Jet Reconstruction in PHENIX

Jet Reconstruction in PHENIX

Mike McCumber – University of Colorado &

Barbara Jacak – Stony Brook UniversityWith thanks to Yue Shi Laiand John Chen

2WWND – PHENIX Jets - Jacak

Where does the lost energy go? We don’t know! Medium enhances gluon radiation/splitting:

extra gluons at small angles (in/near jet cone)

radiated gluons thermalize in medium (i.e. they’re gone!)

remain correlated with leadingparton, but broaden/change jet


Leading particles are suppressed

Very similar at LHC and RHIC!Is QGP fully opaque to jets produced deep inside?

blue pointsPHENIXp0

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Dijet reaction plane dependence

Away side is more suppressed out-of-plane

Energy loss is path length dependent

So, medium is not totally opaque!

p0-h 20-60%arXiv:1010.1521

That’s why we (all) dig deeper

Di-jets

Fragments of energy tagged jets (Justin Franz)

Heavy flavor jet correlations (Anne Sickles)

Full jet reconstructionTo allow us to then deconstruct the jet fragment

behavior in QGP

5John C. H. Chen



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Goal: see what happensin Au+Au


11WWND – PHENIX Jets - JacakKey issue is event-to-event fluctuations!



Fake rejection efficiency effect in p+p?Embedding!




Requiring a narrow jet same suppression as leading hadron

Hard to reconcile if eloss = splitting inside jet cone


Opening filter width finds lost jets??

Not really…


Lost energy lurks somewhere nearby? Broadening, cones/shoulder, ridges, etc?

Search for jet shape modifications Need different techniques

Look at relatively soft (low-z) fragmentsSignal gets tangled up with the bulk


Let’s look into differences in v3

2-particle (small Dh) v3 higher than large Dh v3

should expect non-flow contribution i.e. jets

RBRC workshop 20110202 John C. H. Chen 20

Quantify jet-related v3• Use jets in p+p to calibrate!• Do a Fourier analysis of the per trigger yield jet

function – JF = SCn cos(n Df) – For Au+Au: combinatorial background

“b0(1+2v2trigv2

partcos2Df)” removed via ZYAM• NB: absolute normalization yields same results

– ZYAM will not change any Fourier coefficients, except C0 and C2

• Various centrality and partner pT bins for initial insights into bulk vs. jet contributions


Fourier Spectra of Jet Function

• No significant contribution above c4• Removing away side jet in pp enhances the codd terms

• The C3 in AuAu has contributions from both jet and bulk!

v3 from jet

v3 from jet+bulk


Fourier Spectra with high partner pT

• Little/no v3 enhancement for high pT partners!• Awayside is suppressed in central collisions• Fourier coefficients agree with “pp-nearside only”


Conclusions QGP is very, but not fully opaque to jets

punch-thru at pT>3 GeV: energy not thermalized Reconstructed jets suppressed as leading hadrons

But what’s in a jet?Holds for relatively narrow Gaussians/conesHow to find/reconstruct a modified jet?

Gluon splitting puts energy outside normal jet fragmentation zoneg-jet correlations show evidence for low-z hadron

enhancementMesses up normal jet finding, shape must change!

Fourier analysis shows v3 = bulk + jet contributionsThe devil (and shape info) is in the details Let’s get the details right!


Backup



sPHENIX Upgrade Concept+ oneexistingMuonArm w/a new absorber

2T mid-y magnet, I.d.~ 60cm (could be up to ~ 1m) Compact EMCal DE/E ~ 20%/√E (Si/W & Scint/W?) Intermediate tracker ~80 resolution (GEM or Si) Compact HCAL for jet reco (first HCAL at RHIC!) Forward spectrometer optimized for electrons, g, hadrons Hadron ID: forward yes, mid-y ?


HCAL: unique jet capability at RHIC

HCAL energy requirement removes sensitivity to fake high pT tracks

Modest HCAL segmentation (Dh Df = 0.1) and resolution DE/E ~ 45%


sPHENIX Upgrade Concept

+ DAQ/Trigger: 50B events!


sPHENIX physics reach

50B events!

Jets, photons quarkonia

RBRC workshop 20110202

John C. H. Chen

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vn from two particle correlations• Standard: v2(v4): single particle vs. reaction

plane dN/d(f-y) • Can also measure vn via two particle correlation

– PHENIX: Phys. Rev. Lett. 89, 212301 (2002)– dNAB/df = N(1+ S(2Cncos(nDf))), Cn = vn

AvnB

• the two particles are in the same event, therefore share the same reaction plane

• When pTA = pT

B, vn = sqrt(Cn)• With low partner pT (below 1 GeV), the jet

contribution can be ignored, but not at high pT

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John C. H. Chen

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v2, v3 from two particle correlations

• v2 agrees with previous PHENIX measurements at low pT• v3

– Nonzero– Increases with pT (NB: may have non-flow effects in this method)– Increases with centrality



If you find the jets,they’re pretty normal



RHIC and LHC

Energy dependence is a key tool for understanding RHIC provides a sweet spot for

Strong coupling; dialing medium properties/ baselineRapidity range selecting importance of initial stateDominated by quark jets, access 15<ET,jet<60 GeVSampling large luminosity with min bias trigger

Documents

Jet Reconstruction in PHENIX