Test of fundamental symmetries via Test of fundamental symmetries via the Primakoff effectthe Primakoff effect

Liping GanLiping Gan

University of North Carolina WilmingtonUniversity of North Carolina Wilmington

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OutlineOutline1.1. Physics MotivationPhysics Motivation

– QCD Symmetries and Properties of QCD Symmetries and Properties of ππ00, , ηη and and ηη’’

2.2. Primakoff Progarm at Jlab Primakoff Progarm at Jlab – Measurement Measurement ππ0 0 lifetime lifetime at 6 GeVat 6 GeV– Experiment of Experiment of ((22)) at 12 GeV at 12 GeV

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QCD Symmetries and light mesonsQCD Symmetries and light mesons

)1()1()3()3( BARL UUSUSU

QCD Lagrangian in Chiral limit (mq→0) is invariant under:

UA(1) is explicitly broken:

(Chiral anomalies) Γ(0→), Γ(→), Γ(’→) Mass of 0

Chiral symmetry SUL(3)xSUR(3) spontaneously breaks to SU(3) 8 Goldstone Bosons (GB)

SUL(3)xSUR(3) and SU(3) are explicitly broken: GB are massive Mixing of π0, η, η/

The π0, η, η’ system provides a rich laboratory to study the symmetry structure of QCD at low energies.

Primakoff Program at Jlab 6 & 12 GeV

Precision measurements of Precision measurements of electromagnetic properties of electromagnetic properties of 00, , , , via Primakoff effect.via Primakoff effect.

a)a) Two-Photon Decay Widths: Two-Photon Decay Widths: 1)1) ΓΓ((00→→) @ 6 GeV) @ 6 GeV

2)2) ΓΓ((→→) )

3)3) ΓΓ((’’→→))

b) Transition Form Factors at low

Q2 (0.001-0.5 GeV2/c2):F(*→ 0), F(* →), F(* →)

Input to Physics: precision tests of Chiral symmetry and anomalies determination of light quark mass ratio -’ mixing angle

Input to Physics: 0, and ’ electromagnetic interaction radii is the ’ an approximate Goldstone boson?

33

ΓΓ((00→→) Experiments @ 6 GeV) Experiments @ 6 GeV

eVF

mNc 725.7576 23

3220

0→ decay proceeds primarily via the chiral anomaly in QCD. The chiral anomaly prediction is exact for massless quarks:

Corrections to the chiral anomaly prediction:

Calculations in NLO ChPT:Γ(0) = 8.10eV ± 1.0% (J. Goity, et al. Phys. Rev. D66:076014, 2002)Γ(0) = 8.06eV ± 1.0% (B. Ananthanarayan et al. JHEP 05:052, 2002)Calculations in NNLO SU(2) ChPT:Γ(0) = 8.09eV ± 1.3% (K. Kampf et al. Phys. Rev. D79:076005, 2009)

Precision measurements of (0→) at the percent level will provide a stringent test of a fundamental prediction of QCD.

Calculations in QCD sum rule: Γ(0) = 7.93eV ± 1.5% (B.L. Ioffe, et al. Phys. Lett. B647, p. 389,

2007)

Γ(0) is one of the few quantities in confinement region that QCD canis one of the few quantities in confinement region that QCD can

calculate precisely to higher orders!calculate precisely to higher orders!

4

π

k1

k2

5

Primakoff Method

2 3 42 2Pr

. .3 4

8( ) sine m

d Z EF Q

d m Q

ρ,ω

Challenge: Extract the Primakoff amplitude

12C target

Primakoff Nucl. Coherent

Interference Nucl. Incoh.

Requirement:

Photon flux

Beam energy

0 production Angular resolution

Features of Primakoff cross section:

•Peaked at very small forward angle:Peaked at very small forward angle:

•Beam energy sensitive:Beam energy sensitive:

•Coherent processCoherent process

2

2

Pr 2E

mpeak

)log( , 2Pr

4Pr EZdEd

d

peak

PrimEx-I (2004)PrimEx-I (2004)

JLab Hall B high resolution, high intensity photon tagging facility

New pair spectrometer for photon flux control at high beam intensities 1% accuracy has been achieved

New high resolution hybrid multi-channel calorimeter (HyCal)

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00 Event selection Event selection

We measure: incident photon energy: E and time energies of decay photons: E1, E2 and time X,Y positions of decay photons

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Fit Differential Cross Sections to Extract Fit Differential Cross Sections to Extract ΓΓ((00))

PrimEx-I (2004) PrimEx-I (2004) Theoretical angular distributions smeared with experimental resolutions are fit to the data on two nuclear targets:

88

Verification of Overall Systematical UncertaintiesVerification of Overall Systematical Uncertainties

4.9 5.0 5.1 5.2 5.3 5.4 5.5

Energy (GeV)

0.055

0.060

0.065

0.070

0.075

0.080

0.085

Systematic Uncertainty

P R E L I M I N A R Y

Uncertainties:StatisticalSystematic

Compton Forward Cross Section

Klein-NishinaPrimex Compton Data

+ e +e Compton cross section measurement

e+e- pair-production cross section measurement:

Systematic uncertainties on cross sections are controlled at 1.3% level.

99

PrimEx-I Result

PRL 106, 162303 (2011)

(0) = 7.820.14(stat)0.17(syst) eV

2.8% total uncertainty 1010

Goal for PrimEx-IIGoal for PrimEx-II

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PrimEx-II projected 1.4%

~8K Primakoff events ~30K Primakoff events

( E = 4.4-5.3 GeV)

Primakoff

1212

Primakoff

PrimEx-II Data Analysis in ProgressPrimEx-II Data Analysis in Progress

1313

Tagger timing calibration

σ =1.5 ns

Tagger-HYCAL coincident time

Absolute tagging efficiency

( E = 4.4-5.3 GeV)

1414

Primakoff

With constraint

Without constraint Preliminary result

ΓΓ((→→) Experiment @ 12 GeV) Experiment @ 12 GeV

)(2

1ˆ re whe,

22

222

duud

s mmmmm

mmQ

2. Extract -’mixing angle:

3. Determine Light quark mass ratio:

H. Leutwyler Phys. Lett., B378, 313 (1996)

1. Resolve long standing discrepancy between collider and Primakoff measurements:

1515

Q 2

1616

Challenges in the Challenges in the →→ Primakoff Primakoff experimentexperiment

η

3/12

2

Pr

2

2 AEE

mNCpeak

larger momentum transfer (coherency, form factors, FSI,…)

mass is a factor of 4 larger than 0 and has a smaller cross section

larger overlap between Primakoff and hadronic processes;

Compared to 0:

Hydrogen

4Pr

3peak

d E

d m

4He targets

171717

Measurement of Γ(Measurement of Γ(→→) ) in Hall D at 12 in Hall D at 12 GeVGeV

Incoherent tagged photon beam (~10.5-11.5 GeV) Pair spectrometer and a TAC detector for the photon flux control 30 cm liquid Hydrogen and 4He targets (~3.6% r.l.) Forward Calorimeter (FCAL) for → decay photons CompCal and FCAL to measure well-known Compton scattering for control of overall systematic uncertainties.Solenoid detectors and forward tracking detectors (for background rejection)

CompCal

FCAL

η

Approved Beam TimeApproved Beam Time

Days

Setup calibration, checkout

2

Tagger efficiency, TAC runs

1

4He target run 30

LH2 target run 40

Empty target run 6

Total 79

1818

Estimated Error BudgetEstimated Error Budget

Contributions Estimated Error

Photon flux 1.0%

Target thickness 0.5%

Background subtraction 2.0%

Event selection 1.7%

Acceptance, misalignment

0.5%

Beam energy 0.2%

Detection efficiency 0.5%

Branching ratio (PDG) 0.66%

Total Systematic 3.02%

Statistical 1.0%

Systematic 3.02%

Total 3.2%

Systematical uncertainties (added quadratically):

Total uncertainty (added quadratically):

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Transition Form Factors Transition Form Factors F(F(**→→p)p) (at Low Q(at Low Q22))

• Direct measurement of slopesDirect measurement of slopes

– Interaction radii:Interaction radii:FFγγγγ*P*P(Q(Q22))≈1-1/6▪<r≈1-1/6▪<r22>>PPQQ22

– ChPT for large NChPT for large Ncc predicts relation predicts relation between the three slopes. Extraction between the three slopes. Extraction of of ΟΟ(p(p66) low-energy constant in the ) low-energy constant in the chiral Lagrangianchiral Lagrangian

• Input for light-by-light scattering for Input for light-by-light scattering for muon (g-2) calculationmuon (g-2) calculation

• Test of future lattice calculationsTest of future lattice calculations

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SummarySummary Precision measurements of the π0, η and η’ will provide

rich data sets to test the fundamental symmetries of QCD. tests of chiral symmetry and anomaliestests of chiral symmetry and anomalies light quark mass ratiolight quark mass ratio --’ mixing angle’ mixing angle 00,, and and ’ electromagnetic interaction radii’ electromagnetic interaction radii

A comprehensive Primakoff program has been developed A comprehensive Primakoff program has been developed at Jlab to measure at Jlab to measure ΓΓ((pp →→)) and and F(F(**→→p)p) of of π0, η and η’.. Two experiments on Two experiments on ΓΓ((0 0 →→)) were performed in Hall B at 6 GeV. were performed in Hall B at 6 GeV.

PrimEx-I: PrimEx-I: ΓΓ((00) ) 7.82 7.82 0.14(stat.) 0.14(stat.) 0.17(syst.) eV (2.8% total) 0.17(syst.) eV (2.8% total)

Phys. Rev. Lett., 106, 162302 (2011)Phys. Rev. Lett., 106, 162302 (2011)

PrimEx-II was performed and analysis is in progress. The PrimEx-II was performed and analysis is in progress. The 00 lifetime lifetime at level of at level of 1.4% precision 1.4% precision is expected. is expected.

A new precision experiment on A new precision experiment on ΓΓ((ηη→→)) is approved to run in Hall D is approved to run in Hall D at 12 GeVat 12 GeV.. 2121

This project is supported by the U.S. This project is supported by the U.S. National Science Foundation grants PHY-National Science Foundation grants PHY-

0079840 (MRI) and PHY-1206043.0079840 (MRI) and PHY-1206043.

Thank youThank you

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