Title: Deeply Virtual Compton Scattering DVCS at 6 GeV with polarized beam and polarized target using the C
1Deeply Virtual Compton Scattering (DVCS) at 6
GeV with polarized beam and polarized target
using the CLAS detector
Latifa Elouadrhiri Jefferson Lab for the CLAS
Collaboration
2DVCS at 6 GeV with polarized target and polarized
beam using the CLAS detector
- H. Avakian, S. Boyarinov, V.D. Burkert, L.
Elouadrhiri1,2, M. Ito, Y. Sharabian, E. Smith,
S. Stepanyan - Jefferson Lab
- J. Ball, P. Bertin, A. Camsonne, R. De Masi, F.
Descamps, M. Garçon, F-X. Girod, M. Guidal, H-S.
Jo, - M. Mazouz, M. Mac Cormick, B. Michel, C. Munoz
Camacho, S. Niccolai1, F. Sabatie, E. Voutier - LPC (Clermont) / LPSC (Grenoble) / IPNO (Orsay)
/SPhN (Saclay) - CEA /DSM/DAPNIA CNRS/IN2P3
- K. Joo1, N. Markov, M. Ungaro, B. Aaho
- University of Connecticut
- A. Biselli1
- Fairfield University
- S. Kuleshov, O. Pogorelko, P. ShiskovInstitute
of Theoretical and Experimental Physics, Moscow - H. Aznauryan, N, Dashyan, K. EgiyanYerevan
Physics Institute - V. Koubarovsky, P. StolerRensselaer Polytechnic
InstituteM. Amarian, G. Dodge, H. Juengst,
S.E. Kuhn, A. Radyushkin, L. WeinsteinOld
Dominion UniversityM. VanderhaeghenCollege of
William and Mary - S. Chen
- Florida State University
1Co-spokesperson 2Contact person
3Deeply Virtual Compton Scattering (DVCS) with
CLAS Exclusive ep ? e'p ?
We propose to study the DVCS with
- longitudinally polarized target
- 6 GeV polarized electron beam
- optimized CLAS configuration to
- detect all 3 particles in the final state
- DVCS is one of the key reactions to
- determine the Generalized Parton
- Distributions (GPDs) experimentally.
- It is the simplest process that can be described
in terms of GPDs. -
4 GPDs Deeply Virtual Exclusive Processes
handbag mechanism
Deeply Virtual Compton Scattering (DVCS)
x
g
x longitudinal quark momentum fraction
xx
x-x
2x longitudinal momentum transfer
t
xB
x
2-xB
5 Beyond form factors and quark distributions
Generalized Parton Distributions (GPDs)
M. Burkardt, Interpretation in impact parameter
space
Proton form factors, transverse charge current
densities
6 Link to DIS and Elastic Form Factors
7Accessing GPDs Through DVCS
- GPDs are universal, they can be
- determined in any suitable process
Eo 11 GeV
Eo 6 GeV
Eo 4 GeV
DVCS
BH
BH
TBH given by elastic form factors TDVCS
determined by GPDs
DVCS
sUL (BH) Im(DVCS) sinf h.t.
BH-DVCS interference generates beam and target
asymmetries that carry the nucleon structure
information.
DVCS/BH comparable, allows asymmetry, cross
section measurements
8Separating GPDs Through Polarization
Polarized beam, unpolarized target
DsLU sinfF1H x(F1F2)H kF2Edf
H, H, E
Kinematically suppressed
Unpolarized beam, longitudinal target
H, H
DsUL sinfF1Hx(F1F2)(H df
Unpolarized beam, transverse target
H, E
DsUT sinfk(F2H F1E) .. df
Global analysis of polarized and unpolarized data
needed for GPD separation
9Status of GPDs Studies at Jefferson Lab
GPD Reaction Obs. Expt Status
ep?ep?
(DVCS) BSA CLAS 4.2 GeV Published PRL
CLAS 4.8- 5.75 GeV Preliminary (
s) Hall A 5.75 GeV Fall 04 CLAS 5.75
GeV Spring 05 ep?ep? (DVCS) TSA CLAS 5.65
GeV Preliminary e(n)?en? (DVCS) BSA Hall
A 5.75 GeV Fall 04 ed?ed? (DVCS) BSA
CLAS 5.4 GeV under analysis ep?epee- (DDVCS)
BSA CLAS 5.75 GeV under analysis
From ep ? epX
Dedicated set-up
Dedicated set-up
No other proposals at Jefferson Lab are available
for the study of the DVCS process with a
polarized target.
10DVCS with Polarized Target, Experimental Situation
Experimental Studies with CLAS Data were
collected as a by-product during the Eg1 2000
run 5.75 GeV with NH3 longitudinally polarized
target, ltQ2gt 1.8 GeV2
HERMES Experiment Preliminary target spin
asymmetries have been shown by HERMES
Collaboration DIS2005 Workshop, Madison (2005)
11 Experimental Setup for the proposed
experiment
- CLAS Detector
- Nearly 4p acceptance
- Large kinematical coverage
- Detection of charged and neutral particles
- Electron Beam
- Energy 6 GeV
- Polarization 75
- Solid Target
- Longitudinally polarized NH3 target
- Polarization 75
- 12C 15N target
- Inner Calorimeter (IC)
-
High resolution calorimeter to detect photons at
small angles (4o to 15o)
12Hall B Longitudinally Polarized Target
- Dynamically polarized NH3
- 5 Tesla magnetic field
- dB/B 10-4
- 1K LHe cooling bath
- NH3 polarization75
- 12C, 15N, and 4He targets to measure the
dilution factor
13Magnetic Shielding for Møller Electrons
without magnetic field
14CLAS Setup for DVCS Experiments
SC Helmholtz magnet
Inner calorimeter (PbWO4)
424 crystals, 16 mm long, pointing geometry,
1.2 degree/crystal, APD readout
Calibration via p0??? s 7.5 MeV
?
Photon detection in IC and EC (view
from target)
M?? (GeV)
15Kinematics and Acceptance with CLAS IC
- DVCS studies require
- high Q2
- low t
The much improved acceptance for photon
detection, and the longer running time will
allow us to extend the kinematics range to higher
Q2, and to map out the xB and t dependence in
small bins
16 Target Spin Asymmetry f Dependence
6 GeV run with NH3 longitudinally polarized
target (CLAS IC) 60 days of beam time
- CLAS eg1 (preliminary)
- CLAS (eg1IC) projected
A dedicated CLAS experiment with longitudinally
polarized target will provide a statistically
significant measurement of the kinematical
dependences of the DVCS target SSA
17 Target Spin Asymmetry Q2 Dependence
18 Target Spin Asymmetry t- Dependence
Higher t values will also be measured. The
interpretation within the handbag formalism
needs to be clarified.
19 Target Spin Asymmetry t- Dependence
20Target Spin Asymmetry x- Dependence
21Target Spin Asymmetry Q2- Dependence
22Beam Time Request
We request 60 days of beam time with polarized
beam (Pe gt 75) and polarized target (PT gt 75)
No special equipment is needed for this
experiment, a similar setup has been used in eg1,
the only new component is the Inner Calorimeter
(IC) - IC was used recently in the e1-DVCS
experiment - the combination of polarized target
and IC prototype was used earlier
in a successful test run in November 2003
This experiment will run concurrently with
PR-05-113 and has identical requirements for
beam and experimental equipment.
23Summary
- Studies of hard exclusive electroproduction of
photons are underway at JLab, allowing access to
the GPDs. - The proposed measurements with longitudinally
polarized target and polarized beam with the CLAS
detector, together with the Hall-A and Hall B
DVCS programs, will contribute uniquely to
exploratory measurements of DVCS as a means of
accessing the GPDs. - This program will
- greatly improve the precision of the DVCS data
on target spin asymmetry giving access to the
imaginary part of H - provide the first significant measurement of the
double spin asymmetry probing the real part of
H and H
24(No Transcript)
25DVCS eg1 Separating DVCS Photons from Polarized
Protons in NH3
Events from both p0 and unpolarized target
nucleons are suppressed
Geometry cut qgxlt 1o
26DVCS MC separating DVCS photons
Angular cut most efficient in separating p0
27CLASInner Calorimeter (IC)
424 PbWO4 ..crystals
IC
IC sE/E0.0034/E0.038/vE0.022
CLASIC
CLAS
Reconstruction efficiency of high energy p0 with
IC increases 4 times due to small angle coverage
CLAS
IC at CLAS opens new avenue for studies of spin
and azimuthal asymmetries in hard exclusive
processes g, p0,h,r
28DVCS with a polarized target New CLAS experiment
DsLL cosfReF1Hx(F1F2)(H xE/2)..
5.7 GeV run with NH3 longitudinally polarized
targetIC
Projections for 60 days
The double spin asymmetry in DVCS with
longitudinally polarized target will provide
access to the real part of Compton form factors
29GPD and DVCS
(at leading order)
Beam or target spin asymmetry contain only
ImT, therefore GPDs at x x and -x
Cross-section measurement and beam charge
asymmetry (ReT) integrate GPDs over x
(M. Vanderhaeghen)
30D.E.S. an experimental challenge
Missing mass MX2
- Resolution
- Exclusivity
- Luminosity
- High transfers
ep ? epX MAMI 850 MeV
ep ? epX Hall A 4 GeV
Accessible kinematical domain
p0
?
ep ? epX CLAS 4.2 GeV
Np
N
ep ? e?X HERMES 28 GeV
(? ?)
31Projected results (sample)
Dependence of j asymmetry and total cross-section
as a function of xB, t, Q2 , j (372 bins)
E01-113 V. Burkert, L. Edouardrihi, M. Garçon, S.
Stepanyan et al. Run March-May
2005
32CLAS/DVCS (ep ? epX) at 5.75 GeV
H. Avakian L. Elouadrhiri
PRELIMINARY
PRELIMINARY
0.15 lt xBlt 0.4 1.50 lt Q2 lt 4.5 GeV2 -t lt 0.5 GeV2
GPD based predictions (Vanderhaeghen)
p0 are suppressed due to analysis cuts (only low
t), residual contribution (p/? 5-15) estimated
from MC