1. Large acceptance magnetic spectrometer for the 12 GeV 2 GEp experiment (at Jefferson Lab) E. Cisbani INFN Rome – Sanità Group and Italian National Institute of Health for the SBS collaboration 126/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab12 Outlook Electromagnetic form factors at high Q 2 Experimental requirements Spectrometer details http://hallaweb.jlab.org/12GeV/SuperBigBite DNP 2013 – Newport News – 26/Oct/2013

2. Form Factors: discovery and formalism R.W. McAllister, R. Hofstadter Phys. Rev. 102 (1956) 851 “First measurement of the proton electromagnetic radius”: RMS E/M radius of =(0.74 ± 0.24) 10 -13 cm 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab122 Nucleon electromagnetic current operator has two “unknown” functions (Dirac and Pauli FFs) that describe the internal structure of the nucleon (one photon exchange approx.): In terms of Sachs FFs: Elastic Cross section (Rosenbluth): Sachs FFs are FT of the charge and magnetization distributions in the nucleon (in Breit frame)

3. Proton G E /G M – an «unexpected» discrepancy 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab123 Rosenbluth Separation: assume single photon approximation Polarization transfer from the incident electron to the scattered proton Prior to JLab/2000, expectations were that proton G E /G M fairly constant with Q 2 At JLab, new class of experiments show proton G E /G M decreasing linearly with Q 2 Two Photon Exchange – favorite candidate DA3: T. Averett HA2: M. Kohl

4. Proton G E /G M - Theoretical models Many theoretical models – VMD (Iachello, Lomon, Bijker), generally good description of all FF – Relativistic CQM (Miller, Gross,...) spin dependent quark density – Lattice QCD, start to give prediction – Dyson-Schwinger, dressed quarks, diquark correlation,... – pQCD-based: G E /G M  const Q 2   – GPD-based: direct connection to quark OAM, FF’s constraint GPD’s Most of them agree with current data but diverge at higher, unexplored, Q 2 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab124

5. «Modern» Form Factor measurements at high Q 2 Method: Measure (one photon approx.) Many systematics effects (theory and exp.) cancel in ratio At Q 2 ~10 GeV 2 expected: FoM pol_trans ~ 10  FoM targ_pol (target polarization cannot tolerate large L) 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab125 Challenges at high Q 2 : Maximize (coincidence) acceptance Maximize luminosity Mazimize polarization efficiency Maximize beam polarization (... having the needed beam energy)... keeping costs at «affordable» level

6. 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab12 6 Jefferson Lab - CEBAF after 2013 CHL-2 Upgrade magnets and power supplies add Hall D (and beam line) 6 GeV CEBAF (< 2013) Max Current: 200  A Max Energy: 0.8 - 5.7 GeV Long. Polarization: 75-85% 12 GeV CEBAF (>2013) Max Current: 90  A Max Energy Hall A,B,C: 10.9 GeV Max Energy Hall D: 12 GeV Long. Polarization: 75-85% Doubling Beam Energy

7. Proton G E /G M at large Q 2 by polarization transfer Beam: Current= 75  A, Polarization= 85% long. Energy= 6, 8 and 11 GeV Target: H 2 Liquid Length= 40 cm Luminosity = 8 · 10 38 Detectors: P-arm: SBS + Polarimeter E-arm: BigCal + Coordinate 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab127 GOAL: Extend the measurement of the proton form factor ratio G E /G M to the maximum Q 2 that is possible with 11 GeV beam with constraints: Absolute error < 0.1 Beam time = 60 days GEp5 experiment in HallA (SBS)

8. New SuperBigbite Spectrometer (SBS) in Hall A 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab128 Large luminosity “Large” acceptance Forward angles Reconfigurable detectors Large luminosity “Large” acceptance Forward angles Reconfigurable detectors Support event rate 10x higher than with standard small acceptance spectrometer GEM chambers to handle the high rate of the background High photon up to 250 MHz/cm 2 and electron 160 kHz/cm 2 background

9. Large Luminosity  Large Background Must be supported by the detectors  GEM technology Must be handled by the trigger: – spatial and time correlation between electron and proton elastically scattered – «high» energy threshold in segmented CALO’s 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab129 Good tracking resolution needed - momentum resolution: 1 % - angular resolution: 1 mrad - vertex reconstruction: 5 mm Hit Red:  0 photoproduction Black: Elastics Blue: Sum For E miss <0.35 GeV, remaining  0 background:  10% Adequate proton polarization precession reconstruction (next slide)

10. GEp5: Proton Polarimeter (PP) 10 Number of scattered protons: Require: Dipole magnet to precess P l at target to P y pp Polarimeter only measures components of proton spin that are transverse to the proton’s momentum direction Track in Track out Track in Track out P y pp P x pp N=number of scattered proton, P e beam polarization where  refers to electron beam helicity 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab12 Maximize P e A (a.u.) Use azimuthal asymmetry of the proton scattering off matter induced by spin-orbit coupling

11. Beam SBS Dipole Magnet / 48D48 from BNL 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1211 Magnet Parameters  Integral field strength 1.82 T-m 2.28 T-m with pole shims  Yoke length 1.22 m  Gap: 47 cm  121.9 cm  Yoke Weight 85 tons  6 1008 steel sectors, largest is 18.3 tons Adapted from Robin Wines / JLab  (deg)(mrs) 512 1572 3076 Magnetic field needed for: Momentum measurement Polarimetry Sweep off low energy charged particles Yoke modifications to allow beam pipe passage at forward angle kinematics

12. GEM Working principle 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1212 Ionization Multiplication Readout Multiplication Recent Technology: F. Sauli, Nucl. Instrum. Methods A386(1997)531 GEM foil: 50  m Kapton + few  m copper on both sides with 70  m holes, 140  m pitch Strong electrostatic field in GEM holes SBS Gain vs Particle Flux

13. SBS - GEM Front Tracker Six 150x40 cm 2 chambers with small dead area (~10%) Each chamber consists of 3 50x40 cm 2 lightweight 3xGEM modules with x/y strip readout (0.4 mm pitch) Readout electronics based on high channel density APV25 ASIC driven by VME64x modules 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1213 Large SNR Use x/y charge correlation for false hit suppression

14. GEM Front Tracker MonteCarlo Realistic MC and digitization Tracking efficiency 99%-85% depending on background Track parameter resolutions at acceptable values even at largest background 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1214

15. CH 2 Polarimeters with GEM tracking Two Polarimeters in series to increase statistics by ~50% Each polarimeters consists of CH 2 analyzer (50 cm) and four 50x2000 cm 2 GEM chambers Each chamber is made of five 50x50 cm 2 GEM modules Similar design of GEM front tracker, optimized for focal polarimetry (less demanding particle rate respect to main tracker) 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1215 N. Liyanage et al. / UVa  pp (deg) Number of scattered protons

16. 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1216 PJ6: B. Quinn G. Franklin et al. / Carnegie Mellon

17. High Luminosity, impact on Trigger / DAQ 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1217 Must efficienty select electron elastic scattering by angular correlation First level (L1) from electron arm – Energy information (with cuts to reduce inelastic) – Rate (from SLAC high energy data and RCS experiments): Hadron Arm: – Energy information (with cuts to reduce inelastic) – Rate: 1.5 MHz Second level (L2) from two-arm coincidence: – in 30 ns gate: 9 kHz – AND geometrical correlation: 2 kHz Ethr/Emax %50758590 Rate [kHz]14002036038 DJ4: A. Camsonne

18.  SBS, is a cost effective, new magnetic spectrometer; will use the recent GEM technology to operate at high luminosity, providing “large” acceptance and high reconstruction accuracy  SBS will permit unprecedented measurements of the proton and neutron Form Factors at high Q 2 as well on SIDIS physics Conclusions 26/Oct/2013 (DNP2013)E. Cisbani / SBS for GEp5 @ JLab1218 Likely from 2016 NC9: A. Puckett http://hallaweb.jlab.org/12GeV/SuperBigBite Expected results on proton G E /G M Kinematics and expected accuracy E (GeV) Q 2 (GeV 2 ) Days  G E /G M 6.65.010.023 8.88.0100.032 11.012.0300.074