New Photon Results from CDF Costas Vellidis Fermilab

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

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 o Searches o X H γγ Inclusive- 4/24/13 DIS 2013 – C. Vellidis 2

Diphoton cross sections _ p p 4/24/13 DIS 2013 – C. Vellidis 3

Prompt production in hadron colliders Hard QCD (“direct” production): colinear singularity D /q~a/as Born: a 2 Compton+radiation a sa 2 Fragmentation: a 2 Suppressed by isolation cut “Box”: Dominant at the LHC 4/24/13 DIS 2013 – C. Vellidis 4

Prompt production in hadron colliders Hard QCD (“direct” production): colinear singularity D /q~a/as Born: a 2 Compton+radiation a sa 2 Fragmentation: a 2 Suppressed by isolation cut Possible heavy resonance decays: “Box”: Dominant at the LHC 4/24/13 Higgs boson DIS 2013 – C. Vellidis Extra dimensions 5

Previously published results – CDF PRL 107 (2011) 102003 PRD 84 (2011) 052006 5. 4 fb-1 • Identified the importance of resummation, q g fragmentation in the modeling of diphoton cross sections. 4/24/13 DIS 2013 – C. Vellidis 6

Previously published results – D 0 ar. Xiv: 1301. 4536 Full Run II data set PT 1(2)>18(17) Ge. V/c, |η 1, 2|<0. 9 R( , )>0. 4, ETiso<2. 5 Ge. V • Sherpa describes data the best in the intermediate PT( ) and low regions. 4/24/13 DIS 2013 – C. Vellidis 7

Previously published results. JHEP– 1301 ATLAS (2013) 086 PT 1(2)>25(22) Ge. V/c, |η 1, 2|<2. 37 R( , )>0. 4 4/24/13 DIS 2013 – C. Vellidis 8

Previously published results – CMS JHEP 1201 (2012) 133 �DIPHOX discrepancy for PT( )>30 Ge. V and ( , )<π/2 4/24/13 DIS 2013 – C. Vellidis 9

Collinear diphoton production • Fragmentation – a higher-order effect The p. QCD cross section is divergent when q and are collinear logarithmic enhancement of the cross section o Handled with a fragmentation function – MCFM, DIPHOX o Affects low m( ), moderate PT( ) and low regions o • Higher order subprocesses (2 3 at 1 -loop and 2 4 at “tree” level) needed to describe the enhancement 4/24/13 DIS 2013 – C. Vellidis 10

Resummation • Remove singularities [PT( )->0] by adding initial gluon radiation RESBOS: Low-PT analytically resummed calculation (NNLL) matched to high-PT NLO o PYTHIA and SHERPA: Use parton showering to add gluon radiation in a Monte Carlo simulation framework which effectively resums the cross section (LL) o Affects low PT( ) and = p regions o PRD 76, 013009 (2007) Fixed-order calculation contains singular terms at and M( ) ≠ 0 of the form or 4/24/13 DIS 2013 – C. Vellidis 11

Updated diphoton cross section measurements • Use the full 9. 5 fb-1 CDF run II dataset • Select isolated diphoton events o Background subtraction using track isolation information • Pythia evaluation of efficiency/acceptance/unfolding • Compare results with new predictions 4/24/13 DIS 2013 – C. Vellidis 12

The Tevatron and CDF Tevatron: �Proton-antiproton accelerator �√s = 1. 96 Te. V �Delivered ~12 fb-1 �Recorded ~10 fb-1 for each experiment CDF �Collider Detector at Fermilab �Tracking (large B field): ◦ ◦ Silicon tracking Wire Chamber ◦ ◦ Electromagnetic (EM) Hadronic A big thank you to Accelerator Division! �Calorimetry: �Muon system 4/24/13 DIS 2013 – C. Vellidis 13

Photon identification and event selection Isolation cone: R=0. 4 rad CP 2: pre-shower CES: shower maximum profile γ EM Cal HAD Cal § 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: 4/24/13 • Fiducial to the central calorimeter: | |<1. 1 • ET 17, 15 Ge. V ( events) • Isolated in the calorimeter: Ical = Etot(R=0. 4) - EEM(R=0. 4) 2 Ge. V • Low HAD fraction: EHAD/EEM 0. 055 + 0. 00045 Etot/Ge. V • At most one track in cluster with p. Ttrk 1 Ge. V/c + 0. 005 ET /c • Shower profile consistent with predefined patterns: 2 CES 20 • Only one high energy CES cluster: ET of 2 nd CES cluster 2. 4 Ge. V + 0. 01 ET DIS 2013 – C. Vellidis Imply that R( , ) or R( , j) 0. 4 14

Theoretical predictions • PYTHIA LO parton-shower calculation – including and j with radiation [T. Sjöstrand et al. , Comp. Phys. Comm. 135, 238 (2001)] • SHERPA LO parton-shower calculation with improved matching between hard and soft physics [T. Gleisberg et 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. Binoth et al. , Phys. Rev. D 63, 114016 (2001)] • RESBOS: Low-PT analytically resummed calculation matched to high-PT NLO [T. Balazs et al. , Phys. Rev. D 76, 013008 (2007)] • NNLO calculation with q. T subtraction [L. Cieri et al. , http: //arxiv. org/abs/1110. 2375 (2011)] 4/24/13 DIS 2013 – C. Vellidis 15

Theoretical predictions • PYTHIA LO parton-shower calculation – including and j with radiation [T. Sjöstrand et al. , Comp. Phys. Comm. 135, 238 (2001)] Integrated crossmatching section (pb) • SHERPA LO parton-shower calculation with improved between hard and soft physics [T. Gleisberg et al. , JHEP 02, 12. 3 007±(2009)] Data (CDF) 0. 2 ± 3. 5 stat syst RESBOSNLO calculation including non-perturbative 11. 3 • MCFM: Fixed-order fragmentation DIPHOX et al. , Phys. Rev. D 60, 11300610. 6 at LO [J. M. Campbell (1999)] MCFM 11. 5 PYTHIA + j 9. 2 • DIPHOX: Fixed-order NLO calculation including non-perturbative fragmentation SHERPA 12. 4 at NLO [T. Binoth et al. , Phys. Rev. D 63, 114016 (2001)] • RESBOS: Low-P to high-PT NLO NNLO 11. 8 T analytically resummed calculation matched [T. Balazs et al. , Phys. Rev. D 76, 013008 (2007)] • NNLO calculation with q. T subtraction [L. Cieri et al. , http: //arxiv. org/abs/1110. 2375 (2011)] 4/24/13 DIS 2013 – C. Vellidis 16

m( ) • Good agreement between data and theory for M >30 Ge. V/c 2 except PYTHIA 4/24/13 DIS 2013 – C. Vellidis 17

PT( ) 4/24/13 DIS 2013 – C. Vellidis 18

PT( ) - ratios NB: Vertical axis scales are not the same PYTHIA NNLO DIPHOX MCFM SHERPA RESBOS • RESBOS agrees with low PT( ) data the best • SHERPA agrees with low PT( ) data well • NNLO and SHERPA describe the “shoulder” of the data 4/24/13 at PT( ) = 20 – 50 Ge. V/c (the “Guillet shoulder”) DIS 2013 – C. Vellidis 19

( ) 4/24/13 DIS 2013 – C. Vellidis 20

( )- ratios NB: Vertical axis scales are not the same PYTHIA NNLO DIPHOX MCFM SHERPA RESBOS • RESBOS and SHERPA describe ( ) = p region • Fixed order calculations do not describe ( ) = p region • NNLO describes ( ) = 0 region 4/24/13 DIS 2013 – C. Vellidis 21

Summary of diphoton cross sections • High precision 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 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 emission • 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 PRL 110, 101801 (2013) (supplemental material online) 4/24/13 DIS 2013 – C. Vellidis 22

Photon+heavy flavor (b/c) cross sections _ p p b-jet 4/24/13 DIS 2013 – C. Vellidis 23

+b/c+X production • Photon produced in association with heavy quarks provides valuable information about heavy flavor excitation in hadron collisions LO contribution: Compton scattering (Qg�Q ) dominates at low photon p. T - QQ ) o NLO contribution: annihilation (qq� dominates at high photon p. T o Q q g -q Compton scattering ~ aa. S 4/24/13 Annihilation ~ aa. S 2 DIS 2013 – C. Vellidis 24

Previous results – D 0 PLB 714, 32 (2012) – 8. 7 fb-1 +b+X PRL 102, 192002 (2009) − 1 fb-1 PLB 719, 354 (2013) – 8. 7 fb-1 +c+X • Good agreement for +b+X • Discrepancy for +c+X 4/24/13 Discrepancies in both channels. DIS 2013 – C. Vellidis 25

Previous results – CDF: PRD 81, 052006 (2010) - 340 pb-1 • Measure low p. T cross section using a special trigger • +b+X agrees with NLO up to 70 Ge. V 4/24/13 DIS 2013 – C. Vellidis 26

Analysis overview • Measure +b/c+X cross section using 9. 1 fb-1 inclusive • photon data collected with CDF II detector Use ANN (artificial neural network) to select photon candidates o Fit ANN distribution to signal/background templates to get photon fraction • Use Sec. Vtx b-tag to select heavy-flavor jets o Fit secondary vertex invariant mass to get light/c/b quark fractions • Use Sherpa MC to get efficiency/unfolding factor o Photon ID efficiency, b-tagging efficiency, detector acceptance and smearing effects • Cross section o 4/24/13 DIS 2013 – C. Vellidis 27

4 theoretical predictions • NLO – direct-photon subprocesses and fragmentation subprocesses at O(aas 2), CTEQ 6. 6 M PDFs [T. P. Stavreva and J. F. Owens, PRD 79, 054017 (2009)] • k. T-factorization – off-shell amplitudes integrated over k. Tdependent parton distributions, MSTW 2008 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, CT 10 PDFs [T. Gleisberg et al. , JHEP 02, 007 (2009)] _ _ • Pythia 6. 216 – ME subprocesses: g. Q� Q, qq� g followed by gluon splitting: g�QQ, CTEQ 5 L PDFs [T. Sjöstrand et al. , JHEP 05, 026 (2006)] 4/24/13 DIS 2013 – C. Vellidis 28

+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 • k. T-factorization and Sherpa agree with data reasonably well • Pythia with doubled gluon splitting rate to heavy flavor describes the shape 4/24/13 DIS 2013 – C. Vellidis 29

+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 • k. T-factorization and Sherpa agree with data reasonably well • Pythia with doubled gluon splitting rate to heavy flavor describes the shape 4/24/13 DIS 2013 – C. Vellidis 30

Summary of photon+b/c cross sections • High precision +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. • k. T-factorization and Sherpa agree with data reasonably well • Pythia with doubled gluon splitting rates to heavy flavor describes the data shape 4/24/13 DIS 2013 – C. Vellidis 31

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 results can help the precision measurements of H boson in the channel. • … and we are not done yet!! 4/24/13 DIS 2013 – C. Vellidis 32

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Interesting kinematic variables • =0 PT 1 p 2 4/24/13 PT 2 _ p 1 • • o Search for resonances. o Sensitive to activity in the event. o Sensitive to production mechanism. DIS 2013 – C. Vellidis 34

Interesting kinematic variables • =0 PT 1 _ p p 1 • 2 • PT 2 Special case Search for resonances. o Sensitive to activity in the event. o Sensitive to production mechanism. • Fragmentation/higher order diagrams =0 _ p p o o Two ’s go almost collinear o Low m( ), intermediate PT( ), low ( ) • Resummation o Low PT( ), high ( ) 2 4/24/13 1 DIS 2013 – C. Vellidis 35

Background subtraction using track isolation Signal: direct diphotons Background: jets misidentified as photons – j , jj • 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 Probability (Itrk<1 Ge. V) 4/24/13 Background Probability (Itrk<1 Ge. V) DIS 2013 – C. Vellidis 36

Background subtraction • For a single , a weight can be defined to characterize it as signal or background: o = 1 (0) if Itrk ( ) 1 Ge. V/c o s = signal probability for Itrk 1 Ge. V/c o b = background probability for Itrk 1 Ge. V/c • For , use the track isolation cut for each photon to compute a per-event weight under the different hypotheses ( , +jet and dijet): Both photons fail e. g. leading passes/trailing fails Leading fail, trailing passes Leading passes, trailing fails Both photons pass 4/24/13 Transfer matrix Function of s and b DIS 2013 – C. Vellidis 37

Signal fractions • Average � 40% • Better at high mass: o o 60 -80% for m(�� ) � 80 -150 Ge. V/c 2 � 80% for m(�� )>150 Ge. V/c 2 o � 70% for PT(�� ) >100 Ge. V/c • Better at high PT(�� ): • 15 -30% sys. errors 4/24/13 DIS 2013 – C. Vellidis 38

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% 4/24/13 DIS 2013 – C. Vellidis 39

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%) 4/24/13 DIS 2013 – C. Vellidis 40

Integrated cross section (pb) Data (CDF) 12. 3 ± 0. 2 stat ± 3. 5 syst RESBOS 11. 3 ± 2. 4 DIPHOX 10. 6 ± 0. 6 MCFM 11. 5 ± 0. 3 SHERPA 12. 4 ± 4. 4 PYTHIA gg+gj NNLO 4/24/13 9. 2 11. 8 + 1. 7 – 0. 6 DIS 2013 – C. Vellidis 41

Comparison with D 0 4/24/13 DIS 2013 – C. Vellidis 42

A closer look at fragmentation: DIPHOX isolation study iso < 2 Ge. V Fragmentation strength is missing from the DIPHOX calculation possibly because of the approximate application of the isolation requirement at the parton level 4/24/13 DIS 2013 – C. Vellidis 43

A closer look at fragmentation: DIPHOX isolation study ETiso < 2 Ge. V Total Direct 1 -frag 2 -frag ETiso < 10 Ge. V 4/24/13 DIS 2013 – C. Vellidis 44

Event selection • Use inclusive photon trigger to select photon events o Trigger efficiency is approximately 100% for ET>30 Ge. V • Interaction vertex in the fiducial region • Photon candidate must pass a neural-net based photon ID ANN>0. 75 o | |<1. 05, 30<ET<300 Ge. V, divided into 8 ET bins o • Jets are reconstructed with Jet. Clu cone size 0. 4 and must be positively tagged. o | |<1. 5, ET>20 Ge. V • R( , jet)>0. 4 4/24/13 DIS 2013 – C. Vellidis 45

ANN photon ID • Trained with TMVA (Toolkit for Multivariate Data Analysis) • 7 input variables to take into account difference between and p 0/ : • • 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 o o Signal – prompt photons Background – jets with prompt photons removed prompt photons p 0, 4/24/13 DIS 2013 – C. Vellidis 46

True photon fraction • Fit data ANN distribution using signal and background templates to get true photon fraction 4/24/13 DIS 2013 – C. Vellidis 47

True photon fraction (continued) • Systematics Photon energy scale o Vary inputs to photon ID ANN according to their uncertainties o Vary Photon ID ANN template binning to test sensitivity to shapes o 6% at low ET, 2% at high ET. o 4/24/13 DIS 2013 – C. Vellidis 48

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 o B-hadrons are heavy: will have higher mtag spectrum than charm or light jet fakes o 4/24/13 DIS 2013 – C. Vellidis 49

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 4/24/13 DIS 2013 – C. Vellidis 50

Light/c/b-jet fractions (continued) Results from fitter. 4/24/13 DIS 2013 – C. Vellidis 51

Systematics on b/c-jet fractions • Jet energy scale: affects acceptance • Uncertainty in tracking efficiency: scale secondary vertex mass templates by ± 3% o Dominant systematic effect • Difference between single-quark and di-quark jets • Total systematic error is ~20% 4/24/13 DIS 2013 – C. Vellidis 52

Efficiency×Acceptance • Use Sherpa MC to unfold photon ID efficiency, b-tagging • 4/24/13 efficiency, detector acceptance and smearing effects. Systematic effects evaluated o o o photon energy scale and ID jet energy scale b-tagging efficiency Generator PDF DIS 2013 – C. Vellidis 53