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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
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