study of the k*(892) 0 signal in pp alice events

3/12/2003 ACAT03 - Giuseppe Lo Re

Study of the K*(892)0 signal in pp ALICE

events

Giuseppe Lo Re Giuseppe Lo Re INFN-CNAF, Bologna (Italy)INFN-CNAF, Bologna (Italy)

ACAT03, 12/3/2003ACAT03, 12/3/2003


SummarySummary

Physics motivationsPhysics motivations Computing tools Computing tools ALICE simulations for pp collisionsALICE simulations for pp collisions Conclusions and outlookConclusions and outlook


Physics motivationsPhysics motivations


Resonance

Mass c (fm) Decay

(770) 0.769 1.3 +-

(782) 0.783 23 +-

K*(892)0 0.896 4 k+-

f0(980) 0.980 2- 4.9 +-

(1020) 1.019 44 kk Modifications of properties of mesons Modifications of properties of mesons

resonances and their production rate resonances and their production rate give information on the nuclear give information on the nuclear medium and possible QGP phase medium and possible QGP phase transitiontransition


Resonances which decay into strongly inte- racting hadrons may not be reconstructed due to rescattering of daughters inside the system.

The study of such resonances may also probe the role of the rescattering phase between chemical freeze-out and kinetic freeze-out (regeneration mechanism)

Finally, the study of K*(892) is also interesting due to its strange quark content.

Combined measurements of K*(892) and mesons are particularly useful in this respect.


K0*(892) signal in

Au+Au @ snn=130 GeV

(STAR Collaboration)

K0*(892) signal in

Pb+Pb @160 AGeV (NA49 Collaboration)


AliRoot/ROOT framework for simulation and analysis

550 Pb+Pb HIJING (peripheral) events 4x104 PYTHIA pp minimum-bias events Full reconstruction in TPC+ITS Use of AliEN to handle pp events

Computing toolsComputing tools


We used AliEn used both for production, reconstruction and analysis of pp events for the reconstruction of the k*(892)0

AliEn is the ALICE implementation of a distributed computing infrastructure.

• 1% native code, 99% Open Source packages and perl modules

• used over about 30 sites

• during last years 16,000 jobs have been succesfully run uner AliEn and more than 20TB of data produced

http://alien.cern.ch


Production

Reconstruction


Example of jdl file used for our analysis jobsExecutable="Analysis.sh";Packages="AliRoot::3.09.07";InputFile="LF:/alice/cern.ch/user/g/glore/k0Starpp.C";Arguments="--macro k0Starpp.C";InputData={"LF:/alice/simulation/2002-04/V3.08.Rev.01/00005/*/galice.root", "LF:/alice/simulation/2002-04/V3.08.Rev.01/00005/*/galiceSDR.root", "LF:/alice/simulation/2003-02/V3.09.06/00147/*/tpc.tracks.root"};Split="event";OutputFile={"its.tracks.slow.root","its.clusters.slow.root","hm.root"};Email="[email protected]";

AliEn job submition system already incorporate the “job splitting” feature.


PYTHIA generates 1.7 K*(892)PYTHIA generates 1.7 K*(892)0 0 (14 TeV cms (14 TeV cms energy) with 70 k*energy) with 70 k*ππ-- combinations per event combinations per event

Several factors reduce them during Several factors reduce them during reconstrutionreconstrution Geometrical acceptance (-0.9<Geometrical acceptance (-0.9<ηη<0.9)<0.9) Branching ration of K*(892)Branching ration of K*(892)0 0 in in kk++ππ- - (2/3)(2/3) Tracking efficiency (overall for low pTracking efficiency (overall for low pTT tracks and tracks and

for kfor k++ which decay inside the TCP) which decay inside the TCP) At the end there are 0.02 K*(892)At the end there are 0.02 K*(892)0 0 (our (our

findable candidates)findable candidates) with 1.4 combinations with 1.4 combinations per eventper event

ALICE simulations for ALICE simulations for K*(892)K*(892)00


Ideal particle Ideal particle identificationidentification

After kinematical cuts:

Found K*(892)0/evt S/B (2) Rec.Eff. S/S+B

0.018 0.102 98 % 11.1

Kinematical cuts used:Angles of daughters w.r.t. parent: k < 2 rad, < 1 rad

K*(892)0/evt S/B (2) S/S+B 0.02 0.10 11.1

M=894.9±2.4

Γ=59.1±11.6


q(+)

q(-)

qt(-)

PK*(892)

qt(+)

ql(+)

ql(-)

ql(+) - ql(-)

ql(+) + ql(-) =

(, qt) pairs from different parent particles fall into different elliptical loci

Additional cut introduced by means of the Armenteros-Podolanski plot (, qt)


Armenteros Plot

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

-1 -0,5 0 0,5 1

alpha

qt

rho(770)

omega(782)

phi(1020)

k0s

Delta

Deltabar

Lambda

Lambdabar

K*(892)

K*(892)Combinatorial background

After cut on Armenteros:Found K*(892)0 /evt S/B (2) Rec.Eff. S/S+B0.014 0.146 79 % 8.9

Cut on Armenteros plot:

-0.12<α<0.67

0.25<qT<0.33


Particle identification open task in Particle identification open task in ALICEALICE

It has to combine information from It has to combine information from several subdetectors (mainly ITS, several subdetectors (mainly ITS, TPC, TOF, TRD)TPC, TOF, TRD)

We explored the worst scenario We explored the worst scenario considering all the possible pos/neg considering all the possible pos/neg pair combinations arising from pair combinations arising from ((ππ++,k,k++,p) x (,p) x (ππ--,k,k--,p) ,p)

Missing particle identificationMissing particle identification


The true combinations (left) are e embedded in a large combinatorial background and there is a strong contamination from other resonances, overall ρ(770) and ω(782).


Cuts used:• Armenteros:

-0.12<α<0.67 0.25<qT<0.33• p pos track p > 1.6 GeV/c

With these cuts we obtain S/B=0.06. To extract the signal we need to use the mixed events techiques.M=895±2 Γ=59±11


Conclusions and outlookConclusions and outlook We carried out a detailed simulation study of

K*(892)0 in pp collisions at 14 TeV in the c.m.s. The two extreme hypotheses have been considered

as far as particle identification is concerned Even without PID and with a no so large amount of

events K*(892)0 study is feasible in ALICE AliEn has been successfully used both for

production and analysis

To be done: Increase statistics profitting by next ALICE

production (ADC will start at the beginning of 2004) Check how PID will affect the pp results


STAR results @ 200 AGeV

Quark Matter, 2002

pp

Transverse mass spectrum, yields and particle ratios extracted from the data.

Results from STAR point out that no reduction of such resonance is observed in AA collisions despite expected losses due to rescattering effects.


No. of K*(892)0 in central (b=3 fm) Pb+Pb collisions vs energy


b (fm) K*(892)0/evt Ratio signal/combinatorial

11 11101110 1.3 x 10-6

22 940940 1.5 x 10-6

55 710710 2.1 x 10-6

77 500500 2.9 x 10-6

99 290290 4.9 x 10-6

1111 100100 1.5 x 10-5

True pairs vs combinatorial background as a function of b

Ratio k*/combinatorial

0,00E+00

5,00E-06

1,00E-05

1,50E-05

2,00E-05

0 5 10 15

b (fm)

Rat

io Serie1


After reconstruction:

pt-range Findable K*(892)0 /evt S/B (2))

> 0 6.0 5 x 10-4

>3 GeV/c 0.5 5 x 10-3


Before cuts: S/B = 5 x 10-3

True signal

All pairs


Closest distance between tracks

All pairs True signal


Momenta of daughters

All pairs

True signal


Summary of cuts for Pb-Pb:

Transverse momenta of daughters: p > 1.5 GeV/c

pk > 1.7 GeV/c

Impact parameters of tracks: d,k < 150 m

Closest distance between tracks: dpn < 200 m

Angles of daughters wrt parent: k < 0.14 rad, < 0.3 rad

Relative angle between tracks: rel < 0.5 radOverall effect of cuts:

S/B from 0.005 to about 0.1

0.14 K*(892)/evt 27% rec. efficiency


Combinatorial background evaluated by the mixed event spectrum


Evolution of difference signal with the statistics


Centroid at (0.887 0.017) GeV/c2

S/(S+B) = 2.5 for 550 events


True signal

Addition of Armenteros cut:

0.07 K*(892)/evt

S/B = 0.23

Rec.Eff = 15%


Invariant mass spectra

All pairs

True signal


S/(S+B) = 2.7 for 550 events


True signal Overall signal

= (52 ± 2 ) MeV = (60 ± 10 ) MeV

Verificare se conviene metterla

study of the k*(892) 0 signal in pp alice events

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