# Presentation: 276695

## Collective motion at 5.5 TeV(from RHIC to the LHC)

**Raimond Snellings**

## Hunting the Quark Gluon Plasma

**Hunting the Quark Gluon Plasma**

**Strong collective motion (elliptic flow)**
**s****QGP and nearly perfect liquid**

**Nucl. Phys. A 757 (2005)**** **

- Raimond.Snellings@nikhef.nl

## Anisotropic Flow

- Assumption all correlations between particles due to flow, similar to vn{EPm}
- Non flow correlation contribute order (1/N), problem if vn≈1/√N

- Non flow correlation contribute order (1/N3), problem if vn≈1/N3⁄4

- N. Borghini, P.M. Dinh and J.-Y Ollitrault, Phys. Rev. C63 (2001) 054906

- Can be conveniently calculated using generating functions, extended to vn{∞} using Lee-Yang zeros, reliable vn>1/N

- Raimond.Snellings@nikhef.nl

## The first RHIC v2{EP} results

**Magnitude, p****t**** and mass dependence**
**A strongly interacting, more thermalized system which is for more central collisions behaves consistent with ideal fluid behavior! **
**Hydro studies show that the system needs to thermalize early (~1 fm/c)**
**Best description by QGP EoS!?**

- Raimond.Snellings@nikhef.nl

## Can we test the EoS (the effect of the phase transition)?

**Test the effect of four different EoS; qp is lattice inspired, Q has first order phase transition, H is hadron gas with no phase transition and T a smooth parameterization between hadron and QGP phase**

- Pasi Huovinen, arXiv:nucl-th/0505036

- Raimond.Snellings@nikhef.nl

## Dependence on the EoS!

**EoS Q and EoS T (both have significant softening) do provide the best description of the magnitude of the mass scaling in v****2****(p****t****)**
**The lattice inspired EoS (EoS qp) in ideal hydro does as poorly as a hadron gas EoS! **

- Pasi Huovinen, arXiv:nucl-th/0505036

- Detailed agreement between ideal hydro and measured v2(mass,pt) an accident? (Hirano and Gyulassy arXiv:nucl-th/0506049).
- Before we can make a connection to the EoS using v2(pt,mass) much more work needed in theory (test different EoS, viscosity, hadronic phase)

- Raimond.Snellings@nikhef.nl

## Higher harmonics

**Higher harmonics are expected to be present, for smooth azimuthal distributions the higher harmonics will be small v****n**** ~ v****2****n/2**
**Data follows the smooth scaling**

**STAR, PRL 92 (2004) 062301**

- Raimond.Snellings@nikhef.nl

## v4 as function of centrality

**To first order similar behavior as v****2****(p****t****), increasing up to 3 GeV/c after which there is a slow decrease**

**STAR preliminary**

**Y. Bai**

- Raimond.Snellings@nikhef.nl

## What do we learn from v4?

**Ratio v****4****/v****2****2**** is sensitive to degree of thermalization (****Borghini and Ollitrault nucl-th/0506045****)**
**v****4****(p****t****)/v****2****(p****t****)****2**** is 1/2 for ideal hydro (more accurate for increasing values of p****t****) **
**Observed integrated ratio is larger than unity**
**Incomplete thermalization**
**Do we have intuitive test if the ratio is related to the degree of thermalization?**
**ratio v****4****/v****2****2**** expected to decrease as the collisions become more central**
**ratio v****4****/v****2****2**** expected to increase as function of transverse momenta**

- Raimond.Snellings@nikhef.nl

## Difference between v2{2} and v2{4} 

**In more central Au+Au collisions the difference between v****2****{2} and v****2****{4} increases from 10% at low-p****t**** to about 40-50% at intermediate-p****t**** **

**Y Bai**

- Raimond.Snellings@nikhef.nl

## Centrality dependence of v2{EP) and v2{4} (year 4 data) 

**At intermediate-p****t**** the centrality dependence can even change order!**

**Y Bai**

- Raimond.Snellings@nikhef.nl

## Ratio v4/(v2{4})2

**Ratio larger than unity and for more peripheral collisions increasing fast as function of transverse momentum**
**Need theory input how this would look in microscopic model**

**Y. Bai**

**STAR preliminary**

- Raimond.Snellings@nikhef.nl

## Energy Dependence

**Elliptic flow in hydro sensitive to EoS (C****s****)**
**Elliptic flow in LDL sensitive to density and transport cross sections of the constituents**
**Data shows rather smooth dependence consistent with LDL**

**QGP 3 634-714 U. Heinz and P. Kolb**

- Raimond.Snellings@nikhef.nl

## QGP

**Q****G****P**

**QGP**

- Wanna see this?

- Fine-tune the “hadronic” focus!

**focus:**
**hadron corona**

**RHIC, the (s)QGP, according to Hirano **

- Raimond.Snellings@nikhef.nl

## focus

**Villasimius**

- Raimond.Snellings@nikhef.nl

## focus

**Villasimius**

- Raimond.Snellings@nikhef.nl

## At the LHC the main contribution to v2 is from the QGP phase!

**(black line) QGP contribution to the v****2****, increases with colliding energy**
**(red dots) total observed signal: QGP + hadron phase**
**At the LHC about 80% of the integrated flow signal is generated in the QGP phase!**
**Magnitude is large which makes the measurement easier**

- Raimond.Snellings@nikhef.nl

## Non-flow at the LHC (HIJING)

**<M> ~ 2000**

**<M> ~ 20**

**HIJING events with v****2**** =0**
**For low multiplicity events v****2****{EP} goes up to 0.6!**

**E. Simili**

- Raimond.Snellings@nikhef.nl

## First RHIC non-flow estimates

**First RHIC non-flow estimates**

**RS (STAR), Nucl. Phys. A 698, 193 (2002)**

**K.H. Ackermann et al (STAR), Phys. Rev. Lett 86, 402 (2001)**

**The non-flow component in HIJING is approximately centrality independent and at LHC energies 0.08 for random subevents, 0.04 for eta subevents, and can be reduced to 0.02 for eta subevents with large rapidity gap (> 1 unit model dependent statement, we know that HIJING does not describe the correlations at RHIC)**
**0.04 is similar to what was observed at RHIC, therefore at midcentral events the true flow correlations is expected to dominate by an order of magnitude (both M and v****2**** are expected to be larger)! **

- Raimond.Snellings@nikhef.nl

## Flow from RHIC to the LHC

**At RHIC**
**Strong collective behavior **
**Strongly interacting partonic matter**
**Theory: **
**microscopic picture still missing**
**connection to the EoS needs more work **
**Experiment: more detailed probes become available **
**can v****4**** tell us in more detail about the degree of thermalization? **
**At the LHC**
**Current expectations are that we can easily measure anisotropic flow**
**The QGP phase is expected to dominate the flow signals**
**better access to the EoS above T****c**

**M. Lisa: the v****2**** puzzle**

**}**

- Raimond.Snellings@nikhef.nl

## ALICE Detector

**ALICE Detector**

**TPC**

**PHOS**

**Muon arm**

**TOF**

**TRD**

**HMPID**

**PMD**

**ITS**

**~1000 people**
**90 institutes**
**30 countries**

- Raimond.Snellings@nikhef.nl

## Inner Tracking System

**The ITS is the center of the ALICE tracking system**
**needed to get reasonable momentum resolution at higher p****t**
**needed to reconstruct secondary vertices**
**needed to track low momentum particles **

**low mass: 7 % *****X*****0**

| 6 layers |  | R |  r |  Z |
| --- | --- | --- | --- | --- |
| Layer 1 | pixels | 4 cm | 12 m | 100 m |
| Layer 2 | pixels | 8 cm | 12 m | 100 m |
| Layer 3 | drift | 15 cm | 38 m | 28 m |
| Layer 4 | drift | 24 cm | 38 m | 28 m |
| Layer 5 | double sided strip | 38 cm | 17 m | 800 m |
| Layer 6 | double sided strip | 43 cm | 17 m | 800 m |

- Raimond.Snellings@nikhef.nl

## ITS + TPC 

**Impact parameter resolution is crucial**
**for the detection of short-lived particles**
**- charm and beauty mesons and baryons**
**At least one component has to be better **
**than 100 ********m (c******** for D****0**** meson is 123 ********m)**

- Raimond.Snellings@nikhef.nl

## Completed SSD Ladder

**Completed SSD Ladder**

**End Cap**

- Raimond.Snellings@nikhef.nl

## ALICE Flow preparations

**ALICE various detectors enable reaction plane determination (ITS + TPC, PMD,FMD, ZDC)**
**First theory prediction of charged particle flow (and the QGP EoS) can be tested with just one day of data taking**
**More stringent tests will come from measuring jet correlation versus the reaction plane and the flow of heavy quarks (dead cone in radiative energy loss, more sensitive to collisional energy loss)**

- Raimond.Snellings@nikhef.nl

## How ideal is nearly perfect?

**How well is the system created in heavy-ion collisions at RHIC described as an ideal fluid? What can we say about the EoS (theorist claimed perfect fluid behavior with QGP EoS)? **
**Elliptic flow (v****2****)**
**Centrality dependence**
**Mass and p****t**** dependence (T and ********0****)**
**Energy dependence**
**v****4**
**v****4 ****/**** ****v****2****2**

- P.F. Kolb and U. Heinz, in Quark Gluon Plasma, nucl-th/0305084

- Raimond.Snellings@nikhef.nl