Identified particle studies at the LHC with the ALICE experiment P. Foka a on behalf of Panos Christakoglou b,c for the ALICE Collaboration a GSI b NIKHEF

Identified particle studies at the LHC with the ALICE experiment

P. Fokaa on behalf of Panos Christakogloub,c

for the ALICE Collaboration

a GSIb NIKHEF

c Utrecht University

31.08.2010 [email protected] - Quark Confinement and the Hadron Spectrum IX

Introduction

ALICE is designed to study the physics of the strongly interacting matter, the Quark Gluon Plasma, produced in nucleus-nucleus collisions at the LHC

The physics program of ALICE has already started with the study of proton-proton collisions at unprecedented high energies:o calibrate and prepare our detectors for the future heavy-

ion collisions,o the measured properties of these collisions will set the

baseline for the nucleus-nucleus collisions, o what are the properties of high multiplicity events

(collectivity, flow)? In this talk: results from pp collisions at √s = 0.9 and 7 TeV

o identified particleso pbar/p ratio


ALICE @ the LHC

31.08.2010 [email protected] - Quark Confinement and the Hadron Spectrum IX 3

PID in ALICE

PID for hadrons in the central barrel (|η| < 0.9)o ITS: Excellent (3σ) separation from ~50 MeV/c for πo TPC: π from 200 MeV/c, Κ from 300 MeV/co TOF: K from 500 MeV/c up to 2.5 GeV/c, p up to 3.5 GeV/co HMPID: intermediate to high momenta (up to 5 GeV/c)

Photons with the dedicated spectrometer (PHOS - |η| < 0.12) Electrons in the central barrel:

o ITS + TPC for low momentumo TRD from P ~ 1GeV/c (beauty measurements feasible even @1GeV/c!)

Muons reconstructed in the forward region (muon arm: -4 < η < -2.4) Strange particles identified via their topology


PID – momentum reach

For more details see the talk of

Orlando Villalobos

ITS commissioning


Design goalso Optimal resolution for primary vertex

and track impact parameter Minimize distance of innermost layer from

beam axis (<r>≈ 3.9 cm) and material budget

o Maximum occupancy (central PbPb) < few %

o dE/dx information in the 4 outermost layers for particle ID in 1/β2 region

Installed in 2007. Successfully commissioned during the

cosmics runs in 2008 and 2009.

Layer

Type

Radius (cm)

Length (cm)

Resolution (m)

PbPb dN/dy=6000

r z Part./cm2 Occupancy (%)

1 SPD 3.9 28.2 12 100 35 2.1

2 SPD 7.6 28.2 12 100 12 0.6

3 SDD 15.0 44.4 35 25 3 2.5

4 SDD 23.9 59.4 35 25 1.5 1.0

5 SSD 38.0 86.2 20 830 0.6 4.0

6 SSD 43.0 97.8 20 830 0.45 3.3

For more details see the talk of Emanuelle Biolcati dE/dx resolution ~ 13%

Main TPC characteristicso Cylindrical in shape, with an active

volume that has an inner radius of about 85 cm, an outer radius of about 250 cm, and an overall length along the beam direction of 500 cm (largest TPC ever built)

o Cylindrical field cage filled with ~90 m3 of Ne/CO2/N2 gas mixture (90:10:5)

o Drift time of ~90 μso Many (>90) 3D points (+dE/dx) per

track Since August 2009 more than 750

million events (cosmics, krypton, and laser) recorded, with and without B-field.o First round of calibrations (dE/dx,

momentum, alignment, gain) completed before collisions.

TPC commissioning



J. Alme et al. (ALICE TPC), arXiv:1001.1950 (subm. to NIM)

TPC particle identification

dE/dx resolution ~ 5-6%

September 2009 (cosmic)

December 2009 (cosmic)

TOF


18 sectors, 2π covering in |η| < 0.9

Granularity: 2.5x3.5 cm2 at ∼3.7 m from the primary vertex;

Fully installed 95% channels operational Resolution at present ∼90 ps

9

Kaon pT distributions stable & decays

K → K0

S →

6 ways to measure Kaons

K p

%73.1

%27.3

%87.4

%13.21

%43.63

00

0

0

0

K

K

eK

K

K

π- kinks

(99%)


• Kaons from kinks• K0s decaying into a pair of pions• ITS, TPC, TOF, HMPID

HMPID

Data collected in December 2009 pp @ √s = 900 GeV Good agreement between the 3 detectors (ITS, TPC, TOF) Shows that detectors’ calibration/understanding and analysis methods are OK Statistics not sufficient for more differential studies

Identified particle spectra – Tsallis fit


pp @ LHC: multiplicity ≈ AA collisions at lower √so Does collective behavior develop with multiplicity?

Tsallis Blast Wave (PRC79 051901, 2009)o Boltzmann-Gibbs statistics replaced by “Tsallis statistics”o Adds one parameter q (quantifies degree of non equilibrium)

ITS included in these plotso Provides a significant reduction of the extrapolation to zero pto Constrains models (e.g. flow)

Ongoing study @ 7TeV (possibility for differential analysis – high statistics)

Combined spectra (ITS+TPC+TOF)

~250K collision candidates at 900GeV (December 2009)> 100M collision candidates at 7TeV (March2010 - …)

Prospects for the spectra measurements


Baryo-chemical potential μB and Chemical freeze-out Temperature TchI.Kraus et al., in arXiv0711.0974 [hep-ph]

I.Kraus et al., J.Phys.G32 (2006) S495A.Andronic et al., Nucl. Phys. A772 (2006) 167 J.Rafelski et al., Eur. J. Phys. C45 (2006) 61 (non equilibrium)

Expectations at LHC: Tch =161±4 MeV μB =0.8+1.2-0.6 MeVA.Andronic et al., Last Call for Predictions, in arXiv0711.0974 [hep-ph]

But the ratios can be used for other studies as well…

Baryon number transport – Motivation


Where does the conserved baryon number (BN) reappear after the pp collision?o G.C. Rossi and G. Veneziano, Nucl. Phys B123 (1977) 507.o B.Z. Kopeliovich and B. Zakharov, Z. Phys. C43 (1989) 241.

Different approaches based on theory:o Baryon considered as bound quark-diquark state within QGSM. BN transport implies

breaking the diquark pair.o Gluonic mechanism aka String Junction (SJ). BN transport implies the stopping of the

SJ.

u

u

d u

u

d

Conventional approach - QGSM

Within QGSM one expects no BN transport (an asymmetry ~0) at LHC energies No BN transported at mid-rapidity from the fragmentation region

du

u

SJ

String Junction

P(y) ~ e(a J 1)y

P(y)const

BN transport (asymmetry) even at large rapidity gaps (large energies). Veneziano: Probability exponentially suppressed with aJ ~ 0.5 (aJ: J intercept) Kopeliovich: Probability constant with rapidity

LHC’s large rapidity gap between the incoming protons (yp-max = ±9.6) will give us the opportunity to distinguish between the different models.

Δy = ybeam – ybaryon = ‘rapidity loss’

AB NB N

B

NB NB

RNB

NB

Baryon number transport – Experimental results


BRAHMS: Phys. Lett. B607 (2005) 42

p+p - Au+Au @√s = 200GeV

p+p Au+Au 20% central PYTHIAHIJING-B

STAR: Phys.Rev.Lett.86 (2001) 4778

Lessons from RHIC

A. Falkiewicz: DIS2008, London

Lessons from HERA

Proton excess at mid-rapidity can be attributed to the BN transport from the beam at RHIC energies

No sign of any rapidity or pt dependence

PYTHIA systematically overestimates the proton ratio

HIJING-B (includes a SJ formalism) describes the experimental data

Initially reported an asymmetry of ~8% for Δy ~ 7.o Results never

published due to large systematic uncertainties caused by the high beam-gas rate.

Results reported at the DIS2008 are compatible with an asymmetry for Λs ~0

AuAu@√sNN = 130 GeV

Baryon number transport – Corrections


Np

N p

corrected

Np

N p

raw

Cabsorption Ccross sec tion Csecondaries p CcutsC feed down

Fluka in full agreement with the data Clear disagreement between the experimentally measured values and the input curves of GEANT3-GEANT4 (data points lower by a factor of 2-3 depending on the momentum). Recent physics lists provided by the G4 team reproduce the data points

Bendiscioli and Kharzeev, Riv.Nuovo Cim.17N6, 1-142 (1994)

Baryon number transport – Transverse momentum dependence


Results show no sign of any transverse momentum dependence for both energies.

Experimental points are compared with different model predictions that include variation of BN transport mechanisms:o PYTHIA tunes having a

standard prescription for transferring the BN over large rapidity intervals (D6T, ATLAS-CSC, Perugia-0), describe the data well.

o Perugia-SOFT underestimates the data points

o HIJING-B clearly underestimates the pt dependence (particularly at the lower energy)K. Aamodt et al. [ALICE Collaboration],

Phys. Rev. Lett. 105, 072002 (2010)

Baryon number transport – Energy dependence


p

p

1

1 Be( J P )y

Energy dependence of the ratio parameterized based on the contribution of different diagrams describing the p(bar) production (pair production at mid-rapidity and BN transfer) Intercept of the Pomeron set to 1.2 based on fit on the energy dependence of the multiplicity. Junction intercept fixed to 0.5 The curve describes the (high energy) points well.

o The lower ISR points are overestimated due to the contribution of yet another diagram which is suppressed at high energies.

J 0.5P 1.2B 11.5

Energy [TeV] 0.9 7

ALICE 0.957 ± 0.006

0.991 ± 0.005

PYTHIA

ATLAS-CSC (306) 0.96 1.0

Perugia-0 (320) 0.95 1.0

Perugia-SOFT (322)

0.88 0.94

QGSM

ε=0 0.98 1.0

ε = 0.076, αJ = 0.5 0.96 0.99

ε = 0.024, αJ = 0.9 0.89 0.95

HIJING-B 0.83 0.97

K. Aamodt et al. [ALICE Collaboration], Phys. Rev. Lett. 105, 072002 (2010)

Conclusion

ALICE in a very good shapeo Most detectors perform close to specso Physicist perform also close to specs

Pbar/p ratio published in PRL Identified particle spectra paper under internal review

The identified particle spectra coming from different analyses/detectors agree remarkably well between each other.o Differential analysis (e.g. vs multiplicity) feasible with the large

stats 7TeV sample ongoing The pbar/p ratio has been measured at both 0.9 and 7TeV

o The data points favor the existence of the string junction with the value of the intercept of the J being 0.5 (Veneziano)

o Models with additional transfer (QGSM with ε = 0.9, HIJING/B) are disfavored.


Still ALICE being mainly a HI experiment, we look forward to November/December

BACKUP


ITS calibration and PID (SDD + SSD)


Charge distribution measured on all the SDD moduleso ~95% of the detector included in the

readout during data taking

Charge distribution measured on all the SSD moduleso 90% of the detector active in 2009, (<1.5%

bad strips)o S/N ~40

dE/dx resolution ~ 13%

For more details see the talk of

Emanuelle Biolcati

Identified particle spectra


Data collected in December 2009 pp @ √s = 900 GeV Good agreement between the 3 detectors (ITS, TPC, TOF) Shows that detectors’ calibration/understanding and analysis methods are OK Statistics not sufficient for more differential studies

Documents

Identified particle studies at the LHC with the ALICE experiment P. Foka a on behalf of Panos Christakoglou b,c for the ALICE Collaboration a GSI b NIKHEF