Zγ Generator and Background Studies Lindsey Gray University of Wisconsin at Madison EWK: Multiboson Meeting 9 April, 2009

Lindsey Gray, UW Madison Zγ Production Direct Zγ coupling = zero In Standard Model Two Channels Photon radiated by quark “Outer Zγ” Photon radiated by lepton “Inner Zγ” Useful for calibration Mz = Mllγ Rate affected by Trilinear Gauge Coupling Rate accurately predicted in SM Look for excess outer Zγ “Inner Zγ” Say FSR is useful for calibration ISR is signal l = e, μ “Outer Zγ” Signal  Lindsey Gray, UW Madison 9 April, 2009

New Physics Accessible With Zγ Possible causes, if excess is observed: Composite vector boson models Could give electric dipole moment to Z Higgs  Zγ Any model which adds particles that decay into Zγ. 4th Generation of Quarks 4th Generation of Quarks can be seen through production of ultraheavy vector quarkonium with constituent quarks ‘Q’ (mass of roughly 1 TeV. The pseudoscalar “eta” quarkonium gives no contribution to the cross section. Initial legs shown as gluons since at the LHC, and for quarkonium in general, the production mode is primarily gluon fusion.   Leads to increase in cross section. Lindsey Gray, UW Madison 9 April, 2009

Anomalous Electric Dipole Moment is the center of mass energy. ‘O’ is the combination of interacting fields ‘j’ denotes vector or axial vector couplings ‘n’ is the order of the correction ‘f’ is the Anomalous Coupling constant (AC) ‘Λ’ is the scale of new physics interactions Standard Model Zγ 3.3 pb per lepton channel Shown: anomalous electric dipole moment. (f63 = .08) Enhanced rate of Zγ 3.4 pb per lepton channel Λ = 1 TeV 4.3 pb per lepton channel Λ = 5 TeV The A-EDM term in the vertex function is proportional to the emitted photon energy. Comes from terms like Z_{mu,sigma}F^{mu,rho}Z_{sigma,rho}, add in levi-civita symbol to get all terms. The magnetic quadrupole term goes as (Z momentum) * (emitted photon energy) but gets scaled by another factor of 1/mZ^2 comes from terms ZFZF, permuting lorentz indices as needed. Λ = 5 TeV √s =10 TeV Λ = 1 TeV Plots generated with program described in: U. Baur, T. Han, J. Ohnemus Phys. Rev. D 57, 2923 (1998) Standard Model Outer Zγ Lindsey Gray, UW Madison 9 April, 2009

Search for Excess Energetic Photons from Outer Zγ Anomalous couplings and new resonances enhance Zγ production cross-section Enhancement occurs for events with energetic photons Rare in SM Outer Zγ Excess of high ET photons compared to standard model indicates new physics √s =10 TeV Λ = 5 TeV Λ = 1 TeV Standard Model Outer Zγ Lindsey Gray, UW Madison 9 April, 2009

Current Anomalous Coupling Limits Place limits by modeling Zγ photon ET of various anomalous coupling strengths Determine what range of coupling strengths is consistent with ET distribution seen in data Tevatron measured limits on anomalous couplings: New Physics Scale Λ > 1 TeV Determined by Tevatron mass reach. Anomalous Coupling f63 < .083 At Λ = 1 TeV Anomalous Coupling 2.0 fb-1 Limits on CP Conserving Vector (h3) and Axial Vector (h4) Couplings Jianrong Deng, Al Goshaw, Thomas Phillips Jan 31, 2008 http://www-cdf.fnal.gov/physics/ewk/2008/Zgamma/ Lindsey Gray, UW Madison 9 April, 2009

High Level Electron Trigger Electron HLT Find groups of energy in ECAL Reconstruct tracks near deposit Match energy deposit to tracks Recover energy losses to bremsstrahlung by extending included calorimeter area in phi direction. For Zγ study at LHC startup: Use isolated electron trigger to tag possible Zγ events. Isolate electrons by summing nearby calorimeter deposits to check for activity. Electron pT >15 GeV Electron E_T threshold may drop to 10 GeV by LHC start up (only say if someone asks). • Lindsey Gray, UW Madison 9 April, 2009

Muon High Level Trigger Muon HLT Find track in muon system Reconstruct tracks in tracker pointing towards muon system track Match muon system track to tracker track For Zγ study at LHC startup: Zγ events use non-isolated muon trigger to tag possible events. Muon pT > 5 GeV μ- Side Note: The matching criteria can be set to use chi-square minimization matching instead of delta-R matching. • Lindsey Gray, UW Madison 9 April, 2009

Photon Reconstruction Photons reconstructed from collections of associated crystals with energy in ECAL called SuperClusters. Starts from a “seed” crystal of > 1 GeV Make 5x5 crystal “seed cluster” if seed crystal is local maximum Add up to 17 1x5 rows in each direction in phi, keeping rows with energy sum > .1 GeV All SuperClusters are Photon candidates ET > 10 GeV H/E < .2 Requires no matched pixel detector hit. The presence in CMS of material in front of the calorimeter results in bremmstrahlung and photon conversions. Because of the strong magnetic field the energy reaching the calorimeter is spread in φ. The spread energy is clustered by building a cluster of clusters, a "supercluster", which is extended in φ. R9 The shower shape variable R9 is effective in distinguishing photon conversions in the material of the tracker. Photon candidates with large values of R9 either did not convert or converted late in the tracker and have good energy resolution. Photons converting early have lower values of R9 and worse energy resolution. The variable R9 has been shown to be very useful also in discriminating between photon sand jets. This occurs both because of the conversion discrimination – either of the photonsfrom a pi0 can convert – and because, looking in a small 3×3 crystal area inside the supercluster, the R9 variable can provide very local isolation information about narrow jets. R9 Crystal f Crystal h ■ Crystals in Seed Cluster ■ Other crystals within Supercluster --- Supercluster boundary Lindsey Gray, UW Madison 9 April, 2009

Photon Identification Photon reconstruction begins with SuperCluster > 10 GeV. Other particles can create a 10 GeV SuperCluster. Jets fragmenting primarily to π0 .001 of jets fake photons (# jets to # photons ~ 1000:1) Electrons Photon ID selects reconstructed photons passing various quality cuts. HCAL < 10 GeV, near reconstructed photon. ECAL < 10 GeV near reconstructed photon. Require < 2 tracks near reconstructed photon. Require that 80% of ECAL energy is within 3x3 crystals. Electrons appear more spread out in phi than direct photons due to bending in magnetic field. ■ Crystals in Seed Cluster ■ Other crystals within Supercluster --- 3x3 region --- Supercluster boundary Note that the cuts mentioned here are very loose cuts which were chosen to provide the greatest photon acceptance without regard to purity. We will see that we need much improvement to pick out the outer Zgamma signal. Chris Seez , photon workshop talk. Crystal f Crystal h Lindsey Gray, UW Madison 9 April, 2009

Electron Reconstruction Calorimeter Reconstruction Create superclusters of ECAL energy to include bremmstrahlung photons. ET > 4 GeV H/E < .1 Tracker Reconstruction Require calorimeter deposit matched to reconstructed track, ΔR < .15 pT > 3 GeV Pixels Tracker Strips ET pT • e- γ Lindsey Gray, UW Madison 9 April, 2009

Lindsey Gray, UW Madison Muon Reconstruction Standalone Reconstruction Muon system only Tracker Reconstruction Match tracks to regions in the calorimeter consistent with a minimum ionizing particle. Match within Global Reconstruction Match tracker tracks to muon system tracks by minimizing a ‘quality’ variable. ‘Δd’ is distance between end of tracker track and beginning of muon track Standalone Muon Track Inner Detector You need to explain the difference here between the HLT muon reconstruction and the offline muon reconstruction. Track Quality Lindsey Gray, UW Madison 9 April, 2009

Zγ & Z+Jets Event Simulation Zγ generated with Pythia 6.409 LO matrix element cross section calculation Higher order initial (final) state radiation is approximated Z+jets background generated with MadGraph Matrix element cross section calculation for Z + N ≤ 4 Jets Detector simulated using Full Simulation (GEANT) for signal and FastSim for background. GEANT simulates passage of particles through matter. FastSim is a parameterization of GEANT CMS simulation with faster execution time. Detector simulation GEANT 4 FastSim Hard scattering Pythia MadGraph Hadronization, showers, IFSR PYTHIA Reconstruction of event CMSSW Lindsey Gray, UW Madison 9 April, 2009

Zγ Generator Comparison Pythia Baur Generator LO or NLO QCD Matrix Element LO NLO Anomalous Couplings No Yes Tunable Pythia Based Hadronization Interface to Pythia in Progress Number of Zγ Events vs. Photon ET Baur Zγ Generator Developed by Dr. Ulrich Baur (U. Buffalo) et al. Calculates NLO Zγ cross section using Monte Carlo Tunable anomalous couplings & new physics scale Λ Accurately models photon ET for outer Zγ Baur SM Outer Zγ Pythia SM Outer Zγ Events Lindsey Gray, UW Madison 9 April, 2009

Comparing Baur to Tevatron Data CDF measures inner & outer Zγ = 4.6 ± 0.2 (stat) ± 0.3 (sys) pb = 1.2 ± 0.1 (stat) ± .17 (sys) pb D0 measures inner & outer Zγ as well = 4.4 ± .27 (stat) ± .27 (sys) pb All measurements agree with Baur MC predictions: = 4.5 ± 0.4 pb (Inner + Outer Zγ) = 1.21 ± 0.1 pb (Outer Zγ Only) 2.0 fb-1 Note that these numbers are for tevatron energies, LHC Outer Zγ cross section is ~5 times higher. But Z+jets is a factor of 14 times larger at LHC Baur Anomalous Coupling 1.1 fb-1 Lindsey Gray, UW Madison 9 April, 2009

Z+Jets Background to Outer Zγ 1 in 1000 jets fragment primarily to π0 σZ+Jets = 251 pb @ Tevatron (to leptons) σZ+Jets = 3700 pb @ LHC (to leptons) Similar kinematics to Outer Zγ CDF Z+Jets pT measurement matches NLO MCFM well. MCFM: Monte Carlo for Femtobarn Measurement (dev. by CDF Collab.) Give accurate background prediction for CDF Zγ measurement CMS Z+Jets will be measured in 200 pb-1 Expect more Z + multiple jets Aside: Due to more gluons being present in protons at LHC, the compton-like ( q + gluon -> q + Z) channel diagram contributes more than at Tevatron. Also, the quark bremsstrahlung diagram (with Z in s-channel) will contribute in a different way than at Tevatron since the anti-quark in this case is coming from the sea instead of being a valence quark of an anti-proton (vastly different PDFs!). These differences force the Z+jets cross section to be remeasured at LHC since we cannot simply extrapolate from the Tevatron results due to these different diagrams contributing. Lindsey Gray, UW Madison 9 April, 2009

Zγ Signal and Z+Jets Background Require electrons, muons and photons to be within the tracker and to pass trigger. (-2.5 < η < 2.5) Require e±: ET > 15 GeV & μ±: pT > 5 GeV Removes poorly reconstructed e± and μ±. Starting With: 105 Signal 28k Bkg [200pb-1] Zγ -> eeγ MC Z+jets MC Add % and number left. Annouce that I’m doing this. Purity? Low tail coming from faked leptons being associated with leptons from Z. Change title to explain Z+jets and Zgamma background! Zγ->μμγ MC Z+jets MC 200pb-1 200pb-1 e μ Lindsey Gray, UW Madison 9 April, 2009

Cut on Dilepton Invariant Mass Require dilepton mass near Z peak (70 < Mll < 100) Majority of signal Zs are on shell Suppresses Inner Zγ What’s Left: 85 Signal, 81% 21k Background, 75% Reject Reject Add % and number left. Annouce that I’m doing this. 200 pb ^-1!!!!!! Purity? Low tail coming from faked leptons being associated with leptons from Z. e μ Zγ -> eeγ MC Z+jets MC Zγ->μμγ MC Z+jets MC Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: H/E Hcal-to-Ecal energy ratio of a reconstructed photon. Jets have a larger hadronic energy fraction. Hence, so do many jets that fake photons. Cut at H/E = .025 What’s Left: 75 Signal, 74% 9k Background, 33% % rejection and total left! # of background # of signal every plot. Combine converted and unconverted plots. Z+jets Zγ EM Supercluster g ECAL jet ECAL HCAL reject Supercluster Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: R9 Cut on ratio of E3x3 to Esupercluster ( “R9”) EM deposits from Jets will be more spread out. Except energetic π0’s Cut at r9 = .90 What’s Left: 45 Signal, 43% 2k Background, 7.9% Z+jets Zγ 200pb-1 f h reject Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: Track Isolation Count number of reconstructed tracks in a cone near the photon with pT > .5 GeV Faked photons have more tracks in .4 ΔR cone. Cut at Number of Tracks = 2 What’s Left: 41 Signal, 39% 1.5k Background, 5.3% Cut at 2 retains conversions. Z+jets Zγ Isolation Cone ΔR=0.4 γ reject Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: ET Isolation Σ (Hcal ET + Ecal ET + Track pT)/ET, Supercluster in annulus around reconstructed photon. Faked photons have more energy and tracks in the .06 < ΔR < .4 annulus. Cut at (Isolation Sum)/ET = .4 What’s Left: 25 Signal, 24% 480 Background, 1.5% Z+jets Zγ Signal Cone ΔR=0.06 Isolation Cone ΔR=0.4 γ reject Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: Phi Width Since π0 -> γγ, faked photons will appear wider in phi due to the opening angle between the photons. Cut at Phi Width < .015 What’s Left: 17 Signal, 16% 300 Background, 1.0% The rejection factor may look bad here but this is an artifact of running out of statistics. In raw numbers there are actually more signal events than background, and more signal events are lost than background events so it appears that this cut is not doing much. Essentially the Z+Jets sample space is not well-filled enough. Z+jets Zγ f h reject Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: Minimum ΔRlγ ΔRlγ > 1.3 cut applied after previous photon cuts. Further rejects Z+Jets background and Inner Zγ Added advantage of avoiding singularity in the Zγ cross section from photon collinearity Improves cross section prediction What’s Left: 9 Signal, 8.5% 38 Background .13% E, mu bigger, try making DeltaR cut larger? Final answer on photons,,,, indicate e reject reject Z+jets Zγ Z+jets Zγ μ Lindsey Gray, UW Madison 9 April, 2009

Cut on llγ Invariant Mass Inner Zγ events with large photon ET can pass ΔRlγ cut. Dilepton+photon invariant mass will be near Z mass. Majority of outer Zγ will be outside of Z peak. Cut at Mllγ > 105 GeV What’s Left: 8 Signal, 7.6% 10 Background .035% Title of slide -> Invariant Mass cut … all titles go to cut being applied. Combine current title with third bullet. Z+jets Zγ Z+jets Zγ e μ reject reject Lindsey Gray, UW Madison 9 April, 2009

Summary of Signal & Background Zγ (Outer, Anom. Coup.) Z+jets Initial Sample 105 28k 70 < Mll < 100 GeV 85 21k Photon ID Cuts 18 310 ΔR(l±, γ) > 1.3 9 36 Mllγ > 105 GeV 8 (11) 10 200pb-1 Lindsey Gray, UW Madison 9 April, 2009

Conclusion and Next Steps Signal to background is roughly 1:1 on Z peak. 8 (11, with Anom. Coup.) Events & 10 Background Next Steps: Improve Signal-to-Background to 2:1 Measure Z+Jets background in data in tandem with Zγ measurement and apply fake rate 200 pb-1 analysis allows SM Zγ measurement Sensitive to new physics Assuming maximum allowed anomalous coupling, 3 events & 1 background (NLO prediction) Photon ET > 100 GeV 3 events make it into the detector and pass cuts for f = .1, 5 TeV scale. With .7 background 3 sigma!!! Note that this is a back of the envelope calculation, since I cannot simulation AC’s in my current setup. 0.011 events make it into the detector and pass cuts for no AC. .7 background. Lindsey Gray, UW Madison 9 April, 2009

Backup Slides

Anomalous Coupling: Helicity Angle Sensitive to new physics Introduction of new physics can change favored polarization. Angle between Z momentum in lab frame and daughter lepton in rest frame. Spins of daughter particles related to Z polarization. Different distributions for longitudinal and transverse Z Different daughter spin combinations required. @ 10 TeV Standard Model Tevatron Limit Λ = 5 TeV scale Quartic coupling WWZgamma l^+, l^- to “positive lepton” Lindsey Gray, UW Madison 9 April, 2009

Resonance Search: Dalitz Plot New physics manifests as bands in the Dalitz Plot. Shown: SM Zγ Higgs -> Zγ Would appear as an enhanced segment along the Z band. Lindsey Gray, UW Madison 9 April, 2009

Higgs Branching Ratios Higgs branching ratio to Zγ is phase space heavily suppressed. Dominated by vector boson pair production Probability for all three particles to be in fiducial region small. Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: ECAL Isolation Σ (Ecal ET) in annulus around reconstructed photon. As jets are more spread out than photons, the ET sum will be larger for jets with a large EM fraction. Cut at 80% signal acceptance -> Ecal Isolation < 7.5 GeV Define annulus size. Isolation = 7.5 GeV Z+jets Zγ Scaled to 100pb-1 reject Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: Track ET Isolation Σ (Track ET) in annulus around reconstructed photon. Prompt and converted photons will have fewer energetic tracks near than a jet. Cut at ~75% signal acceptance -> Track Isolation < 3 GeV Define annulus size. Isolation = 3 GeV Z+jets Zγ Scaled to 100pb-1 reject Lindsey Gray, UW Madison 9 April, 2009

Selecting Signal Photons: Number of Nearby Tracks Reconstructed photons embedded within jets will have more nearby tracks than isolated photons. Cut at 80% signal acceptance -> # Tracks < 3 #Tracks = 3 Z+jets Zγ Scaled to 100pb-1 reject Lindsey Gray, UW Madison 9 April, 2009

Integrated Luminosity LHC 2009-2010 Expected Yield Month LHC Status Protons/Bunch Peak Luminosity Integrated Luminosity 1 Beam Commissioning First Collisions 2 Pilot Physics 3x1010 1.2x1030 100-200 nb-1 3 5x1010 3.4x1030 ~ 2pb-1 4 2.5x1031 ~ 13pb-1 5 7x1010 4.9x1031 ~ 25pb-1 6 50 ns Bunches 4.0x1031 ~ 21pb-1 7 1.1x1032 ~ 60pb-1 8 9 Total: 200 – 300 pb-1 Lindsey Gray, UW Madison 9 April, 2009