Mark Harvey Brookhaven National Laboratory July 18-24, 2004 Hot Quarks 2004 Workshop

Mark Harvey, BNL Hot Quarks 2004 July 18-24

Measurement of Invariant Differential Measurement of Invariant Differential Cross Sections of Identified Charged Cross Sections of Identified Charged Hadrons in p+p Collisions at RHICHadrons in p+p Collisions at RHIC

Mark HarveyMark Harvey

Brookhaven National Brookhaven National LaboratoryLaboratory

July 18-24, 2004 July 18-24, 2004

Hot Quarks 2004 WorkshopHot Quarks 2004 Workshop

Taos Valley, New Mexico, USATaos Valley, New Mexico, USA


Physics MotivationPhysics Motivation Differential Invariant Cross Section in p+p CollisionsDifferential Invariant Cross Section in p+p Collisions

– fundamental for understanding the particle production infundamental for understanding the particle production in p+p collisionsp+p collisions– baseline measurement for disentangling nuclear effects baseline measurement for disentangling nuclear effects

which arise in d+Au and Au+Au collisionswhich arise in d+Au and Au+Au collisions– Hard-scattered partons give rise to hadronic sprays; i.e., Hard-scattered partons give rise to hadronic sprays; i.e.,

jetsjets

Physics implications:Physics implications:– Careful examination of the Nuclear Modification factors; Careful examination of the Nuclear Modification factors;

e.g., Re.g., RdAudAu and R and RAuAuAuAu

– Initial state multiple scattering “broadens” the momentum Initial state multiple scattering “broadens” the momentum distribution and enhances the high pdistribution and enhances the high pT T yield compared to yield compared to point-like scaling from p+p collisionspoint-like scaling from p+p collisions

– Lack of high momentum enhancement Lack of high momentum enhancement jet suppression jet suppression


Differential Invariant Cross Differential Invariant Cross SectionSection Experimental Definition:Experimental Definition:

– Measurement of Luminosity (Measurement of Luminosity (LL) in p+p collisions ) in p+p collisions Beam-Beam Counter (BBC) triggered events Beam-Beam Counter (BBC) triggered events

– EdEd/d/d33p = 1/2p = 1/2 1/p 1/pTT 1/ 1/LL dN/dydp dN/dydpTT

wherewhere LL = N = NeventsBBCeventsBBC//ppppBBCBBC

Application to A+A collisions:Application to A+A collisions:– The differential invariant yield in A+A collisions The differential invariant yield in A+A collisions

may be decomposed into a soft phenomenological may be decomposed into a soft phenomenological piece and a hard pQCD component piece and a hard pQCD component

EdNEdNABAB/d/d33p = Np = Npartpart EdN EdNsoftsoft/dyd/dyd22ppTT + N + Ncollcoll 1/ 1/ppppinin EdN EdNhardhard/dyd/dyd22ppTT

Cross section sensitive to two important pieces of Cross section sensitive to two important pieces of physics!physics!– yields described in a two component model yields described in a two component model

Soft and hard production mechanismsSoft and hard production mechanisms


DDDD

UUUU

DDDDDDDDDDDD

DDDDUU

DDDDDDDDDDDD

DDDDUU

UUDDDD

UUUUUU

DDDD

UUUUUU

DDDD

UUUU

DDDDDDDDDDDD

DDDDUU

DDDDDDDDDDDD

DDDDUU

UUDDDD

UUUUUU

DDDD

UUUUUU

Participants

Spectators

Spectators

b

NuclearSystem A

NuclearSystem A

Hadronic Collisions

The number of spectator nucleons may be expressed as Nspect= 2A – Npart

Npart: No. of nucleons participating inelastically in interaction process DDDD

UUUUUUDDDD

UUUUUU

DDDD

UUUUUUDDDD

UUUUUU

●Ncoll: Binary collisionstwo particle interactions

pp

b: Impact Parameter

x

z


PHENIX Detector

Beam-Beam Counter (BBC)Trigger, timing and collision

informationDrift Chamber (DC)Charged particle tracking

and momentum informationPad Chambers (PC1-PC3;

in analysis, use only PC1)3D space-point information

on charged particles

Time-Of-Flight (TOF) Detector

Timing information and charged hadron identification

Identified Charged Hadron Analysis Detection Elements:


Particle Detection and Measurement

TOF BBC

High Resolution Time-of-Flight (TOF)

detector – TOF time resolution in Au+Au is 115 ps, relative to 2 cut in m2; K/ separation up to 2 GeV/c; p/K separation extends up to pT = 4 GeV/c… Beam-Beam Counter (BBC) provides start clock trigger

In p+p, clean pion and kaon separation out to |p| ~ 1.8 GeV/c; p/K In p+p, clean pion and kaon separation out to |p| ~ 1.8 GeV/c; p/K separation separation beyond 3 GeV/c -- TOF timing resolution ~135 psbeyond 3 GeV/c -- TOF timing resolution ~135 ps

m2 vs. momentum p+p @ √200 GeV


Differential Invariant Differential Invariant Cross Section in p+p Cross Section in p+p collisionscollisions

Pion spectra, exhibit concave shape well described by gamma-type function;

“ApT 2-λe-pT/T”

Proton spectra, Characterized by gamma function

Kaon spectra, Fall-off exponentially in pT

+, K+, p -, K-, p

At low pT (< 1.2 GeV/c), each particle species goes like f(pT) = e-bpT (b=6); similar to behavior observed at ISR energies

PHENIX Preliminary PHENIX Preliminary


Differential Invariant Cross Differential Invariant Cross SectionSection

Magnitude of the charged pion averagecross section is inexcellent agreementwith published pi zero work

Phys. Rev. Lett. 91, 241803 (2003)

The p+p XSECT for pions measuredout to 10 orders of magnitude as afunction of pT!


Central Central • low plow pTT; slopes vary ; slopes vary w.r.t. massw.r.t. mass

• at higher pat higher pTT, , produced (anti) produced (anti) proton yield proton yield equivalent to pion equivalent to pion yield yield

Peripheral Peripheral • dependence in mass dependence in mass

is less pronounced is less pronounced

• particle production particle production yield similar to p+p yield similar to p+p

Au+Au pAu+Au pTT Spectra @ √s = 200 GeV Spectra @ √s = 200 GeV(central vs. peripheral)(central vs. peripheral)

Phys.Rev.C69:034909,2004


d+Au pd+Au pTT Spectra @ √s = 200 GeV Spectra @ √s = 200 GeV(4 centrality classes)(4 centrality classes)

•particle production yield decreases with increasing centrality

•pions; power law for all centralities

•kaons and protons; pT

exponential in each centrality class


-/+; 0.97 0.001 0.02

K-/K+; 0.90 0.01 0.03

p/p; 0.72 0.01 0. 02

p+p Particle Ratiosp+p Particle Ratios

pion, Kaon and proton ratios are flat in pT

Shaded boxes represent systematic error estimates

PHENIX Preliminary

PHENIX Preliminary

PHENIX Preliminary


p p

/+ K-/K+ p/p

Particle Ratios for Particle Ratios for three Collision Systemsthree Collision Systems

slide prepared by Felix Matathias


d

Au

/+ K-/K+ p/p




AuAu

/+ K-/K+ p/p




AuAu

Like particle ratios: agree very well independent of collision system


/+ K-/K+ p/p



•K/ Ratios increase steadily with increasing pT

•No apparent indication of saturation in this limited pT range

KK++//++ Ratios; 3 Collision systems Ratios; 3 Collision systems

•All three systems have comparable magnitudes – somewhat enhanced for most central Au+Au collisions slide prepared by Felix

Matathias


p/p/ Ratios for three Ratios for three Collision SystemsCollision Systems

•p+p, min bias d+Au and peripheral Au+Au are directly comparable •In p+p, p/ Ratios increase rapidly for pT < 1.4 GeV/c – flattens around 0.4 (0.3) for the positive (negative) particles at higher pT

Central Au+Au dramatically higher for pT > 1.4 GeV/c New Physics!



A look at RA look at RAAAA

●RAA considerably less than 1 for ’s; implication jet quenching due to hard scattered parton absorption in hot medium; p’s and K’s indicate other new physics.

• ’s are suppressed in central collisions; seem to be approaching unity for increasing pT in peripheral collisions

• K’s appear to flatten out within limited pT window in both central and peripheral collisions, respectively

• p’s increase fairly rapidly at low pT ; however, the protons are different and are consistent with no suppression!

Wor

k in P

rogre

ss

RRAAAA was computed in the was computed in the following way:following way:RRAAAA

NcollNcoll = = YYAAAA/(Ncoll(Y/(Ncoll(Ypppp*(*(BBCBBC//inelppinelpp))))))


SummarySummary Differential invariant cross section of identified Differential invariant cross section of identified

charged hadrons in p+p collisions charged hadrons in p+p collisions (paper (paper preparation for publication in process)preparation for publication in process)– baseline for d+Au and Au+Au baseline for d+Au and Au+Au – Excellent agreement between charged pion Excellent agreement between charged pion

average and published pi zero resultaverage and published pi zero result– High precision measurement of pions out to 10 High precision measurement of pions out to 10

orders of magnitude!orders of magnitude! Particle Ratios:Particle Ratios:

– Like particles; agree very well, independent of Like particles; agree very well, independent of collision systemcollision system

– K/K/ ratios rise steadily in limited p ratios rise steadily in limited pTT range range– p/p/ ratios saturate for all systems except Au+Au ratios saturate for all systems except Au+Au

central – may be viewed as flow effect since central – may be viewed as flow effect since protons are much heavier than pions; ergo, flow protons are much heavier than pions; ergo, flow contribution to their slope ~ m <ucontribution to their slope ~ m <utt>>2 2 ; see; see

Phys.Rev.C69:034909,2004


Summary ContinuedSummary Continued

Essentially, REssentially, RAAAA pions are suppressed in central pions are suppressed in central collisions – rising steadily peripheral… magnitude collisions – rising steadily peripheral… magnitude slightly increased for Kaons; however, they slightly increased for Kaons; however, they saturate in limited psaturate in limited pT T window; Protons are not window; Protons are not suppressed at higher psuppressed at higher pT T -- very different from -- very different from pions!pions!– Particle production mechanisms may be Particle production mechanisms may be

described with similar source in soft domain described with similar source in soft domain (p(pTT < 1.5 GeV/c) for < 1.5 GeV/c) for , K, K and p (pbar), and p (pbar), respectively – difference in production probably respectively – difference in production probably limited to large plimited to large pTT regime. regime.

More work to be done on RMore work to be done on RdAudAu and R and RAuAuAuAu before before physics result is ready for “prime time”physics result is ready for “prime time”

Documents

Mark Harvey Brookhaven National Laboratory July 18-24, 2004 Hot Quarks 2004 Workshop