Probing Chiral Dynamics with photons

QCD Town Meeting-January 2007

Probing Chiral Dynamics with photons

Henry R. Weller Duke University and Triangle Universities Nuclear Laboratory

HIS PROGRAM


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, HRW

www.tunl.duke.edu/events/cd2006/proceeding.html


Chiral Anomaly(from Yelena Prok for the PrimEx Collaboration)

The 0 decay rate is a fundamental prediction of confinement scale QCD.

Chiral Anomaly – the closed-loop trianglediagram results in axial vector current non-conservation, even in the limit ofvanishing quark masses.

The anomaly leads to the reduced decayamplitude, in leading order (chiral limit)

where F= 92.42+/-0.25 MeV is the pion decay constant.

1-GeV0251304

.πF

αA

π

emγγ


Decay WidthThe 0 decay width is related to the amplitude:

is presently known to 10%

The goal of the PrimEx Experimentis to measure the decay width toan accuracy of 1.5%. ChPT calculationsIncluding effects of md-mu being non-zeroIncrease by 4.5%.

eV044.0725.764

2

0

Am


Success of ChPT at pion-thresholdLinearly Polarized Photon asymmetry for the p0p reaction at an

average energy of 159.5 MeVMAINZ 2001


Difficulties!e + p e’ + p + at low Q2 --MAINZ


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,

)

Goal: Extract high precision data in a fine grid of Q2 and W

from Q2 0.04 0.14 in steps of 0.01 (GeV/c)2 and

from W 0 20 MeV above threshold in steps of 1 MeV:

T(* ) L L (

* )

LT (* )

TT (* )

LT ' (

* )


LH2

Target• 10 - 15 cm Liquid Hydrogen( LH2)• 125 m Al Foil

Luminosity• 3 - 5 x 1037 Hz/cm2

HRS

Electron

BigBite

BeamDump

HRSLuminosityMonitor

MWDC(15 Planes)p

Two Segmented Scintillator Arrays

Electron Beam15 A

e

Pion Electro-Production in the US BigBite Collaboration


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


New measurements of P – for the proton and neutron at LEGS using the (SPHICE) frozen-spin solid HD target


LEGS data for the ‘neutron’


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

* + p N

N/Delta Physics at Mainz (IASA (Athens), MIT, Mainz,…)

Np

u du

Detect: e' + p

ore' + +

in coincidence

C2/M1 vs. Q2 (0p channel)

Lattice QCD Results

Dynamical Modelwith pion cloud

W=1232 MeV

Dynamical Modelwithout pion cloud

Effective Field Theory CalculationsGail/HemmertPascalutsa/Vanderhaeghen


HIS –A free-electron laser generated -ray source


Upgraded Facility

RF System with HOM Damping

1.2-GeV Booster Injector


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 /s

Dec. 07 Circ. Pol. Up to 110 MeV, >108 /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 s)

Expect to have energies up to 160 MeV by Spring 09


The GDH integrand for deuterium below pion threshold @ HIS

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 107 /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.


The upgraded BLOWFISH array as of January, 2005.



Use the intense polarized beams at HIS 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.

Compton@HIS Collaborationsee www.tunl.duke.edu/~mep/higs/compton.pdf)


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@HIS Collaboration

The HINDA Array(S NaI Detector Array)




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

= 3.42 +/- 1.70 x 10-4 fm

(with Baldin sum rule value of 13.82

11.0 +/- 1.4 ; 2.8 +/-1.4 )

A ~50% error in – which will impact future measurements.


100% Linearly polarized beams at HIS can improve this

Simulation (Blaine Norum) assumed:

E = 120 MeV

Target: 80 mg/cm2

107 /s

280 hours


Determination of the electric and magnetic polarizabilities of the protonusing 100% linearly polarized gammas@HIS –a ~300 hr experiment will yield ~5% errors on both now~and (now~50%).


Compton scattering of 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 ChPT calculations O(p4) (from Phillips and Choudhury)


Solid curve->N = 12; Dashed curve->N = 6; N = 9


Presently, results from 55 and 66 MeV disagree with those obtained from 94 MeV data. eg. 94 MeV (SAL) data yield 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).


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.


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: which can be written in terms of

E1E1) and 4(=are the largest.


HIS Proposal for measuring the proton spin-polarizabilities

Spokesperson – 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.



R. Miskimen, theory curves: Hildebrandt, Griesshammer, Hemmert,Nucl-th/0308054

100 hrs for each target spin orientation

Projection for double-polarized Compton scattering from proton

Total beam time for protonmeasurement: 450 hrs


Experiments are being developed by Dr. Haiyan Gao at Duke/HIS 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.



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.


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.


Estimate of the experimental uncertainties in the individual spin polarizabilities

For example, at 90o, the longitudinal cross section difference is sensitive to while the transverse polarization cross section difference is sensitive to

The value of 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)).


•Proton HIS projected

uncertainties

•Neutron HIS projected uncertainties

p1=1.1 0.25 n

1=3.7 0.40

p2=-1.5 0.36

n2=-0.1 0.50

p3=0.2 0.24 n

3=0.4 0.50

p4=3.3 0.11 n

4=2.3 0.35

•Projected HIS measurement on Nucleon Spin •Polarizabilities (quasifree) (all in 10-4 fm4)

•McGovern et al. NLO heavy baryon Chiral Perturbation Theory



Threshold pion-photoproduction from the proton @ HIS

p(0)p

Co-spokesperson: Aron Bernstein

The first experiment:

A measurement of the Target analyzing power at EMeV.


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.


•Phase I•Calorimetry Only

•60 CsI Crystals

•All Phases•Veto Scint.

•Phase II•Tracking

•2 BGO Layers +•2 Sets of MWPC

•14 Plastic•Scintillators

The Neutral Meson Spectrometer (NMS)



A measurement of the imaginary part of the s-wave production amplitude (E0

+) provides a determination of the charge exchange scattering length acex(np).

Requires measurement of the polarized target analyzing power T().

Motivation

Isospin Symmetry Breaking


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 (+n -> 0p).

Isospin conservation implies

acex (+n -> 0p) = -acex (-p -> 0n).

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 (+n -> 0p).


Resources at HIS

Mirror development is the key to pion threshold Physics at HIS.

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.


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 0 lifetime.

2. Pion-electroproduction from the proton near threshold at Mainz and JLAB. ChPT at finite Q2. 3. N/ 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 HIS.Obtain ~5% measurements of p and p.

6. Double-polarization measurements at LEGS using the HD target.

7. Spin-polarizability measurements for both p and n at HIS using polarized p, d and 3He targets.Test ChPT and Lattice QCD results

.8. Pion-threshold measurements at HIS using polarized beam and target.


EXTRA SLIDES•HIS –A free electron laser generated -ray source


HISAnticipated Schedule for 2007

Linearly polarized beams below ~65 MeV will be available in early 2007.

Measure Compton scattering from the deuteron at ~50 MeV using a scintillating target (unpolarized).

Circularly polarized beams (OK-5) will be available in late 2007 up to ~110 MeV.

Measure GDH on the deuteron up to 50 MeV using Blowfish and the frozen-spin target.


•Spin-exchange optical pumping

•Optical pumping of alkali atoms (Rubidium)•Spin-exchange of 3He with Rubidium

•High pressure target (~10 bar), 3He pol’n ~40 to 50%•Target will be 40 cm in length giving 1 x 1022 atoms/cm2


•Extending Gamma Energy Range (4 kA Wiggler Op)

•Extending Wiggler Current 4 kA max

•Operational Concerns•Saturated magnetic fields•Additional power supplies

•Filter/bassbar system upgrades•1.2 GeV operation to reach 158 MeV with 150

nm mirrors

•158 MeV


190 nm mirrors have been proven to work in our environment…these will produce 110 MeV gammas.

165 nm mirrors will produce 140 MeV beams once OK-5 is operating at 4kA.

Schedule for FEL Cavity Mirror R&D

Date Milestone

July 2006 Delivery of 1st mirror sets with coatings for 190, 180 and 165 nm

May 2007 Intracavity evaluation of 1st set of 190, 180 and 165 nm mirrors

Oct. 2007 Delivery of 2nd mirror sets with coatings for 180 and 165 nm

Nov. 2007 Intracavity evaluation of 2nd set of 180 and 165 nm mirrors


Recent results from Choudhury, Nogga and Phillips for elastic scattering from 3He



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.

22

4

43

3

2

sin8

0 QFQ

E

m

Z

d

dem

emP


0 production on 208PbE

vent

s/0.

04 d

eg


Frozen Spin Polarized Deuterium Target

Butanol Polarization ~ 80 %Polarizing Field ~ 2.5 THolding Field ~ 0.6 T~4 x 1023 d/cm2


COMPTON ON d WITH A SCINTILLATING TARGETVertical axis : light output from target detector

Horizontal axis: Missing energy (binding energy)Courtesy of Rory Miskimen


Our measurement will determine to +/- 0.10, where

Im[E0+(p -> 0p)] = p/m

and Re[E0+ (p -> +n)] acex (+n -> 0p)

Re[E0+ (p -> +n)] is well measured (=28.06 +/- 0.27 +/- 0.45), giving us acex (+n -> 0p).

Isospin conservation implies acex (+n -> 0p) = -acex (-p -> 0n).

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 -> 0p).


Recent (PRC C71, 044002 (2005)) HBChPT calculations of Choudhury and Phillips indicate appreciable sensitivity of x observed in Compton scattering from the deuteron to 1n at 135 MeV. Test for consistency!


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Probing Chiral Dynamics with photons