Gerd J. Kunde Dilepton Tagged Jets at LHC Gerd J. Kunde LANL Paul Constantin Maria A. Castro Camelia Mironov in collaboration with Ramona Vogt and Charles Gale       h

Gerd J. Kunde Two-parton DiJet events in QGP: Observed mostly via LEADING HADRONS ONLY High-p T hadron cross section modification (R AA ) Two-hadron azimuthal correlations Shape parameters j T, k T Conditional yields – I AA Initial state is not measured  - Must rely on other measurements or - Models of initial state - Background: - Physical (correlated, v 2 -like) - Combinatorial (flat) Jet Studies in Past and Present

Gerd J. Kunde Photon-parton DiJet events in QGP Replace one final parton with a photon Initial State is Measured ! Background Both physical and combinatorial are uncorrelated (flat) Lower cross section Photon-tagging …. The Future ….

Gerd J. Kunde “Some More” Jet Study Motivation Away-width broadening with centrality. Two-hadron correlations convolutes fragmentation and broadening N part kTkT pp AuAu N part Y pp AuAu Away-yield with centrality One p Ttrigg Xp Tassoc combination (trigg=photon, assoc=hadron) Y Z=p Thad /p Tphot pp Centrality “Medium modification” of fragmentation function. Two-hadron correlations give Convoluted FFs: X E =p Tassoc /P Ttrigg =Z assoc /Z trigg Several (>4) p Ttrigg Xp Tassoc combinations for each centrality

Gerd J. Kunde Proposed already in 1996, but …  Yields low at RHIC ….  Experimentally extremely difficult X.N.-Wang in PRL

Gerd J. Kunde New Approach Di-Lepton Tagging  Instead of real photon tagging one tags with virtual photon that decays into a dilepton !  Background: Drell-Yang and Semileptonic Heavy Quarks  DIRECT ENERGY LOSS MEASUREMENT Tag gives the pt of the hard scatter q+qbar   * + Jet  l + l - +Jet Srivastava, Gale, Awes - PRL C 67 (2003)

Gerd J. Kunde Cross Section Estimate: Dilepton+Jet q+qbar  g+  *  g+ l + l - q+g  q+  *  q+ l + l -  Jet-dilepton diagrams are the NLO correction to LO DrellYoung diagrams  Given dilepton mass M, the DY cross section decreases exponentially, while the dilepton-jet cross section decreases like a powerlaw. Srivastava, Gale, Awes - PRL C 67 (2003)

Gerd J. Kunde Physics Background l+l+ L-L- K 0 pair ±± ±± Open heavy quarks produce correlated dileptons opposing hardons very much like the signal … Srivastava, Gale, Awes - PRL C 67 (2003)

Gerd J. Kunde Rapidity correlation of the dilepton and the recoiling jet Jet-rapidity integrated dilepton rates for various pair masses √ =0.4GeV Srivastava, Gale, Awes - PRL C 67 (2003) Predictions for RHIC Rates too low Srivastava, Gale, Awes - PRL C 67 (2003)

Gerd J. Kunde Predictions for LHC Jet-rapidity integrated dilepton rates for various pair masses Rapidity correlation of the dilepton and the recoiling jet Srivastava, Gale, Awes - PRL C 67 (2003)

Gerd J. Kunde LHC Jet Studies “Peter Jacobs” Plot: Annual Yields

Gerd J. Kunde LANL Studies  We currently have a 3 year LDRD-ER grant from LANL to explore jet tagging at LHC in general and CMS (Compact Muon Solenoid) specifically.       h

Gerd J. Kunde LANL Studies Go from analytic solutions to generator to be able to simulate the detectors.

Gerd J. Kunde LANL Studies Generate Signal in Pythia, Scale.. Generate Background in MNR Determine Rates and Yields Determine Signal/Background Experimental Background Suppression Extract Jet Hadrons via Azimuthal Correlation Extract “In-Medium” Fragmentation Function Computing is expensive ….

Gerd J. Kunde The Diagrams Pythia 6.32HVQMNR

Gerd J. Kunde Understanding Heavy Background: Theory NLO (HVQMNR) (Mangano, Nason, Ridolfi) PYTHIA total CERN yellow report on heavy flavor production: hep-ph/ All heavy quarks codes, i.e. FONL (MNR), Cascade and FONLL predictions are within a factor ~ 2 hep-ph

Gerd J. Kunde LANL Studies for Gamma *  For gamma * to study yield in 3 mass windows

Gerd J. Kunde LANL Studies –Annual Yields  Z 0 is the tag with the highest annual yields

Gerd J. Kunde LANL Studies - Gamma *  Signal and heavy quark background

Gerd J. Kunde LANL Studies - Gamma *  At LHC the gamma* tags are difficult  (unless there is strong heavy quark suppression)

Gerd J. Kunde Displaced Track Study for Background Reduction  LHC experiments have powerful vertex detectors, resolutions of about micron vtx dca p lepton p meson lepton = e ±, μ ± meson = D ±, B ± (0,0,0)

Gerd J. Kunde Background Suppression via DCA cut  About a factor 5 suppression  This is only an estimate, need full detector simulation

Gerd J. Kunde LANL Studies - Z 0  Signal and heavy quark background

Gerd J. Kunde LANL Studies - Z 0  Z 0 tags look very promising

Gerd J. Kunde LANL Studies - Z 0  Signal to background ration is good above 20 GeV/c

Gerd J. Kunde LANL Studies  Several thousand tagged jets in the first year

Gerd J. Kunde LANL Studies Generate Signal in Pythia, Scale.. Generate Background in MNR Determine Rates and Yields Determine Signal/Background Experimental Background Suppression Extract Jet Hadrons via Azimuthal Correlation Extract “In-Medium” Fragmentation Function

Gerd J. Kunde LANL Studies

Gerd J. Kunde  p+p : z=p T associated /p T trigger  Fragmentation function:  A+A : distribution of particles associated with a trigger after medium modification  have to disentangle the ‘jet’ component from the global ‘flow’ “Regular Hadron”Azimuthal Correlations CARTOON flow+jet jet C(ΔΦ) flow BKG = B(1+2v 2 (p T asso )v 2 (p T trig )cos(2  )) p+p A+A Back side Same side Trigger Particle Associated Particles hPt hadorn tagged (triggered) jet

Gerd J. Kunde Azimuthal Correlations: Z0/γ*+jet  no flow for dilepton  flat global background  p T jet ~ p T Z0/γ*  jet energy determined  no ambiguities (π 0 ->2γ, η etc) as in gamma+jet BKG = B(1+2v 2 (p T asso )v 2 (p T trig )cos(2  ))

Gerd J. Kunde LANL Studies This is not yet scaled for pb-pb

Gerd J. Kunde LANL Studies

Gerd J. Kunde LANL Studies  Estimate of “in-medium fragmentation function ” measurement

Gerd J. Kunde Last Slide Z 0 is a weakly interacting probe to analyze the strongly interacting matter at LHC The dilepton trigger gives direct and accurate access to the initial momentum of the away-side jet The Z 0 dimuon tagged jets are a clean signal that can be measured to high momentum Reasonable rates to try a measurement of the fragmentation function in pb-pb collisions