Search for New Physics via η Rare Decay

Search for New Physics via η Rare Decay Liping Gan University of North Carolina Wilmington, NC, USA July, 2009 Liping Gan, UNCW

Contents Ø Physics Motivation • Why η meson is interesting? • η→ 0 0 Ø Suggested experiments at Jlab Ø Summary July, 2009 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 the Standard Model July, 2009 Liping Gan, UNCW

Some Interesting η 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(p 6) 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 × 10 − 5 C π0 e + e − <4 × 10 − 5 C 4π0 <6. 9 × 10 − 7 CP, P July, 2009 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)<3 x 10 -17 • The η→ 0 0 is one of a few available flavor-conserving reactions listed in PDG to test CP violation. • Unique test of P and PC symmetries, and search for new physics beyond SM July, 2009 Liping Gan, UNCW

History of the η→ 0 Measurements After 1980 A long standing “η” puzzle is still un-settled. July, 2009 Liping Gan, UNCW

High Energy η Production (GAMS Experiment on η→ 0 at Serpukhov) • • • Experimental result was first published in 1981 The η’s were produced with 30 Ge. V/c - beam in the -p→ηn reaction Decay ’s were detected by leadglass calorimeter Final result (D. Alde et al. ) Major Background • - p → 0 0 n • η → 0 0 0 July, 2009 ~40 of η→ 0 events BR(η→ 0γγ)=(7. 1± 1. 4)x 10 -4 (η→ 0γγ)=0. 84± 0. 17 e. V Liping Gan, UNCW

Low energy η production (CB experiment on η→ 0 at AGS, by S. Prakhov et al. ) η → 0 0 0 -p→ 0 0 n • • The η’s were produced with 720 Me. V/c - beam through the -p→ηn reaction Decay ’s energy range: 50500 Me. V July, 2009 Liping Gan, UNCW Final result 1600 of η→ 0 events (η→ 0γγ)=0. 45± 0. 12 e. V γγ)=0. 45± 0. 12

Low Energy η Production Continue (KLOE, by B. Micco et al. , Acta Phys. Slov. 56 (2006) 403) • Produce Φ through e+e- collision at √s~1020 Me. V • 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)x 10 -5 (η→ 0γγ)=0. 109± 0. 035± 0. 018 e. V July, 2009 Liping Gan, UNCW

What can be improved at 12 Ge. V Jlab? • High energy tagged photon beam to reduce the background from η→ 3 0 Ø Lower relative threshold for -ray detection Ø Improve calorimeter resolution • Tag η by recoiled particles to reduce non-resonance 0 0 background • High resolution PWO Calorimeter • Large statistics to provide a precision measurement of Dalitz plot Ø Higher energy resolution → improve 0γγinvariance mass Ø Higher granularity→ better position resolution and less overlap clusters July, 2009 Liping Gan, UNCW

Suggested Experiments in Hall D at Jlab Counting House Photon Tagger Glue. X 75 m Simultaneously measure the η→ 0 , η → 0 0: • η produced on LH 2 target with 11 Ge. V tagged photon beam γ+p → η+p • Tag η by measuring recoil p with Glue. X detector • Forward calorimeter with PWO insertion to detect multi-photons from the η decay July, 2009 Liping Gan, UNCW FCAL

Invariant Mass Resolution σ=3. 2 Me. V σ=6. 9 Me. V PWO M σ=6. 6 Me. V M Oct 31, 2008 Pb glass Liping Gan, UNCW M 0 σ=15 Me. V M 0

S/N Ratio vs. Calorimeter Granularity PWO Pb Glass dmin=4 cm dmin=8 cm S/N=1. 4 July, 2009 Liping Gan, UNCW S/N=0. 024

Summary • Jlab 12 Ge. V will provide a great opportunity for the precise measurements of various η rare decays to test P, CP and C symmetries, and search for new physics beyond the Standard Model • Proposed simultaneous measurements on BR(η→ 0 ) and BR(η → 0 0) will test the χPTh prediction, P and CP symmetries. • Jlab 12 Ge. V high intensity tagged photon beam to produce η’s. • Tag η’s by measuring recoil p with Glue. X to reduce the p→ 0 0 p background • High resolution and high granularity PWO crystal calorimeter to reduce the η → 0 0 0 background July, 2009 Liping Gan, UNCW

The End July, 2009 Liping Gan, UNCW

Rate Estimation • The η production rate: LH 2 target length L=30 cm, ρ=0. 0708 g/cm 3 The +p→η+p cross section ~1 μb Photon beam intensity Nγ~1. 5 x 107 Hz • The η→ 0 detection rate: BR(η→ 0 )~4 x 10 -4 , detection efficiency ~11. 4% July, 2009 Liping Gan, UNCW

Study of the η→ 0 Decay • A stringent test of the χPTh prediction at Ο(p 6) level Ø Tree level amplitudes (both Ο(p 2) and Ο(p 4)) vanish; Ø Ο(p 4) loop terms involving kaons are suppressed large mass of kaon Ø Ο(p 4) loop terms involving pions are suppressed by G parity Ø The first sizable contribution comes at Ο(p 6) level • A long history that experimental results have large discrepancies with theoretic predictions. • Current experimental limits in PDG is BR(η→ 0 )<4. 4 x 10 -4 July, 2009 Liping Gan, UNCW

Theoretical Status on η→ 0 By E. Oset et al. Unitarized χPTh with new PDG inputs July, 2009 0. 33± 0. 08 Liping Gan, UNCW

CB Data Analysis II (by N. Knecht et al. phys. Lett. , B 589 (2004) 14 Final result 121± 37 of η→ 0 events BR(η→ 0γγ)=(2. 7± 0. 9± 0. 8)x 10 -4 (η→ 0γγ)=0. 32± 0. 15 e. V July, 2009 Liping Gan, UNCW

Kinematics of Recoil Proton Recoil Pp vs θη (Deg) Angle θη (Deg) • Polar angle ~55 o-80 o • Momentum ~300 -1400 Me. V/c Recoil θp (Deg) vs Pp (Ge. V) July, 2009 Liping Gan, UNCW

Missing Mass E =11. 5 Gev ΔP/P=1. 5% Δθ=7 mrad Missing Mass (Ge. V) July, 2009 Liping Gan, UNCW