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The mysteries of QCD! or

The mysteries of QCD! or. “What Sasha did to unravel them”. What characterizes QCD. QED (Abelian): Photons have do not carry color/electric charge Flux is not confined  1/r potential  1/r 2 force. Confinement. Asymptotic Freedom. Small Distance High Energy. Large Distance

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The mysteries of QCD! or

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  1. The mysteries of QCD! or “What Sasha did to unravel them” BNL Council - July 2009

  2. What characterizes QCD • QED (Abelian): • Photons have do not carry color/electric charge • Flux is not confined  1/r potential  1/r2 force Confinement Asymptotic Freedom Small Distance High Energy Large Distance Low Energy E ~ 1/l Perturbative QCD Strong QCD • QCD (Non-Abelian): • Gluons carry color charge: • Flux tubes form  potential ~ r  constant force • self-interacting force carriers  gluons BNL Council - July 2009

  3. as(Q2) ~ 1 / log(Q2/L2) The Landscape of QCD Plasma ≡ ionized gas which is macroscopically neutral & exhibits collective effects Usually plasmas are e.m., here color forces • T >> LQCD: • weak coupling as(Q2, T)  deconfined phase BNL Council - July 2009

  4. Why Heavy Ion Physics Q1: How to (re)-create this deconfined state? Q2: How to (re)-creat energy densities 10-20 x normal nuclear density? Q3: How to liberate quarks and gluons from ~1 fm confinement scale? A: Create an energy density  Relativistic Heavy Ion CollisionsCollide “large” nuclei at “large” energies BNL Council - July 2009

  5. b 2. Initial State Role of event geometry and gluon distributions • Final State • Yields of produced particles • Thermalization, Hadrochemistry 3. Plasma(?) Probes of dense matter Heavy Ion Collisions • Event characterization • Impact parameter b is well-defined in heavy ion collisions • Event multiplicity predominantly determined by collision geometry • Characterize this by global measures of multiplicity and/or transverse energy BNL Council - July 2009 BNL Council - July 2009 5 E.C. Aschenauer

  6. BBC ZDC ZDC The PHENIX Detector p0, h, g detection • Electromagnetic Calorimeter (PbSc/PbGl): • High pT photon trigger to collect trigger to collect p0's, h’s, g’s • Acceptance: |h|<0.35, f = 2 x p/2 • High granularity (~10*10mrad2) p+/ p- • Drift Chamber (DC) for Charged Tracks • Ring Imaging Cherenkov Detector (RICH) • High pT charged pions (pT>4.7 GeV). Relative Luminosity • Beam Beam Counter (BBC) • Acceptance: 3.0< h<3.9 • Zero Degree Calorimeter (ZDC) • Acceptance: ±2 mrad Local Polarimetry • ZDC • Shower Maximum Detector (SMD) EMCal Sasha was involved from the very beginning in the design, building and commissioning of the PbSc Calorimeter  crucial for p0 and g detection BNL Council - July 2009

  7. EMCal part of trigger has two sums to collect photon shower 2×2 tower non-overlapping sum (threshold at 0.8 GeV) 4×4 tower overlapping sum (3 thresholds possible  lowest at 1.4 GeV) p0 h (0) PHENIX EMCal • Need good calibration of EMCal: • trigger homogeneity • good resolution of p0 • background suppression EMCal-RICH trigger Eg>2GeV • Sasha, calibrated the Calorimeters • and was one of the major players to • analyze the early PheniX data on the • ET distribution @ mid-rapiditiy • Key-publ. #1 /Publication #34 • 129 citations 2×2 4×4 7 BNL Council - July 2009

  8. q(x1) Hard Scattering Process X g(x2) Universality (Process independence) Interpret Results Through Perturbative QCD • “Hard” probes have predictable rates given: • Parton distribution functions (need experimental input) • Partonic hard scattering rates (calculable in pQCD) • Fragmentation functions (need experimental input) 8 BNL Council - July 2009

  9. |h| < 0.35 PRL 95, 202001 (2005) pQCD in Action at Ös=200 GeV p0 Fraction pions produced • Sasha, again was one of the major players • for this crucial paper. • This time he extracted the cross section • for p0 production and worked together with • theorists under the leaders ship of W. Vogelsang • that pQCD can be used to describe the RHIC data • Key-publ. #2 /Publication # 46 • 231 citations h~0 9 BNL Council - July 2009

  10. How to Measure Nuclear Effects ? • Compare Au+Au with p+p Collisions  RAA Nuclear Modification Factor: Average number of NN collision in an AA collision No “Effect”: R < 1 at small momenta R = 1 at higher momenta where hard processes dominate Suppression: R < 1 BNL Council - July 2009

  11. High-pT Suppression – Matter is Opaque • First Observations: • Photons are not suppressed • Good! g don’t interact with medium • Ncoll scaling works • Hadrons are not suppressed in peripheral collisions • Good! medium is not dense • Hadrons are suppressed in central collisions • Huge: factor 5 • Sasha, was one of the principal authors of the paper • showing that there are no nuclear modifications seen • colliding dAu. • This paper together with the observation of Jet quenching • are the proof for new stated in matter. • Key-publ. #3 /Publication # 51 • 318 citations What about dAu? No suppression BNL Council - July 2009

  12. Absolute Polarimeter (H jet) Helical Partial Snake Strong Snake RHIC as a Polarized p+p Collider RHIC pC Polarimeters Siberian Snakes BRAHMS & PP2PP PHOBOS Siberian Snakes Spin Flipper PHENIX STAR Spin Rotators Various equipment to maintain and measure beam polarization through acceleration and storage Partial Snake Polarized Source LINAC AGS BOOSTER 200 MeV Polarimeter Rf Dipole AGS Internal Polarimeter AGS pC Polarimeter BNL Council - July 2009

  13. RHIC Polarimetry • Proton-carbon (pC) polarimeter • For fast measurements (< 10 s!) of beam polarization • Take several measurements during each fill • Polarized hydrogen-jet polarimeter • Dedicated measurements (~weeks) to calibrate the pC polarimeter • Three-fold purpose of polarimeters • Measurement of beam polarization to provide feedback to accelerator physicists • Measurement of beam polarization as input for spin-dependent measurements at the various experiments • Study of polarized elastic scattering BNL Council - July 2009

  14. scattered proton (polarized) proton beam polarized proton target or Carbon target recoil proton or Carbon Polarimetry • E950 experiment at AGS became RHIC pC polarimeter • Measure Pbeam to ~30% • H jet polarimeter designed to determine Pbeam to 5% • Achieved uncertainty dP/P of 4.2% in 2008! • Both use asymmetries in processes that are already understood to determine the beam polarization • Use transversely polarized hydrogen target and take advantage of transverse single-spin asymmetry in elastic proton-proton scattering 14 BNL Council - July 2009

  15. Run5 Run6 Polarimetry results • HJet results for target asymmetry are consistent between Run5 and Run6. • Results from beam asymmetry differ, indicating change in polarization. Sasha, is currently leading the analysis of the polarimeter data to provide reliable polarisation numbers to the collaboration. Also here his contribution was absolutely essential to reach the goal of 5% systematic uncertainty on the polarisation. BNL Council - July 2009

  16. The Spin of the Proton Nobel Prize, 1943: "for his contribution to the development of the molecular ray method and his discovery of the magnetic moment of the proton" mp = 2.5 nuclear magnetons, ± 10% (1933) Proton spins are used to image the structure and function of the human body using the technique of magnetic resonance imaging. Otto Stern Sir Peter Mansfield Paul C. Lauterbur Nobel Prize, 2003: "for their discoveries concerning magnetic resonance imaging" BNL Council - July 2009

  17. Naïve parton model Unpolarised structure fct. Gluons are important ! BUT Full description of Jq and Jg needs orbital angular momentum 1989 EMC measured S = 0.120 0.094 0.138 ± ± DG Spin Puzzle Sea quarksDqs News on the spin structure of the nucleon BNL Council - July 2009

  18. e+e- ? pQCD DIS Probing Dg(x) Through Polarized p+p Collisions Leading-order access to gluons  DG BNL Council - July 2009

  19. DG DS~0.25 What do we know about DG? • Recall the unpolarized data. • In the polarized case, much less data exists, covering much smaller x and Q2 range. • Even with this small range of data, polarized quark distribution is reasonably well constrained. • DS~25% of proton spin •  most of proton spin in either gluon spin, or OAM. • From fixed target DIS, gluon is poorly constrained. BNL Council - July 2009

  20. Results for p0 ALL PHENIX Run6 (s=200 GeV) Sasha, again was one of the major players for the first paper on the ALL for p0. This paper showed that against all expectations the gluon polarisation in the proton is small  Key-publ. #4 /Publication # 60 50 citations arXiv:0810.0694 Statistical uncertainties are on level to distinguish “std” and “0” scenarios GRSV model: “G = 0”: G(Q2=1GeV2)=0.1 “G = std”: G(Q2=1GeV2)=0.4 BNL Council - July 2009

  21. Relationship between pT and xgluon arXiv:0810.0694 arXiv:0810.0694 • NLO pQCD: 0 pT=212 GeV/c • GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 ) • Note: the relationship between pT and xgluon is model dependent • Each pT bin corresponds to a wide range in xgluon, heavily overlapping with • other pT bins • Data is not very sensitive to variation of G(xgluon) within measured range • Any quantitative analysis assumes some G(xgluon) shape Log10(xgluon) BNL Council - July 2009

  22. arXiv:0810.0694 Sensitivity of p0 ALL to DG Generate g(x) curves for different Calculate ALL for each G Compare ALL data to curves (produce 2 vs G) Sasha, developed this c2-method to extract a limit on the gluon polarisation from the measured ALL  Key-publ. #6 /Publication #115 7 citations BNL Council - July 2009

  23. Gluon Compton scattering dominates At LO no fragmentation function Small contribution from annihilation g DgDq DqDq Prompt g Production at Ös=200 GeV • Sasha, again was one of the major players • for this crucial paper. • This time he extracted the cross section • for direct g production and worked together with • theorists under the leaders ship of W. Vogelsang • that pQCD can be used to describe the data. • Direct g data are very important as they eliminate one • of the complications with p0 – gluon fragmentation • Key-publ. #5 /Publication # 87 • 58 citations 23 BNL Council - July 2009

  24. Hard Scattering Process g DgDq DqDq Direct photon • First step, direct photon cross section. • ALL results from Run5 with very small statistics • Will need significant higher statistics for this measurement • Background ALL estimates increase errors by ~30% at low pT • Currently studying other methods to estimate background Isolation cut R=0.5, f=0.1 minE=0.15GeV Pmin=0.2GeV Pmax=15GeV BNL Council - July 2009

  25. c2DIS c2SIDIS Duv Ddv Du Dd Ds Dg DS Kretzer -0.049 -0.051 206 225 0.94 -0.34 -0.055 0.28 KKP -0.11 -0.045 206 231 0.70 -0.26 0.087 0.31 0.813 -0.458 0.036 -0.115 -0.057 0.242 DSS NLO FIT to World Data NLO @ Q2=10 GeV2 D. De Florian et al. arXiv:0804.0422 • includes all world data from DIS, SIDIS and pp • Kretzer FF favor SU(3) symmetric sea, not so for KKP, DSS • DS ~25-30%in all cases BNL Council - July 2009

  26. x small-x 0.001· x · 0.05 RHIC range 0.05· x · 0.2 large-x x ¸ 0.2 The Gluon Polarization • Dg(x) very small at medium x • best fit has a node at x ~ 0.1 • huge uncertainties at small x • small-x behavior completely • unconstrained Dg(x) small !? Need to enlarge x-range BNL Council - July 2009

  27. Summary • Sasha is a unique scientist, who has made significant contributions studying nuclear physics • measurements of ET in AuAu (Key-publ. #1) • pQCD is applicable at RHIC (Key-publ. #2) • no medium modifications in dAu (Key-publ. #3) • the polarisation of gluons is small (Key-publ. #4) • the measurement of direct photons at RHIC (Key-publ. #5) • developing a method to related ALL to DG (Key-publ. #6) • unique contributions to designing hardware (PbSc-calorimeter) to make the important measurements above possible I hope you agree with me Sasha should be granted tenure BNL Council - July 2009

  28. BACKUP SLIDES BNL Council - July 2009

  29. Du(x), Dd(x) ~ 0 • In measured range (0.023 – 0.6) • No indication forDs(x)<0 Polarised opposite to proton spin Polarised parallel to proton spin Polarized Quark Densities • First complete separation of • pol. PDFs without assumption on • sea polarization Dd(x) < 0 • Du(x) > 0 good agreement with NLO-QCD BNL Council - July 2009

  30. 160 GeVμ SM2 SM1 6LiD Target The contemporary experiments Trigger-hodoscopes μFilter ECal & HCal 50 m STAR Detector Beams: √s=200 GeV pp; 50% polarization Lumi: 50 pb-1 RICH MWPC Beam: 27.5 GeV e±; <50>% polarization Target: (un)-polarized gas targets; <85%> polarization Lumi: pol: 5x1031 cm-2/s-1; unpol: 3x1032-33 cm-2/s-1 Data taking finished June 2007 Straws Gems Drift chambers Beam: 160 GeV m: 80% polarization Target: 6LiD: 50% polarization (2002-2006) NH3: 80% polarisation (2007) Lumi: 5x1032 cm-2s-1 Micromegas Silicon SciFi BNL Council - July 2009

  31. First Results BNL Council - July 2009

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