# Presentation: 483989

## J. Burward-Hoy

*Department of Physics and Astronomy, University at Stony Brook, New York*
- for the PHENIX Collaboration
- Outline of Topics
-   Motivation
-   Identifying , K, p  in PHENIX
-   Single Particle Pt spectra
-   Radial flow
- hydrodynamics-based parameterization
-   Discussion and conclusion

- Transverse Momentum Spectra of Identified Hadrons in s = 130 GeV Au-Au Collisions

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## Motivation

- Motivation

- , K, p, anti-p
- 	carry most of energy
- 	collectively flow at t
- 	decouple at Tfo

- low pt:  soft processes
- multiple hadronic rescattering
- hydrodynamic behavior

- high pt:  hard processes
- hard scattering, jets
- pQCD

- RHIC:  Ecm = 130 GeV
- Au on Au collisions

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## Detecting , K, p  in PHENIX

- Detecting , K, p  in PHENIX

- pt = p sin(0)

- PC1 and Event vertex
- polar angle

- DC
- main bend plane

- DC resolution
- p/p ~  1%  3.5% p

- TOF resolution  115 ps

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
No need to spend too much time on.
  The momentum is reconstructed by the Drift Chamber which measures the bend angle of the track with respect to an infinite momentum track.  The DC and TOF resolutions allow excellent particle identification over a broad momentum range.

## Corrections to the Raw Spectra

- Used MC single particles and track embedding to correct for
- 	Tracking inefficiencies and momentum resolution
- 	Geometrical acceptance
- 	Decays in flight (’s and K’s)

- Correction is p and PID dependent

- Particle Acceptance

- 0.2 GeV/c

- -0.35 <  < 0.35

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
Because tracks that are reconstructed in a high track density are lost, this inefficiency is corrected for using single particles embedded into real events.  As there is no perfect detector, the momentum resolution which affects the shape of the momentum spectra after 2.5 GeV/c is corrected for.  Pions and Kaons also decay in flight before they reach the TOF and this is corrected for.  However, the largest correction is geometrical:  the TOF wall is half of one arm in the spectrometer and is particle dependent.  The negative particles have a higher correction simply because they “miss” the TOF wall in one sector (how they are bent in the magnetic field).

## pt Spectra of Identified Hadrons

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
Here are the fully normalized spectra of all types of events combined (called minimum bias).  The left-hand side are positive pi, K, and p, and the right are negatives.  First of all, we have pi/K separation out to 1.5 GeV/c and pi/p out to 2.2 GeV/c.  The protons appear to dominate the spectra at pt>2.0 GeV/c.  The spectra are also different in slope:  the protons appear to cross  the pions at 1.8 GeV/c.  There also appear to be a lot of anti-protons when compared to the protons.  There is ongoing discussion as to what is causing the broadening of the proton spectra:  presumably a boost in the transverse direction?

## Protons Cross the Pions? 

- p crosses 

- p crosses K

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
As a comparison, a model that uses perturbative QCD (which describes the spectra at CERN SPS energies) is compared to the data.  In this model, called HIJING, the protons cross the kaons while in the data, the protons cross the pions.  This pQCD  based model does not include the collective effects as is described by hydrodynamics.  The fact that HIJING fails to reproduce the tails, indicates that this broadening of the proton spectra (resulting in a crossing point) is due to soft collective effects such as radial expansion and not hard processes as described using pQCD.

## Centrality selected pt spectra. . .

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## <pt> Across Participant Number 

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## Identified particle mt-m0 Spectra

- If static thermal source,
- then spectra are parallel

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
Take the pt spectra and transform the horizontal scale to transverse kinetic energy, mt-m0.   The exponential shape of the spectra can be described by an effective temperature, Teff.  For particles produced at the same kinetic energy, the protons have a larger effective temperature than  the pions.  If these particles were emitted from a static thermal source, then they would all have the same effective temperature.   It appears as if the spectra are not emitted from a static source but from one that is boosted.

## Effective Temperature and HIJING

- HIJING

- No radial flow in HIJING

- To measure the expansion parameters, use hydrodynamics-based
- parameterization. . .

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
As a comparison to the model that uses pQCD and no collective processes, HIJING, the particles are emitted from a static thermal source.  The data, in comparison, are not.

In order to measure this expansion from the spectra directly, the hydrodynamics-based parameterization is fit simultaneously to the pions, kaons, and protons at the same kinetic energy  mt-m0<1 in order to minimize the contributions from hard processes.  A region of overlap is observed and the result of the fit follows.

## Hydrodynamics-based parameterization

- parameters
- 	normalization A
- 	freeze-out temperature Tfo
- 	surface velocity t

- t

- 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 1
- particle density distribution f() ~ const

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
A small piece of hadronic matter that behaves like a fluid element is in local thermal equilibrium.  This fluid element gets boosted with a boost angle rho.  This boost angle rho  is parameterized by a velocity profile of the particles as they traverse this freeze-out hypersurface.  A flat particle density distribution on this freeze-out hypersurface is assumed.  Current work is in modifying this assumption:  for instance, if the particle density distribution is not a box shape, but instead a gaussian shaped distribution offset from the center (hollow shell).  The three parameters are strongly correlated:  Tfo and Beta_t are anti-correlated.  If the Tfo increases, then Beta_t decreases.  The parameter A is the normalization and this affects the yield.  The parameter Tfo changes  the slope of the logarithmic distribution.  The parameter Beta_t increases the mt of the particle (moves a particle at an initial value pt to a higher pt value).  The effect is to broaden the distribution.  For the same boost velocity, the heavier particles result in a broader momentum distribution than for the lighter particles.
  This parameterization was used by NA44 at the CERN SPS to describe the expansion in PbPb collisions at sqrt(s) 17 GeV.  Before the first year of physics running at RHIC in the PHENIX experiment, I compared this parameterization to the pion spectra for a variety of collision systems at SPS energies.

## PHENIX Preliminary

- 5% central data

- Tfo ~ 104  21 MeV
- t ~ 0.7  0.1
- 	< t > ~ 0.5  0.1

- Systematic errors estimated
-  ~8% in Tfo    ~5% in t

- Arrows indicate upper pt in fit

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## Parameter Space:  2 Contours of -K-p

- 5% central

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## Overlap Region in Parameter Space 

- Overlap Region in Parameter Space

- Tfo ~ 125 - 83 MeV ~ 104 MeV
- t ~ 0.6 - 0.8  ~ 0.7
- 	< t> ~ 0.4 - 0.6 ~ 0.5

- CERN Pb-Pb NA49:
- T ~ 132 - 108 MeV ~ 120 MeV
- t ~ 0.43 - 0.67 ~ 0.55

- 2 contour overlap

- Systematic errors estimated  ~8% Tfo    ~5%  t

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

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

- flowing hadronic fluid AND particle cascade
- 	uses Hydrodynamics + Relativistic Quantum Molecular Dynamics (RQMD) cascade
- more constrained  predictive power
- 	no scaling of nucleons to match data
- 	0 ~ 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

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## Conclusions

- Fully normalized, centrality selected , K, p/pbar spectra in 130 GeV Au-Au collisions are measured in PHENIX (Summer 2000 runs)
- 	significant p and pbar contribution to hadron spectra starting at ~ 2 GeV/c
- 	STAR and PHENIX pbar consistent
- Both Teff and <pt> depend on Npart.   Teff depends on m0 for 5% central and minimum bias events.  There seems to be less of a dependence in the 60 - 92% centrality.
- The data suggest sizeable radial flow at RHIC
- A simple model that assumes hydrodynamic behavior is fit simultaneously to the 5% central data.
- Good 2  fits for a finite range of anti-correlated parameters
- 		**T****fo****  ~ 125 - 83 MeV (~ 8% syst.)****	********t****  ~  0.6 - 0.8 ( ~ 5% syst.)  **
**	****	****	****	****	****	****	****< ********t****> ~ 0.4 - 0.6**
- In comparison to NA49:
- 		Tfo ~ 132 - 108 MeV 		 	t ~ 0.43 - 0.67
- H2H model (D. Teaney, E. Shuryak, et. al)
- 		, K:  	Tfo  ~ 135 MeV     			<t >~  0.55
- 		nucleons:	Tfo  ~ 120 MeV     			<t >~  0.6
- Reduce 20% systematic uncertainty in overall normalization.

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## 	|mmeas2 - mcent2| < 2m22

- 	momentum p
- 	pathlength L		 m = p/  where  = L/ct
- 	time-of-flight t
- 	|mmeas2 - mcent2| < 2m22

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

- H. Hamagaki

- Time-of-Flight resolution

- Momentum resolution

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
Don’t spend too much time on.
  The particle identification is made using a momentum and detector resolution dependent cut and the measured centroid in the mass-squared distribution for each particle species respectively. 

## Event centrality:  how “head-on” is the collision?

- The fraction of counts in the Beam-beam
- Counters.

- A. Denisov

- The fraction of energy deposited in
- the Zero-degree Calorimeters.

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
Spend a lot of time on!  
  In all the RHIC experiments, there are Zero-degree calorimeters placed north and south along the beam direction.  In PHENIX, the Beam-beam Counter and Zero-degree calorimeters and used together to make a correlation measurement.  This correlation is the fraction of energy deposited in the ZDC versus the number of BBC counts detected in PHENIX.  The more peripheral the event, the more spectator nucleons are detected in the ZDC and the less counts in the BBC.  The more central the event, the less spectator nucleons deposit their energy in the ZDCs and the more counts are recorded in the BBC.  In the more central events, the track density is higher, as is observed in the DC track multiplicity distribution per event.  The more peripheral the event, the less the number of tracks (we have a lot of these types of collisions).  The more central the event, the higher the track density (the larger the number of produced particles).
  A model-dependent calculation is made using a Glauber model and Woods-Saxon nuclear density distribution that determines the number of participants for each percentage of the total geometrical cross section measured (wounded nucleon model).  At present, the experiments are discussing a less model-dependent method for determining the number of participating nucleons.  

## H2H ModelThe Effect of Weak Decays

-   - + p

- K0s  + + -

- The measured contribution to nucleon spectra from such “real” background is forthcoming.

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## From Hydrodynamics:Radial Flow Velocity Profiles

- Plot courtesy of P. Kolb

- At each “snapshot”
- in time during the
- expansion, there
- is a distribution
- of velocities
- that vary with the
- radial position r

- Velocity profile
- at  ~ 20 fm/c
- “freeze-out”
- hypersurface

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## Effective Temperature and Linear Fit

**T****eff**** = T****fo**** + m****0**** <********t****>****2**

- Systematic errors included

- 5% central
- Tfo ~ 132 - 166 MeV
- <t> ~ 0.4 - 0.6

- Compared to hydrodynamics-based parameterization:
- 		Tfo within 30%  and <t> within 6%

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## 2 (Tfo,t) Contours

- K

- p

- 2 (Tfo,t) Contours

- 

- positive

- negative

- PHENIX Preliminary

- PHENIX Preliminary

- PHENIX Preliminary

- PHENIX Preliminary

- PHENIX Preliminary

- PHENIX Preliminary

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

## The PHENIX Detector

- -0.35 <  < 0.35
- 4.5M min. bias events

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
Don’t spend too much time on.

## Relevant CERN SPS Observables

- Bjorken’s formula:
- initial energy density
- <0> ~ 1/R20 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 + A

- A + A

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
One also observes the transverse boost increases with the size of the incident nuclei, while the freeze-out temperature remains constant.  There is more radial expansion in the heavier systems because there are more particles produced which behave collectively.  From an independent measurement of the produced neutral pion energy, dEt/dy, an initial energy density is calculated at SPS energies of 3 GeV/fm3, using Bjorken’s formula and assuming the thermalization, or fromation time, is 1 fm/c.  One can estimate the <e0> by measuring 0.8 GeV for dEt/dN and dN/dy.

## CERN SPSHydrodynamics-Based Parameterization

- The spectra are well described using hydrodynamic assumptions.

- CERN Pb-Pb NA49:
- T ~ 132 - 108 MeV ~ 120 MeV
- t ~ 0.43 - 0.67 ~ 0.55

- The PHENIX Experiment         J. Burward-Hoy

- July 20, 2001

**Notes:**
Different collision systems are shown here:  from the heaviest to the lightest (pW).  The hydrodynamics-based parameterizationn can describe the spectra over the full pt range for all collision systems execept for pW.  In pW, there are fewer produced particles, so the systemshould not behave hydrodynamically (the spectrum is more concave in shape and looks more similar to pp collisions).
  NA49 used a different parameterization.  The  freeze-out temperature that is below the pion mass (not enough energy to produce more pions) and a flow velocity of roughly half the speed of light is  measured from the hadron spectra.