Charles Gale McGill Intermediate-mass lepton pairs in relativistic heavy-ion collisions Charles Gale McGill

McGill The physics of (very) hot and dense matter is best explored in the laboratory with relativistic nuclear collisions Photons and dileptons are penetrating probes Introduction and Outline New physics: collective, many-body effects Quark-gluon plasma In-medium modifications –Modified spectral densities –Chiral symmetry restoration –Mixing effects –Pion dispersion relation

Charles Gale McGill Outline, cont’nd Experiments (IM): DLS, Helios, NA-38, -50, -60 CERES,WA98, HADES, PHENIX Electromagnetic radiation as a tool for hadronic tomography: –Low mass dileptons –Intermediate mass dileptons –Low p T photons –High p T photons –High p T intermediate mass dileptons SPS RHIC LHC Sangyong Jeon’s talk

Charles Gale McGill Why? Investigation of the QCD phase diagram S. B. Ruster et al., PRD 72, (2005) F. Karsch, E. Laermann, hep-lat/

Charles Gale McGill How? The information carried by EM probes Emission rates: [photons] [dileptons] The electromagnetic spectra will be direct probes of the in-medium photon self-energy They are hard probes: EM signals as probes for hadronic tomography McLerran, Toimela (85), Weldon (90), Gale, Kapusta (91)

Charles Gale McGill The current-current correlator A model for the hadronic electromagnetic current: VMD The current-field identity (J. J. Sakurai) Spectral density The photon/dilepton signal can tell us about the in-medium spectral densities of vector mesons. Rates need to be integrated over the space-time history, with some dynamical model

Charles Gale McGill What is expected (dileptons) Low masses receive significant contribution from radiative decays High masses dominated by DY Intermediate mass region interesting from QGP perspective, (Shuryak (78), Shor (89)) Photons: similar story, but featureless spectra Experiments: DLS, Helios, TAPS, NA38, - 50, WA98, CERES, PHENIX, HADES, NA60

Charles Gale McGill Vector Meson Spectral Densities: A Sample Calculation I Ralf Rapp and Charles Gale, Phys. Rev. C 60, (1999)

Charles Gale McGill The interaction is constrained by basic hadronic phenomenology Chiral, Massive Yang-Mills: O. Kaymakcalan, S. Rajeev, J. Schechter, PRD 30, 594 (1984) Parameters and form factors are constrained by hadronic phenomenology: Masses & strong decay widths Electromagnetic decay widths Other hadronic observables: e.g.

Charles Gale McGill Low Masses:Vector Meson Spectral Densities:Hot Meson Gas The spectral density is flattened and broadened. Even more with baryons. Rapp, Gale (PRC, 99)

Charles Gale McGill NA60 Comparison of data to RW, BR and Vacuum  p T dependence Sanja Damjanovic Quark Matter 05 (and this meeting) New!

Charles Gale McGill Two approaches: H. Van Hess, R. Rapp, nucl-th/ T. Renk, J. Ruppert, hep-ph/ See J. Ruppert’s talk this aft. Many-body (in-medium) effects are observed!

Charles Gale McGill The intermediate mass sector: some background Direct connection to Hard Probes Off-shell effects are potentially important for effective hadronic interactions Gao & Gale, PRC 57, 254 (1998) DD _ DY NA50 Pb-Pb 158 GeV central collisions charm DY A. Shor, PLB 233, 231 (1989)

Charles Gale McGill On the dangers of extrapolations… (a) B. A. Li, Phys. Rev D 52, 5165 (1995). (b) Gomm, Kaymakcalan, Schechter, Phys. Rev. D 30, 2345 (1984). (c) Janssen, Holinde, Speth, Phys. Rev. C 49, 2763 (1994). (d) Ko, Rudaz, Phys. Rev. D 50, 6867 (1994). (e) Xiong, Shuryak, Brown, Phys. Rev. D 46, 3798 (1992). Gao & Gale, PRC 57, 254 (1998) But, a lot of data exists!...

Charles Gale McGill e+ e- Data: A Wealth of Information OLYA CMD DM-1(2) ARGUS M3N 

Charles Gale McGill I. Kvasnikova, C. Gale, and D. K. Srivastava, PRC 65, (2002) Z. Huang, PL B361, 131 (1995)

Charles Gale McGill A larger comparison Agreement across theoretical models Those channels are mostly absent from the spectral densities used in comparisons with CERES and the new NA60 data.

Charles Gale McGill Li and Gale, PRC (1998) Intermediate mass data A. L. S. Angelis et al. (Helios 3), Eur. Phys. J. (1998) R. Rapp & E. Shuryak, PLB (2000)

Charles Gale McGill NA50 Data (cont’nd) I. Kvasnikova, C. Gale, and D. K. Srivastava, PRC 2002 In agreement with multiplicity dependence Includes detector acceptance & efficiency (O. Drapier, NA50)

Charles Gale McGill NA60 IMR analysis: weighted offset fits (A. David’s talk)  or Fix Charm contribution to “world average” value Fix Charm contribution to NA50 p-A expected value Fit always requires ~2 times more Prompts 1 Extract prompts by fixing Open Charm contribution

Charles Gale McGill Low and Intermediate masses: partial summary Thermal sources shine in the LMR and IMR. No great sensitivity to the QGP. Intermediate-mass excess is not charm enhancement! The new data is precise enough to consider a differentiation of space-time models DY? At low M, medium-enhanced multiple parton scatterings might be large (Qiu, Zhang (02), Fries, Schaefer, Stein, Mueller (00). pA measurement.)

Charles Gale McGill A recent analysis: (van Hees & Rapp, hep-ph/ ) Sensitive to the space-time modeling: Still sensitive to the low-mass spectral densities Analyses should be redone with those

Charles Gale McGill Homework Unite (standardize?) space-time modeling [nD hydro, fireballs, transport approaches…]. The power of the data is fully realized if a general-purpose acceptance filter exists. (On the way!...) Chiral symmetry? Still not obvious… An independent access to a 1 spectral density is missing. More work on the theory side too. (Urban, Buballa, Hochsch. & Wambach, PRL, 88, (2002))

Charles Gale McGill

Charles Gale McGill hadrons q q leading particle leading particle Jet-quenching hadrons q q leading particle suppressed leading particle suppressed Source of energy loss: medium-induced gluon Bremsstrahlung (+ elastic scattering?)

Charles Gale McGill Quenching = Jet-Plasma interaction. Does this have an EM signature? The plasma mediates a jet-photon conversion Fries, Mueller & Srivastava, PRL 90, (2003)

Charles Gale McGill Photon sources Hard direct photons Fragmentation Thermal photons from hot medium Jet-photon conversion Jet in-medium bremsstrahlung

Charles Gale McGill Dilepton sources Drell-Yan dileptons Thermal dileptons Jet-virtual photon conversion

Charles Gale McGill Energy loss in the jet-photon conversion? Jet bremsstrahlung? Use the approach of Arnold, Moore, and Yaffe JHEP 12, 009 (2001); JHEP 11, 057 (2001) Incorporates LPM Complete leading order in  S Inclusive treatment of collinear enhancement, photon and gluon emission Can be expressed in terms of the solution to a linear integral equation

Charles Gale McGill E loss/gain: some systematics Includes E gain Evolves the whole distribution function S. Jeon’s talk

Charles Gale McGill Jet characteristics:

Charles Gale McGill Time-evolution of quark distribution The entire distribution is evolved by the collision Kernel(s) of the FP equation Turbide, Gale, Jeon, and Moore (2004)

Charles Gale McGill Jet-plasma dileptons? Same basic idea as photons, details are slightly different: –High p T cut helps with background subtraction Go beyond LO, do a HTL analysis

Charles Gale McGill The thermal “baseline” calculation agrees with that of M. Thoma, C. T. Traxler, Phys. Rev. D 56, 198 (1997)

Charles Gale McGill Dileptons from jet-thermal interactions Jet-thermal as large as DY/heavy quark decay (RHIC) Jet-thermal still as large as DY. S/B could improve with harder pT cut. At RHIC, there is a contribution to the IM region In-medium jet bremsstrahlung will also add to the signal No heavy quark energy loss Signal as large as it is for photons Turbide, Gale, Srivastava, Fries, PRC (2006)

Charles Gale McGill But: other signature of jet-photon conversion? Jet-plasma photons will come out of the hadron-blind region. “Optical” v2 < 0 Turbide, Gale, Fries (PRL 06)

Charles Gale McGill Photons from primordial interactions and fragmenting jets All photons (NN, frag, jet-photon conv., bremss., Th.)

Charles Gale McGill v2 from “Isolated photon cut” is negative Photons associated with a “crowded photon cut” show v2 with changing sign Same game can be played with dileptons (in progress) See talk by U. Heinz Similar story for the LHC

Charles Gale McGill Jet-plasma interactions: measurable EM signatures! These are fairly robust with respect to changing temperature & dynamics RHIC & LHC: –Jet-plasma interactions: dilepton channel: signal competes with Drell-Yan (NLO) Towards a consistent treatment of jets & EM radiation Intermediate-mass dileptons New data will put further stringent tests on models, both rates & space-time modeling Conclusions, part I

Charles Gale McGill Conclusions, part II Low and mass dileptons: NA60 data can distinguish between models. In-medium effects! RHIC/LHC: There are measurable electromagnetic signatures of jet-plasma interaction: those constitute complementary observables to signal the existence of conditions suitable for jet-quenching Photon v2: a revealing probe EM radiation and hard probes: the start of a beautiful friendship… EM radiation: change of paradigm

Charles Gale McGill Interested in the techniques discussed here? Want to know more? Found where fine books are sold (July 2006)

Charles Gale McGill

Charles Gale McGill Chatterjee, Frodermann, Heinz, Srivastava, nucl-th/

Charles Gale McGill Jet-plasma photons: S. Jeon’s talk

Charles Gale McGill New (preliminary) PHENIX Data

Charles Gale McGill

Charles Gale McGill Vector Meson Spectral Densities, II (adding baryons) R. Rapp & J.Wambach, 1999

Charles Gale McGill Soft RHIC: There is a window Turbide, Rapp & Gale PRC (2004)

Charles Gale McGill Same spectral densities:Low mass dileptons and real photons S. Turbide, R. Rapp, and C. Gale, PRC (2004)

Charles Gale McGill Same spectral densities as low mass dileptons Same dynamical model; same boundary conditions Cronin contribution estimated from pA data (E629, NA3) QGP: small Turbide, Rapp & Gale PRC 2004