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A Reanalysis of the Reported Observation of the ΛΛ H Hypernucleus

A Reanalysis of the Reported Observation of the ΛΛ H Hypernucleus. 4. S. D. Randeniya & E. V. Hungerford University of Houston USA. October 10 -14 2006, Mainz, Germany. Experiment E906. Cylindrical Detection System (CDS ). Coil. CDC. k -. Target. k +. TOF. SIDE VIEW. FRONT VIEW.

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A Reanalysis of the Reported Observation of the ΛΛ H Hypernucleus

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  1. A Reanalysis of the Reported Observation of the ΛΛH Hypernucleus 4 S. D. Randeniya & E. V. Hungerford University of Houston USA October 10 -14 2006, Mainz, Germany

  2. Experiment E906 Cylindrical Detection System (CDS) Coil CDC k- Target k+ TOF SIDE VIEW FRONT VIEW Beam : Momentum analyzed 1.8 GeV K- Target : 9Be K+ were detected in a magnetic spectrometer Technique : Coincident pion decay spectroscopy

  3. Coincident Pion Decay Spectrum

  4. Motivation Decay of ΛΛH Hypernucleus 4 ~ 8.9 ( 0 - 2 ) - 7.78 P + d+ Λ 7.75 ΛH+ p 3 2.39 3He + Λ 1.15 1+ 0+ 0.0 D. E. Kahana et al PRL C 68 (2003) ΛHe 4

  5. Details of the Monte Carlo Simulation • Pion Decays • Simulated decays of single and double Lambda s hypernuclei starting from at rest systems. • Simulation includes decays to 2-body & 3-body afinal states. • Simulation includes decays to & from excited xstates as well as ground states. • Simulation used the new weak value for Λ-Λapotential, ΔBΛΛ

  6. ΛΛY A ΛΛH 4 ΛΛH 5 ΛΛHe 5 ΛΛHe 6 6 ΛΛHe ΛΛHe 7 Probable double Lambda Hypernuclei Produced in 9Be(K-,K+)X Reaction

  7. Pion Decay Spectra • For the simulation pion spectra calculated in following Mreferences were used. M. Danszy, et al, PRL11 (1963) , Y. Yamamoto, et al, NPA625 (1997), T. Motoba, et al, NPA534 (1991) T. Motoba, et al, NPA489 (1988) • Simulated spectra were spread by the standard deviation Mof the momentum resolution of the CDS, 4 MeV/c. • Natural decay widths for 3-body decay spectra were used Mas directly obtained from the above references.

  8. Background • Comes from quasi-free Ξ’s & quasi-free Λ’s produced in M9Be(K-,K+)X reaction. J. K. Ahn, et al PRL 87 (2002) Background • Considering the statistical precision of data a background that is constant up to spectrum edges and then decrease as Gaussian with FWHM = 1.5 MeV/c at the limit Plow = Phigh was used.

  9. Fits to the Experimental Data • Fit projected experimental data by the simulation Ausing Chi Square minimization Mprocedure. • This procedure equally weighted each pair of Aprojections. • Error for each experimental data point is taken Aas square root of number of events.

  10. Fit to High Momentum Region Projection on to Plow Projection on to Phigh

  11. Decay mode Normalization No. of MC events No.of counts fit 3ΛH/ 4ΛH 0.002163 45000 97 3ΛH/ 3ΛH 0.001608 45000 72 4ΛH/ 4ΛH 0.002026 45000 91 Background 0.020000 25000 500 Results for High Momentum Region

  12. Variation of Chi Square Case A : 3ΛH / 4ΛH coincidence Case B : 3ΛH / 4ΛH with all other pairs Chi Square drops from 75/51 DOF to 43/49 DOF

  13. Decay mode Normalization No. of MC events No.of counts fit 3ΛH/ 4ΛH 0.002163 45000 97 3ΛH/ 3ΛH 0.001608 45000 72 4ΛH/ 4ΛH 0.002026 45000 91 Background 0.020000 25000 500 ΛΛHe 0.003197 10900 35 7 Results for Low Momentum Region All Kept constant • 3-body decay of single hypernuclear modes influence the Mlow momentum region.

  14. Decay of ΛH -ΛH in Coincidence 3 4

  15. Fit to Low Momentum Region Projection on to Plow Projection on to Phigh

  16. Global Representation Projection on to Plow Projection on to Phigh Cuts Plow : between 92 - 137 MeV/c Phigh : between 101 – 143 MeV/c

  17. Variation of Chi Square for the Global Fit Projection on to Plow Projection on to Phigh Case A : 7ΛΛHe Case B : 7ΛΛ He with 3ΛH/ 4ΛH Case C : 7ΛΛ He with 3ΛH/ 4ΛH, 3ΛH/ 3ΛH Case D : 7ΛΛHe with 3ΛH/ 4ΛH, 3ΛH/ 3ΛH, 4ΛH/4ΛH

  18. Decay modes / DOF 7ΛΛHe/ 3ΛH, 4ΛH 100/50 7ΛΛHe/ 3ΛH, 4ΛH/ 3ΛH, 3ΛH 97/49 7ΛΛHe/ 3ΛH, 4ΛH/ 4ΛH, 4ΛH 67/49 7ΛΛHe / all single hypernuclei 58/48 Variation of Chi Square for the Global Fit

  19. Decay mode Normalization Normalization No. of MC events (constant) (Varied) 7ΛΛHe 0.003197 0.003204 10900 3ΛH/ 4ΛH 0.002163 0.002338 45000 3ΛH/ 3ΛH 0.001608 0.001613 45000 4ΛH/ 4ΛH 0.002026 0.002425 45000 Variation in Normalization for the Global Fit Chi Square Constant : 62/52 DoF Varied : 58/48 DoF

  20. 3 4 7 Production Ratio of ΛΛHe to ΛH / ΛH coincidence For 2-body decay of 7ΛΛHe Assuming non-mesonic decay width is about 50% No. of counts from the fit = 20 Total # of 7ΛΛHe hypernuclei produced = 512

  21. 3ΛH / 4ΛH Coincidence Y. Yamamoto et al NPA 625 (1997) No. of counts obtained from the fit = 27 Total # of 3ΛH / 4ΛHcoincident events produced = 221 Production Ratio 7ΛΛHe to 3ΛH / 4ΛH coincidence = 2.32 ~ 2

  22. Data can be explained without the inclusion of decay of ΛΛH. 4 • More likely that ΛΛHe was observed in the experiment along Mwith a back ground of 3 single hypernuclear pairs described Mbefore. 7 • Analysis supports the weak value of ΔBΛΛ, for ΛΛHe = ~ 1 MeV. 7 Conclusions • No evidence of any other single or double lambda hypernuclei.

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