Measurement of the differential photon+ c-jet cross section and the ratio of differential photon+ c and photon+ b cross sections in proton-antiproton collisions at sqrt(s) = 1.96 TeV

We present measurements of the differential cross section $d\sigma/dp_{T}^{\gamma}$ for the associated production of a $c$-quark jet and an isolated photon with rapidity $|y^{\gamma}|<1.0$ and transverse momentum $30<p_{T}^{\gamma}<300$ GeV. The $c$-quark jets are required to have $|y^{jet}|<1.5$ and $p_{T}^{jet}>15$ GeV. The ratio of differential cross sections for photon+ c and photon+ b production as a function of $p_{T}^{\gamma}$ is also presented. The results are based on data corresponding to an integrated luminosity of 8.7 fb$^{-1}$ recorded with the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider at $\sqrt{s}=$1.96 TeV. The obtained results are compared to next-to-leading order perturbative QCD calculations using various parton distribution functions, to predictions based on the $k_{T}$-factorization approach, and to predictions from the Sherpa and Pythia Monte Carlo event generators.

We present measurements of the differential cross section dσ/dp γ T for the associated production of a c-quark jet and an isolated photon with rapidity |y γ | < 1.0 and transverse momentum 30 < p γ T < 300 GeV. The c-quark jets are required to have |y jet | < 1.5 and p jet T > 15 GeV. The ratio of differential cross sections for γ + c to γ + b production as a function of p γ T is also presented. The results are based on data corresponding to an integrated luminosity of 8.7 fb −1 recorded with the D0 detector at the Fermilab Tevatron pp Collider at √ s =1.96 TeV. The obtained results are compared to next-to-leading order perturbative QCD calculations using various parton distribution functions, to predictions based on the kT-factorization approach, and to predictions from the sherpa and pythia Monte Carlo event generators.  to extract the c-jet fraction. Using this event selection 54 criteria, we reproduce the results for the γ + b-jet cross 55 section, measure the γ + c-jet cross section and calculate 56 the ratio σ(γ +c)/σ(γ +b) in bins of p γ T . Common experi-57 mental uncertainties and dependence on the higher-order 58 corrections in theory are reduced in the ratio, allowing a 59 precise study of the relative σ(γ + c)/σ(γ + b) rates.

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The D0 detector is a general purpose detector de- Ref.
[5], in the efficiency and acceptance calculations the 113 photon is required to be isolated at the particle level by level includes all stable particles as defined in Ref. [12].

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The photon acceptance varies within (82 − 90)% with a 120 relative systematic uncertainty of (2−5)%, while the effi- tively. An independent fit is performed in each p γ T bin.

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It yields photon purities between 62% and 99%, which  The data, corrected for photon and jet acceptance, 223 reconstruction efficiencies and the admixture of back-224 ground events, are presented at the particle level [12] for  Table I.

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Next-to-leading order (NLO) perturbative QCD pre- The γ + c-jet production cross sections dσ/dp γ T in bins of p γ T for |y γ | < 1.0, p jet T > 15 GeV and |η jet | < 1.5 together with statistical uncertainties (δstat), total systematic uncertainties (δsyst), and the uncorrelated component of δsyst (δ unc syst ). The column δtot shows total experimental uncertainty obtained by adding δstat and δsyst in quadrature. The last four columns show theoretical predictions obtained within NLO QCD, kT-factorization, and by the pythia and sherpa event generators.  The c-jet fraction in data after subtraction of lightjet background as a function of p γ T derived from the template fit to the heavy quark jet data sample after applying all selections. The error bars include statistical and systematical uncertainties. Binning is the same as given in Table I. about +14%/ + 5% in the last p γ T bin.

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266 Table I   The σ(γ + c)/σ(γ + b) cross section ratio in bins of p γ T for |y γ | < 1.0, p jet T > 15 GeV and |η jet | < 1.5 together with statistical uncertainties (δstat), total systematic uncertainties (δsyst), and the uncorrelated component of δsyst (δ unc syst ). The column δtot shows total experimental uncertainty obtained by adding δstat and δsyst in quadrature. The last four columns show theoretical predictions obtained using NLO QCD, kT-factorization, pythia and sherpa event generators.  The ratio of γ + c-jet and γ + b-jet production cross sections for data together with theoretical predictions as a function of p γ T . The uncertainties on the data include both statistical (inner error bar) and total uncertainties (full error bar). Predictions given by kT-factorization [20, 21], sherpa [10] and pythia [11] are also shown. The pythia predictions with a contribution from the annihilation process increased by a factor of 1.7 are shown as well. The predictions for intrinsic charm models [26] are also presented.
Experimental results as well as theoretical predictions for 348 the ratios are presented in Table II.

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The best description of data is achieved by increasing the 372 rates by a factor of 1.7 with χ 2 /ndf ≃ 0.7 (compared to 373 χ 2 /ndf = 4.1 if such a factor is unity). However, accord-374 ing to our estimates using the signal events simulated 375 with sherpa, there are also about (10-35)% (higher for 376 larger p γ T ) events with two c-jets. Assuming that one jet 377 is coming from gluon initial state radiation followed by 378 g → cc splitting, the required overall correction factor 379 would be smaller by about (8-24)%.

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In conclusion, we have measured the differential cross