New Photon Results from CDF

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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 - PowerPoint PPT Presentation

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New Photons Results from CDF

New Photon Results from CDFCostas VellidisFermilabDIS 2012, Marseilles, April 22

Photon analyses at CDFPhoton-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 measurementsSearches4/24/13DIS 2013 C. Vellidis2HXggInclusive-gDiphoton cross sections4/24/13DIS 2013 C. Vellidis3pggp_Prompt gg production in hadron colliders Born: a2

Compton+radiation asa2

Dg/q~a/asFragmentation: a2Suppressed byisolation cut

Box: Dominantat the LHC

Hard QCD (direct gg production):colinearsingularity4/24/134DIS 2013 C. VellidisPrompt gg production in hadron colliders Born: a2

Compton+radiation asa2

Dg/q~a/asFragmentation: a2Suppressed byisolation cut

Box: Dominantat the LHC

Hard QCD (direct gg production):Possible heavy resonance decays:

Higgs bosoncolinearsingularityExtra dimensions4/24/135DIS 2013 C. VellidisIdentified the importance of resummation, qg fragmentation in the modeling of diphoton cross sections.

6PRL 107 (2011) 102003PRD 84 (2011) 0520065.4 fb-14/24/13DIS 2013 C. VellidisPreviously published results CDFPreviously published results D0Sherpa describes data the best in the intermediate PT() and low regions.

7PT1(2)>18(17) GeV/c, |1,2|0.4, ETiso25(22) GeV/c,|1,2|0.44/24/13DIS 2013 C. VellidisPreviously published results CMSDIPHOX discrepancy for PT()>30 GeV and Df(g,g)0] by adding initial gluon radiation RESBOS: Low-PT analytically resummed calculation (NNLL) matched to high-PT NLOPYTHIA 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

114/24/13DIS 2013 C. VellidisPRD 76, 013009 (2007)

orFixed-order calculation contains singular terms at and M(gg) 0 of the form

Updated diphoton cross section measurementsUse the full 9.5 fb-1 CDF run II datasetSelect isolated diphoton eventsBackground subtraction using track isolation informationPythia evaluation of efficiency/acceptance/unfoldingCompare results with new predictions12

4/24/13DIS 2013 C. Vellidis

The Tevatron and CDFTevatron:Proton-antiproton accelerators = 1.96 TeVDelivered ~12 fb-1Recorded ~10 fb-1 for each experimentCDFCollider Detector at FermilabTracking (large B field):Silicon trackingWire ChamberCalorimetry:Electromagnetic (EM)HadronicMuon system

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4/24/13DIS 2013 C. VellidisA big thank you to Accelerator Division!

Photon identification and event selection14Used 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: ||30 GeV/c2 except PYTHIA gg

174/24/13DIS 2013 C. VellidisPT()184/24/13DIS 2013 C. VellidisPT() - ratiosRESBOS agrees with low PT() data the bestSHERPA agrees with low PT() data wellNNLO and SHERPA describe the shoulder of the data at PT(gg) = 20 50 GeV/c (the Guillet shoulder)19NB: Vertical axis scales are not the same DIPHOXRESBOSPYTHIANNLOMCFMSHERPA4/24/13DIS 2013 C. Vellidis()204/24/13DIS 2013 C. Vellidis()- ratiosRESBOS and SHERPA describe Df(gg) = p regionFixed order calculations do not describe Df(gg) = p regionNNLO describes Df(gg) = 0 region

21NB: Vertical axis scales are not the same DIPHOXRESBOSPYTHIANNLOMCFMSHERPA4/24/13DIS 2013 C. VellidisSummary of diphoton cross sectionsHigh 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 )

The RESBOS calculation provides the best description of the data at low PT and large , where resummation is important, but fails in regions sensitive to nearly collinear gg emission

The NNLO calculation provides the best description of the data at low , but still not very good at very low mass and at high PT

More in PRL 110, 101801 (2013) (supplemental material online)224/24/13DIS 2013 C. VellidisPhoton+heavy flavor (b/c) cross sections4/24/13DIS 2013 C. Vellidis23pgp_b-jetg+b/c+X productionPhoton produced in association with heavy quarks provides valuable information about heavy flavor excitation in hadron collisionsLO contribution: Compton scattering (QgQg) dominates at low photon pTNLO contribution: annihilation (qqQQg) dominates at high photon pT24Compton scattering ~ aaSAnnihilation ~ aaS2Qgqq--4/24/13DIS 2013 C. Vellidis-Previous results D025PRL 102, 192002 (2009) 1 fb-1 Good agreement for g+b+X Discrepancy for g+c+XPLB 714, 32 (2012) 8.7 fb-1g+b+XPLB 719, 354 (2013) 8.7 fb-1Discrepancies in both channels.g+c+X4/24/13DIS 2013 C. VellidisPrevious results CDFMeasure low pT cross section using a special triggerg+b+X agrees with NLO up to 70 GeV

26CDF: PRD 81, 052006 (2010) - 340 pb-14/24/13DIS 2013 C. Vellidis

Analysis overviewMeasure g+b/c+X cross section using 9.1 fb-1 inclusive photon data collected with CDF II detectorUse ANN (artificial neural network) to select photon candidatesFit ANN distribution to signal/background templates to get photon fractionUse SecVtx b-tag to select heavy-flavor jetsFit secondary vertex invariant mass to get light/c/b quark fractionsUse Sherpa MC to get efficiency/unfolding factorPhoton ID efficiency, b-tagging efficiency, detector acceptance and smearing effectsCross section 274/24/13DIS 2013 C. Vellidis

4 theoretical predictionsNLO 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. Lipatov et 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. Gleisberg et al., JHEP 02, 007 (2009)]

Pythia 6.216 ME subprocesses: gQgQ, qqgg followed by gluon splitting: gQQ, CTEQ5L PDFs [T. Sjstrand et al., JHEP 05, 026 (2006)]28__4/24/13DIS 2013 C. Vellidisg+b+X cross sections29 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 shape4/24/13DIS 2013 C. VellidisNB: Vertical axis scales are not the same g+c+X cross sections304/24/13DIS 2013 C. Vellidis 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 shapeNB: Vertical axis scales are not the same Summary of photon+b/c cross sectionsHigh 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

Pythia with doubled gluon splitting rates to heavy flavor describes the data shape314/24/13DIS 2013 C. VellidisConclusionsThe 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 results can help the precision measurements of H boson in the gg channel.

and we are not done yet!!4/24/13DIS 2013 C. Vellidis324/24/13DIS 2013 C. Vellidis33Interesting kinematic variables Search for resonances. Sensitive to activity in the event. Sensitive to production mechanism.

4/24/13DIS 2013 C. Vellidis34

PT1PT2h=0g1g2pp_DfInteresting kinematic variables Search for resonances. Sensitive to activity in the event. Sensitive to production mechanism.

Fragmentation/higher order diagramsTwo gs go almost collinearLow m(gg), intermediate PT(gg), low Df(gg)ResummationLow PT(gg), high Df(gg)

4/24/13DIS 2013 C. Vellidis35h=0g1g2pp_Df

Special caseh=0g1g2pp_PT1PT2Background subtraction using track isolationSensitive 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

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Signal: direct diphotonsBackground: jets misidentified as photons jg, jj

Signal Probability (Itrk100 GeV/c15-30% sys. errors

384/24/13DIS 2013 C. VellidisSignal fractions

EfficiencyAcceptanceEstimated using detector- and trigger-simulated and reconstructed PYTHIA events

Procedure iterated to match PYTHIA kinematics to the data

39Uncertainties in the efficiency estimation:3% from material uncertainty1.5% from the EM energy scale3% from trigger efficiency uncertainty6% (3% per photon) from underlying event (UE) correctionTotal systematic uncertainty: ~7-15%4/24/13DIS 2013 C. VellidisExperimental systematic uncertaintiesTotal 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%)

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4/24/13DIS 2013 C. Vellidis4/24/13DIS 2