EMCal meeting 1/34 Gustavo Conesa Balbastre Review on direct photon measurement and jet correlations...

EMCal meeting 1/34

Gustavo Conesa Balbastre

Review on direct photon measurement and jet

correlations with EMCal

EMCal meeting 2/34

Outline

Introduction: Why direct photon measurement and correlation with jets.

Photon / 0 discrimination in EMCal: Shower shape analysis Summary of work done by Cynthia Hadjidakis

Direct prompt photon identification in EMCal: Isolation cut Summary of work done by Gustavo Conesa and Amaya

Casanova

Tagging jets with photons: Gamma in PHOS: Summary of work made by Gustavo

Conesa Gamma in EMCal: Summary of work made by Guénolé

Bourdaud

EMCal meeting 3/34

Introduction:Direct photons as probes for QGP

Direct EM probes convey unperturbed information and their production probe the medium Tag medium-modified jets:

Prompt photons from 2->2 hard process (E > 10 GeV) Medium modified production:

Fragmentation photons (E < Ejet) Medium produced photon:

Bremsstrahlung and jet conversion (E < Ejet) Thermal photons (E < 10 GeV)

Challenge: Disentangle the different sources. Neutral mesons decay.

But decay photons provide a first choice probe of medium effects

Identify real photons (EM calorimetry, trigger) and e+e- from virtual and converted photons (tracking and PID, trigger)

EMCal meeting 4/34

Introduction:Why photon-tagged jets?

Medium effects redistribute (qL) the parton energy, Ejet, inside the hadron

jet (multiplicity, jT).

If we measure E ≈ Ejet

^̂AA BB

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

HI environment hinders precise reconstruction of Ejet.

Jet

EMCal meeting 5/34

Introduction: How many direct photons?

10k/year

Large sample of direct LO -jet for pT < 30 GeV/c in PHOS and pT < 50 GeV/c in EMCal …

… but0 = 0,01-0,1 for pT > 10 GeV/cWe need a good 0 PID

EMCal meeting 6/34

-0 discrimination

Three regions of analysis

well separated clusters invariant mass analysis

< 15 GeV/c in EMCal< 30 GeV/c in PHOS

merged clustersnot spherical shower shape analysis

5 - 40 GeV/c in EMCal 30 - 100 GeV/c in PHOS

increasing pT

Opening angle << 1 cellall 0’s at this energy are in jets isolation cut

> 40 GeV/c only method in EMCal

R

PHOS/EMCal

TPC

candidate

IP

Isolated if:•no particle in cone with pT > pT thres

• or pT sum in cone, pT < pT

thres

EMCal meeting 7/34

PHOS identified spectrum pp and PbPb annual statistics

Yaxian M. poster QM2008

IC: R =0.3, (pT)=2 GeV/c IC: R =0.2, pT>2 GeV/c

At least one count up to ~100 GeV, counting rates for correlations good up to 30 GeV.

ALICE-INT-2005-014G. Conesa et al., NIM A 580 (2007) 1446

2 PHOS modules

EMCal meeting 8/34pGeV/cpGeV/c

-0 discrimination in EMCal: Shower Shape Analysis

identified as identified as

Uniform and 0 distributions, weighted to match INCNLO predictions

identified : 02 < 0.25

identified 0: 02 > 0.25

PID

eff

icie

ncy

as

as

See Cynthia’s H. talk about EMCal PID during PWG4 meeting in 11 December 2007 for more details

p+p

PID

eff

icie

ncy

Pb+Pb

identified as

identified as

as

as

EMCal meeting 9/34

/0 discrimination in EMCal Shower Shape Analysis

Nd

irec

t

/ N

from

pGeV/c pGeV/c

p+p 14 TeV

central Pb+Pb 5.5 TeVfactor 5 suppression

→ 0 suppression factor = 5-10 for pT =[10-30] GeV/c in p+p

→ 0 suppression factor > 5 for pT =[15-30] GeV/c in Pb+Pb

→ Ndirect / Nfrom ~ 1 in Pb+Pb for pT =[20-30] GeV/c

See Cynthia’s H. talk about EMCal PID during PWG4 meeting in 11 December 2007 for more details

EMCal meeting 10/34

Study presented for the CD2 Photons are correctly identified with a 90% efficiency

in pp collisions and more than 60% in PbPb collisions in the pT range from10 to 100 GeV/c

0 are misidentified as photons and with an efficiency that varies from 20 to 10 % going from 10 to 20 GeV and increases to 40 % at 40 GeV in pp collisions, similar in PbPb collisions

The PID helps to improve the ratio direct 0 in the region from 10 to 40 GeV, but it is still too small.

An additional condition to separate direct photons from the rest is needed: Isolation Cut

/0 discrimination in EMCal Shower Shape Analysis, Summary and conclusions

EMCal meeting 11/34

Direct photon identification in EMCal:Event generation

pp PYTHIA collisions : 3 simulation cases:

1) pp @ √14 TeV2) pp @ √5.5 TeV, merged with HIJING, no quenching in PYTHIA.3) pp @ √5.5 TeV, merged with HIJING, quenching: qhat = 50.

+jet in final state (MSEL=10) – jet Prompt is the signal under study.

2 jets in final state (MSEL=1) jet – jet These events constitute the background: decay , fragmentation and hadrons. Jet-Jet Event generation with jets containing at least one 0 with pT>5 GeV/c in the

acceptance of EMCAL.: production of fragmentation photons suppressed. Also did a pp simulation without trigger in the same bins, similar number of

events, to correct for this bias effect. ~10 k events in different pT hard bins.

1) Pb-Pb collisions @ √s = 5.5A TeV: pp simulations 2) and 3) merged with HIJING central events (b < 3fm) @ √s = 5.5A TeV.

2) Simple PID with shower shape used to discriminate photons from other particles: if 0

2 < 0.25 cluster is a photon (Cynthia H., PWG4 meeting, 12/07)

3) Full ALICE simulation with AliRoot 4.07 Release.4) Fidutial cut applied to all events.

See my talk in Prague ALICE meeting.

EMCal meeting 12/34

Direct photon identification in EMCal: Generated and reconstructed+PID spectra: -jet : pp @ √14 TeV

50 % of convert in the material before EMCal (5-10% in ITS-TPC). Cluster reconstruction efficiency is almost 95% but with shower shape selection the efficiency descends to 60-80% due to the non photon shape of some converted clusters.

PYTHIAPYTHIA

EMCal meeting 13/34

Cluster reconstruction efficiency is almost 90%.With shower shape selection the efficiency descends to 45-75%

PYTHIAPYTHIA

Direct photon identification in EMCal: Generated and reconstructed+PID spectra: -jet : pp+PbPb @ √5.5

TeV

EMCal meeting 14/34

Direct photon identification in EMCal: jet-jet clusters rejection with photon PID

pp @ pp @ √14 TeV√14 TeV PbPb @ PbPb @ √5.5 TeV√5.5 TeV

The jet cluster rejection goes from 0.3 (large value due to decay The jet cluster rejection goes from 0.3 (large value due to decay correctly identified correctly identified as as , no invariant mass analysis is done) to around 0.02 in pp collisions. There is an , no invariant mass analysis is done) to around 0.02 in pp collisions. There is an increase at 30-40/c GeV because PID for larger pincrease at 30-40/c GeV because PID for larger pTT cannot separate effectively cannot separate effectively

overlapped overlapped from from 00 decay. In Pb-Pb rejection worsens, from 0.5 to 0.05. decay. In Pb-Pb rejection worsens, from 0.5 to 0.05.

Decay Decay not overlapped, not overlapped,

Overlapped decay Overlapped decay rejection no more feasible rejection no more feasible

EMCal meeting 15/34

Direct photon identification in EMCal: Prompt photon / jet clusters with and without PID

pp @ pp @ √14 TeV√14 TeV PbPb @ PbPb @ √5.5 TeV, qhat=0√5.5 TeV, qhat=0 PbPb @ PbPb @ √5.5 TeV, qhat = 50√5.5 TeV, qhat = 50

With PID prompt With PID prompt to jet clusters (decay to jet clusters (decay , pi0, hadrons) , pi0, hadrons) ratio increases significantly but it is not enough.ratio increases significantly but it is not enough.

EMCal meeting 16/34

Direct photon identification in EMCal: Isolation Cut : Prompt photon / jet clusters

Ratio isolated clusters in -jet / isolated clusters in jet-jetClusters selected with PID 2

0< 0.25

pp @ pp @ √14 TeV√14 TeV PbPb @ PbPb @ √5.5 TeV√5.5 TeV PbPb @ PbPb @ √5.5 TeV, qhat = 50√5.5 TeV, qhat = 50

Prompt photons signal larger than jet-jet clusters Prompt photons signal larger than jet-jet clusters background for pbackground for pTT larger than around 15 GeV/c for pp larger than around 15 GeV/c for pp

and quenched PbPb eventsand quenched PbPb events

EMCal meeting 17/34

pp @ 14 TeVpp @ 14 TeV

Direct photon identification in EMCal:Isolated Spectra

PbPb @ 5.5 TeV, qhat=0PbPb @ 5.5 TeV, qhat=0 PbPb @ 5.5 TeV, qhat=50PbPb @ 5.5 TeV, qhat=50

With PIDWith PID

With PIDWith PID

With PIDWith PID

IC Parameters: R=0.4, pTth = 0.5 (pp), 2 (PbPb) GeV/c

Isolation seems to work in pp and PbPb quenched events for pT > 15-20 GeV/c.I would like to have larger amount of jet-jet simulations to quantify better the effect of other particles background at high pT

EMCal meeting 18/34

Direct photon identification in EMCal: Prompt & Fragmentation photons: pT distribution

PYTHIA pp collisions √s=14 TeV

|| < 1

Pythia produces non hadronic decay photons: Prompt photons: Compton and

annihilation processes Jet-Jet events:

Initial state photons (ISR), radiated by hard parton before scattering. Few

Final state photons (FSR), scattered partons radiate / fragment into bremsstrahlung / fragmentation photons

Pure Pythia Generation, millions of events in several pT hard bins.

Spectrum of all photons in || < 1 in all plots.

Isolation done on the pure PYTHIA particles, R=0.4, pT

th = 1 GeV/c. Particles with status code 1

EMCal meeting 19/34


|| < 0.5

NLO calculation thanks to Lamia B.

Direct photon identification in EMCal: Prompt & Fragmentation photons: pT distribution

EMCal meeting 20/34

Direct photon identification in EMCal: Direct & Fragmentation photons Isolation efficiency.

Prompt and ISR are isolated, FSR at most 50% are not isolated, high z. Are isolated fragmentation photons similar to prompt photons?

Prompt photons and isolated fragmentation photons have a correlation with particles in the away side, not in the near side.

But correlation/fragmentation function of both isolated fragmentation and prompt photons seems not to follow exactly the same trend due to the fact that isolated fragmentation photons do not carry all the parton energy (more in back-up).

EMCal meeting 21/34

Direct photon identification in EMCal :

Summary & conclusions

jet-jet and -jet events, pp and Pb-Pb collisions, quenched and not quenched, have been generated and fully reconstructed.

A simple PID and Isolation Cut have been applied and the measurements seem feasible for prompt energies larger than 10-20 GeV/c in pp and Pb-Pb quenched collisions.

Need a large production of jet-jet events to improve background estimation after isolation and use a more sophisticated PID.

PYTHIA predicts that fragmentation photons in jet-jet events are produced in a same amount as prompt photons. Most of them are isolated, carry a large value of the parton energy.

EMCal meeting 22/34

Tagging jets with photonsOld approach

Search identified prompt photon (PHOS or EMCal) with largest pT (E > 20 GeV).

Strategy (event by event):

min max

leading

Search leading particle : -leading180º Eleading > 0.1 E

R

Reconstruct the jet in TPC and EMCal (if available):

With Standard jet algorithms, only high pT, not enough statistics.

Used method: Particles around the leading with pT

> 0.5 GeV/c ,inside a cone of R = 0.3. PYTHIA events generated in a similar way as in

previous analysis.

IP

EMCal

TPC

ALICE-INT-2005-014

G. Conesa et al., NIM A 585(2008) 28

EMCal/PHOS

EMCal meeting 23/34

Pb-Pb collisions, pT, part > 0.5 GeV/c

Tagging jets with photons in PHOSReconstructed jet selection 40 GeV jets

TPC alone

TPC+EMCAL

p-p collisions, pT, part > 0.5 GeV/c

ALICE-INT-2005-014


EMCal meeting 24/34

TPC alone

TPC+EMCAL

p-p collisions, pT, part > 0.5 GeV/c

TPC alone

TPC+EMCAL

Pb-Pb collisions, pT, part > 2 GeV/c

ALICE-INT-2005-014


Tagging jets with photons in PHOSReconstructed jet selection 40 GeV jets

EMCal meeting 25/34

E > 20 GeV/c; TPC+EMCal detect jet particles, PHOS

Pb-Pb collisions

Background

Signal

HIC background

Any neutral signal in PHOS

z = pT, jet particle /E

Prompt identified in PHOS

If signal is quenchedIf signal is quenched

ALICE-INT-2005-014


HI Background subtracted statistically, accumulate a fake fragmentation function with particle in cone at opposite and same as jet

Tagging jets with photons in PHOSFragmentation function

EMCal meeting 26/34

Charged + EMWith quenched 0

PNNCAB

PAB

AB dT

dNR

Systematic errors due

to jet(0)-jet background

Sensitive to medium modifications at low z if larger than ~5% in both configurations. Same result using TPC alone to reconstruct the jet

ALICE-INT-2005-014


Tagging jets with photons in PHOSFragmentation function RFF

EMCal meeting 27/34

Enough counting rate to do the measurement only in the pT range 20-30 GeV.

Good sensitivity to modifications in the jet, being the jet inside or outside EMCal.

0.1 < z < 0.5, region where measurement is sensitive. For z < 0.1, too large HI background fluctuations For z > 0.5, too large statistical fluctuations.

Study was done with fast reconstruction of the jet: pT smearing of generated particles EMCal resolution similar to PHOS …

Method selects jets as a function of pT of the leading, applying a cut depending on the photon energy. Possible bias, use better a grid in the detectors as done in normal

jet finders and avoid the pT cut. Should be repeated with fully reconstructed events and a fine

tuned method.

Tagging jets with photons in PHOSConclusions and Summary

EMCal meeting 28/34

Generation of gamma-jet events, with E>30 GeV, pp, pp+HI and quenched pp + HI.

PID and isolation cut applied to the photons.

New approach: Search jet core in all event UA1 like, core defined as

Jet axis must be in

Construct fragmentation function with

Tagging jets with photons in EMCalStudy done by Guénolé Bourdaud

EMCal meeting 29/34

Jet selected, collect all charged particles around jet axis in a cone of R=0.7

Subtract HI background FFin = signal + bkg. FFout = bkg only. FFcorr : = FFsignal . ! Available range.

Tagging jets with photons in EMCal Fragmentation function calculation

EMCal meeting 30/34

Ratio pp / PbPb

Tagging jets with photons in EMCal Fragmentation function, Ejet = 100 GeV

EMCal meeting 31/34

Realistic spectrum simulated: 30 < E-jet GeV

pp events with PYTHIA. Pb-Pb events with

PYTHIA+"PYQUEN afterburner« merged in HIJING events.

1/10 of a year statistic. range usable is

0.5 < < 3.2

Tagging jets with photons in EMCal Final Fragmentation function and RFF

EMCal meeting 32/34

Conclusion of gamma tagging jets with gamma in EMCal

The modification of the fragmentation function is usable with 30 GeV for 0.5 < < 3.2.

HI Background is the main source of error. More studies of bkg subtraction are needed.

bkg area, min pT cut,

testing other kind of algorithm... Jet-Jet background still not studied.

EMCal meeting 33/34

TO DO Photon Isolation:

Larger sample of background (0, hadrons) needed.

Check predictions with other generators

Gamma-Jet tagging Study from photons at 20 GeV, PHOS and

EMCAL? Study how to improve background

subtraction. Check the effect of the jet-jet background.

EMCal meeting 34/34

GRID data sets

Available (if the grid works, the SE is not down, God is kind, …) Check http://pcalimonitor.cern.ch/job_details.jsp pp events

LHC08u: gamma (PHOS) – jet, 15 < E < -1 GeV, 3M events LHC08p: gamma (PHOS) - jet quenched, qhat=50, 15 < E < -1, 4M

events LHC08v: jet-jet, 15<Ejet<50 GeV, 4M events LHC08r: jet-jet, 50<Ejet<-1 GeV, 3M events LHC08q: jet-jet, 100<Ejet<-1 GeV, 800k events Events stored in directory: /alice/sim/PDC_08/LHC08* Need to check if this amount of jet-jet events are enough for gamma

isolation. PbPb events: HIJING central, 100k events

Desirable pp events

Gamma (EMCAL) – jet pp+PbPb events: Currently testing the grid scripts

Generate new pp and merge immediately with the available PbPb Gamma (EMCAL/PHOS) – jet (quenched, not quenched) jet-jet (quenched/not quenched) A couple of quenching scenarios? q= 20 and q=50, models PQM, PYQUEN?

EMCal meeting 35/34

Back-up

EMCal meeting 36/34

PHOS identified spectrum pp and PbPb annual statistics

Yaxian M. poster QM2008

IC: R =0.3, (pT)=2 GeV/c IC: R =0.2, pT>2 GeV/c

Statistics limits to ~100 GeV

ALICE-INT-2005-014G. Conesa et al., NIM A 580 (2007) 1446

EMCal meeting 37/34

jet-jet clusters: effect of the 0 trigger 1 0 with pT > 5 GeV/c in EMCal per event

Number of clusters found Number of clusters found in in 00 triggered pp jet-jet triggered pp jet-jet events divided by events divided by clusters found in non clusters found in non triggered events.triggered events.

From now on pp From now on pp triggered pp jet-jet triggered pp jet-jet events will be multiplied events will be multiplied by the function fitted in by the function fitted in the figure to apply the figure to apply correction for the correction for the triggering bias on the triggering bias on the hadron contribution. hadron contribution.

The fragmentation The fragmentation photon yield is much photon yield is much more suppressed (not more suppressed (not considered in the cluster considered in the cluster points and next plots)points and next plots)

Reconstructed clusters

Pythia generated particles (more events than in rec. clusters)Where the

correction should be more or less

f(pT<30) =0.86+1.55 e -0.072 pT

EMCal meeting 38/34

Fidutial cuts

Structures in front of EMCAL increase the amount of conversions, more than the 50% expected.Apply fidutial cuts to get rid of extra particles in analysis of candidates to prompt photons (but extra clusters can be inside the isolation cone).About 25% of the calorimeter acceptance after the cuts is taken out.

With fidutial cutsWith fidutial cuts With fidutial cutsWith fidutial cutsWith PIDWith PID With PIDWith PID

EMCal meeting 39/34

Other approach: photon conversionsStudy performed by Ana Marin (GSI)

Loss of efficiency at high pT under investigation

Needs to be improved !

Identify photons converting in the beampipe, ITS and TPC

Clean photon identificationProvide directional information Non vertex background (important source of systematic errors in measurement of direct photons) can be rejected.

Independent measurement of the same quantities, with different systematics compared to PHOS/EMCAL. Increase level of confidence in the results Counting annual statistics for pT > 20 GeV/c (very very rough stimations)

pp @

√s=14 TeV

PbPb @ √s=5.5A TeV

EMCal 20000 20000

PHOS 3000 3000

Tracking 4000 4000

EMCal meeting 40/34

Azimuthal correlation: Direct converted– charged particles Study performed by Ana Marin (GSI)

detected in Central Barrel

Isolation Cut: R=0.2, pT>0.7GeV

EMCal meeting 41/34

• pT threshold candidate isolated if:

• no particle in cone with pT > pT thres

• pT sum in cone, pT < pTthres

• p T min of all particles (charged and neutral) in cone is at least 0.5 GeV/c

• Consider in cone particles :• Charged in TPC acceptance: ||<0.7, 0º<<360º

• Neutral in

• EMCal acceptance: ||<0.7, 80º<<190º• PHOS acceptance: ||<0.12, 220º<<320º

• Prompt are likely to be produced isolated.

• Two parameters define isolation:

• Cone size 22R

Isolation cut method

R

PHOS/EMCal

TPC

candidate

IP

ALICE-INT-2005-014 - G. Conesa et al, NIM A 580 (2007) 1446

Reminder

EMCal meeting 42/34

Generated spectra jet : pp @ √14 TeV

50 % of convert in the material before EMCal (5-10% in ITS-TPC). Cluster reconstruction efficiency is almost 95% but with shower shape selection the efficiency descends to 60-80% due to the non photon shape of some converted clusters. PID rejects 15% of clusters generated by real photons and from 50 to 25% of converted photons.

PYTHIAPYTHIA

EMCal meeting 43/34

Generated spectra jet : pp+PbPb @ √5.5 TeV

With PIDWith PID

With PIDWith PID

Cluster reconstruction efficiency is almost 90%.With shower shape selection the efficiency descends to 45-75%PID rejects from 45% to 10% of clusters generated by photons and from 60 to 30% of converted photons.

EMCal meeting 44/34

Isolation Cut: EfficiencyRatio isolated clusters / total clusters

No PID

-jet

jet-jet

pp @ pp @ √14 TeV√14 TeV PbPb @ PbPb @ √5.5 TeV√5.5 TeV PbPb @ PbPb @ √5.5 TeV, qhat = 50√5.5 TeV, qhat = 50

Isolation rejection for jet clusters can be better than 99 Isolation rejection for jet clusters can be better than 99 % in pp and quenched PbPb events and p% in pp and quenched PbPb events and pTT > 20 GeV/c > 20 GeV/c

EMCal meeting 45/34

Isolation Cut: Efficiency pp @ √14 TeV

R=0.3Ratio isolated clusters / total clusters

No PID pTth = 0.5 GeV/c

-jet

jet-jet jet-jet

-jet

EMCal meeting 46/34

Isolation Cut: Efficiency pp+PbPb @ √5.5 TeV, no quenching


No PID pTth = 2 GeV/c

-jet

jet-jetjet-jet

-jet

EMCal meeting 47/34

Isolation Cut: Efficiency pp+PbPb @ √5.5 TeV, qhat = 50


No PID pTth = 2 GeV/c

-jet

jet-jet jet-jet

-jet

EMCal meeting 48/34

Isolation efficiencyDirect / Fragmentation ||<1

Direct & Fragmentation Isolation efficiency.

Prompt and ISR are isolated, FSR at most 50% are not isolated. Fragmentation photon (FSR) yield is larger than prompt photon for pT < 50 GeV/c but

with isolation at pT < 20 GeV/c ISR yield is small, I will not consider it in next slides. No away side correlation.


EMCal meeting 49/34

Fraction of parton energy carried by the fragmentation photon

pT > 5 GeV/c


Obviously, fragmentation photon isolation is more efficient when it has an small part of the parton (near side jet) energy. Is hadron correlation with fragmentation photons and prompt photons the same?Could we reduce further the amount of low z fragmentation photons correlating with the away jet and putting a threshold on the energy? I will check.

EMCal meeting 50/34

-jet energy/phi smearing

Jet energy reconstructed with the PYTHIA jet finder.We have to be careful when we say that is back and has the energy of the jet. There is an smearing to take into account.


pT/pTjet > 0.5pT/pTjet > 0.9

EMCal meeting 51/34

Correlation Function:

Plots for quark jets (similar for gluon jets)As expected, without isolation fragmentation have a correlation in the near and away sides, direct only in the away side. Isolated fragmentation only correlate in the away sideTo understand: why away side descends a bit in isolated FSR photons.

All charged hadrons with pT > 2 GeV/c


EMCal meeting 52/34

Fragmentation Function: zT

All charged hadrons with pT > 0.1 GeV/c inside cone of size R=1 around jet axis

Difference in FF for fragmentation and prompt due to z<1 for fragmentation photons?


Gluon Jet Quark JetpT FSR / pT jet > 0.5

EMCal meeting 53/34

100 GeV -jets, no bkg.

Fraction of reconstructed jet energy vs RReconstructed jet energy in HI /HI Background fluctuation

For Ejet = 30 GeV and R = 0.25 ! Ejet / fluctuations bkg = 2.

Tagging jets with photons in EMCalJet energy reconstruction

EMCal meeting 1/34 Gustavo Conesa Balbastre Review on direct photon measurement and jet correlations...

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Transcript of EMCal meeting 1/34 Gustavo Conesa Balbastre Review on direct photon measurement and jet correlations...