High Pt physics with TOF ALICE

B.V.Zagreev

Bologna - 22.01.2008

Outlook

• High Pt physics motivation

• Why TOF is relevant detector for this physics?

• RHIC results

• Conclusion

• ITEP group activity

Motivation

• Investigation of early stage of hot & dense matter evolution

• 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

2ˆLqCE Rs

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

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

M.E. - ALICE PWG4 meeting - CERN January 15. 2008 - 3

• 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

How to use TOF ALICE for high Pt physics?

• 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 (TOF) range – From RHIC data the p/π~1 at high Pt

=> we can enlarge TOF PID range

• Actually we have got additional parameter – leading particle momentum vector and now can measure identified particle with respect to this direction (and reaction plane).

What we know from RHIC?

• 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

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…

• PID in this range (few GeV) can clarify situation => we have wide field for activity

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-

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

What should be done?

• Fragmentation calculations and measurements – relative to leading particle energy z’ = phadron/Eleading particle or ’=ln(Eleading particle/phadron)

– 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

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.

ITEP group activity

• Simulation of residual correlations in strange particles femptoscopy with TOF (ALIFEMTO package) (Mikhailov, Stavinsky)

• Short living resonances feasibility studies (Kiselev)

• Direct (thermal & prompt) photons generator for ALIROOT (Kiselev)

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