ALICEALICE ExperimentExperiment @@ LHCLHC
A Large Ion Collider Experiment dedicated to heavy-ion collisions however, running also pp program zPhysics motivation zExperimental conditions zPhysics performance
5 October 2005 Physics Programme of ALICE Experiment K.Safarik 1 WHY HEAVY IONS AT THE LHC? ... factor ~30 jump in √s ...
J. Schukraft QM2001: hotter - bigger -longer lived
Central collisions SPS RHIC LHC
s1/2(GeV) 17 200 5500
3 dNch/dy 500 850 2–8 x10
ε (GeV/fm3) 2.5 4–5 15–40 εLHC > εRHIC > εSPS V (fm3) 103 7x103 2x104 Vf LHC> VfRHIC> Vf SPS f
τLHC > τRHIC > τSPS τQGP (fm/c) <1 1.5–4.0 4–10
τ0 (fm/c) ~1 ~0.5 <0.2
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 2 LHC Energy For A-A collisions:
Ecms = 5500 A GeV 2 7 Elab = Ecms / (2A mN) = 1.61 × 10 A GeV 9 12 for lead ions Elab Pb-Pb = 3.35 × 10 GeV = 3.35 × 10 MeV
Further we need Harald Fritzsch Identity (definition of Anglo-Saxon pound £AS) -30 2 × 10 £AS = me (= 0.511 MeV) and some other definitions (gravitational acceleration g, g = 1 in/tr2 (1 s = 19.65 tr, trice) (speed of light c) c = 6 × 108 in/tr 2 -14 mec = 72 × 10 £AS in (= 0.511 MeV)
-12 1 MeV = 1.41 × 10 £AS in Finally
Elab Pb-Pb = 1 £AS × 4.7’’ (= 0.45 kg × 12 cm)
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 3 LHC Energy (cont.) And for pp collisions:
Elab pp(14TeV) = 0.15 £AS in ≈ ¼£AS × ½’’ = ⅛ £AS × 1’’ = …
For those who don’t like to be seated on a lead ion (and to fly inside LHC vacuum pipe) 9 Ecms Pb-Pb = 5500 A GeV = 1.14 × 10 MeV (HFI, etc.) -3 Ecms Pb-Pb = 10 £AS × 1.6’’ (= 0.45 g × 4 cm)
Still, macroscopic energy !!! (one can actually hear it)
But the size of ions is by factor more than 10-12 smaller
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 4 Novel aspects Qualitatively new regime z Probe initial partonic state in 108 a novel Bjorken-x range (10-3 –10-5) : Ö nuclear shadowing, 106 Ö high-density saturated )
gluon distribution (CGC) 2 Ö effectively moves RHIC 104 forward region to mid- (GeV
rapidity at LHC 2 M z Larger saturation scale 10 GeV102 1/6 δ (QS=0.2A √s = 2.7 GeV) particle production J/ψ dominated by the saturation region 100 10-6 10-4 10-2 100 ALICE PPR CERN/LHCC 2003-049 x
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 5 Novel aspects Qualitatively new regime z Hard processes contribute significantly to the total AA cross-section (σhard/σtot = 98%) LO p+p y=0 (h++h-)/2 √s = 5500 GeV Ö Bulk properties dominated π0 200 GeV by hard processes 17 GeV
Ö Very hard probes are abundantly produced LHC
RHIC z Weakly interacting probes SPS become accessible (γ, Z0, W±)
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 6 Moreover Qualitative improvements:
Vanishing net baryon density (μB Æ 0): closer to early Universe, closer to Lattice QCD
High energy density Æ maybe approaching the limit of an “ideal” gas of QCD quanta
(F.Karsch) Stronger thermal radiation Dominant processes in particle production Hard probes: SPS: soft RHIC: soft and semi-hard 9Heavy flavours LHC: semi-hard and hard
9Jets and jet quenching 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 7 What multiplicity do we expect? old estimates: dNch/dy = 2000 – 8000, now we can extrapolate from RHIC data (from K.Kajantie, K.Eskola) 15.0 5 ) <1 part η |
10.0 η /d 3 ch
/(0.5N 10 ch dN N 5.0 5 dNch/dη ~ 15002500 1.0 2 10 102 103 102 103 104 √s (GeV) hep-ph0104010
z ALICE optimized for dNch/dy = 4000, checked up to 8000 (reality factor 2)
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 8 but ...... z The major uncertainties in the energy dependence are still there Ö only some improvement with the RHIC data! z Still no safe way to extrapolate Ö shadowing/saturation (might decrease charged multiplicity) Ö jet quenching (might increase it dramatically) Ö A-scaling (importance soft vs. hard changes with energy) z Simple scaling form RHIC (log–log plot) ~2500
z → safe guess dNch/dη ~ 1500 – 6000
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 9 Experimental conditions @ LHC z pp commissioning starts after April 2007 z Agreed initial Heavy-Ion programme at LHC
Initial few years (1HI ‘year’ = 106 effective s, ~like at SPS) 2 - 3 years Pb-Pb L ~ 1027 cm-2s-1 1 year p - Pb ‘like’ (p, d or α ) L ~ 1029 cm-2s-1 1 year light ions (eg Ar-Ar) L ~ few 1027 to 1029 cm-2s-1 plus, for ALICE (limited by pileup in TPC): reg. pp run at √s= 14 TeV L ~ 1029 and < 1031 cm-2s-1 Later: different options depending on Physics results z Heavy-ion running is part of LHC initial programme, first run expected by the end of 2008
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 10 ALICE Physics goals (has to cover in one experiment what at the SPS was covered by 6-7 experiments, and at RHIC by 4!!)
Global observables: • Deconfinement: Multiplicities, η distributions charmonium and bottonium spectroscopy Degrees of freedom as a function •Chiral symmetry restoration: of T: hadron ratios and spectra, neutral to charged ratios, res. decays dilepton continuum, direct photons •Fluctuation phenomena - critical Early state manifestation of behavior: collective effects: event-by-event particle comp. and spectra elliptic flow • Geometry of the emitting source: Energy loss of partons in quark HBT, impact parameter via zero-degree gluon plasma: energy flow jet quenching, high pt spectra, open • pp collisions in a new energy domain charm and open beauty
¾ Large acceptance ¾ Wide momentum coverage ¾ Good tracking capabilities ¾ PID of hadrons and leptons ¾ Selective triggering ¾ Good secondary vertex reconstruction ¾ Excellent granularity ¾ Photon Detection Use a variety of experimental techniques! 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 11 LargeSolenoid Heavy-ion magnet 0.5 T ColliderCosmic-ray (LHC) trigger
Forward detectors •PMD • FMD, T0, V0, ZDC Specialized detectors •HMPID •PHOS
Central tracking system MUON Spectrometer •ITS • absorbers •TPC • tracking stations •TRD • trigger chambers •TOF • dipole magnet 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 12 US EMCaL (under discussion)
RICH Pb-Scintillator EMCal Δη × Δφ = 1.4 × 120°
TPC
TRD ITS TOF
PHOS
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 13 ALICE Collaboration
CROATIA ROMANIA MEXICO S. KOREA CHINA ITALY ARMENIA USA ~ 1000 Members UKRAINE INDIA (63% from CERN MS)
JINR FRANCE ~30 Countries ~80 Institutes
RUSSIA CERN
SWITZERLAND FINLAND DENMARK GERMANY GREECE SLOVAKIA NETHERLANDS UK POLAND 1200 PORTUGAL CZECH REP. ALICE TRD SWEDEN NORWAY HUNGARY 1000 Collaboration statistics 800 MoU 600
400 TP
200 LoI 0 1990 1992 1994 1996 1998 2000 2002 2004
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 14 ALICE detector acceptance
η 2 Central Detectors ITS tracking 1 TRD TOF 0 PHOS HMPID TPC -1 ITS multiplicity -2 0 100 1 2 3 20 pt
Muon arm 2.4<η<4 Photon Multiplicity Detector 2.3<η<3.5 Forward Multiplicity Detector -5.4<η<-1.6, 1.6<η<3
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 15 ALICE LAYOUT: TRACKING Inner Tracking System (ITS): (and event characterization) 6 Si Layers (pixels, drift, strips) Vertex reconstruction, dE/dx TPC -0.9<η<0.9 Tracking, dE/dx -0.9<η<0.9
TRD electron identification, tracking
-0.9<η<0.9 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 16 If you thought this was difficult ...
NA49 experiment: A Pb-Pb event
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 17 and this was even more difficult ...
STAR A central Au-Au event @ ~130 GeV/nucleon
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 18 … then what about this! ALICE Pb-Pb central event
N (-0.5<η<0.5)=8000 05/10/2005 Physicsch Programme of ALICE Experiment K.Safarik 19 Tracking performance
Entries 5014 Tracking 1.4 Mean 2.48 RMS 1.533 eff. In TPC 1.2 Underflow 0 Good tracks Overflow 0 vs. pT 1
Tracking efficiency 0.8
0.6 TPC and ITS tracking efficiency – better 0.4 then 90% Fake tracks 0.2
0 123456 Pt (GeV/c)
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 20 TrackTrack reconstructionreconstruction inin TPCTPC--ITSITS
ppT resolutionresolution zThe track momentum is measured (mainly) by TPC zWith ITS: resolution improves by a factor ~10 for high pT tracks
¾ Lever arm larger by 1.5 accounts for a factor ~ 2
¾ Remaining effect due to high resolution of points measured in ITS
¾ More improvement comes including the TRD in the tracking
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 21 TrackingTracking--II:II: MomentumMomentum resolutionresolution
resolution ~ 9% at 100 GeV/c excellent performance in hard region!
05/10/2005 Physics Programme of ALICE Experiment K.Safarik 22 ALICEALICE PIDPID • π, K, p identified in large acceptance (2π * 1.8 units η) via a combination of dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) - 3.5 (K/p) GeV/c •Electrons identified from 100 MeV/c to 100 GeV/c (with varying efficiency) combining Si+TPC+TOF with a dedicated TRD •In small acceptance HMPID extends PID to ~5 GeV •Photons measured with high resolution in PHOS, counting in PMD, and in EMC
π/K TPC + ITS K/p Alice uses ~all (dE/dx) e /π known techniques!
TOF e /π π/K K/p
HMPID π/K (RICH) K/p 0 1 2 3 4 5 p (GeV/c)
TRD e /π PHOS γ /π0
1 10 100 p (GeV/c) 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 23 UnderUnder study:study: extensionextension ofof PIDPID toto eveneven higherhigher momentamomenta
z Combine TPC and TRD dE/dx capabilities (similar number of samples/track) to get statistical ID in the relativistic rise region
8 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 24 ALICEALICE TPCTPC 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 25 LHCLHC ExperimentsExperiments 012 10 100 T=ΛQCD Qs pt (GeV/c) Single particle spectra Jet reconstruction Correlation studies Hard processes Bulk properties Modified by the medium ALICE PID CMS&ATLAS 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 26 Parton Energy Loss zDue to medium-induced gluon emission QGP path length L QCD process: @ LHC emitted gluon itself radiates ⇒ΔE ∝ L2 hard cold parton matter LHC zAverage energy loss (BDMPS model): ω c 2 =Δ / ∝ αωωω Rs ˆ LqCddNdE ∫0 Casimir coupling factor: Medium transport coefficient 4/3 for quarks ∝ gluon density and momenta 3 for gluons R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997) 291. C.A.Salgado and U.A.Wiedemann, Phys. Rev. D68 (2003) 014008 [arXiv:hep-ph/0302184]. 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 27 Parton Energy Loss zEffects: ÖReduction of single inclusive high pt particles Parton specific (stronger for gluons than quarks) Flavour specific (stronger for light quarks) Measure identified hadrons (π, K, p, Λ, etc.) + partons (charm, beauty) at high pt ÖSuppression of mini-jets same-side / away-side correlations ÖChange of fragmentation function for hard jets (pt >> 10 GeV/c) Transverse and longitudinal fragmentation function of jets Jet broadening → reduction of jet energy, dijets, γ-jet pairs zp+p and p+A measurements crucial 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 28 Heavy Quarks – dead cone zHeavy quarks with momenta < 20–30 GeV/c → v << c zGluon radiation is suppressed at angles < mQ/EQ “dead-cone” effect ÖDue to destructive interference ÖContributes to the harder fragmentation of heavy quarks zYu.L.Dokshitzer and D.E.Kharzeev: dead cone implies lower energy loss D mesons quenching reduced QRatio D/hadrons (or D/π0) enhanced and sensitive to medium properties Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202]. 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 29 Detection strategy for D0 → K- π+ zWeak decay with mean proper length cτ = 124 μm zImpact Parameter (distance of closest approach of a track to the primary vertex) of the decay products d0 ~ 100 μm zSTRATEGY: invariant mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices ÖMeasurement of Impact Parameters ÖMeasurement of Momenta ÖParticle identification to tag the two decay products 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 30 Track reconstruction in TPC-ITS d0 measurement Measurement of impact parameters is crucial for secondary vertex reconstruction 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 31 Selection of D0 candidates z Secondary vertex: from minimization of distance between the 2 tracks d K × d π <<0 0 0 (in |M[K,π]-M(D0)| < 3σ=36 z After reconstruction and rejection of (π,π) pairs cos θpointing≈ 1 MeV/c): S/B = 4.6 ⋅ 10-6 K,π z Geometric & Kinematic selection (track dist. < 300 μm, pT > 800 MeV/c) increases S/B by a factor 100 S/B ~ 10-4 increase S/B z Displaced vertex selectionby factor: ~103! Öpair of tracks with large impact parameters Ögood pointing of reconstructed D0 momentum to the primary vertex increases S/B by a factor 1000 S/B ~ 0.1 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 32 Hadronic charm Combine ALICE tracking + secondary vertex finding capabilities (σd0~60μm@1GeV/c pT) + large acceptance PID to detect processes as D0ÆK-π+ ~1 in acceptance / central event ~0.001/central event accepted after rec. and all cuts Results for 107 PbPb ev. (~ 1/2 a run) significance vs pT S/√B+S ~ 37 S/√B+S ~ 8 for 1 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 33 Charm in hadronic decay pp Similar study for 109 pp minimum bias collisions Acceptance practically down to the pt → 0 (as for heavy-ion) 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 34 CharmCharm inin pppp (D(D0 →→ KKππ)) SensitivitySensitivity toto NLONLO pQCDpQCD paramsparams μ μ m RF ,,, PDFs √s = 14 TeV c μ μ μ μ00 RF mc ,,, PDFs μ μ00 down to pt ~ 0 ! 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 35 DD0 →→ KKππ inin pPbpPb StatisticalStatistical andand systematicsystematic errorserrors 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 36 0 Sensitivity on RAA for D mesons A.Dainese nucl-ex/0311004 Low pt (< 6–7 GeV/c) Nuclear shadowing + kt broadening + ? thermal charm ? ‘High’ pt (6–15 GeV/c) here energy loss can be studied (it’s the only expected effect) 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 37 D quenching (D0 →K-π+) z Reduced A.Dainese nucl-ex/0311004 1 / dpdN tAA RAA ×= Ncoll / dpdN tpp z Ratio D/hadrons (or D/π0) enhanced and sensitive to medium properties 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 38 D/hadrons ratio (2) hadron parton parton parton pt = zpt (pt )’ = pt – ΔE zRD/h is enhanced only by the dead-cone effect hadron hadron zEnhancement due(pt to different)’ = pt quark/gluon– z ΔE loss not seen zIt is compensated by the harder fragmentation of charm Energy loss observed in RAA is not ΔE but zΔE zc→D ≈ 0.8; zgluon→hadron ≈ 0.4 (for pt>5 GeV/c) ΔEc = ΔEgluon/2.25 (w/o dead cone) zc→D ΔEc ≈ 0.9 zgluon→hadron ΔEgluon D h Without dead cone, RAA ≈ RAA 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 39 Beauty: semi-leptonic decays detection strategy d0 and pT distributions for “electrons” from different sources: Distributions normalized to the same integral in order to compare their shapes 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 40 Semi-electronic Beauty detection simulation results Signal-to-total ratio and expected statistics in 107 Pb-Pb events Expected statistics (107 Pb-Pb events) 90% purity pT > 2 GeV/c , 200 < |d0| < 600 μm 40,000 e from B 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 41 Estimation of uncertainties on the pT - differential cross section of beauty electrons Final B-decay electron pT distribution stat (11% norm. err. not shown) pt-dep. syst 11% norm. err. (not shown) E loss calculations: N. Amesto, A. Dainese, C.A. Salgado, U.A. Wiedemann, hep-ph/0501225 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 42 Extraction of a minimum-pT-differential cross section for B mesons Using UA1 MC method (*), also adopted by ALICE μ B min The B meson cross section per unit of rapidity at midrapidity with pT > pT is obtained from a scaling of the electron-level cross section measured within a given electron phase space Φe B dσ B min B T > pp T )( dσ B min ,beautye e dy pp σ )()( ×Φ=> The semi-electronic T T meas eB dy σ Φ )( B.R. is included here MC σ ,beautye e )( ×Φ= meas F →Be e The phase space used is T η ΔΔΔ≡Φ dp 0},,{ where ΔpT are the previously used bins, Δη = [-0.9, 0.9] and Δd0 = [200,600] μm (*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405 C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 43 Extraction of a minimum-pT-differential cross section for B mesons Using electrons in 2 < pT < 16 GeV/c stat p -dep. syst obtain B-meson t 2 < p min < 23 GeV/c 11% norm. err. T (not shown) E loss calculations: N. Amesto, A. Dainese, C.A. Salgado, U.A. Wiedemann, hep-ph/0501225 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 44 Semi-electronic Beauty detection + X pT quark distribution Under study B → e X and use charged particle in X with displaced vertex – b jet tagging Analysis of the electron pT distribution useful for beauty production cross section measurement. But, what about the quark pT distribution? Example: B → e + D0 ( → K+π ) + X 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 45 BeautyBeauty fromfrom muonmuon rawraw yieldsyields • Fits with fixed shapes from the Monte Carlo & beauty amplitude as the only free parameter (next: tray c also free) • Uses 3 different data samples L =×510cms26− 2− 1 6 central Pb-Pb 5 % Running time 10 s Single muons Dimuons @ Dimuons @ low mass high mass (Very) large statistics is M (GeV/c 2) 0 - 5 5 - 20 expected Nμμ from bb 39678 ± 180 6314 ± 71 p t 1.5 - 2 2 – 2.5 2.5 - 3 3 - 4 4 - 5 5 - 6 6 - 9 9 - 12 12 - 15 15 - 20 20 - 100 (GeV/c) 2.7 10 6 1.8 10 6 ± 1.1 10 6 1.0 10 6 ± 4105 1.7 105 1.3 10 5 2.1 104 5103 ± 1.8 103 N from b 474 ± 30 μ ± 620 675 ± 636 684 ± 474 ± 326 ± 294 ± 123 60 ± 38 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 46 Jet reconstruction z Jets are produced copiously 2 20 100 200 pt (GeV) 100/event 1/event 100K/year ALICE Acceptance ET Njets 4 108 central PbPb collisions/month threshold Underlying event fluctuations Event-by-event well Single particle spectra distinguished50 GeV objects2 × 107 Correlation studies Reconstructed jets 5 6 10 events 100 GeV 6 × 105 150 GeV 1.2 × 105 200 GeV 2.0 × 104 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 47 50 – 100 GeV jets in Pb–Pb At large enough jet energy – jet clearly visible But still large fluctuation in underlying energy η–φ lego plot with Δη 0.08 × Δφ 0.25 C. Loizides 50 GeV jet 100 GeV Central Pb–Pb event (HIJING simulation) with 100 GeV di-jet (PYTHIA simulation) 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 48 Energy fluctuation in UE Mean energy in a cone of radius R coming from underlying event Fluctuation of energy from an underlying event in a cone of radius R 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 49 More quantitatively ... Intrinsic resolution limit for ET = 100 GeV = out-of-cone fluctuations For R < 0.3: ΔE/E = 16% from Background (conservative dN/dy = 5000) 14% from out-of-cone fluctuations 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 50 Jet quenching z Excellent jet reconstruction… but challenging to measure medium modification of its shape… 1 vacuum 0.8 0.6 medium Medium induced 0.4 R redistribution of jet 0.2 Et = 50 GeV energy occurs inside (R) 0 cone ρ 1 0.8 0.6 0.4 Et = 100 GeV z Et=100 GeV (reduced average jet energy 0.2 fraction inside R): 0 Ö Radiated energy ~20% 0 0.2 0.4 0.6 0.8 1 2 2 Ö R=0.3 ΔE/E=3% R=√(Δη +Δφ ) UE C.A. Salgado, U.A. Wiedemann hep-ph/0310079 Ö Et ~ 100 GeV 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 51 Irreducible limits on jet energy resolution z Small radius of jet cone (R = 0.3) Ö we don’t see 30% of energy Ö underlying event fluctuation ~ 15 GeV – 15% for 100 GeV jet z Larger jet-cone radius (R = 0.7) Ö we don’t see 10% of energy Ö underlying event fluctuation ~ 45 GeV – 45% for 100 GeV jet z We cannot just add non-seen energy outside jet cone Ö as is usually done in pp where jet shape is known Ö that depends on energy distribution which we have to study z It’s impossible to know jet energy better than 25 – 30% (for 100 GeV jets) Ö we are now at 34 %, pretty close… 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 52 Jet structure observables at the LHC z How close can we get to the ideal case Ö Measure unquenched parton energy by measuring the jet energy. Ö Determine energy loss and transverse heating by measuring the fragmentation function and kT spectra. jT Energy-Loss Spectrum E = 100 GeV Θ z = p /E L Unquenched Quenched (AliPythia) ΔE = 20 GeV Quenched (Pyquen) 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 53 Limit experimental bias ... z By measuring the jet profile inclusively. Ö Low-pT capabilities are important since Quenched (AliPythia) for quenched jets sizeable fraction of Quenched (Pyquen) energy will be carried by particles with pT < 2 GeV. γ, Ζ z Exploit γ-jet correlation Ö Eγ = Ejet Ö Caveat: limited statistics 2(103) smaller than jet production Ö Does the decreased systematic error compensate the increased statistical error ? Energy radiated Not visible after Ö Certainly important in the intermediate outside core pT-cut. energy region 20 < ET < 50 GeV. 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 54 Jet structure observables: kT z Unmodified jets characterized by R = Θ 0 1fm tform = 1/(ΘjT) Unquenched tsep = 1/Θ Quenched (AliPythia) z Relation between R and formation Quenched (Pyquen) time of hard final state radiation. Ö Early emitted final state radiation will also suffer energy loss. Ö Watch for R – dependence of 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 55 PromptPrompt γγ spectrumspectrum (1(1 yearyear running)running) 05/10/2005 Physics Programme of ALICE Experiment K.Safarik 56 Frag