CLAS12 DDVCS. N. Baltzell (Jefferson Lab) ECT Workshop, October 24-28, 2016

Transcription

1 CLAS1 DDVCS N. Baltzell (Jefferson Lab) ECT Workshop, October 4-8, 016

2 Motivation

3 New CLAS1 LOI for di-muon Electroproduction Includes simultaneously: - Double Deeply Virtual Compton Sca4ering (DDVCS) process for study of Generalized Parton Distribu>ons - J/ψ produc5on near threshold region for study of nucleon gluonic structure ep e " p" γ * (J / ψ) e " µ + µ ( p ") LOI Contact: S. Stepanyan in a wide kinema5cal range in: x B, Q, M µµ, t Compared to e + e -, the μ + μ - final state eliminates ambiguity and an>- symmetriza>on issues for DDVCS reduces combinatorial background under J/ψ s ll + ll - mass peak

4 Accessing GPDs Experimentally Spin asymmetries (Im, x=ξ) HERMES, CLAS, Hall A, JLAB1, COMPASS Charge asymmetry and TCS ( Re ) HERMES, COMPASS. JLAB1 Cross sec>ons ( Re ) H1, Hall A, JLAB1, COMPASS DDVCS (x ξ ) JLAB1 * See Stepan s talk tomorrow on TCS/JPsi- photoproduc5on with CLAS1

5 GPDs at x ξ via DDVCS Beam spin asymmetry measurements give acces to the imaginary part of the DVCS amplitude. In DDVCS, assuming dominance of H GPD, can access: ( ) + H ( ξ ξ #,ξ,t) H ξ! ξ,ξ,t ξ! x B x B ; ξ =! ξ Q +! Q Q Guidal & Vanderhagen Allows mapping GPDs in (x, ξ, t) independently although restricted to 0 < ξ - ξ < ξ Handbag formalism predicts a BSA sign change between space- like dominated and 5me- like dominated regime 100x lower cross sec5on than DVCS

6 Experiment

7 CLAS1 Detector in JLab Forward, θ < 40 SC Torus Magnet Threshold+Imaging Cerenkov Drib Chambers FTOF Scin5llators EC/PCAL EM Calorimeters Small- θ Tagger System Central Detectors, θ > 35 5T SC Solenoid Magnet Si/Micromega Trackers TOF and Neutron scin5llators Turn CLAS1 into a muon detector? Handle increased luminosity necessary for DDVCS (100x, to 1037 cm- s- 1)? Managable trigger and background rates?

8 CLAS1 Modifications for ep e " p " µ cm s 1 Remove HTCC and install in its ac5ve region - a new Moller cone that extends up to 7 o - a new PbWO 4 calorimeter that covers 7 o to 30 o (π azimuthal) - GEM tracker upstream of the calorimeter for vertexing - Downstream of the calorimeter, a 30 cm Tungsten absorber shielding the whole acceptance of the CLAS1 FD - Central detectors removed o Loca5on of HTCC mirrors 7 o 5 o 30 o S = πl [(tg (30 o ) tg (7 o )] = 3600cm ; l = 60cm S! 7 o 17 (4) 40 GEMs 13 (0) 0 PbWO 4 60 W shield PbWO 4 modules with APD readout - ~ 100 modules

9 CLAS1: Di-muon Configuration Calorimeter/shield configura5on serves as absorber for the muon detector (CLAS1 FD) and fully protects the forward drib chambers from electromagne5c and hadronic background Scapered electron detected in the new calorimeter GEM based tracking detectors aid reconstruc5on of charged par5cle vertex (momentum and angles)

10 Integrated Occupancy [%] Drift Chamber: Occupancy CLAS1 simula5on sobware, GEMC, with 5 cm long target, 50 ns 5me window, 4 ns beam bunches, used to es5mate detector occupancies Moeller beamline shield geometry configured to minimize rates. Tungsten absober thickness (+calorimeter) chosen to op5mize background rates and muon momentum resolu5on and energy loss Integrated Occupancy vs. Absorber Thickness cm - s - 1 Region 1 Region Occupancy [%] Drift Chamber Occupancy for ddvcs_30_cm_tst_out Region1: 1.38% Region: 1.97% Region3: 3.39% Absorber Thickness [cm] Sector

11 PbWO 4 Calorimeter for e - detection Similar to Inner Calorimeter of CLAS6 Total of ~100 modules, mounted at 60 cm from the target, covering 7 o to 30 o Small size modules, 1.3x1.3 cm, in the inner part, 7 o to 1 o. x cm modules in the outer part Readout with APDs, similar to IC, HPS ECal, and FTCal HPS Ecal modules run successfully at rates of ~1.5 MHz and performed very well: σ/e 4%/ E and σ t 0.5 ns γ Full simula>ons expect maximum rate with 15 MeV threshold to be 3 MHz, with largest contribu>on from photons.

12 GEM Tracker GEM based tracking detectors have been used in several JLAB experiments, e.g. Hall- B Bonus, eg6 4 He, and Proton Charge Radius experiments High rate GEM trackers that can handle up to 1 MHz/cm rates are currently being fabricated for Hall- A SBS and being prototyped for SoLID. "disk design, five tracking detectors, first detector at 40 cm from the target polar angular coverage 5 o to 35 o. Each disc will be divided azimuthaly into six trapezoidal sec5ons D readout strips, with radial and φ- readout strips the area of the readout for the strip at 5 o 0.18 cm (4.5 cm x 0.04cm) Effec>ve expected max rates ~600 khz per strip π π MHz/cm S. Stepanyan, CLAS collaboration meeting

13 Muon Detection and Trigger Rates Muons punch through the absorber and are detected in CLAS1 FD. Muon- ID: Track in DC with matched MIP energy cluster in PCAL/EC. Resolu5ons and energy- loss simulated and accounted for in projec5ons Based on GEANT4 (GEMC) simula5ons background rates from charged tracks (mostly pions) in CLAS1 FDC will be 150 khz (+) and 190 khz (- ) MIP energy cut in PCAL/EC reduces these rates to 75/95 khz (from those only 40% are from the target 30/38 khz respec5vely) With 50 ns trigger 5me coincidence window, the rate of two oppositely charged MIP par5cles in CLAS1 FD will be 360 Hz well within CLAS1 DAQ specs à Can run with two charged par>cle CLAS1 FD trigger Momentum Resolu5on (GeV)

14 eµ + µ - Event ID and Background Rates The expected rate for BH (DDVCS) events in the kinema>cs of interest is 0.0 Hz. Muon Pair oppositely charged MIPs in CLAS1 FD FDC tracks reconstructed EC/PCal MIP energy deposi5on Tight ECAL/FTOF 5ming cuts to select same beam bucket Matching GEM tracks poin5ng to target Invariant mass > 1 GeV Simula5ons result in.5 Hz such accidental muon- like pairs Expect 0.6 Hz true muon- pairs from Bethe- Heitler Electron PbWO 4 calorimeter clusters with E > 0.4 GeV And a matching nega5vely charged GEM track Inclusive electron rate, plus fakes with same signature (150 khz), is 800 khz. Combining electron rate with pair rate, in 4 ns window, gives 0.01 Hz. Reduces to <0.004 Hz background via missing mass requirement.

15 Projections

16 CLAS1 Di-Muon Electroproduction CLAS1 Modified Detector, 11 GeV Beam, 5 cm liquid H target 100 days at cm - s - 1

17 CLAS1 DDVCS beam spin asymmetry Sign change with change of kinema5cs from Space- like to Time- like dominance region Asym. Q (.0-3.0)GeV Q' ( ) GeV ] [GeV Asym. 0. Q (.0-3.0)GeV 0.3 Q' ( ) GeV Φ LH [deg], Q Q (.0-3.0)GeV Q' (.4-3.) GeV Φ LH [deg] 0. Asym Asym. Q (.0-3.0)GeV Q' ( ) GeV Φ LH [deg] Q [GeV The VGG code was used for DDVCS BSA GRAPE- dilepton event generator was used to es5mate rates ] Φ LH [deg]

18 J/ψ Electroproduc5on Included For Free Produced via gluon exchange (no charm in nucleons) Small size qq state due to large mass of c- quark Unique probe of the gluon field of the target Wealth of data at W > 10 GeV, well above threshold, (HERA, FNAL) probing gluon GPDs. S.J. Brodsky, E. Chudakov, P. Hoyer, and J- M. Laget, Phys.Lep. B498, 3-8 (001) No electroproduc5on data exists near threshold * See Stepan s talk tomorrow on near- threshold J/ψ photoproduc5on with CLAS1

19 CLAS1 J/ψà µµ Electroproduc5on Study W- and t- dependences at different Q (0. GeV, 0.5 GeV, and 1.5 GeV ) Study decay muon angular distribu5ons to extract R=σ L /σ T Q (GeV) Q (GeV) W (GeV) t (GeV) 1 S. Stepanyan, CLAS collaboration meeting

20 CLAS1 J/ψà µµ Electroproduc5on Vector Dominance Model (VDM) is used to relate electro- and photo- produc5on cross sec5ons For the photoproduc5on cross sec5on, - gluon exchange model from S.J. Brodsky et al. is used. All Q Q =0. GeV 1/b*d /dw/dq /dt t=t min nb GeV Q =1.5 GeV 0. GeV 0.5 GeV W (GeV) 10-5 Q =0.5 GeV Q =1.5 GeV ds/dt nb GeV t (GeV/c) -

21 Summary Double-DVCS will extend GPD measurements to x!=ξ regions Expected sensitivity to sign-flip of BSA between timelike- and spacelike-dominated regions DDVCS requires high luminosity and (ideally) muon detection, and can be measured in Hall-B at JLab with a modified CLAS1 detector shielding of Forward Detector s full acceptance to allow orders of magnitude higher luminosity aand use as a muon detector system recover electron detection with PbWO 4 calorimeter near target, and GEM trackers for enhanced and high-rate vertexing The same experimental setup is well suited for measurement of near-threshold J/ψ electroproduction With possibilities for future studies of inclusive J/ψ à µµ, including on nuclei, and J/ψ-Ν interaction. LOI : PAC44 Report: S. Stepanyan, CLAS collaboration meeting