Probing Chiral Dynamics with photons Henry R. Weller Duke University and Triangle Universities Nuclear Laboratory HI S PROGRAM QCD Town Meeting-January 2007
A wide variety of physical processes can be used to study Chiral Dynamics, guided mainly by the results of Ch. PT, 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 2006 Organizers: H. Gao, B. Holstein, HRW www. tunl. duke. edu/events/cd 2006/proceeding. html QCD Town Meeting-January 2007
Chiral Anomaly The 0 (from Yelena Prok for the Prim. Ex Collaboration) 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 F = 92. 42+/-0. 25 Me. V is the pion decay constant. QCD Town Meeting-January 2007
Decay Width The 0 g decay width is related to the amplitude: is presently known to 10% The goal of the Prim. Ex Experiment is to measure the decay width to an accuracy of 1. 5%. Ch. PT calculations Including effects of md-mu being non-zero Increase G by 4. 5%. QCD Town Meeting-January 2007
Success of Ch. PT at pion-threshold Linearly Polarized Photon asymmetry for the p 0 p reaction at an average energy of 159. 5 Me. V MAINZ 2001 QCD Town Meeting-January 2007
Difficulties! e + p e’ + p + 0 at low Q 2 --MAINZ QCD Town Meeting-January 2007
Precision Measurement of the Electroproduction of 0 Near 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
Pion Electro-Production in the US Big. Bite Collaboration Target • 10 - 15 cm Liquid Hydrogen( LH 2) • 125 mm Al Foil LH 2 Beam Dump e p Big. Bite Electron Beam 15 m. A Luminosity • 3 - 5 x 1037 Hz/cm 2 HRS Electron HRS Luminosity Monitor MWDC(15 Planes) Two Segmented Scintillator Arrays
This experiment (now E 04 -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
New measurements of s. P – s. A for the proton and neutron at LEGS using the (SPHICE) frozen-spin solid HD target QCD Town Meeting-January 2007
LEGS data for the ‘neutron’ QCD Town Meeting-January 2007
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 theoretical uncertainty is the smallest and the discrepancy with multipole analysis of pi-photoproduction data the largest QCD Town Meeting-January 2007
N/Delta Physics at Mainz (IASA (Athens), MIT, Mainz, …) * + p D + N Detect: e' + p or e' + + in coincidence u u d N p D
C 2/M 1 vs. 2 ( 0 p Q channel) W=1232 Me. V Lattice QCD Results Dynamical Model without pion cloud Dynamical Model with pion cloud Effective Field Theory Calculations Gail/Hemmert Pascalutsa/Vanderhaeghen
HI S –A free-electron laser generated -ray source QCD Town Meeting-January 2007
Upgraded Facility 1. 2 -Ge. V Booster Injector RF System with HOM Damping QCD Town Meeting-January 2007
Upgrade Schedule Commissioning of Booster and Ring with OK-4—underway now! Nuclear Physics Program begins—March, 2007 March 07 Aug 07 Dec. 07 Linear Pol. - Below 65 Me. V, >2 x 108 g/s Circ. Pol. Up to 110 Me. V, >108 g/s These are TOTAL intensities. Beam on target is: TOTAL x 1. 5 x % resolution (ex. 5% res. at 100 Me. V: 7. 5 x 106 g/s) Expect to have energies up to 160 Me. V by Spring 09 QCD Town Meeting-January 2007
The GDH integrand for deuterium below pion threshold @ HI S A 400 hour run will allow us to measure the GDH integrand between 5 and 100 Me. V to an overall accuracy of about 3% or better, assuming a beam of 1 x 107 g/s with ~5% energy spread. An experiment to measure the GDH integrand for 3 He below pion threshold is also being developed by Haiyan Gao et al. QCD Town Meeting-January 2007
The upgraded BLOWFISH array as of January, 2005. QCD Town Meeting-January 2007
QCD Town Meeting-January 2007
Compton@HIg. S Collaboration (see www. tunl. duke. edu/~mep/higs/compton. pdf) Use the intense polarized beams at HIg. S 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 spinpolarizabilities of the proton and the neutron. QCD Town Meeting-January 2007
The HINDA Array (HI S Na. I Detector Array) Recently NSF/MRI funded project—a high resolution-high acceptance gamma-ray spectrometer consisting of eight 10”x 12” Na. I detectors in 3” thick segmented Na. I shields. The Compton@HI S Collaboration QCD Town Meeting-January 2007
QCD Town Meeting-January 2007
QCD Town Meeting-January 2007
Electric and Magnetic Polarizability of the proton • Recent results (B. Pasquini) of a free fit to data yield: a = 11. 52 +/- 2. 4 x 10 -4 fm 3 b = 3. 42 +/- 1. 70 x 10 -4 fm 3 (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
100% Linearly polarized beams at HIg. S can improve this Simulation (Blaine Norum) assumed: E = 120 Me. V Target: 80 mg/cm 2 107 /s 280 hours QCD Town Meeting-January 2007
Determination of the electric and magnetic polarizabilities of the proton using 100% linearly polarized gammas@HI S –a ~300 hr experiment will yield ~5% errors on both a ( now~20%) and b (now~50%). QCD Town Meeting-January 2007
Compton scattering of g rays from the deuteron at LUND G. 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 Ch. PT calculations O(p 4) (from Phillips and Choudhury) QCD Town Meeting-January 2007
Solid curve->a. N = 12; b. N = 3 Dashed curve->a. N = 6; b. N = 9 QCD Town Meeting-January 2007
Presently, results from 55 and 66 Me. V disagree with those obtained from 94 Me. V data. eg. 94 Me. V (SAL) data yield a. N - b. N ~ 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
The LUND experiment will make ~5% measurements at five angles and 3 energies between 40 and 110 Me. V. 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
Spin polarizabilities. Measuring these requires polarized beams and polarized targets. They are predicted (Ch. PT) to be different for the n and the p. There are four “dipole” spin polarizabilities: 1, 2, 3, 4 which can be written in terms of E 1 E 1, E 1 M 2, M 1 E 2, M 1 M 1. 1 (~ E 1 E 1) and 4(= M 1 M 1) are the largest. QCD Town Meeting-January 2007
HIg. S Proposal for measuring the proton spinpolarizabilities Spokesperson – Rory Miskimen • A 200 hr. run at 120 Me. V will give helicity dependent cross sections at the 3% level, which translates into ~10% measurments of spinpolarizabilities 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
QCD Town Meeting-January 2007
Projection for double-polarized Compton scattering from proton Total beam time for proton 100 hrs for each measurement: 450 hrs target spin orientation R. Miskimen, theory curves: Hildebrandt, Griesshammer, Hemmert, Nucl-th/0308054 QCD Town Meeting-January 2007
Experiments are being developed by Dr. Haiyan Gao at Duke/HIg. S to measure the spinpolarizabilities of the neutron. Haiyan Gao has built a high pressure spinpolarized 3 He target. Target thickness will be about 1022 atoms/cm 2 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
QCD Town Meeting-January 2007
Proposed set-up using the Na. I detector array (HINDA) and the 88 neutron detector array for quasi-elastic Compton scattering studies using the polarized 3 He target. QCD Town Meeting-January 2007
Present proposed experiments • New theoretical calculations by Choudhury, Nogga and Phillips make extraction of spin-polarizabilities possible from elastic scattering data from 3 He. • 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 fm 4. QCD Town Meeting-January 2007
Estimate of the experimental uncertainties in the individual spin polarizabilities For example, at 90 o, the longitudinal cross section difference is sensitive to g 1 , while the transverse polarization cross section difference is sensitive to g 4. The value of g 0 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
• Projected HI S measurement on Nucleon Spin • Polarizabilities (quasifree) (all in 10 -4 fm 4) • Proton HI S • Neutron HI S projected uncertainties • p 1=1. 1 0. 25 • n 1=3. 7 0. 40 • p 2=-1. 5 0. 36 • n 2=-0. 1 0. 50 • p 3=0. 2 0. 24 • n 3=0. 4 0. 50 • p 4=3. 3 0. 11 • n 4=2. 3 0. 35 • Mc. Govern et al. NLO heavy baryon Chiral Perturbation Theory QCD Town Meeting-January 2007
QCD Town Meeting-January 2007
Threshold pion-photoproduction from the proton @ HIg. S p(g, p 0)p Co-spokesperson: Aron Bernstein The first experiment: A measurement of the Target analyzing power at E = 158 Me. V. QCD Town Meeting-January 2007
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
The Neutral Meson Spectrometer (NMS) • 14 Plastic • Scintillators • All Phases • Veto Scint. • 2 BGO Layers + • 2 Sets of MWPC • Phase II • Tracking • 60 Cs. I Crystals • Phase I • Calorimetry Only QCD Town Meeting-January 2007
QCD Town Meeting-January 2007
Motivation Isospin Symmetry Breaking A measurement of the imaginary part of the s-wave production amplitude (E 0+) provides a determination of the charge exchange scattering length acex(p+n p 0 p). Requires measurement of the polarized target analyzing power T(q). QCD Town Meeting-January 2007
Simulations (Bernstein et al. ) The results indicate that we can measure Im. E 0+ with a statistical uncertainty of 3. 7% in 200 hours of actual data taking at 158 Me. V. This gives us the value of acex (p+n -> p 0 p). Isospin conservation implies acex (p+n -> p 0 p) = -acex (p-p -> p 0 n). 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 -> p 0 p). QCD Town Meeting-January 2007
Resources at HI S Mirror development is the key to pion threshold Physics at HIg. S. Present mirrrors take us up to 110 Me. V. Although a development plan is in place for 165 nm mirrors (140 Me. V), additional resources are needed to assure that 160 Me. V 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
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. 2. 3. Prim. Ex at JLAB—a precision measurement of the p 0 lifetime. Pion-electroproduction from the proton near threshold at Mainz and JLAB. Ch. PT at finite Q 2. N/D Physics at Mainz: the pion-cloud to quark-parton transition. 4. Compton scattering from the deuteron at LUND—neutron polarizabilities. 5. Precision measurements of the polarizabilities of the proton at HIg. S. Obtain ~5% measurements of ap and bp. 6. Double-polarization measurements at LEGS using the HD target. 7. Spin-polarizability measurements for both p and n at HIg. S using polarized p, d and 3 He targets. Test Ch. PT and Lattice QCD results . 8. Pion-threshold measurements at HIg. S using polarized beam and target. QCD Town Meeting-January 2007
• HI S –A free electron laser generated EXTRA SLIDES -ray source QCD Town Meeting-January 2007
HIg. S Anticipated Schedule for 2007 Linearly polarized beams below ~65 Me. V will be available in early 2007. Measure Compton scattering from the deuteron at ~50 Me. V using a scintillating target (unpolarized). Circularly polarized beams (OK-5) will be available in late 2007 up to ~110 Me. V. Measure GDH on the deuteron up to 50 Me. V using Blowfish and the frozen-spin target. QCD Town Meeting-January 2007
• Spin-exchange optical pumping • Optical pumping of alkali atoms (Rubidium) • Spin-exchange of 3 He with Rubidium • High pressure target (~10 bar), 3 He pol’n ~40 to 50% • Target will be 40 cm in length giving 1 x 1022 atoms/cm 2 QCD Town Meeting-January 2007
• Extending Gamma Energy Range (4 k. A Wiggler Op) • Extending Wiggler Current 4 k. A max • Operational Concerns • Saturated magnetic fields • Additional power supplies • Filter/bassbar system upgrades • 1. 2 Ge. V operation to reach 158 Me. V with 150 nm mirrors QCD Town Meeting-January 2007 • 158 Me. V
Schedule for FEL Cavity Mirror R&D 190 nm mirrors have been proven to work in our environment…these will produce 110 Me. V gammas. 165 nm mirrors will produce 140 Me. V beams once OK-5 is operating at 4 k. A. Date Milestone July 2006 Delivery of 1 st mirror sets with coatings for 190, 180 and 165 nm May 2007 Intracavity evaluation of 1 st set of 190, 180 and 165 nm mirrors Oct. 2007 Delivery of 2 nd mirror sets with coatings for 180 and 165 nm Nov. 2007 Intracavity evaluation of 2 nd set of 180 and 165 nm mirrors QCD Town Meeting-January 2007
Recent results from Choudhury, Nogga and Phillips for elastic scattering from 3 He QCD Town Meeting-January 2007
QCD Town Meeting-January 2007
Primakoff Effect • The 0 photoproduction from Coulomb field of the nucleus. • Production ( *! 0) and decay ( 0! ) mechanisms imply the Primakoff cross section is proportional to the 0 lifetime. QCD Town Meeting-January 2007
Events/0. 04 deg 0 production on 208 Pb QCD Town Meeting-January 2007
Frozen Spin Polarized Deuterium Target Butanol Polarization ~ 80 % Polarizing Field ~ 2. 5 T Holding Field ~ 0. 6 T ~4 x 1023 d/cm 2 QCD Town Meeting-January 2007
COMPTON ON d WITH A SCINTILLATING TARGET Vertical axis : light output from target detector Horizontal axis: Missing energy (binding energy) Courtesy of Rory Miskimen QCD Town Meeting-January 2007
Our measurement will determine b to +/- 0. 10, where Im[E 0+(gp -> p 0 p)] = b pp+/mp and b = Re[E 0+ (gp -> p+n)] acex (p+n -> p 0 p) Re[E 0+ ( p -> +n)] is well measured (=28. 06 +/- 0. 27 +/- 0. 45), giving us acex ( +n -> 0 p). Isospin conservation implies acex ( +n -> 0 p) = -acex ( -p -> 0 n). The latter is well known from the width of pionic hydrogen (-0. 1301 +/- 0. 0059) after a decade of work. Our measurement will give a comparable accuracy for acex ( +n -> 0 p). QCD Town Meeting-January 2007
Recent (PRC C 71, 044002 (2005)) HBCh. PT calculations of Choudhury and Phillips indicate appreciable sensitivity of Sx observed in Compton scattering from the deuteron to 1 n at 135 Me. V. Test for consistency! QCD Town Meeting-January 2007
QCD Town Meeting-January 2007
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