EG4 Update

Krishna AdhikariOld Dominion University

Oct 12, 2012

CLAS-EG4 (E03-006 (NH3) + E06-017 (ND3)): a measurement of 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-B from February to May, 2006.

Experiment with polarized beam and polarized targets

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g1 is one of the two spin-structure functions. Structure functions characterize the deviation from point-like behavior of the target and thus give information about its structure and dynamics

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 PT with Bernard, Hemmert, Meissner

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

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

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Methodology to measure GDH sumMethodology 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 is small at low Q2 values; extract g1, then evaluate 1, the GDH sum and

higher moments.

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

NMR Signal after ESR Crash

The polarization appeared tobe much larger, but the signalhad a distortion.

The distortion is less than 4% relativecontribution to the total area, but this may be the cause of the PbPt disagreement

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Long anneal + Cold Irradiation+ New material added in

Deuteron NMR Polarimetry

Tracking efficiency M. Ripani• Look for:

– time-based tracks in non-first entries in EVNT that may lost electrons (look at CC hit, Nphe & p-distribution)

– hit-based tracks in any entry (CC hit, Nphe & p-distribution) – neutral hits (by re-cooking the luminosity scan with a special RECSIS

setting that also looks for neutrals as secondary trigger) and check if they look like electrons (CC hit, photoelectron number, EC hit & deposited energy distributions)

• Preliminary results: indicate possible electron losses of less than 1 % globally, still to be studied as a function of momentum, apparently with very small dependence on luminosity, in that the global inefficiency does not go beyond 1 % for various runs at increasing beam current.

• Acknowledgement: Thanks to S. Stepanyan for the strategy, especially on the neutrals.

Possible electron candidate in an entry other than the first, which satisfies standard EG4 cuts + Nphel>5, except HBT instead of TBT, but first entry satisfies standard EG4 cuts (TBT) and mom. distribution looks fine 

Deuteron Contamination(S. Koirala, EG1-DVCS )

Deuteron Contamination K. Adhikari, S. Kuhn

Event Selection

Conclusions on Deuteron contamination

• Contamination calculated (from 2 GeV data) ≈ 4.418%. • No ’pure’ Gaussian spectrum for deuteron, therefore, no

unambiguously separation of deuteron from proton in ND3. • Fit looks reasonably well (with contamination only a few

percent); no narrow clean proton peak on top of deuteron, can safely conclude that EG4 did NOT have the same contamination problem as EG1-DVCS.

• To accommodate the lack of reliable un-ambiguity, a rather generous systematic error will be assumed later on.

• 1.3 GeV ND3 data not used - the CLAS acceptance constrains coincident detection of exclusive (quasi-)elastic e-p events.

DC smearing in GPP (Simulation) K. Adhikari, S. Kuhn

•GSIM does not include factors such as temperature, alignment, dead channels, electronic malfunction etc • GSIM Post Processor (GPP) takes into account some of those effects.•The GPP can change the DC, SC, CC & EC signals produced in the simulation. •The DC signals can be changed by (a) accounting for the dead wires according to the calibration database, (b) shifting the DOCA mean value, and (c) smearing the hit signals according to the resolution determined by the calibration database or according to the command line input. • Likewise, SC signals can be changed with a parameter input for smearing the time resolution. And, for the CC & EC signals, the GPP can use the hardware threshold.

∆E of 2.3 GeV simulated elastic only proton-target events (no internal radiative effects)

DC smearing in GPP (Simulation)

Average Rad. Length K. Adhikari, S. Kuhn

Radiation length averaged over all possible vertices inside the target volume

For EG4

For EG1b

•High-energy electrons predominantly lose energy in matter by bremsstrahlung, and high-energy photons by e+e− pair production.

• External radiative effect corrections needs amount of material the track passed through before the detection.

•characteristic radiation length X0 (g cm−2) for a given material

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.• Then run GSIM, GPP & RECSIS on them.• Compare with experimental data.

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Unpolarized Polarized

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

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

• Using simpler simulation than GSIM• Working on understanding systematic effects from cuts, radiative

length input, detector resolution and detector efficiency. The difficulties are: – 1) There is an unphysical theta dependence in the result – 2) The value of the experimental cross section is too low compared to expectation

from NMR+Moller.

• The simulated cross section is under control and the difficulties are with the experimental elastic cross section.

• Also, 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).

Summary & Future Work

• Recently finished working on ND3 target contamination, GPP-DC-smear parameter, Radtiation length

• Working on PbPt – K. Slifer & S. Phillips• Working on Tracking efficiency – M. Ripani• Simulation work to extract physics quantities

from ND3 data underway – K. Adhikari, S. Kuhn

• Simulation on NH3 data underway – H. Kang, A. Deur

Schematic of OVC (Outer Vacuum Can) Exit window

Calculation of Radiation Lengths Due to Target & Beam line materials

Courtesy: M. Zarecky

Heat shields

77K 4K

Super-insulation blanckets

Heat shield

OVC exit window

RADB and RADA calculated for EG4

Illustrating cases of Max. track lengths in Target, Wall, & NMR

For EG1B Set Up

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