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Charm Quark Content Probe in Proton with γ+c Production: Good Testbed for QCD Tests

This production study by Tara Shears at the University of Liverpool focuses on γ+c events to probe charm quark content in the proton. With a mix of LO and NLO production, the study involves exploring heavy flavor sensitivity to new physics. Initial results show indications of excess at high Et, prompting further investigation and data analysis.

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Charm Quark Content Probe in Proton with γ+c Production: Good Testbed for QCD Tests

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  1. g + b, g + c production Tara Shears, University of Liverpool

  2. Motivation • Good testbed for quantitative QCD tests •  +c events could be used to probe charm quark content of proton • bb, cc events: imperfect NLO description •  + heavy flavour sensitive to new physics (eg. chargino neutralino production)

  3. LO NLO Production Dominates for gc Diagrams equal for gb Coupling  charge2 s(cg) ~ 4.s(bg) b quark ~ 60% c quark content of p (PRD 012003)

  4. Method: Apply standard run 2 g selection Estimate fakes from CPR info Use tagging algorithm for b/c id Run 1 used lepton pt We use sec. vtx tag (SECVTX – will update with better) Divide data into Et bins, tag, take b,c frac. from MC => s Datasets: CPH108 (25 Iso trigger) Good online run, clc, smx, cal, trigger, svx Good offline cal,cot L = 66.05 3.76 pb-1 MC: Pythia g + jet (LO) Will use madgraph for NLO Method / data

  5. Photon + jet sel. eff. Require at least 1 jet > 15 GeV, >=2 tracks, for tagging

  6. Tagging eff. & composition From Pythia MC..

  7. Data s(gq) = N(gq)/(eff(gjet).eff(tag).eff(trg).L) = no.tags * q fraction Not known yet

  8. Systematic errors • Photon + jet selection: ±1.7% from g id (test on Z, loose cuts) • Jet e scale: not yet done • Fake rate est.: use standard procedure • B/c fractions: take arbitrary ±10% • SECVTX systematics: not yet done (small for top) • Trigger systematics: not yet done • Luminosity: use quoted ±5.8%

  9. Results 1. gb Nb. E(trg) = 1 here!

  10. Results 2. gc Nb. E(trg) = 1 here!

  11. Indications of excess at high Et? Points: data (stat. Error and sysstat shown by notches) Histogram: Pythia g+jet (LO)

  12. Indications of excess at high Et? Points: data (stat. Error and sysstat shown by notches) Histogram: Pythia g+jet (LO)

  13. Work plan Immediately: • Trigger efficiency (+sys.) • SECVTX tagging sys., jet selection sys. • Other photon backgrounds (eg. e->g) (small) • Add more data Next: • Tighten photon cuts to reduce fake, use CES • Derive b/c fraction from data • Use improved b/c tag • Compare to NLO (Madgraph?) Longer term: • Extend to lower photon Et

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