# Presentation: 183768

## Soft and intermediate pT physics highlights from QM2006

- Bedanga Mohanty

- Soft and intermediate pT physics highlights from QM2006

- Baryon production
- Flow
- Intermediate pT ~ Recombination
- New data at forward rapidity
- Freeze-out properties
- Predictions for LHC

- Selected topics ......

-             HIT
- 12th December 2006

## Baryon production

- Change of shape most pronounced at SPS energies : Peak  dip structure
- Mid-rapidity net-baryon density decreases rapidly

- We had seen this result

- Low energy SPS results got added at QM2006

- Results from : C. Blume (NA49), B. Mohanty(STAR), I.G. Bearden (BRAHMS)

## Baryon production

- Helium - supposed to be formed from p + n have a opposite shape (concave) - independent of energy
-           Insight into coalescence mechanism ?

## Baryon production

- Proton yields : Interplay of baryon production and baryon transport at mid rapidity

**peripheral**

**central**

- Degree of stopping similar at AGS and SPS - less at RHIC

## Conclusion : Baryon production

-  Change in shape of dN/dy of net baryons occurs around SPS energy (Peak to dip structure)
-  The nuclei production (coalescence of nucleons) have a dN/dy shape which is independent of collision energy
-  Proton production is similar for beam energy : 17.3 to 200 GeV. Unique interplay of baryon production and transport
-  Degree of stopping similar for AGS and SPS. More transparency at RHIC

## Flow

- Measurements : collision energy, collision species, particle type, pT, rapidity, centrality
- This QM : Summary and Future directions for the flow studies

- Results from : S. Voloshin (STAR), P. Sorensen (STAR), Y. Bai (STAR), G. Wang (STAR),
- R. Nouicer (PHOBOS), C. Loizides (PHOBOS), A. Taranenko (PHENIX), S. Sanders (BRAHMS)H. Liu (STAR), R. Bhalerao, I. G. Bearden (BRAHMS), D. Hoffman (PHOBOS), A. Tang, S.L. Blyth (STAR), S. Esumi (PHENIX)

## Elliptic flow : Mass ordering, KE scaling,baryon-meson effect

- Low pT :Mass ordering

- Low pT : Scaling when plotted as mT - m0

- Scenario qualitatively as expected from hydrodynamics

- At intermediate pT - may due to particle mass or due to baryon-meson

## Elliptic flow : Quark number and universal scaling 

- Universal scaling observed when data presented normalized to quark content

## Elliptic flow : Driven by collision geometry 

## Directed flow : depends on beam energy    

**v****1**** depends on energy,  not on system size.**

## Elliptic flow : D-mesons and thermalization ?  

- Nbinary scaling indicates charm production at initial stage of the
- collisions

## Charm collectivity : thermalization ?  

- Model dependent (Blast Wave) analysis of J/  and non-photonic electrons (from semi-leptonic decays of mesons having charm quarks) spectra consistent with small transverse radial flow and larger freeze-out temperature

**Peter Braun-Munzinger**
**Shinchi Esumi**

## Flow  : Degree of thermalization

**Scaled flow values allow constraints for several transport coefficients.**

- v4 /v22 a detailed probe of ideal hydro behavior and related to the degree of thermalization!
- Large systematic uncertainty (from non-flow) difficult to conclude about thermalization

## Elliptic flow : Situation at SPS ?  

- Scaling at low pT not
- so prominent when plotted as mT - m0

- pT reach may be not
- sufficient to see the quark number scaling

- SPS way below hydro-dynamical results. RHIC is in that regime

- V2 ~ dN/dy

## Flow : Longitudinal scaling

- We observed this for multiplicity

## Elliptic flow : next steps (Theory/phenomenology) 

- Scaled flow values allow constraints for several transport coefficients

- Attempts are being made to study properties of the matter formed in heavy ion collisions

## Elliptic flow : next steps (experimental) 

- All the previous results we saw are average value which varies e-by-e by 35-40%
- Most of this variation is understood in terms of e-by-e variation in initial event shape

## Elliptic flow : next steps - how to take care of effect of initial geometry  

- Same impact parameter - shapes can be different at participant level

## Conclusion : Flow

- From the experimental data

- Future directions

-  At low pT mass ordering of v2 values observed and at intermediate pT ordering by quark content (baryon-meson)
-  Universal scaling observed across pT, centrality, ion species and particle type - when data presented as a function of v2/n* Vs. mT-m0/n
-  v2 is driven by collision geometry and v1 by beam energy
-  Longitudinal scaling observed for all components of measured flow

-  Time to draw conclusions about property of the medium from the experimental measurements
-  Understand the event-by-event variation in flow values
-  How to calculate the eccentricity
-  Experimental work needed on D-meson flow and v4/v22 to address the issue of thermalization
- Lee-Yang Zeroes method is less biased by non-flow correlation.
-      Nucl. Phy. A 727 (2003) 373-426

## Recombination

- V. Greco, C.M. Ko and I. Vitev,
- PRC 71 (2005) 041901

- Specific Energy dependence
-  p/ (62.4 GeV) > p/ (200 GeV)

- Results from :B. Mohanty(STAR), S. Blyth (STAR), J. Bielcikova (STAR), C. Blume(NA49), L.Ruan (STAR)
- R. Hwa and C. B. yang

## Recombination : Baryon/Meson ratio

## Recombination : Baryon/Meson ratio

## Recombination : Correlation

- Correlation observed - prominent peak at near side
- No dependence on strange quark content
- Does that mean recombination mechanism has failed ?

## Rudi Hwa .....	STAR

- Rudi Hwa .....	STAR

- At face value the data falsify the prediction and discredits RM.

- I now explain why the prediction was wrong and how the data above can be understood.

- Recombination still works, but we need a new idea.

- Yang’s talk tomorrow is still right.

- Recombination failed ? - Not yet - there are new ideas

## Conclusion : Recombination

- Baryon to meson ratios

- Azimuthal correlations

- Some of the features are qualitatively consistent with recombination picture
- Lack of quantitative agreement
- Similar shape of the ratios across beam energy 17.3 to 200 GeV may not be consistent within the current recombination framework

- Initially data on Omega-hadron correlation presented at QM2006 seemed to falsify the recombination picture
- Subsequent discussions at QM2006 - led to the need for more careful understanding of the data from both theoretical and experimental side.
- Data needs to be presented after taking care of the effect due to extended correlation structure in eta - “ridge”

## New results from forward rapidity

- What changes?

- What doesn’t?

- Results from : I. G. Bearden (BRAHMS), C. Nygaard (BRAHMS), S. J. Sanders (BRAHMS), T. M. Larsen (BRAHMS), J. H. Lee (BRAHMS), L. Molnar (STAR)

## RdAu vs eta 

- We had seen this : RdAu is suppressed as we go to forward rapidity
-                                          What about RAA ?

## Inclusive charged hadron RAA similar

-   Inclusive charged hadron  RAA similar at mid and forward rapidity

## Identified particle RAA, 200GeV Au+Au

-                   Identified RAA similar at mid and forward rapidity

## V2 Identified particles 200GeV Au+Au

****=0

****≈3

- 

- K

- p

-                                v2(pT) similar at forward and mid rapidity
- Remember integrated v2 (shown by PHOBOS) changes with rapidity

## How about K/ vs. pbar/p?

- Chemistry changes with rapidity at RHIC.
- Forward rapidity at RHIC ~ mid rapidity at SPS

##   How about correlation : Forward and mid-rapidity

**Trigger: 3<p****T****trig****<4 GeV/c,  **
**Associated: FTPC: 0.2<p****T****assoc****< 2 GeV/c,  ****TPC: 0.2<p****T****assoc****< 3 GeV/c**

-  Away side in pp: broader at
-   forward than mid-rapidity

**pp MB**

-  Away side in dAu:
-   similar between forward
-   and mid-rapidity

**dAu MB**

##  Compare correlation in Au+Au : Forward and mid-rapidity

- Away-side correlations are very similar!
- Energy loss picture is the same for mid- and
-      forward rapidities?

**AuAu 0-10%**
**AuAu 0-5%**

**Trigger: 3<p****T****trig****<4 GeV/c,  **
**Associated: FTPC: 0.2<p****T****assoc****< 2 GeV/c,  ****TPC: 0.2<p****T****assoc****< 3 GeV/c**

## Conclusion : At forward rapidity

- What changes?
- dN/dy
- pbar/p
- Chemistry
- V2 (integral)
- Initial state (RdAu)

- What doesn’t?
- Suppression (RAA)
- V2 (pt)
- Away-side azimuthal Correlation

## Conditions close to kinetic freeze-out 

- Results from : L. Ruan (STAR) A. Irodanova (STAR), D.Das (STAR)

- Smooth evolution of Freeze-out parameters with dNch/d
- Seems dNch/dy finally matters or  these are not the correct observable to study the dynamics

## Chemical Freeze-out conditions 

- Tch is fairly constant with dNch/d but s for Cu+Cu system seems bit higher

- Cu+Cu @ 200 GeV

- Cu+Cu @ 62.4 GeV

## LHC predictions : Multiplicity

- Multiplicity

- Net baryons

- Results from :U. Wiedemann, J. Cleymans

## LHC predictions : Freeze-out conditions

- Chemical Freeze-out temperature : similar to RHIC

- Baryon chemical potential ~ 1 MeV

## LHC predictions : Flow

- Based on simple extrapolation : v2 ~ 0.08

## Conclusion : LHC predictions

- dN/dy            ~ 1100 - 1600 at mid-rapidity
- Rapidity loss ~ 2 - 2.5 units
- Tch                         ~ 166 MeV at mid-rapidity
- B                          ~ 1     MeV at mid-rapidity
- v2                           ~ 0.08  at mid-rapidity

-                                Thanks for your attention!