Prospects in ALICE for f mesons

Prospects in ALICE for mesons

Daniel Tapia Takaki (Birmingham, UK)

for the ALICE Collaboration

International Conference on STRANGENESS IN QUARK MATTER Levoca, Slovakia – June 2007

24th June 2007 - SQM Daniel Tapia Takaki (Birmingham) 2

Resonances in ALICE ALICE Detector & PID capabilities Simulation method & MC predictions signal and background predictions Conclusions

Structure of Talk


Resonances in ALICE• ALICE is a general-purpose heavy-ion (HI) experiment designed to study the

physics of strongly interacting matter and the Quark Gluon Plasma (QGP) in nucleus-nucleus collisions at the CERN LHC.

• Resonances are a useful probe with which to study the QGP. (see Wed afternoon session).

• ALICE will allow the study of resonance production in pp and Pb-Pb collisions.

• This talk is devoted to the prospects of meson production

at the ALICE experiment.

ALICE: Physics Performance Report, Vol. II. B. Alessandro et al., ALICE Collaboration. J. Phys. G: Nucl. Part. Phys. 32 1295-2040, 2006. (See A. Badala talk on Thursday)


Interest in production

• Interesting due to its quark content. It is sensitive to strangeness production.

• It interacts weakly with non-strange hadrons in the hadronic phase due to its small cross section.

• Several theoretical predictions suggest changes in the mass and width due to medium-induced effects.

• The in hadronic and leptonic mode. The dileptons will have a different medium interaction. Proposed as a probe of chiral symmetry restoration.


Interest in production in pp collisions

• Production of the can be measured early in the running of LHC, because of its narrow width, which gives it good S/B.– Interesting for itself, as

one more hadronic measurement. Could be done at several energies.

measurements not very high precision at Tevatron, so even “low” energy points from LHC startup are interesting.

M = 1019 ± 2 (stat) MeV/c2

=6.5 ± 0.7 (stat) MeV/c2

900 ->K+K - events

<Pt> vs μ

NΦ/Nh vs μ

T. Alexopoulos, et al., Z. Phys. C. 67, 411-416 (1995)

Tevatron experiment E735, √s = 1.8 TeV


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

The ALICE experiment

•ITS - Tracking, vertex finding and PID by dE/dx.

• Time Projection Chamber, used for tracking and particle identification (PID) by dE/dx.

•TRD – tracking and electron identification.

•TOF – Tracking and hadron identification by Time of Flight.

ALICE studies both pp and Pb-Pb collisions.


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

1 10 100 p (GeV/c)

TRD e / PHOS /

TPC + ITS (dE/dx)

/K

/K

/K

K/p

K/p

K/p

e /

e /

HMPID (RICH)

TOF

ALICE Particle Identification capabilities

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

Alice uses ~ all known techniques!


Detector simulation & MC predictions

• The simulation of the pp (Pb-Pb) physics is generated by PYTHIA (HIJING).

• The output is then passed to the ALICE simulation and reconstruction algorithm – using the ALICE offline computing framework known as AliRoot.

• Results from fast-simulation (pp) and detailed simulation (Pb-Pb) are presented.

PYTHIA’s prediction for pp mb at ALICE. Rapidity distribution for the meson at the generation level.


Background estimation

2212

21 ppEEminv

• A good estimation of the shape and size backgrounds is essential for the study of resonances measurement.

• Like-sign and mixed events are popular techniques.

• Both methods were implemented in AliRoot.

Mass (GeV/c2)

PYTHIA pp mb @ 14 TeV cms energy

4x106 events – No PID was used.

K+K- spectrum

~ 1 hr nominal run.Inv. Mass with no PID.


Background estimation (2)

• Same-event background

• Like-sign same-eventSame-event backgroundLike-sign same-event

• Same-event background

• Like-sign same-event

• Mixed event

• Either method works well. This agrees with reported results. Physical Review C 72 014903 (2005).

K+K- spectrum

K+K- spectrum

Ratio of same-event background to Like-sign same event inv. Mass.

2x106 events.



Mass Mass

Mass Mass

Sam

e ev

ent

Mix

ed e

ven

t K+K+ pairs

K-K- pairs

Background estimation (3)

•The ratio of same to mixed event for the K+K+ and K-K- pairs.

•The signal can be obtained subtracting the background from either method.

K+K+ pairs

K-K- pairs

Ratio of Like-sign same event to mixed event mass distribution.

Ratio of Like-sign same event to mixed event mass distribution.

PYTHIA pp mb @ 14 TeV cms energy2x106 events.


Like-sign

Signal – background subtracted


ΦK+K-

• 2 x106 PYTHIA mb pp events.• Fast-simulation results.• Perfect PID.

Background subtracted

• Reconstructed mass and width consistent with generated.

Number of found consistent with the number generated.


Results in Proton-Proton collisions with no PID

PYTHIA mb pp @ 14 TeV cms energy

• ALICE should be able to measure the meson early in the LHC running - even before the PID system become available.

Mass (GeV/c2)

2.4<Pt<2.6 GeV

ΦK+K-

K+K- spectrum

4x106 events – No PID was used.~ 1 hr nominal run.Inv. Mass with no PID.

2.4<Pt<2.6 GeV


meson in Pb-Pb collisions

• 4,000 HIJING central Pb-Pb events.• Detailed simulation method.• Perfect PID

ΦK+K-

K+K-spectrum

HIJING Pb-Pb @ 5.5 TeV~ 1/2 min nominal run.

Reconstructed transverse-momentum

K-

K+

K+K-


Conclusions• The ALICE experiment will allow the study of resonances in great detail. It

has excellent PID. A study of the meson in hadronic (and leptonic) decay channels will be possible.

• Like-sign and mixing-event were tested for background subtraction. They give consistent result.

• The analysis might be one of the first resonance measurements in ALICE because of its good S/B ratio.

• ALICE should be able to study the meson in pp collisions before the PID system become available.

• In Pb-Pb collisions the meson can also be measured (even with small statistics).

Prospects in ALICE for f mesons

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