DVCS cross section measurements at JLab
Carlos Munoz Camacho,for the JLab Hall A Collaboration and the DVCS Collaboration
Los Alamos National Laboratory
Hard Exclusive Processes at JLab 12 GeV and a Future EICOct 29-30, 2006
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 1
E00-110 kinematics
Plastic scintillator array
LH2 targete
Beam
PbF2 Electromagnetic
calorimeter
HRS
p
e
γ
Kin Q2 xB θγ∗ s(GeV2) (deg.) (GeV2)
1 1.5 0.36 22.3 3.5
2 1.9 0.36 18.3 4.2
3 2.3 0.36 14.8 4.9
I Measurement of both helicity-dependent andhelicity-independent DVCS cross sections independently
I Q2−dependence of helicity-dependent cross section
Goal:Test twist-2 dominance of DVCS at moderate Q2 ∼ 2 GeV2.
. . . and if so, access combinations of GPDs.
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 2
Helicity-dependent and helicity-independent cross sections
Accurate determination of φγγ dependence of dΣ =σ→−σ←
2and dσ =
σ→+σ←
2Q2 = 2.3 GeV2, 〈t〉 = −0.28 GeV2, xBj = 0.36
=m CI,exp(F)
=m CI(Feff)
Total fit
<e CI,exp(F)
<e [CI + ∆CI ]exp(F)
<e CI(Feff)
Bethe-Heitler
Total fit
ff 1 freeparametereach
9>>=>>;1 freeparametereach
fixed
dσ: - rich and complex φγγ structure beyond BH- interesting & complementary GPD information (real part)
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 3
Q2−dependence: twist-2 dominance
0.4 < −t < 0.12 (GeV2)
=m CI(F)
)2 (GeV2Q1.4 1.6 1.8 2 2.2 2.4
0
0.5
1
1.5
2
2.5
3
3.5
4
=m CI(Feff)
)2 (GeV2Q1.4 1.6 1.8 2 2.2 2.4
0
0.5
1
1.5
2
2.5
3
3.5
4
I No Q2−dependence in =m CI(F) within 3% statistical error bars
I Sets an upper limit for twist-4 and higher ≤ 10%
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 4
GPD linear combinations and integrals
)2
< t > (GeV-0.3 -0.25 -0.2 -0.15
-3
-2
-1
0
1
2
3
4
5
2=1.5 GeV2 QIIm C2=1.9 GeV2 QIIm C2=2.3 GeV2 QIIm C
(VGG)IIm C
2=2.3 GeV2 QIRe C2=2.3 GeV2) QI C∆+I- Re (C
(VGG)I Re C
) (VGG)I C∆+I- Re (C
I Possible (likely) contribution of DVCS2 terms in these interference results
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 5
DVCS2 contribution
1.- Helicity-correlated cross section: =maginary part
d5Σd5Φ
=12
[d5σ+
d5Φ+
d5σ−
d5Φ
]=
sin(φγγ)Γ=1 =mhCI(F)
i− sin(2φγγ)Γ=2 =m
hCI(Feff)
i| {z }
Interference BH-DVCS
+ sin (φγγ)Γ=1 ηs1=mhCDVCS(Feff,F∗)
i| {z }
|DVCS|2 (twist-3)
I Different φγγ dependence of Twist-2 & Twist-3 interference terms:⇒ independent determination
I sinφγγΓ=1 term determines observable =m[CI,exp(F)
]:
=m[CI,exp(F)
]= =m
[CI(F)
]+〈ηs1〉=m
[CDVCS(Feff,F∗)
]|〈ηs1〉|E00−110 < 0.01
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 6
DVCS2 contribution
d5σ
d5Φ=
12
[d5σ+
d5Φ+
d5σ−
d5Φ
]=
d5σ(|BH|2)d5Φ︸ ︷︷ ︸
Known from FF
+ Γ η CDVCS(F ,F∗)︸ ︷︷ ︸|DVCS|2 (twist-2)
+
(Γ<0 − cos(φγγ)Γ<1 )<e[CI(F)
]+ Γ<0,∆<e
[CI + ∆CI
](F) + cos(2φγγ)Γ<2 <e
[CI(Feff)
]︸ ︷︷ ︸Interference BH-DVCS
I <e[CI, exp(F)
]= <e
[CI(F)
]+ 〈ηc1〉 CDVCS(F ,F∗)
I <e[CI, exp + ∆CI, exp
](F) = <e
[CI + ∆CI
](F) + 〈η0〉 CDVCS(F ,F∗)
|〈η0,c1〉|E00−110 < 0.05
ηc1 and η0 depend on beam energy ! =⇒Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 7
DVCS2: proposed separation (with JLab 6 GeV!)
Q2 = 1.9 GeV2, xB = 0.36, s = 4.9 GeV2
(GeV)beamE4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 6 6.2
6 G
eV C
/ Cδ
-1
-0.8
-0.6
-0.4
-0.2
-0
0.2
0.4
0.6
0.8
1 -14.4 -15.3 -16.8 -18.2 -18.7BH (at 180 deg)
(twist-2)2DVCS (twist-3)2DVCS
Inteference (twist-2)Inteference (twist-3)DIS
Unpolarized cross section
(GeV)beamE4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 6 6.2
6 G
eV C
/ Cδ
-1
-0.8
-0.6
-0.4
-0.2
-0
0.2
0.4
0.6
0.8
1 (twist-3)2DVCS
Inteference (twist-2)
Inteference (twist-3)
DIS
-14.4 -15.3 -16.8 -18.2 -18.7
Helicity-dependent cross section (deg) *γθ
Possible DVCS2 separation by changing beam energy
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 8
JLab 12 GeV proposal PR12-06-114 (J. Roche, C. Hyde-Wright, B. Michel, C.M.C et al.) – Approved by PAC-30
Kinematic coverage
JLab12 with 3, 4, 5 pass beam(6.6, 8.8, 11.0 GeV beam energy)
Bjx0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
)2 (G
eV2
Q
0
5
10
2<4 GeV2W
11 GeV≤beam
Unphysical with E
= 6.6 GeVbeamE
= 8.8 GeVbeamE
= 11.0 GeVbeamE
= 5.75 GeVbeamE
DVCS measurements in Hall A/JLab
Beam time (days)Q2 xBj
(GeV2) 0.36 0.50 0.603.0 34.0 24.55 13.1 54.8 46.3 47.2 75.1 136.0 167.7 139.0 20
Total 6 20 62
1 GeV2 range in tmin − t
88 days250k events/setting
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 9
JLab 12 GeV proposal PR12-06-114 (J. Roche, C. Hyde-Wright, B. Michel, C.M.C et al.) – Approved by PAC-30
Experimental configuration (e p → e γ X)
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 10
JLab 12 GeV proposal PR12-06-114 (J. Roche, C. Hyde-Wright, B. Michel, C.M.C et al.) – Approved by PAC-30
Missing mass resolution
(Cf. Table V for all kinematic settings)
6.6 GeV setting 11 GeV setting
E00-110 This proposal
Very similar M2X resolution ⇒ same exclusivity with e γ detection only.
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 11
JLab 12 GeV proposal PR12-06-114 (J. Roche, C. Hyde-Wright, B. Michel, C.M.C et al.) – Approved by PAC-30
Cross sections
I Model byVanderhaeghen, Guichon& Guidal (VGG), withfactorized t−dependence
I 250k events/setting or40k events per t−bin
I Similar statisticalaccuracy as E00-110
Helicity-independent cross sections (pb/GeV4)
6.6 GeV setting Q2 = 3.0 GeV2, xBj = 0.36
Helicity-dependent cross sections (pb/GeV4)
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 12
JLab 12 GeV proposal PR12-06-114 (J. Roche, C. Hyde-Wright, B. Michel, C.M.C et al.) – Approved by PAC-30
Cross sectionsHelicity-independent cross sections (pb/GeV4)
8.8GeV setting Q2 = 4.8 GeV2, xBj = 0.50 11 GeV setting Q2 = 9.0 GeV2, xBj = 0.60
Helicity-dependent cross sections (pb/GeV4)
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 13
JLab 12 GeV proposal PR12-06-114 (J. Roche, C. Hyde-Wright, B. Michel, C.M.C et al.) – Approved by PAC-30
Systematic errors
Type Relative errors (%)E00-110 proposed
Luminosity target length and beam charge 1 1HRS-Calorimeter Drift chamber multi-tracks 1.5 1
Acceptance 2 2Trigger dead-time 0.1 0.1
DVCS selection π0 subtraction 3 1e(p,e’γ)πN contamination 2 3radiative corrections 2 1
Total cross section sum 4.9 4.1
Beam Polarization ∆P/P 2 1Total cross section difference 5.3 4.2
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 14
Backup slides
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 15
Missing mass squared e p → e γ X (E00-110)
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
0
1000
2000
3000
4000
5000 Raw
contribution0π
subtracted0π cut2
XM
Obtained from) DATAγ γH(e,e
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
0
1000
2000
3000
4000
5000 Xγe p -> e pγe p -> e
Inclusive contamination
p) scaledγH(e,e
cut2XM
Competing channels:
I π0 electroproduction: e p → e p π0X → e p γ γ X
I Associated DVCS: e p → e N π γ
I Non-resonant: e p → e N π γ M2X > (M + mπ0)2
I Resonant: e p → e (∆ or N∗)γ m2∆ = 1.52 GeV2
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 16
π0 substraction (π0 → γγ)
decaySymmetric
Pion center−of−mass Laboratory frame
θ
Direction of the boost
Direction of the boostAsymmetricdecay
I Symmetric decay: minimum angle in lab of 4.4◦ for Emaxπ0 = 3.5 GeV
⇒ Clusters separation
I Asymmetric decay: sometimes only 1-cluster⇒ Mistaken for DVCS event
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 17
π0 substraction (π0 → γγ)
decaySymmetric
Pion center−of−mass Laboratory frame
θ
Direction of the boost
Direction of the boostAsymmetricdecay
Substraction procedure:
1. Compute kinematics of each detected π0 (2 clusters in calorimeter).
2. Randomize the decay : sample cos θ randomly between [-1,1] a bignumber of times (∼ 5000).
3. Compute the ratio of 2-cluster/1-cluster events generated by this π0
(∼ 30% in average).
Repeating this procedure for each detected π0 provides an automatic
normalization of the contamination as a function of Q2, t, ϕ, . . .
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 18
π0 subtraction results for different (t, φγγ) bins
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.33 GeV
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.28 GeV
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.23 GeV
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.17 GeV
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 19
π0 subtraction results for different (t, φγγ) bins
0 0.5 1 1.5 2 2.50 0.5 1 1.5 2 2.5-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.33 GeV
0 0.5 1 1.5 2 2.50 0.5 1 1.5 2 2.5-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.28 GeV
0 0.5 1 1.5 2 2.50 0.5 1 1.5 2 2.5-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.23 GeV
0 0.5 1 1.5 2 2.50 0.5 1 1.5 2 2.5-200
0
200
400
600
800
1000
1200
1400
cut2XM
2<t>=-0.17 GeV
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 20
π0 subtraction results for different (t, φγγ) bins
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
-100
0
100
200
300
400
<43φ, 317<2<t>=-0.23 GeV <43φ, 317<2<t>=-0.23 GeV
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
-100
0
100
200
300
400
<130φ, 43<2<t>=-0.23 GeV <130φ, 43<2<t>=-0.23 GeV
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
-100
0
100
200
300
400
<216φ, 130<2<t>=-0.23 GeV <216φ, 130<2<t>=-0.23 GeV
)2 (GeV2XM
0 0.5 1 1.5 2 2.5)2 (GeV2
XM0 0.5 1 1.5 2 2.5
-200
-100
0
100
200
300
400
<302φ, 216<2<t>=-0.23 GeV <302φ, 216<2<t>=-0.23 GeV
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 21
π0 subtraction results for different (t, φγγ) bins
0 0.5 1 1.5 2 2.50 0.5 1 1.5 2 2.5-200
-100
0
100
200
300
400
<43φ, 317<2<t>=-0.23 GeV <43φ, 317<2<t>=-0.23 GeV
0 0.5 1 1.5 2 2.50 0.5 1 1.5 2 2.5-200
-100
0
100
200
300
400
<130φ, 43<2<t>=-0.23 GeV <130φ, 43<2<t>=-0.23 GeV
0 0.5 1 1.5 2 2.50 0.5 1 1.5 2 2.5-200
-100
0
100
200
300
400
<302φ, 216<2<t>=-0.23 GeV <302φ, 216<2<t>=-0.23 GeV
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 22
π0 subtraction vs. θlab
(deg)labθ-24 -22 -20 -18 -16 -14 -12 -10 -80
200
400
600
800
1000
1200
2<t>=-0.37 GeV
(deg)labθ-24 -22 -20 -18 -16 -14 -12 -10 -80
200
400
600
800
1000
1200
1400
1600
2<t>=-0.33 GeV
(deg)labθ-24 -22 -20 -18 -16 -14 -12 -10 -80
200
400
600
800
1000
1200
1400
1600
1800
2<t>=-0.28 GeV
(deg)labθ-24 -22 -20 -18 -16 -14 -12 -10 -80
500
1000
1500
2000
2500
2<t>=-0.23 GeV
(deg)labθ-24 -22 -20 -18 -16 -14 -12 -10 -80
500
1000
1500
2000
2500
3000
3500
2<t>=-0.17 GeV
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 23
GPDs from cross sections vs. GPDs from asymmetries
)2< t > (GeV-0.3 -0.25 -0.2 -0.150
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5IE00-110 Im C
)]2)2∈(2-y)(1+B/(8 K xBH0[c(E00-110)LUA>φ<sin
(VGG)IIm C
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 24
GPDs from cross sections vs. GPDs from asymmetries
Even within a model (VGG). . . :
-t(GeV2) =mCI 〈sinφ〉[cBH0 /8KxB(2− y)(1 + ε2)2] Error
0.19 7.22 4.65 36%
0.30 4.47 2.40 46%
0.46 2.22 0.92 59%
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 25
Cross sections for each t bin (〈Q2〉=2.3 GeV2)
(deg)γγϕ0 90 180 270 360
0
0.01
0.02
0.03 2<t>=-0.33 GeV
(deg)γγϕ0 90 180 270 360
0
0.01
0.02
0.03 2<t>=-0.28 GeV
(deg)γγϕ0 90 180 270 360
0
0.01
0.02
0.03 2<t>=-0.23 GeV
(deg)γγϕ0 90 180 270 360
0
0.01
0.02
0.03 2<t>=-0.17 GeV
)IIm (C)eff
IIm (C
E00-110Fit
σ1-
)4) (nb/GeVγγϕdtdBdx2dQ
-σ4d - γγϕdtdBdx2dQ
+σ4d( 21
(deg)γγϕ0 90 180 270 360
0
0.02
0.06
0.08
0.1
0.12 2<t>=-0.33 GeV
(deg)γγϕ0 90 180 270 360
0
0.02
0.04
0.06
0.08
0.1
0.12 2<t>=-0.28 GeV
(deg)γγϕ0 90 180 270 360
0
0.02
0.06
0.08
0.1
0.12 2<t>=-0.23 GeV
(deg)γγϕ0 90 180 270 360
0
0.02
0.04
0.06
0.08
0.1
0.12 2<t>=-0.17 GeV
BH)IRe (C
)IC∆+ IRe (C)eff
IRe (C
E00-110Fit
σ1-
)4 (nb/GeVγγϕdtdBdx2dQ
σ4d
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 26
Counts
(deg.)ϕ0 50 100 150 200 250 300 350
(deg.)ϕ0 50 100 150 200 250 300 350
-+N+
N
-1000
-800
-600
-400
-200
0
200
400
600
0.12±): -2.16 unpIRe(C
0.08±): 0.47 unpIC∆+unp
IRe(C
0.45±): -0.56 effIRe(C
/n=1.872χTotal Fit:
2, <t>=-0.37 GeV2>=2.3 GeV2
(deg.)ϕ0 50 100 150 200 250 300 350
(deg.)ϕ0 50 100 150 200 250 300 350
-+N+
N
-1000
-800
-600
-400
-200
0
200
400
600
800
0.12±): -2.48 unpIRe(C
0.09±): -0.05 unpIC∆+unp
IRe(C 0.53±): -1.46 eff
IRe(C
/n=1.722χTotal Fit:
2, <t>=-0.33 GeV2>=2.3 GeV2
(deg.)ϕ0 50 100 150 200 250 300 350
(deg.)ϕ0 50 100 150 200 250 300 350
-+N+
N
-1000
-500
0
500
1000
0.12±): -2.08 unpIRe(C
0.08±): 0.56 unpIC∆+unp
IRe(C
0.60±): 0.61 effIRe(C
/n=2.232χTotal Fit:
2, <t>=-0.28 GeV2>=2.3 GeV2
(deg.)ϕ0 50 100 150 200 250 300 350
(deg.)ϕ0 50 100 150 200 250 300 350
-+N+
N
-1000
-500
0
500
1000
0.12±): -1.80 unpIRe(C
0.08±): 1.29 unpIC∆+unp
IRe(C
0.79±): 1.02 effIRe(C
/n=0.772χTotal Fit:
2, <t>=-0.23 GeV2>=2.3 GeV2
(deg.)ϕ0 50 100 150 200 250 300 350
(deg.)ϕ0 50 100 150 200 250 300 350
-+N+
N
-1000
-500
0
500
1000
1500
0.15±): -0.81 unpIRe(C
0.09±): 2.19 unpIC∆+unp
IRe(C
1.45±): 3.40 effIRe(C
/n=1.092χTotal Fit:
2, <t>=-0.17 GeV2>=2.3 GeV2
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 27
Calorimeter radiation damage
E00-110 experience:
I Dose dominated by e and π0 above 15◦ and Møller below 10◦
I Dose grows a factor 5 from 11.5◦ to 7.5◦
I 20% gain loss without loss in M2X/energy resolution
New experiment strategies:
I Minimum angle of the closest block: 7◦
I Luminosity equal to the peak luminosity in E00-110 taking into
account the distance to the target: L = 4 · 1037(D/110 cm)2 cm−2s−1
I Blue light curing (MAMI-A4): 17 h to cure a transparency loss of 25%
Curing every 6th day of running at the minimum angle
Total of 12 curing days for 88 beam days
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 28
Physics reach
1. Q2 variation:I 2:1 range at each xBjI Accurate measurement of twist-2 dominance
2. xBj variation (ξ dependence):I Precision data on variation of t−dependence with xI Study of transverse correlations
3. t variation:I 5 bins in 0 < tmin − t < 1 GeV2
I Fourier-conjugate to the spatial distributions of quarks asa function of their momentum fraction x
4. π0 electroproduction cross section:I Dominance of Twist-2 (isolation of leading twist)I Sensitive to nucleon GPDs H and E (× the π DA)
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 29
π0 electroproduction: σL + σT/ε
At leading twist:
dσL
dt=
12Γ
∑hN ,hN′
|ML(λM = 0, h′N , hN )|2 ∝ 1Q6
σT ∝1
Q8
ML ∝[ ∫ 1
0dz
φπ(z)z
] ∫ 1
−1dx
[1
x− ξ+
1x + ξ
]×
{Γ1Hπ0+Γ2Eπ0
}
Different quark weights: flavor separation of GPDs
|π0〉 = 1√2{|uu〉 − |dd〉} Hπ0 =
1√2
{23Hu +
13Hd
}|p〉 = |uud〉 HDV CS =
49Hu +
19Hd
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 30
Upgrades (from E00-110)
1. Expanded PbF2 calorimeter: 11×12 + 76 blocks.
I Higher acceptance for π0 measurements/subtraction.I Increased t−acceptance: ∆(tmin − t) = 1 GeV2.
2. Electronics:
I ARS system (as E00-110) + Upgraded calorimeter trigger(2 thresholds to increase ep → epπ0 statistics).
I FPGA & VME upgrades to increase livetime & bandwidth.
3. No proton detection: calorimeter can handle 4× E00-110 rate
4. Flared beam pipe to minimize secondary background incalorimeter.(Background dominated by Møller and π0 → γγ from target)
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 31
Model prediction for Q2, xBj and t dependenciesI Sample of statistical &
systematic errors on
coefficients
I Total of 55 data points
I Full t−dependence at each
(Q2,xBj) point
)2 (GeV2Q2 3 4 5 6 7 8 9
IIm
C
0
0.5
1
1.5
2
2.5
3=0.36Bx=0.50Bx=0.60Bx
Bjx0.3 0.35 0.4 0.45 0.5 0.55 0.6
-0.5
0
0.5
1
1.5
2
2.5 (F)IIm C
(F)IRe C
] (F)I C∆+IRe [C
)2-t (GeVmint0 0.1 0.2 0.3 0.4 0.5
IIm
C
0
1
2
3
4
5
6=0.36Bx=0.50Bx=0.60Bx
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 32
Summary
I Absolute DVCS cross sections in almost the completekinematic region of JLab12
I Precision determination of Twist-2 and Twist-3 observables:ξ, t (and Q2) scan
I π0 electroproduction cross sections
. . . using the successful experimental technique of E00-110 (nucl-ex/0607029)
This experiment requires 88 days of beam + 12 days for calorimeter curing
Future extentions: DVCS on the neutron, recoil polarimetry. . .
Carlos Munoz Camacho, for the Jefferson Lab Hall A Collaboration and the DVCS Collaboration Oct 29, 2006
DVCS in Jefferson Lab Hall A 33