Transversely Polarized Neutron DVCS with SoLID-SIDIS Setup Zhihong Ye Duke University 05/15/2015, SoLID Collaobration Meeting

Wigner distributions ( Belitsky, Ji, Yuan ) (or GTMDs) 5D 3D 1D (X. Ji, D. Mueller, A. Radyushkin) 2 One of the main goal to develop SoLID is the 3D mapping of the nucleon structure, so besides doing TMDs, we should do GPDs!.

GPD SoLID  Generalized Parton Distributions (GPD):  Encode Information of the parton distribution in both the transverse plane and longitudinal direction.  Four GPDs for quarks or gluons:  Connect to FF & PDFs: e.g.  X  Longitudinal quark momentum fraction (not experimental accessible) ξ  Longitudinal momentum transfer. In Bjorken limit: ξ = x B /(2-x B ) t  Total squared momentum transfer to the nucleon: t = (P-P’) 2 3  Angular Momentum Sum Rule (Ji’s Sum Rule): (X. Ji, PRL 78, 610 (1997) Quark O.A.M.

GPD SoLID  Deeply Virtual Compton Scattering (DVCS): BH DVCS Interference-Term from Nucleon FF, F 1 & F 2 Compton Form Factor (CFF): Re( H ) Im( H ) Can access GPDs via DVCS by measuring the Ф dependence of DVCS & Interference Terms (similarly for other three) In the asymmetry: 4 CFFs access GPDs at x=ξ (DDVCS doesn’t have this limit)

GPD SoLID  DVCS with polarized electron beam and targets: 5 NH3: Transversely polarized (proton) He3: Transversely & Longitudinally polarized (neutron) PolarizationAsymmetriesCFFs Longitudinal BeamA LU Longitudinal TargetA UL Long. Beam + Long. Target A LL Transverse TargetA UT Long. Beam +Trans.Targt A LT Suppressed at t  0 where F 1 n  0 but should be sensitive at large t

 Beam Energy, E0 = 8.8 / 11.0 GeV  Scattered Electrons & Real Photons : Large Angle: 3.5<P<7.0 GeV, 16<θ<24, Φ~2π Forward Angle: 1.0 <P<7.0 GeV, 8<θ<14.8, Φ~2π  Reconstruct neutron missing mass to maintain the exclusivity  Measure Asymmetries (BSA, TSA, DSA)  Using the SoLID-SIDIS configuration: Forward-Angle : Detect electrons & photons Large-Angle : Detect electrons & photons DVCS with Polarized He3 Mode#1: In run group with SIDIS  Need to add the photon trigger Mode#1: In run group with SIDIS  Need to add the photon trigger Mode#2: Dedicated run with additional beam-time  Remove hardron triggers, HGC... Mode#2: Dedicated run with additional beam-time  Remove hardron triggers, HGC... 6

7  Trigger Design: DVCS with Polarized He3 There will be many low-energy photons from secondary scattering, radiations etc. To remove accidental coincidence triggers, we need to raise the EC threshold (P>2GeV/c is still fine)

 Acceptance DVCS with Polarized He3 Recoil neutrons: (1) at large angles (2) P~0.4GeV/c It will be very difficult to detect neutrons

 Kinematic Coverage DVCS with Polarized He3  Integrated Rate: 9

10 DVCS with Polarized He3 21 days on E0=8.8GeV, 48 days on E0=11GeV Binning: 4D Asymmetries:  Asymmetry Binning and Projection

 Asymmetry Projection: DVCS with Polarized He days on E0=8.8GeV, 48 days on E0=11GeV

12 TSA on x at one Q2 bin Two transversely polarized direction (x->0/180degree, y->90/270 degree), 5-Q2-bins, so: BSAx5, TSAx5x2, DSAx5x2  25 such kind of plots

Neutron Missing Mass The electron resolutions (from GEM tracking reconstruction): δP/P ~ 2%, δθ ~ 0.6mrad, δΦ ~ 5mrad The photon angular resolutions are determined by the EC position resolution and the electron vertex reconstruction: δx_EC = 1cm, δy_EC=1cm, δz_vertex=0.5cm For the energy resolution, I used the value now we can archieve: 5% No exclusive pi0 model yet, so I use the uniform phase space for the pi0 events, and scale the histograms with one common factor (0.01). 13

Neutron Missing Mass The electron resolutions (from GEM tracking reconstruction): δP/P ~ 2%, δθ ~ 0.6mrad, δΦ ~ 5mrad The photon angular resolutions are determined by the EC position resolution and the electron vertex reconstruction: δx_EC = 1cm, δy_EC=1cm, δz_vertex=0.5cm For the energy resolution, I used the value now we can archieve: 5% No exclusive pi0 model yet, so I use the uniform phase space for the pi0 events, and scale the histograms with one common factor (0.01). 14 Preliminary We will learn from the new Hall-A 12GeV-DVCS data. From Marco Carmignotto in Hall-A DVCS

From LOI to Proposal These are my naïve personal points of view: a)Need to make clear how strong the physics case are Will be the first trans-polarized n-DVCS, how important? GPD-E n  Flavor Decomposition  quark OMA (Ji’s Rum rule)  Nucleon Spin, and what is more? What asymmetries are most important (or feasible to measure )? BSA, TSA, DSA, Cross Sections … Need a fitting model to get CFFs from asymmetries Helps from Michel Guidal & Marie Boer will be essential. b)Need to make sure the exclusivity of the measurement Hardware/trigger/DAQ requirements for photon detection? We try a lot of efforts to reject photons in SIDIS but how about keeping them? What resolutions are needed to cleanly identify neutrons? Do we need a better EC design to improve missing mass spectrum? Do we need a recoil neutron detector? >60degrees & < 0.4GeV/c c)Need to understand backgrounds and how to handle then How to detect pi0 events and subtract them from missing mass? How to evaluate and deal with proton-channel from He3? What other channels can mix in? d)Need to evaluate systematic errors e)More …

Summary 16  Director Review committee strongly recommended to develop GPD programs.  No approved experiment on transversely polarized neutron-DVCS at Jlab.  SoLID-SIDIS can be directly used for the DVCS measurement: a) Electron+Photon coincidence trigger (instead of electron+hardron in SIDIS) b) Need to reconstruct neutron missing mass spectrum to make sure the exclusivity c) Need a better EC resolution to detect photons and hence controll backgrounds d) May need additinal callibration runs or more beam time to improve precision and reduce systematics.  Still a lot of work are needed to be done before we have the actual proposal next year! Highly welcome colleagues to join and help us!  If we develop this physics case, more DVCS experiments can be followed up: Longitudinal neutron DVCS, Transverse proton DVCS,

Backup Slides 17

GPD SoLID  DVCS with polarized electron beam and targets: 18