ALICE physics by the TOF/ITEP group

09.10.08 RRC "Kurchatov Institute", Moscow S.Kiselev 1

ALICE physics by the TOF/ITEP group

S. Kiselev, for the TOF/ITEP group Short-lived resonances

Motivation for f0, Δ++ and a1 analysis

Estimations of S/B for pp and AA events Jet chemical composition study

Motivation TOF for jet study

Fast generators of direct photons Promp photons Thermal photons in Hot Hadron Gas (HHG) scenario Thermal photons in Qurk Gluon Plasma (QGP) scenario

Summary


Short-lived resonances. Data and ALICE activity

a1(1260) π ~0.5 0.5

ρ0(770) π+ π- ~100 1.3 p+p/d+A/Au+Au -70 p+p/Au+Au

Δ++(1232) p π+ ~100 1.6 p+p/d+Au -40

f0(980) π+ π- 66 2.6 p+p/Au+Au

K*(892) π K ~100 4 p+p/d+Au/Au+Au -10 p+p/Au+Au

Σ*(1385) Λ π 88 5.5 p+p/d+Au/Au+A 0

Λ*(1520) p K 45 12.6 p+p/d+Au/Au+Au 0 p+p/Au+Au

Ξ*(1530) Ξ π ~100 21 p+p/d+Au/Au+Au 0

ω(782) π+ π- π0 89 23 p+p/d+Au 0

ω(782) π0 9 23 p+p/d+Au/Au+Au 0

ω(782) π+ π- 2 23

ω(782) e+e- 7 10-2 23 p+p/d+Au/Au+Au in prog.

Φ(1020) K+ K- 49 44 p+p/d+Au/Au+Au 0 p+p/Au+Au

Φ(1020) e+e- 3 10-2 44 p+p/d+Au/Au+Au in prog. p+p

channel B.R.(%) c (fm) RHIC data Δm (MeV) ALICE studies

Life Time


RHIC data: Masses and Widths

• No mass or width modification of η, ω, Φ, Λ*, Σ* or Ξ*

• Mass shift observed for K*, Δ++ and ρ0 at low-pT possible explanations

– π+ π- rescattering in p+p collisions

– Medium modifications

– Bose-Einstein correlations

• ρ0 at high-pT No apparent mass shift!

R. Rapp, Nucl.Phys. A725, 254 (2003), E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322

P. Fachini et.al., J.Phys.G33:431-440,2007

G.D. Lafferty, Z. Phys. C 60, 659 (1993); R. Rapp, Nucl.Phys. A725 (2003) 254-268

S. Pratt et al., Phys.Rev. C68 (2003) 064905

P.Fachini SQM07


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.

Recent suggestion by Maiani et al. (Phys. Lett. B645(2007)138) to use

this observable to solve the problem of the real quark composition of some resonances as the fo(980)( or

?)

][ ss ]][[ qssq

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

f0 motivation

09.10.08 RRC "Kurchatov Institute", Moscow S.Kiselev

5

Δ++ Mass and Width• Δ++ mass shift observed in both

minimum bias p+p and d+Au at √sNN = 200 GeV

• Width agrees with PDG for both systems within errors

• possible explanations: π+ π- rescattering in p+p collisions, P. Fachini et.al., J.Phys.G33:431-440,2007 PDG

PDG

Δ++ motivationP.Fachini SQM07


a1 motivation Volker Koch, workshop on dileptons at CBM, GSI,

2007: in the case of a full restoration of the symmetry the

spectral functions of the ρ meson and its chiral partner the a1 meson become degenerate.

it has been proposed to measure the a1 mass spectrum in a hot and dense medium and compare it to the mass spectrum of the ρ meson

If the degeneracy would be observed it is expected to serve as an unambigious experimental signal for the detection of chiral symmetry restoration in the hot and dense medium.


Input info and assumptions Before to study with AliRoot it is worth to make fast estimation Background: SHAKER events

dNch/dy = const pt distribution: π – fit to Tevatron data, others – mt scaling: dN/dpt

= [(mtπ +2)/(mt +2)]12.3 dNπ/dpt

K/π = 0.2, p/π = 0.074, /π0 = 0.17 Signal

dNres /dy = const, pt distribution – mt scaling Ratios weakly depend on beam energy and event centrality:

(dNres/dy)/ (dNch/dy) f0/ π- = 0.07 (STAR data) 0.0275 Δ++/p = 0.22 (STAR data) 0.0064 a1

+/ π+ = 0.013 (A.Andronic) 0.0051 Cut pt > 0.2 GeV/c, momentum resolution σp/p = 1% No matter between a target and TOF

optimistic estimation of the signals


p+p: S/B(2σ)resonance

m MeV

MeV

channel

BR (%)

dNres/dy

dNch /dy

accep (%) at pt=0.5

S/B (%) S √S+B

f0 980 70 K+K- 11 0.0275 ~28 8860/19327 = 45.9 52.8

f0 980 70 π+π - 52 0.0275 ~33 47121/1367900 = 3.4 39.6

Δ++ 1232 118 π+p 100 0.0064 ~20 12546/171398 = 7.3 29.3

a1+ 1260 400 π+γ 100 0.0051 ~2 1001/286866 = 0.35 1.9

a1+ 1260 150 π+γ 100 0.0051 ~2 1003/60616 = 1.7 4.2

a1+ 770 150 π+γ 100 0.0051 ~2 933/279455 = 0.33 1.8

very small signal from a1, even in p+p, S/B ~ 10-3 %


Au+Au: other centralities

S/B ~ (dNch/dy)-1

dNch /dy statistics S/B (%) S /√(S+B)

5 106 12546/171398 = 7.3 29.3

125 104 3150/1061100 = 0.3 3.1

500 103 1292/1677720 = 0.077 1.0

2000 102 498/2676780 = 0.019 0.3

Δ++ π+p


short-lived resonances: summary

Short-lived resonances: mass shift in p+p for some of resonances

estimations of signals from resonances f0, Δ++ and a1 with TOF/ALICE have been made:

- p+p: S/B ~ 10% (~0.004% for a1)

- Au+Au: S/B is smaller as S/B ~ (dNch/dy)-1, low signals from f0 and Δ++

- like-sign or event-mixing techniques should be used

- to have S/√(S+B) ~10, 105 events are needed

- S/B increases as a function of pt

Netx step: p+p simulations in the AliRoot package

Jets: motivation

Initial production at high-pT is calculable in perturbative QCD and can be calibrated by reference measurements

These partons will first travel through a dense color medium. They are expected to lose energy through collision energy loss and medium induced gluon radiation, “jet quenching”.

The magnitude of the energy loss depends on the gluon density of the medium and on the path length

gluon radiation

Use jets and high-pT particles to probe the medium

Goal: measure medium properties• Density, temperature, number of

degrees of freedom• Dynamical properties e.g. viscosity

However, we still need to calibrate our probe:• Fragmentation, hadronisation in the vacuum• … and in the medium• Calibrate/constrain energy loss mechanism• Check initial production rates

09.10.08 11RRC "Kurchatov Institute", Moscow S.Kiselev

Jets: TOF PID performance

At first glance it is impossible to study high Pt with TOF


Single inclusive hadron distribution vs Single inclusive hadron distribution vs ξξ

N. Borghini & U. WiedemannHep-ph/0506218

=ln(EJet/phadron)

Quenching effect: decreases of the particles at high z (low ) & increases of the particles at low z (high )

z = phadron/Ejet

Hump-backed plateau

Medium effects introduced at parton splitting

• ALICE should be well dedicated to test this range (tracking down to 100 MeV/c)• EMCal => improves Ejet determination

Fragmentation strongly modified at phadron~1-5 GeV/c even for the highest energy jets


M.Estienne. - PWG4 15. 01.2008

Jets: TOF can help to study jet modification

We can use high Pt (even not identified) charged particle or photon as a trigger and study accompanying particles!

Fragmentation strongly modified at phadron~1-5 GeV/c even for the highest energy jets. We even don’t need jet reconstructions: instead of z we

can use z’ = phadron/Eleading particle (need theoretical predictions!)

Fragmentation distributions should also depend on particle type. (need theoretical predictions!)

=>we need PID in this range to study jet chemical composition. (From RHIC data the p/π~1 at high Pt => we can even enlarge TOF PID range)


Jets: Azimuthal correlations


Jets: Azimuthal correlations

Lot of theoretical explanations of double away-side peak: deflected jet, large gluon radiation, shock waves (Mach cones), Cerenkov radiation

Long-range Δη correlation on the near-side (ridge): coupling of induced radiation to the longitudinal flow, turbulent color fields, anisotropic plasma, interplay of jet-quenching and strong radial flow…

Chemical composition of away side jet is different compare with trigger jet (fragmentation in vacuum)


Jets: summary ALICE TOF can be used for the jet composition study. Next steps:

Simulations on a generator (PYQUEN, HYDJET++, …) level: double peak, barion/meson ratio,… relative to leading particle energy distribution

z’ = phadron/Eleading particle or ’=ln(Eleading

particle/phadron)

analysis for different types of particles (π, K, p, φ…) Simulations in the AliRoot package



Prompt photons: pp data fit + binary scaling

PHENIX hep-ph/0609037

(√s)5 Ed3σ/d3p = F(xT,y) One can use a data tabulation of

the F(xT,y) to generate prompt photons.

A+B:

Ed3N/d3p(b)=

Ed3σpp/d3p AB TAB(b)=

Ed3σpp/d3p Ncoll(b)/σppin

Nuclear effects (Cronin, quenching, …) are not taken into account.

Realization: GePP.C macros for ROOT


GePP: resultsComparison with RHIC data Prediction for LHC


Bjorken -(1+1)-HydroDynamics (BHD)

Proper time and rapidity y Phys.Rev.D27(1983)140

There is no dependence onLorenz boost variable y:

Landau hydrodynamical model, viscosity and conductivity are neglected


Photon spectrum in BHDPhoton spectra follow from convoluting the photon production rates with the space–time evolutionFor a longitudinally expanding cylinder

For proper time and rapidity y`

For an ideal gasMain parameters: initial 0 , T0 and Tf (at freeze-out)

Connection with the local rest frame

Input function – production rate E dN/d4xd3p (E,T)

Phys.Rep.364(2002)98

0 ↔ yield, T0 ↔ spectrum slopeTf ↔ weak sensitivity, Tf = 100 MeV


Rates: HHG scenario

C.Song, Phys.Rev.C47(1993)2861 an effective chiral Lagrangian with π, ρ and a1 mesons to calculate the processes ππ →ργ , πρ → πγ, and ρ →ππγ .

C.Song and G.Fai, Phys.Rev.C58(1998)1689.

parameterizations for photon rates.

Realization: GeTP_HHG.C macros for ROOT

GeTP_HHG: SPS and RHIC dataSPS RHIC


one can fit SPS data at high pt

one can fit RHIC data but with not reasonable parameters

Rates from QGP -1st order


Perturbative thermal QCD applyingHard Thermal Loop (HTL) resummation

Phys.Lett.B510(2001)98

Rates from QGP -2nd order


Thermal photon production in the QGP is a non-perturbative mechanism that can not be accessed in perturbative HTL resummed thermal field theory

2-loop contribution is the same order in αs

3-loop ….

One must consider the QGP rates as an educated guess. PL B510(2001)98

Rates from QGP


Annihilation with scattering (aws) dominates at high E

The Landau-Pomeranchuk-Migdal (LPM) effect (not taken into account in out study) reduces the 2-loop rates by ~30% in E/T > 1

Realization: GeTP_QGP.C macros for ROOT

GeTP_QGP: SPS and RHIC dataSPS RHIC


GeTP_QGP: prediction for LHC


2+1 hydro, F.Arleo, D. d’Enterria, D. Peressounko, nucl-th/0707.2357

The same τ0 , T0: steeper HHG spectrum in 1+1 due to radial flow in 2+1

Direct photon generators: summary


• 3 fast generators of direct photons have been proposed: - GePP.C – prompt photons (pp data fit + binary scaling) - GeTP_HHG.C – thermal photons in the HHG scenario - GeTP_QGP.C – thermal photons in the QGP scenario in Bjorken (1+1) hydrodynamics + other assumptions: ideal massless gas, µq =0, 1st order phase transition• One can fit SPS and RHIC data• Predictions for LHC• Next steps: implement the generators into AliRoot package, take in account the LMP effect, …

Summary


The TOF/ITEP group activity

ALICE physics PWG

1. Short-lived resonances PWG2

2. Jets composition PWG4

3. Direct photon generators PWG4

ALICE physics by the TOF/ITEP group

Documents

Transcript of ALICE physics by the TOF/ITEP group