EG4 Update

Sebastian KuhnOld Dominion University

June 21, 2013With help from Krishna Adhikari, Alexandre Deur, Marco Ripani and the

EG4 group

CLAS-EG4 (E03-006 (NH3) + E06-017 (ND3)): a measurement of g1 and the extended GDH (Gerasimov-Dreall-Hearn) integral for the proton and neutron (deuteron) at very low Q2 (0.015 – 0.5 GeV2)

Performed in Jlab Hall-Bfrom February to May, 2006.Analysis crew as of today:Hyekoo Kang, Krishna Adhikari (Ph.D. Students) andAlexandre Deur, Marco Ripani, Karl Slifer, Sarah Phillips, Elena Long, Xiaochao Zheng, Sebastian Kuhn

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Importance of Generalized GDH Sum Rule• Generalized GDH Sum Rule, being defined

for all Q2, provides a useful tool to study the transition from hadronic to partonic descriptions of Strong interaction.

– Very high Q2 (> ~5 GeV2): (Bjorken limit): pQCD

– High Q2 (> ~1 GeV2): Operator Product Expansion

– Intermediate Q2 region: Lattice QCD calculations

– Low Q2 region (< ~0.1 GeV2): Chiral Perturbation Theory Calculations:

Relativistic Baryon cPT with D, Bernard, Hemmert, Meissner;

Heavy Baryon cPT, Ji, Kao, Osborne; Kao, Spitzenberg, Vanderhaeghen

– The experimental measurement of the GDH integral will be very important to test and constrain such calculations.

1

Expected precision for deuteronExpected precision for proton

Methodology to measure GDH sum

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How to extract g1?

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N-+, N++ the # of events detected for the parallel & anti-parallel beam-target polarizations

Ni, t, , f and PbPt the # of incident electrons (Faraday cup), target areal-density, the detector acceptance, detector efficiency, and the product of beam-target polarizations respectively.

How to measure the helicity dependent absolute cross-section difference?

g2 contribution is small at low Q2 values; extract g1, then evaluate 1, the GDH

sum and higher moments.

Methodology to measure GDH sumPractical Approach:

Normalize for PbPt, target thickness, overall efficiency using well-known cross section difference in the (quasi-)elastic region

Method I:

Use model of world data on all structure functions, radiative effects etc. to generate simulated count differences on polarized species (p, d) for opposite beam helicities

Run through GSIM, GPP, RECSIS, higher level analysis

Apply corrections for efficiency (CC, tracking,…), backgrounds

Compare with data (count differences)

Iterate with varying input for g1 to extract “true g1”

Method II:

Use full simulation of complete target (NH3, ND3 + He, foils…) tuned to agree with data; determine acceptance*efficiency from ratio MC reconstructed/MC thrown

Correct measured count rate differences for all factors on previous slide, apply corrections for g2 etc., extract g1

PBPT from QE Asymmetry vs Polarimetry

NMR&Moller

QE Asym

Stat errors only

Analysis by Sarah Phillips

(Deuteron Run) S. Phillips, K. Slifer

Very good agreement between the methods before ESR Crash/Material change

afterwards, NMR+Moller is larger than the asymmetry result.

Each data point represents average over a run-group1) 51582 – 516012) 51602 – 516793) 51680 – 51779

4) 51791 – 518705) 51874 – 52040

before ESR crash

After ESR crash

PbPt for NH3 runs (simulation) H. Kang, A .Deur

• Working on absolute proton polarized elastic cross-section difference.

• Initially used simpler simulation than GSIM• Now, working on repeating this work with GSIM (more detailed

simulation but more of a "black box" so it's harder to understand and to be sure to control everything GSIM does).

Simulation of Deuteron Data K. Adhikari, S. Kuhn

• “RCSLACPOL” program (Incorporates both internal & external radiative effects) generates polarized & unpolarized cross sections (both Born and radiated)

• Based on the standard approach by Shumeiko and Kuhto as well as Mo and Tsai, including external radiation in the target.

• Extensively tested & used – at SLAC (E142, E143, E154, E155 & E155x) & Jlab (EG1a/b). • Updated with the most recent models on polarized and unpolarized structure functions (F1,

F2, A1 & A2) and an implementation of the folding algorithm developed by W. Melnitchouk and Y. Kahn for structure functions of the deuteron.

• The models fitted to & tested with data from EG1b as well as world data on both A1 and A2 over a wide range of Q2 and W, including the resonance region and the DIS region.

• For EG4, we have combined this code with the event generator “STEG” developed by the Genova group – RCSLACPOL generates cross-section map & STEG generates events accordingly.

But: Strange RECSIS features…

Data GSIM

…lead (?) to discrepancies between data and simulation…

Spectra look different!

Use qVTX and fDC1-pos for fiducial cuts

Remove areas of clear CC inefficiency

⇒ somewhat improved agreement(will have to select stable region for PbPtDF)

CC inefficiency 1: <nphe>

CC inefficiency 2: 1 – (Events passing all cuts/Events passing EC cuts only)

CC inefficieny 3: Fit to use for weighting MC events

Summary & Future Work• Finished most of the data analysis tasks• Extensive work on simulation with GSIM ongoing –

try to understand differences with data– GSIM Simulation work to extract physics quantities from

ND3 data underway – K. Adhikari, S. Kuhn

– GSIM Simulation on NH3 data underway – H. Kang, A. Deur, M. Ripani

• Expect first results on the deuteron by end of this year

• Hope for publications next year