study of short-lived resonances in alice

Study of short-lived resonances in ALICE

A. Badalà – INFN Sezione di Catania- Italy for the ALICE Collaboration

Contents

•Physics motivations

•ALICE detector

•Results on strange resonances (K*(892),(1520),(1020),..) from simulated p-p events @ 900 GeV and @14 TeV

•Summary

Why short-lived resonances?

Resonances are strongly decaying particles which have lifetimes of about a few fm/c (i.e resonance ~ fireball )

Resonances c (fm) (770) +- 1.3 f0(980) +- 2.6 K*(892)0 K 3.9(1520) Kp 13 (1020) K+K- 44

Modifications of properties of resonances (peak,width)

Partial chiral symmetry restoration

Interaction of the resonances and/or their daughters with fireball medium

Resonances may give information on the dynamics and on the chiral property of the hot and dense matter which is produced in the collision

A. Badalà- SQM07- Levoča – 24/06/-29/06/07 2

Resonances as a probe of chiral symmetry restoration

Resonance mass shift and width broadening have been suggested as a signature of chiral symmetry restoration

The best probes are resonances reconstructed by their leptonic decay channel since leptons are less likely to rescatter in the hadronic

medium

A. Badalà- SQM07- Levoča – 24/06/-29/06/07

R. Arnaldi et al. (NA60 Collaboration) Phys. Rev. Lett. 96(2006)162302

A significant excess of +- pairs is observed above the yield

expected from neutral meson decay. Its shape is consistent

with a contribution from +- annihilation

Models based on in-medium broadening scenario seem

able to reproduce data, while moving mass models seem

ruled out

NA60 RESULTSIn-In@

158AGeV

3

Resonances from jets

High pT resonances from the away side jet could be modified by the partonic medium, but they are so fast to have low probability to be affected by the hadronic medium

Recently suggestion to study chiral symmetry

restoration by comparing resonance production in event

classes based on azimuthal distribution

respect to jet direction First attempt has been done studying h(high

pt)-(1020) correlations C. Markert, 23rd Winter Workshop on Nuclear Dynamics Big Sky, Montana,

USA


Interactions of resonances in hadronic nuclear medium

No interaction

Rescattering

Due to the rescattering , resonances may not be reconstructed

Regeneration

Pseudo-elastic collisions may regenerate resonances

The yields of resonances detected by their hadronic decay can be influenced by effects of rescattering and regeneration which depends on:

•the time between the chemical and the thermal freeze-out

• the lifetime of the resonances

• the interaction cross-section of the decay particles.

The resonances may probe the timescale between the chemical and the kinetic freeze-out


p+p and Au+Au @ sNN =200 GeV

Suppression of K* and *


Resonance/non-resonance ratio

B.I. Abelev (Star Collaboration) nucl-ex 0604019

At RHIC energies thermal models are able to

reproduce the ratios of stable particles

Deviations from these ratios have be used to estimate the time interval between

thermal and chemical freeze-out (UrQMD) = 13±3 fm/c

Lower limit (<4 fm/c, T=160 MeV) from measured K*/K and */ ratio by a thermal model with a rescattering phase (G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 and

C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045)6

(*) Extraction of the signal/yields

(*) Mass and widths of resonances

(*) Transverse momentum and transverse mass spectra

(*) Particle ratios

Elliptic flow

Nuclear modification factors: RCP and RAA

Main observables concerning the study of resonances

in pp and AA collisions

7

Elliptic flow

Baryons

Mesons

For KET >1 GeV, mesons and baryons scale separately

Universal scaling is observed for mesons and baryons when

quark number scaling is employed


S. Adare et al. (Phenix coll.) nucl-ex 0608033

Elliptic flow for resonances

Measurement of flow for meson and baryon resonances is of great interest to further validate the picture sorting of this

scaling i.e. that partonic collectivity dominates the transverse expansion dynamics.

Mass meson ~ Mass proton

v2 of mesons confirms this

universal scalingS. Afanasiev et al. (PHENIX Coll. ) nucl-ex 0703024

Au-Au @200 GeV


Nuclear Modification Ratios (RCP) for resonances

RHIC results have shown as, in the intermediate pt region, nuclear modification factors depend on the constituent

quarks rather than on particle mass.

Recent suggestion by Maiani et al. (Phys. Lett. B645(2007)138) to use

this observable to solve the problem of the real quark composition of some resonances as the fo(980)( or

?)

][ ss ]][[ qssq


ALICE ( A Large Ion Collider Experiment)

ITSLow pT trackingVertexing

TPCTracking, dE/dx

TRDElectron ID

TOFPID

HMPIDPID (RICH) @ high pT

PHOSγ, π0

PMDγ multiplicity

MUON-ARM μ-pairs MUON-ARM μ-pairs


EMCAL Jets

reconstruction

11

Reconstruction of short-lived resonances is improved by optimal performance on:

vertex reconstruction

Pb-Pb

p-p

Primary vertex in ALICE is reconstructed by means of

tracklets in the two innermost pixel layers and

by a Kalman vertex procedure for p-p events

< 40 m

~ 5 m



primary vertex reconstructionprimary vertex reconstruction

tracking efficiency

In ALICE Kalman filter strategy allows a good tracking performance down to very low momenta

ITS + TPC




tracking efficiencytracking efficiency

momentum resolution

pt/pt ~ 3 % at 100 GeV/c

pt/p

t(%)

pt(GeV/c)

pt/pt <0.7% for pt<2 GeV/c


Reconstruction of short-lived resonances is largely improved by optimal performance on:



momentum resolutionmomentum resolution

track impact parametertrack impact parameter

particle identification

with ITS and TPC at low momenta…

and TOF at high momenta…


stable hadrons (, K, p): 100 MeV < p < 5 GeV (few 10 GeV)

dE/dx in silicon (ITS) and gas (TPC) + Time-of-Flight (TOF) + Cerenkov (RICH)

decay topology (K0, K+, K-, )

K and decays up to at least 10 GeV

leptons (e, ), photons, 0, electrons in TRD: p > 1 GeV, muons: p > 5 GeV, 0 in PHOS: 1 < p < 80 GeV

Particle Identification


Resonance K*(892) Φ(1020) *(1520) Decay channel (B.R.) K (~100%) K+K- (49%) N K (45%)

Width [MeV/c2] 50.8 4.5 15.6 Life time [fm/c] 3.9 44 13

Several activities are going on in ALICE concerning the study of such resonances, both in pp and AA collisions, with contributions from several groups. (Other contributions to this conference from P.Ganoti and D. Tapia-Takaki).

•Software code development

•Test distributed analysis of events

•Optimization of reconstruction tools

•Background estimation

•Efficiency evaluation

Study of short-life resonances in ALICE


Results from p-p events @ 900 GeV and 14 TeV

Events of PYTHIA were generated and fully reconstructed using

•Realistic simulation of the detector response for the whole ALICE assembly

•Realistic clusters and tracks reconstruction

2 Data Sets

2 x 105 minimum bias p-p PHYTIA events @ 900 GeV. Running scenario at LHC startup

1.5 x 106 minimum bias p-p PHYTIA events @ 14 TeV (about 0.2% 1-year data taking)

PDC06 data, distributed GRID

analysisA. Badalà- SQM07- Levoča – 24/06/-29/06/07 18

Studied dependence on event selection criteria

●Charged multiplicity

●z-vertex location

Study of the combinatorial background by the mixed-event technique

Multiplicity

z-vertex

Comparison of the event mixing background to the “true” combinatorial backgroung

‘True’ background = (Signal) – (True pairs)

Only events with Δm<5 and Δzv < 3 cm mixed


Like-sign technique also explored

K* K*

Comparison of the like-

sign background to the “true” combinatorial background

p-p@900 GeV


Unlike sign

Like-sign

20

Perfect PID Realistic PID

PID influence on K*(892)

reconstruction

True K* = 7599

Found K* = 7488

S/B = 0.138

S/√B = 30.68

True K* = 4306

Found K* = 4139

S/B = 0.11

S/√B = 20.28

Maxprob > 0.7 (K)No PID (π)

Maxprob > 0.7 (K)Maxprob > 0.7 (π)

No thresh on maxprob

True

Found

Perfect PID Realistic PID

p-p@900 GeV

(1020) and *(1520) with realistic PID

True (± 2σ) = 186

Found (±2σ) = 168

S/B = 2.87

S/√B = 13.86

p-p@900 GeV


True Λ (± 2σ) = 146

Found Λ (± 2σ) = 128

S/B = 1.23

S/√B = 19.5

*

*

22

Results for p-p collisions @14 TeV

Detailed analysis for K*(892)0 on PID

perfomances

1.5 x 106 PYTHIA events

Mass resolution ~ 3MeV/c2

K*


Found K*(±2)=89182

True K*(±2)=85360

23

K*(892)0 pT-analysis with realistic PID

pT= 0 - 0.5 pT= 1.5 - 2

pT= 3.5 - 4

p-p@14 TeV


Correction matrix


(1020) and *(1520) with realistic PID p-p@14 TeV

(1020)

(1020)

(1520)

(1520)

Mass resolution 1.2 MeV/c2


True =4893

Found =4967

True *=3879

Found *=3649

26

● Short-lived resonances in pp collisions @ LHC energies could be studied in ALICE from the very beginning

● With a small sample of events [O(105)] @ 900 GeV and realistic PID:

● Extraction of yields at least for K*(892), Φ(1020), Λ*(1520)

● Rough pT - distribution for K*(892) up to 1.5 GeV/c

● Particle ratios Φ/K*, Λ*/K*, Φ/Λ* measurable

● Analysis of O(106) pp events at 14 TeV fully reconstructed on the GRID

● Resonance yields with large statistics

● pT-analysis

● Correction matrix (y,pT)

● Extension to other resonances is in progress.

Summary

K*(892)0


EXTRA SLIDES

K*(892) pt-distribution @ 900 GeV

pT-spectrum for realistic PID

2 x 105 events 3500 K*

Practical limit for 2 x105 events


Overall number of particles + antiparticles generated by PYTHIA@900 GeV:

1.34 K*(892)/event0.08 (1520)/event0.23 Φ(1020)/event

Resonance yield

Exp.data

PYTHIA

K*(892) yield


(1020)

K*(892)0

1 GeV/c<pt<2 GeV/c2 GeV/c<pt<3 GeV/c

Inside same event, correlations between

K+ and π- candidates

K- and π+ candidates

Evaluate invariant mass spectrum

Combinatorial background:

Signal extraction (unlike-sign)

Mixed-event technique

Like-sign technique

Example: K*(892) Kπ (~100%)

)()(2)( mNmNmNKKSignLike

ALICE PID A common BAYESIAN approach is adopted by every ALICE detector

performing PID;The probability w(i|s) to be a particle of type i (i = e,, , K, p...) if a signal s

(dE/dx, TOF,...) is detected, is:

π...μ,e,kk

i

Ck|srCi|sr

s|iw

r(s|i)(Detector response function)conditional probability density functions to get a signal s in a

detector, if a particle of i-type hits the detector

Ci (particle concentration)a priori probability to find a

particle of type i in the detector

,...,,

)|()|(

)|(

ekk

i

iSRCiSRC

SiW

Probability to be a particle of i-type (i = e, , , K, p, … ), if we observe a vector S= {sITS, sTPC, sTOF, …} of PID signals in different detectors is:

)|()|(,...,

isriSR ddTPCITSd

Combinated response function

Mass resolution

~4000 HIJING events

Mass resolution ~3 MeV

preliminary

Temperature and lifetime from (1520) / and K*/K

results between : T= 175 MeV => = 4-6 fm/c = 0 fm/c => T= 110-130 MeV

Dependence of the two ratios K*/K and (1520)/, on the chemical freeze-out temperature and time interval between chemical and kinetic freeze-out. Model: termally produced particle yields + rescattering phase. Then regeneration is not taken into account.

G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239

C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045.

(1520)/ = 0.034 0.011 0.013

K*(892)/K = 0.19 0.05

> 4 fm/c for T=160 MeV

0-20% most central Au+Au

Identified particle spectra

ALICE has unique capabilities to reconstruct and to identify particles:Global tracking (ITS-TPC-TRD) (pt/pt ~ 3% at 100 GeV/c) + dE/dx (low pT + relativ. rise), TOF, HMPID, PHOS, … Reconstruction by invariant mass and topological decay , K, p: 0.1- 0.15 <pt< 50

GeV/c

pT (GeV/c)

PID in the relativistic rise

K

p

Estimated pt range for particle identification for 107 central Pb-Pb events (1-year data taking)

Weak or strong decaying particles: up to 10-15 GeV/c

14

ALICE performance on:



momentum resolutionmomentum resolution

track impact parameter

Pb-Pb

p-p

<100 m @ pt> 1GeV/c


K*(892)± KS0 + π± B.R. ~ 33%

π+ + π- B.R. ~ 69%

Total B.R. ~ 23 %

Preparation of tools for K*(892)±

analysis

p-p@900 GeV

K*+

Nuclear Modification Ratios (RCP) for resonances

RHIC results have shown as, in the intermediate pt region, nuclear modification factors depend on the constituent

quarks rather than on particle mass.

L. Maiani et al., Phys. Lett. B645(2007)138

A two components recombination/fragmentation model shows clear distinction for the Rcp of the f0(980) resonance with or

content.

][ ss ]][[ qssq


study of short-lived resonances in alice

Documents

study of resonances

strange resonances

interactions of resonances

baryon resonances

widths of resonances

badal sqm07

jetshigh pt resonances

mass meson