EG4 Update Krishna Adhikari Old Dominion University Oct 12, 2012
CLAS- EG4 (E (NH 3 ) + E (ND 3 )): a measurement of the extended GDH (Gerasimov-Dreall- Hearn) integral for the proton and neutron (deuteron) at very low Q 2 (0.015 – 0.5 GeV 2 ) Performed in Jlab Hall-B from February to May, Experiment with polarized beam and polarized targets g 1 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 Q 2, provides a useful tool to study the transition from hadronic to partonic descriptions of Strong interaction. – Very high Q 2 (> ~5 GeV 2 ): (Bjorken limit): pQCD – High Q 2 (> ~1 GeV 2 ): Operator Product Expansion – Intermediate Q 2 region: Lattice QCD calculations – Low Q 2 region (< ~0.1 GeV 2 ): 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. 11
Methodology to measure GDH sum How to extract g 1 ? N -+, N ++ the # of events detected for the parallel & anti-parallel beam-target polarizations N i, t, f, and P b P t 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? g 2 is small at low Q 2 values; extract g 1, then evaluate 1, the GDH sum and higher moments.
P B P T 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-group 1) – ) – ) – ) – ) – before ESR crash After ESR crash
NMR Signal after ESR Crash The polarization appeared to be much larger, but the signal had a distortion. The distortion is less than 4% relative contribution to the total area, but this may be the cause of the PbPt disagreement ESR Crash Deuteron Target Polarization 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 X 0 (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 (F 1, F 2, A 1 & A 2 ) 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.
Unpolarized Polarized
PbPt for NH 3 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 ND 3 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 ND 3 data underway – K. Adhikari, S. Kuhn Simulation on NH 3 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 77K4K 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 EG 1 B Set Up ???