1 / 60

Dinesh K. Srivastava Variable Energy Cyclotron Centre Kolkata 700 064, India

Single Photons from Relativistic Heavy Ion Collisions : Delivering Much More Than Their Original Promise. Dinesh K. Srivastava Variable Energy Cyclotron Centre Kolkata 700 064, India. 20 th International Conference on Ultra-Relativistic Nucleus- Nucleus Collisions, Jaipur , India.

ophrah
Télécharger la présentation

Dinesh K. Srivastava Variable Energy Cyclotron Centre Kolkata 700 064, India

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. Single Photons from Relativistic Heavy Ion Collisions : Delivering Much More Than Their Original Promise Dinesh K. Srivastava Variable Energy Cyclotron Centre Kolkata 700 064, India 20th International Conference on Ultra-Relativistic Nucleus- Nucleus Collisions, Jaipur, India

  2. Thirty two years ago: E. L. Feinberg, Nuv. Cim. A 34 (1976) 391, pointed out that: Direct photons; real or virtual are penetrating probes for the bulk matter produced in hadronic collisions, as - They do not interact strongly. - They have a large mean free path. Since then relentlessefforts by researchers from across the world have established these as reliable probes of hot and dense matter.

  3. Electromagnetic Probes Penetrating probes are emitted at all stages then survive unscathed (ae <<as). “Historians” of the heavy ion collision: encode all sub-processes at all times A jet passing through QGP Different processes: different characteristic spectra

  4. Direct PhotonsDifferent Sources - Different Slopes Rate Photons are result of convolutions of the emissions from the entire history of the nuclear collision, so we need rates & a model for evolution. Hadron Gas Thermal Tf QGP Thermal Ti “Pre-Equilibrium”? • Hydrodynamics. • Cascades. • Fire-balls. • Cascade+Hydro. “New” Jet Re-interaction √(Tix√s) pQCD Prompt x√s Eg

  5. Partonic Processes for Production of Prompt Photons in Hadrons Fragmentation Compton Annihilation Calculate using NLO pQCD [with shadowing & scaling with TAA(b) for AA, partons remain confined to individual nucleons; do not forget the iso-spin! ] The quarks will lose energy before fragmenting if there is QGP; suppressing the fragmentation contribution. See e.g., Jeon, Jalilian-Marian, Sarcevic, NPA 715 (2003) 795, “QM-2002”.

  6. NLO pQCD description of world prompt- photon data. Aurenche et al. PRD 73 (2006) 094007. See also Gordon & Vogelsang (1994). Most suitable scale is m=mR=mF=pT/2. Do not forget that m=pT/3 for pions !!! Why should they be different?

  7. In the QGP we also have: g Medium induced bremsstrahlung; First calculated byZakharov, JETP Lett. 80 (2004) 1; Turbide et al, PRC 72 (2005) 014905. Zhang, Kang, & Wang, hep-ph/0609159. Annihilation with scatterring;First calculated by Aurenche et al, PRD 58 (1998) 085003. Complete leading order results: Arnold, Moore, Yaffe, JHEP 0112 (2001) 009. How about NLO?

  8. Examples of Hadronic Processes Involving p & r for Production of Photons • Include pra1 pg • Xiong et al, PRD 46 (1992) 3798; • Song, PRC 47 (1993) 2861. • Include baryonic processes. • Alam et al, PRC 68 (2003) 031901. • Medium modifications; (Series of • valuable papers, T and mb) • Alam et al, Ann. Phys. 286 (2001) • 159. • Include strange sector, massive • Yang- Mills theory, form-factors, • baryons, t-channel exchange of • w mesons etc. • Turbide, Rapp, Gale, PRC 69 • (2004) 014903. First calculated by Kapusta, Lichard, & Seibert, PRD 44 (1991) 2774.

  9. Complete Leading Order Rates from QGP &Exhaustive Reactions in Hadronic Matter Rates are similar !! We need QGP at higher T0 for golden photons to clearly outshine others. Arnold, Moore, & Yaffe, JHEP 0112 (2001) 009. Turbide, Rapp, & Gale, PRC 69 (2004) 014903.

  10. Upper Limit of Single Photons, WA80 Ruled out hadronic gas with limited hadrons: p, r, w, & h. Pb+Pb@SPS S. and Sinha, PRL 73 (1994) 2421; Dumitru et al., PRC 51 (1995) 2166. Sollfrank et al., Lee & Brown, Arbex et al., . Cleymans, Redlich, & S., PRC 55 (1997) 1431. However, nhad >> 2-3 /fm3 ! For No Phase Transition.

  11. QGP or Hot Hadrons? Enter WA98 QGP + prompt g v0.ne.0 Hadrons (mhad 0 at Ti=205 MeV for all hadrons) Huovinen et al, PLB 535 (2002) 109. QGP or hadrons ( nhad >> 1/fm3 at Ti = 245-275 MeV) Alam et al, PRC 63 (2001) 021901 ( R).

  12. 2-loop  Complete O(aS) for QGP & pra1 Exhaustive Hadronic Reactions for hadrons S., PRC 71 (2005) 034905. S. & Sinha, PRC 64 (2001)034902 (R ). Hydrodynamics, QGP + rich EOS for hadrons & accounting for the prompt photons

  13. So, what did we learn from the single photon data at SPS energies? • Hadronic gas with limited degrees of freedom is definitely ruled out. • Massively medium modified hadonic gas with mhad0 at T0~ 200 MeV or an over-dense hadronic gas with nhad >> 1/fm3 at t0 is not ruled out. • QGP initial state describes the data well. • Initial temperature could be 210 – 350 MeV, depending on t0 , profile, & v0.What is a good t0? Should v0 be non-zero? RHIC should provide higher initial temperatures. More importantly RHIC ushers in a paradigm shift by producing jets and quenching them! Reference pp data available. Hope

  14. Interaction of hard-scattered parton with dense matter Jet Photon Conversion “External Probe!!” Hard scattered parton Fries, Mueller, & S. , PRL 90 (2003) 132301.

  15. Jet-Initiated EM Radiations from QGP • Annihilation and Compton processes peak in forward and backward directions: • one parton from hard scattering, one parton from the thermal medium; cutoff p,min > 1 GeV/c. • photon carries momentum of the hard parton • Jet-Photon Conversion • This puts photon production and jet-quenching on the same page!!

  16. Jet-Photon Conversion: Rates quark (-jet) distribution • Annihilation and Compton rates: • thermal medium:

  17. Photons from Passage of Jets through QGP Fries, Mueller, & S., PRL 90 (2003) 132301. This “bremsstrahlung” contribution will be suppressed due to E-loss and there will be an additional jet-induced bremsstrahlung, which is also similarly suppressed, leaving the jet-conversion photons as the largest source for pT = 4-10 GeV.

  18. FMS Results: Comparison to Data • calibrate pQCD calculation of • direct and Bremsstrahlung • photons via p+p data: • for pt<6 GeV, FMS photons give significant contribution to photon spectrum: 50% @ 4GeV. Proper Isospins & Shadowing !!! Fries, Mueller, & S., PRC 72 (2005) 041902( R).

  19. Evolution of jet distribution due to E-loss AMY

  20. AMY and One-Stop Treatment of Jet-Quenching and Jet-Initiated Photons Turbide, Gale, Frodermann, & Heinz, hep-ph/0712.732 (Talk by Gale) Thissupercedes, Turbide, Gale, Jeon, & Moore, PRC 72 (2005) 014906; which used AMY but all the processes were calculated using hard spheres and ignoring transverse expansion.

  21. Q=pT/sqrt(2) for prompt calculations, Turbide et al. (see also Arleo, JHEP 0609, 015 (2006), Liu & Werner, hep-ph/0712.3619 and Liu & Fries, nucl-th/0801.0453 . ).

  22. Parton Cascade Model Embedded in the partonic cascades Renk, Bass, & S., PLB 632 (2006) 632. Bass, Mueller, & S., PRC 66 (2002) 061902 (R). LPM plays a significant role.

  23. Thermalphotons from Au+Au@RHIC d’Enterria & Peressounko, EPJC 46 (2006) 451.

  24. So, what are we seeing at RHIC ? • QGP or partonic initial state describes the data well. • Models of evolution: hydrodynamics, cascades, fireballs. • Initial temperature could be 300 – 580 MeV, depending on t0 : 0.6 - 0.15 fm/c. Chemical equilibrium assumed*. • Emerging evidence for photons from the passage of jets through the plasma. Dileptons should follow. *S., Mustafa, Mueller, S., PRC 56 (1997) 1064.

  25. Not Just T0! • Measure evolution of elliptic flow with thermal photons (v2 >0)! • Help understand dE/dx with photon or dilepton tagged jets. • Study evolution of size with intensity interferometry of photons! • Measure melting of hc etc. by studying diphotons!

  26. Elliptic Flow of Thermal Photons:Measure Evolution of Flow ! Adult life Late times Early times Chatterjee, Frodermann, Heinz, and S., PRL 96 (2006) 202302.

  27. Impact Parameter Dependence of v2

  28. Elliptic Flow of Thermal Dileptons: Measure Evolution of Flow ! Chatterjee, Heinz, Gale, & S., PRC 75, 054909 (2007). See poster by Rupa

  29. Evolution of flow for thermal photons See Poster by Rupa Chatterjee

  30. Azimuthal Anisotropy of Photons from Passage of Jets Through QGP • Jet-photon conversion • (v2 < 0) • Jet-bremsstrahlung • (v2 < 0) • Jet-fragmentation • (v2 > 0) • pQCD (v2= 0) Only the v2 for thermal photons survives. See talk by Gale. Turbide, Gale, and Fries, PRL 96 (2006) 032303, v2 for jet initiated photons over-estimated : transverse expansion was ignored and hard sphere nuclei were used.

  31. Golden Channels : • g + q → γ+ q (Compton) • q + q → γ + g (Annihilation) • pT > 10 GeV/c g Photon tagged jets g-jet correlation • Eg = Ejet • Opposite direction • Direct photons are not affected by the medium • Parton in-medium-modification through the fragmentation function D(z), z = phadron/Eg Wang, Huang, & Sarcevic, PRL 77 (1996) 231. See also, Renk, PRC 74 (2006) 034906, for differentiation of mechanisms of E-loss, and several results at this meeting.

  32. g-tagged hadrons and mechanism for E-loss Renk, PRC 74 (2006) 034906. (STAR & PHENIX)

  33. isolatedphotons γ q Compton g q q γ Annihilation g q g q Jet γ g q g γ q g q Isolation cut can remove the bremmstrahlung photons Bremsstrahlung Several talks and posters at this meeting.

  34. Dilepton vs. photon tagged jets g* • Photon tagged jets: • Difficult measurement: • At low pT, p0 gg large background. • At higher pT, background problem better • but opening angle becomes smaller. Compton • Dilepton tagged jets: • Lower yield but lower back-ground. • Charm and beauty decay could be identified. • M and pT: two handles! • Gold plated standard via Z0 tagging at LHC. S., Gale, & Awes, PRC 67 (2003) 054904; Lokhtin et al, PLB 599 (2004) 260.

  35. Azimuthal tagging of jets with photons/dileptons Jet Jets of a given enegy traversing different path-lengths! Very Valuable. Eg=Ejet Eg=Ejet g

  36. So, where do we stand? • SPS: Results can be understood in terms of a very dense hot hadronic or a partonic initial state. • RHIC: Thermal radiations as well as photons from passage of jets through QGP seen. • Photons from passage of jets through QGP, biggest source at pT~4 - 8 GeV. • Elliptic flow for thermal photons & dileptons will confirm start-up of flow at a very early stage. • The photon or dilepton tagged jets will tell you about dE/dx. Tag a photon at some angle to reaction plain and control < L > covered by the jet !! • The promises of photons and dileptons well beyond their original promise have started materializing! • LHC: An spectacular display of all conceivable aspects of direct photons and dileptons is guaranteed!! • FAIR would explore large mB environments- not well explored as yet.

  37. Let us get critical for a change • The “extent” of thermal and qgp induced photons is total minus prompt contribution. • The prompt contribution calculated at NLO pQCD depends on scale. The fragmentation part depends on E-loss as well. Accurate pp and pA data would help, though we shall never have pn and nn data. • Does one need to include intrinsic kT? • The thermal contribution is known only at leading order. • There is no independent check for hadronic reaction contribution. Medium modifications? • Needed simultaneous description of photons and p0. • & Viscousity.

  38. Collaborators Terry C. Awes Steffen A. Bass Rupa Chatterjee Jean Cleymans Rainer J. Fries Evan Frodermann Charles Gale Ulrich Heinz Berndt Mueller M. G. Mustafa Thorsten Renk Krzysztof Redlich Bikash Sinha Simon Turbide

  39. Back up slides

  40. If I had more time: • Jamal Jalilian Marian, nucl-th/0703069; g/p0 at large y  dynamics of colour gluon condensate & saturation. • Intensity Interferometry of direct photons • D. Peressounko, PRC 67 (2003) 014905; • J. Alam et al., PRC 67 (2003) 054902; • S. A. Bass, B. Muller, D. K. Srivastava, PRL 16 (2004) 162301; • D. K. Srivastava, PRC 71 (2005) 034905. • New Mechanism • Qin, Majumder, Gale, PRC 75 (2007) 064909; charge asymetry  g • Higher Twist Alternative to AMY • Majumder, Fries, Muller, nucl-th/0711.2475 • g/m+m- • B. Sinha, PLB 128B (1983) 112. • D. K. Srivastva and B. Sinha PLB 261 (1991) 1064. • J. K. Nayak et al, nucl-th/0705.1591.(see talk by Nayak).

  41. The Information Content of EM Probes m- Emission rates: m+ Photons: Dileptons: • McLerran & Toimela, • PRD 31 (1985) 545; • Weldon, PRD 42 (1990) 2384; • Gale & Kapusta, • NPB 357 (1991) 65. In- medium photon self energy: Directly related to the in-medium vector spectral densities!

  42. Low, Intermediate, & High Mass Dileptons • Low-mass: Medium modified spectral density • Intermediate mass: Radiation from QGP • High mass: J/y etc., suppression The same model should explain both: Single Photons and Dileptons.

  43. FMS: Centrality Dependence and Jet-Quenching • centrality dependence well described • effect of energy-loss on jets before conversion ~ 20%

  44. Larger kT or Larger Ti? Turbide, Rapp, & Gale, PRC 69 (2004) 014903; Fire-ball, QGP + rich EOS for hadrons

  45. Intermediate Mass; NA50 Kvasnikova, Gale, & Srivastava, PRC 65 (2002) 064903. Acceptance and detector resolution accurately modeled. See also Rapp & Shuryak, PLB 473 (2000) 13.

  46. Photons: pre-equilibrium vs. thermal • pre-equilibrium contributions are easier identified at large pt: • window of opportunity above pt=2 GeV • at 1 GeV, need to take thermal contributions into account • short emission time in the PCM, 90% of photons before 0.3 fm/c • hydrodynamic calculation with τ0=0.3 fm/c allows for a smooth continuation of emission rate • caveat: medium not equilibrated at τ0

  47. Photons: HBT Interferometry • pt=2 GeV: pre-thermal photons dominate, small radii • pt=1 GeV: superposition of pre- & thermal photons: increase in radii Bass, Mueller, & Srivastava, PRL 93 (2004) 16230; Srivastava, PRC 71 (2005) 034905.

  48. Intensity Interferometry of Thermal Photons WA98; 8.3+/-2 fm. D. K. Srivastava, PRC 71 (2005) 034905.

  49. r g* p w, f p Determining TC: w Lends a Hand A little digression p Srivastava et al (to be published); Lichard, PRD 49 (1994) 5812.

  50. Charmonium: “suppression of hc as QGP indicator”! The same idea for J/y suppression carries over to hc. Full width for hc is 17.3 MeV. It should stand “tall and proud” unless it is disturbed by the QGP!! The other charmonium states represent additional tools---it’s all good. K. Haglin, Talk given at Hot Quarks 2006.

More Related