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1/43 Heavy Quarks and Heavy Quarkonia as Tests of Thermalization 2005-11 중중중 중중 (HIM 2005-11) DongJo Kim Yonsei University, Seoul Korea

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  • Heavy Quarks and Heavy Quarkonia as Tests of Thermalization2005-11 (HIM 2005-11) DongJo KimYonsei University, Seoul Korea

  • Outline of TalkA short Overview of RHIC results. RHIC history Jet-Quenching (pion RAA, Jet suppression) Flow ( light hadrons, even heavier particles)Extension from Light quarks to heavy quarks How to measure Heavy flavor ?Semi-leptonic heavy flavor decay (Cocktail/Converter)J/PHENIX heavy flavour measurement Open charm Results( RAA , charm flow ) Radiative energy loss, bottom contribution J/psi Results ( RAA ) Suppression (Screening) vs Enhancement (recombination)

    Toward Precision heavy flavor measurementSummary1-(2)1-(2)4-(1)4-(1)4-(2)

  • RHIC HistoryRHIC program is operating very successfully.PHENIX online data transfer and reconstruction remarkable

  • Selected Results at RHICJet suppression in central Au + Au collisionsSuppression apparently flat for pt up to 10 GeV/cAbsence of suppression in d+Au

    Strong elliptic flowScaling of v2 with eccentricity shows that a high degree of collectivity built up at a very early stage of collision Evidence for early thermalizationData described by ideal hydrodynamic models fluid description of matter applies.

  • Particle Spectra EvolutionPeripheralCentralK. Adcox et al, Phys Lett B561 (2003) 82-92

  • Nuclear Modification Factor: RAAWe define the nuclear modification factor as:

    RAA is what we get divided by what we expect.By definition, processes that scale with the number of underlying nucleon-nucleon collisions (aka Nbinary) will produce RAA=1.RAA is well below 1 for both charged hadrons and neutral pions.nucl-ex/0304022 S.S. Adler et al.Au+Au->p0+X PRL 91 (2003) 072301Factor 5

  • Initial State effects ruled out !Dramatically different and opposite centrality evolution of Au+Au experiment from d+Au control.Jet Suppression is clearly a final state effect. Au + Au d + Au ControlPreliminary DataFinal DataPHENIX PreliminaryInitial State Effects OnlyInitial + Final State Effects

  • The matter is extremely opaque Suppression is very strong (RAA=0.2!) and flat up to 20 GeV/c

    Energy loss of partons in dense matterA medium effect predicted in QCD( Energy loss by colored parton in medium composed of unscreened color charges by gluon bremsstrahlung : LPM radiation )Gyulassy, Wang, Vitev, Baier, Wiedemann See nucl-th/0302077 for a review. Baier, Dokshitzer, Mueller, Peigne, Shiff, NPB483, 291(1997), PLB345, 277(1995), Baier hep-ph/0209038

  • Azimuthal Angular CorrelationsJet Quenching !

  • Collective FlowIdentified charged hadron v2 indicatesEarly thermalizationConstituent quark scaling Partonic collectivityEven flows, within the errors consistent with other hadrons

  • Summary of RHIC results with light quarks Collective Flow and Jet Quenching of light partons strongly suggest that QGP is discovered. One of the central questions in high energy heavy ion physics is whether a quark-gluon Plasma (QGP) has been discovered at RHIC. (M.Gyulassy and L. McLerran, nucl-th/0405013, M.Gyulassy, nucl-th/0403032)

  • Extension from light quarks to Heavy Quarks Collective Flow and Jet Quenching of light partons strongly suggest that QGP is discovered. Further detailed tests of jet tomography using heavy quarks could be decisive as a complementary test of the theory. Open charm suppression, which can now be measured at RHIC by comparing pt distributions of D-mesons in d-Au and Au-Au collisions, is a novel probe of QGP dynamics. J/psi suppression or enhancement mechanism should be nailed down with high statistical and systematical precision. One of the central questions in high energy heavy ion physics is whether a quark-gluon Plasma (QGP) has been discovered at RHIC. (M.Gyulassy and L. McLerran, nucl-th/0405013, M.Gyulassy, nucl-th/0403032)

  • Why Heavy Quarks ? Heavy quarks (charm and beauty) - produced early in the collision. Live long enough to sample the plasma Intrinsic large mass scale allows precise calculations What can we look in order to find out the characteristics or properties of the medium(QGP)

    Yields of charm and beauty pairs compared to first principle lattice simulations determine the energy density and temperature J/ suppressionComparison between light and heavy quark suppression distinguishes between theoretical models of energy loss in the QGP Charm vs Light quark energy loss ( Jet-Quenching )Mass dependence of diffusion of heavy quarks determines plasma properties, e.g. viscosity and conductivity Charm flow B. MullerS. Bethkecbx100

  • How to measure Heavy Flavor ?Experimentally observe the decay products of Heavy Flavor particles (e.g. D-mesons)

    Hadronic decay channels DKp, D0p+ p- p0Semi-leptonic decays De(m) K ne

    PHENIXSingle electron measurements in p+p, d+Au, Au+Au sNN = 130,200,62.4 GeVSTARDirect D mesons hadronic decay channels in d+AuD0KDKD*D0 Single electron measurements in p+p, d+Au

  • PHENIX detector at RHICDesigned to measure electrons, muons, photons and hadrons.

    Key Parameters: Electrons:-0.35 < y < +0.35Radiation Length < 0.4%PID with RICH/EMC Muons:1.2 < |y| < 2.2

    Very high data and trigger bandwidth

  • How does PHENIX see the J/ ?J/ e+e identified in RICH and EMCal|| < 0.35 p > 0.2 GeV

    J/+ identified in 2 fwd spectrometers1.2 < || < 2.4p > 2 GeV

    Centrality and vertex given by BBC in 3

  • New Electron ResultsS/B > 1 for pT > 1 GeV/cRun04: X=0.4%, Radiation length Run02: X=1.3%Signal/BackgroundWe use two different methods to determine the non-photonic electron contribution (Inclusive = photonic + non-photonic ) Cocktail subtraction calculation of photonic electron background from all known sources Converter subtraction extraction of photonic electron background by special run with additional converter (X = 1.7%)Charm/Bottomelectrons

  • Non-Photonic Electron SpectraClear high pT suppression developing towards central collisions

  • Suppression of High pT CharmStrong modification of the spectral shape inAu+Au central collisionsis observed athigh pT

  • Theory ComparisonTheory curves (1-3) from N. Armesto, et al., hep-ph/0501225(4) from M. Djordjevic, M. Gyulassy, S.Wicks, Phys. Rev. Lett. 94, 112301Data favor models with large parton densities and strong coupling

    Main uncertainty:Bottom contribution at high pT

  • Charm Flows ? Charm quark exhibit a degree of thermalization ~ comparable to that of light partonsTheory curves from: Greco, Ko, Rapp: Phys. Lett. B595 (2004) 202v2 (D) = v2 (p) v2 (D) = 0.6 v2 (p) v2 (D) = 0.3 v2 (p)

  • Charming? Summary Electrons from heavy flavor decays were measured at s = 200 GeV in Au+Au collisions at RHIC

    Nuclear modification factor RAA shows a strong suppression of the electrons at high pT in Au+Au collisions

    Observed RAA favors models with large parton densities and strong coupling

    Charm flows! v2(D) ~ 0.6 x v2(p) , indicating substantial coupling of the charm quarks to the bulk dynamics of the medium

  • Beauty Limits Suppression Factor?M. Djordjevic et al., nucl-th/0507019

  • Not All Theorists AgreeNow Armesto et al. also include beauty and can find consistent results with RAA = 0.4

  • Charm suppression and FlowIn a calculation by Teaney and Moore (hep-ph/0412346), they calculate the expected elliptic flow (v2) and transverse momentum modifications for different charm quark diffusion coefficients(free parameter). The two effects go hand in hand.

  • "Direct Comparison is Certainly Misguided..."PHENIX Data Results Speak for Themselves

  • A .Different predictions on J/ behaviour when QGP is formedColor screening will lead to suppression of charmonium production in heavy ion collisions (T. Matsui, H. Satz, Phys. Lett. B178(1986)416).Lattice QCD results show that the confining potential between heavy quarks is screened at high temperature. This screening should suppress bound states such as J/. However, recent lattice results indicate that the J/ spectral functions only show modest modification near the critical temperature, and thus may not be suppressed until higher T.But after taken the recombination into account, much less suppression or even enhancement is predictedA. Andronic, P.B. Munzinger et al., nucl-th/0303036 L. Grandchamp, R. Rapp, hep-ph/0103124 R.L. Thews et al., Phys. Rev. c63(2001)054905

    Heavy Quarkonia B .Disentangle Normal nuclear effectsGluon shadowing, Nuclear AbsorptionInitial state energy loss , Cronin effect.

  • NA50 ConclusionsA clear onset of the anomaly is observed. It excludes models based on hadronic scenarios since only smooth behavior with monotonic derivatives can be inferred from such calculations Phys. Lett. B 450, 456 (1999).Model assuming: charm production scales as DY color octet c-c is absorbed by nucleons with a s = 6.2 mb no absorption with comovers p,r

  • Normal Nuclear + ShadowingForward rapidityTheory Vogt:nucl-th/0507027Model of cold nuclear matter effects in agreement with dAuUnderpredicts suppression in AuAu and CuCu

  • Looks Like CERN Suppression?Suppression level is similar between the two experiments, but 1) the collision energy is 10 times higher (200GeV wrt 17GeV) 2) the rapidity window for NA50 is |y|[0,1]Comparison with NA50 data presented wrt Npart and normalized to NA50 p+p point.

  • Too Much Suppression in Theory!Models that were successful in describing SPS datafail to describe data at RHIC too much suppression

  • RegenerationImplementing regeneration: much better agreement with the dataAt RHIC, Recombination compensates stronger QGP screening?But still there are uncertainties in their calculations

    Uncertainty is large !

  • J/ Summary Suppression for most central collisions is similar to NA50 Energy density and gluon density at RHIC should be much higher (2-3 times, 200GeV vs 17GeV)? At RHIC: Recombination compensates stronger QGP screening?

  • Needed Input of Total CharmInput from both STAR and PHENIX is needed.

  • More in the Future... Reduce systematic errors and finalize CuCu and AuAu data. Improved statistics for baseline Run-5 Proton-Proton and future p-A or d-A Working on J/y v2, but statistically very challenging with Run-4 and Run-5 data sets BUP06 Au-Au running !!!Not approved!!! Shush!!!

  • Summary A wealth of new PHENIX data on heavy quarks and heavy quarkonia.

    Charm is a very optimal probe of thermalization and properties of the medium, but the price for this may well be the loss of a probe via quarkonia for deconfinement.

  • The precision Measurements Detector upgradePrecise measurement of Displaced vertexOnium measurementsTrigger RHIC II Luminosity

  • Silicon Vertex Detector Four barrel layersTwo ALICE pixel bus layersTwo strip-pixel layersFour end-cap pixel layersDisplaced vertex ( ~50 m)Full azimuthal inner tracking || < ~2.4Improve acceptance for -jet correlations, D KConnect to tracks in central and muon armsTag heavy flavor decaysc,b e,B J/Improve onium resolutionEliminate decay hadronsReduce high-pT background

  • Nose Cone CalorimeterReplace central arm magnet nosecones (Cu) w/ tungsten-silicon calorimetersCoverage at forward/backward rapidity: 0.9 < || < 3.5/0 separation for pT < 30 GeV/c Jet identification identification gives good acceptance for c J/ +

  • Muon Trigger UpgradeThree layers of RPCs with 2D (,) pad readoutProvides online momentum measurement to improve Level-1 trigger rejectionSingle-particle pT cutW spin-measurements in ppTwo-particle Minv cutonium measurements in AANecessary to take complete advantage of luminosity upgradesProvides improved high-multiplicity background rejection

  • RHIC II Luminosity CAD Guidancex 35 increase for ppx 10 increase for CuCux 15 increase for dAux 15 increase for AuAuhttp://rhicii-heavy.bnl.gov/doc/RHIC_II_Luminosity_Roser.xls

  • RHIC II Yields ADF, MJL GuidanceAssume CAD Maximum Average Luminosity Projection, 12 week runs, known PHENIX uptime (60%) to get Live Delivered Luminosity.Use measured values when possible to calculate pp s, B.R.s.Assume nuclear scaling - (AB), w/=1 for , =0.92 for others.Use stated RF efficiency, diamond size to get vertex cut efficiency.Use measured PHENIX performance, assume PHENIX SiVTX, Nosecone Calorimeter, Muon Trigger upgrades to get acceptances, efficiencies.

  • Onium Yields Precision measurements of the J/Exploratory measurements of the other onium states.Steep increase at s = 500 GeV illustrates the significant difficulties for measurements at lower energies.

  • Synergistic Benefits of Detector/Luminosity Upgrades for Open Heavy Flavor MeasurementDetector upgrades assist by determining decay vertex.Allows direct measurement of charm via D KReduces backgrounds at low-pTAllows statistical separation of c/b at high-pTAllows direct elimination of hadron decay muons.Luminosity upgrades extend pT reach and allow reduction of systematic errors.Additional special runs (e.g., w/ different converter thicknesses and locations, different field configurations, etc.)Finer binning of DCA dependence for c/b separation.Better determination of punchthrough absorption.

  • Backup Slides

  • Not All Experiments Agree EitherRAA agrees, but the proton-proton references are different by ~ 50%.

  • Comparison

  • NA50

  • Regenerationadditional inclusion of 1)transverse energy fluctuations and 2) trigger energy loss

  • Transverse MomentumCu+Cu (|y|[1.2,2.2])Au+Au (|y|[1.2,2.2])

  • Hydrodynamic?Calculation is a parameter free hydrodynamic flow result using parameters from nucl-th/0212068.Arbitrary normalization.PHENIX PreliminaryGold-Gold Central 0-20%J/y for |y|
  • Balancing Effects

  • Rapidity Dependence

  • Common Feature: Rapidity NarrowingSee talk by Thews

  • What do the Theorists Have to Say?

  • Participant Scaling?

  • Charm Quarks and Thermalization....Salgado - charm energy loss including mass effects and gluon effects

  • Magdalena - charm and beauty energy loss and mass effects

  • Molnar

  • More Regeneration

  • Super-Sensitive / Super-ComplexJ/y by its heavy mass and direct coupling to incoming gluons at RHIC energies is sensitive to initial parton distribution functions (PDF).

    Modifications of these PDFs in nuclei will affect the initial production rate of charm-anticharm quark pairs.

    Production of direct J/y is suppressed by the need for an additional radiated gluon to conserve quantum numbers, so another mechanism is needed.

    Hadronic or pre-hadronic interactionscan suppress J/y yields.

  • Nuclear Parton Distribution FunctionsAt low x ~ 10-2, a suppression of partons is observed in the nuclear wavefunction (shadowing).

    This suppressing any hardprocess coupling to thosepartons relative to point-likescaling (a = 1).

    At high x ~ 10-1, an enhancement (anti-shadowing)may enhance hard processes.

    Color Glass Condensate orSaturation Physics gives a universal QCD explanationfor low x shadowing.

  • Evolution of Modified PDFsAs one probes a proton or nucleus at higher momentum transfer (shorter wavelength), there is an enormous growth of low x gluons.Thus we might expect that saturation or shadowing effects will play a larger role in higher energy collisions sensitive to a similar range of x.

  • Initial Parton Energy LossIf the incoming hadron de-hadronizes as it interacts in the nucleus, an individual high-x parton starts to radiate (losing energy).DxAt lower energies (SPS, FNAL fixed target) where one is near J/y production threshold, a small energy loss can result in a strong suppression of production.

    Chart2

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    RHIC

    SPS

    J/Y

    D-Y

    E(CM) in GeV

    J/Psi relative cross section

    Sheet1

    SchulerJunkD-YPsi/D-Y

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    1900.820858699310.04997057216.426842181

    1920.822562204810.049327012116.6756949046

    1940.82423372710.048696890116.9257980513

    1960.82587415510.048079825717.1771453575

    1980.827484345110.047475452217.4297306536

    2000.82906512310.046883415617.683547862

    2020.830617284410.046303373817.9385909939

    2040.832141596710.045734996818.1948541483

    2060.833638800410.045177965718.4523315088

    2080.835109609810.044631972418.7110173423

    2100.836554714710.044096719218.9709059967

    2120.837974780910.043571918419.231991899

    2140.839370451710.043057291819.4942695536

    2160.840742348310.042552570419.7577335402

    2180.842091071510.042057494420.0223785126

    2200.843417201710.041571811920.2881991966

    2220.844721300310.041095279820.5551903883

    2240.846003910410.040627662420.8233469529

    2260.847265557310.040168731921.0926638231

    2280.848506749410.039718267521.3631359973

    2300.849727978810.039276055621.6347585386

    2320.850929722110.038841889321.9075265732

    2340.852112440910.038415568222.1814352889

    2360.853276582210.037996898222.4564799343

    2380.854422579310.037585691122.7326558168

    2400.85555085210.037181764623.0099583022

    2420.856661807510.036784941923.2883828127

    2440.857755840610.036395051623.5679248265

    2460.85883333410.036011927723.848579876

    2480.859894659210.035635408924.1303435473

    Sheet1

    RHIC

    SPS

    J/Y

    D-Y

    E(CM) in GeV

    J/Psi relative cross section

    Sheet2

    Bill Zajc:"Fitting" to Angelis et al, Phys. Lett 87B, 398,

    I get

    s^{3/2} d\sigma/{dm dy} ~ (1 - m/\sqrt{s})^{16}

    The integral yield beyond some mDY goes as one powerhigher, I.e, 16 --> 17.

    Sheet3

  • Parton Energy LossE772 and E866 at Fermilab dE/dx = 2.73 0.37 0.5 GeV/fm (from hadronization due to confinement)dE/dx ~ 0.2 GeV/fm (from gluon radiation due to nuclear environment)

    This is the first observation of a non-zero energy loss effect in such experiments.Dxg*m+m-Drell-Yan production in proton-nucleus collisions is sensitive to parton energy loss..Johnson, Kopeliovich, Potashnikova, E772 et al.Phys. Rev.C 65, 025203 (2002) hep-ph/0105195Phys. Rev. Lett. 86, 4487 (2001) hep=ex/0010051Must carefully separate nuclear shadowing effects and energy loss effects both of which lead to suppression of Drell-Yan pairs.

  • Initial Parton Multiple-ScatteringDxInitial state multiple-scattering of the parton leads to an enhancement in the pT of the final J/y product. This enhancement is often referred to as the Cronin Effect.Despite the phenomenological success of incorporating this multiple scattering, there are still open questions about this mechanism. Also, multiple scattering inherently leads to radiation.

  • Re-InteractionsAfter production of the charm-anticharm pair, it may re-interact during its traversal of the remaining nuclear material.These re-interactions may be of a pre-cursor to the J/y (color octet cc-g state) or of the physical J/y itself.1

    In heavy ion reactions, the quarkonia state may be further suppressed due to color screening in medium.2

    1Arleo, Gossiaux, Gousset, Aichelin, hep-ph/9907286 2Matsui, Satz, Phys. Lett. B178: 416 (1986).2NA50 Phys. Lett. B521, 195 (2001)

    The matter is so opaque that even a 20GeV/c pi0 is stopped. The common pattern observed for eta mesons strongly suggests thatThis suppression is established at the partonic phase, while the near-unity value of the direct photon yield demonstrates that the binary scalingFrom p+p yields to the Au+Au system is well-calibrated.The J/ suppression discovery at SPS was originally attributed to Debyescreening of cc in a wQGP paradigm. Recent lattice QCD results now indicatethat heavy quark correlations persist perhaps up to 2Tc. This is another indicationfor the strongly coupled nature of sQCD. The suppression of J/ in AAis also strongly influenced by initial state and final state hadronic (comover)effects. It will be no easier to deconvolute these competing effects at RHIC.These observables of course need to be measured at RHIC, but one should notexpect an easy interpretation.

    1I thank T.D.Lee for discussions and suggesting the sQGP designation of the matter discovered at RHIC todistinguish it from weakly interacting, Debye screened plasmas, wQGP, which may only exist at temperaturesT Tc.

    The J/ suppression discovery at SPS was originally attributed to Debyescreening of cc in a wQGP paradigm. Recent lattice QCD results now indicatethat heavy quark correlations persist perhaps up to 2Tc. This is another indicationfor the strongly coupled nature of sQCD. The suppression of J/ in AAis also strongly influenced by initial state and final state hadronic (comover)effects. It will be no easier to deconvolute these competing effects at RHIC.These observables of course need to be measured at RHIC, but one should notexpect an easy interpretation.

    1I thank T.D.Lee for discussions and suggesting the sQGP designation of the matter discovered at RHIC todistinguish it from weakly interacting, Debye screened plasmas, wQGP, which may only exist at temperaturesT Tc.

    And why heavy quarks?Heavy quarks mass such as c,b is much larger than light quarks, so coupling constant is small.So Heavy quarks are produced early stage in the collision, can live long enough to sample the plasma.2nd Intrinsic large mass scale allows precise calculations.3rd By looking at the mass dependence of diffusion of heavy quarks determines plasama propertiesSuch as viscosity and conductivity.4th Yield of charm and beauty pairs compared to first principle lattice simulation can determine the energy density and temperature.5th Comparison between light and heavy quark suppression distinguishes between theoretical models of energy loss in the medium.Cherenkov light in RICHElectrons are measured by DCPC1RICHEMCal Number of Hit PMT Ring shape Energy Momentum matching

    Cocktail subtraction calculation of photonic electron background from all known sources Systematic errors are bin at low pt,small S/B ratio(Non-photonic/photonic)Converter subtraction extraction of photonic electron background by special run with additional converter (X = 1.7%)Limited statistics at high pt

    Conflicts withQ_hat radiative? Charm quark energy loss ?1.Light quark/gluon energy loss results2.Entropy limit ( how much Light /heavy ? )Ans : Within radiative energy-loss calculations in a gluon plasma, Raa Data require significantly larger transport coefficients than expected within pQCD.pT>3GeV , Bottom contribution is larger?Dead-cone effect significantly limits bottom quark energy loss The observed elliptic flow is significantly larger than was originally expected from kineticcalculations of quarks and gluons [7], but in fairly good agreement with simulations basedupon ideal hydrodynamics [8, 9, 10, 11]. This result suggests that the medium responds asa thermalized fluid and that the transport mean free path is small [7, 12, 13].However, this interpretation of the elliptic flow results is not universally accepted [14,15]. Hadronization may amplify the underlying partonic elliptic flow [16]. Indeed, partoncoalescence is one mechanism which may amplify the hadronic elliptic flow relative to itspartonic constituents [15, 17, 18, 19, 20]. On physical grounds, it seems unlikely that thetypical mean free path is much smaller than a thermal wavelength, 1/(2T) . Indeed it hasrecently been conjectured that the hydrodynamic diffusion coefficient /(e + p) is strictlylarger than half a thermal wavelength [21],It is impossible to have a large elliptic flow without also predicting a significant suppressionof charm quarks. Indeed, if future measurements find the charm elliptic flow strong, and thespectrum not suppressed, the present authors must logically conclude that hydrodynamicsis not responsible for the observed elliptic flow. This strong conclusion might be mitigatedif coalescence or some other exotic hadronization mechanism manages to make the D mesonelliptic flow significantly larger than the underlying c-quark elliptic flow

    Model of cold nuclear matter effects in agreement with dAuUnderpredicts suppression in AuAu and CuCubaseline calculations of initial-state shadowing and final stateabsorption effects on J/ production in nucleus-nucleus collisions

    Models that were successful in describing SPS datafail to describe data at RHIC - too much suppressionphysics objection is the last sentence "The Jpsi transverse momentum spectra support recombination scenario for both Cu_Cu and Au-Au Collisions." Even though in that particular figure from Thews this appears to be true, I am almost certain that this conclusion is wrong. See Itzhak's excellent summary talk at Quark Matter. Both I and many others believe Thews has a very large Cronin parameterization. Also there is a correlation of normal nuclear absorption and Cronin not properly accounted for in his calculation. See the paper hep-ph/9702273. Not for this proceedings, but I can reproduce this calculation and show how much it lowers the in just the normal nuclear absorption case. In my proceedings I tried to be non-commital about recombination, saying that we need updated calculations for pT, y, centrality and reduction of our systematic errors. The main benefits are in three areas. Firstly, by selecting electrons with a distance of closest approach (DCA) to the primary vertex larger than ~100 m, the background will be suppressed by several orders of magnitude and thereby a clean and robust measurement of heavy flavor production in the single electron channel will become available. Secondly, because the lifetime of mesons with beauty is significantly larger than that of mesons with charm, the VTX information will allow us to disentangle charm from beauty production over a broad pT range. Thirdly, a DCA cut on hadrons will reduce the combinatorial background of K to an extent that a direct measurement of D mesons through this decay channel will become possible. In addition, the VTX detector will substantially extend our pT coverage in high pT charged particles, and it also will enable us to measure +jet correlations.

    Our luminosity inputs were of course taken from CAD guidance at this web page. Skipping to the bottom line we see the Steep ?Steep increase at s = 500 GeV illustrates the significant difficulties for measurements at lower energies.

    DCA ?Pp star higher?1) Let us first address the ET fluctuations. From the minimum bias (MB) event distribution of transverse energy,dN/dET , as measured in the NA50 apparatus [57] one finds a rapid falloff beyond ET = 100 GeV, the so-calledknee of the distribution. The tail of the latter, which reaches beyond ET = 100 GeV, is associated with fluctuationsin transverse energy at fixed geometry for b = 0. Events which fluctuate beyond ET > 100 GeV contain a largerinitial entropy and consequently a hotter initial temperature and a longer plasma phase which implies additional J/suppression (charm and J/ production being a hard process are not coupled to fluctuations in the soft sector). Toaccount for this phenomenon [53], we replace in our calculations the total entropy at fixed impact parameter, Stot(b),2) However, as has been suggested by Capella et al. [56], there might be an additional feature in the large ET -regionunrelated to J/ physics, which can be gleaned from the Drell-Yan (DY) over minimum bias data, cf. right panelof Fig. 6. The theoretical ratio DY/MB (dotted line) computed by NA50 flattens out at large values of ET > 100GeV, whereas the data seem to indicate a slight turnover [57]. The argument [56] to explain this turnover (whichequally applies to the J/ event sample) is that for DY-events the hadronic transverse energy deposited in thecalorimeter is slightly reduced as compared to the corresponding MB-events due to triggering on the DY (or J/)pair (2.9 GeV< MDY