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LL spin correlations and spin selected HBT

LL spin correlations and spin selected HBT. Fei Du, Sandweiss’ group, Yale. Outline: Lambda and its decay Spin correlations Spin selected HBT. L and its decay. L (uds) m = 1115.683 ± 0.006 MeV c t = 7.9 cm Asymmetry in decay. L detection at STAR.

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LL spin correlations and spin selected HBT

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  1. LL spin correlations and spin selected HBT Fei Du, Sandweiss’ group, Yale • Outline: • Lambda and its decay • Spin correlations • Spin selected HBT DOE review, 09/15/2003

  2. L and its decay L(uds) • m = 1115.683 ± 0.006 MeV • ct = 7.9 cm Asymmetry in decay DOE review, 09/15/2003

  3. L detection at STAR Topological method: pair up decay products (p and p-) with geometry and invariant mass cuts Preliminary DOE review, 09/15/2003

  4. How to find out the L spin Two transformations: • 1st: transform to the CMS of the di-L pair • 2nd: transform each proton to the rest frame of its parent L. • Take the proton momentum direction as an indicator of the L spin direction. DOE review, 09/15/2003

  5. LL spin correlations • Spin correlation at low : due to Fermi-Dirac statistics. • For LL system, at low Q, s-wave state (l=0) dominates (symmetrical space wavefunction), thus total spin S = 0. (↑↓-↓↑) • Spins are anti-aligned. DOE review, 09/15/2003

  6. Complication I – Q is never 0 • Finite Q→ source radius DOE review, 09/15/2003

  7. Complication II – spin direction is not perfectly measured Calculation done by G. Alexander et. al.: Use of Spin-Correlations to Study Low Energy LL and LL Space Symmetries and Resonances, Phys. Lett. B352:162, 1995 DOE review, 09/15/2003

  8. Spin correlation golden formula DOE review, 09/15/2003

  9. ALEPH data DOE review, 09/15/2003

  10. Preliminary Preliminary Preliminary Preliminary Preliminary Preliminary DOE review, 09/15/2003

  11. Fit dN/dy to 1 + ky Preliminary DOE review, 09/15/2003

  12. HBT (Bose-Einstein correlation) DOE review, 09/15/2003

  13. Aligned spins: Anti-aligned spins: HBT (Fermi-Dirac correlation) DOE review, 09/15/2003

  14. Better treatment DOE review, 09/15/2003

  15. HBT with spin selection DOE review, 09/15/2003

  16. Preliminary Preliminary Preliminary DOE review, 09/15/2003

  17. Outlook • With next year’s data (~ 20x more statistics than shown in the plots here), things will become much clearer. • Also we can use tighter cut on spin alignment with more statistics. DOE review, 09/15/2003

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