Physics and Outlook for Eta Rare Decays at Physics and Outlook for Eta Rare Decays at Jlab Jlab

Liping GanLiping GanUniversity of North Carolina WilmingtonUniversity of North Carolina Wilmington

Physics MotivationPhysics Motivation• Why the Why the ηη is unique for symmetry tests is unique for symmetry tests• ChPT, C-violating and P-conserving new physics ChPT, C-violating and P-conserving new physics

Proposed Proposed η η rare decay experiment in Hall Drare decay experiment in Hall D

CLAS data mining in Hall BCLAS data mining in Hall B

Summary and discussionSummary and discussion

OutlineOutline

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““We have to remember that what we observe We have to remember that what we observe is not nature herself, but nature exposed to is not nature herself, but nature exposed to our method of questioning.”our method of questioning.”

Werner HeisenbergWerner Heisenberg

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Challenges in PhysicsChallenges in Physics

Confinement QCDConfinement QCD Chiral perturbation theory (ChPT)Chiral perturbation theory (ChPT) Lattice QCDLattice QCD

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QCD at different energies

New physics beyond the New physics beyond the Standard Model (SM)Standard Model (SM) New sources of symmetry New sources of symmetry

violation violation Dark matterDark matter Dark energyDark energy

Why Why ηη is a unique probe is a unique probe

η decay width Γη =1.3KeV is narrow (relative to Γ=8.5 MeV)The lowest orders of η decays are filtered out, enhancing the contributions from higher orders by a factor of ~7,000 compared to decays.

A Goldstone boson due to spontaneous breaking of QCD chiral symmetry is one of key mesons bridging our understanding of low-energy hadron dynamics and underlying QCD

Eigenstate of P, C, CP, and G: Study violations of discrete symmetries

G PCI J =0 0

The η decays are flavor-conserving reactions effectively free of SM backgrounds for new physics search.

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The η Decay Modes

PDG 2011

5

The light blue sliver represents BR = 0.7%.

All other η rare decays would be invisible on

this pie chart.

ηη Neutral Decays Neutral Decays Mode Branching

Ratio(PDG)

Physics Highlight

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

3γ <1.6<1.6  ××  1010  −−  55 C

2π0 <3.5<3.5  ××  1010  -4-4 CP, P

4γ <2.8<2.8  ××  1010  -4-4 Suppressed (<10-11)

2π0 γ <5<5  ××  1010  −−  44 C

π0 γ <9<9  ××  1010  −−  55 C, L, gauge inv.

3π0 γ <6<6  ××  1010  −−  55 C

4π0 <6.9<6.9  ××  1010  −−  77 CP, P

3π0 (32.57(32.570.23)%0.23)% Quark mass md-mu

2γ (39.31(39.310.20)%0.20)% Anomaly, ’ mixing By PrimEx

Allowed Rare DecayAllowed Rare Decay ηη→→00

Precision measurements of both the branching ratio and the Dalitz distribution of →0 are critical to model-independently determine two Low Energy Constants (LEC’s) of the O(p6) counter-terms in the chiral Lagrangian.

ChPT is highly developed and well-tested in the domain of pionic and kaonic reactions. →0 is one of a few important channels to benchmark the success of ChPT in the -sector.The major contributions to →0 are two O(p6) counter-terms in the chiral Lagrangian a rare window for the high order ChPT contributions.

counter-termO(p6)

L. Ametller, J. Bijnens et. al., Phys. Lett., B276, 185

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ηη→→00 and Other Rare Decays and Other Rare Decays →0 is an important “door-way” channel for interpretation of other rare decays searching for new sources of C- or CP-violation KL Sector: CP violation search KL →0l+l-

Sector: C and CP search →0l+l-

CP conserving background

L.M. Sehgal, Phys. Rev., D38, 808 (1988)

A cross-check of LEC's with different processes test the foundations of ChPT.

C and CP conserving background

C and CP violating

J.N. Ng, et al., Phys. Rev., D46, 5034 (1992)

KL π0 2γ was recently measured by KTeV to estimate the CP conserving contributions

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CP violating

Status of Status of ηη→→00: Partial Decay Width: Partial Decay Width

99

0.33 0.08

There have been about 20 experiments since 1966.

Experiments After 1980

PTh by Oset et al., Phys. Rev. D77, 07300 (2008)

Average ~0.44 eV

1010

Prakhov et al., Phys. Rev. C78, 015206 (2008)

Status of Status of η→η→00: Dalitz Distribution: Dalitz Distribution

Combined BR and Dalitz measurement model-independent determination of two LEC’s of the O(p6) counter- terms in the chiral Lagrangian

Projected JEF

CB-AGS

Measurement of Measurement of ηη→→330 0

1111

→30 is the most promising channel to determine an accurate light quark mass ratio.

Recent experimental results are from the low energy -production facilities and more sensitive to the threshold effect in the -detection. Proposed measurement at high energy will be comparable to existing data in statistics but significant different systematics.

Offers an independent experimental verification.

Slope

32i

i=1

T2Z= -13 T（ ）

Phys. Lett., B694, 16 (2010)

Exp.

Theory

2 2

2 2 2

1 ,d u

s

m mQ m m

2d um mm

4

QQDT

zzA 21)( 2000

The Four Classes of C, P, and T Violations The Four Classes of C, P, and T Violations (Assuming CPT Invariance) (Assuming CPT Invariance)

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For class 4: For class 4: few experimental probes available few experimental probes available not well tested experimentally for EM and strong interactions not well tested experimentally for EM and strong interactions The current constraint: 1 GeV EDMs place an ambiguous constraint on the new TVPC physics;EDMs place an ambiguous constraint on the new TVPC physics; “ “new TVPC physics could arise at scales as light as a few GeV.” new TVPC physics could arise at scales as light as a few GeV.” ((M. Ramsey-Musolf et. al., phys. Rev., D63, 076007 (2001) ))

B. Nefkens and J. Price, Phys. Scrip., T99, 114 (2002)

Experimental probes

EDM, even ’s

P-violating exp., -decays,K-, B-, D-meson decaystests involving , ’, , , J/ decays

C InvarianceC Invariance Maximally violated in the weak Maximally violated in the weak

interaction and is well tested.interaction and is well tested.

Assumed in SM for both the Assumed in SM for both the electromagnetic (EM) and strong electromagnetic (EM) and strong interactions, but interactions, but it is not it is not experimentally well tested. experimentally well tested.

C-violating C-violating η η decays will provide decays will provide unambiguous, direct constraints unambiguous, direct constraints on new C-violating and P-on new C-violating and P-conserving physics (class 4). conserving physics (class 4).

Testing C-invariance will provide a better understanding of new source of CP violation asymmetry in SM: left handed doublets and right-

handed singlets.

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Final State

Branching Ratio

(upper limit)

Gammas in

Final State

3γ < 1.6•10-5

3 π0γ < 9•10-5

2π0γ < 5•10-4

5 3γπ0 Nothing

published

3π0γ < 6•10-5

7 3γ2π0 Nothing

published

C Violating η neutral decays

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Experimental ImprovementExperimental Improvement on on ηη→→33γγ

The upper limit for the branching ratio at ~90% CL is estimated by:

BR upper limit

2 bkg

accep

fN

SM contribution: BR(η→3γ) <10-19 via P-violating weak interaction. A new C- and T-violating, and P-conserving interaction was proposed by Bernstein, Feinberg and Lee (Phys. Rev., B139, 1650).

A calculation due to such new physics by Tarasov suggests: BR(3)< 10-2 ( ) (Sov.J.Nucl.Phys., 5, 445)

Improve BR upper limit by one order of magnitude to tighten the constraint on C-violating, P-conserving new physics

Proj. JEF

1~newf

P and CP ViolatingP and CP Violating ηη→→0 0 0 0

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The nEDM measurements access the static property of the particle. A non- zero nEDM violates P and T directly, and indirectly violates CP under the assumption of CPT conservation.The →20 decay is related to a dynamic process and it violates P and CP directly. →20 is flavor-conserving counterpart of the corresponding flavor-changing CP-violating KL →20.

Proj. JEF

World Competition in η Decays

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JEF at Jlab

Low energy -facilities

High energy -facility

CBELSA/TAPS at ELSA

e+e-

Collider

Fixed-target

photoproduction

hadroproduction

Filter Background with Filter Background with ηη Energy Boost ( Energy Boost (00))

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Major BackgroundMajor Background η →η →00000066 --pp→ → 000 0 ++ neutronneutron

GAMS ExperimentGAMS Experiment --pp→η→η p ( p ( EE= 30 GeV= 30 GeV ) )

Jlab:Jlab: pp→η→ηpp (E = 9-11.7 GeV)

CB-AGS ExperimentCB-AGS Experiment --pp→η→η p p ((EE=730 MeV=730 MeV))

η η →→00 00 00

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Proposed Experiment in Hall D Proposed Experiment in Hall D

Simultaneously measure η neutral decays: η→0, η→3, and …

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ηη produced on LH produced on LH22 target with target with 9-11.7 GeV tagged photon beam9-11.7 GeV tagged photon beam: : γγ+p+p → → ηη+p+p Reduce non-coplanar backgrounds by by detecting recoil p’sdetecting recoil p’s

with GlueX detector with GlueX detector Upgraded Forward Calorimeter with Upgraded Forward Calorimeter with High resolution, high granularityHigh resolution, high granularity PbWOPbWO44 ( (FCAL-IIFCAL-II) to detect multi-photons from the ) to detect multi-photons from the ηη decays decays

FCAL

Detection of Recoil Proton with GlueXDetection of Recoil Proton with GlueX

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Recoil proton kinematicsRecoil proton kinematics Polar angle ~55Polar angle ~55oo-80-80oo

Momentum ~200-1200 Momentum ~200-1200 MeV/cMeV/c

New Equipment: FCAL-IINew Equipment: FCAL-II

2020

PrimEx HyCal FCAL-II: 118x118 cm2 in Size (3445 PbWO4)2cm x 2cm x 18cm per module

FCAL-II (PbWO4) vs. FCAL (Pb glass)

Property Improvement factor

Energy σ 2Position σ 2

Granularity 4Radiation-resistance 10

S/N Ratio vs. Calorimeter TypesS/N Ratio vs. Calorimeter Typessignalsignal: , background: : , background: 0 03

FCAL-II (PbWO4)

FCAL (Pb glass)

S/N=10:1

S/N=0.1:1

Hadronic Backgrounds Reduction in 4Hadronic Backgrounds Reduction in 4 States States

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Event SelectionElasticity is EL=ΣE/ Etagged-

Energy conservation for γγ+p+p → → ηη+p +p reactionreaction: ΔE=E()+E(p)-E(beam)-M(p)

Co-planarity Δ= ()- (p)

Note: Statistics is normalized to 1 beam day.BG will be further reduced by requiring that only one pair of ’s have the 0 invariant mass.

Signal: 0

Rate EstimationRate Estimation

23 24 20.0708 30 6.022 10 1.28 10 p/cm1p A

LN NA

The The +p+p→→ηη+p cross section ~70 nb +p cross section ~70 nb ((J.M. Laget , Phys.Rev. , C72, 022202 (2005) and A. Sibirtsev et al. Eur.Phys.J., A44, 169 (2010)))

Photon beam intensity Photon beam intensity NNγγ~4x10~4x1077 Hz Hz (for E(for Eγγ~9-11.7 GeV)~9-11.7 GeV)

• The The ηη→→00 detection rate: detection rate: BR(BR(ηη→→00 )~2.7x10 )~2.7x10-4 -4

Average geometrical acceptance is ~20% (118x118 cmAverage geometrical acceptance is ~20% (118x118 cm22 FCAL- FCAL-II)II)

Event selection efficiency ~70%Event selection efficiency ~70% 2222

05 43.1 10 2.7 10 0.2 0.70 12 events/day N

Jlab Eta Factory (JEF)

7 24 33

5

4 10 1.28 10 70 10

3.6 Hz

3.1 10 ( 's/day)

pN N N

Beam Time RequirementBeam Time Requirement

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Run type Beam Time (days)

LH2 Production 100

Empty target and target out 7

Tagger efficiency, TAC runs 3

FCAL-II commissioning, Calibration

12

Luminosity optimization 14

Total 136

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Projected JEF ResultsProjected JEF Results

Proj. JEFBR U

pper

Lim

it

BR U

pper

Lim

it

𝜂 𝜂 Charged ModesCharged Modes

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Extension of PhysicsExtension of Physics 𝜂𝜂 ˈ ˈ decaysdecays Dark photon searchDark photon search: 𝜂: 𝜂→→γγUU ( (U →eU →e++ee--))

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��

CLAS data mining in Hall BCLAS data mining in Hall B(by M. Amaryan et. al.)(by M. Amaryan et. al.)

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SummarySummary 12 GeV tagged photon beam with GlueX setup will provide a great

opportunity for precise measurements. It offers two orders of magnitude reduction of the backgrounds of neutral rare η decays compared to other facilities in the world.

Perform a simultaneous measurement of η decays to all neutral final states: η→0, measure BR (~4% precision) and Dalitz distribution to

determine two O(p6) LEC’s in the chiral Lagrangian. Improve BR upper limits by 1-2 orders of magnitude for SM

forbidden decays (potentialy 2-3 orders of magnitude): η →3 and other C-violating neutral channels offer the best window for C-

violating and P-conserving new physics. η →00 is a direct P- and CP-violation test, and a flavor-conserving counterpart

of the corresponding flavor-changing P- and CP-violating KL →20 . A new measurement on η →30 with a significant different

systematics to constrain the light quark mass ratio.

Extend to η charged decay channels and η’ decays. Dark photon search: 𝜂→γU (U →e+e-)

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Call for theoretical supportCall for theoretical support

Feasibility:Feasibility: ““The proposed measurements appear to be feasible and the experiment The proposed measurements appear to be feasible and the experiment is well suited for the tagged Hall D photon beam.” is well suited for the tagged Hall D photon beam.”

Issues: Issues:

““The PAC recognizes the scientific interest of performing new The PAC recognizes the scientific interest of performing new measurements of rare eta decays with improved sensitivity to test the SM. measurements of rare eta decays with improved sensitivity to test the SM. However, the PAC identified some issues, mainly related to the theoretical However, the PAC identified some issues, mainly related to the theoretical implications of these measurements.”implications of these measurements.”

“ “For the SM forbidden decays more work should be done to identify For the SM forbidden decays more work should be done to identify physics scenarios which could imply branching ratios closer to the physics scenarios which could imply branching ratios closer to the experimental sensitivities. The PAC suggests that these issues be experimental sensitivities. The PAC suggests that these issues be addressed in close collaboration with the theory community working in this addressed in close collaboration with the theory community working in this field, which should be involved in helping strengthen the physics case.”field, which should be involved in helping strengthen the physics case.”

““Similar remarks apply to the impact the η → πSimilar remarks apply to the impact the η → π00 2γ decay (as well as the 2γ decay (as well as the main background channel η → 3πmain background channel η → 3π00 which is offered as a means to constrain which is offered as a means to constrain the light quark mass ratio from the slope of the Dalitz distribution) would the light quark mass ratio from the slope of the Dalitz distribution) would have on chiral perturbation theory. “have on chiral perturbation theory. “

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Jlab PAC40 report on the JEF proposal

The EndThe End

Thanks you!Thanks you!

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Tests of C Invariance (PDG 2012) Tests of C Invariance (PDG 2012)

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