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Physics and Outlook for Eta Rare Decays at Jlab

Physics and Outlook for Eta Rare Decays at Jlab. Liping Gan University of North Carolina Wilmington. Physics Motivation Why the η is unique for symmetry tests ChPT, C-violating and P-conserving new physics Proposed η rare decay experiment in Hall D CLAS data mining in Hall B

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Physics and Outlook for Eta Rare Decays at Jlab

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  1. Physics and Outlook for Eta Rare Decays at Jlab Liping Gan University of North Carolina Wilmington • Physics Motivation • Why the η is unique for symmetry tests • ChPT, C-violating and P-conserving new physics • Proposed η rare decay experiment in Hall D • CLAS data mining in Hall B • Summary and discussion Outline

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

  3. Challenges in Physics QCD at different energies • Confinement QCD • Chiral perturbation theory (ChPT) • Lattice QCD • New physics beyond the Standard Model (SM) • New sources of symmetry violation • Dark matter • Dark energy

  4. Why η is a unique probe • 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 • 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. • Eigenstate of P, C, CP, and G: Study violations of discrete symmetries • The η decays are flavor-conserving reactions effectively free of • SM backgrounds for new physics search.

  5. The η Decay Modes The light blue sliver represents BR = 0.7%. All other η rare decays would be invisible on this pie chart. PDG 2011

  6. η Neutral Decays

  7. Allowed Rare Decayη→0 • 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. L. Ametller, J. Bijnens et. al., Phys. Lett., B276, 185 O(p6) counter-term • 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.

  8. η→0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- CP conserving background CP violating  L.M. Sehgal, Phys. Rev., D38, 808 (1988) KLπ0 2γ was recently measured by KTeV to estimate the CP conserving contributions •  Sector: C and CP search →0l+l- C and CP violating C and CP conserving background J.N. Ng, et al., Phys. Rev., D46, 5034 (1992) • A cross-check of LEC's with different processes • test the foundations of ChPT.

  9. Status of η→0: Partial Decay Width There have been about 20 experiments since 1966. Experiments After 1980 Average ~0.44 eV PTh by Osetet al., Phys. Rev. D77, 07300 (2008)

  10. Status of η→0: Dalitz Distribution Prakhovet al., Phys. Rev. C78, 015206 (2008) CB-AGS Projected JEF Combined BR and Dalitz measurement model-independent determination of two LEC’s of the O(p6) counter- terms in the chiral Lagrangian

  11. Measurement of η→30 Phys. Lett., B694, 16 (2010) •  →30 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. Exp. Slope Theory

  12. The Four Classes of C, P, and T Violations (Assuming CPT Invariance) B. Nefkens and J. Price, Phys. Scrip., T99, 114 (2002) Experimental probes P-violating exp., -decays, K-, B-, D-meson decays EDM, even ’s tests involving , ’, , , J/ decays • For class 4: • few experimental probes available • not well tested experimentally for EM and strong interactions • Thecurrent constraint:  1 GeV • EDMs place an ambiguous constraint on the new TVPC physics; • “new TVPC physics could arise at scales as light as a few GeV.” • (M. Ramsey-Musolf et. al., phys. Rev., D63, 076007 (2001))

  13. C Invariance C Violating η neutral decays • Maximally violated in the weak interaction and is well tested. • Assumed in SM for both the electromagnetic (EM) and strong interactions, but it is not experimentally well tested. • C-violating η decays will provide unambiguous, direct constraints on new C-violating and P-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.

  14. Experimental Improvement on η→3γ • 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 The upper limit for the branching ratio at ~90% CL is estimated by:

  15. P and CP Violatingη→0 0 Proj. JEF • 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  →20 decay is related to a dynamic process and it violates P and CP • directly. •  →20 is flavor-conserving counterpart of the corresponding • flavor-changing CP-violating KL →20.

  16. World Competition in η Decays e+e- Collider Low energy -facilities High energy -facility hadroproduction Fixed-target CBELSA/TAPS at ELSA JEF at Jlab photoproduction

  17. Filter Background with η Energy Boost (0) CB-AGS Experiment -p→η p(E=730 MeV) Jlab:p→ηp(E =9-11.7 GeV) η →000 GAMS Experiment -p→η p ( E= 30 GeV) • Major Background • η →0006 • -p→ 00 +neutron

  18. Proposed Experiment in Hall D FCAL Simultaneously measure ηneutral decays:η→0, η→3, and … • η produced on LH2 target with 9-11.7 GeV tagged photon beam: • γ+p → η+p • Reducenon-coplanar backgrounds by detecting recoil p’swith GlueX detector • Upgraded Forward Calorimeter with High resolution, high granularity • PbWO4 (FCAL-II) to detect multi-photons from the η decays 18

  19. Detection of Recoil Proton with GlueX • Recoil proton kinematics • Polar angle ~55o-80o • Momentum ~200-1200 MeV/c

  20. New Equipment: FCAL-II PrimEx HyCal FCAL-II: 118x118 cm2 in Size (3445 PbWO4) 2cm x 2cm x 18cm per module S/N Ratio vs. Calorimeter Typessignal: , background: FCAL (Pb glass) FCAL-II (PbWO4) vs. FCAL (Pb glass) S/N=0.1:1 FCAL-II (PbWO4) S/N=10:1

  21. Hadronic Backgrounds Reduction in 4 States • Event Selection • Elasticity is • EL=ΣE/Etagged- • Energy conservation • for γ+p → η+p reaction: • 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

  22. Rate Estimation • The +p→η+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 Nγ~4x107 Hz (for Eγ~9-11.7 GeV) Jlab Eta Factory (JEF) • The η→0 detection rate: • BR(η→0 )~2.7x10-4 • Average geometrical acceptance is ~20% (118x118 cm2 FCAL-II) • Event selection efficiency ~70%

  23. Beam Time Requirement

  24. Projected JEF Results BR Upper Limit BR Upper Limit Proj. JEF

  25. 𝜂 Charged Modes

  26. Extension of Physics • 𝜂ˈ decays • Dark photon search: 𝜂→γU (U →e+e-) 𝜂

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

  28. Summary • 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 →00 is a direct P- and CP-violation test, and a flavor-conserving counterpart of the corresponding flavor-changing P- and CP-violating KL →20 . • A new measurement on η →30 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-)

  29. Call for theoretical support Jlab PAC40 report on the JEF proposal • Feasibility: “The proposed measurements appear to be feasible and the experiment is well suited for the tagged Hall D photon beam.” • Issues: • “The PAC recognizes the scientific interest of performing new measurements of rare eta decays with improved sensitivity to test the SM. However, the PAC identified some issues, mainly related to the theoretical implications of these measurements.” • “For the SM forbidden decays more work should be done to identify physics scenarios which could imply branching ratios closer to the experimental sensitivities. The PAC suggests that these issues be addressed in close collaboration with the theory community working in this field, which should be involved in helping strengthen the physics case.” • “Similar remarks apply to the impact the η → π0 2γ decay (as well as the main background channel η → 3π0 which is offered as a means to constrain the light quark mass ratio from the slope of the Dalitz distribution) would have on chiral perturbation theory. “

  30. The End Thanks you!

  31. Tests of C Invariance (PDG 2012)

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