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Brahim Moreno Students' seminar at Bosen Workshop
ΔVCS and Generalized Parton Distributions
'epe
CLAS@Jlab
Brahim Moreno Students' seminar at Bosen Workshop
Outline
I. Generalized Parton Distributions
II. Beam Spin asymmetry
III. The experiment at Jlab
IV. First look at the Data
Brahim Moreno Students' seminar at Bosen Workshop
Generalized Parton Distributions
(GPDs)
Brahim Moreno Students' seminar at Bosen Workshop
In the Bjorken limit:
Large
Low
Fixed
General GPDs physics case
t
γ or mesonl’
l
γ*
N N’
standard notation
GPDs appear in the amplitudes of exclusive reactions
GPDs are a new way of describing the nucleon
l
)( 2Q
GPDs
γ
N
l’
N’
22 'llQ
2'NNt
'
2
2 llNb EEm
Qx
Brahim Moreno Students' seminar at Bosen Workshop
z
)( b
0
x
b
y
Nucleon form factor
)(xf
x1
x
xp
z
zy
Parton distribution
1
),( bxf
0
GPDs
GPDs : combine information from form factors and parton distribution
xfractionmomentumallongitudinawithcenternucleonfrombatbeto
nucleontheinquarkaforamplitudeyprobabilittherepresent
x
xp
z
zy
epep eXep MNlNl ''
Beam Spin Asymmetry
Brahim Moreno Students' seminar at Bosen Workshop
Beam Spin Asymmetry (BSA)
general case
kk
kk
dd
ddA
NN
NN
PA
1
k = number of independent variables P = polarization of incoming lepton
MNlNl ''
l = lepton, N= nucleon
l’= scattered lepton, N’= recoil hadron, M= photon or meson
Brahim Moreno Students' seminar at Bosen Workshop
Beam Spin Asymmetry (BSA)
DVCS example '' pepe
epep
Interference between DVCS and Bethe-Heitler processes
2
+ +
DVCS BHBH
cos1
sin
Aβ,α are combinations of
GPDs
BSA grants access to nucleon GPDs
Brahim Moreno Students' seminar at Bosen Workshop
Beam spin asymmetry: ΔVCS case
'epe
e
e’
γ* γ
Np
л
-N-Δ transitions at a partonic level
- large Nc approximation: ΔVCS can be
described in terms of standard GPDs
77
77
dd
ddA
GPDs N-Δ
L.L. Frankfurt, M. V. Polyakov,M. Strikman, M.VanderhaeghenPhys. Rev. Lett. 84: 2589-2592 (2000)
P.A.M Guichon, L.Mossé, M.Vanderhaeghen
Phys. Rev. D68 034018 (2003)
Brahim Moreno Students' seminar at Bosen Workshop
+ eep
+
2ΔVCS BHBH
FIRST measurement
P.A.M Guichon, L.Mossé,
M.Vanderhaeghen
Phys. Rev. D68 034018 (2003)
Brahim Moreno Students' seminar at Bosen Workshop
The experiment at Jefferson lab
Brahim Moreno Students' seminar at Bosen Workshop
Thomas Jefferson Laboratory (USA, Virginia)
Hall BHall B
Brahim Moreno Students' seminar at Bosen Workshop
Cherenkov Countersfor e/л separation
CLAS detector
Time-of-flight
counters (TOF)
Drift chambers (DC)to determine trajectories
to detect showering particles
Electromagnetic Calorimeter (EC, LAC)
Torus magnet
of charged particles
eep0 eep
for separation (DVCS)0
high energy resolution photon detector
Inner calorimeter (IC)
2005 data taking 35 days (from march to may 2005)
December 2006 : first thesis published (DVCS BSA)
2008 : second data taking period
Chronology
my arrival
2005 calibrations
2007 : ongoing analysis (DVCS , , , cross sections, , BSA ) 0 0
beam energy 5.776 GeV
Brahim Moreno Students' seminar at Bosen Workshop
First look at the data
Brahim Moreno Students' seminar at Bosen Workshop
Analysis plan
pepeeep '0''
Basic event selection: 1 electron, 1 proton, 3 photons
- reconstruct Δ particles via neutral pion reconstruction
- develop exclusivity cuts
- background and contamination studies
- Beam Spin Asymmetry results
e
e’
γ* γ
Np
л
Which one to choose ?
Before going further it would
be wise to have a preview of
the decay particles of Δ phase
space
Development of a kinematic
filter
Delta reconstruction
different photon combinations
GeVM p GeVM p
GeVM GeVM GeVM
GeVM p
Brahim Moreno Students' seminar at Bosen Workshop
Phase space generatorFirst look at the data
Brahim Moreno Students' seminar at Bosen Workshop
t random number uniformly distributed
Kinematic generator
max2
min22 ,QQQ
ν: random number uniformly distributed max2
min2 QQ eE,0
Q2: random number uniformly distributed
maxmin , ttt
t
0t mint max
LE LDVCS
E
ee’
γ* γ
Np
лt
Prediction for ΔVCS
8% events under 0 GeV
0'' peeep
)(0
GeVEE DVCS
DVCS photon = most
energetic one
First look at the dataSelection cuts
Selection cuts epepeep 0
Before cutsAfter cuts
Selection cuts: cut on epepeep 0
M
0m
m A B
Selection cuts epepeep 0
A = second resonance region (~1.5 GeV)
B = third resonance region (~1.65 GeV)
Brahim Moreno Students' seminar at Bosen Workshop
Complementary slides
Brahim Moreno Students' seminar at Bosen Workshop
Kinematic generator
1** cos pEE p
Lp 1
** cos00 pEEL
2** cos00
2
pEEL
2** cos00
1
pEEL
Δ
γ
p
γ
0
*p
2
*p*
p
1
Brahim Moreno Students' seminar at Bosen Workshop
Kinematic generator
1cos uniformly distributed 1,1 1** cos pEE p
Lp
Lp
LL EEE 0
2cos uniformly distributed 1,1 2cos12
0
0
0
1
m
EL
LLL EEE1
02
Kinematic generator: validation '' pepe
generator resultdata
Selection cuts epepeep 0
epep
epMM
epE
epp
epp
X
X
Xy
Xx
2
0epep
0
2
m
epMM X
02 epMM X
02 eMM X
Brahim Moreno Students' seminar at Bosen Workshop
Data analysisbackground and contamination
Overview
0 eep
R
RR
epep
epepep
epepep
0
0
000
0
epepep
epepep RR
Brahim Moreno Students' seminar at Bosen Workshop
Data
e1-dvcs experiment first part of 01-113 experiment
35 days (from march to may 2005) approved for 60 days
beam energy 5.776 GeV
123410.2 scmluminosity
to be completed next year
accumulated charge mC5.59
hydrogen target
More about GPDs
Standard GPDs
txE ,, txE ,,~
txH ,,~ txH ,,
γ
p’
e
e’
γ*
p
x-ξx+ξ
t
4 GPDs for each quark flavour
txC ,,1
txC ,,3
txHM ,, txH E ,,
txC ,,2
txC ,,4
txHC ,,
Transition N-Δ GPDs
3 transition vector GPDs
4 transition pseudo-vector GPDs
In the large Nc limit
txEtxEHtxH duMM ,,,,
3
2,,
txHtxHtxCtxC du ,,~
,,~
3,,,, 11
txEtxEtxCtxC du ,,~
,,~
4
3,,,, 22
Particle ID
Brahim Moreno Students' seminar at Bosen Workshop
cut on reconstructed vertex position
Particle ID: electron
Scattered electron identification
Fiducial cuts (EC,DC)
Cut on lost energy in inner part of EC: E_in>60 MeV
Cut on E/p vs p
Momentum threshold : p > 800 MeV
Cut on number of p.e’s produced in CC: 10*N > 25
id = 11
Brahim Moreno Students' seminar at Bosen Workshop
Particle ID: electron
Fiducial cuts (EC)
Cut on lost energy in inner part of EC
Brahim Moreno Students' seminar at Bosen Workshop
Particle ID: electron
pp
ppp
pppEtot
22
22
10.155,210.819,1)(
10.55,4115.03216.0)(
)(5.2)(
Cut on E/p vs p
Brahim Moreno Students' seminar at Bosen Workshop
Particle ID: proton
recoil proton identification
cut on reconstructed vertex position
Fiducial cuts (θ,φ)
Cut on calmes
Brahim Moreno Students' seminar at Bosen Workshop
photon identification:E > 150 MeV
Particle ID: photon
detected in ICfiducial cuts to avoid photons with hit near IC edgeassume all particles detected in IC are photons
detected in EC Fiducial cuts (EC) cut on β = l/t
Brahim Moreno Students' seminar at Bosen Workshop
Fiducial cuts
195.00
0
))(sin(27)(
52.0
93.08.16)(
),()()(
)(
pp
pp
ppp
p
cut
cut
cut
66.0
sin5.104.1)(
27),(
8.16
0
0sec
pp
p otor
o
electron
proton
photon
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