Search for New Physics via η Rare Decay Liping Gan University of North Carolina Wilmington March, 2008 Liping Gan, UNCW

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

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

Theoretical Status on η→0 By E. Oset et al. Unitarized χPTh with new PDG inputs 0.33±0.08 March, 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 March, 2008 Liping Gan, UNCW

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

CB Data Analysis II (by N. Knecht et al. in 2004) Final result 121±37 of η→0 events BR(η→0γγ)=(2.7±0.9±0.8)x10-4 (η→0γγ)=0.32±0.15 eV March, 2008 Liping Gan, UNCW

What can be improved? 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 0γγinvariance mass Higher granularity→ better position resolution and less pile-up clusters Large statistics to provide a precision measurement of Dalitz plot March, 2008 Liping Gan, UNCW

Experimental Design 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 March, 2008 Liping Gan, UNCW

Kinematics of Recoil Proton Polar angle ~65o-80o Kinetic energy ~20-300 MeV Momentum ~200-800 MeV/c March, 2008 Liping Gan, UNCW

Acceptance March, 2008 Liping Gan, UNCW

Invariance Mass of 0 March, 2008 Liping Gan, UNCW

The η production rate: LH2 target length L=30cm, ρ=0.0708 g/cm3 Rate Estimation The η production rate: LH2 target length L=30cm, ρ=0.0708 g/cm3 The +p→η+p cross section ~1 μb Photon beam intensity Nγ~1.5x107 Hz The η→0 detection rate: BR(η→0 )~4x10-4 , detection efficiency ~11.4% March, 2008 Liping Gan, UNCW

Summary High energy and high intensity tagged photon beam First tagged η experiment by measuring recoil p with GlueX High resolution calorimeter with PWO4 crystal insertion to reduce the major backgrounds 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 involving photons in the final states to test P, PC and C symmetries, and search for new physics beyond Standard Model March, 2008 Liping Gan, UNCW