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Spin Physics with the PHENIX Detector

Explore the spin structure of protons and polarized PDF asymmetry analysis using the PHENIX detector. Measure spin asymmetries for cross sections and extract spin-dependent PDFs.

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Spin Physics with the PHENIX Detector

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  1. Spin Physicswith the PHENIX Detector Mickey Chiu University of Illinois at Urbana 21st Winter Workshop on Nuclear Dynamics, Breckenridge

  2. Nucleon Spin Physics EMC PLB 206:364 (1988) 1240 Citations!! (as of 02/08/05) • protons are the fundamental stable ground state of QCD • the proton is still not yet understood • “proton spin crisis” 1990 1995 2000

  3. Polarised PDFAsymmetry Analysis Collaboration M. Hirai, S. Kumano and N. Saito, PRD (2004) • Valence Dist’s are determined well • Sea Distribution poorly constrained • Gluon can be either pos, 0, neg!

  4. RHIC Spin Evolution Absolute Polarimeter (Pol-Jet Tgt) Local Polarimeter ZDC/SMD Polarimeter Spin Rotators AGS Cold Snake AGS Warm Snake AGS pC CNI Polarimeter RHIC pC CNI Polarimeter BRAHMS & PP2PP PHOBOS RHIC PHENIX STAR Siberian Snakes Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter Rf Dipoles 200 MeV Polarimeter

  5. What Do We Measure at RHIC? • We measure spin asymmetries for cross sections • ALL: double helicity asymmetry • Useful in extracting Dg(x), Dq(x) etc. AN:Twist-3 etc AL:Parity Violation ATT: Transversity

  6. RHIC Spin: L and P Progress 4 days 4 days >4 weeks >4 weeks 2.5 weeks • Run 2: AN • ~7 nb-1/day • (0.15/pb),PB~15% • Run-3:ALL • 10 nb-1/day 0.35/pb,PB~26% • (AGS) 40% • Run-4:ALL • Only Machine Studies • 30nb-1/day • 0.12/pb,PB~40% • (AGS) 50% • Run-5 :ALL • ~11 weeks

  7. Mid-Rapidity 0 and charged hadron Production in p+p at s = 200 GeV PRL 91, 241803 (2003) NLO pQCD W. Vogelsang et al. CTEQ6M PDF KKP FF =2pT, pT, 1/2pT PHENIX Preliminary • NLO QCD Calculation Cross-sections consistent with Data • CTEQ5M pdf • KKP and Kretzer Fragmentation Fcns • Necessary Confirmation that pQCD can be used successfully at RHIC to extract spin dependent pdf’s. • Same comparison fails for lower energies

  8. Getting Polarization Information BBC preliminary AN = 0.108±0.0087 • Large Neutron AN was discovered at IP12 • Cause not yet well understood • A possible diffractive process? • Charge Exchange? • ZDC/SMD can make a local polarimetry measurement at PHENIX • Allows us to measure independently the polarization

  9. Measuring ALL • To determine g, look at ALL: • R is the relative luminosity, and can be measured (to some accuracy) at PHENIX using the BBC or ZDC. • Our Goal: dR/R < 0.1% for each fill dALL < 2×10-3(expected ALL for pions ~ 3×10-3 @pT=3 GeV/c)

  10. Constraints on Dg(x) w/ p0 Production ALL • pp p0X is sensitive to gggg and gqgq PHENIX Results from Run-3 To Appear in PRL

  11. Other Probes of g GS95 hadrons DG(x) prompt photon cceX bbeX J/ x See Talks by Takao Sataguchi, Youngil Kwon, Sergey Butsyk

  12. Single Transverse SpinAsymmetries E704 PRL 92 (2004) 171801 Fermilab E-704 reported Large Asymmetries AN in pion productions • Transversity x Spin-dep fragmentation (Collins effect), or • Intrinsic-kT imbalance (Sivers effect) , or • Higher-twist effects • Sterman and Qiu Initial State Twist 3 • Koike Final State Twist 3 • Or combination of above left right

  13. Calculating AN • Look for left-right asymmetry with respect to beam spin and direction • OR look either on left or right side and compare p0 production for + and - spin states Two methods provide important check of systematic errors Racc = relative acceptance of left and right detectors Rlumi = relative luminosity of + and - spin states

  14. AN of Neutral Pions and Non-Identified Charged Hadrons Neutral pions AN for both charged hadrons and neutral pions consistent with zero at midrapidity. Polarization scaling error ~30% not included p0 PHENIX Preliminary Charged hadrons h- h+ PHENIX Preliminary Data taken 0.15 pb-1 and 15 % beam polarization

  15. Sivers and Why it is Interesting J=1/2 <LZ> = ? • Non-Zero Sivers function means that there is a left/right asymmetry in the kT of the partons in the nucleon • Probes space-time structure of nucleon wave-function • Testable kT dependence of nucleon wave-function testable • Sivers requires quark orbital angular momentum • Centrality dependent effects • Quark Shadowing in central region causes kT asymmetry? • Red Shift/Blue Shift effects in peripheral regions? • ST (P  kT) is T-odd and naively thought to vanish • FSI effects found by Brodsky et.al. that allow T-odd function to be non-zero

  16. Sivers Fcn from Back2Back Analysis Boer and Vogelsang, Phys.Rev.D69:094025,2004, hep-ph/0312320 • 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

  17. Unpolarized Results from Run03 p+p Boer and Vogelsang, PRD69:094025,2004 Run03 -charged dn/d anti-aligned 1/Ntrig dN/d (au) 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)

  18. 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 (but k factor only ~10% different?) • 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

  19. 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

  20. 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

  21. Combined Effects Full di-jet Sivers Reduced by lower <P>, di-hadron smearing Run03 p+p gamma-charged, 0.35/pb • Given 0.35/pb of data, we should be able to get 1% statistical significance in AN using gamma-charged measurements of jet dphi • 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% • Have not evaluated systematic errors yet (underlying event…) • Can also do this in Longitudinal collisions (Collins effect?)

  22. Some Future Measurements • Upgrades • Muon Trigger for W Bosons (Wei) • Measure sea quark polarization • Nose Cone Calorimeter (Vasily) •  + jet  G, extends x-range • Silicon Vertex Tracker (Gerd) • heavy flavor and jet reconstruction • Searches for new physics (RHIC can become a polarized parton collider) • Anomalous Parity Violation in Jet Production • Contact Interaction (Scale  ~ 3.3 GeV at RHIC) • New Gauge Boson Z’

  23. Summary • There are a variety of QCD phenomena that are not understood in our most basic QCD object, the proton • QCD is complicated • PHENIX Has Measured 0 ALL out to pt ~ 5 GeV/c • Demonstration of ability to do spin physics • First constraints on g(x) • 10 times statistics for 0, h, , c, b ALL expected in upcoming run • 0 and charged AN at xF = 0 is 0 • Start of transverse physics program • Have access to Sivers function via • Possibly accesses orbital angular momentum

  24. Backup Slides

  25. AN Systematic Errors In addition to calculating the asymmetry using more than one method, potential systematic errors have been investigated in the following ways: • Measured asymmetry of background • Immediately outside the p0 mass peak • In the mass region between the p0 and the h • Compared independent measurements for two polarized beams • Compared results for left and right sides of detector • Compared minimum bias and triggered data samples • Examined fill-by-fill consistency of asymmetry values • Used the “bunch shuffling” technique to check for systematic errors • Randomly reassign the spin direction to each bunch in the beam • Recalculate the asymmetry • Repeat many times (1000) to produce a “shuffled” asymmetry distribution centered around zero • Compare width of shuffled distribution to statistical error on physics asymmetry

  26. AN of Neutral Pions and Non-Identified Charged Hadrons at Midrapidity qg gg qq Mainly sensitive to g-g and g-q interactions

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