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Probing Chiral Dynamics with photons

Probing Chiral Dynamics with photons. Henry R. Weller Duke University and Triangle Universities Nuclear Laboratory HI g S PROGRAM.

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Probing Chiral Dynamics with photons

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  1. Probing Chiral Dynamics with photons Henry R. Weller Duke University and Triangle Universities Nuclear Laboratory HIgS PROGRAM QCD Town Meeting-January 2007

  2. A wide variety of physical processes can be used to study Chiral Dynamics, guided mainly by the results of ChPT, an expansion of the Lagrangian for low energy QCD about the chiral limit, mq=0.I want to mention a few of these today.Reference:International Workshop on Chiral Dynamics 2006Organizers: H. Gao, B. Holstein, HRWwww.tunl.duke.edu/events/cd2006/proceeding.html QCD Town Meeting-January 2007

  3. Chiral Anomaly(from Yelena Prok for the PrimEx Collaboration) The p0 decay rate is a fundamental prediction of confinement scale QCD. Chiral Anomaly – the closed-loop triangle diagram results in axial vector current non-conservation, even in the limit of vanishing quark masses. The anomaly leads to the reduced decay amplitude, in leading order (chiral limit) where Fp = 92.42+/-0.25 MeV is the pion decay constant. QCD Town Meeting-January 2007

  4. Decay Width The p0ggg decay width is related to the amplitude: is presently known to 10% The goal of the PrimEx Experiment is to measure the decay width to an accuracy of 1.5%. ChPT calculations Including effects of md-mu being non-zero Increase G by 4.5%. QCD Town Meeting-January 2007

  5. Success of ChPT at pion-thresholdLinearly Polarized Photon asymmetry for the gpp0p reaction at an average energy of 159.5 MeVMAINZ 2001 QCD Town Meeting-January 2007

  6. Difficulties!e + p  e’ + p + p0 at low Q2 --MAINZ QCD Town Meeting-January 2007

  7. Precision Measurement of the Electroproduction of p0Near Threshold at JLAB: A Test of Chiral QCD Dynamics Co-spokespersons J. Annand, D. Higinbotham, R. Lindgren, V. Nelyubin, and B. Norum, ) q QCD Town Meeting-January 2007

  8. Pion Electro-Production in the US  BigBite Collaboration Target • 10 - 15 cm Liquid Hydrogen( LH2) • 125 mm Al Foil HRS Electron Beam Dump e LH2 p BigBite Electron Beam 15 mA MWDC(15 Planes) Two Segmented Scintillator Arrays HRS Luminosity Monitor Luminosity • 3 - 5 x 1037Hz/cm2

  9. This experiment (now E04-007) is scheduled to be run in Nov 2007, but may be delayed until April 2008 due to budget problems. QCD Town Meeting-January 2007

  10. New measurements of sP – sA for the proton and neutron at LEGS using the (SPHICE) frozen-spin solid HD target QCD Town Meeting-January 2007

  11. LEGS data for the ‘neutron’ QCD Town Meeting-January 2007

  12. LEGS The LEGS group has now completed taking data for both polarized p and polarized d targets. They have used their recently commissioned TPC to measure the charged pion channels. This will provide very accurate results for the GDH and the forward-spin-polarizability integrals for both p and n. Measuring them simultaneously will provide accurate values of the GDH n-p difference, where the theoretical uncertainty is the smallest and the discrepancy with multipole analysis of pi-photo-production data the largest QCD Town Meeting-January 2007

  13. d u u N/Delta Physics at Mainz (IASA (Athens), MIT, Mainz,…) g* + p  Dp + N Detect: e' + p or e' + p+ in coincidence N p D p

  14. C2/M1 vs. Q2 (p0p channel) W=1232 MeV Lattice QCD Results Dynamical Model without pion cloud Dynamical Model with pion cloud Effective Field Theory Calculations Gail/Hemmert Pascalutsa/Vanderhaeghen

  15. HIgS–A free-electron laser generated g-ray source QCD Town Meeting-January 2007

  16. 1.2-GeV Booster Injector RF System with HOM Damping Upgraded Facility QCD Town Meeting-January 2007

  17. Upgrade Schedule Commissioning of Booster and Ring with OK-4—underway now! Nuclear Physics Program begins—March, 2007 March 07  Aug 07 Linear Pol.- Below 65 MeV, >2x108 g/s Dec. 07  Circ. Pol. Up to 110 MeV, >108 g/s These are TOTAL intensities. Beam on target is: TOTAL x 1.5 x % resolution (ex. 5% res. at 100 MeV: 7.5 x 106 g/s) Expect to have energies up to 160 MeV by Spring 09 QCD Town Meeting-January 2007

  18. The GDH integrand for deuterium below pion threshold @ HIgS A 400 hour run will allow us to measure the GDH integrand between 5 and 100 MeV to an overall accuracy of about 3% or better, assuming a beam of 1 x 107g/s with ~5% energy spread. An experiment to measure the GDH integrand for 3He below pion threshold is also being developed by Haiyan Gao et al. QCD Town Meeting-January 2007

  19. The upgraded BLOWFISH array as of January, 2005. QCD Town Meeting-January 2007

  20. QCD Town Meeting-January 2007

  21. Compton@HIgS Collaboration (see www.tunl.duke.edu/~mep/higs/compton.pdf) Use the intense polarized beams at HIgS to obtain very precise values of the electric and magnetic polarizabilities of the proton and the neutron. Perform double polarization experiments to obtain precise values of the spin-polarizabilities of the proton and the neutron. QCD Town Meeting-January 2007

  22. The HINDA Array(HIgS NaI Detector Array) Recently NSF/MRI funded project—a high resolution-high acceptance gamma-ray spectrometer consisting of eight 10”x12” NaI detectors in 3” thick segmented NaI shields. The Compton@HIgS Collaboration QCD Town Meeting-January 2007

  23. QCD Town Meeting-January 2007

  24. QCD Town Meeting-January 2007

  25. Electric and Magnetic Polarizability of the proton • Recent results (B. Pasquini) of a free fit to data yield: • = 11.52 +/- 2.4 x 10-4 fm3 b = 3.42 +/- 1.70 x 10-4 fm3 (with Baldin sum rule value of 13.82 a=11.0 +/- 1.4 ; b= 2.8 +/-1.4 ) A ~50% error in b – which will impact future measurements. QCD Town Meeting-January 2007

  26. 100% Linearly polarized beams at HIgS can improve this Simulation (Blaine Norum) assumed: Eg = 120 MeV Target: 80 mg/cm2 107g/s 280 hours QCD Town Meeting-January 2007

  27. Determination of the electric and magnetic polarizabilities of the protonusing 100% linearly polarized gammas@HIgS –a ~300 hr experiment will yield ~5% errors on both a ( now~20%) and b (now~50%). QCD Town Meeting-January 2007

  28. Compton scattering of g rays from the deuteron at LUNDG. Feldman, M. Kovash, A. Nathan, B. Schroder, H.R. Weller et al. • This will give us the so called isoscalar polarizabilities. Since the proton is “known”, this gives the values for the neutron. • The following shows ChPT calculations O(p4) (from Phillips and Choudhury) QCD Town Meeting-January 2007

  29. Solid curve->aN = 12; bN = 3Dashed curve->aN = 6; bN = 9 QCD Town Meeting-January 2007

  30. Presently, results from 55 and 66 MeV disagree with those obtained from 94 MeV data. eg. 94 MeV (SAL) data yield aN - bN ~ 2.5 while we expect a value of ~10 if the proton and neutron have the same values for this difference (as expected from Chiral Symmetry). QCD Town Meeting-January 2007

  31. The LUND experiment will make ~5% measurements at five angles and 3 energies between 40 and 110 MeV. The goal is to obtain errors for the isoscalar polarizabilities comparable to those which exist for the proton. This experiment will be run in 2007. QCD Town Meeting-January 2007

  32. Spin polarizabilities. Measuring these requires polarized beams and polarized targets. They are predicted (ChPT) to be different for the n and the p. There are four “dipole” spin polarizabilities: g1,2,3,4 which can be written in terms of gE1E1, E1M2, M1E2, M1M1. g1 (~gE1E1) and g4(=gM1M1) are the largest. QCD Town Meeting-January 2007

  33. HIgS Proposal for measuring the proton spin-polarizabilitiesSpokesperson – Rory Miskimen • A 200 hr. run at 120 MeV will give helicity dependent cross sections at the 3% level, which translates into ~10% measurments of spin-polarizabilities using the HINDA array. Sensitivity estimates for all four spin-polarizabilities are based upon calculations of Hildebrandt, Griesshammer and Hemmert. QCD Town Meeting-January 2007

  34. QCD Town Meeting-January 2007

  35. Projection for double-polarized Compton scattering from proton 100 hrs for each target spin orientation Total beam time for proton measurement: 450 hrs R. Miskimen, theory curves: Hildebrandt, Griesshammer, Hemmert, Nucl-th/0308054 QCD Town Meeting-January 2007

  36. Experiments are being developed by Dr. Haiyan Gao at Duke/HIgS to measure the spin-polarizabilities of the neutron. Haiyan Gao has built a high pressure spin-polarized 3He target. Target thickness will be about 1022 atoms/cm2 with a length of 40 cm. Polarizations of ~40% have been achieved. • Effect of the reduced target thickness is offset by the increased sensitivity in the observables. QCD Town Meeting-January 2007

  37. QCD Town Meeting-January 2007

  38. Proposed set-up using the NaI detector array (HINDA) and the 88-neutron detector array for quasi-elastic Compton scattering studies using the polarized 3He target. QCD Town Meeting-January 2007

  39. Present proposed experiments • New theoretical calculations by Choudhury, Nogga and Phillips make extraction of spin-polarizabilities possible from elastic scattering data from 3He. • With a gamma intensity of 2 x 107/sec and the target and detector system just described, a 350 hour experiment will give neutron spin polarizabilities with errors of about +/- 0.5 x 10-4 fm4. QCD Town Meeting-January 2007

  40. Estimate of the experimental uncertainties in the individual spin polarizabilities For example, at 90o, the longitudinal cross section difference is sensitive to g1 , while the transverse polarization cross section difference is sensitive to g4. The value of g0 for the proton was fixed from the Mainz experiment with an error of +/- 13%. (Could improve the resutls by considering additional constraints (B. Pasquini)).. QCD Town Meeting-January 2007

  41. Projected HIS measurement on Nucleon Spin Polarizabilities (quasifree) (all in 10-4 fm4) McGovern et al. NLO heavy baryon Chiral Perturbation Theory QCD Town Meeting-January 2007

  42. QCD Town Meeting-January 2007

  43. Threshold pion-photoproduction from the proton @ HIgSp(g,p0)pCo-spokesperson: Aron Bernstein The first experiment: A measurement of the Target analyzing power at Eg = 158 MeV. QCD Town Meeting-January 2007

  44. These experiments will provide stringent tests of • The predictions of Chiral Perturbation Theory • Predictions of isospin breaking due to the mass differences of the up and down quarks. QCD Town Meeting-January 2007

  45. The Neutral Meson Spectrometer (NMS) 2 BGO Layers + 2 Sets of MWPC 14 Plastic Scintillators 60 CsI Crystals All Phases Veto Scint. Phase II Tracking Phase I Calorimetry Only QCD Town Meeting-January 2007

  46. QCD Town Meeting-January 2007

  47. Motivation Isospin Symmetry Breaking A measurement of the imaginary part of the s-wave production amplitude (E0+) provides a determination of the charge exchange scattering length acex(p+np0p). Requires measurement of the polarized target analyzing power T(q). QCD Town Meeting-January 2007

  48. Simulations (Bernstein et al.) The results indicate that we can measure ImE0+ with a statistical uncertainty of 3.7% in 200 hours of actual data taking at 158 MeV. This gives us the value of acex (p+n -> p0p). Isospin conservation implies acex (p+n -> p0p) = -acex (p-p -> p0n). The latter is well known from the width of pionic hydrogen (0.1301 +/- 0.0059) after a decade of work. Our result will give a comparable accuracy for acex (p+n -> p0p). QCD Town Meeting-January 2007

  49. Resources at HIgS Mirror development is the key to pion threshold Physics at HIgS. Present mirrrors take us up to 110 MeV. Although a development plan is in place for 165 nm mirrors (140 MeV), additional resources are needed to assure that 160 MeV is reached (150 nm mirrors) with full flux in a timely manner. Funding presently limits operations to 1000 hrs/yr. In order to execute this program we would like to increase this to 3000 hours per year. This requires significant additional $upport. QCD Town Meeting-January 2007

  50. A wide variety of process can be used to study Chiral Dynamics, guided mainly by the results of CHPT, an expansion of the Lagrangian for low energy QCD about the chiral limit, mq=0. EXAMPLES: 1. PrimEx at JLAB—a precision measurement of the p0 lifetime. • Pion-electroproduction from the proton near threshold at Mainz and JLAB. ChPT at finite Q2. • N/D Physics at Mainz: the pion-cloud to quark-parton transition. • Compton scattering from the deuteron at LUND—neutron polarizabilities. • Precision measurements of the polarizabilities of the proton at HIgS. Obtain ~5% measurements of ap and bp. • Double-polarization measurements at LEGS using the HD target. 7. Spin-polarizability measurements for both p and n at HIgS using polarized p, d and 3He targets. Test ChPT and Lattice QCD results . 8. Pion-threshold measurements at HIgS using polarized beam and target. QCD Town Meeting-January 2007

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