Test of QCD Symmetries via Measurements on Light Pseudoscalar Mesons

China, 2009China, 2009 Liping Gan, UNCWLiping Gan, UNCW

Test of QCD Symmetries via Test of QCD Symmetries via Measurements on Light Measurements on Light Pseudoscalar MesonsPseudoscalar Mesons

Liping GanLiping Gan

University of North Carolina WilmingtonUniversity of North Carolina Wilmington


ContentsContents

1.1. Physics MotivationPhysics Motivation– Symmetries of QCD Symmetries of QCD – Properties of Properties of ππ00, , ηη and and ηη’’

2.2. PrimEx experimental program at Jlab PrimEx experimental program at Jlab 12 GeV12 GeV– Primakoff experimentsPrimakoff experiments– Rare decays of Rare decays of ηη and and ηη’’


What is symmetry?What is symmetry?SymmetrySymmetry is an invariance of a physical system to a is an invariance of a physical system to a set of changes .set of changes .

Symmetry and symmetry breaking are fundamental in the laws of Symmetry and symmetry breaking are fundamental in the laws of physicsphysics

Noether’s theoremSymmetry Conservation Symmetry Conservation

LawLaw


Continuous Symmetrys of QCD in the Chiral Continuous Symmetrys of QCD in the Chiral LimitLimit

chiral limit:chiral limit: is the limit of vanishing quark masses mis the limit of vanishing quark masses mqq→ 0.→ 0. QCD Lagrangian with quark masses set to zero:QCD Lagrangian with quark masses set to zero:

qq

s

d

u

q

GgD

GGqiDqqiDqL

LR

s

RRLLoQCD

)1(2

1

2/

4

1

5,

)(

Large global symmetry group:Large global symmetry group:

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


Fate of SymmetrysFate of Symmetrys


Discrete Symmetries of QCD Discrete Symmetries of QCD

Charge: CCharge: CParity: PParity: PTime-Reversal: TTime-Reversal: TCombinations: CP, CT, PT, CPTCombinations: CP, CT, PT, CPT


Lightest pseudoscalar mesonsLightest pseudoscalar mesons • Chiral SUChiral SULL(3)XSU(3)XSURR(3) (3)

spontaneously brokenspontaneously broken Goldstone Goldstone mesons mesons ππ00, , ηη88

• Chiral anomaliesChiral anomalies Mass of Mass of ηη00 P→→ ( P: ( P: ππ00, , ηη, , ηη׳׳))

• Quark flavor SU(3) Quark flavor SU(3) breakingbreaking

The mixing of The mixing of ππ00, , ηη and and ηη׳׳

Some Interesting Some Interesting ηη Rare Decay Channels Rare Decay Channels

Mode Branching Ratio Physics Highlight

π0 π0 <3.5 × 10 − 4 CP, P

π0 2γ ( 2.7 ± 0.5 ) × 10 − 4 χPTh, Ο(p6)

π+ π− <1.3 × 10 − 5 CP, P

π0 π0 γ <5 × 10 − 4 C

3γ <1.6 × 10 − 5 C

π0 π0 π0 γ <6<6 ×× 1010 −− 55 C

π0 e+ e− <4<4 ×× 1010 −− 55 C

4π0 <6.9<6.9 ×× 1010 −− 77 CP, P


The The ππ00, , ηη and and ηη’ system provides a rich ’ system provides a rich laboratory to study the symmetry structure of laboratory to study the symmetry structure of QCDQCD..

http://pdglive.lbl.gov/popupblockdata.brl?nodein=S014R37&inscript=Y&fsizein=1&dclumpin0=AN






















































PrimEx Program at JlabPrimEx Program at Jlab

(1) (1) Primakoff experiments Primakoff experiments to measure:to measure:

– Two-Photon Decay Widths: Two-Photon Decay Widths: ΓΓ((ππ0 0 →→) ) @ 6 GeV@ 6 GeV

ΓΓ((ηη → →),), ΓΓ((ηη׳׳ → →)) – Transition Form Factor FTransition Form Factor Fγγγγ*P*P

of of ππ00, , ηη and and ηη׳׳ at low Qat low Q22 (0.001--0.5 GeV(0.001--0.5 GeV22/c/c22))

(2) Measure the branching branching ratios of ratios of ηη and and ηη’’ rare rare decaysdecays

*


Experimental StatusExperimental Status

Decay width Transition Form Factor


Corr. )( ..0 meKKmm

ΓΓ((ηη→→33)=)=ΓΓ((→→))××B.B.R.R.

)(2

1ˆ ,

22

222

duud

s mmmmm

mmQ

Determine the quark masse Determine the quark masse ratioratio


Mixing angles of Mixing angles of ηη--ηη׳׳

• Mixing angles:Mixing angles:

)(cos)(sin

)(sin)(cos00

0

008

008

• DecayDecay constants:

000

888

000

888

cos ,sin

sin ,cos

ffff

ffff

Γ(η/η’ →→)) widths are crucial inputs for obtaining fundamental mixing parameters.


Two-Photon Decay WidthsTwo-Photon Decay Widths

Test chiral anomaly predictions:Test chiral anomaly predictions:

kkF

iA

kkF

iA

kkF

iA

0

8

34

8)(

34)(

4)(

0

8

0

Features of Features of anomaly:anomaly:

•Unique property of the Unique property of the quantum theory.quantum theory.

•Calculable exactly to Calculable exactly to all orders in the chiral all orders in the chiral limitlimit


Number of colors in QCDNumber of colors in QCD • In the past 30 years, many textbooks stated that In the past 30 years, many textbooks stated that Γ(π0 →γγ)

was the best probe to determine the number of quark colors was the best probe to determine the number of quark colors at low energyat low energy

• Recent calculations pointed out that Recent calculations pointed out that Γ(π0→γγ) is less is less sensitive to Nsensitive to Ncc due to partial cancellations of the WZW term due to partial cancellations of the WZW term with a Goldstone-Wilczek termwith a Goldstone-Wilczek term

• The decay amplitude of the single field (The decay amplitude of the single field (η0) depends strongly depends strongly on Non Ncc and yield under the inclusion of mixing also a strong N and yield under the inclusion of mixing also a strong Ncc dependence for the dependence for the η decay decay

• Both the Both the Γ(η→γγ) and and Γ(η’→γγ) decays are suited to decays are suited to confirm the number of colorsconfirm the number of colors


Transition Form Factors at Low QTransition Form Factors 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


Primakoff ProcessPrimakoff Process

22

..4

43

3

2Pr

3

sin)(8

QFQ

E

m

Z

d

dme

Challenge:

Extract the Primakoff amplitude

with unprecedented accuracy

ρ,ω


Cross SectionCross Section

)log(

2

2Pr

4Pr

2

2

Pr

EZd

Ed

dE

m

peak

peak

Features of Primakoff cross section:

•Beam energy sensitiveBeam energy sensitive

•Peaked at very small forward Peaked at very small forward angleangle

•Coherent processCoherent process


PrimEx PrimEx Experiment on Experiment on 00 at 6 at 6 GeVGeV

JLab Hall B high resolution, high intensity photon tagging facility

New pair spectrometer for

photon flux control at high

intensities

New high resolution hybrid multi-channel calorimeter

PrimEx-I Experiment: PrimEx-I Experiment: ΓΓ((00) Decay Width) Decay Width

• Nuclear targets: 12C and 208Pb;

• 6 GeV Hall B tagged beam;

• experiment performed in 2004


12

C208Pb


Projected PrimEx-II



12 GeV Experimental Setup12 GeV Experimental Setup

• New high New high energy photon energy photon taggertagger

• Improved Improved PrimEx PrimEx calorimeter calorimeter HYCAL with all HYCAL with all PbWOPbWO4 4

• Choose the light Choose the light targets targets 44HeHe and and 11HH

China, 2009China, 2009 Liping Gan, UNCWLiping Gan, UNCW23

Proposed Experiment on Proposed Experiment on ΓΓ((ηη→→)) with GlueX with GlueX SetupSetup

General characteristics of proposed experiment:

• Incoherent bremsstrahlung photon beam Eγ =10.5 – 11.7 GeV (~10-4 r.l. Au radiator, 5.0 mm beam collimator)• High resolution, high segmentation HyCal Calorimetor• 30 cm LH2 target (~3.6 r.l.)

75 m

Counting House

Advantages of Hydrogen targetAdvantages of Hydrogen target


• no inelastic hadronic no inelastic hadronic contribution;contribution;

• no nuclear final state no nuclear final state interactions;interactions;

• proton form factor is well proton form factor is well known;known;

• better separation between better separation between Primakoff and nuclear Primakoff and nuclear processes;processes;

• new theoretical new theoretical developments of Regge developments of Regge description of hadronic description of hadronic processes. processes.


Statistics and Beam Time RequestStatistics and Beam Time Request

LH2 target run 45 days

Empty target run 5 days

Tagger efficiency, TAC

3 days

Setup calibration and checkout

7 days

Total 60 days

Target: 30 cm (3.46% r.l.) LH2, Np=1.28x1024 p/cm2

Photon intensity: 7.6x106 γ/sec in Eγ = 10.5–11.7 GeV

Total cross section on P for θη=0 - 3.50,

Δσ = 1.1x10-5 mb (10% is Primakoff). N(evts) = Np x Nγ x Δσ x ε(eff.)x(Br. Ratio)

= 1.28x1024x7.6x106x1.1x10-

32x0.6x0.4 = 2.6 x 10-2 events/sec

= 2200 events/day = 220 Primakoff events/day

Statistics: 45 days of run on LH2:

1% stat. error

Beam time request:


Estimated Error Budget on Estimated Error Budget on ΓΓ((ηη →→))

Contributions Estimated Error

Photon flux 1.0%

Target number 0.5%

Background subtraction 1.0%

Event selection 0.8%

Acceptance, misalign. 0.5%

Beam energy 0.2%

Branching ratio (PDG) 0.66%

Total Systematic 1.9%

Statistical error 1.0%

Systematic error 1.9%

Total Error 2.2%

Systematical errors:

Total estimated error:

Some Some ηη Rare Decay Channels Rare Decay Channels

Mode Branching Ratio Physics Highlight

π0 π0 <3.5<3.5 ×× 1010 −− 44 CP, P

π0 2γ (( 2.72.7 ±± 0.50.5 )) ×× 1010 −− 44 χPTh, Ο(p6)

π+ π− <1.3<1.3 ×× 1010 −− 55 CP, P

π0 π0 γ <5<5 ×× 1010 −− 44 C

3γ <1.6<1.6 ×× 1010 −− 55 C

π0 π0 π0 γ <6<6 ×× 1010 −− 55 C

π0 e+ e− <4<4 ×× 1010 −− 55 C

4π0 <6.9<6.9 ×× 1010 −− 77 CP, P



Study ofStudy of ηη→→0 0 0 0 ReactionReaction

• The Origin of CP violation is still a mysteryThe Origin of CP violation is still a mystery

• CP violation is described in SM by the phase in the Cabibbo-CP violation is described in SM by the phase in the Cabibbo-Kobayashi-Maskawa quark mixing matrix. A recentKobayashi-Maskawa quark mixing matrix. A recent SM SM calculation predicts BR(calculation predicts BR(ηη→→0 0 00)<3x10)<3x10-17-17

• The The ηη→→0 0 0 0 is one of a few available flavor-conserving is one of a few available flavor-conserving reactions listed in PDG to test CP violation.reactions listed in PDG to test CP violation.

• Unique test of P and PC symmetries, and search for new Unique test of P and PC symmetries, and search for new

physics beyond SMphysics beyond SM


History of the History of the ηη→→00 Measurements Measurements

A long standing “η” puzzle is still un-settled.

After 1980


High Energy High Energy η η Production Production((GAMS Experiment on GAMS Experiment on ηη→→00 at Serpukhov at Serpukhov))

• Experimental result was first Experimental result was first published in 1981published in 1981

• The The ηη’s were produced with ’s were produced with 30 30 GeV/cGeV/c -- beam in the beam in the --pp→η→ηn n reactionreaction

• Decay Decay ’s were detected by lead-’s were detected by lead-glass calorimeterglass calorimeter

Major BackgroundMajor Background --pp→ → 0000n n • η →η →000000

Final result Final result (D. Alde (D. Alde et et al.al.))

~40 of ~40 of ηη→→00 events events

BR(BR(η→η→00γγγγ)=(7.1±1.4)x10)=(7.1±1.4)x10-4-4

((η→η→00γγγγ)=0.84±0.17 eV)=0.84±0.17 eV

Low energy Low energy η η production production (CB experiment on (CB experiment on ηη→→00 at AGS, at AGS, by S. Prakhov by S. Prakhov et al. )et al. )

• The The ηη’s were produced with ’s were produced with 720720 MeV/c MeV/c -- beam through beam through the the --pp→η→ηn reactionn reaction

• Decay Decay ’s energy range: 50-’s energy range: 50-500 MeV500 MeV

η η →→00 00 00 -p-p→ → 00 00 nn

Final resultFinal result

1600 of 1600 of ηη→→00 events events

((η→η→00γγγγ)=0.45±0.12 eV)=0.45±0.12 eVChina, 2009China, 2009 Liping Gan, UNCWLiping Gan, UNCW

July, 2009July, 2009 Liping Gan, UNCWLiping Gan, UNCW

What can be improved at 12 GeV Jlab?What can be improved at 12 GeV Jlab?• High energy tagged photon beam High energy tagged photon beam to reduce the background from to reduce the background from

η→ η→ 3300

Lower relative threshold for Lower relative threshold for -ray detection-ray detection Improve calorimeter resolution Improve calorimeter resolution

• Tag Tag ηη by measuring recoiled particles to reduce non- by measuring recoiled particles to reduce non-resonance resonance 0000 backgroundbackground

• High resolution PWO Calorimeter High resolution PWO Calorimeter Higher energy resolution → improve Higher energy resolution → improve 00γγγγ invariance mass invariance mass Higher granularity→ better position resolution and less overlap clustersHigher granularity→ better position resolution and less overlap clusters

• Large statistics Large statistics to provide a precision measurement of Dalitz plot to provide a precision measurement of Dalitz plot

30 GeV/cE 720 MeV/cE

production 1020 MeV

s


Suggested Experiment in Hall D at JlabSuggested Experiment in Hall D at Jlab

75 m

Counting HousePhoton

TaggerGlueX FCAL

• ηη produced on LH produced on LH22 target with target with 11 11 GeV tagged photon beam GeV tagged photon beam γγ+p+p → → ηη+p+p

• Tag Tag ηη by measuring recoil p with by measuring recoil p with GlueX detectorGlueX detector

• Forward calorimeter with Forward calorimeter with PWO PWO insertioninsertion to detect multi-photons to detect multi-photons from the from the ηη decay decay

Simultaneously measure the η→0, η →00:

July, 2009July, 2009 Liping Gan, UNCWLiping Gan, UNCW

S/N Ratio vs. Calorimeter GranularityS/N Ratio vs. Calorimeter Granularity

PWO

dmin=4cm

S/N=1.4

Pb Glass

dmin=8cm

S/N=0.024


SummarySummary

Fundamental input to Fundamental input to Physics:Physics:

•Determination of quark mass Determination of quark mass ratioratio•Mixing parameters Mixing parameters ⇒ ⇒ decaydecay constants and mixing angles constants and mixing angles of of η―ηη―η׳׳•Test chiral anomaly Test chiral anomaly predictionspredictions•Confirm number of colors NConfirm number of colors Ncc

•ΟΟ(p(p66) low-energy-constant in ) low-energy-constant in Chiral LagrangianChiral Lagrangian

Test P, CP and C symmetries, and search for new physics beyond Standard Model

(1) (1) Primakoff experiments Primakoff experiments to to measure:measure:– Two-Photon Decay Widths: Two-Photon Decay Widths:

Γ Γ((0 0 →→),), ΓΓ((ηη→→),), ΓΓ((ηη׳׳ → →))– Transition Form Factor FTransition Form Factor Fγγγγ*P*P

of of ππ00, , ηη and and ηη׳׳ at low Qat low Q22 (0.001-0.5 GeV(0.001-0.5 GeV22/c/c22))

(2) Measure the branching branching ratios for ratios for ηη and and ηη’ ’ rare rare decaysdecays

Oct 31, 2008Oct 31, 2008 Liping Gan, UNCWLiping Gan, UNCW

Invariant Mass ResolutionInvariant Mass Resolution

PWO

Pb glassσ=15 MeV

σ=6.9 MeVσ=3.2 MeV

σ=6.6 MeV

M M00

M00M


Why do we need 12 GeV beam?Why do we need 12 GeV beam?

)log( 2Pr

4Pr EZdEd

d

peak

Increase Primakoff cross section:

Better separation of Primakoff reaction from nuclear processes:

Momentum transfer to the nuclei becomes less reduce the incoherent background

Unique CEBAF beam quality

3/12

2

Pr

2

2 AEE

mNCpeak

Challenges in Modern Physics Challenges in Modern Physics

The properties of strong force at large distance represents one of the The properties of strong force at large distance represents one of the biggest intellectual challenges in physics.biggest intellectual challenges in physics.

Color confinementColor confinement: the potential energy between (in this case) a quark and an antiquark increases while increasing the distance between them.

• What are the building blocks of matter?

• What happens if one tries to separate two quarks?

Solution: Understanding symmetries of nature

Strong force

Strong force obeys the rules of Quantum Chromodynamics (QCD)



Experimental Resolutions: Prod. Angle Experimental Resolutions: Prod. Angle

Precision Primakoff measurement requires high resolutions in:

• Production angle (fit);

• Invariant mass (background)

• Energy (elasticity)


Experimental Resolutions (contd.) Experimental Resolutions (contd.) γγ invariant mass Energy conservation

(elasticity)

High resolution, high granularity calorimeter is critical in:• event selection;• extraction of Primakoff from hadronic processes


PrimEx 12 GeV Project HistoryPrimEx 12 GeV Project History

•This program had been reviewed by 3 special high energy PACs:

PAC18 (2000)PAC23 (2003)PAC27 (2005)

• It is included in the CEBAF 12 GeV CDR With the following statement in the Abstract:

“… Precision measurements of the two-photon decay widths and transition form factors of the three neutral pseudoscalar mesons via the Primakoff effect will lead to a significant improvement on our knowledge of chiral symmetry in QCD, in particular on the ratios of quark masses and on chiral anomalies.”


Low Energy Low Energy η η Production Continue Production Continue

(KLOE, by B. Micco et al., Acta Phys. Slov. 56 (2006) 403)(KLOE, by B. Micco et al., Acta Phys. Slov. 56 (2006) 403)

• Produce Produce ΦΦ through e through e+ee- collision at collision at √s~1020 MeV√s~1020 MeV

• The decay The decay η→η→00γγγγproceeds through: proceeds through: Φ→Φ→ηη, , η→η→00γγγγ, , 00→→γγγγ

Final resultFinal result68±23 of 68±23 of ηη→→00 events events

BR(BR(η→η→00γγγγ)=(8.4±2.7±1.4)x10)=(8.4±2.7±1.4)x10-5-5

((η→η→00γγγγ)=0.109±0.035±0.018 eV)=0.109±0.035±0.018 eV


Determine the quark masse Determine the quark masse ratioratio

)(2

1ˆ ,

22

222

duud

s mmmmm

mmQ

..)()3( RB

There are two ways to determine the quark mass ratio:

•Γ(η→3π) is the best observable for determining the quark mass ratio, which is obtained from Γ(η→γγ) and known branching ratios:

•The quark mass ratio can also be given by a ratio of The quark mass ratio can also be given by a ratio of meson masses: meson masses:

)(1)(

222

22

2

22 m

mm

mm

m

mQ

QCDKK

kk

o

Documents

Test of QCD Symmetries via Measurements on Light Pseudoscalar Mesons