1 / 26

Jet quenching

Jet quenching. Hard-scattering probes. Probing the medium. QGP. I will make an artificial distinction of the “medium” and “the probe” In fact: both are produced in the collision Medium: The bulk of the particles; dominantly soft production and possibly exhibiting some phase.

imelda
Download Presentation

Jet quenching

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. Jet quenching Hard-scattering probes

  2. Probing the medium QGP • I will make an artificial distinction of the “medium” and “the probe” • In fact: both are produced in the collision • Medium: The bulk of the particles; dominantly soft production and possibly exhibiting some phase. • Probe: Particles whose production is calculable, measurable, and thermally incompatible with (distinct from) the medium. • The basic idea: • Things to learn • Measure the density of the medium • Is the medium colored ( i.e. deconfined) ? Specific pQCD predictions for induced gluon radiation since 1990s

  3. High pT Particle Production in pp hadrons Parton Distribution Functions hadrons Hard-scattering cross-section leading particle Fragmentation Function Jet: A localized collection of hadrons which come from a fragmenting parton c a Parton Distribution Functions Hard-scattering cross-section Fragmentation Function b d “Collinear factorization”

  4. Calibrating the Probe(s) schematic view of jet production hadrons leading particle q Thermally-shaped Soft Production q hadrons leading particle “Well Calibrated” Hard Scattering • Measurement from elementary collisions. Leading particles spectra used as a “proxy” to jets. p+p->p0 + X hep-ex/0305013 S.S. Adler et al.

  5. Calibrate the probe and then use it ! Au+Au p0 + X (peripheral) Au+Au p0 + X (central) leading particle hadrons Strong suppression hadrons leading particle • Single-particle spectrum and QCD predictions Peripheral spectra agree well with p+p (data & pQCD) scaled by Ncoll Central data exhibits suppression!

  6. Quantifying the nuclear effect yield in A+A/number of equivalent p+p collisions RAA = yield in p+p

  7. AA AA If no “effects”: RAA < 1 in regime of soft physics RAA = 1 at high-pT where hard scattering dominates Suppression: RAA < 1 at high-pT AA RAA Normalization 1. Compare Au+Au to nucleon-nucleon cross sections 2. Compare Au+Au central/peripheral Nuclear Modification Factor: nucleon-nucleon cross section <Nbinary>/sinelp+p Thomas K Hemmick

  8. Central Mid-Central Peripheral Suppression of high-pT hadrons in AuAu collisions RAA(pT) (h++h-)/2 p0 Binary collision expectation Phenix: Phys.Rev. C69 (2004) 034910  See a strong suppression of high pT yields in AuAu Central Collisions

  9. High pT Particle Production in A+A: why suppressed? Parton Distribution Functions Intrinsic kT , Cronin Effect Shadowing, EMC Effect Hard-scattering cross-section c a Partonic Energy Loss b d hadrons FragmentationFunction leading particle suppressed (pQCD context…)

  10. Initial state effect I: Cronin enhancement Cronin Effect: Multiple Collisions broaden high PT spectrum • Multiple scattering in the initial state leads to pT smearing and then enhancement

  11. Initial vs final state suppression 10 5 pT (GeV/c) • Calibrating the probes- pp reference data -agrees with NLO pQCD • Peripheral Collisions -Scale with Ncoll • Central Collisions DO NOT SCALE! • Is it • Suppression of low-x gluons in the initial state? • Energy loss in a new state of matter? Central 0-10% p+p → p0 + X PHENIX

  12. d+Au Control Experiment Proton/deuteron nucleus collision Nucleus- nucleus collision • Collisions of small with large nuclei were always foreseen as necessary to quantify cold nuclear matter effects. • Recent theoretical work on the “Color Glass Condensate” model provides alternative explanation of data: • Jets are not quenched, but are a priori made in fewer numbers. • Color Glass Condensatehep-ph/0212316; Kharzeev, Levin, Nardi, Gribov, Ryshkin, Mueller, Qiu, McLerran, Venugopalan, Balitsky, Kovchegov, Kovner, Iancu • Small + Large distinguishes all initial and final state effects.

  13. RAA vs. RdA for Identified p0 Initial State Effects Only d+Au Initial + Final State Effects Au+Au d-Au results rule out CGC as the explanation for Jet Suppression at Central Rapidity and high pT

  14. Charged Hadron Results Cronin Effect: Multiple Collisions broaden high PT spectrum • Striking difference of d+Au and Au+Au results. • Charged Hadrons higher than neutral pions.

  15. Centrality Dependence • Dramatically different and opposite centrality evolution of Au+Au experiment from d+Au control. • Jet Suppression is clearly a final state effect. Au + Au Experiment d + Au Control Experiment Final Data Preliminary Data

  16. Control experiment: colorless probe q g Confirm that jet quenching is due to energy loss in the medium. Deduce the medium density. Photons shine ! Pions and etas – suppressed !

  17. Back to back jets (di-jets) Escaping Jet “Near Side” Lost Jet “Far Side” Tomographic information on the medium single particle spectra tell you a lot, but you should be able to learn even more from di-jets

  18. p+p Trigger particle with high pT > pT cut 1 yield/trigger 0 Df to all other particles with pT > pT cut-2  /2  0 Au+Au yield/trigger elliptic flow random background 0  /2  0 statistical background subtraction Au+Au ??? Au-Au yield/trigger suppression? 0  /2  0 Azimuthal Correlations from Jets pp jet+jet STAR Jet correlations in Au-Au via statistical background subtraction

  19. Central Au + Au STAR Disappearance of the “Away-Side” Jet Azimuthal angular correlation of charged particles Escaping Jet “Near Side” Peripheral Au + Au STAR PRL 90, 082302 (2003) d+Au Min Bias Lost Jet “Away Side” Near Away Near PHENIX Preliminary Suppression of away side jet in central Au+Au collisions

  20. Jet quenching: conclusions • Strong suppression of high-pT hadrons and disappearance of the away-side jet in central AuAu • No such effects in dAu • No suppression of photons in AuAu • => Jet quenching is due to final state ( the presence of medium) • The medium is extremely dense : dN/dy(gluons) ~ 1000 – indicative of QGP

  21. Jet quenching Splash! • Suppression of leading particles • Disappearance of the away side jet ( tomographic information) • Suppression depends on pathlength through the medium • Looking for the lost energy …. We came about a splash !

  22. Shock waves ? • It looks like the medium quenches the jets, but it also responds to the propagation of the fast moving parton • If you look closely, you will find the lost energy at lower momenta ! • And … it looks like we have a tool to measure the speed of sound in QGP !

  23. Here is what the data look like • The shapes of jets are modified by the matter. • Mach cone? • Cerenkov? • Can the properties of the matter be measured from the shape? • Sound velocity • Di-electric constant • Di-jet tomography is a powerful tool to probe the matter

  24. Pair opening angle Trigger particle Cherenkov cones? Mach cones? Suggestive of…

  25. Jets maybe deflected due to the radiual flow in the medium Testable via 3-particle correlations Present data ( not yet conclusively) supports Mach cones Other ideas: shock waves vs bent jets

More Related