Outline o Direct s in LO, NLO and beyond in p+p and HI o -h Statistical Analysis Method o Nuclear Modification, Surface Bias and the search for Grey Probes o Correlations with Isolation Cuts o Testing NLO and Vacuum Jet Fragmentation o Flavor Dependence of Energy Loss o Conclusions Outline o Direct s in LO, NLO and beyond in p+p and HI o -h Statistical Analysis Method o Nuclear Modification, Surface Bias and the search for Grey Probes o Correlations with Isolation Cuts o Testing NLO and Vacuum Jet Fragmentation o Flavor Dependence of Energy Loss o Conclusions 5/7/2009 2WSU Seminar o Are we studying the medium or the model? e.g., can partons skip through the medium? o The grey observable problem (Fragility) What are the differential probes? o How can we separate the E-loss from the medium response and is that even the right thing to do? o The details: Initial state, pre-equilibrium, hydro, 5/7/2009 WSU Seminar3 QGP Brick Parton beam q How can +jet events provide additional information? Ideal Jet Tomography: Tomography with auto-generated hard probes in an expanding medium: 5/7/2009 WSU Seminar4 Compton Annihilation 200 GeV, CTEQ6 + LO + (KKP) < 0.35 o Small # of diagrams o Compton scattering dominant Probe the gluon distribution Favor (up) quark recoil jets use to study quark E-loss in Au+Au o Exact balance w/ recoil jet + transparent to medium Initial energy of away-side parton determined o Small # of diagrams o Compton scattering dominant Probe the gluon distribution Favor (up) quark recoil jets use to study quark E-loss in Au+Au o Exact balance w/ recoil jet + transparent to medium Initial energy of away-side parton determined 5/7/2009 WSU Seminar5 Bremsstrahlung Diagrams Isolated / Inclusive x-section NLO Calculations: Vogelsang (top), ZOWW (bottom) Di-jets contribute: Fragmentation s ~ 30 % of direct 200 GeV Spoils momentum balance Near-side parton subject to Eloss Isolation Cut Isolation cuts can be used to remove some frag. s ~ 10 % of s are non-isolated % of 0 s are isolated Isolated clusters are not sufficient to identify direct s Di-jets contribute: Fragmentation s ~ 30 % of direct 200 GeV Spoils momentum balance Near-side parton subject to Eloss Isolation Cut Isolation cuts can be used to remove some frag. s ~ 10 % of s are non-isolated % of 0 s are isolated Isolated clusters are not sufficient to identify direct s 5/7/2009 6WSU Seminar Direct 200 GeV 62 GeV NLO consistent with data using scale of = p T /2 But there is still room for ~40% effects NLO consistent with data using scale of = p T /2 But there is still room for ~40% effects NLO works great! within errors For 0 62 GeV NLO works but resummation drastically reduces scale uncertainty For 0 62 GeV NLO works but resummation drastically reduces scale uncertainty o Direct s disused in global fits to gluon PDF debate not settled o Measuring both inclusive and isolated s is useful o Determining the momentum balance important o In this study: Use LO + k T to compare to NLO and to simplify calculation o Direct s disused in global fits to gluon PDF debate not settled o Measuring both inclusive and isolated s is useful o Determining the momentum balance important o In this study: Use LO + k T to compare to NLO and to simplify calculation 5/7/2009 WSU Seminar7 Aurenche et al. Phys.Rev. D (2006) Apanasevich et al., PRD 59, (1999) PHENIX, PRD 74, (2006) Measurement of pair p T (k T ) indicate need for extra transverse kick beyond NLO World data can be described by NLO only with exception of certain fixed target data o Only constraint on gluon PDF at high x is jet x-section o May be absorbing beyond Standard Model effects into PDF Need cross check from +jet o By measuring different rapidity ranges NLO shown not to be fully compatible with data o Cannot be explained by: Uncertainty in the PDF Scale dependence o Only constraint on gluon PDF at high x is jet x-section o May be absorbing beyond Standard Model effects into PDF Need cross check from +jet o By measuring different rapidity ranges NLO shown not to be fully compatible with data o Cannot be explained by: Uncertainty in the PDF Scale dependence 5/7/2009 8WSU Seminar Triple differential +jet x-sections from D0 D0, PLB666, 435 (2008) JHEP 0609, 015 (2006) o Below 13 GeV R AA confirming LO picture o Nuclear modification at higher p T ? o Medium Induced sources? Induced bremsstrahlung Jet-Photon Conversion o So far no proof, but need data on v 2, correlations, etc. 5/7/2009 WSU Seminar9 Qin et. al, hep-ph/ PRC75, (2007) BDMPS No sign of suppression in Cu+Cu Other detectors used: o BBC: triggering, centrality, vertex o ZDC: centrality o RICH: electron veto by Cherenkov radiation o TOF: Identify hadrons by time-of-flight Other detectors used: o BBC: triggering, centrality, vertex o ZDC: centrality o RICH: electron veto by Cherenkov radiation o TOF: Identify hadrons by time-of-flight 5/7/2009 WSU Seminar10 8.1/ E(GeV) 2.1 % 5.9/ E(GeV) 0.8 % PbSc Electromagnetic Calorimeters Electromagnetic Calorimeters PbGl Drift Chamber Central Tracking: Drift Charmber and Pad Chambers 5/7/ WSU Seminar Underlying Event = Cominatorial Bknd + Elliptic Flow o Adding in efficiency and acceptance corrections: Note: Alternate normalization and ZYAM give same results PHENIX PRC78, (2008) o Treat UE as a flat background o Subtract by 2 Gauss + const fit o Treat UE as a flat background o Subtract by 2 Gauss + const fit o Two-source model: Jet + comb. bknd In p+p collisions: In Au+Au collisions: o Also false correlation from multiplicity resolution: o Estimate background by mixed-event multiplicity modulated by elliptic flow Inclusive PTY is a weighted sum of decay and direct contribution Note: Direct defined to be everything not decay Inclusive PTY is a weighted sum of decay and direct contribution Note: Direct defined to be everything not decay Rearrange and express in terms of the direct photon excess R = N inclusive /N decay Rearrange and express in terms of the direct photon excess R = N inclusive /N decay 5/7/ WSU Seminar PHENIX also measures x-sections for > 99% of the decay photon sources so estimating Y decay should be easy p+p Au+Au 5/7/2009 WSU Seminar13 Compare the conditional yield binned by parent and daughter p T Daughter-h slightly larger decay feed-down effect Consider worst case: p+p, low p T, fully statistical subtraction S/B ~ 0.1 Assuming the background looks like 0 -h is a bad assumption for s from 0 decay nevermind and fragmentation s! 5 < p T,t < 7 X 1 < p T,a < 2 GeV PYTHIA Using 0 -h as a proxy for ( 0 )-h True 0 Raw 0 Ratio = Correction Linear correction function How to obtain the unbiased decay associated yield using a pair-by-pair weighting 5/7/ WSU Seminar Reconstructed 0 s MC Decay Mapping True 0 s True s Measured s Recon Eff. Corr Single Eff = GEANT 0 in p+p: PRD76, (2007) In Au+Au: PRC76, (2007) 0 reconstruction by invariant mass gives a biased distribution Reconstruction efficiency: Correct to known shape of the 0 distribution Need decay correlation as function of decay p T Mapping function: Decay 0 s in MC with detector acceptance, resolution Some merged decay s removed by shower shape cuts Merging Efficiency: Determine from GEANT simulation 5/7/ Au+Au collisions: o correlations difficult to measure in Au+Au collisions o Instead, the ratio of -h to 0 -h in p+p is applied as a correction factor in Au+Au Au+Au collisions: o correlations difficult to measure in Au+Au collisions o Instead, the ratio of -h to 0 -h in p+p is applied as a correction factor in Au+Au p+p collisions: o Directly measure 0 -h and -h in p+p, > 95% of decay correlation o Decay feed-down effect visible for both species o Opening angle effect negligible p+p collisions: o Directly measure 0 -h and -h in p+p, > 95% of decay correlation o Decay feed-down effect visible for both species o Opening angle effect negligible Run GeV WSU Seminar 5/7/2009 WSU Seminar16 o Disappearance of opposite-side correlations compared to p+p o Near-side yield consistent with zero with large uncertainties 5-7 X 3-5 GeV 5/7/2009 WSU Seminar17 Run 4 Au+Au 200 GeV Centrality 0-20 % I AA o Highest precision at high p T,h due to combinatorial bknd o Geometrical suppression: hadron R AA = I AA o For a static medium I AA gives the surface:volume o h-h data should look different o Lower p T,h stats still too poor o Highest precision at high p T,h due to combinatorial bknd o Geometrical suppression: hadron R AA = I AA o For a static medium I AA gives the surface:volume o h-h data should look different o Lower p T,h stats still too poor 5/7/2009 WSU Seminar18 p T = 15 GeV BDMPS Renk, PRC74, (2005) o Surviving single and di-hadrons always biased towards small E-loss o Since the fixes the initial E of the jet varying z T (=p T,h /p T, ) changes the mean path-length through the medium o By moving to lower z T, should be able to find partial E-loss o Surviving single and di-hadrons always biased towards small E-loss o Since the fixes the initial E of the jet varying z T (=p T,h /p T, ) changes the mean path-length through the medium o By moving to lower z T, should be able to find partial E-loss ZOWW Single hadrondi-hadron -hadron AuthorFormalismOrderHydroInduced Rad ZOWWEffective FFNLO1DNo RenkASW?LO3DNo Qin et al.AMYNLO?3DYes 5/7/2009 WSU Seminar19 STAR o Qin and ZOWW show very similar shape o Renk shows decreased sensitivity o What is the source of the discrepancy? o Qin and ZOWW show very similar shape o Renk shows decreased sensitivity o What is the source of the discrepancy? 5/7/2009 WSU Seminar20 Borghini & Wiedemann, hep-ph/ o Modified splitting functions used to calculate medium effects o Cone from large angle emission or collective response? o MLLA shower evolution for sub-leading radiation o MC implementations under development (QPYTHIA, YaJEM, ) o Difficult to calculate h-h because of trigger bias o With -h we can reach the hump-back plateau at RHIC o Modified splitting functions used to calculate medium effects o Cone from large angle emission or collective response? o MLLA shower evolution for sub-leading radiation o MC implementations under development (QPYTHIA, YaJEM, ) o Difficult to calculate h-h because of trigger bias o With -h we can reach the hump-back plateau at RHIC p+p data Polosa and Salgado, PRC75, (2007) 5/7/2009 WSU Seminar21 Run 7 o Theory predicts that direct emission is dominated by induced production at 5 GeV o Still 30 % at 10 GeV o Jet-plasma = Induced brems. + jet conversion o Theory predicts that direct emission is dominated by induced production at 5 GeV o Still 30 % at 10 GeV o Jet-plasma = Induced brems. + jet conversion o Small near-side yield compared to 0 -h o No discernable difference between p+p and Au+Au o Induced brems. may have different near-side production than jet conversion should have separate predictions for near-side o Small near-side yield compared to 0 -h o No discernable difference between p+p and Au+Au o Induced brems. may have different near-side production than jet conversion should have separate predictions for near-side Qin et al. arXiv: Obtain higher precision by identifying direct s event-by event 5/7/ WSU Seminar Isolation Cut: Total track momentum + cluster energy in cone of 0.5 radians < 10% E of photon Isolation Cut: Total track momentum + cluster energy in cone of 0.5 radians < 10% E of photon Decay tagging: Remove 0 and by invariant mass reconstruction Decay tagging: Remove 0 and by invariant mass reconstruction Note: Some direct s are also removed by isolation cut. Its actually a different measurement! Note: Not ALL background can be removed e-by-e. Still need to perform residual statistical subtraction! Need to know how much back- ground was already removed Estimate efficiency of isolation cut on decay s with recon. 0 s Need to re-evaluate decay probability for only s which survive cuts tagged Not isolated Missed,Isolated Isolated,direct 5/7/2009 WSU Seminar23 o Near-side: Small inclusive -h yield o Away-side: Direct smaller than 0 -h (Lower Q 2, color factor, diff. trigger bias, ) o Isolated direct away-side smaller than inclusive direct (systematics correlated) [rad] 1/Nt rig dN/d 5/7/ WSU Seminar o Well described by a Gaussian for < 3 GeV o 0 has a tail hard gluon radiation, o Do isolated s also have a tail? o Well described by a Gaussian for < 3 GeV o 0 has a tail hard gluon radiation, o Do isolated s also have a tail? p OUT = sin p T,h 1 < p T,h < 5 GeV Runs GeV p T, 5/7/2009 WSU Seminar25 o Maybe 3 GeV, but quickly drops below fit as p OUT p Tt o In 5 GeV Prompt events cant radiate a 5 GeV gluon at 90 degrees o Isolation criterion restricts the phase space for 2 3 emission 1 < p T,h < 5 GeV 5/7/2009 WSU Seminar26 Partonic Hadronic From 0 -h near-side correlations PRD74:072002, 2006 For -h correlations Di-hadron kinematics 1 < p T,h < 5 GeV 5/7/2009 WSU Seminar27 o Parton kinematics from PYTHIA used to determine k T from p OUT o k T values compatible w/ other observables o Should be compared to pair p T from NLO o PYTHIA-free k T extraction on the way 5/7/2009 WSU Seminar28 o How do x E distributions relate to FFs? o x E distributions are fit with an exponential which fits reasonably well in data and MC o Compare to pQCD using NLO calculations and LO + k T Monte Carlo generator Open symbols = 0 Closed = direct Run GeV 1 < p T,h < 5 GeV o General expression for opposite-side hadron pairs o Using LO x-section parton-parton scattering processes summing over all flavor permutations o Add Gaussian k T /j T smearing (only k T shown) o Using CTEQ6 PDFs o Try different FFs (KKP, DSS, AKK05/08) 5/7/2009 WSU Seminar29 Examples of PDFs and Q=7 GeV 5/7/2009 WSU Seminar30 zTzT CTEQ6 + LO + (kT) +KKP k T ON k T OFF 1 < p T,h < 5GeV o NLO from ZOWW reproduces z T distributions remarkably well o Data also reproduced by LO after addition of k T o Indicates that NLO is doing a reasonable job with the momentum balcance o Calculation of the pair p T from NLO would be definitive o NLO from ZOWW reproduces z T distributions remarkably well o Data also reproduced by LO after addition of k T o Indicates that NLO is doing a reasonable job with the momentum balcance o Calculation of the pair p T from NLO would be definitive ZOWW arXiv: 5/7/2009 WSU Seminar31 All FF set describe isolated fairly well k T effect matters, LO by itself doesnt cut it Shape of input FF matters we are measuring the FF! However, mix of processes does. Annih. only finds a steeper slope than data we are looking at Compton scattering = closed points 5/7/2009 WSU Seminar32 FF sets give a much larger spread in predictions. KKP and DSS come closest k T matters although not as much as choice of FF set Overall shape of FF doesnt matter, consistent with previous PHENIX measurement However, mix of processes does matter relative shape of quark vs gluon FF matters 0 = open points 5/7/2009 WSU Seminar33 CTEQ6 + LO + k T + DSS 1 < p T,a < 5 GeV o Ratio of + to charged hadrons for the away-side jet o As z 1 pure Compton gives 8:1, but effect is diluted e.g, by k T smearing o Agreement w/ theory valuable check on -h extraction method o NLO predictions please! 200 GeV CMOR (ISR): NPB327 (1989) w/ NLO from Aurenche et. al 63 GeV A mystery: Flavor Dependence o From color factor expect 9/4 more energy loss for gluon jets o Counter to observation o Frequent claim: Protons come from gluon jets (AKK 05) o If so, why dont we see less proton than pions at high p T ? o 3 possibilities: Both quarks and gluons always lose all their energy Flavor conversion by rescattering Gluon Proton FF not really favored o It would be useful to have a less ambiguous tag of parton flavor A mystery: Flavor Dependence o From color factor expect 9/4 more energy loss for gluon jets o Counter to observation o Frequent claim: Protons come from gluon jets (AKK 05) o If so, why dont we see less proton than pions at high p T ? o 3 possibilities: Both quarks and gluons always lose all their energy Flavor conversion by rescattering Gluon Proton FF not really favored o It would be useful to have a less ambiguous tag of parton flavor 5/7/2009 WSU Seminar34 STAR PRL97, (2006) 5/7/2009 WSU Seminar35 In new AKK set gluon proton is much less favored than previously STAR data is used without hyperon feed-down corrections AKK08: NPB803:42-104, 2008 Data: PLB 637 (2006) 161 5/7/2009 WSU Seminar36 o Identifying the partner targets specific FFs, e.g., gluon proton o Can probe low z, a region poorly constrained by single particle measurements o Conditional yields with and 0 triggers are a much better way to constrain flavor dependence of Eloss o Identifying the partner targets specific FFs, e.g., gluon proton o Can probe low z, a region poorly constrained by single particle measurements o Conditional yields with and 0 triggers are a much better way to constrain flavor dependence of Eloss -h 0 -h 5 < p T,t < 7 GeV o PHENIX method of extracting -h correlation correlations is rigorous and our results are credible o Nuclear modification at moderate values of z support geometrical suppression picture but cannot yet learn much about the density profile o No observation of large near-side contribution from medium induced photon production o Results in p+p collisions corroborate NLO baseline (Compton dominance), but more can be done to convince ourselves o Correlations with direct and 0 triggers are powerful method to explore the flavor dependence of parton E-loss than single particle observables 5/7/2009 WSU Seminar37