Strangeness analysis in ALICE

Strangeness analysis in ALICE

o genuine p+p physicso PbPb physicso analysis status, studies in PPR2o prospects

K0s and hyperons

Ludovic Gaudichet, INFN TorinoVietri sul Mare 30/05/2006

p+p analysis

29/05/2006 - Vietri sul Mare

Ludovic Gaudichet INFN, Torino 3

p+p collisions at LHC

Yields and pt spectra at mid-rapidity of K0s, Λ, Ξ and Ω and their anti-particles

Baryon asymmetry :Is the baryon number carried by gluons also ? (comparison to gluonic baryon junction models) Particle production mechanisms, in soft / intermediate / hard regimesBeside gluons, u and d, strange quark is the only component of low pt multiparticle interaction which is statistically significant

- comparison with pythia, HERWIG, ...- minimum bias / underlying events- Λ/Λbar and jets

Feed-down corrections : needed to determine yield of proton ! Comparison to thermal models, interesting by itself and will serve heavy ion analysis Baseline for the analysis of heavy ion collisions

2A

p+p analysis



“day one” analysis

Provided that we understand our detector, we could publish : K0

s yield and spectrum at mid-rapidity Rough yields of Λ and Λbar

130 Λ

Already interesting for constraining pythia and understanding baryons production mechanisms

Estimation with pythia 6.2 and ATLAS tuning.Could be more !

104 events

p+p analysis



Results of first run 7.107 events (200h at 100Hz)

K0s yield and spectrum at mid-rapidity

Λ and Λbar yields and pt spectra up to pt = 8 GeV/c Ξ and Ξbar yields and pt spectra up to pt = 4 GeV/c 190 Omegas ... or hopefully more !

926k Λ 19k Ξ

p+p analysis

PbPb analysis



Strangeness enhancement

Tounsi et al.

PbPb analysis

B. Hippolyte,Moriond 2004



Strangeness enhancement

J. Rafelski

Statistical Equilibrium / non-equilibrium ?Difficult to know at RHIC, but big difference at LHC :

However :• Hard processes will compete with soft processes. 2 sources of strangeness, one equivalent to p+p !

• In p+p an increase of the volume could also gives some more phase space for strangeness production !

• Canonical to Grand Canonical transition still have to be there !?

• Scaling with Nbin ?

PbPb analysis



Intermediate transverse momentum

between soft (hydrodynamics) and hard (pQCD) regimes 2-3 GeV/c and 6-7 GeV/c at RHIC

Little known, between collective effects and hard scatteringa lot to learn about hadronisation and its dynamics

What :

Why :

PbPb analysis



Intermediate pt PbPb analysis

Constituent quark scaling :

P.R. Sorensen QM05 talk



Rcp in heavy ion collisionsperipheral 2 centralbinary T

CP central 2 peripheralbinary T

N /

N /

d N dp dyR

d N dp dy

PbPb analysis

K0s and hyperons in

ALICE



2nd vertex reconstruction

K0s -

DCA to primary vertex

Daughter DCA

Angle between V0 momentum and primary vertex

-

V0 cuts, selecting Λ

Bachelor DCA to primary vertex

DCA V0-Bachelor

4 parameters 5 parameters

Angle between cascade momentum and primary vertex

+ vertex radius +



Performance of topology reconstructionin PPR2 : p+p collisions

Even without charged track PID !No limit in pt other than statistic !



Effect of event multiplicityIn p+p collisions the reconstruction rate is a function of the multiplicity :

Small dependence from the primary vertex resolution + pt hardening of hyperon spectra

in PPR2 : p+p collisions



Reconstruction factors & raw spectra 109 eventsin PPR2 : p+p collisions



Reconstruction in PbPb collisions

Λ

Ξ

Ω

in PPR2 : PbPb collisions



Raw spectra in PbPb at 5.5 TeVin PPR2 : PbPb collisions

Λ

Ξ

Ω



Signal selection by the LDA

LDANeural netClassical cuts

LDA is :Faster than anything else, more reliable than neural networks Significance increases by 20% Amount of selected signal increases by 60%

Λ Ξ

Linear Discriminant Analysis+ succession of cuts in the n-dim space of parameters



Conclusion Hadron production at LHC energy Baseline for the analysis of heavy ion collisions

Soft physics : thermal production, hydrodynamics a perfect fluid at LHC ? Strangeness is a good probe

Intermediate transverse momentum : key regime for the understanding of the collision dynamics large portion of produced particle at LHC striking advantage of Strangeness

Analysis of K0s and hyperons tested in p+p and PbPb collisions

Strange objects (V0 and cascades) available for any analysis like tracks Room for improvement : Linear Discriminant Analysis Next Data Challenge on the way : preparing analysis of p+p ! Analysis code within the PWG2 of ALICE : to be discussed ...

p+p

PbPb

Backup slides



To do next : Physics Data Challenge 06Lacks in PPR2 : systematic from the primary vertex resolution

full study of Omega reconstruction efficiency

What PDC 06 will provide :

• 108 events• More realistic simulations

• calibration (dead channels, mis-alignment, ...)• Trigger simulation

Ξ reconstruction rate, scaled by the difference seen in PbPb

Last Data Challenge : test of the analysis speed and the CPU requirement !



Event cocktail for PDC 06PDC 06

Minimum bias events, as defined by pythia 6.2, ATLAS tuning Events enriched with Ω and Ωbar

Have enough statistic Compensate for pythia possible underestimation of strangeness75000 enriched events with Ω, 75000 with Ωbar

STAR

UA5

SPS

Pythia6.36.2

bar

√s

dN/dy (-0.5<y<0.5)

K0s

SPS

CDF

STAR

UA5

Pythia

6.36.2

√s



Event cocktail for PDC 06PDC 06

Minimum bias events, as defined by pythia 6.2, ATLAS tuning Events enriched with Ω and Ωbar

Have enough statistic Compensate for pythia possible underestimation of strangeness75000 enriched events with Ω, 75000 with Ωbar

SPS

RHIC

Pythia

6.2

6.3

√s

K0s, Λ and Ξ estimation are

acceptable, but Ω



Baryon excess : Λ/K0s

• Low pt limit can be define by the validity range of Hydro.

• At high pt limit, the baryon and meson should merge again.

• BUT seen in p+p too ! (UA1 & CDF)

PbPb analysis



Λ/K0s in pythia



<pT> versus mass in p+p at RHIC



thermal particle production



RAA in heavy ion collisions

We can also do RAA

Several effects here :• shadowing at low pt• Cronin effect • strangeness enhancement• jet quenching

H. Caines, STAR

PbPb analysis



Azimuthal correlation at high pT

Strangeness analysis in ALICE

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