DVCS at 6/12 GeV, and ideas for the EIC

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
DVCS at 6/12 GeV, and ideas for the EIC
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3 Aubière, France
Electron-Ion Collider Workshop
Mar 14-15, 2010
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 1

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Motivation
DVCS experimentally: interference with Bethe-Heitler (BH)
At leading twist:
d 5 → σ −d 5 ← σ = Im (T BH · T DV CS )
d 5 → σ +d 5 ← σ = |BH| 2 + Re (T BH · T DV CS ) + |DV CS| 2
∫ +1
T DV CS =
∫ +1
−1
H(x, ξ, t)
P dx
−1 x − ξ
} {{ }
Access in helicity-independent cross section
Carlos Muñoz Camacho
H(x, ξ, t)
dx
x − ξ + iɛ + · · · =
− iπ H(x = ξ, ξ, t) + . . .
} {{ }
Access in helicity-dependent cross-section
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 2

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Motivation
The DVCS program “worldwide”
◮ HERMES at DESY:
◮ Beam (BSA), charge (BCA) and transverse target (TSA)
asymetries published
◮ Several ongoing analysis + recoil detector installed 1 year
before shutdown: results to come. . .
◮ Hall A and Hall B partially overlapping, partially
complementary, active programs:
◮ Hall A: high accuracy, limited kinematics
◮ Hall B: wide kinematic range, limited accuracy
◮ Very different systematics
◮ COMPASS at CERN? (proposal preparation underway)
◮ The roadmap:
◮ Early results (≈ 2001) from non-dedicated exp. (HERMES+CLAS)
◮ First round of dedicated experiments in Halls A/B in 2004/5
◮ Second round on 2008–2010
◮ Compeling DVCS program in Halls A/B at 11 GeV (≈2013-15)
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 3

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Non-dedicated experiments
HERMES
27.5 GeV polarised
e + /e − beam of HERA
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 4

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Non-dedicated experiments
CLAS and HERMES (2001): beam spin asymmetries
A LU : PRL 87, 182002 (2001)
A UL : PRL 87, 182001 (2001)
〈Q 2 , x B , −t〉 = 2.6 GeV 2 , 0.11, 0.27 GeV 2 0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
0 50 100 150 200 250 300 350
φ (deg)
A
〈Q 2 , x B , −t〉 = 1.25 GeV 2 , 0.19, 0.19 GeV 2
◮ Both results show, with a limited statistics, a sin φ behaviour
◮ Not fully exclusive
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 5

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Non-dedicated experiments
Beam charge asymmetry (HERMES)
A C
0.2
0.1
0
-0.1
-0.2
Integrated
0 0.5 1 1.5 2 2.5 3
|φ| (rad)
cosφ
A C
0.6
0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
As a function of t
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
-t (GeV 2 )
Phys. Rev. D75, 011103 (2007)
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 6

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
0 0.5 0 0.2
0 5 10
0 0.5 0 0.2 0 5 10
0 0.5 0 0.2 0 5 10
0 0.5
Non-dedicated experiments
Beam charge asymmetry (2008)
A C
cosφ
0.4
0.2
PRD75, 011103
this work
DD:Fac,D
DD:Fac,no D
DD:Reg,D
DD:Reg,no D
0
A C
cos(0φ)
0
-0.1
A C
cos(2φ)
A C
cos(3φ)
0.1
0
-0.1
0.1
0
-0.1
0 0.2 0.4 0.6 0 0.1 0.2 0.3
overall
-t (GeV 2 )
x B
5 0 2 4 6 8 10
Q 2 (GeV 2 )
Carlos Muñoz Camacho
JHEP 0806, 066 (2008)
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 7

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
0.2
0
-0.2
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
-0.15 -0.1 -0.05 0 0.05 0.1 0.15
0 0.5
0 0.2
0 5 10
0 0.5 0 0.2 0 5 10
0 0.5
0 5 10
Non-dedicated experiments
Transverse target spin asymmetry
sin(φ-φ
A s
)
UT
0.2
0
-0.2
8.1% scale uncertainty
A UT, DVCS
J u =0.6
0.4
0.2
A UT, I
J u =0.6
0.4
0.2
sin(φ-φ
A s
)cosφ
UT
0.2
0
cos(φ-φ
A s
)sinφ
UT
-0.2
-0.4
0.2
0
-0.2
0 0.2 0.4 0.6
overall
-t (GeV 2 0 0.1 0.2 0.3 0 2 4 6 8 10
)
xB Q 2 (GeV 2 )
JHEP 0806, 066 (2008)
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 8

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Non-dedicated experiments
Recoil detector at HERMES
Missing mass squared ep → eγX
1000N/N DIS
0.3 e +
data
-
e data
0.2
MC sum
elastic BH
associated BH
semi-inclusive
0.1
0
0 10 20 30
2
2
M x (GeV
)
Integration window:
−2.25 GeV 2 < M 2 x < 2.89 GeV 2
◮ Not fully exclusive
◮ Recoil detector operated during last year of data taking
◮ Analysis underway and results to come
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 9

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall A E00-110
E00-110 experimental setup
High Resolution Spectrometer
100-channel scintillator array
132-block PbF 2 electromagnetic calorimeter
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 10

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall A E00-110
Exclusivity
Missing mass squared ep → eγX (E00-110)
Raw H(e,e’γ)X Missing Mass 2 (after accidental subtraction).
[ H(e,e’γ)X - H(e,e’γ)γY ]: Missing Mass 2
H(e,e’γ)p
H(e,e’γ)∆…
+H(e,e’γp) sample,
Normalized to H(e,e’γ)
•••H(e,e’γp) simulation
Exclusivity ensured by missing mass technique
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 11

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
2
|BH+DVCS|
2
|BH|
2
|BH+DVCS|
2
- |BH|
2
2
2
2
Hall A E00-110
DVCS cross section in the valence region (Hall A: E00-110)
◮ Helicity-dependent cross
section ( → σ − ← σ ) at
Q 2 = 1.5, 1.9 and 2.3 GeV 2 .
)
4
DVCS cross section (nb/GeV
0.04
0.03
0.02
0
0
-0.02
-0.03
-0.04
0.02
0
0
-0.02
< t > = - 0.33 GeV
E00-110
Total fit
Twist - 2
90 180 270
φ
2
0.04
0.02
0
-0.02
-0.04
0.02
0
-0.02
(deg)
< t > = - 0.28 GeV
90 180 270
2
0.04
0.02
0
-0.02
-0.04
0.02
0
-0.02
φ (deg)
< t > = - 0.23 GeV
90 180 270
2
0.04
0.02
0
-0.02
-0.04
0.02
0
-0.02
φ (deg)
< t > = - 0.17 GeV
90 180 270
2
φ (deg)
= 1.5 GeV
Q
= 1.9 GeV
Q
◮ Helicity-independent
cross section ( → σ + ← σ ) at
Q 2 = 2.3 GeV 2 only .
)
4
DVCS cross section (nb/GeV
0.02
0
-0.02
0.1
0.05
0
2
< t > = - 0.33 GeV
E00-110
Total fit
Twist - 2
E00-110
2
< t > = - 0.28 GeV
2
< t > = - 0.23 GeV
2
< t > = - 0.17 GeV
beam helicity-independent beam helicity-dependent
90 180 270
90 180 270
90 180 270
90 180 270
φ (deg)
φ (deg)
φ (deg)
φ (deg)
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 12

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall A E00-110
E00-110 results
)
4
DVCS cross section (nb/GeV
0.02 beam helicity-dependent
0
-0.02
0.1
0.05
beam helicity-independent
2
|BH+DVCS|
2
|BH|
0
0 90 180 270 360
φ (deg)
(H, H ~ , E)
I
Im C
5
4
3
2
1
2
2
Q = 1.5 GeV
2
2
Q = 1.9 GeV
2
2
Q = 2.3 GeV
VGG model
0
0.15 0.2 0.25 0.3 0.35
2
-t (GeV )
Twist-2: dominant contribution
Contributions from BH 2 , DVCS 2
and BH-DVCS interference
Phys. Rev. Lett. 97, 262002 (2006)
Physics Today, March 2007
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 13

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall A E00-110
E00-110 results
4
3.5
0.02 beam helicity-dependent
3
)
4
DVCS cross section (nb/GeV
0
-0.02
0.1
0.05
beam helicity-independent
2
|BH+DVCS|
2
|BH|
0
0 90 180 270 360
φ (deg)
2.5
2
1.5
1
0.5
0
1.4 1.6 1.8 2 2.2 2.4
2 2
Q (GeV )
Twist-2: dominant contribution
Contributions from BH 2 , DVCS 2
and BH-DVCS interference
Phys. Rev. Lett. 97, 262002 (2006)
Physics Today, March 2007
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 13

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall A E03-106
DVCS on the neutron: experiment E03-106 at JLab
I exp
)
n
Im(C
3
2
1
0
-1
-2
-3
-4
LD 2 target (F2 n(t) ≫ F 1 n(t) !) J u=-0.4
J d=-0.6
J u=0.3
J d=0.2
J u=0.6
J d=0.8
2
t (GeV )
σ → − σ ← = Γ(A sin ϕ + . . . )
-0.5 -0.45 -0.4 -0.35 -0.3 -0.25 -0.2 -0.15 -0.1
Charged particle veto
in front of scintillator array
A = F 1 (t)H +
Carlos Muñoz Camacho
x B
[F 1 (t) + F 2 (t)]
2 − x ˜H t
−
B 4M 2 · F 2(t) · E
} {{ }
Main contribution for neutron
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 14

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall A E03-106
DVCS on the neutron: experiment E03-106 at JLab
LD 2 target (F2 n(t) ≫ F 1 n (t) !)
J d
1
0.8
0.6
0.4
JLab Hall A
n-DVCS
Charged particle veto
in front of scintillator array
0.2
+ J u
J d = 0.18
5
± 0.14
-0
-0.2
Lattice QCDSF
-0.4
-0.6
-0.8
HERMES Preliminary
p-DVCS
-1
-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 1
J u
σ → − σ ← = Γ(A sin ϕ + . . . )
A = F 1 (t)H +
Carlos Muñoz Camacho
x B
[F 1 (t) + F 2 (t)]
2 − x ˜H t
−
B 4M 2 · F 2(t) · E
} {{ }
Main contribution for neutron
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 14

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall B E1-DVCS
BSA in a large kinematic domain (Hall B)
2 2
Q (GeV )
0.2
2
-t = 0.28 GeV
A =
→
σ −
←
σ
→
σ +
←
σ
≈
α sin φ
1 + β cos φ
Simple models do not
reproduce the data
Carlos Muñoz Camacho
4
3
2
1
0.1 0.2 0.3 0.4 0.5
x B
0.0
-0.2
0.2
0.0
-0.2
Analysis of cross sections underway
2
-t = 0.49 GeV
0 90 180 270 360
φ (deg)
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 15

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
0.3
0.2
0.1
0
0 0.5 1 1.5
0.3
0.2
0.1
0
0.3
0.2
0.1
0
0 0.5 1 1.5
0 0.5 1 1.5
0.3
0.2
0.1
0
0.3
0.2
0.1
0
0.3
0.2
0.1
0
0 0.5 1 1.5
0 0.5 1 1.5
0 0.5 1 1.5
0.3
0.2
0.1
0
0.3
0.2
0.1
0
0.3
0.2
0.1
0
0.3
0.2
0.1
0
0 0.5 1 1.5
0 0.5 1 1.5
0 0.5 1 1.5
0 0.5 1 1.5
0.3
0.2
0.1
0
0.3
0.2
0.1
0
0.3
0.2
0 0.5 1 1.5
0 0.5 1 1.5
0.1
0
0 0.5 1 1.5
Hall B E1-DVCS
BSA in a large kinematic domain (Hall B)
0.3 0.10 < x < 0.15
B
)
2
(GeV
2
α(t)
0.2
0.1
Q
0
4
0 0.5 1 1.5 2
|t| (GeV )
3
A =
→
σ −
←
σ
→
σ +
←
σ
≈
α sin φ
1 + β cos φ
2
Simple models do not
reproduce the data
1
0.1 0.2 0.3 0.4 0.5
x B
Carlos Muñoz Camacho
Analysis of cross sections underway
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 15

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall B
Target spin asymmetry A UL (Hall B)
Not dedicated result:
0.4
0.2
A UL
0
-0.2
-0.4
-0.6
0 50 100 150 200 250 300 350
φ
Degree
Dedicated experiment took data in Hall B earlier this year
Sensitivity to GPD ˜H
Other upcoming experiments (at 6 GeV):
◮ More DVCS on unpolarized proton
◮ DVCS on a transversely polarized target (conditionally approved)
◮ DVCS on nuclei (He 4 )
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 16

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
E07-007: DVCS·BH – DVCS 2 separation
E07-007 (Hall A)
σ(ep → epγ) = |BH| 2
} {{ }
+ I(BH · DV CS)
} {{ }
+ |DV CS| 2
} {{ }
Known to ∼ 1% Linear combination of GPDs Bilinear combination of GPDs
DVCS cross section has a very rich azimuthal structure:
◮ Azimuthal analysis allows the separation of the different contributions to I
if DVCS 2 is negligeble.
◮ If DVCS 2 is important, I and DVCS 2 terms MIX in an azimuthal analysis.
◮ The different energy dependence of I and DVCS 2 allow a full separation.
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 17

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
E07-007: DVCS·BH – DVCS 2 separation
E07-007 (Hall A)
σ(ep → epγ) = |BH| 2
} {{ }
+ I(BH · DV CS)
} {{ }
+ |DV CS| 2
} {{ }
Known to ∼ 1% Linear combination of GPDs Bilinear combination of GPDs
DVCS cross section has a very rich azimuthal structure:
◮ Azimuthal analysis allows the separation of the different contributions to I
if DVCS 2 is negligeble.
◮ If DVCS 2 is important, I and DVCS 2 terms MIX in an azimuthal analysis.
◮ The different energy dependence of I and DVCS 2 allow a full separation.
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 17

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
E07-007: DVCS·BH – DVCS 2 separation
E07-007: Rosenbluth-like DVCS 2 –I separation in Hall A
E b =6.0 GeV
E b =3.64 GeV
◮ Clean separation of BH-DVCS intereference term from pure DVCS 2
◮ Scaling test on the real part of the DVCS amplitude
◮ Rosenbluth separation of σ L /σ T for ep → epπ 0
BH
4
Simulated data
D
d σ
4
BH
C
(nb/GeV ) Simulated data
DVCS
4 2
C (F,F*)
Re
(nb/GeV )
Fit
dQ dx B
dtdϕ
I
γγ
Re
1-σ
Re
d 4 σ (nb/GeV 4 Fit
Re (C )
I
)
Re (C I I
I I
γγ
Re C
+ ∆C )
Re (C +∆ C )
0.5
I
1-σ
Re (C ) 3
0
eff 2.5
2
2
2
2
=-0.33 GeV 2
=-0.28 GeV
=-0.23 GeV
=-0.17 GeV
0.14 =-0.28 GeV
-0.5
2
=-0.23 0.14 I
GeV
I
2 2
0.14
0.14
0.14
0.14 Re (C +∆ C )
=-0.17 GeV
-1
0.14
1.5
0.12 0.12 3
0.12
0.12 1
0.12 -1.5
0.12
0.12
0.5
0.1 2.5
0.1
0.1-2
0.1
0.1 0.1 0
0.1
2
-2.5
0.08
0.08 0.08
0.08 0.08 -0.5
0.08
1.5
-3
0.06
0.06
-0.35 -0.3 -0.25 -0.2
0.06
0.06
-0.15
-1
-0.35 -0.3 -0.25 -0.2 -0.15
0.06
0.06
1
2
2
t (GeV )
t (GeV )
0.04 0.04
0.04 0.04
0.04
0.5
0.04
0.04
0.02
0.02
eff
0.02
DVCS
0.02 0
0.02
Re C
0.02
C
0.02
0
0 5
0
40
0 -0.5
4 0
0
0
270 ϕ (deg)
360 -0.02
-0.02
0 0 90 90 180 180 270 ϕ (deg) 270 360 -0.02
ϕ (deg)
360
0 -0.02
0 90 90 180 270 180 ϕ (deg)
360 -0.02
3
270 ϕ (deg)
360
0 90 -0.02
0 180 30
-0.2 -0.15
-1
-0.35 -0.3 -0.25 -0.2 -0.15
90 270 ϕ (deg) 180 360
270 ϕ (deg)
360 -0.02
γγ
γ γ
2
γ γ
γ γ
0 90
20
2
γγ
1
2
t (GeV )
t (GeV ) γ γ
γ γ
0.5 2
=-0.28 GeV
0.5 2
=-0.23 0 GeV
0.5 2 10
=-0.17 GeV
0.5 2
-1
=-0.33 GeV
0.5 2
=-0.28 GeV
0.5 2
=-0.23 GeV
0.5 2
DVCS
DVCS
0
=-0.17 GeV
Simulated data 0.4
C (F,F*)
0.4-2C
0.4
I
0.4 40Re (C)
-3
-0.35 0.4 -0.3 -0.25 -0.2 -0.15
-10
0.4 -0.35 -0.3 -0.25 -0.20.4
-0.15
Fit
0.3
I I
0.3
0.3 2
2
I Re (C+ ∆C )
I I
t (GeV )
t (GeV )
I
1-σ Re C 30
0.3
Re (C )
Re (C +∆ C )
0.3
I I
0.3
0.3
0.2
eff
30.2
Re (C +∆ C )
0.2
2
GeV
0.1 2
=-0.17 20 GeV 3
2.5 E07-007 Systematic uncertainty
0.1 0.2 0.08
0.1 0.2
0.1 0.2
0.2
0.06 102.5
2
1.5
0.04 2
0.1
1
0.02
0 0.1
0 0.1
0.1
0
270 ϕ (deg)
360 0 0 90 1.5
180 270 ϕ (deg)
360 0.5 E00-110: assuming DVCS 2 =0
0 90 180 270 ϕ (deg)
360 0 90 180 270 ϕ (deg)
360
-0.02
γγ
1
0
γ γ
0
0
γ γ
0
γ γ
0
-0.2 -0.15
-0.04 -10
0 -0.06 90 -0.35 0.5
180 270 -0.3
ϕ (deg)
360 -0.5 -0.25 0 90 -0.2 180 -0.15
270 ϕ (deg)
360 0 90 180 270 ϕ (deg)
360 0 90
-0.3 2
2
t (GeV ) -0.25-0.08
-0.20
-0.15
-1
-0.35 -0.3 -0.25
γγ
t (GeV ) -0.2 -0.15
γ γ
γ γ
90 180 270 360
-0.1
ϕ (deg)
0 90 180 270 2
t (GeVϕ
) (deg)
360
2
-0.5
t (GeV )
γ γ
γ γ
-0.2 -0.15
-1
eff -0.35 -0.3 -0.25 -0.2 DVCS -0.15
2
GeV
Re C 0.1 2
Carlos Muñoz =-0.17 GeV
C
2 Camacho
2
t (GeV ) 0.08
40
t (GeV
LPC Clermont-Ferrand, CNRS/IN2P3
)
0.06 Co-spokespersons: C.M.C., J. Roche, C. Hyde-Wright, P. Bertin
DVCS at 6/12 GeV 0.04 and ideas for EIC 30
18
DVCS

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-A program
JLab Hall A at 11 GeV
)
2
(GeV
2
Q
JLab12 with 3, 4, 5 pass beam
(6.6, 8.8, 11.0 GeV beam energy)
DVCS measurements in Hall A/JLab
10
5
0
Carlos Muñoz Camacho
2
2
W

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-A program
Future possibilities
◮ DVCS on the neutron at 12 GeV
◮ Extention to the full kinematic domain available with JLab at 12GeV
◮
Systematic uncertainties improved
◮ Recoil polarimetry (R+D)
◮ A full DVCS program requires proton polarization measurements
◮
◮
Observables of proton recoil polarization in ⃗ep → e⃗pγ
are functionally equivalent to the
observables ⃗e⃗p → epγ for polarized targets
Conceptual design of a large acceptance recoil polarimeter
(longitudinal and transverse proton polarization) under development
◮ High luminosity (> 10 37 cm −2 s −1 ) 3 He target
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 20

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-A program
Polarized 3 He target in JLab/Hall A
◮ n lum. of 10 36 /cm 2 /s (14 atm × 40 cm)
◮ ”Background” luminosity:
◮ p in 3 He+entrance/exit windows
◮ 10 37 /cm 2 /s total luminosity
◮ Polarization: 50%
◮ Nuclear physics dilution factor 0.86 (d-state)
◮ -2.8% p polarization
◮ Long. & Trans.
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 21

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-A program
3 He target upgrade conjecture
◮ Separate polarization and target volumes
◮ Increase throughput by a factor of 10 to 100
◮ Cool and/or compress 3 He in target area by a factor of 10
(10K at 10 atm × 20 cm)
◮
Rapid cycling of 3 He through target
◮ Reduce depolarization effect of target density, beam current,
target walls
◮ Replace thick glass with thin metallic walls
◮ Neutron luminosity of 10 37 /cm 2 /s
◮ Proton luminosity 2 · 10 37 cm 2 /s
◮ Endcaps ≤ 10 37 /cm 2 /s
◮ Target polarization: 0.5 · (0.86 n − 0.028 p)
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 22

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-A program
Neutron DVCS off a 3 He target
⃗n(⃗e, e ′ γ)n via 3 ⃗ He(⃗e, e)X
◮ Long or Trans normal polarization
◮ Target single spin cross sections
◮ dσ ∼ sin ϕ (twist-2): Im[BH·DVCS]
◮ Unpolarized protons in 3 He cancel
◮ Target double spin
◮ dσ ∼ c0 + c 1 cos ϕ: Re[BH 2 +(BH·DVCS)+DVCS 2 ]
◮ Unpolarized protons cancel
◮ Transverse sideways: sin ϕ → cos ϕ
◮ All other “neutron” observables (total σ, beam-spin) have
large incoherent proton contributions
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 23

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-A program
Cross section projections (VGG at 10 37 cm −2 s −1 )
Q 2 = 4 GeV 2 , x B = 0.36, k = 8.8 GeV,
t min − t = 0.15 GeV 2 , 20 days
Q 2 = 2.3 GeV 2 , x B = 0.36, k = 8.8 GeV, t = −0.26 GeV 2 , 10 days
Polarization sideways (‖) to (e, e ′ ) plane
◮ 50%×80% polarization
Polarization normal (⊥) to (e, e ′ ) plane
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 24

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-B program
E12-06-119: DVCS with CLAS at 11 GeV
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 25

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-B program
Beam spin asymmetry
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 26

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Hall-B program
Target spin asymmetry
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 27

½ººÆÊÄÁÈÊÌÇÆÁËÌÊÁÍÌÁÇÆË ¾
Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Advantages
DVCS with EIC: small x at high Q 2
◮ Gluon GPDs
­£ ­
Ü· Ü
Ô Ô¼
ÙÖ½ºÐÙÓÒÒÖÑÓÖÔÐÝÎÖØÙÐÓÑÔØÓÒËØØÖÒ´Î˵º Ø
ÒÓØ×Ò×ÐØÓÐÙÓÒÈ×ÒØÝÛÐÐÒÓØÙÖØÖ×ÖºÅÓÖØÐ×Ò ÓØÒØÖØÓÒÖÓÒÓÚÖܸÒØÓÒØÖÙØÓÒÒÐÖÒÓÙØÓÓÑÔÒ×Ø Ø«××ÙÔÔÖ××ÓÒºÌÎËÜÔÖÑÒØ×ÖÒØ×Ø×׸ÛÖܼ¿¸× ÏÒÜ×ÚÖÝ×ÑÐиØÑÓÑÒØÙÑÖØÓÒ×Ü ÒÜ·ÖÚÖÝ×ÑÐÐÒ×ÓÑÔÖØ
ÓÙÒÒØÖÚÛÔÔÖ׸½¾℄º
ÏÐÈ×ÖÐØØÓÐÖÝÒÓÛÒÕÙÒØØ××ÓÖÑØÓÖ×ÒÔÖØÓÒ×ØÖÙØÓÒ׸ ½ºº¾ ØÝÓÒØÒÛÐØÓÒÛÒÓÖÑØÓÒºÌÒÛØÙÖÓÈ××ÚÒÝØÖ ÈÝ××ÒØØÖÒ×ÚÖ×ÔÐÒ
ØÔÒÒ¸ÛÒØÖÓÙ×ÒÛÑÓÑÒØÙÑ×кÌØÖØ×Ö×ÓÐÚÝØ
ÛÖØÚÖØÙÐÔÓØÓÒ×ØØÖÒÚÒØÓÙÖ׺Ì×ÒØÖÔÖØØÓÒÓØÚÖÐظ ÒØÑÓÑÒØÙÑØÖÒ×ÖØ×ÒÔÒÒظÒÓÙÖÖ¹ÓÒÙØØÓØ×ÔØÐÐÓØÓÒ ÚÖØÙÐØÝɾ×ÐØ××ÓÖع×ØÒÖÓÒÓØØÖءɺÅÒÛÐØ ÚÖØÙÐÔÓØÓÒÓÒ×ÔØÐ×Ð×ÑÐÐÓÑÔÖØÓØØÖØ×ÞÔÓØÓÒÓ
ÔÓÒÖÝÙÖÖؽ¿¸½℄ÒÒÖÐÞÝн℄¸×ÐÐÙ×ØÖØÒº½ºº
[ 1
dxH(x, x)
◮ Sum rules (ex: orbital angular momentum)
∫ 1
−1
◮ Dispersion relations
Carlos Muñoz Camacho
Re H(ξ) = PV
dx x [H(x, ξ, 0) + E(x, ξ, 0)] = J
∫ 1
−1
ξ − x − 1
ξ + x
]
+ C
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 28

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Kinematics
Collider vs fixed target kinematics
◮ Fixed target: q ∗ , q and p ′ are all co-linear at t min
◮ Collider: Boost γ P ≫ 1 along the beam direction
(into collider frame)
Non-parallel boost to q, q ′ and p ′
Recoil proton at very small angles: t = −(4ξ 2 M 2 + t ⊥ )/(1 − 2ξ)
tan θ p ′ ≃
√ t⊥
P (1−2ξ)
Typically, we need to detect protons at
a few mrad (∼ 5) from the beamlines
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 29

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Projections
Projections (Q 2 = 10 GeV 2 , x B = 0.05)
◮ Projections using VGG model for
GPDs and L = 10 34 Hz/cm 2
◮ Total cross-section larger than BH
Plots by C. Hyde
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 30

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Projections
Projections (Q 2 = 5 GeV 2 , x B = 0.02)
◮ Total cross-section dominated by BH in this kinematics
◮ Electron spin asymmetry particularly sensitive
Plots by C. Hyde
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 31

Introduction Initial results Dedicated experiments Future 6 GeV 12 GeV EIC Conclusion
Summary and conclusions
JLab results:
◮ Twist-2 dominance at relative low Q 2 (a few GeV 2 )
◮ Many polarization observables needed: both target and beam
◮ Different beam/collision energies needed
◮ Absolute cross-sections better than asymmetries
Opportunities with EIC:
◮ Lower x at sufficiently high Q 2
◮ Higher Q 2 lever arm to better understand/handle higher twists
Challenges of EIC:
◮ Luminosity (small cross-sections)
◮ Very forward recoil detection needed
Carlos Muñoz Camacho
LPC Clermont-Ferrand, CNRS/IN2P3
DVCS at 6/12 GeV and ideas for EIC 32