p-y bertin
DESCRIPTION
p 0 exclusive electro production. Q 2 =2.3 GeV 2 , X Bj =.36. P-Y BERTIN Jefferson Laboratory and Université BLAISE PASCAL- IN2P3/CNRS for the DVCS HALL A collaboration. - PowerPoint PPT PresentationTRANSCRIPT
P-Y BERTIN
Jefferson Laboratory and Université BLAISE PASCAL- IN2P3/CNRS
for the
DVCS HALL A collaboration
0 exclusive electro productionQ2=2.3 GeV2, XBj=.36
LH2 / LD2 targetPolarized Electron Beam
Scattered Electron
Left HRS
Electromagnetic Calorimeter
DVCS events are identified with MX
2
Beam energy = 5.75 GeV
Beam polarization = 75%
Beam current = ~ 2 and 4 μA
Luminosity = 1 and 4. 1037 cm-2.s-1 nucleon-1
- >6.3°
- Čerenkov based Electromagnetic Calorimeter
-Specific Scattering Chamber
-Customized Electronics & Data Acquisition
Two-arm experiment : spectrometer and calorimeter
Exclusivity
Raw dataSimulation X cross sections
p(e,e’0)
(Mp+m)2
Photon detection threshol correction th
q
2
'1 1
q’1 being the smallest enegy photon of Th= 1.00 GeV = 1.15 GeV = 1.25 GeV
p
At Q2=2.3 GeV2 and xbj=.36
•The continuum is significant compared to the p(e,e’0)p•The resonances are washed out into the continuum.
As seen also in DIS
Q2=2.0 GeV2
Q2=0 GeV2
(Mp+m)2
(Mp+2m )2
(Mp+3m )2
0Br=8.5%
-t GeV2 0.1 0.2 0.3
0.01
0.02
0.03
0
0
RbepepTot .1)(
b=-2 GeV-2 From Hall B
(Mp+m)2
(Mp+2m )2
(Mp+3m )2
0Br=8.5%
0Br=100%
0Br=85%
in our cut ~1% 0p
But we detect only e’0 => all the process interfere =>sum of the amplitudes What I am doing ? Semi inclusive DIS and Duality ??
For each exclusive 0 event selected in the cut on Mx2
The physic variable are determined exactly
Q2, xbj with the spectrometer t with the position in the calorimeter ~2-3 mrd)
Photon’s in the inner calorimeter (99 Block from 132)Window coincidence +/- 3 nsAccidentals esubstractedWindow 105<mMeV
td
d
dtdxdQ
d
Bj
2
3
2coscos)1(2
dt
d
dt
d
dt
d
dt
d
dt
d TTLTLT
sin)1(2 '
dt
d TL
Analyze in the formalism of on photon exchange
)()Re(cos2 2*2
*1
*2
2
2
1 FFFFT
)]cosRe(2[sin2
1 *4
*33
*24
*1
2
4
2
3*2 FFFFFFFFTT
Chew, Goldberger, Low and Nambu
Decomposition in CGLM amplitude: 0 cm angle ~ -(t-tmin)
)Re(cos2 6*
5*2
6
2
5 FFFFL
])cos()cosRe[(sin2
16
**3
*4
*15
**4
*3
*2
* FFFFFFFFTL
])cos()cosIm[(sin 6**
3*
4*
15**
4*
3*
2*
' FFFFFFFFTL
6 amplitudes complexalLongitudinFF
TransverseFFFF
6,5
4321 ,,,
rT
rL
rTT
rTL
rTL’
Reduced response functions r‘s
All the trivial kinematics dependence , photon flux, , sin,…. Taken in account in the, Monte Carlo with radiative corrections , detector resolution,….
Use the same extraction method that the used for DVCSwhich take in account the bin migration by a global linear fit on 10(t)x24(f) experimental bins
rTL~5x(rT+rL )
PRELIMINARYQ2=2.3 GeV2
xBj=0.36
=0.64
Corrected for real+virtual RCCorrected for efficiencyCorrected for acceptanceCorrected for resolution effects
LT
TL
TT
'TL
Systematic errors include : trigger threshold stability ( 1 to 1.2 GeV) missing mass cut ( .9 to 1.15 GeV2 ) extrapolation at fixed Q2 and fixed XBj. spectrometer, luminosity……
Extrapoled at fixed:
+
coupling to n, with re-scattering
Regge trajectory Exchange ( , and B1)
J. M. Laget’s Prediction underestimates the cross-sections by a factor 5
JML x5
JML x5
JML x5
JML x5
and
L
T
= ???
Next experiment 2009 will allow a full
Rosenbluth separation
s
Factorization hold only forlongitudinal amplitude
L Longitudinal part Prediction from
model (VGG) based on Hand bag model and GPD
VGG M Vanderhaeghen P. Guichon and M Gidal
VGG x 5
1
+-0 +-
2
+-0
But quid of two photons exchange?
How to check validity of the one photon exchange ??
END
Photon electroproduction
Analysis – Exclusivity check using Proton Array and MC
Normalized (e,p,)triple coincidence events
Using extra recoil Proton-detector, we have checked the missing mass spectrum of double-coincidence events with those of a triple -coincidence.
Monte-Carlo(e,)X – (e,p,)
2 cutXM
The missing mass spectrum using the Monte-Carlo gives the same position and width. Using the cut shown on the Fig.,the contamination from inelastic channels is estimated to be under 3%.
Experimental observables linked to GPDs
Experimentally, DVCS is undistinguishable with Bethe-Heitler
However, we know FF at low t and BH is fully calculableInterference term allows access to linear amplitude Using a polarized beam on an unpolarized target 2 observables can be measured:
42
2
4 4
2
2
m2 I
ReBH BH D
DVC
B
BH
C
S
V S
B
dT T
dx dQ dtd
d dT
dx dQ d
T
tdT
At JLab energies,|TDVCS|2 was supposed small
42 2
2
4 42 2
2
2
Im2
Re DVCBH BH DVCS
B
BH DVCS DVCSDVCS
B
SdT T T
dx dQ dtd
d dT T T
dx dQ
T
tT
d d
Kroll, Guichon, Diehl, Pire, …
1
42
1 0 1 22
22
24 4
2
1 2
1 2
0 1 2 3
1 22
1( , , ) cos cos 2
1 ( , , ) cos cos 2 cos3
( ) ( )
( ) (
( , , )sin sin 2
)
( ) (
)
BH BH BHB
B
BI I I I
I IB
B
dx Q t c c c
dx dQ dtd
x Q t
x Q td d
dx dQ dtd
c c c c
s s
Tests of scaling
1. Twist-2 terms should dominate and All coefficients have Q2 dependence which can be tested!
Difference of cross-sections
2 22.3 GeV
0.36B
Q
x
Corrected for real+virtual RCCorrected for efficiencyCorrected for acceptanceCorrected for resolution effectsChecked elastic cross-section @ ~1%
Twist-2Twist-3
Extracted Twist-3contribution small !
PRL97, 262002 (2006)
New work by P. Guichon !
Q2 dependence and test of scaling
<-t>=0.26 GeV2, <xB>=0.36
No Q2 dependence: strong indication forscaling behavior and handbag dominance
Twist-2Twist-3
Total cross-section 2 22.3 GeV
0.36B
Q
x
Corrected for real+virtual RCCorrected for efficiencyCorrected for acceptanceCorrected for resolution effects
Extracted Twist-3contribution small !
PRL97, 262002 (2006)
And it is impossible to disentangle DVCS2 from the interference term
22
2
4
)Re(2 DVCSDVCSBHBH TTTT
dtddxdQ
d
large
We have proposed to use different beam energies (different BH) to :
( experiment approved and planned to run end 2009)
1. Isolate the BH-DVCS interference term from the pure DVCS2
Contribution (as a function of Q2)
• Extraction of both linear and bilinear combinaton of GPDs • Additional test of DVCS scaling ( unpolarized cross section)
2. Measure 5 response functions of the deep virtual 0 channel
•First test of factorization in ep ep0 using L
•If test is positive , valuable complementary ( flavor) information in GPDs
This proposal: assuming DVCS2=20
On the deuterium
Deuterium=proton+neutron+deuteron
- Hydrogen=proton
= neutron + deuteron
Mn2 Mn
2+t/2Missing mass assuming a proton target
2
0( ) ( )hS N N d N N d
Helicity Asymmetry
n-DVCS
d-DVCS
PRELIMINARY
PRELIMINARY
Deuteron contribution compatible with zero at large -t
F. Cano & B. Pire calculation
Eur. Phys. J. A19, 423(2004).
PRELIMINARY
Neutron contribution is small and compatible with zeronnn HHxE~
0.346.0)(
Results can constrain GPD models (and therefore GPD En)VGG Code : M. Vanderhaeghen, P. Guichon and M. Guidal
PRELIMINARY
peep
DeeD
neen
peep
)',(
)',(
)',(
)',(
0
the Scaling test is positive
Transverse -Transverse large. Description in terms of Quarks GPD and Hadronic description ( Regge exchange) miss by a factor 5~15 the data .
K
K VGG model misses by 30%
DVCS2 must be taken into account
0 KBKM
nnn HHxE ]~
0.346.0)([
0 KAgree with F. Cano B. Pire model
To summarize
New data taking in 2009 using 2 beam energies:
Full extraction of linear terms and bilinear terms of GPDs
Full separation of T and L for 0 electro production
At Q2=1.5, 1.9, 2.3 GeV2
We have demonstrated that : high precision DVCS measurements are doable using a high resolution spectrometer and a calorimeter
Full DVCS program in Hall A (up to Q2=9 GeV2) already approved with the 12 GeV upgrade
END
100 150 MeV
0 Invariant mass
FWHM=21 MeV
(Mp+m)2
p(e,e’0)
Raw dataSimulation X cross sections
Photon detection threshol correction th
q
2
'1 1
q’1 being the smallest enegy photon of
DVCS Analysis
Normalized (e,p,)triple coincidence events
Check of the missing mass spectrum of double-coincidence events with the a triple -coicidence using a Auxilliary Proton array
Monte-Carlo(e,)X – (e,p,)
2 cutXM
The missing mass spectrum using the Monte-Carlo gives the same position and width. Using the cut shown on the Fig.,the contamination from inelastic channels is estimated to be under 3%.
Raw
Raw –0
(e,p,)
After :
-Normalizing H2 and D2 data to the same luminosity
-Adding Fermi momentum to H2 data
2 principle sources of systematic errors :
-The contamination of π0 electroproduction on the neutron (and deuteron).
- The uncertainty on the relative calibration between H2 and D2 data
A. Belitsky,D Muller A Kirchner Compton form factor :
nn
Bj
Bjnunp
I EtFM
tHtFtF
x
xHFC )(
4
~))()((
2 2
2
211
Deuteron contribution compatible with zero at large -t
F. Cano & B. Pire calculation
Eur. Phys. J. A19, 423(2004).
PRELIMINAY
Neutron contribution is small and compatible with zero
Results can constrain GPD models (and therefore GPD En)
Analysis – Exclusivity check using Proton Array and MC
Normalized (e,p,)triple coincidence events
Using extra recoil Proton-detector, we have check the missing mass spectrum of double-coincidence events with the a triple -coicidence .
Monte-Carlo(e,)X – (e,p,)
2 cutXM
The missing mass spectrum using the Monte-Carlo gives the same position and width. Using the cut shown on the Fig.,the contamination from inelastic channels is estimated to be under 3%.
p
At Q2=2.3 GeV2 and xbj=.36
•The continuum is significant compared to the p(e,e’0)p•The resonances are washed out into the continuum.
As seen also in DIS
Q2=2.0 GeV2
Q2=0 GeV2
After :
-Normalizing H2 and D2 data to the same luminosity
-Adding Fermi momentum to H2 data
2 principle sources of systematic errors :
-The contamination of π0 electroproduction on the neutron (and deuteron).
- The uncertainty on the relative calibration between H2 and D2 data
2
0( ) ( )hS N N d N N d
Helicity Asymety
Mx2 Mx
2+t/2Missing masse assuming a proton target
Deuterium=proton+neutron+Deuton
- Hydrogen=proton
= neutron + deuton
2 (1 ) cos cos2L TT L TTddt
d dd
ddt tt
ddtd
)()(cos2 2*
2*
1*2
2
2
1 FFFFT
)]cos(2[sin2
1 *4
*33
*24
*1
2
4
2
3*2 FFFFFFFFTT
Chew, Goldberger, Low and Nambu ==> CGLM
Decomposition in CGLM amplitude:
0 cm angle ~ -(t-tmin)
)(2sin *2 LT
TT
k
k’
q=k-k’
q’