# Presentation: 816301

## Energy Dependence of (Global)Hadronic Observables

## Global Observables

- Try to characterize the “basic” features of heavy ion events with as few parameters as possible
- Soft physics:
- Particle production dominated by *p*t < 2 GeV/*c*
- Systematic studies important
- Vary control parameter like beam energy and system size
- Focus of this talk:	Energy Dependence 						+ Central Collisions

## Global ObservablesPhase Diagram

- QGP

- Hadron Gas

- B

- T

- Color
- Super
- Conductor

- _Ultimate goal_:
- To determine the
- trajectory of the system

- Chemical and thermal
- freeze-out parameter
-  hadronic side

- Can one learn anything
- beyond this?

## Global ObservablesTopics of this Talk

- Stopping
- Rapidity spectra
- Particle production
- Transverse mass spectra
- Fluctuations

- Energy dependence of:

## StoppingRapidty Shift y

- How does the rapidity shift ***y* evolve with beam energy?

- Determines the energy available in the produced fireball

- Baryon number distributions at

- lower energies:

- higher energies:

## StoppingObservable: Net-Protons

- Central Pb+Pb 158 *A*GeV

- Subtract the distribution of anti-protons from
- the proton distribution
- Resulting distribution reflects the baryon transfer

- NA49

- Phys Rev. Lett. 82 (1999) 2471

## Stopping Energy Dependence of Net-Protons

- BRAHMS,
- nucl-ex/0313023

- The shape of the distributions
- changes dramatically with energy

- AGS: baryonic system  RHIC: mesonic system
-  Large implications in the hadronic sector

## StoppingEnergy Dependence of y 

- BRAHMS,
- nucl-ex/0313023

- Seems to increase linearly
- at AGS and SPS:
- 	***y */*y*beam  0.27

- Rapidity shift:

- _But_: No further increase
- to RHIC energies!

- Need more data points
- on this plot

## Rapidity DistributionsPions

- D. Ouerdane, QM04

- Pion rapidity distributions fit perfectly to
- Gaussians at all energies

- Boost invariance of particle production?

## Rapidity DistributionsLandau Scenario in p+p

- Prediction:
- d*N*/d*y*  is Gaussian of a width  = 2*L* given by:
- (simplified model)

- L. D. Landau, Izv. Akad. Nauk. SSSR 17 (1953) 52
- P. Carruthers and M. Duong-Van,  Phys. Ref. D8 (1973) 859

- Pion production ~ Entropy
- Isentropic expansion
- Description of the pion gas as a 3D relativistic fluid

## Rapidity DistributionsLandau Scenario in A+A

- D. Ouerdane, QM04

- Reasonable description of pion rapidity widths:

- But not perfect at RHIC: Still more logitudinal flow

## Rapidity DistributionsEvolution with Particle Type

- NA49
- central Pb+Pb

- Pions and kaons at
- 40, 80, 158 AGeV:
- Phys. Rev. C66 (2002)
- 054902

- -)  (K+)> (K-)

- Change of
- shape only for 
- All others:
-    Gaussians

**Notes:**
20 GeV Lambdas !

## Particle ProductionTotal Yields

- Central Au+Au, Pb+Pb

- Only 4 Multiplicities shown.
- Much more has been measured at mid-rapidity

- Attempt to measure
- rare particles
- at lower energies

## Particle ProductionLandau Scenario p+p vs A+A

- G. Roland, QM04

- Deviations at lower energies

-  p+p

-  A+A

- Prediction of simple
- Landau scenario for
- total yields

## Particle ProductionStatistical Hadron Gas Model

- Becattini et al.,
- Phys. Ref. C69 (2004) 024905

- Assumption of chemical
- equilibrium at the
- freeze-out point

-  Particle production can
-     be described with a few
-     parameter: *V*, *T*, **B, **s

## Particle ProductionChemical Freeze-Out

- J. Cleymans and K. Redlich
- Phys. Rev. Lett. 81 (1998) 5284

- A universal curve
- (*E */*N * = 1GeV)
- seems to describe
- all A+A systems at
- chemical freeze-out

## Particle ProductionAntibaryon-Baryon Ratios

- Change of B with
- *s* directly modifies
- Antibaryon-Baryon Ratio

- NA49 Preliminary

- Clear hirachy of the
- energy dependence
- with strangeness content

## Particle ProductionRatio of Strange to Non-Strange

- Pronounced maximum in K+/+ and /, absent in p+p

- Only partially (Kaons!) described by hadron gas model

-    Parameter (*T*, B) dependend on *s*
-     Freeze-out for const. *E*/*N* = 1GeV  relation between *T* and B
-      Fix *T* on pion multiplicities
- 	P. Braun-Munzinger, J. Cleymans, K. Redlich, and H. Oeschler, 	Nucl. Phys. A697 (2002) 902

- K-/-

- K+/+

- /

**Notes:**
Lambda mit neuen Werten!!!!
averaged Pions for lambdas!

## Transverse Mass Spectra 

- E895

- NA49

- PHENIX

- PHENIX

- NA49

- NA49

- E895

- PHENIX

- E895:    nucl-ex/0306033
- NA49:    Phys. Rev. C66 (2002) 054902, nucl-ex/0403023
- PHENIX: Phys. Rev. C69 (2004) 024904, nucl-ex/0307022

- Convave
-  Resonances

- Exponential

- Shoulder
-  Radial flow

## Transverse Mass SpectraEnergy Dependence of mt

- Energy dependence of mt changes around 30 *A*GeV

## Transverse Mass SpectraBlast Wave Model

- Basic blast wave model:
-   Common freeze-out of all particle types
-   Boost invariant longitudinal expansion
-   Transverse expansion is modelled by a velocity profile
-   “Standard” version:

- Schnedermann, Sollfrank, and Heinz,
- Phys. Rev. C46

- Extended version:
-   Resonance contribution included
-   Baryonic resonances introduce dependence on B
-   Chemical freeze-out: T and B taken from freeze-out curve
-   Thermal freeze-out: System cools down, therefore assume:
-   Conservation of entropy
-   Conservation of effective particle numbers

- U. Wiedemann and U. Heinz,
-      Phys. Rev. C56 (1997) 3265
- B. Tomasik, nucl-th/0304079

## Transverse Mass SpectraBlast Wave Fits

## Transverse Mass SpectraEnergy Dependence of Fit Parameter

- Fit to -, K- and p

- Box-shaped
- source profile
- and linear
- velocity profile

- Energy dependence of the fit parameter does
- change around 30 *A*GeV
- Possible to disentangle *T* and T ?

- T

- T

## FluctuationsCritical Point

- Endpoint of the first order
- phase transition line
-  crossover on left side

## FluctuationsObservables

- Averaged pt
- Particle Ratios
- Charge
- Multiplicity

- Scan the phase boundary
- by varying energy (and system size)

- Needs probably fine step sizes
- Only limited attempts so far

- M. Stephanov,
- hep-ph/0402115

- Observables:

## FluctuationsEnergy Dependence of pt Fluctuations

- FluctuationsEnergy Dependence of pt Fluctuations

- No energy dependence
- visible so far

- 20 and 30 AGeV data still coming
- But will perhaps require fine steps (also in system size)

- H. Sako, QM04

## FluctuationsParticle Ratios

- FluctuationsParticle Ratios

- Compare to mixed event
- reference
-   Resolution
-   Finite number statistics

-  Extraction of dynamical
-     fluctuations

- Event-by-event fluctuations
- of e.g. K/

- C. Roland QM04

- NA49

- NA49

## FluctuationsEnergy Dependence of K/ Fluctuations

- Clear energy dependence
- of K/ fluctuations observed
-  Decrease with energy

- Fluctuation from UrQMD
- independent of energy
-   Non-zero value due to energy
-     and strangeness conservation

- Data wider than reference

## FluctuationsEnergy Dependence of p/ Fluctuations

- Clear energy dependence
- of p/ fluctuations observed
-  Increase with energy

- Similar trend seen in UrQMD
-   Resonance contribution changes
-     with beam energy

- Data narrower than reference
-   Can be caused by resonances

## FluctuationsCharge Fluctuations

- _Hadron Gas_:
- 	Charge unit = 1

- _Quark Gluon Plasma_:
- 	Charge unit = 1/3

-  Reduced fluctuations in
-     QGP phase

- S. Jeon and V. Koch, Phys. Rev. Lett. 85 (2000) 2076
- M. Asakawa, U. Heinz, and B. Müller, Phys. Rev. Lett. 85 (2000) 2072

## FluctuationsObservable for Charge Fluctuation

- FluctuationsObservable for Charge Fluctuation

- Suitable observable should
- take into account:
- Impact parameter fluctuations
- Acceptance effects
- Net charge of the system
-  Net charge:  *q* = *N*+ - *N*-

- Mixed events wider:
-  charge conservation not included

## FluctuationsCharge Fluctuations at SPS (NA49)

- _GCC_: 	Global Charge
- 	Conservation

- Extreme cases:
- q =  0:  independent emission
- q = -1:  local charge conservation

## FluctuationsEnergy Dependence of Charge Fluctuations

- Energy dependence visible

## Summary   

- Differential study reveals a lot of structure in (global) hadronic observables
- Things that do change drastically:
- AGS: baryonic system  RHIC: mesonic system
- Stopping saturates at SPS
- Maximum in the strangeness production around 30* A*GeV
- Partly explained by baryon number, but not completly
- Reflection of phase transition?
- Energy dependence of mt spectra changes as well
- Follows chemical freeze-out (maybe stronger change)
- Clear energy dependence in K/ fluctuations
- Things that do not really change:
- Rapidity distributions of mesons: Gaussians
- Boost invariance  Landau?
- Search for the tricritical point

## The End

## Particle ProductionPions / Number of Wounded Nucleons

- Change of energy
- dependence of pion
- production at ~30 AGeV

## Energy Density and StoppingCharged Particle Density at Mid-Rapidity

- G. Roland, QM04