Transcript Possibility for Double DVCS measurement in Hall A Alexandre Camsonne SBS Meeting June 4th 2013

Possibility for Double DVCS
measurement in Hall A
Alexandre Camsonne
SBS Meeting
June 4th 2013
Double DVCS
g* + p
g‘* + p’
l+ + l-
Guidal and Vanderhaegen : Double deeply virtual Compton scattering
off the nucleon (arXiv:hep-ph/0208275v1 30 Aug 2002)
Belitsky Radyushkin : Unraveling hadron structure with generalized
parton distributions (arXiv:hep-ph/0504030v3 27 Jun 2005)
Double Deeply Virtual Compton
Scattering
D = p1-p2 = q2-q1
p = p1+p2
q = ½ (q1+q2)
Q2= - q2
scattered electron
x=
Q2
2p.q
scattered proton
h=
outgoing virtual photon
D.q
p.q
Q2= -(k-k’)2
xbj=
Q2
2p1q1
lepton pair from virtual photon
Double DVCS
• Detect dilepton pair instead of real photon
• Allow to vary skewness h of the reaction
• Charged particle in final state can use
spectrometer to measure momentum
( less requirement on calorimeter energy
resolution)
Double DVCS and Virtual Bethe Heitler
• Interference of Double DVCS and virtual Bethe
Heitler
Kinematical coverage
JLab 11 GeV
25 GeV
40 GeV
DVCS
h=x
Hu(h
, x)
2
𝑄 2 > 𝑀𝑙 + 𝑙−
2
𝑄 2 < 𝑀𝑙 + 𝑙−
• DVCS only probes h = x
line
• Example with model of
GPD H for up quark
• Jlab : Q2>0
h
x
• Kinematical range
increases with beam
energy ( larger dilepton
mass )
DDVCS cross section
•VGG model
•Order of
~0.1 pb = 10-36cm2
•Virtual Beth and
Heitler
•Interference term
enhanced by BH
•Contributions from
mesons small when far
from meson mass
DDVCS measurement
• Need high luminosity
– Hall B : 1035- 1036 cm-2s-1
– mEIC : 1.5x 1034 cm-2s-1
– Want 1038cm-2s-1 ideally 1039 cm-2s-1
• Pair detection : clean trigger
• Ideally look at muons channel to avoid ambiguity
with initial electron
( muon source low luminosity )
DDVCS measurement
• Large acceptance to get the whole angular
coverage of the pair
• Forward angle for increase of Bethe and
Heitler interference
Hall A DVCS experiment
qg*g
p g*
g
Polarized
electron
S&T Review
July 24th 2007
10
Hall A DVCS experiment
ep  egX
Missing mass with 3-4 % resolution du calorimeter
11
Designing a DVCS experiment
Measuring cross-sections differential in 4 variables requires:
 A good knowledge of the acceptance
e p → e (p) g
Scattered electron
The HRS acceptance
is well known
R-function
cut
Emitted photon
The calorimeter has a simple
rectangular acceptance
Perfect acceptance
matching by design !
Virtual photon « acceptance »
placed at center of calorimeter
g
g*
Simply:
t: radius
j: phase
Hall A DVCS experiment
•
•
•
•
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13x16 PbF2 Calorimeter
39 cm x 48 cm at 110 cm = 154 msrd
Energy resolution about 3%
Centered on Virtual photon
Exclusivity by missing mass technique
detecting photon only
• Limited in luminosity by calorimeter
( background and radiation hardness )
Dimuon detection
• No ambiguity with scattered electron
• Can go through material
– clean trigger
– Less radiation hardness concern
• Charged particles : can use spectrometer ( reduce
background and improved resolution compared to
calorimeter )
• Difficulties
– Minimum ionizing
– Efficiency of detection
– Pion background
0.5 % momentum resolution at 5 GeV
Possible similar setup with SBS
• HRS+SBS
• Pros
– Virtual photon very well defined
– High momentum resolution
– Good vertex resolution
– Good control of acceptance
• Cons
– Small acceptance : need to run at high luminosity
Designing a DVCS experiment
Measuring cross-sections differential in 4 variables requires:
 A good knowledge of the acceptance
l+
e p → e (p) g*
l-
Scattered electron
The HRS acceptance
is well known
R-function
cut
l+
g*
l-
g*
Simply:
t: radius
j: phase
Possible HRS/SBS layout
Option with BigBite and SBS
• BigBite as electron arm, same setup as SIDIS :
– Pros
• Larger acceptance
– Cons
• Lower momentum resolution
• Sensitive to background
• Cross sections more difficult because more sensitive of
background
E12-09-018: SIDIS on polarized 3He @ 12 GeV
E12-09-018, 11 GeV
E12-09-018, 8.8 GeV
E06-010, 5.9 GeV
11/7/2015
Experiment E12-09-018
• Approved by JLab PAC38 (August
2011), 64 days, A- rating
• Spokespersons:
• G. Cates (UVA)
• E. Cisbani (INFN)
• G. Franklin (CMU)
• A. Puckett (LANL—currently
JLab, near future UConn)
• B. Wojtsekhowski (JLab)
• In two-months production run, E1209-018 will reach ~1000X statistical
FOM of E06-010 n, ~100X
HERMES p
• Electron arm: BigBite at 30 deg as
in E06-010 + A1n detector upgrades
• Hadron arm: Super BigBite (SBS)
at 14 deg.
• Target: high-luminosity polarized
Helium-3
SBS Summer 2013 Collaboration Meeting
20
Double DVCS
• Challenges
– Pion muon discrimination
• Record shower profile
– Vertex reconstruction : to reduce background
( might need vertex tracker )
– Need detector without shielding for accurate
momenta and vertex resolution ( GEM ) might limit
luminosity
– First step go for asymmetries
– Need to determine uncertainties on cross section
(tracking and muon detection efficiency )
Muons and pion shower
Muon identification
• Add material to stop other electromagnetic process
• Scintillator planes for muon trigger
• Use sampling calorimeter to look at shower : layers
of material + GEM or Micromegas with pads and
digital readout ( CALICE, SdHCAL, dHCAL )
p
m
GEM or MicroMegas
Pion showers
Muon only
does energy
loss
Micromegas readout
Micromegas DHCAL
• LAPP Annecy France
Micromegas DHCAL
• LAPP Annecy France
Micromegas DHCAL
Cost electronics
• For 32 cm x 48 cm = 1536 cm2
• 3m x 3m = 90 000 cm2
• MicroROC Digital chips ASICs : 320 chips = 20
480 channels for 25 K$ about 100 K$ per
plane
• Compatible with SRS
• Micromegas detector 32 cm x 48 cm about
3000 $
Other possible readouts
• RPC
• GEMs
• Silicium detectors…
Possible detectors to reuse
• Gen neutron detector
• SRC neutron detector
• Any layered detector : add pad planes
Conclusion
• Opportunity to measure double DVCS at
JLab12 GeV in dimuon channel with high
statistics
• SBS can make a first measurement on limited
kinematic range
• Simulation work and detector R&D
• Early Career Grant for SBS to build
MicroMegas Workshop
• Proposal next PAC