Presentation on theme: "1 , , (and measurements in ALICE. 2 ’s sensitive only to production processes, do not interact, sensitive to: initial parton distributions: Intrinsic."— Presentation transcript:
1 , , (and measurements in ALICE
2 ’s sensitive only to production processes, do not interact, sensitive to: initial parton distributions: Intrinsic k T, k T Broadening, Shadowing, Anti-shadowing, Saturation, … some final state effects (parton/hadron rescatterings): Thermal, Jet/Parton Radiation or fragmentation after Eloss,… “The virtue of and Measurements” To properly deduce the properties of the produced QCD matter we must separately distinguish initial state effects from final state effects. Experimental virtues (calorimeter measurement): Measure and in same detector Identified particles to very high p T ’s abundantly produced ’s produced in final state (fragmentation or recombination): initial parton distributions: as for large final state effects: Rescattering (low p T ), Absorption, k T Broadening, Jet/Parton Energy Loss,…
3 Centrality Dependence of High p T Suppression PHENIX nucl-ex/ Trend of yield with centrality (impact parameter) follows expected binary collision scaling behavior (=constant) and agrees with pQCD (=1). Direct are not suppressed - strong evidence that hadron suppression is due to final state, i.e. parton energy loss.
4 Direct Photons and Production for Central Au+Au PHENIX nucl-ex/ High p T yield consistent with binary scaled pQCD in contrast to factor of 5 suppression of & hadron yields. Direct are not suppressed - strong evidence that hadron suppression is due to final state, i.e. parton energy loss. Errors don’t preclude a thermal contribution at low p T
5 Centrality Dependence R AA for suppression increases with increasing nuclear overlap volume. suppression same as - behaviour agrees with “meson-like” expectation PHENIX preliminary
6 inclusive jets GeV few x 10 4 /year for E T >150 GeV E FS = 250 GeV (PHOS 80 GeV) Extend measurements to much higher p T From Peter Jacobs
7 Photons (all in fact): Continum Spectrum with Many Sources Turbide, Rapp, Gale EE Rate Hadron Gas Thermal T f QGP Thermal T i Pre-Equilibrium Jet Re-interaction pQCD Prompt Final-state photons are the sum of emissions from the entire history of a nuclear collision. +Weak+EM decay ’s ( ) = Bkgd
8 Resolution: PHOS vs EMCal - PHOS wins Due to much better energy resolution, lower occupancies, and lower tower thresholds PHOS will be the preferred detector for low pT photon measurements. PHOS: 3.5%/sqrt(E) EMCal: 12%/sqrt(E) or worse?
9 Tower granularity 0 separation - PHOS wins 0 opening angle shower shape discrimination Heather Gray, LBNL/Cape Town rejection for p T <~30 GeV/c At high p T merging of showers of photon pairs from decays become indistinguishable from single photons - become a background. Use EMCal vs PHOS comparisons to determine (PHOS rate limited) Other “tricks” like tagging conversion rate As p T increases ’s dominate preliminary
10 So…Why Large EMCal in ALICE? Measure neutral energy of jets –Improves jet energy resolution, ~30% -> ~15% –PHOS is too small to contain jet Extend PHOS measurements , 0, and e +/- to higher p T Increase acceptance for (EMCal/PHOS) + jet(TPC) Allow back-to-back coincidences – (PHOS) + jet (TPC+EMCal) – (EMCal) + leading 0 (PHOS) – (EMCal/PHOS) + e +/- from D,B decay (heavy q jet) (PHOS/EMCal)
11 ALICE EMCal is large enough for jet measurements PROBLEM: Underlying event non-jet energy: Radius Cone Energy (GeV) Jet Energy fraction within cone radius 22 0 /2 3 /2 TPC PHOS EMCal Jet R=0.3, 0 Use “small” jet-cone, R~0.3
12 Direct / 0 Ratio Ratio / 0 provides figure of merit for direct gamma measurement: / 0 ~ 10% easy ~ 3-5% limit 0 suppression by factor of ~5-10 (jet quenching) would allow direct photon measurement down to a few GeV/c Expectations for 0 suppression at high pT at LHC?
13 Empirical Investigation of Energy Loss Observe 0 spectra in p+p have power-law form: If we interpret suppression as a p T shift from Energy Loss: where then The Energy Loss, or p T Shift S loss, can then be extracted from R AA as
14 Suppression / Energy Loss vs Centrality Gyulassy, Vitev, Wang: 1D expansion, simple geometric scaling Large gluon density dN g /dy~1000, Large energy density. If behaviour extrapolates to LHC, expect even larger p T independent suppression
15 Further Illumination with Direct Photons High p T direct produced in hard q-g Compton-like scatterings. Sensitive to PDFs, (especially gluons). In the HI case, from initial hard scattering escape. Can be used to tag recoiling jet to study jet energy loss (“Jet Quenching”), which may produce additional Brems. ’s. Leading Particle Direct Hadrons g q Brems. Thermal Additional thermal ’s produced in scatterings in QGP or hadronic phase of collision. If ”Gluon Saturation” occurs, initial (and 0 ) will be suppressed. With parton Eloss, the fragmentation contribution could also be suppressed.
16 Investigate yields vs Reaction Plane (Pathlength) = 0° = 90° Measure Reaction Plane using BBCs Measure Yields vs. orientation w.r.t. RP Expect largest E-loss or suppression at = 90 in “ long” direction Interplay between flow (v 2 ) and Supression? Both give expectation of in-plane enhancement. Long path, large Eloss
17 and inclusive v 2 analysis show large v 2 to high p T - effect of suppression? (more later) Inclusive show similar large v 2 Use measurement as input to MC to predict decay v 2 - if no direct signal, or v 2 (direct ) = v 2 (bgd ), then should have v 2 (bgd ) = v 2 (incl ) Use Direct measurement R= Total / Decay then v 2 (direct ) = ( R*v 2 (incl ) - v 2 (bgd ) ) / (R-1) Or, assume v 2 (direct ) = 0 to extract R. Gives agreement with measurement of R=0 in this p T range. (Proof of principle at this point) p T (GeV/c) PHENIX preliminary
18 ALICE studies using Measurements Measure direct in p+p: –Extract fragmentation contribution by analysis with/without isolation cuts Measure direct in A+A: –Search for effects of gluon saturation Thermal region (PHOS): –Other techniques - HBT, conversions Measure direct vs Reaction Plane in A+A: –q+g Compton isotropic, Thermal flows, Fragmentation enhanced or suppressed with pathlength? Measure +jet : –The measures p T of the recoiling parton - measure modified recoil Fragmentation Function to extract parton energy loss directly.