Photons and Jets from the first year of ALICE A Photons and Jets from the first year of ALICE A. Marin, for the ALICE Collaboration

Outline The ALICE experiment The 2010 data sample Physics results in pp Photon physics Jets First results in PbPb

ALICE:The dedicated HI Experiment Size: 16 x 26 meters Weight: 10,000 tons Detectors: 18 3

ALICE Status ALICE Detector Installation 2009-2010 Complete: ITS, TPC, TOF, HMPID, FMD, T0, V0, ZDC, Muon arm, Acorde PMD, DAQ Partial installation: PHOS(3/5) 7/18 TRD 2-4/6 EMCAL ~ 50% HLT P. Kuijer 4

The 2010 data sample p+p@7TeV: >800M MB, >100M m triggers, >25M high multiplicity Pb+Pb@2.76ATeV: ~30M nuclear collisions

LHC: Entering a new regime C W Fabjan 2008 J. Phys. G: Nucl. Part. Phys. 35, 104038 Cross-sections of interesting probes expected to increase by factors ~ 10 ( cc ) to ~ 102 ( bb ) to ~ > 105 (very high pT jets) ; Hard probes of the medium accessible at LHC Direct photons are abundantly produced at LHC

Photon physics in ALICE Measurement of p0 and h mesons in pp@7TeV and PbPb@2.76ATeV Highest energy available in lab Test of pQCD cross section predictions Reference data for PbPb Main source of background in direct photon/heavy flavour electron measurement Measurement of Direct photons (not from decays) in pp@7TeV and PbPb@2.76ATeV PbPb: hard processes in QGP medium, thermal properties of early phase g-Jet (g-hadron) Study quark energy loss in the medium Fragmentation function: Ejet ~ Eg (HK 22.2, HK 22.3)

3 independent measurements: Conversions, PHOS, EMCAL 0 and h reconstruction pp  0 + Xn  e+e-e+e- (m0 = 0.135 GeV/c2, BR = 0.988) pp   + Xn (m = 0.548 GeV/c2, BR = 0.393) e+ e-  Y X 3 independent measurements: Conversions, PHOS, EMCAL run 104792, event 2248

V0 : Secondary vertex reconstruction Reconstruction of (K0S,L, L ) converted photons in material (Z) gZ ge+e-Z For analysis: Package for fitting decay particles based on the Kalman Filter Specific energy loss in the TPC -3sdE/dx<dE/dx-dE/dx(e)<+5s dE/dx p rejection for p>1GeV, dE/dx > dE/dx(p) m(g)=0 constrain to vertex c2(g) < 30 Strict cut for material studies

Photons from pair conversions: g-ray image of ALICE converted photons in material (Z): gZge+e-Z ALICE material budget (11.4% X0) agrees within +3.4,-6% with its implementation in GEANT simulations

p0 and h mesons @ 7TeV p0 h

Data 7 TeV: p0 invariant mass in pt bins Combinatorial bck using mixed events Mgg 0.17-0.3 GeV/c2 for normalization Very low pt reached with the conversion method

Data 7TeV: h invariant mass in pt bins Mgg 0.6-0.7 GeV/c2 for normalization

Raw yields. Reconstruction efficiency With 9.5 x 107 Minimum Bias collisions: 0 measured in 0.4 GeV/c < pt < 7GeV/c  measured in 0.6 GeV/c < pt< 6 GeV/c

Differential p0 invariant yield Differential p0 invariant yield measured in pp collisions@7 TeV

Comparsion to NLO NLO predictions from W. Vogelsang s pp=70mb used New ALICE measurement s pp= 62.3±0.4(stat) ±4.3(syst.) mb Method and calculations described in: [1] F. Aversa et al., Nucl. Phys. B327, 105 (1989). [2] B. Jäger et al., Phys. Rev. D67, 054005 (2003). [3] D. de Florian, Phys. Rev. D67, 054004 (2003).

h/p0 ratio The h/p0 ratio is measured in pp collisions @7TeV for 0.6 GeV/c <pt<6 GeV/c. In agreement with Pythia expectations and with the world data measured in hadron-hadron collisions, taken from Phys. Rev.C 75 0224909 (2007).

Excess exponential in pT Direct photons at RHIC PHENIX Coll.:Phys. Rev. Lett. 94, 232301 (2005) PHENIX Coll.:Phys. Rev. Lett. 104 (2010) 132301 pp consistent with NLO pQCD calculations AuAu larger than calculation for pT<3.5GeV/c Excess exponential in pT T=221± 23(stat)±18(sys) MeV

How many direct photons @ LHC? Measurement was done at RHIC ... but more difficult at LHC g/p0 = 0,01-0,1 for pT > 20 GeV/c We need a good distinction direct/decay g Cern Yellow Report 2004-009, hep-ph/0311131

Photon decay cocktail Work in progress Work in progress

Jets HK 22.4, HK 22.5, HK 22.6, HK 22.7, HK 40.9

Jet properties from di-hadron correlations Near side (intra-jet): “Single” jet properties, fragmentation Away side (inter-jet): Di-jet, hard scattering, properties, KT effects 'near'side 'away' side UE Trigger particle

Correlation functions:√s= 0.9 and 7 TeV Large statistics allows up to 30 GeV/c of the trigger particle

Jet properties from di-hadron correlations Measure of average transverse momentum of fragmentation products relative to jet axis All measurements agree within the errors Expected independence on trigger particle pT and √s confirmed

partonic hadronic/measured Away side width and kT z t ˆ x h k T 2 = 1 p o u - j y ( + ) √(p/2)x√<kT2> partonic hadronic/measured ALICE preliminary ALICE preliminary Confirmed expected increase of momentum imbalance of parton pair

Full Jet reconstruction in ALICE in 2010 Using central tracking detectors Charged jet reconstruction only Different jet finders UA1 cone algorithm FASJET Suite (kT, anti-kT, SIScone) Cone size 0.4 Comparison to PbPb Maximum efficiency of central barrel |hjet|<0.5 Jet finding in PbPb Low momentum cut off (150 MeV)

Raw Jet Spectrum: p+p @7TeV Jets |h|<0.5 Tracks |h|<0.8 Jet spectrum with charged particles safely reconstructed out to 70 GeV

First PbPb collisions in ALICE 0-5% cent: dNch/dh ~ 1584 ± 4 (stat) ± 76 (syst)

"Jet quenching" from charged particle spectra HK22.1 Suppression of high pt particles ( ~ leading jet fragments) Rising with pt ! Accuracy limited by pp reference => need pp at 2.76 TeV ! ALICE, Phys. Lett. B 696 (2011) 30

PbPb@2.76 ATeV: p0 invariant mass in pt bins p0 can be reconstructed from 0.4 GeV/c to 12 GeV/c

First step towards p0 RAA p0 raw yield vs pt First step towards p0 RAA

Jet quenching from High pT correlations Clear away side correlation in p+p @7TeV Df Away side correlation in central Pb-Pb washed out up to pT,trig>10GeV

Raw anti-k T Jet Spectrum in Pb+Pb Event-by-event background subtracted,not unfolded. Effect of background fluctuations/smearing apparent. Detailed correction currently prepared.

Conclusions and outlook ALICE took data succesfully during the 2010 run for pp and PbPb collisions p0 (and h) mesons differential yields measured in pp collisions at 7 TeV. Basic ingredients for a direct photon measurement Jet properties measured in pp collisions from di-hadron correlations Full jet reconstruction is done using different algorithms. Work is still ongoing to apply all corrections High pt suppresion of charged particles is observed in central PbPb collisions. Jet quenching at LHC Uncorrected p0 pt spectrum and jet pt spectrum have been shown. Work is ongoing to obtain RAA(p0) and fully corrected jet pt spectrum

ALICE TALKS PV 5.1 ALICE in Wonderland: first results from the ALICE experiment at the LHC — •Peter Braun-Munzinger HK 7.8 Online Drift Velocity Calibration with the Laser System of the ALICE-TPC — •Mesut Arslandok HK 12.9 Central diffractive meson production in p+p collisions at √s=7 TeV at the ALICE experiment — •Xianguo Lu HK 14.8 The SysMES Inventory Module in the ALICE HLT Cluster — •Jochen Ulrich, Camilo Lara, Stefan Böttger, Timo Breitner, Pierre Zelnicek, and Udo Kebschull HK 14.9 Virtual Machine Scheduling in the ALICE HLT — •Stefan Boettger, Jochen Ulrich, Camilo Lara, Timo Breitner, Pierre Zelnicek, and Udo Kebschull HK 15.3 Korrelationen von schweren Quarkteilchen in hochenergetischen Kern-Kern-Reaktionen — •Andre Mischke HK 15.4 Performance Studies for the Measurement of ψ′ via the Decay Channel ψ‵ → J/ψ π+π− → e+e− π+π− with the ALICE Detector — •Moritz Pohl, Christoph Blume, and Frederick Kramer HK 15.6 Messung von Dielektronen niedriger Masse mit dem ALICE Detektor in Proton-Proton und Blei-Blei Kollisionen — •Markus Konrad Köhler HK 20.5 A Common Read-Out Receiver Card for ALICE DAQ and HLT — •Heiko Engel and Udo Kebschull HK 22.1 Suppression of Charged Particle Production at Large Transverse Momentum in Central Pb−Pb Collisions at √sNN=2.76 TeV — •Jacek Otwinowski HK 22.2 Rekonstruktion von π0 und η Mesonen mittels Photon Konversionen in ALICE in Proton Proton Kollisionen am CERN LHC — •Friederike Bock HK 22.3 Rekonstruktion von π0-Mesonen mittels Photon-Konversionen mit ALICE in PbPb-Kollisionen am CERN LHC — •Radoslav Rusanov

ALICE TALKS HK 22.4 Jet and High-pT Measurments with the ALICE Experiment at the LHC — •Bastian Bathen, Tom Dietel, and Christian Klein-Bösing HK 22.5 Quark and gluon composition of jets in proton-proton collisions at √s = 7 TeV with ALICE at the LHC — •Hermes Leon Vargas HK 22.6 Two- and Three-Particle Jet-Like Correlations in the ALICE Experiment at the LHC — •Jason Glyndwr Ulery HK 22.7 Charged Particle Momentum Distribution in Jets in ALICE — Bastian Bathen, •Oliver Busch, and Christian Klein- Bösing HK 22.8 ALICE TRD GTU Online Tracking and Trigger Performance in pp and PbPb Collisions — •Felix Rettig, Stefan Kirsch, and Volker Lindenstruth HK 22.9 Beauty and beauty-jet measurement via displaced vertices with ALICE in p+p collisions at √s = 7 TeV — •MinJung Kweon HK 28.1 Alice HLT TPC Tracking of PbPb-Events on GPU and CPU — •David Rohr and Sergey Gorbunov HK 28.2 Development of a trigger system to test and calibrate ALICE-TRD super-modules — •Jonas Anielski HK 39.20 Ein Driftgeschwindigkeitsmonitor für den ALICE TRD — •Friederike Poppenborg HK 39.57 ALICE Grid Computing at the GridKa Tier-1 center — •Christopher Jung and Kilian Schwarz HK 40.1 Measurement of transverse momentum spectra of identified hadrons from pp and PbPb collisions with the ALICE experiment — •Alexander Kalweit HK 40.2 Neutral strange hadron reconstruction in pp and PbPb collisions at LHC energies — •Simone Schuchmann

ALICE TALKS HK 40.3 Measurement of nuclei and antinuclei with the ALICE experiment at the LHC — •Nicole Martin and Alexander Kalweit HK 40.5 Event-by-event fluctuations of mean transverse momentum in pp collisions at √s = 900 GeV and 7 TeV measured by the ALICE experiment — •Stefan Heckel HK 40.6 Analyse der Pionenquelle durch HBT-Interferometrie mit ALICE — •Johanna Gramling HK 40.7 Analyse von Pseudorapiditäts-Dichtekorrelationen mittels Multiplizitätsverteilungen in pp- und PbPb-Kollisionen mit ALICE — •Maren Hellwig HK 40.8 Mini-Jet Activity as Function of Charged Multiplicity — •Eva Sicking HK 40.9 Underlying Event measurement in pp collisions with the ALICE detector — •Sara Vallero for the ALICE collaboration HK 40.10 Results of the Quality Assurance for the High Level Trigger Applications for the ALICE TRD — •Theodor Rascanu HK 61.1 vom ALICE Tier2 zum FAIR Tier0 - Computing at GSI — •Kilian Schwarz HK 63.2 Photons and Jets from the First Year of ALICE — •Ana Marin HK 64.1 Measurement of the J/ψ Production Cross Section in pp Collisions at √s=7 TeV with ALICE at the LHC and Perspectives for PbPb Collisions — •Frederick Kramer, Ionut Arsene, Christoph Blume, Julian Book, Anton Andronic, WooJin J. Park, and Jens Wiechula HK 64.2 Electrons from heavy flavour decays with the ALICE experiment in proton-proton collisions at √s= 7TeV — •Raphaelle Bailhache HK 64.3 Messung des Wirkungsquerschnitts von Hadronen mit schweren Quarks in Proton-Proton Kollisionen mit dem ALICE Experiment — •Fasel Markus

ALICE TALKS HK 64.4 Messung der Produktion schwerer Quarks in Pb+Pb Kollisionen mit dem ALICE Detektorsystem — •Yvonne Pachmayer HK 64.5 Reconstruction of open charm in the decay channel D0→K−π+ with ALICE — •Robert Grajcarek HK 64.6 Open charm production in the D*+ → D0 π+ decay channel with ALICE — •Yifei Wang

ALICE COLLABORATION 39

Backup slides

Differential invariant cross section PHOS + Conversions

Background density Strong change within one centrality bin. Better correlation in multiplicity

Testing Background Fluctuations Embedding of single tracks: δ-probe for jet finding at random position Random Cones: Sum in circular area at random position (excluding the two leading jets)

Charged Jets Dh Df Dh Df Jet quenching 10-20% peripheral 168 GeV jet E -> jet E’ (=E-DE) + soft gluons (DE) 47 GeV 102 GeV 0-10% central Dh Df

Charged particle multiplicity density dNch/dh ~ 1584 ± 4 (stat) ± 76 (syst) somewhat on high side of expectations growth with √s faster in AA than pp PRL 105, 252301 (2010)

Centrality dependence of Charged particle multiplicity density Centrality dependence of the multiplicity is found very similar at √sNN=2.76 and √sNN=0.2TeV. Scale different by a factor 2.1 PRL 106, 032301 (2011)

Un-triggered CF

Probing Hot QCD Matter with hard probes “highly penetrating observables (particles, radiation) used to explore properties of matter that cannot be viewed directly!” High pT particles: p0,h, direct g Jets p+p collisions provide a baseline

Hard probes p+p: parton scattering  fragmentation  jet can be calculated in perturbative QCD collinear factorization A+A: partons traversing medium lose energy gluon radiation, elastic collisions energy loss different for g, light/heavy quarks (color factor, dead cone effect) X.-N. Wang, M. Gyulassy, Phys. Rev. Lett. 68 (1992) 1480 Goal: Use in-medium energy loss to measure medium properties leading particle a b c d hadrons Parton distribution function Matrix element Fragmentation function measured in DIS initial state (saturation?) e+e- final state (energy loss?) pQCD

https://wiki.bnl.gov/TECHQM/index.php/Main_page RAA for p0, h and direct g RAAg~=1 RAAp0,h ~=0.2 The hadron spectra at RHIC from p+p, Au+Au and d+Au collisions establish existence of parton energy loss from strongly interacting, dense QCD matter in central Au-Au collisions <q> = 4 – 13 GeV2 / fm dNg/dy~1400+-200 S. Bass et al. PRC79 (2009) 024901 ^ https://wiki.bnl.gov/TECHQM/index.php/Main_page Theory-Experiment Collaboration on Hot Quark Matter

jT systematics: formulae If trigger and associated hadrons fragment independently: First approximation: arcsin(x)~x and because <jT2>=2<jy2>: Two approximations follow: <1/p2>~1/<p>2 <p> is taken from inclusive (rather than jet) spectrum 52

Why photon-tagged jets? ^ Medium effects redistribute (q L ) the parton energy, Ejet, inside the hadron jet (multiplicity, jT). Redistribution can be best measured with the Fragmentation Function... If we know Ejet. HI environment hinders precise reconstruction of Ejet. Borghini,Wiedemann, hep-ph/0506218 Quenching increases low-pT particles 1/Njet dN/dx If we measure Eg ≈ Ejet Quenching reduces high-pT particles

Photon Detection in ALICE PHOS (1000 x 0.24 in h) (PHOS/CentralBarrel=0.037) high resolution (energy and spatial) small coverage EMCAL larger coverage: 120O x 1.4 in η (EMCAL/CentralBarrel=0.26) coarser spatial resolution than PHOS available in 2010 gZ→ e+e- Z Conversions (Central Barrel) large coverage: 360O x 1.8 (2.4) in h (Conversion/CentralBarrel=0.08) low conversion probability : 8% (16%)

Interaction of photons with matter Photoelectric effect Compton scattering Pair production: Eg>1.02MeV Electromagnetic Calorimeters: The complete photon energy is deposited in the detector (electromagnetic shower) Photon measurement via pair conversions: Determine photon momentum and direction by measuring e+/e- from a single g conversion in tracking detectors ALICE ( ITS+TPC+TRD)

Direct photon sources ...in a large background from p0 and h decays Why? Do not interact strongly. Carry information about the early state. q g γ q g γ qg Compton Scattering Bremsstrahlung, fragmentation qq Annihilation Thermal photons from QGP and hadron gas Photons from Jet re-interaction in the medium ...in a large background from p0 and h decays

Photon Production: different sources Turbide, Gale, Jeon, and Moore PRC (2004) 014906 Photons are abundantly produced at LHC Jet-photon conversion in the plasma dominates 8<pT<14 GeV Prompt hard NN scattering dominant for p T>20GeV at LHC

Data 7 TeV: p0 invariant mass in pt bins Combinatorial bck using mixed events Mgg 0.17-0.3 GeV/c2 for normalization Very low pt reached with the conversion method

Data 7TeV: h invariant mass in pt bins Mgg 0.6-0.7 GeV/c2 for normalization

Raw yields. Reconstruction efficiency With 9.5 x 107 Minimum Bias collisions: 0 measured in 0.4 GeV/c < pt < 7GeV/c  measured in 0.6 GeV/c < pt< 6 GeV/c

Differential p0 invariant yield Differential p0 invariant yield measured in pp collisions@7 TeV

h/p0 ratio The h/p0 ratio is measured in pp collisions @7TeV for 0.6 GeV/c <pt<6 GeV/c. In agreement with Pythia expectations and with the world data measured in hadron-hadron collisions, taken from Phys. Rev.C 75 0224909 (2007).

PbPb@2.76 ATeV: p0 invariant mass in pt bins p0 can be reconstructed from 0.4GeV/c to 12GeV/c

First step towards p0 RAA p0 raw yield vs pt First step towards p0 RAA