The η Rare Decays in Hall D Liping Gan University of North Carolina Wilmington Oct 31, 2008 Liping Gan, UNCW

Contents Physics Motivation Why η meson is interesting? η→0 η→00 Experimental Design Calorimeter Requirement Summary Oct 31, 2008 Liping Gan, UNCW

Why η Meson Is Interesting? One of the Goldstone bosons due to spontaneous chiral symmetry breaking The heaviest member in the octet pseudoscalar mesons Provide a rich program to investigate evidences of symmetry breaking and the new physics beyond Standard Model Oct 31, 2008 Liping Gan, UNCW

The Neutral η Decay (from B.Nefkens) Oct 31, 2008 Liping Gan, UNCW

Study of the η→0 Decay A stringent test of the χPTh prediction at Ο(p6) level Tree level amplitudes (both Ο(p2) and Ο(p4)) vanish; Ο(p4) loop terms involving kaons are suppressed large mass of kaon Ο(p4) loop terms involving pions are suppressed by G parity The first sizable contribution comes at Ο(p6) level A long history that experimental results have large discrepancies with theoretic predictions. Current experimental limits in PDG is BR(η→0 )<4.4x10-4 Oct 31, 2008 Liping Gan, UNCW

Study of η→0 0 Reaction The Origin of CP violation is still a mystery CP violation is described in SM by the phase in the Cabibbo-Kobayashi-Maskawa quark mixing matrix. A recent SM calculation predicts BR(η→0 0)<3x10-17 The η→0 0 is one of a few available flavor-conserving reactions listed in PDG to test CP violation. Current experimental limit in PDG is BR(η→0 0)<4.3x10-4 Unique test of P and PC symmetries, and search for new physics beyond SM Oct 31, 2008 Liping Gan, UNCW

History of the η→0 Measurements After 1980 A long standing “η” puzzle is still un-settled. Oct 31, 2008 Liping Gan, UNCW

GAMS Experiment on η→0 at Serpukhov Experimental result was first published in 1981 The η’s were produced with 30 GeV/c - beam in the -p→ηn reaction Decay ’s were detected by lead-glass wall Final result (D. Alde et al.) ~40 of η→0 events BR(η→0γγ)=(7.1±1.4)x10-4 (η→0γγ)=0.84±0.17 eV Major Background -p→ 00n η →000 Oct 31, 2008 Liping Gan, UNCW

CB experiment on η→0 at AGS About 3x107 η’s data were collected in 1998 at AGS, BNL The η’s were produced with 720 MeV/c - beam through the -p→ηn reaction NaI crystal ball calorimeter with 672 modules Decay ’s energy range: 50-500 MeV Oct 31, 2008 Liping Gan, UNCW

CB Data Analysis I (by S. Prakhov et al. in 2005) η →000 -p→ 00n Final result 1600 of η→0 events BR(η→0γγ)=(3.5±0.9)x10-4 (η→0γγ)=0.45±0.12 eV Oct 31, 2008 Liping Gan, UNCW

What can be improved? KLOE GAMS-2000 CB collaboration Tagged η to reduce non-resonance 00 background Higher beam energy to reduce the background from η→ 00 0 Lower relative threshold for -ray detection Improve calorimeter resolution Calorimeter with PWO4 insertion Higher energy resolution → improve 0γγinvariant mass Higher granularity→ better position resolution and less overlap clusters Large statistics to provide a precision measurement of Dalitz plot KLOE GAMS-2000 CB collaboration Oct 31, 2008 Liping Gan, UNCW

Experimental Design In Hall D η produced on LH2 target with 11 GeV tagged photon beam Tag η by measuring recoil p with GlueX Forward calorimeter with PWO4 insertion to detect multi-photons from the η decay Oct 31, 2008 Liping Gan, UNCW

Kinematics of Recoil Proton Recoil Pp vs θη (Deg) Angle θη (Deg) Polar angle ~55o-80o Momentum ~300-1400 MeV/c Recoil θp (Deg) vs Pp (GeV) Oct 31, 2008 Liping Gan, UNCW

Missing Mass E=11.5 Gev ΔP/P=1.5% Δθ=7 mrad Missing Mass (GeV) Oct 31, 2008 Liping Gan, UNCW

Invariant Mass Resolution σ=6.9 MeV σ=3.2 MeV PWO M0 M σ=6.6 MeV σ=15 MeV Pb glass M M0 Oct 31, 2008 Liping Gan, UNCW

Requirement on Calorimeter Granularity PWO D=4cm S/N=1.4 PWO D=6cm S/N=0.29 Minimum separation between two showers better than 4cm is required Pb Glass D=8cm S/N=0.024 Pb Glass D=12cm S/N=0.011 Oct 31, 2008 Liping Gan, UNCW

Minimum size of the Calorimeter (GeV) Det size (cm2) Hole size (cm2) Acceptance (%) 9 100×100 6×6 5.7 10×10 5.5 11.5 22.1 20.9 118×118 13.9 13.5 35.1 33.2 Large central hole size 10cm×10cm is OK Minimum of 118cm×118cm calorimeter is required to have ~30% acceptance Oct 31, 2008 Liping Gan, UNCW

Summary An exciting physics program to search tagged η rare decays will be developed in hall D at 12 GeV. A high energy and position resolutions, and high granularity calorimeter is crucial Minimum calorimeter size is 118cm×118cm with a central hole up to 10cm×10cm Precision measurement on (η→0) to test the χPTh prediction at Ο(p6) order Measurements of branching ratio/upper limits for various rare and forbidden η decays (such as η→0 0) involving photons in the final states to test P, PC and C symmetries, and search for new physics beyond Standard Model Oct 31, 2008 Liping Gan, UNCW

KLOE Result by B. Micco et al., 2006 Produce Φ through e+e- collision at √s~1020 MeV The decay η→0γγproceeds through: Φ→η, η→0γγ, 0→γγ Final result 68±23 of η→0 events BR(η→0γγ)=(8.4±2.7±1.4)x10-5 (η→0γγ)=0.109±0.035±0.018 eV Oct 31, 2008 Liping Gan, UNCW