t.m. cormier wayne state university for the alice – usa collaboration

ALICE-USA Collaboration

T.M. Cormier Wayne State University

for the

ALICE – USA Collaboration

Jet Physics in ALICE and a Proposed Electromagnetic Calorimeter


Creighton UniversityKent State UniversityLawrence Berkeley National LaboratoryMichigan State UniversityOak Ridge National LaboratoryPurdue UniversityThe Ohio State UniversityUniversity of California, BerkeleyUniversity of California, DavisUniversity of California, Los AngelesUniversity of HoustonUniversity of TennesseeUniversity of Texas at AustinUniversity of WashingtonWayne State University


Why Jets in Heavy Ion Collisions? or Isn’t there a better way to make a living?


Why Jets in Heavy Ion Collisions?

Jets in Heavy Ion Collisions Provide ……

• A unique look at the QCD Radiation length of Dense, Strongly Interacting (Colored) matter (QGP).

• A tomographic tool to quantitatively study the QGP medium when benched marked with pp running or peripheral heavy ion collisions.


The basic physics …..

Parton energy loss via induced gluon radiationin the dense medium


Collision Centrality Scaling of Inclusive hadron Spectra at RHIC

CentralPeripheral


Baryons versus Mesons


Recent data from STAR at RHIC:

Away-side Jet Absorbed in Central Collisions!

CentralCollisions

PeripheralCollisions


How will this physics look in ALICE?

Vitev and Gyulassy

SPS: WA98RHIC: PHENIX

Inclusive o prediction

Data:

Range of initial state gluonDensity dN/dy = 2000 - 3500

Perhaps as little as a few %of hadrons from hard collisions will survive in thisPT range


away side jet signal

STAR TPC data AuAu

ALICE TPC is the perfect tool for this Physics

Simulation of -correlation due to mini jets in central PbPb


1/R dN/dR correlationof high PT hadrons

Fragmentation Function of Correlated Particles

Background of uncorrelatedParticles

Low PT jets and mini-jets


TPC and inner tracker allow flavor tagging in low PT jets

Hadronic Charm reconstruction


What about jets at high PT in ALICE?

• Rates / Signal to Background?

• What can be measured?

• Trigger?

• TPC at high PT?

• Reconstruction in the presence of complex underlying event?


Opportunity at the LHC to go beyond inclusive measurements

100 and 200 GeV Jets imbedded in Central PbPb Event

Underlying Event dominates jet energy resolution at lower PT


Jet energy resolution is not a significant issue because there is no significant jet energy loss to be measured…..

100 GeV PYTHIA Compared to Wiedeman et al for 20 GeVparton energy loss

Jet energy loss is apparent only for limited cone radii.


100 GeV Jet Fragmentation following 20 GeV Parton Energy Loss at Low Z in a Schematic Model

Z

0.00 0.02 0.04 0.06 0.08 0.10

10000

20000

30000

40000

50000

60000

70000

100 GeV Parton

80 + 20 GeV Partons

80 + 10 + 10 GeV Partons

Z

0.0 0.1 0.2 0.3 0.4 0.51

10

100

1000

10000

100 GeV Jet Fragmentation following 20 GeV Parton Energy Loss at High Z in a Schematic Model

80 + 10 + 10 GeV Partons80 + 20 GeV Partons

100 GeV Parton

Primary jet quenching effect is thus redistribution of energy along and perpendicular to the jet axis.

The goal of the ALICE jet physics program is to measure this energy redistribution, it’s dependence on centrality and flavor.


Pb/Sci EMCal x = 1.4 x 2/3 (Trigger, , o, direct and thermal

TPC

TRD

TOF

PHOS

RICH

ITS


Trigger with EMCal = electromagnetic energy + ~40 - 50% hadronic energy

Trigger turn-on versus EjetTrigger bias independent of PT

Of charged hadrons within ~10%


ITS+TPC+TRDlong trackinglever arm in ALICE9% at 100 GeV/c

PT/PT (%)


100 GeV/c jets in pp

16%

Jet reconstruction:

Poor man’s energy flow analysis:

Ejet =A*PTch + B*EMCal


PbPb Central 25%

pp 16%

Resolution for 100 GeV jets in pp and PbPb versus cell ET cut

PbPb events include full mini jet background from HIJING


The bottom line …. The distribution of energy parallelto (PL ), and perpendicular to ( jT), the jet axis…..

Reconstructed PL distributions for 50 and 100 GeV jetsin central PbPb collisions.


Reconstructed jT distributions for 50 and 100 GeV jetsin central PbPb collisions.

These distributions are particularlyinteresting to search for “transverse heating in the fragmentation process should it proceed within the dense medium


Flavor dependence of jet quenching – two examples of many

Leading particle spectrum for K and lead jets withPT > 75 GeV/c, baryon versus meson quenching

Baryon/anti-Baryon led jetsWith PT > 75 GeV/c - distinctionof quark / gluon quenching


The Detector:Pb/Scintillator with mega-tile technology~ 20k towers in x = 2/3 x 1.4Towers exactly projective with tiles ~ 5cm x 5cmResolution (simulated) E/E )2= (12.2%/E)2 + (0.4%)2

Photo Detectors: 5mm x 5mm APD’sModular design permitting “late” installation


Technical issues: Optical studies with 5cm x 5cm tiles andWLS readout via 0.5mm fiber

Achieve ~1.5 % RMS spatial uniformity


Summary:

• ALICE-USA collaboration is in the process of proposing a modest investment in instrumentation* for an EMCal to better enable high PT jet physics in ALICE.

• The combined power of the EMCal and the ALICE TPC and other detectors permit a complete measurement of the redistribution of jet energy parallel to and perpendicular to the jet axis. Mediummodification of the parton fragmentation process including it’s dependence on energy and flavor (s,c,b) will be measured. These measurements constitute an important extension of on going RHICmeasurements to a to a much hotter, denser and longer lived plasma.

* ~$200k per ALICE-USA institution per year for three years


• All of the above can be studied separately for baryonand meson led jets. Early RHIC data suggests there are significant differences in the quenching in these two cases.

•The calorimeter permits the study of exclusive hard scattering processes such as + jet and Zo + jet.

Summary:


Figure 5. Comparison for ideal jet resolution of the quenched and unquenched fragmentation functions of 100 GeV jets in a schematic model in which a 20 GeV primary parton energy loss is modeled as the production of a 20 GeV jet in consort with an 80 GeV jet. The Statistics correspond to only 1000 events. The properly normalized background for central HIJING PbPb events is shown.

t.m. cormier wayne state university for the alice – usa collaboration

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