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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

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Where does the lost energy go? l We dont know! l Medium enhances gluon radiation/splitting: extra gluons at small angles (in/near jet cone) radiated gluons thermalize in medium (i.e. theyre gone!) remain correlated with leading parton, but broaden/change jet 2 WWND PHENIX Jets - Jacak

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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

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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:1010.1521

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Thats 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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6 WWND PHENIX Jets - Jacak

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9 Goal: see what happens in Au+Au

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10 WWND PHENIX Jets - Jacak

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

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12 WWND PHENIX Jets - Jacak

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

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14 WWND PHENIX Jets - Jacak

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15 WWND PHENIX Jets - Jacak

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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

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

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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

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Lets 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

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RBRC workshop 20110202 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

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RBRC workshop 20110202 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

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RBRC workshop 20110202 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

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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 whats 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 Lets get the details right!

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24 WWND PHENIX Jets - Jacak l Backup

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25 WWND PHENIX Jets - Jacak

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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 ?

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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%

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

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

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l RBRC workshop 20110202 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, 212301 (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

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l RBRC workshop 20110202 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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32 WWND PHENIX Jets - Jacak

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33 WWND PHENIX Jets - Jacak If you find the jets, theyre pretty normal

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34 WWND PHENIX Jets - Jacak

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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