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Published byLilian Cole Modified over 9 years ago
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Possibility for Double DVCS measurement in Hall A Alexandre Camsonne SBS Meeting June 4 th 2013
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Double DVCS p ‘ 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 = p1-p2 = q2-q1 = x bj = p = p1+p2 q = ½ (q1+q2) q pqpq QQ 2p 1 q 1 = QQ 2p q Q q 2 Q -(k-k’) 2
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Double DVCS Detect dilepton pair instead of real photon Allow to vary skewness 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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Kinematical coverage DVCS = JLab 11 GeV 25 GeV 40 GeV H u ( , ) 2 2 DVCS only probes = line Example with model of GPD H for up quark Jlab : Q 2 >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 -36 cm 2 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 : 10 35 - 10 36 cm -2 s -1 – mEIC : 1.5x 10 34 cm -2 s -1 – Want 10 38 cm -2 s -1 ideally 10 39 cm -2 s -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 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
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