1 / 61

Photons at RHIC

Photons at RHIC. Henner B ü sching FIAS – Universi ty of Frankfurt. Jyv äskylä - March 2007. RHIC: 200 GeV pp Run over. RHIC: 200 GeV Run Started. Hoax!. In a perfect world…. News: RHIC is running!. …in a simple world…. …temperature of the QGP can be measured

genna
Download Presentation

Photons at RHIC

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. Photons at RHIC Henner Büsching FIAS – University of Frankfurt Jyväskylä - March 2007

  2. RHIC: 200 GeV pp Run over RHIC: 200 GeV Run Started Hoax! In a perfect world… News: RHIC is running!

  3. …in a simple world… …temperature of the QGP can be measured by thermal photon radiation… …photons don’t interact with the medium… …good probe of the medium… … gamma- jet correlations… XXX’s Diploma Thesis

  4. …in the real world… (g/p0)measured / (g/p0)background gmeasured / gbackground Difficult measurement ! PHENIX Experiment: Need statistics Understand detector? Theory: Do we understand all sources? Experiment: Problem to extract Large uncertainties Theory: Do we understand all sources?

  5. In the real world…a wide field! Photon Tagging Statistical Method Ext. Conversions Virtual g PHENIX Direct g v2 g-jet Shapes Reaction Plane Dependence Intermediate pT Studies Isolation Cut Jet Medium Interactions Thermal g Bremsstrahlung g Precision!

  6. Status So far unfulfilled: Initial temperature via thermal photons Energy loss via g-jet correlations

  7. Punchline first: Where we are 1 Low pT Direct photon spectrum for 1 < pT < 4.5 GeV via internal conversion Run4 data

  8. Punchline first: Where we are 2 High pT Run2 data

  9. Punchline first: Where we are 3 High pT - Proton Reference Run4 data

  10. Who ordered all these photons?

  11. Un-affected by medium Photon Sources in Au+Au photons in A+A direct photons decay photons hard direct fragmentation bremsstrahlung Hard direct photons:Direct component q q g g Annihilation Compton _ g g q q

  12. Affected by medium Photon Sources in Au+Au photons in A+A direct photons decay photons hard direct fragmentation bremsstrahlung g Hard direct photons:bremsstrahlung and fragmentation q g q g g q g q

  13. Photon Sources in Au+Au photons in A+A direct photons decay photons pre-equilibrium hard thermal jet-plasma-interact. direct fragmentation QGP hadron gas jet-g-conv. medium-induc.g bremsstr.

  14. Photon Sources in Au+Au photons in A+A direct photons decay photons pre-equilibrium hard thermal jet-plasma-interact. direct fragmentation QGP hadron gas jet-g-conv. medium-induc.g bremsstr. Jet-plasma interactionjet-photon-conversion

  15. Photon Sources in Au+Au photons in A+A direct photons decay photons pre-equilibrium hard thermal jet-plasma-interact. direct fragmentation QGP hadron gas jet-g-conv. medium-induc.g bremsstr. Jet-plasma interaction:medium-induced bremsstrahlung QGP q

  16. Photon Sources in Au+Au photons in A+A direct photons decay photons pre-equilibrium hard thermal jet-plasma-interact. direct fragmentation QGP hadron gas jet-g-conv. medium-induc.g bremsstr. Created in all phases of the collision Once created, they survive But this makes measurements hard to interpret

  17. Thermal photons relevant below pT ~ 3 GeV/c Hard Photons for pT > ~ 6 GeV/c Jet-Plasma-Konv. hard: thermal: Spectra - Schematic Decay photons(p0→g+g, h→g+g, …)

  18. Spectra – Recent Theory C. Gale, hep-ph/0609301

  19. Let’s measure

  20. STAR: Welcome to the Club p0 g p0 2003 d+Au 2005 p+p

  21. The traditional way Subtraction • Get clean inclusive photon sample • Measure pT spectrum of p0 and h mesons with high accuracy • Calculate number of decay photons per p0 • Done with Monte-Carlo • mT scaling for (h), h’, w, … • Finally:Subtract decay background from inclusive photon spectrum h/p0

  22. Fraction of neutral background(neutron, anti-neutrons) Fraction of charged clusters efficiency acceptance Inclusive Photon Spectrum photon conversion Subtraction

  23. Uncertainties Many systematic uncertainties of p0 and photon measurements are highly correlated! Subtraction

  24. Advantage Good momentum resolution for low pT charged particles (e+e-) allows photon measurement at low pT Less trouble with background from hadrons Disadvantage Radiator needs to be thin: low photon detection probability Necessary to separate conversion pairs from p0 and h Dalitz decays (p0 g+e++e-) New ways I Conversion

  25. New ways II Tagging • Tag all photons, which combined with a photon from a second (less clean) sample can be identified as pion decay product • Correct direct photon candidate sample for contribution from p0decay photons with missing partner and for direct photons with fake partners • Subtract contribution from h, w etc. decays • In central A+A collisions the number of random associations is too high for this approach • Can work at high pT

  26. Results in Au+Au

  27. Direct photons in d+Au It works…

  28. differentminv-distribution Internal Conversion • Any source of real g produces virtual gwith very low mass • minv distribution depends on process • Rate and mass distribution given by same formula

  29. Internal Conversion invariant mass of Dalitz pair invariant mass of Dalitz pair invariant mass of virtual photon invariant mass of virtual photon form factor form factor phase space factor phase space factor

  30. Discussion of results “Thermal”

  31. 2+1 hydro,d’Enterria, Perresounko Low pT – internal conversion Good p+p is missing Ti ~ 300 – 400 MeV

  32. Int. Conversions: d+Au Not as successful as in Au+Au: High background in Run3

  33. Comparison: d+Au & Au+Au We still have to wait for Run5 p+p

  34. p+p and d+Au

  35. Direct photons in p+p Run 3 Run 5 Phys. Rev. Lett. 98, 012002 (2007)

  36. Direct photons in p+p

  37. Initial state: d+Au NLO pQCD from W.Vogelsang Run 3 No indication for nuclear effects

  38. High pT – Au+Au

  39. No energy loss Energy loss RAA at high pT Reference for photons: pQCD

  40. RAA at high pT Reference for photons: measurement

  41. RAA with pQCD RAA with p+p data RAA at high pT

  42. RAA– Centrality Dependence

  43. Scenario: Isospin F. Arleo, JHEP09 (2006) O15 • Shadowing • Isospin (p+n vs. p+p) • Energy loss: • Suppression of direct photons from fragmentation/bremsstrahlung • BDMPS • No medium induced jet-photon conv. direct From fragmentation:~ 30% at pT = 15 GeV/c fragment

  44. Scenario: Isospin II Vogelsang No problem? “primordial” photons unaltered? “medium-induced” photons can be enhanced or suppressed Help from 62 GeV? Lower pT Unclear effects? Jet-g conversion

  45. Scenario: Jet-g-Conversion + Energy loss • Turbide et al. • Phys. Rev. C72 (2005) 014906 + Private communication • AMY formalism for jet-quenching effect for fragmentation photons. • Systematically data points are below theoretical prediction.

  46. isolation

  47. Jet g Isolation Cut Expectation for direct photons: • N+N: isolated • Jet-Photon conversion: isolated • Jet-fragmentation: non isolated • Bremsstrahlung:non isolated • hep-ex/0609031

  48. Flow

  49. f Direct-Photon v2 Spatial anisotropy Momentum anisotropy v2 > 0 for hadrons reaction plane Expectation for direct photons: • N+N: v2 > 0 • Jet-fragmentation: v2 > 0 • Jet-Photon conversion: v2 < 0 • In-medium bremsstr.:v2 < 0 • Net effect: v2 < 0

  50. Direct Photon v2 Turbide, Gale, Fries, Phys.Rev.Lett.96:032303,2006 Expectation for v2: negative, |v2|  3% − 5% Here: Assuming no energy loss: jet-g conversion dominates v2 : v2<0

More Related