Prof Tom Trainor (University of Washington, Seattle, USA)
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TITLE: Two cultures in high energy nuclear physics Since the mid eighties a community originating within the Bevalac program at the LBNL has sought to achieve formation of a color-deconfined quark-gluon plasma in heavy ion (A-A) collisions using successively higher collision energies at the AGS, SPS, RHIC and now the LHC, emphasizing a flowing dense "partonic" medium as the principal phenomenon. During much of the same period the high energy physics (HEP) community studying elementary collisions (e-e, e-p, p-p) developed the modern theory of QCD, emphasizing dijet production (fragmentation of scattered partons to observable hadrons) as the principal (calculable) phenomenon. Initially it was assumed that the QGP phenomenon in most-central A-A collisions might be distinguished from the HEP dijet phenomenon in elementary collisions. However, strong overlaps in phenomenology have revealed significant conflicts between QGP and HEP "cultures," especially at RHIC and LHC energies. In this talk I review some of the history and contrast an assortment of experimental evidence and interpretations from the two cultures with suggested conflict resolution.
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Prof Tom Trainor (University of Washington, Seattle, USA)
- 1. Two Cultures in High Energy Nuclear Physics Tom Trainor November, 2014
- 2. Agenda •Early data on flows –the QGP/flow culture •Jets and fragmentation –the HEP culture •RHIC evidence leading to claim of perfect liquid •p-p collisions as A-A reference •Au-Au spectra and angular correlations •Confront conventional (QGP) RHIC analysis •Examine LHC results in a HEP context •Bayesian inference –a guide for the future 2
- 3. A Tale of Two Cultures 3 QCD large l QCD small l HEP narrative QGP/flow narrative ISR/SppS/FNAL HEP data HERA/LEP BEV/AGS data RHIC/LHC data Compton scattering, fragmentation, jets LGT QFT/CGC e.g. F Gelis nucleon matter flow reality “parton” matter flow reality? 1980s, 90s 2000-present 1980s-present 1980s-present
- 4. Flows at the Bevalac, AGS and SPS directed, radial and elliptic flows, early days 4 A A directed flow “v1” radial flow bt elliptic flow v2 ≈1984 ≈1992 x z deviation from MB interpreted as flow ≈1998 NA35 NA49 Pb-Pb Phys Rev Lett 80, 4136 Phys Lett B 157, 146 (1985) (1998); nucl-ex/9711001 all azimuth structure interpreted as flows memory of b? ‹px› CM
- 5. Jets in p-p at the ISR and SppS First low-energy jet reconstruction – MB jet spectra down to 3 GeV partons 5 simple expression predicts jet spectra for all p-p collision energies above 10 GeV 3 GeV 3 GeV early eighties Phys Rev D 89, 094011 (2014); arXiv:1403.3685 2014
- 6. 6 phadron Parton Fragmentation in e+- e-e - e+ g, Z0 LEP PETRA q q color dipole how are parton fragments (jet hadrons) distributed on momentum? s = Q2 LEP, PETRA fragmentation data: 1988-2000 color dipole radiation: ln(phadron) LEP PETRA e-e ln(pparton) s, Q2 ? an “equilibration” process when plotted on ln(pz) → yz (as from ALEPH) internal structure of jets
- 7. 7 ln(p) rapidity y Fragment Distributions on Momentum xp = ln(1/xp) fragmentation functions on logarithmic variables alternative: fragmentation functions on rapidity y y ln(E p) /m s conventional: fragment momentum relative to parton momentum D(xpD(y,y ,s) max) D(ln(p),s) D(xp,s) xp = phadron/pparton fragmentation function D(x,s) D(y, ymax) LEP PETRA non-pQCD physics! scaling violations FFs self-similar on y DGLAP DGLAP
- 8. 8 Accurate Analysis of Fragmentation 1 1 max ( , ) ( ; , g u y b u p q) up (1 u)q / B( p,q) - - - max max max D(y, y )2n(y ) g(u, y ) fragmentation functions well described by simple model function g(u,ymax) beta distribution on normalized rapidity u accurately models fragmentation functions ( ) ( ) ( , ) ( ) p q B p q p q min max min y y u y y - - (normalized) ymin b (u; p,q) normalized rapidity redundant a form of equilibration via least action e-e - LEP p-p - FNAL D(y,ymax) dijet multiplicity Phys Rev D 74, 034012 (2006); hep-ph/0606249 2006
- 9. 9 The STAR Detector at RHIC Brookhaven National Laboratory -BNL Long Island
- 10. 10 Single RHIC Au-Au Central Collision 4 m 4 m 1500 charged particles UW graphic
- 11. Early RHIC Results – Flows 11 first RHIC paper - STAR v2(b) v2(pt) all hadrons all hadrons ideal hydro isentropic expansion? p-p radial flow Au-Au 휼/풔? bt (b) viscous? “mass ordering” elliptic flow elliptic flow peripheral central Phys Rev Lett 92, 112301 (2004); nucl-ex/0310004 Phys Rev Lett 86, 402 (2001); nucl-ex/0009011 Phys Rev C 72, 014904 (2005); nucl-ex/0409033 spectra azimuth correlations hydro 2003 2000 2004
- 12. Early RHIC Results – Jet Quenching 12 HIJING CGC major problem: 2004 minijets quench “too slow growth” RAA Phys Rev C 73, 064907 (2006); nucl-ex/0411003 away-side jet disappears Phys Rev Lett 91, 072304 Phys Rev C 70, 021902 (2004); nucl-ex/0405027 (2003); nucl-ex/0306024 pt cuts? 3 GeV partons! problem 2004 2003
- 13. The Perfect-Liquid Pronouncement Elliptic flow: “The smallness of dissipative corrections [required for hydro descriptions of v2 data]...is in itself a remarkable and unexpected discovery. […] ...the QGPat RHIC is almost a perfect liquid. […] Elliptic flow measurements confirm...local thermal equilibrium...” early in the collisions. Jet quenching: “The observed jet quenching in Au-Au [collisions] is due to parton energy loss. […] Theoretical analysis of jet quenching...strengthens the casefor multiple strong interactions of the quark and gluon constituentsof the matter made at RHIC.” The CGC: “...the surprising very weak centrality and beam energy dependence[“too slow growth”] observed [in the data, compared to HIJING] is most satisfactorily explained and predicted by the CGC....” The comparison (interpreted to rule out minijets and the TCM in favor of the CGC) “...is one of the strongest lines of empirical evidence...” for the CGC . 13 A tale of two theorists –2004 MiklosGyulassy(Columbia) and Larry McLerran(BNL) NuclPhys A 750, 30 (2005); nucl-th/0405013 PL sQGP CGC IC
- 14. Confronting Perfect-Liquid Claims •Understand minimum-bias dijets in isolation •Understand p-p (N-N) collisions in isolation •Construct a reference for transparentA-A collisions •Determine what is truly novel about A-A collisions 14 IntJ Mod Phys E 23, 1430011 (2014); arXiv:1303.4774 RHIC review: what should a responsible scientist do?
- 15. Minimum-bias p-p Spectra 15 A-A reference is p-p collisions quantum transition! dijets nh ns 2 - no eikonal approximation nch = ns + nh nh ≈ 0.005 ns 2 solid curve is pQCD prediction from FFs and MB jet spectrum subtract S0 NSD yt ln(mt pt ) /m0 two-component model soft + hard (jets) = TCM Phys Rev D 74, 032006 (2006); nucl-ex/0606028 Phys Rev C 80, 044901 (2009); arXiv:0901.3387 Phys Rev D 87, 054005 (2013); arXiv:1210.5217 PYTHIA 2004 2008
- 16. 16 Minimum-bias p-p Correlations subtract soft reference minijet fragments Dr/ √rref same side 1D p-p 2D 200 GeV nch=1 nch=11 pt yt 0.15 1 6 pt (GeV/c) proton fragments away side hadron pt ~ 0.6 GeV/c yt1 yt2 yt2 Dr/ √rref nch parton fragments 0 ln ( ) / t t t y m p m minimum-bias: no trigger condition soft hard spectrum TCM correlation TCM J Phys Conf Ser 27, 98 (2005); hep-ph/0506172 2005
- 17. Au-Au Spectra vs Centrality 17 subtract S0 subtract S0 spectrum hard components solid curve is pQCD prediction from (modified) FFs and MB dijet spectrum centrality evolution of jet contributions to hadron spectra pion hard components full proton spectra pions protons mp spectrum TCM IJMPE 17, 1499 (2008), 0710.4504 Phys Rev C 80, 044901 (2009); arXiv:0901.3387 2007 2009 GLS
- 18. Au-Au Correlations vs Centrality 18 85-95% 55-65% 20-30% 0-5% fraction of total cross section 200 GeV centralities Phys Rev C 86, 064902 (2012); arXiv:1109.4380 peripheral central 2008
- 19. Sample Fit – 62 GeV Au-Au 45-55% data fit residuals SS 2D peak NJ quadrupole AS dipole 1D on eta 2D exponential dijets dijets v2 Phys Rev C 86, 064902 (2012); arXiv:1109.4380 soft 2008
- 20. Sharp Transition in Jet Structure 20 SS 2D peak amplitude AS dipole SS 2D peak width Glauber Model: n = 2Nbin / Npart sharp transition ST ≈ 50% central @ n = 3 ST dijets dijets 2004 Phys Rev C 86, 064902 (2012); arXiv:1109.4380 2008
- 21. Conflict between Narratives •Dense or opaque flowing QCD medium •Strong jet quenching, most jets thermalized •Viscous hydro describes low-viscositymedium •At least 50% of Au-Au collisions are transparent •Almost all jets survive, but quantitative modification •Jet phenomena described quantitatively by pQCD •Hydro fails to describe claimed “flow” phenomena 21 QGP/flow narrative: HEP narrative: IntJ Mod Phys E 23, 1430011 (2014); arXiv:1303.4774 RHIC review: given the same data
- 22. Resolving “Too Slow Growth” 22 Pb-Pb HAA ST n = 3, 50% p-p CGC ST HIJING one basis (CGC) for “perfect liquid” claim dijet frequency per A-A collision predicted hard component HAA HIJING is based on PYTHIA: incorrect 30% of hadrons in central Au-Au collisions are included in resolved dijets CGC falsified by peripheral data p-p Phys Rev C 83, 034903 (2011); arXiv:1008.4759 HIJING PHOBOS ? 50% of s CGC ~ ln(8n)
- 23. Radial Flow vs Jets blast-wave BW fits accommodate hard component – jets 23 soft hard larger T smaller bt smaller T larger bt slope break is jet effect J Phys G 37, 085004 (2010); arXiv:0906.1229 fit fit 19 GeV 200 GeV 17 GeV sum sum BW p 0.5 2 t =
- 24. 24 Elliptic Flow – Standard Narrative x z y py y x 2 2 1 2 2 2 cos2 , tan ( ) y x y x p v y x p - - Reaction plane: z-x plane hydro evolution v2 data “hot and dense matter with partonic collectivity” I D Au Au spectators participants participants hadron density hydro mass scaling 2006
- 25. Nonjet (NJ) Azimuth Quadrupole 25 derived from model fits to 2D angular correlations conventional methods simple formula predicts all centralities and energies 2D method jet bias: nonflow p-p v2 predicted by pQCD! (color dipole) premise: all azimuth structure is flows – no jets Eur Phys J C 62, 175 (2009); arXiv:0907.2686 퐀퐐 = ρퟎ퐯ퟐ ퟐ no jet contribution 2007
- 26. 26 Underestimating Jet Yields simulation STAR data background estimated by ZYAM and v2 1) v2 over-estimated, 2) offset is over-estimated by “ZYAM” true jet yields Au-Au 0-12% (solid) p-p (open), both 200 GeV with correct background Au-Au jet yield six times larger than p-p: near-transparent A-A system ZYAM underestimates jet yields up to 10× true background ZYAM background ZYAM jet yields ZYAM: zero yield at minimum claim jet quenching, parton thermalization J Phys G 37, 085004 (2010); arXiv:0906.1229 ZYAM corrected 0-5%
- 27. 27 NJ Quadrupole Energy Systematics A new QCD phenomenon at RHIC? saturation? 2 2 [2] {2 } ref v D n r r D squeezeout per-pair Bevalac AGS SPS RHIC small-x glue quadrupole star preliminary nucleon hydro AGS Bevalac SPS RHIC per-particle hydro extrapolation is misleading AQ{2D} LHC AQ arXiv:1302.0300 tbp J Phys G LHC? 퐀퐐 = ρퟎ퐯ퟐ ퟐ 2007
- 28. NJ Quadrupole vs A-A Transparency 28 dijet structure scales exactly with the number of binary N-N collisions Nbin – as expected for A-A transparency “elliptic flow” based on re-scattering in a dense medium increases to 60% of its maximum ST ST in either case the energy dependence is consistent with QCD ? but no rescattering arXiv:1302.0300 tbp J Phys G SS jet peak amplitude “elliptic flow”
- 29. 29 NJ Quadrupole Source Boost nonjet quadrupole distributions for identified hadrons centrality average add deuterons hydro is falsified by PID v2 data! R R 200 GeV Au-Au source boost Lambdas only 0-10% minimum-bias data replot v2 data as v2 / pt on yt new information is quadrupole source boost distribution trend predicted dash-dot curve add most-central data viscous hydro “mass scaling” hydro Phys Rev C 78, 064908 (2008); arXiv:0803.4002
- 30. NJ Quadrupole Spectrum 30 unidentified hadrons Phys Rev C 78, 064908 (2008); arXiv:0803.4002 quadrupole boost is centrality independent – no coupling to A-A dense medium universal spectrum FF spectrum centrality dependence fixed boost 퐐(퐲t) ∝ ρퟎ(퐲t, 퐛) 퐯ퟐ(퐲퐭, 퐛)/pt statistical model ! quadrupole source 2010
- 31. 31 ALICE “Higher Harmonics” NJ quadrupole jet structure 2 2 2 2 2 2 2 2 v {2} v {EP} = v {SS}+ v {2D} 2 2 m m v {2} = v {SS} m> 2 ST points from ALICE curves from UW controlled by pt spectrum SS 2D jet peak jet bias J Phys G 40, 055104 (2013); arXiv:1109.2540 7 citations 200 GeV Au-Au Phys Rev Lett 107, 032301 (2011); arXiv:1105.3865 250 citations no h cut sextupole octupole quadrupole
- 32. BEC + electrons 32 Sextupole Relation to SS 2D Peak true SS baseline ST ST SS 2D jet peak 3 parameters SS peak amplitude SS peak h width 50-60% 50-60% BEC SS peak jets note sharp transition ST std fit triangular flow from jets prediction: 1D projection Phys Rev C 88, 014904 (2013); arXiv:1301.2187 Phys Rev C 86, 064905 (2012); arXiv:1206.5428 2008 STAR data 2013 STAR data 2012 140 parameters
- 33. LHC Spectra and Yields 33 prediction ns scale up soft by 1.8 nh scale up hard by 1.82 2.76 TeV is not a simple multiple (2.1) of 200 GeV dijets play a major role fluctuations depend on detector acceptance, change endpoint structure little shape change from 0.2 to 2.76 TeV PHENIX STAR Phys Rev Lett 106, 032301 (2011); arXiv:1012.1657 arXiv:1402.4071 tbp Phys Rev C p-p
- 34. data eikonal ALICE ensemble ‹pt› vs RHIC 34 equivalent dijet production ALICE: All MCs are falsified Phys Lett B 727, 371 (2013); arXiv:1307.1094 PYTHIA
- 35. Two-component Model for ‹pt› 35 simple TCM describes all ‹pt› data hard components jet spectrum width result consistent with hard component from dijets TCM also describes p-Pb, Pb-Pb curves are TCM Phys Rev C 90, 024909 (2014); arXiv:1403.6494.
- 36. ALICE event-wise ‹pt› Fluctuations 36 soft fluctuation systematics, agreement with MB dijet expectations Eur Phys J C 74, 3077 (2014); arXiv:1407.5530 TCM description – dijets dijets 2014 2006 2006 J Phys G 32, L37 (2006); nucl-ex/0509030 C “covariance” 2014 A ≈ 0.4 like nh /ns
- 37. Interaction of Two Cultures 37 QCD large l QCD small l HEP narrative QGP/flow narrative ISR/SppS/FNAL HEP data HERA/LEP BEV/AGS data RHIC/LHC data Compton scattering, fragmentation, jets LGT QFT/CGC e.g. F. Gelis nucleon matter reality “parton” matter reality? 1980s, 90s 2000-present 1980s-present reality data model1 model2 induction prediction measurement Bayesian inference –scientific method –models compete model3 1980s-present ?
- 38. Summary •The QGP/flow culture has captured various HEP jet manifestations from spectra and correlations and reinterpreted them as flows carried by a dense “partonic” medium → “perfect liquid” •Differential measurements and optimized plotting formats reveal the jet character of various claimed flow phenomena –reaffirming the HEP narrative •True novelties of high energy nuclear collisions are (a) a nonjet (and nonflow!) quadrupole and (b) dijet modifications in A-A andp-p, new aspects of QCD 38
- 39. Abstract Since the mid eighties a community originating within the Bevalac program at the LBNL has sought to achieve formation of a color-deconfined quark- gluon plasma in heavy ion (A-A) collisions using successively higher collision energies at the AGS, SPS, RHIC and now the LHC, emphasizing a flowing dense "partonic" medium as the principal phenomenon. During the same period the high energy physics (HEP) community studying elementary collisions (e-e, e-p, p-p) has developed the modern theory of QCD, emphasizing dijet production (fragmentation of scattered partons to observable hadrons) as the principal (calculable) phenomenon. Initially it was assumed that the QGP phenomenon in more-central A-A collisions might be distinguished from the HEP dijet phenomenon in elementary collisions. However, strong overlaps in phenomenology have revealed significant conflicts between QGP and HEP "cultures," especially at RHIC and LHC energies. In this talk I review some of the history and present an assortment of experimental evidence and interpretations from the two cultures with suggested conflict resolution. 39