

4.94 2.32 2.35 23.91 14.80 5832

4.22 1.91 2.95 19.32 18.25 4365

3.5 1.5 3.55 15.58 22.29 3097

4.22 1.91 2.95 19.32 18.25 24000

proton

neutron

xBj=0.364

Beam polarization was about 78% during the experiment

E00-110 (p-DVCS) was finished in November 2004 (started in September)

E03-106 (n-DVCS) was finished in December 2004 (started in November)

Ldt (fb-1)

Left High Resolution Spectrometer

LH2 or (LD2) target

Polarized beam

Electromagnetic Calorimeter (photon detection)

Scintillator Array(Proton Array)

Experimental method

(Proton tagger)Scintillating paddles

scattered electron

( )

e p e p

e D e n p

photon

Proton:(E00-110)

Neutron:(E03-106)

Only for Neutron experimentCheck of the recoil nucleon position

recoil nucleon

Reaction kinematics is fully defined

Calorimeter in the black box

(132 PbF2 blocks)

Proton Array

(100 scintillator blocks)

Proton Tagger

(57 scintillator paddles)

High luminosity measurement

2 13710L cm s

123710.4 scmLnucleon

Up to

At ~1 meter from target (Θγ*=15 degrees)

Requires good electronics

PMT

G=104

x10 electronics

Low energy electromagnetic background

Electronics

1 GHz Analog Ring Sampler (ARS)

x 128 samples x 289 detector channels

Sample each PMT signal in 128 values (1 value/ns)

Extract signal properties (charge, time) with a wave form Analysis.

Allows to deal with pile-up events.

Electronics

Calorimeter trigger

Not all the calorimeter channels are read for each event

Following HRS trigger, stop ARS.

30MHz trigger FADC digitizes all calorimeter signals in 85ns window.

- Compute all sums of 4 adjacent blocks.

- Look for at least 1 sum over threshold

- Validate or reject HRS trigger within 340 ns

Not all the Proton Array channels are read for each event.

Analysis status - What is done

Left HRS efficiency (detectors, tracking …) determined

All good runs selected and total integrated luminosity extracted

Calorimeter calibration done for almost all data

Proton Array calibration done for a part of the data and still in progress

Parameters of the wave form analysis and the clustering optimized

Coincidence time of all detectors precisely adjusted

All geometrical offsets taken into account

Analysis status – preliminary

Sigma = 0.6ns

2 ns beam structure

Time difference between the electron arm and the detected photon

Selection of events in the coincidence peak

Determination of the missing particle (assuming DVCS kinematics)

Check the presence of the missing particle in the predicted block (or region) of the Proton Array

Sigma = 0.9ns

Time spectrum in the predicted block (LH2 target)

Analysis Status – Very preliminary

XeepXeed )',()',( Xeep )',(

Absolute cross sections necessary to extract helicity dependence of neutron

Analysis – Very preliminary

Triple coincidence

Missing mass2 of H(e,e’γ)x for triple coincidence events

Background subtraction with non predicted blocks

Proton Array and Proton Veto are used to check the exclusivity and reduce the background

Analysis – Very preliminary Triple coincidence

Missing mass2 (background subtracted) LH2 target

Analysis – Fermi momentum effect Triple coincidence

Missing mass2 (background subtracted) LD2 targetVery preliminary

π0 electroproduction - preliminary

Invariant mass of 2 photons in the calorimeter

Good way to control calorimeter calibration

Missing mass2 of epeπ0x

3 possible reactions:

epeπ0p

epenρ+ , ρ+ π0 π+

epe π0Δ+

2π production threshold

Sigma = 0.160 GeV2

Sigma = 9.5 MeV

Analysis – Proton Array Calibration

peep 0Used to calibrate the Proton Array

π0 electroproduction - preliminary

Invariant mass of 2 photons in the calorimeter

Good way to control calorimeter calibration

Missing mass2 of epeπ0x

3 possible reactions:

epeπ0p

epenρ+ , ρ+ π0 π+

epe π0Δ+

2π production threshold

Sigma = 0.160 GeV2

Sigma = 9.5 MeV

π0 electroproduction - preliminary

Background subtraction

Accidental π0

Decorrelated photons

π0

π0 electroproduction – background subtraction

]11,5][11,5.[2]11,5][11,5[]3,3][11,5[]11,5][3,3[ saccidental

Analysis – work in progress

wave form analysis (detection) efficiency (almost done)

Acquisition trigger efficiency

Acceptance calculation

Proton Array Calibration (almost done)

Neutron detection efficiency in the Proton Array

Implement neutron tagger analysis

Evaluate Fermi motion consequences

Study knock-out effects in the tagger (data + simulation)

Proton experiment

Neutron experiment

Conclusion

2 13710L cm s

123710.4 scmLnucleon

-Requires wave form electronics

- 10% of detector components almost unusable as expected after 3 months of data taking

We have demonstrated that in Hall A with High Resolution spectrometer and a good calorimeter, we are able to measure:

•Real and Imaginary parts of DVCS•BH interference:

Work at precisely defined kinematics: Q2 , s and xBj

Absolute cross sections and cross section difference are determined with the precision of HRS (better than 5%)

Analysis is in progress

But

Work at a luminosity up to

Deep π0 electroproduction cross-section almost finalized