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

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

The Landscape of QCD Plasma ≡ ionized gas which is macroscopically neutral & exhibits collective effects Usually plasmas are e.m., here color forces T >>  QCD : weak coupling  s (Q 2, T)  deconfined phase E.C. Aschenauer  s (Q 2 ) ~ 1 / log(Q 2 /  2 ) 3 BNL Council - July 2009

Why Heavy Ion Physics Q1: How to (re)-create this deconfined state? Q2: How to (re)-creat energy densities 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 E.C. Aschenauer 4 BNL Council - July 2009

b 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 5 BNL Council - July 2009 E.C. Aschenauer 1.Final State Yields of produced particles Thermalization, Hadrochemistry 2. Initial State Role of event geometry and gluon distributions 3. Plasma(?) Probes of dense matter E.C. Aschenauer 5 BNL Council - July 2009

The PHENIX Detector BBC ZDC EMCal    detection Electromagnetic Calorimeter (PbSc/PbGl):  High p T photon trigger to collect trigger to collect  0 's,  ’s,  ’s  Acceptance: |  |  x   High granularity (~10*10mrad 2 )     Drift Chamber (DC) for Charged Tracks Ring Imaging Cherenkov Detector (RICH)  High p T charged pions (p T >4.7 GeV). Relative Luminosity Beam Beam Counter (BBC)  Acceptance: 3.0<  3.9 Zero Degree Calorimeter (ZDC)  Acceptance: ±2 mrad Local Polarimetry ZDC Shower Maximum Detector (SMD) E.C. Aschenauer 6 BNL Council - July 2009 Sasha was involved from the very beginning in the design, building and commissioning of the PbSc Calorimeter  crucial for  0 and  detection

PHENIX EMCal E.C. Aschenauer 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) 7 2×22×2 4×44×4 hh (0)(0) EMCal-RICH trigger Need good calibration of EMCal: trigger homogeneity good resolution of  0  background suppression E  >2GeV 00 7 BNL Council - July 2009 Sasha, calibrated the Calorimeters and was one of the major players to analyze the early PheniX data on the ET mid-rapiditiy  Key-publ. #1 /Publication # citations

Interpret Results Through Perturbative QCD E.C. Aschenauer 8 Hard Scattering Process X q(x 1 ) g(x 2 ) “Hard” probes have predictable rates given: –Parton distribution functions (need experimental input) –Partonic hard scattering rates (calculable in pQCD) –Fragmentation functions (need experimental input)Universality(Processindependence) 8 BNL Council - July 2009

pQCD in Action at  s=200 GeV E.C. Aschenauer 9 Fraction pions produced  ~0 PRL 95, (2005) |  | < 0.35 00 9 BNL Council - July 2009 Sasha, again was one of the major players for this crucial paper. This time he extracted the cross section for  0 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 # citations

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

High-p T Suppression – Matter is Opaque First Observations: 1.Photons are not suppressed Good!  don’t interact with medium N coll scaling works 2.Hadrons are not suppressed in peripheral collisions Good! medium is not dense 3.Hadrons are suppressed in central collisions Huge: factor 5 What about dAu? No suppression E.C. Aschenauer 11 BNL Council - July 2009 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 # citations

RHIC as a Polarized p+p Collider E.C. Aschenauer AGS LINAC BOOSTER Polarized Source Spin Rotators 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipole RHIC pC Polarimeters Absolute Polarimeter (H jet) P HENIX P HOBOS B RAHMS & PP2PP S TAR AGS pC Polarimeter Partial Snake Siberian Snakes Helical Partial Snake Strong Snake Spin Flipper Various equipment to maintain and measure beam polarization through acceleration and storage 12 BNL Council - July 2009

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 E.C. Aschenauer 13 BNL Council - July 2009

Polarimetry E950 experiment at AGS became RHIC pC polarimeter Measure P beam to ~30% H jet polarimeter designed to determine P beam to 5% Achieved uncertainty  P/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 E.C. Aschenauer 14 recoil proton or Carbon scattered proton polarized proton target or Carbon target (polarized) proton beam 14 BNL Council - July 2009

Polarimetry results HJet results for target asymmetry are consistent between Run5 and Run6. Results from beam asymmetry differ, indicating change in polarization. Run5 Run6 E.C. Aschenauer 15 BNL Council - July 2009 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.

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

E.C. Aschenauer News on the spin structure of the nucleon Naïve parton model BUT 1989 EMC measured  = ± ± Spin Puzzle Unpolarised structure fct. Gluons are important ! Sea quarks  q s GGGG Full description of J q and J g needs orbital angular momentum 17 BNL Council - July 2009

Probing  g(x) Through Polarized p+p Collisions E.C. Aschenauer Leading-order access to gluons   G DIS pQCD e+e- ? 18 BNL Council - July 2009

What do we know about  G? 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.  ~25% of proton spin  most of proton spin in either gluon spin, or OAM. From fixed target DIS, gluon is poorly constrained.  GG E.C. Aschenauer 19 BNL Council - July 2009

Results for  0 A LL PHENIX Run6 (  s=200 GeV) arXiv: GRSV model: “  G = 0”:  G(Q 2 =1GeV 2 )=0.1 “  G = std”:  G(Q 2 =1GeV 2 )=0.4 Statistical uncertainties are on level to distinguish “std” and “0” scenarios E.C. Aschenauer 20 BNL Council - July 2009 Sasha, again was one of the major players for the first paper on the A LL for  0. This paper showed that against all expectations the gluon polarisation in the proton is small  Key-publ. #4 /Publication # citations

Relationship between p T and x gluon Log 10 (x gluon ) arXiv: NLO pQCD:  0 p T =2  12 GeV/c NLO pQCD:  0 p T =2  12 GeV/c  GRSV model:  G(x gluon =0.02  0.3) ~ 0.6  G(x gluon =0  1 )  Note: the relationship between p T and x gluon is model dependent Each p T bin corresponds to a wide range in x gluon, heavily overlapping with Each p T bin corresponds to a wide range in x gluon, heavily overlapping with other p T bins other p T bins  Data is not very sensitive to variation of  G(x gluon ) within measured range  Any quantitative analysis assumes some  G(x gluon ) shape arXiv: E.C. Aschenauer 21 BNL Council - July 2009

arXiv: Sensitivity of  0 A LL to  G Generate  g(x) curves for different Calculate A LL for each  G Compare A LL data to curves (produce  2 vs  G) E.C. Aschenauer 22 BNL Council - July 2009 Sasha, developed this  2 -method to extract a limit on the gluon polarisation from the measured A LL  Key-publ. #6 /Publication #115 7 citations

Prompt  Production at  s=200 GeV E.C. Aschenauer Gluon Compton scattering dominates At LO no fragmentation function Small contribution from annihilation 23  qqqq gqgq BNL Council - July 2009 Sasha, again was one of the major players for this crucial paper. This time he extracted the cross section for direct  production and worked together with theorists under the leaders ship of W. Vogelsang that pQCD can be used to describe the data. Direct  data are very important as they eliminate one of the complications with  0 – gluon fragmentation  Key-publ. #5 /Publication # citations

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

includes all world data from DIS, SIDIS and pp includes all world data from DIS, SIDIS and pp Kretzer FF favor SU(3) symmetric sea, not so for KKP, DSS  ~25-30% in all cases D. De Florian et al. arXiv: Q 2 =10 GeV 2 NLO FIT to World Data Kretzer KKP   DIS   SIDIS uvuv uu dvdv dd ss gg                DSS  E.C. Aschenauer 25 BNL Council - July 2009

The Gluon Polarization x RHIC range 0.05 · x · 0.2 small-x · x · 0.05 large-x x ¸ 0.2  g(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  g(x) small !? Need to enlarge x-range E.C. Aschenauer 26 BNL Council - July 2009

Summary Sasha is a unique scientist, who has made significant contributions studying nuclear physics measurements of E T 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 A LL to  G (Key-publ. #6) unique contributions to designing hardware (PbSc-calorimeter) to make the important measurements above possible 27 BNL Council - July 2009 E.C. Aschenauer I hope you agree with me Sasha should be granted tenure

BACKUP SLIDES E.C. Aschenauer 28 BNL Council - July 2009

good agreement with NLO-QCD Polarised opposite to proton spin Polarized Quark Densities  u(x) > 0 First complete separation of First complete separation of pol. PDFs without assumption on pol. PDFs without assumption on sea polarization sea polarization Polarised parallel to proton spin  d(x) < 0 ~ 0   u(x),  d(x) ~ 0 No indication for< 0 No indication for  s(x) < 0 In measured range (0.023 – 0.6) In measured range (0.023 – 0.6) E.C. Aschenauer 29 BNL Council - July 2009

Beam: 27.5 GeV e ± ; % polarization Target: (un)-polarized gas targets; polarization Lumi: pol: 5x10 31 cm -2 /s -1 ; unpol: 3x cm -2 /s -1 Data taking finished June 2007 The contemporary experiments SM1 SM2 6 LiD Target 160 GeV μ RICH ECal & HCal μ Filter Trigger-hodoscopes Silicon Micromegas SciFi Gems Drift chambers Straws MWPC 50 m Beam: 160 GeV  : 80% polarization Target: 6 LiD: 50% polarization ( ) NH 3 : 80% polarisation (2007) NH 3 : 80% polarisation (2007) Lumi: 5x10 32 cm -2 s -1 STAR Detector Beams: √s=200 GeV pp; 50% polarization Lumi: 50 pb -1 E.C. Aschenauer 30 BNL Council - July 2009

First Results E.C. Aschenauer 31 BNL Council - July 2009