DPG Spring Meeting 2011, Münster (Germany) [email protected] 1 Photons and Jets from the first year of...

DPG Spring Meeting 2011 , Münster (Germany) [email protected] 1

Photons and Jets from the first year Photons and Jets from the first year of ALICEof ALICE

A. Marin, A. Marin, for the ALICE Collaborationfor the ALICE Collaboration

DPG Spring meeting 2011, Münster (Germany) [email protected] 2

OutlineOutline

The ALICE experiment The 2010 data sample Physics results in pp

Photon physics Jets

First results in PbPb


3

Size: 16 x 26 meters

Weight: 10,000 tons

Detectors: 18

ALICE:The dedicated HI ExperimentALICE:The dedicated HI Experiment


ALICE Status

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

ALICE Detector Installation 2009-2010

4P. Kuijer


The 2010 data sampleThe 2010 data sample

•p+p@7TeV: >800M MB, >100M triggers, >25M high multiplicity

•[email protected]: ~30M nuclear collisions


LHC: Entering a new regimeLHC: Entering a new regime

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 LHCDirect photons are abundantly

produced at LHC

C W Fabjan 2008 J. Phys. G: Nucl. Part. Phys. 35, 104038


Photon physics in ALICEPhoton physics in ALICE

Measurement of 0 and mesons in pp@7TeV and [email protected] 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 [email protected]

Highest energy available in lab Test of pQCD cross section predictions Reference data for PbPb PbPb: hard processes in QGP medium, thermal properties of early phase

-Jet (-hadron) Study quark energy loss in the medium Fragmentation function: Ejet ~ E

(HK 22.2, HK 22.3)(HK 22.2, HK 22.3)


0 0 and and reconstruction reconstruction

e+

e-

Y

X

pp 0 + Xn

e+e-e+e-

(m0 = 0.135 GeV/c2, BR = 0.988)

pp + Xn

e+e-e+e-

(m = 0.548 GeV/c2, BR = 0.393)

run 104792, event 2248

3 independent measurements: Conversions, PHOS, EMCAL


VV00 : Secondary vertex reconstruction : Secondary vertex reconstruction

Reconstruction of (K0S,) converted photons in material (Z)

Z e+e-ZFor analysis:

Package for fitting decay particles based on the Kalman FilterSpecific energy loss in the TPC

Strict cut for material studies

-3dE/dx<dE/dx-dE/dx(e)<+5dE/dx

rejection for p>1GeV, dE/dx > dE/dx() m()=0 constrain to vertex2() < 30


Photons Photons from pair conversions:from pair conversions:-ray-rayimage of ALICEimage of ALICE

ALICE material budget (11.4% X0) agrees within +3.4,-6%

with its implementation in GEANT simulations

converted photons in material (Z): Ze+e-Z


00 and and mesons @ 7TeV mesons @ 7TeV

)cos1(2212121 EEM

0


Data 7 TeV:Data 7 TeV:00 invariant mass in p invariant mass in pt t bins bins

Combinatorial bck using mixed events M 0.17-0.3 GeV/c2 for normalization

Very low pt reached with the conversion method


Data 7TeVData 7TeV invariant mass in p invariant mass in pt t binsbins

M0.6-0.7 GeV/c2 for normalization


Raw yields. Reconstruction efficiencyRaw 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 Differential 00 invariant yield invariant yield

Differential0 invariant yield measured in pp collisions@7 TeV


Comparsion to NLOComparsion to NLO

NLO predictionsfrom W. Vogelsang

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).

pp=70mb used

New ALICE measurement

pp= 62.3±0.4(stat) ±4.3(syst.) mb


//00 ratio ratio

The /0 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).


Direct photons at RHICDirect photons at RHIC

PHENIX Coll.:Phys. Rev. Lett. 94, 232301 (2005) PHENIX Coll.:Phys. Rev. Lett. 104 (2010) 132301

Excess exponential in pT

T=221± 23(stat)±18(sys) MeV

•pp consistent with NLO pQCD calculations•AuAu larger than calculation for pT<3.5GeV/c


How many direct photons @ LHC?How many direct photons @ LHC?

Measurement was done at RHIC ... but more difficult at LHC 0 = 0,01-0,1 for pT > 20 GeV/cWe need a good distinction direct/decay

Cern Yellow Report 2004-009, hep-ph/0311131


Photon decay cocktailPhoton 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 Jet properties from di-hadron correlationscorrelations

rjT

'away' side

'near'side

UE

Trigger particle

Near side (intra-jet): “Single” jet properties, fragmentation

Away side (inter-jet): Di-jet, hard scattering, properties,KT effects


Correlation functions:√s= 0.9 and 7 TeVCorrelation functions:√s= 0.9 and 7 TeV

Large statistics allows up to 30 GeV/c of the trigger particle


Jet properties from di-hadron Jet properties from di-hadron correlationscorrelations

rjT

Measure of average transverse momentum of fragmentationproducts relative to jet axis

All measurements agreewithin the errors

Expected independence on trigger particle

pT and √s confirmed

jT2

900 GeV = 678 12 MeV/c

jT2

7 TeV 673 5 MeV/c

jT2

900 GeV = 678 12 MeV/c

jT2

7 TeV 673 5 MeV/c


Away side width and kAway side width and kTT

zt

x̂h

kT2 1

xh

pout2 jTy

2 (1 xh2 )

partonic hadronic/measured

ALICE preliminary

ALICE preliminary

Confirmed expected increase of momentum imbalance of parton pair

√(/2)x√<kT2>


Full Jet reconstruction in ALICE in 2010 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 |jet|<0.5

Jet finding in PbPb Low momentum cut off (150 MeV)

jetjetrec

jetTjetT AApp ,,


Raw Jet Spectrum: p+p @7TeVRaw Jet Spectrum: p+p @7TeV

Jet spectrum with charged particles safely reconstructed out to 70 GeV

Jets ||<0.5Tracks ||<0.8


First PbPb collisions in ALICEFirst PbPb collisions in ALICE0-5% cent: dNch/d ~ 1584 ± 4 (stat) ± 76 (syst)


"Jet quenching" from charged "Jet quenching" from charged particle spectra particle spectra

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

HK22.1


[email protected] ATeV:[email protected] ATeV:00 invariant mass invariant mass in pin pt t binsbins

0 can be reconstructed from 0.4 GeV/c to 12 GeV/c


00 raw yield vs p raw yield vs ptt

First step towards 0 RAA


Jet quenching from High pJet quenching from High pT T

correlationscorrelations

Away side correlation in central Pb-Pb washed out up to pT,trig>10GeV

Clear away side correlation in p+p @7TeV


Raw anti-k Raw anti-k T T Jet Spectrum in Pb+PbJet Spectrum in Pb+Pb

Event-by-event background subtracted,not unfolded.Effect of background fluctuations/smearing apparent.Detailed correction currently prepared.


Conclusions and outlookConclusions and outlook

ALICE took data succesfully during the 2010 run for pp and PbPb collisions

0 (and ) 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 0 pt spectrum and jet pt spectrum have been shown. Work is ongoing to obtain RAA(0) and fully corrected jet pt spectrum


ALICE TALKSALICE TALKS

PV 5.1 ALICE in Wonderland: first results from the ALICE experiment at the LHC — •Peter Braun-MunzingerHK 7.8 Online Drift Velocity Calibration with the Laser System of the ALICE-TPC — •Mesut ArslandokHK 12.9 Central diffractive meson production in p+p collisions at √s=7 TeV at the ALICE

experiment — •Xianguo LuHK 14.8 The SysMES Inventory Module in the ALICE HLT Cluster — •Jochen Ulrich, Camilo Lara, Stefan Böttger, Timo Breitner, Pierre Zelnicek, and Udo KebschullHK 14.9 Virtual Machine Scheduling in the ALICE HLT — •Stefan Boettger, Jochen Ulrich, Camilo Lara, Timo Breitner, Pierre Zelnicek, and Udo KebschullHK 15.3 Korrelationen von schweren Quarkteilchen in hochenergetischen Kern-Kern-Reaktionen — •Andre MischkeHK 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 KramerHK 15.6 Messung von Dielektronen niedriger Masse mit dem ALICE Detektor in Proton-Proton und Blei-Blei Kollisionen — •Markus Konrad KöhlerHK 20.5 A Common Read-Out Receiver Card for ALICE DAQ and HLT — •Heiko Engel and Udo KebschullHK 22.1 Suppression of Charged Particle Production at Large Transverse Momentum in Central Pb−Pb Collisions at √sNN=2.76 TeV — •Jacek OtwinowskiHK 22.2 Rekonstruktion von π0 und η Mesonen mittels Photon Konversionen in ALICE in Proton Proton Kollisionen am CERN LHC — •Friederike BockHK 22.3 Rekonstruktion von π0-Mesonen mittels Photon-Konversionen mit ALICE in PbPb-Kollisionen am CERN LHC — •Radoslav Rusanov



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 PoppenborgHK 39.57 ALICE Grid Computing at the GridKa Tier-1 center — •Christopher Jung and Kilian

SchwarzHK 40.1 Measurement of transverse momentum spectra of identified hadrons from pp and PbPb

collisions with the ALICE experiment — •Alexander KalweitHK 40.2 Neutral strange hadron reconstruction in pp and PbPb collisions at LHC energies —

•Simone Schuchmann



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 GramlingHK 40.7 Analyse von Pseudorapiditäts-Dichtekorrelationen mittels Multiplizitätsverteilungen

in pp- und PbPb-Kollisionen mit ALICE — •Maren HellwigHK 40.8 Mini-Jet Activity as Function of Charged Multiplicity — •Eva SickingHK 40.9 Underlying Event measurement in pp collisions with the ALICE detector — •Sara

Vallero for the ALICE collaborationHK 40.10 Results of the Quality Assurance for the High Level Trigger Applications for the ALICE

TRD — •Theodor RascanuHK 61.1 vom ALICE Tier2 zum FAIR Tier0 - Computing at GSI — •Kilian SchwarzHK 63.2 Photons and Jets from the First Year of ALICE — •Ana MarinHK 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



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 sectionDifferential invariant cross sectionPHOS + ConversionsPHOS + Conversions


Background densityBackground density

Strong change within one centrality bin. Better correlation in multiplicity


Testing Background FluctuationsTesting Background Fluctuations

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


ChargedChargedJetsJets

Jet quenchingjet E ->

jet E’ (=E-E) + soft gluons (E)

47 GeV

102 GeV

0-10% central

192 GeV168 GeV

10-20% peripheral


Charged particle multiplicity densityCharged particle multiplicity density

dNch/d ~ 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 Centrality dependence of Charged particle multiplicity densityparticle 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 Un-triggered CF


Probing Hot QCD Matter with hard probesProbing Hot QCD Matter with hard probes

Hard Probes:“highly penetrating observables (particles, radiation)

used to explore properties of matter that cannot be viewed directly!”

High pT particles: 0,, direct Jets

p+p collisions provide a baseline


Hard probes 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

bc

dhadrons

hadrons

c

chbbaa

abcdba

T

hpp

z

Dcdab

td

dQxfQxfdxdxK

pdyd

d

0

/222

)(ˆ

),(),( Parton distribution function Matrix element Fragmentation function

measured in DISinitial state (saturation?)

e+e- final state (energy loss?)

pQCD


RRAAAA for for 00, , and direct and direct

RAA~=1

RAA

0, ~=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+-200S. Bass et al. PRC79 (2009) 024901

^

https://wiki.bnl.gov/TECHQM/index.php/Main_pageTheory-Experiment Collaboration on Hot Quark Matter


Ta

ya

Tt

ytatatN p

j

p

j 222222 arcsinarcsin

If trigger and associated hadrons fragment independently:

First approximation: arcsin(x)~x and because <jT2>=2<jy

2>:

2222 11

2TaTt

TN ppj

Two approximations follow:(1)<1/p2>~1/<p>2

(2)<p> is taken from inclusive (rather than jet) spectrum

22

2 2TaTt

TaTtNT

pp

ppj

jjTT systematics: formulae systematics: formulae

52

22

2

11

2

TaTt

NT

pp

j


)1

ln()ln(zp

E

Borghini,Wiedemann, hep-ph/0506218

Why photon-tagged jets?Why photon-tagged jets?

Medium effects redistribute (q L ) the

parton energy, Ejet, inside the hadron jet

(multiplicity, jT).

If we measure E ≈ Ejet

^̂

Redistribution can be best measured with the Fragmentation Function... If we know E Ejetjet..

HI environment hinders precise

reconstruction of Ejet.

Quenching increaseslow-pT particles

Quenching reduceshigh-pT particles

1/N

jet d

N/d


Photon Detection in ALICEPhoton Detection in ALICE

PHOS (1000 x 0.24 in (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

→ e+e- Z Conversions (Central Barrel) large coverage: 360O x 1.8 (2.4) in

(Conversion/CentralBarrel=0.08) low conversion probability : 8% (16%)


Interaction of photons with matterInteraction of photons with matter

•Photoelectric effect•Compton scattering•Pair production: E>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 conversion in tracking detectors ALICE ( ITS+TPC+TRD)


Direct photon sourcesDirect photon sources

...in a large background from 0 and decays

q

qg

γ

q

q g

γ

q

q

q

q

g

g

g

γγ

qg Compton Scattering

qq Annihilation

Bremsstrahlung,fragmentation

Thermal photons from QGP and hadron gas

Photons from Jet re-interaction in the medium

Why? Do not interact strongly. Carry information about the early state.


Photon Production: different sourcesPhoton Production: different sources

Photons are abundantly produced at LHCJet-photon conversion in the plasma dominates 8<pT<14 GeVPrompt hard NN scattering dominant for p T>20GeV at LHC

Turbide, Gale, Jeon, and Moore PRC (2004) 014906