Hall B Physics Program and Upgrade Plan

Transcription

1 Hall B Physics Program and Upgrade Plan presented by Volker Burkert and Sebastian Kuhn Outline: Introduction Deeply Virtual Exclusive Processes and GPDs Structure Functions & Semi-Inclusive Processes Equipment Plan JLab User Group Meeting, June 10-12, 2002

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3 Physics Program with CLAS ++ at 12 GeV Internal Nucleon Dynamics and Generalized Parton Distributions Nucleon Structure Functions Semi-exclusive processes - transversity, flavor tagging Elastic and Transition Formfactors Physics at very small Q 2

4 A real 3-dimensional Scotty

5 Scotty Reduced to a Single Dimension density Calcium Water Carbon z

6 Snapshot of a Nucleon (taken through a low resolution microscope) meson cloud quark spin sea quarks valence quarks orbital angular momentum correlations We need to map out the complete wave function of the nucleon!

7 The nucleon structure has been studied in inclusive lepton nucleon scattering experiments for the past 35 years and we learned about: quark longitudinal momentum densities quark helicity densities..

8 The Nucleon Probed in Deeply Inclusive Scattering Longitudinal Parton Momentum Distribution sea quarks xf(x) valence quarks x 1

9 Deeply Virtual Exclusive Processes Inclusive Scattering Forward Compton Scattering θ = 0 Deeply Virtual Compton Scattering (DVCS) t Probes the internal nucleon dynamics at the amplitude level. H(x, ξ, t),.

10 Model of Generalized Parton Distributions Quark distribution q(x) DVCS/BH asymmetry x=ξ qq distribution cross section at fixed ξ

11 Deeply Virtual Processes DVCS DVMP long. only hard gluon hard vertices depends on all 4 GPDs

12 Scaling Cross Sections for Photon and Meson Production 1/Q 6 1/Q 4 In hard scattering, photons dominate at high Q 2

13 Bethe-Heitler as amplifier for the DVCS amplitude Measures DVCSin the interference with BH process: d 4 σ dq 2 dx B dtdφ ~ T DVCS + T BH 2 σ + -σ - ~Im(T DVCS ) T BH At 11 GeV DVCS and BH are comparable in magnitude => measure DVCS cross section

14 DVCS/BH Asymmetry from CLAS 4.25GeV CLAS data show sensitivity to qgq correlations (Belitsky, Mueller, 02)

15 DVCS/BH Asymmetry expected at 11 GeV ep epγ (all final state particles detected) 1000 hours of beam time (one bin of many)

16 DVCS/BH - Target Spin Asymmetry A UL Belitsky, Mueller, 2002 A UL Q2=3GeV2 => Shows different sensitivity to GPD parametrization compared to beam asymmetry.

17 Double-DVCS (D-DVCS) e + e - e - e - -2ξ x+ξ 2(ξ ξ ) x-ξ Q 2 > M ρ 2 H, E, H, E p p D-DVCS allows probing kinematics x = ξ

18 Model of Generalized Parton Distributions Quark distribution q(x) DVCS/BH asymmetry x=ξ qq distribution DDVCS/BH asymmetry x= ξ

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20 ρ ο π + π Decay Distributions at 11 GeV

21 Separated Cross Section for γ*p -> pρ ο (400hrs) x B = => other kinematics -t = GeV 2 measured at the same time. σ L σ T other channels, e.g. pω measured at the same time

22 Separated Cross section for ep eπ + n Rosenbluth separation for σ L /σ T x B = t = GeV 2 + other bins at the same time Measure pπ ο, pη, KΛ, KΣ,.. simultaneously σ L σ TOT σ T

23 (Semi-)Inclusive (Deeply) Inelastic Scattering Extract valence quark distributions of the nucleon Constrain GPDs Quantify higher twist effects Study transition from partonic to hadronic picture in structure and fragmentation functions - Duality? Learn about new distribution functions like transversity Study quark propagation through cold QCD matter

24 But is 11 GeV high enough? CLAS at 4-6 GeV = Constituent Quark Detector Too high in energy for Chiral Perturbation Theory Too low in energy for pqcd Premise: CLAS at 11 GeV = Higher Twist Detector OPE can describe inclusive structure functions and moments down to Q 2 = 1 GeV 2 Duality seems to work nicely for inclusive structure functions - why not for hadronization? We can TEST this premise in both quark distributions (inclusive structure functions) and quark hadronization (fragmentation functions)

25 The Nucleon Studied in Inclusive en Processes Longitudinal Parton Momentum Distribution ensity momentum d q +q q - q 0 x B 1

26 Proton Helicity Asymmetry A1p

27 Deuteron Helicity Asymmetry A 1d (no nuclear corrections)

28 Polarized Structure Function g 2p (x,q 2 )

29 Neutron Structure Function F 2n SLAC (FS)

30 detect slow recoil proton in backwards direction Neutron Structure Function F 2n Uncertainty due to Fermi motion and off-shell effects

31 The Nucleon Studied in Semi-Inclusive en Processes D h (z) π e h 1 K Longitudinal and transverse parton momentum and spin distributions (tagged by flavor) Quark-gluon (quark-quark) correlations and final state interactions Hadronization ensity momentum d d +d d - d u -u 0 x B, k T, 1

32 The Nucleon Studied in Semi-Inclusive en Processes Beam Pol. Targ. Pol. Moments Sensitive to 0 0 <cosφ> <cos2φ> Higher Twist, k T L 0 <sinφ> e(x), H 1 (z) 0 L <sinφ> <sin2φ> Higher Twist, H 1 (z) 0 L T L,T <sin(φ φ S )> <sin(φ+φ S )> Transversity q( 1 x) Flavor-dependent quark polarization

33 Semi-Inclusive Deeply Inelastic Scattering Double Spin Asymmetry Target*Beam Sensitive to contributions from different quark flavors to proton spin d - d

34 Semi-Inclusive Deeply Inelastic Scattering Single Spin Asymmetry Target (perp.) Sensitive to transversity distribution u -u

35 Semi-Inclusive Deeply Inelastic Scattering Single Spin Asymmetry Beam (long.) Sensitive to twist-3 e distribution and Collins fragmentation function H 1 (z) (Data from CLAS at 4 GeV)

36 Semi-Inclusive Deeply Inelastic Scattering Single Spin Asymmetry Target (long.) Sensitive to twist-2 and -3 distribution functions and Collins fragmentation function (Data from CLAS at 4.25 GeV)

37 Semi-Inclusive Deeply Inelastic Scattering on Nuclei

38 Semi-Inclusive Deeply Inelastic Scattering on Nuclei

39 Status of Magnetic Form Factors for Proton and Neutron

40 Projected G Mn data at 11 GeV with CLAS++

41 Physics potentials with forward electron facility Meson spectroscopy, e.g. with 4He - gas targets Heavy baryon spectroscopy Time-like virtual-compton-scattering Structure functions at very low Q2 GDH Sum Rule..others...

42 Requirements for the CLAS upgrade: Retain high statistics capabilities for exclusive processes at beam b energies up to 12 GeV Complement missing mass techniques by more complete detection of hadronic final state Increase maximum luminosity to cm - 2 sec -1 Extend particle ID to higher momenta (e - /π, π + /Κ +, γ/π ο ) Complement CLAS detection system with new Central Detector - tracking and photon detection in angular range 5 o -135 o - veto events with incomplete determination of final state Reduce DC occupancies to reach higher luminosities - reduce DC cell sizes - new magnetic shielding for Moller electrons Upgrade the CLAS Forward detection system - implement new threshold Cherenkov detector - improve time-of-flight resolution - increase calorimeter granularity for π ο /γ separation

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44 CLAS ++ - The Central Detector (CD) Superconducting solenoid shields Moller electrons provides large angle tracking and momentum analysis polarized target operation High density SciFi tungsten calorimeter Time-of of-flight flight detectors, de/dx dx Tracking chamber & silicon strip detector

45 CLAS ++ - Central Detector Concept Superconducting coil flux return yoke Electromagnetic calorimeter SciFi-tungsten Time-of of-flight ~ 1.1m Drift Chamber Micro Strip Detector

46 Magnetic Field Distribution in Flux Return Iron Solenoid Coil Flux Return Iron Central B-FieldB 5 Tesla (Gauss)

47 Magnetic Field Distribution in Solenoid Magnet B-Field(Gauss) -0.3m 0 0.3m z r 0.3m

48 Magnetic Shielding of Moller Electrons 32 MeV < E < 830 MeV 3.5 MeV < E < 7.5 MeV 3 o 3 o => Moller electrons are contained in 3 o cone

49 Moller Electrons in Target Region Without B-Field L=10 35 cm -2 s -1, T = 250nsec

50 Moller Electrons in Target Region With B-Field L=10 35 cm -2 s -1, T = 250nsec, B = 5T solenoid coil B=5T

51 Central Electromagnetic Calorimeter PMT Scintillating Fibers Electromagnetic calorimeter SciFi-tungsten

52 Central Calorimeter - Theta Fiber Readout Scintillating Fibers => prototyping effort underway

53 Central Time-of-Flight Scintillators 50 Scintillator Strips PID by Time of Flight

54 Central Drift Chamber Cathode Pad Layer Cathode Pad Chambers: - 20 pads in azimuth - 40 pads parallel to beam anode wires read out cathode pads read out Anode Wires

55 Central Drift Chamber - Cathode Pads (Detail) Cathode Pads Anode Wires

56 Central Detector - Silicon Strip Detector 10cm Silicon Wafers - vertex reconstruction - high rate operation near target - tracking in full azimuth 5cm beamline

57 Forward Detector System Upgrades Region 1, Region 2, Region 3 Drift Chambers => similar design as current DCs, factor 2 smaller cell sizes Time-of-Fight Detector => improve timing resolution to Forward calorimeter => extend γ/π 0 separation to higher momenta + instrument coil regions with calorimetry (PbWO 4 crystals ) Cherenkov Counter => implement second CC with pion threshold ~ 5GeV

58 New Gas Cherenkov Counter 2x8 Mirrors Torus coils Target Light collection and PMTs

59 Inner Calorimeter in Torus coil region Torus coils Inner Calorimeter e.g. PbWO 4 crystals

60 Forward TOF Detector - Improve Time Resolution - reduce scintillator width to 5cm - add 2nd scintillator layer => δt ~ 50psec

61 Pre-shower Calorimeter Scintillator/lead sandwich, with wavelength shifting fiber readout, ~ 4 rad. length. 3.5cm Scintillator strips, ~1cm thick Lead sheets ~ 1mm thick Wavelength Shifting Fibers embedded in scintillator

62 Data Acquisition & Trigger Trigger Rate: 15 KHz & 10 KBytes/event Level 3 Filter Noise reduction 5 KHz & 5 KBytes/event Data Rate: 25 MBytes/sec

63 CLAS ++ Expected Performance ep eπ + n E=6GeV E=11GeV σ=11mev σ=16mev

64 CLAS ++ Expected Missing Mass Resolution ep eπ + n E = 11 GeV, W = 2-2.5GeV

65 CLAS ++ - Expected Performance Forward Detector Central Detector Angular coverage: Tracks (inbending) 10 o -40 o 42 o o Tracks (outbending) 5 o -40 o 42 o o Photons 3 o -40 o 42 o o Track resolution: δp (GeV/c) 0.003p p p T δθ (mr) 1 5 δφ (mr) Photon detection: Energy range > 100 MeV > 50 MeV δe/e 0.09 (1 GeV) 0.06 (1 GeV) δθ (mr) 6 (1 GeV) 15 (1 GeV) Neutron detection: η eff 0.5 (p > 1.5 GeV/c) Particle id: e/π >>1000 ( < 5 GeV/c) >100 ( > 5 GeV/c) π/k (4σ) < 3GeV/c 0.6GeV/c K/p (4σ) < 5GeV/c 1.1GeV/c

66 ep epγ/m Kinematics at 11 GeV

67 DVCS/BH Interference with CLAS 11 GeV

68 DVCS/BH Asymmetry with CLAS 11 GeV

69 DVCS/BH Asymmetry with CLAS 11 GeV

70 Small Angle Electron Detection Quasi-real photoproduction by tagging ~1 o electrons High hadronic interaction rate Low accidental rate compared to real photon tagging Linearly polarized photons come for free, P = Broad physics potentials in meson spectroscopy, TDVCS, η/η Primakoff experiment,... Detector options are being evaluated - located downstream of CLAS Could exist before the upgrade (no cost impact!)

71 The Mission of CLAS ++ and Hall B The primary goal of experiments using the CLAS ++ detector at energies up to 12 GeV is the study of the nucleon wave function in terms of elementary degrees of freedom. Towards this end, the detector has been optimized for studies of a wide variety of exclusive and semi-inclusive reactions. Inclusive processes, for which the unique properties of the Hall B instrumentation are essential, can be measured as well.