alice physics by the tof/itep group
DESCRIPTION
ALICE physics by the TOF/ITEP group. S. Kiselev, for the TOF/ITEP group Short-lived resonances Motivation for f 0 , Δ ++ and a 1 analysis Estimations of S/B for pp and AA events Jet chemical composition study Motivation TOF for jet study Fast generators of direct photons - PowerPoint PPT PresentationTRANSCRIPT
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
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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
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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
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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
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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
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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.
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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
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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 %
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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
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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
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Jets: TOF PID performance
At first glance it is impossible to study high Pt with TOF
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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
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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)
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Jets: Azimuthal correlations
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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)
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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
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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
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GePP: resultsComparison with RHIC data Prediction for LHC
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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
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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
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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
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one can fit SPS data at high pt
one can fit RHIC data but with not reasonable parameters
Rates from QGP -1st order
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Perturbative thermal QCD applyingHard Thermal Loop (HTL) resummation
Phys.Lett.B510(2001)98
Rates from QGP -2nd order
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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
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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
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GeTP_QGP: prediction for LHC
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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
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• 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
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The TOF/ITEP group activity
ALICE physics PWG
1. Short-lived resonances PWG2
2. Jets composition PWG4
3. Direct photon generators PWG4