september 11, 20011 mass-identified particles produced in s = 130 gev au-au collisions using the...

September 11, 2001 1

Mass-identified Particles Produced in s = 130 GeV Au-Au Collisions

using the PHENIX Detector at RHIC

J. Burward-HoyDepartment of Physics and AstronomyUniversity at Stony Brook, New York


Outline of Topics

MotivationIntroduction to Relativistic

Heavy Ion CollisionsIntroduction to RHICThe PHENIX Detector

– Identifying , K, p in PHENIX

Data reduction and Corrections– Single Particle Pt spectra

Results– Measured physics quantities

Discussion– Transition region between soft

and hard physics– Hydrodynamics model

comparison (U. Heinz and P. Kolb)

Conclusion

STAR event


Physics Objective: nuclear matter under extreme conditionsNuclear Matter Quark-Gluon Plasma Phase

Create a hot region of highinitial energy density

0 ~ few GeV/fm3

fm = 10-15 cm

Quarks and gluons becomeunbound to form a Quark Gluon Plasma (QGP)

Quarks and gluons coalesceinto hadrons (hadronization)

system expands and coolsDetectors measure the produced hadrons and leptons

probe transition regionstudy properties of QGP

Quark Gluon Plasma

hadronization

atoms

now~few s

nuclei RH

IC


Collision Dynamics

, K, p, anti-pcarry most of energycollectively flow at t

decouple at Tfo

low pt: soft processesmultiple rescatteringhydrodynamic behavior

high pt: hard processeshard scattering, jetspQCD

0

R2

0

GeVsE cm 130


Longitudinal

Rapidity y(E,pz) = 1/2 ln (E + pz/E - pz)

Pseudorapidity () = -ln (tan (/2 )

Midrapidity y(E,0) = 0, (/2) = 0

Initial Total EnergyE/A = mo

Center of mass energy s = (p1 + p2) • (p1 + p2)

s = 2mo ~ 130 GeV Transverse

Transverse momentum pT = p sin

Transverse energy mT = pT

2 +m02

Transverse Kinetic Energy mt - m0

Relevant Kinematic Quantities

p = (mTcoshy,pt cos ,pt sin ,mTsinhy)

beam axis +z

r = x2 + y2

y = 1 or = 1

Energy and Momentum: p = (E,p)


Hydrodynamic ExpansionContours of constant

– proper time = t2 -z2

– temperature T– number density n– entropy density s– energy density

Quarks/partons form at ~ 1 fm/c

Hadronic matter (“liquid”)– collectively expands at t

(surface velocity)

Hadrons freeze-out at – temperature Tfo

– radius ~ 6-7 fm/c (HBT)

Space-time Diagram of Expansion


Rapidity Distributions at RHIC: PHOBOS results

• PHOBOS, nucl-ex/010600• flat over at least 2 units of

rapidity • symmetry along z

longitudinal boost invariance• hydrodynamic equations

separable in longitudinal and transverse dimensions– transverse components

independent of rapidity

~ 4Reference: private communication with U. Heinz


The Relativistic Heavy Ion Collider• Two counter-rotating Au

beams– 60 Au ion bunches s apart

• Year-1 ~ 70 for each beam s = 130 GeV

~ 7 times higher CERN~ 30 times higher AGS

• Design value (Year-2) ~ 107 s = 200 GeV


The PHENIX Detector

-0.35 < < 0.35, = /2TOF and DC: ~ /4Event and Trigger Selection

BBC and ZDC both fire|zvtx| < 30 cm

4.5M min. bias events


0-5%

5-10%10-15%

15-20%20-25%

25-30%

Event centrality: how “head-on” is the collision?A. Denisov

/meastot(%) Events

0-5 7,8955-15 15,18815-30 22,68430-60 45,64360-92 47,860min. bias 139,270

PHENIX uses a Glauber calculation to map centrality to number of participants

Spectator nucleonsTo collision axis detectors

Produced , K, p to central arm detectors

Participant nucleons (Np)

Collision axis


Number of Participants

Model-dependent calculation called Glauber

Thickness of nuclear matter direct path of each oncoming nucleon

Inelastic nucleon-nucleon cross section determine if collision occurs A

b

Collision when b < inelnn /

inelnn = 40 mb

n2

n1

ni

Woods-Saxon density profile distribution

Reference: PHENIX Internal Analysis note


Detecting , K, p in PHENIX

x

y ~ q/p

r

z

r

0

pt = p sin(0)PC1 and Event vertexpolar angle

DC main bend plane

DC resolution p/p ~ 1% 3.5% p

TOF resolution 115 ps


The Track ModelFor each track, the track model. . .• Uses a field-integral look-up table

– swim particles through measured magnetic field map with p, z0, 0 – numerically integrate the field integral values at each r – field-integral independent of momentum p > 2 GeV/c– resulting grid is 4D: z0, 0, r, p

• Determines p, 0 ,0

• Determines the full trajectory in PHENIX• Calculates flight distance (length of trajectory)• Finds intersection points between trajectory and detectors

– Projected points are then match to measured points


Track Selection

• Require tracks to be 3D• Project tracks to the TOF

detector• Define a search window

and find a TOF hit• In slices of momentum,

determine (p,,z)• Require tracks to be within

2 of a TOF hit

3D tracks

(p,)

(rad

)

p (GeV/c)(

p,z)

(cm

)

DC Tracks at TOF


momentum p pathlength L m = p/ where = L/ct

time-of-flight t

|mmeas2 - mcent

2| < 2m22

The mass-squared width: how particle identification is done.

2222

224

2

22 442 pmp

Lcm

ptp

m

H. Hamagaki

Time-of-Flight resolutionMomentum resolution


Particle Identification

• Slice mass distribution in momentum

• In each momentum slice, fit gaussian functions

• Extract the mean for each momentum slice

• Determine width of mass,

• Require particles to be within 2 of centroid

Sigma Mean

pt (GeV/c)K

p

p (GeV/c)

m2 (GeV/c2)2


After Data Reduction (“raw” data)Centrality Selected

Minimum Bias


Corrections to the Raw SpectraUsed MC single particles and track embedding to correct for

Tracking inefficiencies and momentum resolutionGeometrical acceptance Decays in flight (’s and K’s)

Correction is p and PID dependent Particle Acceptance

0.2 GeV/c

-0.35 < < 0.35


pt Spectra• measure

(anti)p out to 3.5 GeV/c

• Yield p – pt ~ 1.5 - 2

GeV/c• Crossing

region as Np


Transverse Kinetic Energy Spectra

In the range mt - m0 < 1 GeV, fitto get effective temperature Teff

edmm TmdNeff

t

tt

1


Effective Temperature

To measure the expansion parameters, use hydrodynamicsparameterization. . .

If static thermal source, then spectra are parallel

Minimum bias


From Hydrodynamics:Radial Flow Velocity Profiles

Plot courtesy of P. Kolb

t()

(No QGP phase transition)

2 fm/c20 fm/c

5 fm/c

At each “snapshot”in time during theexpansion, thereis a distributionof velocities that vary with theradial position r

Velocity profileat ~ 20 fm/c “freeze-out”hypersurface


Hydrodynamics Parameterization

parametersnormalization Afreeze-out temperature Tfo

surface velocity t

t

mt

1/m

t dN

/dm

t

TfoA

1/mt dN/dmt = A f() d mT K1( mT /Tfo cosh ) I0( pT /Tfo sinh )

minimize contributions from hard processes fit mt-m0<1 GeV

linear velocity profile t() = t surf. velocity t ave. velocity <t > = 2/3 t boost () = atanh( t() )

integration variable radius r= r/R

definite integral from 0 to 1particle density distribution f() ~ const

t()

1

f()

Ref: Sollfrank, Schnedermann, Heinz, et al


Hydrodynamic Parameterization• Simultaneous fit to all

– (mt -m0 )< 1 GeV

• For – Exclude resonances by fitting pt

> 0.5 GeV/c

• Including resonance region in pions:– Tfo ~ 104 MeV

• Excluding resonance region:– Tfo ~ 121 MeV

5% Most Central 2 Contours


Hydrodynamic Parameterization


Radial Flow and Number of Participants


Measuring the Yield and <pt>For all centralities:• Fit functions and integrate

from 0 to – Extrapolate function over

unmeasured range– Add to data value in

measured range

• Extrapolated amount: 30%– K 40% – (anti)p 25%

K

p

5% most central


dN/dy and Participant Number• dN/dy scaled by Np pair• K and (anti)p scaled by 2 nearly independent of Np

• K and (anti)p dependence on – Ncoll NN binary collisions

• Dashed lines – Systematic in Np

(Glauber calculation)

Systematic uncertainty ~ 13%K ~ 15%(anti)p ~ 14%


<pt> and Participant Number • <pt> increases and

saturates for all particles – most dramatic for p

• compare with pp– interpolated to 130 GeV– open symbols at Np ~ 2– similar to pp for most

peripheral except (anti)protons

• Need to measure pp and pA at RHIC

Systematic uncertainty(anti)p ~ 8%K ~ 10% ~ 7%


Particle Ratios and Np

Independent of Np:– Negative to positive for , K, p

Dependent on Np:K/ and p/+


Particle Ratios and pt

0.670.02

0.830.03

0.940.01


K+/+ and s

NOTE: NA49 (CERN) measured yield integrated over y (different from NA44at midrapidity)


Comparing apples to apples. ..y and


Total Charged Multiplicity

<0> ~ 5 GeV/fm3

This is 70% higher than at CERN-SPS energies


HIJING Spectra


HIJINGHeavy Ion Jet Interaction Generator

No radial flow in HIJING

p crosses K

HIJING

Kp

pt (GeV/c)

1/p t d

N/d

p t

HIJING


Relevant CERN SPS Observables

Bjorken’s formula:initial energy density

<0> ~ 1/R20 dEt/dy<0> ~ 3 GeV/fm3 (NA49) System Size = A1 A2

Teff depends on m0 radial flow Teff = Tfo + m<t>2

Tfo

< t>

p + AA + A


CERN SPSRadial Flow Contribution to Hadron Spectra

The spectra are well described by hydrodynamics.

CERN Pb-Pb NA49: T ~ 120 MeVt ~ 0.55

NA44: T ~ 140 MeVt ~ 0.55

20 MeV difference in Tfo dueto resonances


Transition Between Soft and Hard Physicsat RHIC energies

nucl-ex/0109003QM Proceedings 2001


Hydrodynamics Model Comparison


Conclusions• Significant p and pbar contribution to hadron spectra starting at ~ 1.5-2 GeV/c

– crossing region increases with decreasing with Np

• The data suggest sizeable radial flow at RHIC for the most central:Tfo ~ 12121 MeV t ~ 0.700.01

• Radial expansion decreases with decreasing number of participants• A hydrodynamics model (U. Heinz and P. Kolb) with Tfo fixed at 128 MeV describes

the data– Consistent with measured radial flow from data

• To measure jet quenching, hadron spectra should be measured – pt>2.5-3 GeV/c– At CERN-SPS energies soft physics dominate measured range. Should measure

pt>5 GeV/c

• Total dN/d is consistent with published results. Initial energy density is 70% greater than at CERN-SPS and is

– consistent with PHENIX dEt/d of 5.0 GeV/fm3

• p/ and K/ increase with Np. • K+/+ for most central follows trend with s, most peripheral similar to pp


What the track model does in more detail. . .• assumes reconstructed track comes from z-vertex • uses reconstructed to get p-guess and charge• uses z at DC (on reference radius) and z-vertex to calculate (used as

a guess to 0)

• needs at least 2 X-wire hits in the drift chamber – uses 4D interpolation of field-integral grid to get the field-integral value (f) of each

hit based on p-guess, z-vertex, 0-guess and r

– fits a line to the hits in f and to get p and 0 – repeat iteratively four times

• at the reference radius of the drift chamber– uses 3D interpolation to get field-integral values in r-z plane based on p and 0

– calculates 0 at the vertex and at DC


Two planes: r-phi and r-z

0

fi, i

i = 0 + qfi/p

DC

o

Z vertex

zed

= + o = - g/p

r = 220 cm

y

x r

z


K

p

2 (Tfo,t) Contours

positive negative

PHENIX Preliminary PHENIX Preliminary

PHENIX Preliminary

PHENIX Preliminary

PHENIX Preliminary

PHENIX Preliminary


5-15% Centrality


15-30% Centrality


30-60% Centrality


60-92% Centrality


The H2H Model Comparison (Hydro 2 Hadrons)D. Teaney, E. Shuryak, et. al.

flowing hadronic fluid AND particle cascadeuses Hydrodynamics + Relativistic Quantum Molecular Dynamics (RQMD) cascade

more constrained predictive power no scaling of nucleons to match data0 ~ 16.75 GeV/fm3 0 ~ 1.0 fm/c

p/p ~ 0.5

<0> ~ 10.95 GeV/fm3

, K Tfo ~ 135 MeV <t > ~ 0.55

nucleons ~ 120 MeV <t > ~ 0.6

5% central

NOTE: includes weak decays


Estimated Background Contribution


H2H Model CalculatedWeak Decay Contribution

D. Teaney

- + p

+ + p

K0s + + -

Estimate ~32% from in PHENIXNeed to measure contribution to nucleon spectra from “real” background.


Momentum Scale• Parameterize time and

momentum with an offset and factor– p ~ Ap– t ~ t + B

• Minimize the mass and obtain best fit a and b – m = p/ where = L/ct – individual fit for each particle– simultaneous fit (excluding

pions)• Momentum scale A and time

offset B– 2/dof ~ 7.7– A ~ 1.010.02– (B ~ 0.0070.251 ns)

2 contours of A and B

b (n

s)

A

september 11, 20011 mass-identified particles produced in s = 130 gev au-au collisions using the...

Documents