Jet Reconstruction in PHENIX l Mike McCumber – University of Colorado & l Barbara Jacak – Stony Brook University With thanks to Yue Shi Lai and John Chen

Where does the lost energy go? l We don’t know! l 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 leading parton, but broaden/change jet 2 WWND – PHENIX Jets - Jacak

Leading particles are suppressed Very similar at LHC and RHIC! Is QGP fully opaque to jets produced deep inside? 3 WWND – PHENIX Jets - Jacak blue points PHENIX  0

4 Dijet reaction plane dependence l Away side is more suppressed out-of- plane l Energy loss is path length dependent l So, medium is not totally opaque!  0 -h 20-60% arXiv:

That’s why we (all) dig deeper l Di-jets l Fragments of energy tagged jets (Justin Franz) l Heavy flavor jet correlations (Anne Sickles) l Full jet reconstruction To allow us to then deconstruct the jet fragment behavior in QGP 5 John C. H. Chen

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9 Goal: see what happens in Au+Au

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

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Fake rejection efficiency effect in p+p? 13 WWND – PHENIX Jets - Jacak Embedding!

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16 WWND – PHENIX Jets - Jacak Requiring a narrow jet  same suppression as leading hadron Hard to reconcile if eloss = splitting inside jet cone

Opening filter width finds lost jets?? 17 WWND – PHENIX Jets - Jacak Not really…

Lost energy lurks somewhere nearby? l Broadening, cones/shoulder, ridges, etc? Search for jet shape modifications l Need different techniques Look at relatively soft (low-z) fragments Signal gets tangled up with the bulk 18 WWND – PHENIX Jets - Jacak

Let’s look into differences in v 3 19 WWND – PHENIX Jets - Jacak 2-particle (small  ) v 3 higher than large  v 3 l should expect non-flow contribution i.e. jets

RBRC workshop John C. H. Chen 20 Quantify jet-related v 3 Use jets in p+p to calibrate! Do a Fourier analysis of the per trigger yield jet function –JF =  C n cos(n  ) –For Au+Au: combinatorial background “b 0 (1+2v 2 trig v 2 part cos2  )” removed via ZYAM NB: absolute normalization yields same results –ZYAM will not change any Fourier coefficients, except C 0 and C 2 Various centrality and partner p T bins for initial insights into bulk vs. jet contributions

RBRC workshop John C. H. Chen 21 Fourier Spectra of Jet Function No significant contribution above c4 Removing away side jet in pp enhances the c odd terms The C 3 in AuAu has contributions from both jet and bulk! v 3 from jet v 3 from jet+bulk

RBRC workshop John C. H. Chen 22 Fourier Spectra with high partner p T Little/no v 3 enhancement for high p T partners! Awayside is suppressed in central collisions Fourier coefficients agree with “pp-nearside only”

23 WWND – PHENIX Jets - Jacak Conclusions l QGP is very, but not fully opaque to jets punch-thru at p T >3 GeV: energy not thermalized l Reconstructed jets suppressed as leading hadrons But what’s in a jet? Holds for relatively narrow Gaussians/cones How to find/reconstruct a modified jet? l Gluon splitting puts energy outside normal jet fragmentation zone  -jet correlations show evidence for low-z hadron enhancement Messes up normal jet finding, shape must change! l Fourier analysis shows v 3 = bulk + jet contributions The devil (and shape info) is in the details Let’s get the details right!

24 WWND – PHENIX Jets - Jacak l Backup

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26 WWND – PHENIX Jets - Jacak sPHENIX Upgrade Concept + one existing Muon Arm w/ a new absorber l 2T mid-y magnet, I.d.~ 60cm (could be up to ~ 1m) Compact EMCal  E/E ~ 20%/√E (Si/W & Scint/W?) Intermediate tracker ~80  resolution (GEM or Si) l Compact HCAL for jet reco (first HCAL at RHIC!) Forward spectrometer optimized for electrons, , hadrons l Hadron ID: forward yes, mid-y ?

27 WWND – PHENIX Jets - Jacak HCAL: unique jet capability at RHIC l HCAL energy requirement removes sensitivity to fake high p T tracks Modest HCAL segmentation (  = 0.1) and resolution  E/E ~ 45%

28 WWND – PHENIX Jets - Jacak sPHENIX Upgrade Concept + DAQ/Trigger: 50B events!

29 WWND – PHENIX Jets - Jacak sPHENIX physics reach 50B events! Jets, photons quarkonia

l RBRC workshop l John C. H. Chen l 30 v n from two particle correlations Standard: v 2 (v 4 ): single particle vs. reaction plane dN/d(  Can also measure v n via two particle correlation –PHENIX: Phys. Rev. Lett. 89, (2002) –dN AB /d  = N(1+  (2C n cos(n  ))), C n = v n A v n B the two particles are in the same event, therefore share the same reaction plane When p T A = p T B, v n = sqrt(C n ) With low partner p T (below 1 GeV), the jet contribution can be ignored, but not at high p T

l RBRC workshop l John C. H. Chen l 31 v 2, v 3 from two particle correlations v 2 agrees with previous PHENIX measurements at low p T v 3 –Nonzero –Increases with p T (NB: may have non-flow effects in this method) –Increases with centrality

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33 WWND – PHENIX Jets - Jacak If you find the jets, they’re pretty normal

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35 WWND – PHENIX Jets - Jacak RHIC and LHC l Energy dependence is a key tool for understanding l RHIC provides a sweet spot for Strong coupling; dialing medium properties/ baseline Rapidity range selecting importance of initial state Dominated by quark jets, access 15<E T,jet <60 GeV Sampling large luminosity with min bias trigger