A.Belogianni, P.Ganoti, M.Spyropoulou-Stassinaki University of Athens for the ALICE collaboration

1117/4/200817/4/2008 [email protected]@HSSHEP2008

Comparison of Kaon identification through central barrel detectors signals, with the kink topology in

ALICE experiment at CERN

A.Belogianni, P.Ganoti, M.Spyropoulou-Stassinaki

University of Athens

for the ALICE collaboration


Outline

The ALICE experiment at CERN : physics goals

Kaon ID and spectra using the central barrel detectors signals

Kaon ID and spectra using the “kink” topology

Comparison of the two methods

Future plans


The ALICE detector

ITSLow pt trackingVertexing

ITSLow pt trackingVertexing

TPCTracking, dEdxTPCTracking, dEdx

TRDElectron IDTRDElectron ID

TOFPIDTOFPID

HMPIDPID (RICH) @ high pt

HMPIDPID (RICH) @ high pt

PHOS,0 PHOS,0

MUON -pairs MUON -pairs

PMD multiplicityPMD multiplicity


Physics GoalsStudy of the QGP which is predicted by QCD at extreme conditions of high energy density, achieved in relativistic heavy ion collisions. Signals of QGP may remain in the bulk properties of the collision, and simultaneous observations of multiple QGP signals in the final state would serve as a strong evidence of QGP formation.

The bulk properties include: strangeness baryon production rates collective transverse radial flow

All these can be studied via particle spectra

The study of particle yields and spectra in low, intermediate and hard pT regions is essential in order to distinguish among the various models which aim to describe the particle production.

Test of various models where it is argued that

particle multiplicity density per transverse area of interaction measures the initial gluon density

particle ratios measure the chemical freeze-out conditions

transverse momentum spectra measure the kinetic freeze-out conditions

resonances probe the time interval between chemical and kinetic freeze-out


Pb-Pb

Hadronization: Hadrons are formed from quarks

Chemical freeze-out: end of inelastic interactions (particle yields)

Thermal freeze-out: end of elastic interactions (particle spectra)

Λ(1520)p

πK-

Rescattering

Κ-

p

Λ(1520) K-

pRegeneration

Signal lost

spac

e

time

Signal measured

Resonance Life-time [fm/c] 1.3++ 1.7 f0(980) 2.6 K*(892) 4.0 (1520) 13 ω(783) 23(1020) 45

Resonances may probe the timescale between chemical and kinetic freeze-out


ALICE Particle Identification capabilitiesALICE Particle Identification capabilities

Particle ID from low to high momenta. ALICE can combine the single detector PID information.

ALICE uses ~ all known techniques!

TPC + ITS (dE/dx)

HMPID (RICH)

TOF

1 10 100 p (GeV/c)

TRD e / PHOS /0

/K

/K

/K

K/p

K/p

K/p

e /

e /

0 1 2 3 4 5 p (GeV/c)


Kaon is the lightest strange hadron, with a high branching ratioto the muonic decay channel ( 63,26%) and large geometrical acceptance in the ALICE TPC. This decay can be measured as a “kink”. The reconstruction of the kink topology (secondary vertex with mother and daughter tracks of the same sign) is a key technique for identifying kaons over a momentum range wider than that achieved by combining PID signals from different detectors.

Background of kinks in kaon study are the kinks from pion decays, hadronic interactions in the TPC gas and combinatorics.

The kink topology is important in both Pb-Pb collisions and pp interactions.

K / π identification-separation is based on the different kinematics of their decays to μ+νμ.

K/π separation from kinematics

17/4/200817/4/2008 [email protected]@HSSHEP2008 88

K μνμ 63.43%

Κ ππ021.13%

Κ eπ0νe 4.87% kinks

Κ μπ0νμ 3.27%

Κ ππ0π0 1.73%

Κ πππ 5.58% 3 prong decay

π μνμ 99%

Branching Ratios


Variables like the lab decay angle at a given momentum of the mother particle (K or π) and the qT of the produced daughter muon may be used for K/π separation.

The momentum of the daughter muon in the K/π rest frame is 236 and 30 MeV/c respectively.

This is the maximum qT value of the muon in the Lab frame.

Mother Momentum (GeV/c)

red : Kμ+νμ

blue: πμ+νμ

restrestrest

restrestlab Ep

p*** cos

sintan


Event sample and track selection

1.16 M simulated pp events (s=14 TeV), generated in the frame of the ALICE Physics Data Challenge 2006 (PDC06) have been analyzed at CERN Analysis Facility (CAF).

Track selection cuts :

Track quality cuts

pT > 0.3GeV/c

Cut of 3σ on the impact parameter to select primary tracks


Combined PID from TPC and TOF

When several detectors are capable of separating the particle types, their contributions are accumulated with proper weights, thus providing an improved combined PID.

In the case of Kaons, combining the PID signals from TPC and TOF :

Kaon momentum spectrum (TPC and TOF)


PID using the kink topology

Next step : try to include the kinks in the PID procedure.

Study of the kink sample

- Each reconstructed track is checked whether it is a kink or no.

- If yes, the appropriate cuts are applied in order to obtain a clean sample of kaons.

Cuts to select Kaon kinks:

The kink angle must be greater than the maximum decay angle of the decay πμνμ but less than the corresponding angle for the decay Kμνμ.

The qT > 50MeV/c

The kink vertex is between 110 cm and 230 cm (in the active volume of the TPC).

|η| < 1.1

The invariant mass considering the daughter as a muon is less than 0.6 GeV/c2.


This procedure, after being implemented in reconstructed tracks, will either adds kaons in the corresponding sample, not recognized by the combined PID procedure, or correct those tracks for which the combined PID procedure has assigned wrong particle type.


The kink method for kaon identification looks very promising at intermediate momentum regions (p > 2 - 6 GeV/c) after accumulating enough statistics.


In numbers...

In 1.16 M events we have (0 - 7 GeV/c):

655687 generated kaons in the detectors acceptance

336418 are recognized via combined PID

From the sample of tracks recognized as kinks:

70824 are true kaons

31597 are recognized via combined PID

69728 are recognized by applying the kink cuts


Future Plans

Analysis of the new simulated dataset (PDC07) available where ITS and TRD are added to the combined PID procedure.

Implement the kink analysis in the Λ(1520) study (the group has already published results with the standard PID procedure). An increase of the signal of ~16% is expected from preliminary calculations.

Study of other observables concerning Resonances Study

- Transverse momentum and transverse mass spectra- Particle Ratios (Resonant over no Resonant particles)


For a detailed description

Estimation of Kaon and Pion Yields from the decay Kaon/pion to muon + muon neutrino kink topolgy, in one year of Pb-Pb for ALICE

ALICE-INT-2006-012

Study of Λ (1520) resonance in pp interactions at ALICE and K identification from its decay in muon+neutrino

http://www.ct.infn.it/SPHIC06/

Study of Λ(1520) production in pp interactions at 14 TeV with the ALICE detector

J. Phys. G: Nucl. Part. Phys. 35 (2008) 401 – 407

Talks in collaboration meetings can be found at

http://aliceinfo.cern.ch/Collaboration/Meetings/index.html

(ALICE Weeks and Physics Working Group 2 – Soft Physics)


Backup


Combined PID procedure

Having to combine the PID information coming from different detecting systems implies dealing, in some common way with PID signals of a different nature.

The situation is additionally complicated by the amount of data to be processed.

Thus the particle identification procedure should be as much as possible automatic and should also be capable of combining signals distributed according to quite different density functions.

Combining PID signals in a Bayesian way satisfies all these requirements.

First, the Bayesian PID with a single detector is taken from the detectors response functions.

Then, the method is extended for combining PID measurements from several detectors, thus considering the whole system of N contributing detectors as a single “super-detector”.

A.Belogianni, P.Ganoti, M.Spyropoulou-Stassinaki University of Athens for the ALICE collaboration

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Transcript of A.Belogianni, P.Ganoti, M.Spyropoulou-Stassinaki University of Athens for the ALICE collaboration