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Published byDuane Stevenson Modified over 9 years ago
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Spin transfer coefficient K LL’ in photoproduction at HERMES D. Veretennikov On behalf of the HERMES collaboration DIS08, London
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Λ decay and spin transfer coefficient is “self-analyzing” particle due to its parity violation p - decay Spin transfer coefficient S LL’ K LL’ from longitudinally polarized target K NN’ from transversely polarized target D LL’ from longitudinally polarized beam D NN’ from transversely polarized beam L is primary axis along target or beam polarization L’ is secondary axis along momentum Unpolarized cross-section angle between proton momentum in the rest frame and the spin decay constant, 0.642 ( ), -0.642 ( ) Angular distribution of protons (in rest frame)
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Study of Λ polarization at HERMES DIS, e + p e’ + + X D LL’ spin transfer from longitudinally polarized e + /e - beam in semi- inclusive reaction / Published P.R. D 64 (2001), P.R. D 74 (2006) / Quasi-real photoproduction, e + p → Λ+ X K LL’ spin transfer from longitudinally polarized target D LL’ spin transfer from longitudinally polarized e + /e - beam K NN’ spin transfer from transversely polarized target Pn transverse (spontaneous) Λ polarization / Publish P.R. D 76 (2007) / e’ + * ( Q 2 0 GeV 2 )
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Λ photoproduction mechanism in PYTHIA According to PYTHIA is produced due to diquark fragmentation or due to quark fragmentation Most of events are within photoproduction peak (for 80% events Q 2 < 0.05 GeV 2, 15 GeV) Such that photon is quasi-real
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HERMES experiment Polarized lepton (e - /e + ) beam E e = 27.5 GeV, monthly spin flip ( D LL’ ) Long. / trans. polarized gas targets (H, D), spin flip every 90 s ( K LL’, K NN’ ) Detector is up / down symmetric ( P n )
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Background suppression cuts for leading rejection ( in HERMES acceptance proton is always leading ) : Threshold Cherenkov det. 1996-1997 Ring imaging Cherenkov 1999-2000 h + h - pair background rejection : Vertex separation d(V 1,V 2 ) > 15 cm ( ) event reconstruction Data sample for longitudinally polarized target ( 1996 - 2000 )
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Formalism extraction of K LL’ No MC simulation needed Helicity balanced data sample Moment method Background subtraction
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Photoproduction kinematics Better separate production channels Value of t allows for easy comparison with other experiments
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K LL’ seems to be increasing at small t (diquark fragmentation?) K LL’ is p t independent (0 < p t < 1.2 GeV) Kinematical dependences of K LL’ for
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Statistics for is not enough to see dependences on t or p t Kinematical dependences of K LL’ for
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Spin transfer for and , world data FNAL, E704 pp collisions with transversely polarized beam RICH, STAR pp collisions with longitudinally polarized beam
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World data compilation for spin transfer FNAL result confirms a trend to increase spin transfer at small t
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Conclusion Longitudinal spin transfer from polarized target to the is measured for the first time in quasi-real photoproduction K LL’ = 0.026 ± 0.009 stat ± 0.005 syst Spin transfer is increasing at small t K LL’ is p t independent Longitudinal spin transfer to is compatible with zero for available statistics K LL’ = 0.002 ± 0.022 stat ± 0.008 syst
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