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Recent Photon Analysis Results from CDF at DIS 2013

This presentation by Costas Vellidis at the DIS 2013 conference in Marseilles outlines key photon-related analyses conducted with CDF data, highlighting approximately 30 published papers covering a range of topics. Key focus areas include cross-section measurements and advanced studies on diphoton production dynamics, fragmentation effects, and the implications of new theoretical predictions. The presentation emphasizes the importance of precision measurements in understanding jet dynamics and deep inelastic scattering at the Tevatron. Results are compared with predictions from various Monte Carlo simulations, enhancing our understanding of photon interactions in high-energy physics.

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Recent Photon Analysis Results from CDF at DIS 2013

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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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