1 / 11

Mickey Chiu University of Illinois at Urbana-Champaign RBRC SSA Workshop 2005

New Prospects for SSA Measurements in PHENIX: How can we separate out the various contributions to SSA at RHIC?. Mickey Chiu University of Illinois at Urbana-Champaign RBRC SSA Workshop 2005. 2.  0. . h. Sivers Fcn from Back2Back Analysis.

raoul
Download Presentation

Mickey Chiu University of Illinois at Urbana-Champaign RBRC SSA Workshop 2005

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. New Prospects for SSA Measurements in PHENIX:How can we separate out the various contributions to SSA at RHIC? Mickey Chiu University of Illinois at Urbana-Champaign RBRC SSA Workshop 2005

  2. 2 0  h Sivers Fcn from Back2Back Analysis Boer and Vogelsang, Phys.Rev.D69:094025,2004, hep-ph/0312320 • Non-Zero Sivers function means that there is a left/right asymmetry in the kT of the partons in the nucleon • For a positive Siver’s function, there will be net parton kT to the left (relative to direction of proton, assuming spin direction is up). • Boer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the  distribution of back-to-back jets • There should be more jets to the left (as in picture to the left). • Should also be able to see this effect with fragments of jets, and not just with fully reconstructed jets? • Take some jet trigger particle along ST axis (either aligned or anti-aligned to ST) • Trigger doesn’t have to be a leading particle, but does have to be a good jet proxy • Then look at  distribution of away side particles

  3. Unpolarized Results from Run03 p+p Boer and Vogelsang, PRD69:094025,2004 Run03 -charged dn/d anti-aligned aligned • Asymmetry • numerator is difference between aligned and anti-aligned  dist’s, where aligned means trigger jet and spin in same direction • denominator is simply unpolarized  distribution • On left are some theoretical guesses on expected magnitude of AN from Siver’s • On right are gamma-charged hadron  dist’s from Run03 p+p • 2.25 GeV gamma’s as jet trigger, 0.6-4.0 GeV charged hadrons to map out jet shape • Dotted lines are schematic effect on away side  dist due to Siver’s Fn (not to scale)

  4. Estimated AN from Run03 p+p parametrized AN - • Parametrized AN with , A=0.08, =0.8 • Used this to calculate AN using unpolarized gamma-charged Run03 p+p dN/d • Put asymmetry into distribution and then calculate AN • On right shows statistical significance from Run03 p+p (0.35/pb). • Assumed Poisson statistics • Note that area around =0 can be used as a systematic check (it should be flat) • Also note that AN from Boer/Vogelsang paper is idealized, and the real signal will be reduced

  5. AN Reduction 1: Polarization • Polarization P < 1 just reduces AN by P • Besides that, most of the time the jet is not aligned exactly along the polarization axis, which means AN=AN(j1,) and also the polarization is reduced by cos(j1) • We can make a simple (though wrong) estimate for this effect by calculating the average polarization from a jet spread of /2 around the polarization axis j1 ST j2

  6. AN Reduction 2: Di-Hadron vs. Di-Jets AN away side parton up down unpolarized di-hadron di-jet • Since we don’t reconstruct jets fully, we have to use di-hadron correlations to measure jet . This smears out the di-hadron AN relative to the di-jet AN, with smearing function g (assumed here to be a gaussian, with jT=0.35). • The effect broadens and lowers (by just a little bit) the asymmetry

  7. Combined Effects Full di-jet Sivers Reduced by lower <P>, di-hadron smearing Run03 p+p gamma-charged, 0.35/pb

  8. process contribution to 0 x, pT coverage Vogelsang et al • Boer-Vogelsang paper considers pT ~ 10 GeV jets • x coverage here slightly lower • gluon dominated region

  9. “Radial” Running Modes ST ST SL • Could run in “radially” transverse mode • Preferred mode for this analysis • There could be a transverse component during longitudinal running • Coexist with longitudinal running • Have to worry about longitudinal asymmetry contribution

  10. Measuring Collins in p+p? Belle cos(2h) method Seidl ~ h e+e- p+p • Important test of Universality and Scale Evolution • Collins needs to be known in p+p to get transversity from SSA • p+p is much more complicated • Intrinsic kT as well as radiative effects • Many other diagrams • t-channel “dominates” over s-channel • At LO, this is a dilution of 10-3 • ~5% cos(2h) modulation at Belle becomes 0.5x10-4 modulation at RHIC • unpolarized beam required: ~ 300/pb (200 GeV), 980/pb (500 GeV)

  11. Summary & Observations • It could already be that transversity and Collins are not important in p+p, and that gluon Sivers = 0. • Would be important to verify this independently with techniques that are a priori theoretically unambiguous • Given 0.35/pb of data, we should be able to get 1% statistical significance in AN using gamma-charged measurements of jet  • Expected raw AN could be 3.5% • Could also be as low as 0.5%, or as large as 10% • Effects from P=0.5, jet angle not aligned with transverse polarization, and fragmentation to dihadrons reduces raw AN to ~1.0% • Can Collins be directly measured at RHIC? • Contribution is whatever remains? Sivers Collins Higher Twist

More Related