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New Photon Results from CDF

New Photon Results from CDF. DIS 2012, Marseilles , April 22. Costas Vellidis Fermilab. Photon analyses at CDF. Photon-related analyses have been hot topics at CDF ~ 30 papers published using CDF Run II data on a wide variety of photon-related topics. C ross section measurements

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New Photon Results from CDF

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  1. New Photon Results from CDF DIS 2012, Marseilles, April 22 Costas Vellidis Fermilab

  2. Photon analyses at CDF • Photon-related analyses have been hot topics at CDF • ~30 papers published using CDF Run II data on a wide variety of photon-related topics. • Cross section measurements • Searches Xgg Hγγ Inclusive-g DIS 2013 – C. Vellidis

  3. Diphoton cross sections g _ p p g DIS 2013 – C. Vellidis

  4. Prompt gg production in hadron colliders Hard QCD (“direct”ggproduction): colinear singularity Dg/q~a/as Fragmentation: a2Suppressed by isolation cut Compton+radiationasa2 Born: a2 “Box”: Dominant at the LHC DIS 2013 – C. Vellidis

  5. Prompt gg production in hadron colliders Hard QCD (“direct”ggproduction): colinear singularity Dg/q~a/as Fragmentation: a2Suppressed by isolation cut Compton+radiationasa2 Born: a2 Possible heavy resonance decays: “Box”: Dominant at the LHC Higgs boson Extra dimensions DIS 2013 – C. Vellidis

  6. Previously published results – CDF PRL 107 (2011) 102003 PRD 84 (2011) 052006 • Identified the importance of resummation, qgfragmentationin the modeling of diphoton cross sections. 5.4 fb-1 DIS 2013 – C. Vellidis

  7. Previously published results – D0 arXiv:1301.4536 Full Run II data set • Sherpa describes data the best in the intermediate PT() and low  regions. PT1(2)>18(17) GeV/c, |η1,2|<0.9DR(g,g)>0.4, ETiso<2.5 GeV DIS 2013 – C. Vellidis

  8. Previously published results – ATLAS JHEP 1301 (2013) 086 PT1(2)>25(22) GeV/c,|η1,2|<2.37DR(g,g)>0.4 DIS 2013 – C. Vellidis

  9. Previously published results – CMS JHEP 1201 (2012) 133 • DIPHOX discrepancy for PT()>30 GeV and Df(g,g)<π/2 DIS 2013 – C. Vellidis

  10. Collinear diphoton production • Fragmentation–a higher-order effect • The pQCD cross section is divergent when q and g are collinear logarithmic enhancement of the cross section • Handled with a fragmentation function – MCFM, DIPHOX • Affectslow m(gg), moderate PT() and low  regions • Higher order subprocesses (23 at 1-loop and 24 at “tree” level) needed to describe the enhancement DIS 2013 – C. Vellidis

  11. Resummation • Remove singularities [PT()->0] by adding initial gluon radiation • RESBOS: Low-PT analytically resummedcalculation (NNLL) matched to high-PT NLO • PYTHIA and SHERPA: Use parton showering to add gluon radiation in a Monte Carlo simulation framework which effectively resums the cross section (LL) • Affects low PT() and = p regions PRD 76, 013009 (2007) Fixed-order calculation contains singular terms at and M(gg) ≠ 0 of the form or DIS 2013 – C. Vellidis

  12. Updated diphoton cross section measurements • Use the full 9.5 fb-1 CDF run II dataset • Select isolated diphotonevents • Background subtraction using track isolation information • Pythiaevaluation of efficiency/acceptance/unfolding • Compare results with new predictions DIS 2013 – C. Vellidis

  13. The Tevatron and CDF Tevatron: • Proton-antiproton accelerator • √s = 1.96 TeV • Delivered ~12 fb-1 • Recorded ~10 fb-1 for each experiment CDF • Collider Detector at Fermilab • Tracking (large B field): • Silicon tracking • Wire Chamber • Calorimetry: • Electromagnetic (EM) • Hadronic • Muon system A big thank you to Accelerator Division! DIS 2013 – C. Vellidis

  14. Photon identification and event selection Isolation cone: R=0.4 rad γ CES: shower maximum profile CP2: pre-shower • Used dedicated diphoton triggers with optimized efficiency • Photons were selected offline from EM clusters, reconstructed in a cone of radius R=0.4 in the – plane, and requiring: • Fiducial to the central calorimeter: ||<1.1 • ET 17,15 GeV ( events) • Isolated in the calorimeter: Ical = Etot(R=0.4) - EEM(R=0.4)  2 GeV • Low HAD fraction: EHAD/EEM 0.055 + 0.00045Etot/GeV • At most one track in cluster with pTtrk 1 GeV/c + 0.005ET/c • Shower profile consistent with predefined patterns: 2CES 20 • Only one high energy CES cluster: ET of 2nd CES cluster  2.4 GeV + 0.01 ET EM Cal HAD Cal • Imply that • DR(g,g) or DR(g,j)  0.4 DIS 2013 – C. Vellidis

  15. Theoretical predictions • PYTHIA LO parton-shower calculation – including gg and gj with radiation • [T. Sjöstrandet al., Comp. Phys. Comm. 135, 238 (2001)] • SHERPA LO parton-shower calculation with improved matching between hard • and soft physics [T. Gleisberget al., JHEP 02, 007 (2009)] • MCFM: Fixed-order NLO calculation including non-perturbative fragmentation • at LO [J. M. Campbell et al., Phys. Rev. D 60, 113006 (1999)] • DIPHOX: Fixed-order NLO calculation including non-perturbative fragmentation • at NLO [T. Binothet al., Phys. Rev. D 63, 114016 (2001)] • RESBOS: Low-PT analytically resummed calculation matched to high-PT NLO • [T. Balazset al., Phys. Rev. D 76, 013008 (2007)] • NNLO calculation with qT subtraction [L. Cieriet al.,http://arxiv.org/abs/1110.2375 (2011)] DIS 2013 – C. Vellidis

  16. Theoretical predictions • PYTHIA LO parton-shower calculation – including gg and gj with radiation • [T. Sjöstrandet al., Comp. Phys. Comm. 135, 238 (2001)] • SHERPA LO parton-shower calculation with improved matching between hard • and soft physics [T. Gleisberget al., JHEP 02, 007 (2009)] • MCFM: Fixed-order NLO calculation including non-perturbative fragmentation • at LO [J. M. Campbell et al., Phys. Rev. D 60, 113006 (1999)] • DIPHOX: Fixed-order NLO calculation including non-perturbative fragmentation • at NLO [T. Binothet al., Phys. Rev. D 63, 114016 (2001)] • RESBOS: Low-PT analytically resummed calculation matched to high-PT NLO • [T. Balazset al., Phys. Rev. D 76, 013008 (2007)] • NNLO calculation with qT subtraction [L. Cieriet al.,http://arxiv.org/abs/1110.2375 (2011)] DIS 2013 – C. Vellidis

  17. m(gg) • Good agreement between data and theory for Mgg>30 GeV/c2 except PYTHIA gg DIS 2013 – C. Vellidis

  18. PT() DIS 2013 – C. Vellidis

  19. PT() - ratios NB: Vertical axis scales are not the same • RESBOS agrees with low PT() data the best • SHERPA agrees with low PT() data well • NNLO and SHERPA describe the “shoulder” of the data at PT(gg) = 20 – 50 GeV/c(the “Guillet shoulder”) PYTHIA NNLO DIPHOX MCFM SHERPA RESBOS DIS 2013 – C. Vellidis

  20. () DIS 2013 – C. Vellidis

  21. ()- ratios NB: Vertical axis scales are not the same • RESBOS and SHERPA describe Df(gg) = p region • Fixed order calculations do not describe Df(gg) = p region • NNLO describes Df(gg) = 0 region PYTHIA NNLO DIPHOX MCFM SHERPA RESBOS DIS 2013 – C. Vellidis

  22. Summary of diphoton cross sections • High precision gg cross sections are measured using the full CDF Run II dataset • The data are compared with all state-of-the-art calculations • The SHERPA calculation, overall, provides good description of the data, but still low in regions sensitive to nearly collinear gg emission (very low mass, very low Δϕ) • The RESBOS calculation provides the best description of the data at low PT and large Δϕ, where resummation is important, but fails in regions sensitive to nearly collinear ggemission • The NNLO calculation provides the best description of the data at low Δϕ, but still not very good at very low mass and at high PT • More in PRL110, 101801 (2013) (supplemental material online) DIS 2013 – C. Vellidis

  23. Photon+heavy flavor (b/c) cross sections g _ p p b-jet DIS 2013 – C. Vellidis

  24. g+b/c+X production • Photon produced in association with heavy quarks provides valuable information aboutheavy flavor excitation inhadron collisions • LO contribution: Compton scattering (QgQg) dominates at low photon pT • NLO contribution: annihilation (qqQQg) dominates at high photon pT - - q Q - g q Compton scattering ~ aaS Annihilation ~ aaS2 DIS 2013 – C. Vellidis

  25. Previous results – D0 PLB 714, 32 (2012) – 8.7 fb-1 g+b+X PRL 102, 192002 (2009) − 1 fb-1 PLB 719, 354 (2013) – 8.7 fb-1 g+c+X • Good agreement for g+b+X • Discrepancy for g+c+X Discrepancies in both channels. DIS 2013 – C. Vellidis

  26. Previous results – CDF • Measure low pTcross section using a special trigger • g+b+X agrees with NLO up to 70 GeV CDF: PRD 81, 052006 (2010) - 340 pb-1 DIS 2013 – C. Vellidis

  27. Analysis overview • Measure g+b/c+X cross section using 9.1 fb-1inclusive photon data collected with CDF II detector • Use ANN (artificial neural network) to select photon candidates • Fit ANN distribution to signal/background templates to get photon fraction • Use SecVtxb-tag to select heavy-flavor jets • Fit secondary vertex invariant mass to get light/c/b quark fractions • Use Sherpa MC to get efficiency/unfolding factor • Photon ID efficiency, b-tagging efficiency, detector acceptance and smearing effects • Cross section DIS 2013 – C. Vellidis

  28. 4 theoretical predictions • NLO – direct-photon subprocesses and fragmentation subprocesses at O(aas2), CTEQ6.6M PDFs [T.P. Stavreva and J.F. Owens, PRD 79, 054017 (2009)] • kT-factorization – off-shell amplitudes integrated over kT-dependent parton distributions, MSTW2008 PDFs [A.V. Lipatovet al., JHEP 05, 104 (2012)] • Sherpa 1.4.1 – tree-level matrix element (ME) diagrams with one photon and up to three jets, merged with parton shower, CT10 PDFs[T. Gleisberget al., JHEP 02, 007 (2009)] • Pythia 6.216 – ME subprocesses: gQgQ, qqgg followed by gluon splitting: gQQ, CTEQ5L PDFs[T. Sjöstrand et al., JHEP 05, 026 (2006)] _ _ DIS 2013 – C. Vellidis

  29. g+b+X cross sections NB: Vertical axis scales are not the same • NLO fails to describe data at large photon Et – perhaps gluon splitting is treated at LO • kT-factorization and Sherpa agree with data reasonably well • Pythia with doubled gluon splitting rate to heavy flavor describes the shape DIS 2013 – C. Vellidis

  30. g+c+X cross sections NB: Vertical axis scales are not the same • NLO fails to describe data at large photon Et – perhaps gluon splitting is treated at LO • kT-factorization and Sherpa agree with data reasonably well • Pythia with doubled gluon splitting rate to heavy flavor describes the shape DIS 2013 – C. Vellidis

  31. Summary of photon+b/c cross sections • High precision g+b/c cross sections are measured using the full CDF Run II dataset • The data are compared with parton shower, fixed-order and kt-factorization calculations • NLO does not reproduce data most likely because of its limitation in modeling gluon splitting rates. • kT-factorization and Sherpa agree with data reasonably well • Pythiawith doubled gluon splitting rates to heavy flavordescribes the data shape DIS 2013 – C. Vellidis

  32. Conclusions • The CDF experiment has produced a wealth of QCD physics results and analysis techniques, which is a legacy for the current and future high energy physics experiments • We have achieved an unprecedented level of precision for many photon-related observables • Those results provide valuable information to the HEP community, e.g. the diphoton resultscanhelp the precision measurements of H boson in the gg channel. • … and we are not done yet!! DIS 2013 – C. Vellidis

  33. DIS 2013 – C. Vellidis

  34. Interesting kinematic variables • Search for resonances. • Sensitive to activity in the event. • Sensitive to production mechanism. PT1 h=0 g1 PT2 _ p p Df g2 DIS 2013 – C. Vellidis

  35. Interesting kinematic variables • Search for resonances. • Sensitive to activity in the event. • Sensitive to production mechanism. • Fragmentation/higher order diagrams • Two g’s go almost collinear • Low m(gg), intermediate PT(gg), low Df(gg) • Resummation • Low PT(gg), high Df(gg) PT1 h=0 g1 PT2 _ p p Df Special case g2 h=0 _ p p g2 g1 DIS 2013 – C. Vellidis

  36. Background subtraction using track isolation • Sensitive only to underlying event and jet fragmentation (for fake ) • Immune to multiple interactions (due to z-cut) and calorimeter leakage • Good resolution in low-ET region, where background is most important • Uses charged particles only Signal: direct diphotons Background: jets misidentified as photons – jg, jj Signal Probability (Itrk<1 GeV) Background Probability (Itrk<1 GeV) DIS 2013 – C. Vellidis

  37. Background subtraction • For a single , a weight can be defined to characterize it as signal or background: •  = 1 (0) if Itrk () 1 GeV/c • s = signal probability for Itrk 1 GeV/c • b = background probability for Itrk 1 GeV/c • For gg, use the track isolation cut for each photon to compute a per-event weight under the different hypotheses (gg, g+jet and dijet): e.g. leading passes/trailing fails Both photons fail Leading fail, trailing passes Leading passes, trailing fails Both photons pass Transfer matrixFunction of sand b DIS 2013 – C. Vellidis

  38. Signal fractions • Average 40% • Better at high mass: • 60-80% for m() 80-150 GeV/c2 • 80% for m( )>150 GeV/c2 • Better at high PT(): • 70% for PT() >100 GeV/c • 15-30% sys. errors DIS 2013 – C. Vellidis

  39. Efficiency×Acceptance • Estimated using detector- and trigger-simulated and reconstructed PYTHIA events • Procedure iterated to match PYTHIA kinematics to the data • Uncertainties in the efficiency estimation: • 3% from material uncertainty • 1.5% from the EM energy scale • 3% from trigger efficiency uncertainty • 6% (3% per photon) from underlying event (UE) correction • Total systematic uncertainty: ~7-15% DIS 2013 – C. Vellidis

  40. Experimental systematic uncertainties • Total systematic uncertainty 15-30%, smoothly varying with the kinematic variables considered • Main source is background subtraction, followed by overall normalization (efficiencies: 7%; integrated luminosity: 6%; UE correction: 6%) DIS 2013 – C. Vellidis

  41. DIS 2013 – C. Vellidis

  42. Comparison with D0 DIS 2013 – C. Vellidis

  43. A closer look at fragmentation: DIPHOX isolation study iso < 2 GeV iso < 2 GeV iso < 2 GeV Fragmentation strength is missing from the DIPHOX calculation possibly because of the approximate application of the isolation requirement at the parton level DIS 2013 – C. Vellidis

  44. A closer look at fragmentation: DIPHOX isolation study ETiso < 2 GeV Total ETiso < 10 GeV Direct 1-frag 2-frag DIS 2013 – C. Vellidis

  45. Event selection • Use inclusive photon trigger to select photon events • Trigger efficiency is approximately 100% for g ET>30 GeV • Interaction vertex in the fiducial region • Photon candidate must pass a neural-net based photon ID • ANN>0.75 • |h|<1.05, 30<ET<300 GeV, divided into 8 ET bins • Jets are reconstructed with JetClucone size 0.4 and must be positively tagged. • |h|<1.5, ET>20 GeV • DR(g,jet)>0.4 DIS 2013 – C. Vellidis

  46. ANN photon ID • Trained with TMVA (Toolkit for Multivariate Data Analysis) • 7 input variables to take into account difference between g and p0/h: isolation (2), lateral shower shape (3), Had/Em, CES/CEM • ANN ID improves signal efficiency by 9% at the same background rejection compared with the standard cut-based ID. • Use MC with full detector simulation to get templates • Signal – prompt photons • Background – jets with prompt photons removed prompt photons p0, h DIS 2013 – C. Vellidis

  47. True photon fraction • Fit data ANN distribution using signal and background templates to get true photon fraction DIS 2013 – C. Vellidis

  48. True photon fraction (continued) • Systematics • Photon energy scale • Vary inputs to photon ID ANN according to their uncertainties • Vary Photon ID ANN template binning to test sensitivity to shapes • 6% at low ET, 2% at high ET. DIS 2013 – C. Vellidis

  49. Standard b-jet identification • B-hadrons are long-lived – search for displaced vertices • Fit displaced tracks and cut on Lxy significance (σ ~ 200 mm) • Charm hadrons have similar tag behavior but lower efficiency • Use “tag mass” to deduce the flavor composition of a sample of tagged jets • Mass of the tracks forming the secondary vertex • B-hadrons are heavy: will have higher mtag spectrum than charm or light jet fakes DIS 2013 – C. Vellidis

  50. Light/c/b-jet fractions • Fit data secondary vertex mass using MC templates • Shape of secondary vertex mass for event with fake photon is taken from di-jet data DIS 2013 – C. Vellidis

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