High Pt physics at ALICE PWG4 – High Pt and photons. Excited RHIC results QM2008 – high Pt physics ~ 50%

main RHIC finding (QM2008 – Shuryak) Strong radial and elliptic flows are very well described by ideal hydro => ``the most perfect liquid known Strong jet quenching, well beyond pQCD gluon radiation rate, same for heavy charm quarks (b coming) Jets destroyed and their energy goes into hydrodynamical ``conical flow

Motivation Initial production at high-p T 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. gluon radiation Use jets and high-p T 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

Usually people distinct three Pt regions: – bulk (Pt < 2 GeV) – seems to be driven by thermal properties of the matter. – high Pt > 6 GeV – measured particle spectra are well described by pQCD calculations (except jet quenching effect ). One can use them as hard trigger. – intermediate region – most interesting effects of hard particles (partons) interactions with media. Different theoretical models (jets + recombination/coalescence mechanism), situation is not clear.

Jet quenching

Enhancement of barion production

Enhancement in strange barion production

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…

N. Borghini & U. Wiedemann Hep-ph/ = ln(E Jet /p hadron ) В 2008 г. планируются Монте-Карло симуляции для изучения способности детектора TOF детально исследовать оба эти эффекта для разных типов идентифицируемых частиц. Важна способность детектора идентифицировать частицы, сопровождающие рождение струй и жестких фотонов. 2. Фрагментация сильно изменяется для адронов ~1-5 GeV/c даже при высоких энергиях струи (quenching effect) 1.Азимутальные корреляции. Данные RHIC показывают, что они зависят от типа частиц.

Conclusion The jets at intermediate Pt of few GeV have been shown to be significantly modified in the both their particle composition and their angular and fragmentation distributions compare to p+p collisions. High Pt trigger particle provides additional parameter (direction and momentum of this particle) for such investigations of interactions between hard scattered partons and the medium. ALICE TOF is the relevant detector for this high Pt physics. We need both theoretical and experimental researches in this area.

As compared to jet physics at RHIC, there are two fundamentally new features in central Pb–Pb collisions at the LHC: 1)The multi-jet production per event is not restricted to the minijet region Et < 2 GeV but extends to about 20 GeV 2)Jet rates are high at energies at which jets can be distinguished from the background energy of the underlying event. Hence, event-by-event reconstruction of jets with reasonable energy resolution will be possible.

What should be done? Fragmentation calculations and measurements – relative to leading particle energy z = p hadron /E leading particle or =ln(E leading particle /p hadron ) – for different types of particles (π, K, p, φ…) Different angular correlations of different types of particles, with respect to jet direction, reaction plane etc. Estimation of background from underlying events

Прямые фотоны – пробник кварковой материи Данные PHENIX: γ прямые – h азимутальные корреляции 1.Near side yield ~ 0 small fragmentation photon yield 2.Hint of away side modification (suppressed) in AuAu! (rad) В 2008 г. TOF/ALICE группа ИТЭФ планирует: 1.создание генераторов прямых фотонов 2.изучение с помощью симуляций γ прямые – h корреляций c TOF идентификацией адронов в области р Т = 1 – 4 ГэВ/с 1/N trig dN/d

Resonances φ – meson is of particular interest because – in case of QGP strong enhancement is expected – small cross section of φ interaction with hadron gas – possible bright effect of double mass peak TOF can identify φ up to Pt=4-5 GeV/c Resonances properties (yields, spectra, width, mass) could be different in medium The resonances which are unaffected by the hadronic medium have to be used

Φ Production K + K - and e + e - The leptonic channel yield is a little higher than hadronic channel More accurate measurement is required to confirm whether there is branch ratio modification e+e-e+e- K+K-K+K-

φ – meson angle correlations Such effects probably are enhanced in jet production, as soon as this is a trigger on early stage of reaction.

φ – meson azimuthal correlations

Backup files

28 RHIC – a cartoon (QM Richard Seto – summary of exp. results) hard processes pre-equilibrium (CGC?) Cross over – distinction between hadrons and quarks is ambiguous – q* – But correlations increase - DOF hard to think about partonic thermalization partons cooling – elliptic flow develops hadrons more distinct hadrons cool/decouple radial flow develops q q ee q* q * ee or π * π * ee ππ ee ee means ee (PHENIX/STAR) or μμ (Na60/PHENIX) Tc ~ 190 MeV T time Ti=? sQGP 9fm (?imaging) Paradigm switch that is hard for my brain

QM2008 Prof. Brian A. Cole, Columbia Univ.