Vina PunjabiNorfolk State University

Hall A Collaboration Meeting June 10-11, 2010

GEp-V Experiment to Measure GEp/GMp

‘‘Large Acceptance Proton Form Factor Ratio Measurements up to 14.5 GeV2 Using Recoil-Polarization Method”

E. Brash, E. Cisbani, M. Jones, M. Khandaker, L. Pentchev, C.F. Perdrisat, V. Punjabi, B. Wojtsekhowski (spokespersons),

and the Hall A Collaboration

GEp-V (E12-07-109) was approved for 60 days by JLab PAC32 in August, 2007.

The GEp-V Experiment

For recoil polarization, the two polarization components are in the reaction plane, no normal component: (Akhiezer and Rekalo, Sov. J. Part. Nucl. 4, 277 (1974); Arnold, Carlson and Gross, Phys. Rev. C 23, 363 (1981))

The method superior because of smaller systematics: the Form Factor ratio is independent of the electron polarization Pe and of the polarimeter analyzing power Ay (h is beam helicity ±1).

ε

ε)τ(

PtPoreθ

M

)e'Ee(E

PtP

MpGEpG

2

1

2tan

2

Polarization transfer in or spin-target asymmetryare two different techniques, but give same information

pepe

eppe

Double polarization Method

Statistical uncertainty depends directly on both Pe and Ay.Remaining systematics mostly from spin precession

GEp-V will increase the Q2 range for GEp/GMp up to 14.5 GeV2

Give information about transverse charge densityconstrain GPDs at high tprovide critical test of FF models and reaction dynamics

What Will GEp-V Measure?

Challenges of High Q2 Measurements

Low elastic cross-section dσ/dΩelab J E2/Q12

Lower analyzing power Ay J 1/plab ~ 1/Q2

Overall experimental FOM J dσ/dΩelab Ay

2 J E2/Q16

•Need large acceptance in both electron and proton arm

•To fully take advantage of CEBAF 12 GeV upgrade need new device for detection of proton, SBS

• For electron the existing device BigCal will be used

The Super Bigbite Apparatus

SBS capabilities derived from using a large open-geometry dipolemagnet together with a detector package with direct view of target.

GEM-based tracking system able to tolerate the very high rates.

Experimental Setup for GEp-V

Recoil proton polarization measured using large-acceptance SBS.Double polarimeter with large GEM trackers (50 × 200 cm2) togetherwith a highly segmented hadron calorimeter.Electron detected in coincidence by a large EM calorimeter, ‘‘BigCal”.40-cm long LH2 standard Hall A cryotarget.

Two main purposes for ‘‘BigCal” in GEp-V:• Position correlation between elastic e in BigCal and p in HCAL used in trigger to reduce rates to levels acceptable for DAQ.• Applying kinematic correlations of elastic e in BigCal to analyze where elastic p is expected in front GEM tracker to identify p tracks even at very high random hit multiplicity.• Energy resolution with 20 cm aluminum absorber 0.14/ + 0.02 (From MC by Mark Jones)•1744 lead-glass blocks will be re-arranged in a 20 × 80 matrix.

BigCal for GEp-V

EEE

E

Summary of Technical Review on GEp-VThe Super BigBite project in Hall A has been reviewed. The Technical Review Committee is impressed by the broad scope of the physics program and the anticipated performance of the spectrometer.

The Committee finds that the SBS experimental design has a very high probability of meeting the experimental requirements. The high rate and high resolution capability of the GEM detectors make them the ideal solution for this application. The SBS Collaboration has the required expertise to carry out the project within the time schedule presented.

The SBS project is aiming at the combination of large solid angle coverage at forward angles with the highest luminosity achievable with the upgraded 12 GeV CEBAF.

Remaining uncertainties in background rates and electronics performance can be reduced by performing experimental tests under similar conditions. This should be done as soon as possible since the results could lead to modifications of the segmentation scheme and the readout rates which need to be known before the start of mass production.

o This group will:• Collaborate with INFN on development of GEM modules.• Fabricate GEM modules and assemble second and third trackers (UVa)• Assemble the GEM tracker for BigCal (W&M)• Fabricate FEE for large trackers (Norfolk State)o Detector development facilities (clean-rooms, electrical engineering support, machine shops etc.) already at UVao UVa group recently built the large MWDC package for Bigbiteo UVa group will invite and sponsor visits by INFN technicians to train local technicians and studentso New 4 m x 6 m clean room for production: optimization currently underway

Large GEM Tracker group UVa, W&M, Norfolk State, JLab, Glasgow and CNU

Dubna FPP Test

Next Step in November 2010

SBS will take quality data in a good set of high priority experiments.

Over 100 collaborators from 30 institutions.

Conceptual design report in place.(http://hallaweb.jlab.org/12GeV/SuperBigBite/SBS_CDR/)

Two technical reviews completed.

Prototype GEMs currently undergoing beam test in Hall A.

GEM trackers design / front tracker construction - INFN $1.1M approved.

SBS budget proposal incorporated in JLab’s long-term capital fundingrequest to DOE.

Current Status of SBS Project

I want to thank Mark, Mahbub and Nilanga

for providing transparencies for this talk