1. 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

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

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

4. 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

5. The 2010 data sample
>800M MB, >100M m triggers, >25M high multiplicity
~30M nuclear collisions

6. LHC: Entering a new regime
C W Fabjan 2008 J. Phys. G: Nucl. Part. Phys. 35,
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

7. Photon physics in ALICE
Measurement of p0 and h mesons in and
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 and
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)

8. 3 independent measurements: Conversions, PHOS, EMCAL
0 and h reconstruction
pp  0 + Xn

e+e-e+e-
(m0 = GeV/c2, BR = 0.988)
pp   + Xn
(m = GeV/c2, BR = 0.393) e+ e-  Y X
3 independent measurements:
Conversions, PHOS, EMCAL
run , event 2248

9. 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

10. 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

11. p0 and h 7TeV p0 h

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

13. Data 7TeV: h invariant mass in pt bins
Mgg GeV/c2 for normalization

14. 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

15. Differential p0 invariant yield
Differential p0 invariant yield measured
in pp TeV

16. 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, (2003).
[3] D. de Florian, Phys. Rev. D67, (2003).

17. 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 (2007).

18. Excess exponential in pT
Direct photons at RHIC
PHENIX Coll.:Phys. Rev. Lett. 94, (2005)
PHENIX Coll.:Phys. Rev. Lett. 104 (2010)
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

19. 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 , hep-ph/

20. Photon decay cocktail
Work in progress
Work in progress

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

22. 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

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

24. 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

25. 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

26. 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)

27. 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

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

29. "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

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

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

32. Jet quenching from High pT correlations
Clear away side correlation in Df
Away side correlation in central Pb-Pb washed out up to pT,trig>10GeV

33. 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.

34. 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

35. 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

36. 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 Ein Driftgeschwindigkeitsmonitor für den ALICE TRD — •Friederike Poppenborg
HK 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

37. 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 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

38. 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

39. ALICE COLLABORATION 39

40. Backup slides

41. Differential invariant cross section PHOS + Conversions

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

43. 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)

44. 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

45. 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, (2010)

46. 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, (2011)

47. Un-triggered CF

49. 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

50. 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

51. 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~
S. Bass et al. PRC79 (2009) ^
Theory-Experiment Collaboration on Hot Quark Matter

52. 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

53. 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/
Quenching increases
low-pT particles
1/Njet dN/dx
If we measure Eg ≈ Ejet
Quenching reduces
high-pT particles

54. 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%)

55. 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)

56. 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

57. Photon Production: different sources
Turbide, Gale, Jeon, and Moore
PRC (2004)
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

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

59. Data 7TeV: h invariant mass in pt bins
Mgg GeV/c2 for normalization

60. 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

61. Differential p0 invariant yield
Differential p0 invariant yield measured
in pp TeV

62. 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 (2007).

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

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