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Asymmetry of Jet k T in Longitudinal Polarized p+p Collisions in PHENIX at RHIC

R. Hobbs For the PHENIX collaboration University of New Mexico. Asymmetry of Jet k T in Longitudinal Polarized p+p Collisions in PHENIX at RHIC. Outline. Measuring transverse momentum of partons in the proton Looking for a correlation of this measurement with spin direction

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Asymmetry of Jet k T in Longitudinal Polarized p+p Collisions in PHENIX at RHIC

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  1. R. Hobbs For the PHENIX collaboration University of New Mexico Asymmetry of Jet kT in Longitudinal Polarized p+p Collisions in PHENIX at RHIC

  2. Outline • Measuring transverse momentum of partons in the proton • Looking for a correlation of this measurement with spin direction • Initial measurements in Run03 • Status of Run05 • Summary Oct. 27, 2005 2

  3. * jet jTN jet fragmentation transverse momentum, jT-scaling. kT2F-2N parton transverse momentum,intrinsic + NLO radiative corrections.  kT, jT from azimuthal correl. fragmentation Oct. 27, 2005 3

  4. Origin of kT An example - J/ production. Breaks collinear factorization pTJ/=1.80.230.16 GeV/c Phys. Rev. Lett. 92, 051802, (2004). Oct. 27, 2005 4

  5. Longitudinal jet jet transverse • acoplanar in PL PT space • acoplanar in PX PY space Hard Scattering kT Longitudinal transverse • acoplanar in PL PT space • collinear in PX PY space Oct. 27, 2005 5

  6. kT from Orbital Motion kT larger kT smaller One can consider the possibility that spin-correlated transverse momentum (orbital angular momentum) may contribute to jet kT. e.g., Meng Ta-chung et al., Phys. Rev. D 40 (1989) Oct. 27, 2005 6

  7. o - h correlation functions d+Au Azimuthal correlation function Not corrected for acceptance Corrected for acceptance F Oct. 27, 2005 7

  8. p2out = p2Ta sin2 2k2Tyz2a 2k2Tyz2tx2hxh= pTa /pTt pTt jT jT pTa Jet kinematics partonic hadronic Oct. 27, 2005 8

  9. Spin Sorted Analysis • Do exactly the same analysis sorted on same and opposite helicity bunch crossings, extract <zkt>RMS and look at the difference. Same Helicity Opposite Helicity C(Δφ) C(Δφ) Δφ Δφ Oct. 27, 2005 9

  10. Run03 Data Like sign Unlike sign trigger π0 1< pTt<3 Gev/c 3<pTt<7 Gev/c Associated h 1< pTa<2.5 Gev/c Oct. 27, 2005 10

  11. Systematic Check RMS = 45 • Helicity assignments are randomized, and then the kT difference calculated for each randomized set. • The width of the distribution for all the randomized sets should be the same as our statistical errors on the previous plot. RMS = 90 Oct. 27, 2005 11

  12. Run03 Data Its too early to make a definite statement about the apparent excess as the systematic uncertainties are being evaluated. However, there is an ongoing analysis of 10x more stat. and 2x better polarization in run05  should yield a definite answer. BS variance Oct. 27, 2005 12

  13. Summary • We have an analysis tool that allows us to measure kT - initial state transverse momentum of partons. • We are studying this effect in longitudinal spin-sorted collisions to see if there is a spin-dependent coherent component of kT. • Is there a connection to parton OAM? Theoretical guidance needed! Outlook • Run05 has ~x10 statistics, so that the uncertainty reduced by factor 2-3. • It has ~x2 in polarization, so the effect grows by ~x4. Oct. 27, 2005 13

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