Direct Measurement of Lifetime of Heavy Hypernuclei Using Photon Beam with CLAS and Fission Fragment Detector Liguang Tang Hampton University / JLAB Proposal to be submitted to PAC 31 CLAS Collaboration Meeting, 11/01/2007

Pure BB  BB weak interaction is essential to help to fully understand the strong interaction limit of QCD. It is still a poorly understood sector of Standard Model because:  The weak NN  NN interaction cannot be clearly observed due to extremely high background from strong interaction  The tiny PV amplitude in the NN scattering is very difficult to observe, while PC amplitude is completely masked by strong interaction  The weak NN scattering is “contaminated” by the neutral current, induced by both W  and Z 0 boson exchanges  N  NN is unique to study BB  BB weak interaction: it is weak (  S=1), induced only by the charge current (W  ), both PC & PV amplitudes can be observed Physics Motivations

 N  NN: Non-Mesonic Decay Mode of  -Hypernuclei  -hypernuclei decay via two distinguished modes Mesonic decay (same as the free  ):   p  MeV (~64%) and   n  MeV (~36%) (Pauli block to nucleon except extremely light hypernuclei) Non-mesonic decay (unique):  n  nn MeV (  n )  p  np MeV (  p )  NN  nNN MeV (  2 ) ~ 420 MeV/c for NN ~ 320 MeV/c for NNN , , , , ,  *  N N N  N N N N N

Three types of observable to study the NM decay   N  NN Partial decay widths: (Exclusive but light hypernuclei) -  N  NN transition amplitudes (PC) - Decay width Ratio:  n /  p -  I = 1/2 rule (3/2 contribution ?) Decay asymmetry: (Exclusive but light hypernuclei) - Polarization of hypernuclei - Interference of PC and PV amplitudes in  N  NN Lifetime (  T ): (Inclusive, light to very heavy) - Characteristics of the A dependence - Interaction range, BB short range correlation - Role of  I=3/2 (S.I., HMS) and 1/2 (L.I., OPE) - Significance of  NN  NNN contribution? - Unknown mechanisms, role  inside nucleus

Standard model predicts: 2:1 (1/2) : (3/2) Observations from mesonic decays of K  and  concluded: ~20:1 (  I = 1/2 rule) Suppression of  I = 3/2 transition was explained by the theory of color symmetry of constituent quark, but under predicted the ratio  n /  p Origin is still unknown Weak  N  NN interaction is unique to study the origin of this empirical rule Long Standing Puzzle:  I = 1/2 Rule in Weak  S=1 Non-leptonic Decays

Progress and Puzzle on Partial Decay Widths (Light Hypernuclei only) Early puzzle:  n /  p =1.0 (Exp.) but 0.1 (Th.) Early puzzle:  n /  p =1.0 (Exp.) but 0.1 (Th.) Theory: An error was found in the calculation of kaon exchange amplitude, ratio goes up Theory: An error was found in the calculation of kaon exchange amplitude, ratio goes up Experiment: Better handle on the low energy final state protons, adding neutron detection, adding two nucleon correlation study,…, ratio comes down Experiment: Better handle on the low energy final state protons, adding neutron detection, adding two nucleon correlation study,…, ratio comes down Agreement: R=  n /  p  0.5 Agreement: R=  n /  p  0.5 Example: R( 5  He)=0.45  0.11  0.03, R( 12  C)  0.5 Puzzle on this ratio is settled! Puzzle on this ratio is settled! Fundamental issues are not solved yet Theories are in contradiction on the amplitude of  I = 3/2 transition for the NM decay Current data on the partial decay widths of light hypernuclei cannot conclude the requirement of  I = 3/2 transition There are suggestions that partial decay width study on 4  H is essential for the conclusion Extrapolated R( 4  H) from 5  He and 4  He data were too poor in uncertainty to make conclusion

Puzzle in Decay Asymmetry (  N  NN with  Naturally Polarized) Ref. and Model 5  He 12  C Theory A. Ramos et al. OPE  + K C. Barbero  (  I=1/2)  (  I=3/2) K (  I=1/2) K (  I=3/2) Exp. M. Oka 0.09  0.08 H. Bhang et al   0.26 T. Maruta et al   0.26 Experimental data from two light hypernuclei are in contradictory with theory (one agree but one disagree at least on the sign of  ) Theories cannot conclude the role of HME and  I = 3/2 component, both are dominated by short range interactions. Fundamental issues are not solved

3 rd Observable: Lifetime (A Dependence) - Strictly range related  NM (A)   dr   (r)  2  A (r) If interaction is short ranged, the lifetime should saturate at medium A or below  n /  p  0.5 COSY result suggested a continued decrease of lifetime and cannot be explained by current theoretical models Pure NM decay region High precision lifetime for heavy hypernuclei is essential to help to fully understand the mechanisms of the NM decay and the JLAB experiment is capable to have an unprecedented accuracy

Goal of the JLAB Experiment Direct time measurement Direct time measurement Unprecedented precision: Unprecedented precision: Sys. error <  3 ps Stat. error <  5 ps Challenge or confirm COSY-13 result to Challenge or confirm COSY-13 result to  Put more stringent limits to the  n /  p ratio to test future validity of the  I=1/2 rule on a higher confidence level  Test the significance of other possible decay mechanisms (3-body decay and rescatterings)

Beauty of the JLAB Experiment Precise Beam Structure t 1.67 ps 2.0 ns Hall C HKS Hall B g11 Coincidence time Fission Fragment Detector - LPMWPC Excellent timing resolution  Double TOF measurements  Excellent position reconstruction plus correction by position-time correlation due to the correlated mass relation for the two FF   t ~ ps Excellent decay T 0 calibration  Large amount of prompt fissions from background  and p productions  Precise T 0 and line shape determination    (sys) <  3 ps Super Stable with Photon Beam Tested in Hall B (Summer, 2007)

Schematic Layout of the Experiment 1.5 M   209  Pb P K (GeV/c) E  (GeV) Production threshold E E  limit 0.67 HKS limit - FFD, 1.5 m upstream - Small forward angle,  < ~14 o - Similar to CLAS angle  < ~19 o - Clean photon beam - Large  and kinematics range - Short flight path

Offline Particle ID (CLAS Simulation) Momentum Region  + /p/K + ratio: 100:10:1 Small angle cut applied PID is reasonably good Background induced fissions is essential as tools for calibrations to ensure high precision E = 2.1 GeV/c

Successful Beam Test in Hall B Effective target thickness: 500mg/cm 2 (10x thicker) FFD performed very stable and good characters at maximum beam intensity Differential amplifier can eliminate the RF noise 2-fold: x fold: x FFD Rates CLAS Rates at 27 (nA)(%) Drift chamber peak current18  A TOF (top two average)9.5 kHz TOF (bottom two average)26.3 kHz EC (top two average)24.2 kHz EC (bottom two average)133 kHz A reconstructed T 0 w/o beam position information  = 279 ps

Gain Over E (Using HKS) Experimental conditionE02-017Hall BGain Beam current (nA) Radiator (%) Kinematics acceptance Average kaon survival (%) Integrated d  /d  over  Overall3.83 Experimental Condition Electron beam (I) 50 nA Radiator (r.l.) 5% Intensity (nA  %)250 nA% Summed TOF rate~90 kHz Summed EC rate~380 kHz CLAS DC peak current~10  A FFD 1/4 rate~600 Hz FFD 2/4 rate~300 Hz Coincidence (CLAS & FFD) rate ~ 5 Hz

Yield Rate Fission Probability COSY JLAB-Hall B Much better ratios of Prompt/Delayed fissions 10,

Yield Rate Item Bi Au Kaon single 0.91/s 0.88/s Kaon coincidence (Prompt)40/hour 8/hour Kaon coincidence (Delayed)30/hour 17/hour Kaon accidental6  /s 6  /s Beam Time Request (E = 2.1 GeV) ItemBeam hoursTotal Yield Commissioning 72 - Bi target Au target

Lifetime Extraction & Precision N(t) = N d  dt’  R(t-t’)  e -t/  + N p  R(t) + N KID  R’(t)  -- Four free parameters Systematic precision depends on: Precise line shapes Precise production & decay time zeros Background induced fissions are essential Systematic error: <  3 ps Statistical precision depends on: N d ~ 3000 counts If  t = 200 ps and  = 200 ps Statistical error: ~  5 ps

Summary High precision measurement on lifetime of heavy hypernuclei is crucially important to help uncovering the mastery of short range interaction and role of  I = 1/2 rule High precision measurement on lifetime of heavy hypernuclei is crucially important to help uncovering the mastery of short range interaction and role of  I = 1/2 rule The proposed JLAB experiment is the only one can reach such precision The proposed JLAB experiment is the only one can reach such precision Real photon, FFD, and the Hall B CLAS is the cleanest and best way to carry out this experiment Real photon, FFD, and the Hall B CLAS is the cleanest and best way to carry out this experiment