possibility for double dvcs measurement in hall a alexandre camsonne sbs meeting june 4 th 2013
TRANSCRIPT
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Possibility for Double DVCS measurement in Hall A
Alexandre CamsonneSBS MeetingJune 4th 2013
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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)
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Double Deeply Virtual Compton Scattering
scattered electron
scattered proton
outgoing virtual photon
lepton pair from virtual photon
D = p1-p2 = q2-q1
h =
xbj=
p = p1+p2q = ½ (q1+q2)
.Dqp.q
Q2
2p1q1
x = Q2
2p.q
Q2= - q2
Q2= -(k-k’)2
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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)
• Muon channel can go through large amount of material, possibly clean trigger with coincidence
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Double DVCS and Virtual Bethe Heitler
• Interference of Double DVCS and virtual Bethe Heitler
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x
h
Kinematical coverage
DVCS h = x
JLab 11 GeV25 GeV 40 GeV
Hu( h , x) 𝑄2>𝑀𝑙 ¿ ¿
𝑄2<𝑀𝑙 ¿ ¿22
• DVCS only probes h = x line
• Example with model of GPD H for up quark
• Jlab : Q2>0
• Kinematical range increases with beam energy ( larger dilepton mass )
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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
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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 )
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DDVCS measurement
• Large acceptance to get the whole angular coverage of the pair
• Forward angle for increase of Bethe and Heitler interference
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Hall A DVCS experiment
• 13x16 PbF2 Calorimeter• 39 cm x 48 cm at 110 cm• Energy resolution• Centered on Virtual photon• Energy resolution about 3%• Exclusivity by missing mass technique
detecting photon only
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Dimuon detection
• No ambiguity• Can go through material : clean trigger
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Lepton pairs
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Possible similar setup with SBS
• HRS+SBS• Pros– Virtual photon very well defined– High momentum resolution– Good vertex resolution
• Cons– Small acceptance : need to run at high luminosity
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Option with BigBite and SBS
• BigBite as electron arm :– Pros• Larger acceptance
– Cons• Lower momentum resolution
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Double DVCS
• Challenges– Pion muon discrimination• Record shower profile
– Vertex reconstruction
– Need detector without shielding for accurate momenta and vertex resolution ( GEM )
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Muons and pion shower
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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 )
GEM or MicroMegas
p
m
Pion showers
Muon only does energy
loss
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Micromegas readout
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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 $
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Other possible readouts
• RPC• GEMs• Silicium detectors…
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Possible detectors to reuse
• Gen neutron detector
• SRC neutron detector
• Any layered detector : add pad planes
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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