# Presentation: 864558

## ANISOTROPIC FLOWMEASUREMENTS IN ALICE

- Sudhir Raniwala
- for the ALICE collaboration

- Department of Physics University of Rajasthan Jaipur

## PROLOGUE

- Sudhir Raniwala

- ALICE Letter of Intent in 1993: motivated by
- results from relativistic heavy ion collisions from AGS and
- results from ultra-relativistic heavy ion collisions at SPS
- ALICE Technical Proposal: 1995
- summary of proposed signals listed in chapter 1
- open charm production to study parton kinematics
- prompt photons for thermal radiation
- high pT hadrons for energy loss in plasma
- J/ψ production to probe deconfinement
- Strangeness production and chiral symmetry restoration
- multiplicity fluctuations and critical phenomena
- particle ratios for probing evolution
- line shape parameters for probing evolution
- interferometry to determine freeze-out radius
- Flow was not a consideration for the experiment, or its design......

## INTRODUCTION

- Sudhir Raniwala

- Jean-Yves Ollitrault’s suggestion (1992):
- Finite impact parameter collisions => anisotropic spatial density; unequal pressure gradients (assuming thermalisation) produces an anisotropic momentum distribution of particles. The strength of the anisotropy, and its systematic dependence on various parameters, provides information on the equation of state.
- Flow at the SPS energies was first reported by WA93 experiment (PL B403 (1997) 390). Measurement included contribution from non-flow 
- Discovery of flow at higher energies...... the essence:
- realisation of existence of a reaction plane in AA collisions at high energies
- One of the first results published at RHIC were on observation of flow.

**Notes:**
PHOBOS paper on charged particle multiplicity distribution paper was before STAR paper

## RESULTS FROM SPS AND RHIC

- Sudhir Raniwala

-  SPS
- Consistent results(WA98, NA49, CERES), v2 = v2 (pT, y, part-id, b)

- RHIC
- ~Consistent results
-  pT dependence shows 3 regions
- Low pT  => hydrodynamics
- Intermediate pT => quark coalescence
- High pT => hard scattering, parton energy loss

- STAR Collaboration
-  PR C72 (2005) 014904

- WA98 Collaboration, EPJ C41 (2005) 287

## IDEAL MEASUREMENTS

- Sudhir Raniwala

- v2 = v2 (pT, y, particle-id) for each event => complete event shape.
- Measure v2 = v2 (s, pT, y, particle-id, b), an average event shape (just need azimuthal angle)
- Different techniques with relative merits
- Reaction Plane Method
- Cumulants
- Lee Yang Zeroes
- General rule: more is the multiplicity and flow, better is the determination
- What values do we expect at LHC?

**Notes:**
Different techniques help decreasing systematic errors 

## SCALING OF MULTIPLICITY

- Sudhir Raniwala

- The model perfectly fits RHIC data, and can be easily extrapolated to LHC energy

- Armesto,Salgado,Wiedemann – PRL 94 (2005) 022002

- Charged multiplicity is parametrized as a function of Npart

***λ****** *****= 0.288              *****GBW parameter***
*δ***  = 0.79 ****±**** 0.02          *****fit parameter***
***N******0***** = 0.47      *****overall normalization***

- where :

- Result for PbPb, expect dN/dη ~ 2000 for central PbPb at LHC.

**Notes:**
parametrization of multiplicity:
- what are the ingredients
- show plot in fig.2 (the model works for RHIC)- they provide a convenient param. to extrapolate for LHC

## EXPECTED v2 at LHC 

- Sudhir Raniwala

- Hirano, to check reference....

- EXPECTED v2 at LHC

- N.Borghini and U.A.Weidemann, J.Phy.G 35 (2008) 023001

- Heinz, Kolb, Sollfrank

- Hirano et al ,
- nucl-th/0701075v2

## FLOW MEASUREMENTS IN ALICE

- Sudhir Raniwala

- TPC    (-0.9 < η < 0.9)
- ITS: SPD(-2 < η < 2 (layer 1))
- FMD(-3.4 < η < -1.7,
-                  1.7 < η < 5.0)
- PMD  (2.3 < η < 3.5)
- ZDC   (beam rapidity)
- And everything else, once the reaction plane is known 
- Measure in the range -3.4 < η < 5.0
- Fairly good particle identification over large range. Details in poster by Naomi (P-127)

- Feasibility of measurements:
-  Full simulation(ALIROOT)
-  Independent simulations (a) generator level (b) fast simulation folding detector response
-  Variety of combination of multiplicity and v1 (for ZDC) v2  (for others)

## Designed for dN/dη ~ 8000

- Sudhir Raniwala

- Designed for dN/dη ~ 8000
- Maximum occupancy throughout  the volume varies between 15% - 40%
- Momentum resolution ~1-2% for particles with momentum 100 MeV/c  to 1 GeV/c
- Particles up to 100 GeV/c will be tracked with a 10% resolution (combined tracking including ITS and TRD)

- -0.9 < η < 0.9

## RECONSTRUCTION ABILITY &TWO PARTICLE NON-FLOW CORRELATIONS

- Sudhir Raniwala

- RECONSTRUCTION ABILITY &TWO PARTICLE NON-FLOW CORRELATIONS

- Poster by Naomi van der Kolk (P-127)

##  SPD alone useful for low mult. events, and has higher acceptance (low pT threshold ~15 MeV)

- Sudhir Raniwala

-  SPD alone useful for low mult. events, and has higher acceptance (low pT threshold ~15 MeV)
-  Simulations suggest
-  flow for negative and positively charged particles separately
-  coarse pT binning may be possible

- Layer 1 ׀η ׀ < 2.0
- Layer 2 ׀η ׀ < 1.4

- T. Virgili

## FLOW USING THE FMD

- Sudhir Raniwala

- Can reconstruct v2 to better than 10% accuracy.

| η coverage |
| --- |
| η  <  5.03
η  <  3.68
η  <  2.29
η  < -1.70
η  < -2.01  |

- C.Nygaard (Master’s  Thesis)

## Directed Flow and Zero Degree Calorimeter

- Sudhir Raniwala

**Directed Flow and ****Zero Degree Calorimeter**

- Reaction Plane best determined by measuring spectator neutrons
- Good check on estimated second order event plane.
- Estimate independent (or less dependent) of eccentricity arguments
- Minimal non-flow effects because of large rapidity gap
- Estimate independent of details of evolution of hot and dense matter
- Estimate will yield sign of elliptic flow
- Need to measure this away from mid-rapidity
- Experience from RHIC suggests values of ~ 20%
- Can ALICE do it?
- Poster: Nora de Marco (P-190)

## First order Event Plane Estimate

- Sudhir Raniwala

**First order Event Plane Estimate**

**full event plane resolution (2 arms)**
**sub-event plane resolution (1 arm)**
**The reconstructed resolution is same**
**(Poster P-190, Nora de Marco)**

**50000 Pb-Pb minimum bias events **
**at 2.76 TeVA** have been simulated
- by means of  HIJING generator.
- A fast simulation takes into account
- nuclear fragmentation, Fermi
- momentum, beam parameters,
- detector smearing and directed flow
- of spectator neutrons.

**1****st****-order Event Plane Resolution  v/s Centrality**

## FLOW USING THE PMD

- Sudhir Raniwala

- Determine the event plane: accurate resolution
- For 5% flow and multiplicity 2400 in PMD (1.8 <η < 2.6)
-                        No Scattering                    Moderate Scattering
- Expected Resolution          0.831	                  0.808
- Estimated Resolution         0.836 +/- 0.002           0.812 +/- 0.003

- Measure pT integrated flow for photons (low pT threshold, deduce for neutral pions?)

- WA98 Collaboration, EPJ C41 (2005) 287

## ANISOTROPIC EMISSION OF J/Ψ IN FORWARD RAPIDITY USING EVENT PLANE FROM PMD

- Sudhir Raniwala

- ANISOTROPIC EMISSION OF J/Ψ IN FORWARD RAPIDITY USING EVENT PLANE FROM PMD

- Away from midrapidity
- Glauber absorption isotropic and comover absorption anisotropic
- =>v2 (J/ψ ) ~ - 0.025 (Heiselberg and Mattielo PRC60 (1999) 44902)
- J/ψ from dimuon channel
- measured in DiMuon Spectrometer( – 4.0 < η < -2.5)
- Data taking rate of PMD and DiMuon Spectrometer is same
- Hijing parametrisation, folding detector response
- Luminosity 5. 1026   (Results for 106 seconds of running)
- Different centralities

**Notes:**
Efficiency, mass resolution, trigger probability, simulation for 6 times 10^ 6 events, some other references, may be from DiMuon2004 talk

## INVARIANT MASS SPECTRA OF LIKE SIGN AND UNLIKE SIGN MUONS

- Sudhir Raniwala

| Nμ | Signal
(x 103) | Bkg
(x 103) | S/B
 | Significance |
| --- | --- | --- | --- | --- |
| 5.0 | 167.4 | 487.5 | 0.343 | 207 |
| 5.8 | 176.1 | 650.6 | 0.271 | 194 |
| 7.0 | 173.8 | 879.2 | 0.200 | 169 |
| 7.8 | 192.6 | 1494.1 | 0.129 | 149 |

## BACKGROUND SPECTRA IN 12 AZIMUTHAL BINS

- Sudhir Raniwala

- BACKGROUND SPECTRA IN 12 AZIMUTHAL BINS

## Flow in unlike sign pairs

- Sudhir Raniwala

- Wider mass region => lower S/B
-  => lower flow
- v2 = v2meas (1+S/B)/(S/B)

- Signal in 12 bins

## RESULTS DETERMINE

- Sudhir Raniwala

- Significance depends upon large number of factors
- Significance α √Nevts
- Significance ~ 0.7 / (v2 * f)
- To measure 5% flow with 10% accuracy requires a significance of ~140 for a given S/B. To probe 2.5% flow with similar accuracy will require 4 times as many events.

- “REQUIRED SIGNIIFICANCE”

**Notes:**
Comments from pages 35 and 36 from DiMuon2004 talk

## EPILOGUE

- Sudhir Raniwala

- Though none of the ALICE sub-detectors were initially designed keeping flow in mind, ALICE is now ready to measure flow and every other signal with respect to the reaction plane.

## BACK UP SLIDES

- Sudhir Raniwala

## CONCLUSIONS

- Sudhir Raniwala

- Sudhir Raniwala

- E.Simili

##  ALICE Zero Degree Calorimeter 

- Sudhir Raniwala

** ****ALICE Zero Degree Calorimeter**** **

- The 2 **neutron zero degree calorimeters** **ZNs** have full acceptance for spectator neutrons  (ZN > 8.7).

- The 2x2 ZN segmentation gives a rough localization of the spectator neutron’s spot on the front face of the calorimeter. This localisation provides the first order event plane (spectator neutrons)

- GEANT-based simulation

## RECONSTRUCTION ABILITY

- Sudhir Raniwala

- E.Simili

## FLUCTUATIONS 

- Sudhir Raniwala

- FLUCTUATIONS

- Large multiplicity environment enables determination of fluctuations.....

- A

- ALICE PPR

- Sudhir Raniwala

## QUARK MATTER 2008, February 4-10, Jaipur, India

- Sudhir Raniwala