Identified Particle Production in p+p and d+Au Collisions at RHIC Energies Felix Matathias Doctoral Defense Adviser: Tom Hemmick State University of New York at Stony Brook December 8, 2004, New York
Comparative Nuclear Physics • Yesterday it occurred to me that the core concept of my thesis is not so different than what my wife does for a living. • My wife is a Ph.D. student in Comparative Literature at Stony Brook. • I gave her a call last night and asked her for a short definition of her field. She repeatedly asked my why I needed it and seemed confused (and concerned). • The goal of Comparative Literature is: “…to compare literature in different languages and literature with relation to some other field…” • In that vein, I define the goal of Comparative Nuclear Physics to be: “…compare properties of particle production in different nuclear environments and as a function of particle flavor…” • Obviously this is a narrow definition that I made up to define the goal of my thesis. • It could easily though be extended to a more general definition. • The main point though is that my wife may become interested in what I do.
Comparative Nuclear Physics II • In this work we will be comparing particle production at • Center of Mass Energy: √s=200GeV • Different nuclear environments: • p+p collisions • d+Au collisions • Au+Au collisions • Particle species: pions, Kaons, (anti)protons • The physical observables will be • Differential yield per inelastic collision in the d+Au and Au+Au case • Invariant differential cross sections in the p+p case
The machine • Relativistic Heavy Ion Collider • Brookhaven National Lab • 2 counter-circulating rings • 3.834 km circumference • Superconducting magnets(3.5T) • 192 dipoles per ring • 246 quadrupoles per ring • Time between collisions: 0.213 microseconds • Crossing angle: 0 • Bunch length: 20 cm • Bunches per ring: 56 • Luminosity lifetime: 3-10 hours • Particles per bunch (units 1010): • Au+Au: 0.1 • p+p : 10 • Top energies (each beam): • 100 GeV/nucleon Au+Au. • 100 GeV/nucleon d+Au • 100 GeV polarized p+p
The detector • Maximal Set of Observables • Photons, Electrons, Muons, ID-hadrons • Highly Selective Triggering • High Rate Capability. • Rare Processes. • But rare processes always come late in the game for collider experiments due to limited luminosity. • But I wanted a thesis at some point. • Therefore I utilize the copious production of hadrons, through the strong nuclear force, albeit with a relatively small detector.
Does nuclear size matter ?(Yes, but in mysterious ways) • Comparing particle production in different nuclear environments wouldn’t be that interesting if everything scaled according to the size of the colliding system • Definition of point-like scaling: • . • Do we already know anything about the scaling properties of hard scattering ? • Answer: Yes, we know that scaling is strongly violated!
Straub et.al Phys.Rev.Lett.68(4)1992 Antreasyan et.al.Phys.Rev.D19(3)1979 Cronin Effect • In p+A collisions: • Parameterization done by Cronin et al. (Phys.Rev.D11,3105,1975) • Alpha factors are: • pt-dependent • species-dependent • Cronin effect • Enhancement at high-pt • Shadowing at low-pt • Mechanism: Initial parton multiple scattering Questions that this thesis will answer: What is the size of the Cronin effect at RHIC energies ? What is the species-dependence of the Cronin effect at RHIC energies ? What is the energy dependence of the Cronin effect at RHIC energies compared to Fermilab observations?
Parton Saturation • Linear evolution (DGLAP) leads to violation of unitarity. • At some point, the parton density acquires a negative term:
The onset of parton saturation “Packing” factor Saturation moment: The scale at which non-linear effects start to be important in the hadron wavefunction. Onset of saturation: k~1 Solution in the x-Q plane. For Q>>Q_saturation(t) non-linear effects are negligible and linear evolution effects apply (BFKL, DGLAP)
The net effect of parton saturation is particle suppression. Phys. Let. B561, 93 (2003) Non-saturateddeuteronwave function d “Cronin” Saturatednuclearwave function A “Suppressed” This thesis answers the question: enhancement or suppresion for identified particles ?
A new state of matter F.Karsch, Lect.Notes.Phys 583, 209 (2002) • Hypothesis: hadronic matter undergoes a phase transition as temperature reaches T~170 MeV • Supported by the decrease of the strong coupling constant as a function of energy. • Energy density increases over an order of magnitude in a narrow range of temperatures 10-20 MeV • Lattice QCD provides the most quantitave theoretical support to this day. Understanding the transition as a change of the number of degrees of freedom: Below Tc : dilute gas of 3 states of pions Above Tc : for 2 flavors we have 2(flavors)x2(quark,antiquark)x2(spin states)x3(colors)=24 quark d.o.f. 8(colors of gluons)x2(helicity d.o.f.)=16 gluonic d.o.f.
Formation time t0 = 0.3-1fm/c i ~ 5 - 15 GeV/fm3 Tc ~ 250-350 MeV A new State of Matter II • The quark and gluon degrees of freedom normally confined within hadrons are mostly liberated • The transition occurs when the energy density of matter is of the order of that of matter inside a proton • Energy density about an order of magnitude larger than the energy density inside atomic nuclei: 1-10 GeV / fm3 We can do this! Au+Au collisions at RHIC push matter at these extremes routinely.
Nuclear Modification Factor NN cross section The observable of the day is again….. <Nbinary>/sinelp+p • Scenario 1 : RAA =1 : Scale with # of binary collisions (Ncoll). • Scenario 2 : RAA>1 : Cronin effect (observed in ISR and SPS). • Scenario 3 : RAA<1 : Suppression.
jet production in quark matter hadrons leading particle q q Suppression of high pt particles • Central RAA suppressed by factor of 4.5 • Medium induced energy loss inside the medium • Predominantly via gluon brehmstrahlung emmision • Or, parton saturation ? This question is answered in this thesis for identified particles.
But there is more to it….. Notice: R_CP not R_AA • The suppression pattern seems to be strongly dependent on particle flavor. • Counterintuitive. • If partons from hard scattering are losing energy in the medium, shouldn’t that reflect to all particles produced ? A question that this thesis will answer: Could a higher Cronin effect for the protons explain this effect ? Ncoll scaling at all centralities for the protons.
Furthermore…. • An anomalously high proton to pion ratio was observed. • A spectacular observation that had not been predicted. • Lighter pions are favored due to phase space population. • Fragmentation functions from elementary p+p and e+e collisions seem to be changed inside the medium. • What is the extra source of protons ? A question that this thesis will answer: What are the values of these ratios in elementary p+p and d+Au collisions at the same energy ?
Charged Hadron PID Analysis • Detectorsfor hadron PID • DCH+PC1+TOF+BBC • Df = p/8, -0.35 < h < 0.35 • Momentum Resolution • TOFresolutionsTOF ~ 130 ps. • HadronPID in m2 vs. p space • with asymmetric PID cuts. • 0.2< p < 3.0 GeV/c , • 0.4< K < 2.0 GeV/c, • 0.6< p < 3.7 GeV/c.
PID with BBC+TOF+DCH: Timing calilbrations • Timing Calibrations: • Slat by Slat • Run by Run Global timing offsets
PID with BBC+TOF+DCH Clear separation of particles up to high pt. Stable performance in p+p and d+Au collisions The p+p and d+Au data are both from RHIC RUN03 and therefore detector effects are small in most ratios of p+p and d+Au data.
PID cuts • Width of cuts • 3 parameter simultaneous fit to mass widths for all particles • Parameterization of cuts in Gaussian widths, independent of momentum
Detector acceptance and efficiency corrections • Detector acceptances is studied in detail • Holes are removed by cuts • Independent studies for: • Positive/negative particles • DCH and TOF detectors • North and South sides Detector areas of maximum efficiency are compared to Monte Carlo simulation and efficiency corrections for the entire detector is then calculated.
Matching and fiducial cuts Residual distribution between TOF hit and track model projection. Golden Fiducial cuts Distributions are fitted as a function of momentum for positive/negative particles, for North/South part of the detector
Detector Stability: Excerpts Antiproton/proton vs. RunNumber PID cuts vs. RunNumber Number of tracks vs. RunNumber Acceptance vs. RunNumber
Monte Carlo Corrections • Since Phenix does not cover full acceptance in phi and zed we use Monte Carlo Simulation to correct for geometrical acceptance. • Also in flight decays are corrected for. • Finally all cuts used in real analysis are also used in Monte Carlo analysis and therefore the efficiency of the cuts are thus calculated
Systematic errors TYPE-B: Momentum correlated, all points move in the same direction but not by the same factor • Systematic error evaluation is done by varying cut conditions in the analysis by 1s,2s, etc. • Additional systematic variations are: • Run-by-run variations~5% • Efficiency corrections~3% • Feed-down corrections~10% • In addition the BBC cross section introduces a 10% systematic error on p+p cross sections. TYPE-C: Momentum independent p+p Type-C:
Feed-down corrections Total protons detected by TOF: • A significant fraction of protons and antiprotons detected by the TOF originate from weak decays of: • Hyperons Y(qqs) • Cascades X(qss) • Omegas W(sss) • Since the weak decays take place very close to the vertex, and since the heavier protons take most of the decay momentum, these tracks are virtually indistinguishable from tracks arising from the vertex of the collision. Particle composition from UA5 in 200GeV p+pbar collisions
Input L Spectra in p+p and d+Au from preliminary STAR results and UA5 • ee Construction of effective L Spectrum which then is decayed in PHENIX
Feed-down corrections • Correction is of the order of 30% for protons and antiprotons. • Using the preliminary Antilambda/Lambda ratio 0.85+/-10% from STAR we apply corresponding corrections to protons and antiprotons. • Large systematic error on the feed-down protons arises from large UA5 systematics and preliminary Star results • Systematic error~24%
Centrality determination in d+Au • Centrality determination in d+Au is done with the South BBC (Au-side). • Assumption: BBC signal is proportional to participating Au nucleons. • Glauber Model calculation and BBC simulation response, map the BBCS signal to impact parameter distributions. • Corresponding Ncoll distributions in d+Au are then used to define the nuclear modification factors.
Antimatter/matter: All collision systems Within the errors, all ratios are flat and independent of collision system! Astonishing result since the microscopic mechanism for particle production in p+p and central Au+Au collisions is fundamentally different.
“Who ordered that ?” “Certainly not p+p nor d+Au.” p/p in all systems • Return of the ratio to normal values. • Smooth transition from central to peripheral Au+Au collisions. • d+Au is similar to the most peripheral Au+Au bin. • p+p is lower than d+Au, due to large Cronin for protons
p/p in p+p and d+Au Moderate centrality dependence in d+Au. p+p collisions are lower.