study of short-lived resonances in alice a. badal à – infn sezione di catania contents physics...

Study of short-lived resonances in ALICE

A. Badalà – INFN Sezione di Catania

Contents

•Physics motivations

•Some SPS and RHIC results

•ALICE detector performance

•Some results from simulated p-p events @14 TeV

•Summary

A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/071

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- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 2

Resonances as a probe of chiral symmetry restoration

To study chiral symmetry restoration in terms of mass shift and width

broadening, resonance decays from the early

stage of the medium need to be extracted

The best probes are resonances reconstructed by their leptonic decay channel since leptons are

less likely to rescatter in the hadronic medium. However

regenerated resonances from the late hadronic phase feed

down into this signal

ρ0

ρ0

+

+

-

-

π- π+

ρ0

-

+

ρ0 ρ0π-

π+

π+

π-

Leptonic decay channel probes all

stages of the collision

Hadronic decay channel probes late stages of

the collision


NA60 results

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 outR. Arnaldi et al. (NA60 Collaboration) Phys. Rev.

Lett. 96(2006)162302

In-In@ 158AGeV


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 (reconstructed by their

hadronic decay) in event classes based on azimuthal distribution

respect to jet direction C. Markert, 23rd Winter Workshop on Nuclear Dynamics Big Sky, Montana, USA and SQM07, Levoca (Slovakia)


(1020) from same/away side in/out of plane

side1

side2

near

away

No mass shift or width broadening

visible

side2

side1 near - side

away- side

•Trigger particle: hadron pT > 4.0 GeV/c • Associated particle: resonance (1020) <pT>~ 0.9 GeV/c

C. Markert, SQM07, Levoca (Slovakia)A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 6

Next step: with higher pt

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 been 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)A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 8

(*) 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


K*(892) π K B.R. ~1 c = 4 fm

STAR Preliminary

STAR Preliminary

√sNN = 200 GeV √sNN = 200 GeV

√sNN = 62 GeV

STAR Preliminary

STAR collaboration, Phys. Rev. C71, 64902 (2005)

√sNN = 200 GeV

10

Σ(1385) Λ B.R. 0.88 c = 5.5 fm

Λ(1520) pK B.R. 0.45 c = 12.6 fm

Star collaboration, Phys. Rev. Lett. 96(2006)132301

STAR Preliminary

d+Au √sNN=200 GeVd+Au √sNN=200 GeV

p+p √sNN=200 GeV

Au+Au √sNN=200 GeV

11

Φ(1020) K+ K- B.R. 0.49 c = 44 fm

STAR Preliminary

PHENIX

d+Au √sNN=200 GeV

PHENIX


Au+Au √sNN=62 GeV


Φ(1020) e+e- B.R. 0.000296 c = 44 fm

p+p √sNN=200 GeV d+Au √sNN=200 GeV


PHENIX

PHENIX

PHENIX

S. Huang DIS2007, Munich,Germany


ρ0(770) π+ π- B.R. ~1 c = 1.3 fm

20-40% dAu0.6 ≤ pT < 0.8 GeV/c

STAR Preliminary

√sNN = 200 GeV

40-100% dAu0.6 ≤ pT < 0.8 GeV/c

STAR Preliminary

√sNN = 200 GeV

40-80% Au+Au0.6 ≤ pT < 0.8 GeV/c

STAR Preliminary

√sNN = 62 GeV

0-20% dAu0.6 ≤ pT < 0.8 GeV/c

STAR Preliminary

√sNN = 200 GeV


Mass and widths of resonances

Even in the absence of the phase transition, temperature and density dependent modifications of the mass, width and shape of short-lived resonances are predicted. Possible explanations are:

•Dynamical interactions with the surrounding matter (M. Bleisher and H. Stocker, J. Phys. G30(2004)S111, E. V. Shuryak and G.E. Brown, Nucl. Phys. A717(2003)322)

•Phase-space distortions(S. Pratt and W. Bauer, Phys. Rev. C68(2003)064905, R. Rapp Nucl.Phys. A725(2003)254)


K* Mass and Width

• K*0 pT < 1 GeV mass shift of ~10 MeV observed

• K*± and K*0 pT > 1 GeV mass agrees with PDG for all systems within errors

• Width agrees with PDG for all systems within errors

PDG K*0

PDG K*±

PDG

STAR Preliminary

STAR Preliminary

MC


Φ Mass and WidthSTAR Preliminary

STAR Preliminary

PDG

PDG

• pT > 1 GeV mass and width agree with MC and PDG for all systems

• pT < 1 GeV mass agrees with MC for all systems within errors

• pT < 1 GeV width higher than MC for all systems real physics or detector effect?


mass and widthmass and width

Mass and width of meson reconstructed by KK channel do not depend on centrality

Mass and width in agreement with PDG for all system

d+Au √sNN=200 GeVAu+Au √sNN=200 GeV

S. Huang , DIS2007, Munich Germany

Au+Au √sNN=62 GeV


Particle production in pp collisions dominated by two mechanisms:

a) soft, thermal-like processes at low pT (exponential shape)

b) Hard, parton-parton processes at high pT (power-law shape)

STAR Coll, PRC71(2005)064902

A unique (Levy) function is used to parametrize the overall shape

Transverse spectra


K*0 Transverse Momentum Spectra

Au+Au @62 GeV Cu+Cu @62 GeV Cu+Cu@ 200 GeV

STAR PRELIMINARY STAR PRELIMINARY

STAR PRELIMINARY

K*0 spectra fitted by an exponential function

S. Dash SQM07


→K+K- Spectra

STAR PreliminarySTAR Preliminary

STAR Preliminary

•Change of Φ spectra from exponential in central Au+Au collisions to Levy function shape in peripheral Au+Au Matter formed in peripheral Au+Au collisions favors hard Φ production


SPS puzzle NA49%NA50

NA45 - PRL 96 (2006) 152301]

NA50 reported a yield measured via dileptons larger than yield determined by NA49 in K+K- channel. Further, the mT spectra exhibit a different inverse slope parameter

NA45 has studied the leptonic and the kaon decay modes of the

meson.

Yield and inverse slope parameter agree in both decay modes

Results are in agreement with the

NA49 results

Pb+Au @E/A=158 GeV


SPS results for →+- (NA60)NA60 In-In (pT < 1.6 GeV/c)NA49 Pb-Pb(pT<1.6 GeV/c)NA50 Pb-Pb(pT>1.2 GeV/c)

M. Floris, SQM07

NA60 In-In (pT > 1.1 GeV/c)NA49 Pb-Pb(pT<1.6 GeV/c)NA50 Pb-Pb(pT>1.2 GeV/c)


Difference between NA50 and NA49 was not due to different

decay channel

Agreement with NA49 when the fit is performed in the same range. T value grows with the centrality of the collision

Lower T values and flatter distribution if the fit is performed in

the same pT range of NA50.

This hints for the presence of radial flow → blast wave analysis

Φ Production K+K- and e+e-

• The leptonic channel yield is a little higher than hadronic channel• More accurate measurement is required to confirm if there is

branching ratio modification

e+e-

K+K-

A. Kozlov (Phenix coll.),QM2005


Φ K+K- STAR-PHENIX comparison

J. Rafelski et al.,Phys.Rev. C72 (2005) 024905

• Φ production there is a factor of ~2 difference between PHENIX and STAR

STAR

PHENIX

STAR + PHENIX

Au+Au @ √sNN = 200 GeV


Suppression scales with dNch/dy ~ system size

STAR preliminary

Resonance suppression (system size dependence)

C. Markert, SQM07


For K* seems less re-scattering at lower energies in peripheral collisions

Lower density smaller interactions cross section? Shorter hadronic lifetime less hadronic interactions ?

STAR preliminary

Resonance suppression (energy dependence)Life-time [fm/c]

K(892) = 4.0 (1020) = 45

S. Dash SQM2007

STAR preliminary

C. Markert, SQM07


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


K*(892) elliptic flow

Au+Au @ 200 GeV

C. Nonaka, et al., Phys.Rev.C69:031902,2004

Partonic generation → resonances are produced in a hadronizing QGP → v2 scales with n=2

Hadronic generation → resonances are produced in the hadronic final state via hadron-hadron scattering →v2 scales with n=4 (K*=K+=2+2)

Most of K* are produced in partonic phase and only a

small quantity is originated in rigeneration (Need more precise measurements)

Using the deviations of the measured flow coefficient v2 from the scaling law

given by the quark recombination formalism to probe the amount of hadronic final state interactions


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.

K*(892) and (1020), (mass ~ mass proton), have RCP values close

to the kaon ones.


Nuclear Modification Ratios (RCP) for resonances

Recent suggestion by Maiani et al. to use this observable to solve the problem of the real quark composition of some resonances as the fo(980)

( or ?) ][ ss ]][[ qssq

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

A two components recombination/fragmentation model


ALICE performance on primary 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

A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/0733

ALICE performance on track impact parameter

Pb-Pb

p-p

<60 m @ pt> 1GeV/c


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

ITS + TPC

Tracking efficiencyp

t/pt(%

)

pt(GeV/c)

Momentum resolution

pt/pt <0.7% for pt<2 GeV/c pt/pt ~ 3 % at 100 GeV/c

pt(GeV/c)

35

ALICE performance on 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


Mass resolution

Mass resolution ~3 MeV/c2

0.6<pt<0.8 GeV/c 1.0<pt<1.1 GeV/c

1.6<pt<1.8 GeV/c 2.0<pt<2.1 GeV/c

K*(892)

(1020)

Mass resolution ~ 1.3 MeV/c2


Invariant mass (GeV/c2) Invariant mass (GeV/c2)

K*(892)0

Invariant mass (GeV/c2)

Short-lived resonances in ALICE

Pb-Pb events studied for PPR


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

Now several activities are going on in ALICE concerning the study of such resonances in pp collisions (using PDC06 events).

In particular, resonances reconstructed by their hadronic decay are studied in PWG2. Reconstruction of (1020) by its e+e- decay has also been probed. Catania people have expecially worked on reconstruction of:

•Software code development

•Test distributed analysis of events

•Optimization of reconstruction tools

•Background estimation

•Efficiency evaluation

Study of short-life resonances in ALICE

Started study of +- correlations

In next talk results obtained in p-p simulated

events at 900 GeV and 14 TeV


Φ(1020): signal 5.00 Tp 15.0 Tp 5.11 Tp

25.1 Tp 5.22 Tp 35.2 Tp

5.33 Tp 45.3 Tp

Background estimation

35.2 Tp

For K*(892)0 BAD agreement between background

estimated by event-mixing technique and true

background

35.2 Tp

Jet-like azimuthal correlations in -K pairs generated in

PYTHIA events at 14 TeV.


1

2

Summary

•Many interesting results on short-lived resonances from SPS and RHIC

•ALICE performances (tracking and PID) give us the possibility to do well this kind of physics

•We are working to be ready to analyze first data

EXTRA SLIDES

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

pT= 0 - 0.5 pT= 1.5 - 2

pT= 3.5 - 4

p-p@14 TeV

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

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

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

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

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

K*


Found K*(±2)=89182

True K*(±2)=85360

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

(1020)

(1020)

(1520)

(1520)

Mass resolution 1.2 MeV


True =4893

Found =4967

True *=3879

Found *=3649

• HIJING events with a realistic simulation of detector response

• Use ω and K*0 shape from HIJING to fit the data

• K*0 signal is fixed using STAR measurement

ρ0(770) π+ π-

STAR Preliminary

ρ0

sNN = 200 GeV

K0S

π+ π-

K0S

ω(782) (π+ π-) π0 and π+ π-

ω η (π+ π-) π0 and (π+ π-)

η’ (π+ π-) η and (π+ π-) ρ0η + η’K*(892)0 K π with K misidentified as πK*0 + K*0

misidentified

π+π- Invariant Mass Distribution from Monte Carlo

K*(892)0: like-sign / “true” background

5.00 Tp 15.0 Tp 5.11 Tp

25.1 Tp 5.22 Tp 35.2 Tp

5.33 Tp 45.3 TpGood agreement in all bins of pT

K*(892)0: event mixing / “true” background

5.00 Tp 15.0 Tp 5.11 Tp

25.1 Tp 5.22 Tp 35.2 Tp

5.33 Tp45.3 Tp

BAD agreement except for bins of very small pT

φ1φ2 correlations for πK pairs

25.1 Tp 5.22 Tp 35.2 Tp

ρ0 Mass

• Mass shift observed for all systems• Systematic errors shown for Minimum Bias d+Au 200

GeV

STAR Preliminary

Λ* signal

Formation of hadronic resonances (from jets)

in a chiral medium

side 1

side 2

near

away

Low pt High pt Near side No medium or

late hadronic medium

No medium

Away side Late hadronic medium Partonic or early hadronic medium (depend on formation time) CSR ?

Side 1 & 2 Late hadonic medium Early hadronic medium

Formation time arguments:a.) General pQCD:Formation time [fm/c] ~ pT [GeV]Formation time [fm/c] ~ 1/massb.) Specific string fragmentation (PYTHIA) formalism:Gallmeister, Falter, PLB630, 40 (2005)Intermediate pT resonances form earlyc.) Vitev et al. (hep-ph/0611109): High pT heavy particles and resonances form early

Need to determine the right momenta for trigger and resonance particle

study of short-lived resonances in alice a. badal à – infn sezione di catania contents physics...

Documents

resonances peak

resonances andor

interactions of resonances

yields of resonances

regenerated resonances

fireball medium resonances

hadronic medium

fisica alice lnf