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

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

3. 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

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

5. 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

6. 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

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

8. 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

9. 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: MeV
Oct 31, 2008
Liping Gan, UNCW

10. 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

11. 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

12. 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

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

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

15. 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

16. 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

17. 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

18. 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

19. 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