arXiv subjects
Publications and source records attributed to L. E. Gordon.
QCD motivated polarized parton distributions, evolved directly in $x$-space, are used to predict rates for prompt photon production at RHIC centre of mass energies. Various scenarios for the polarized gluon distributions are considered and compared, and the possibility of using large $p_T$ processes in polarized $pp$ collision experiments to choose between them is analyzed.
QCD motivated polarized parton distributions, evolved directly in x-space, are used to predict rates for prompt photon and Jet production at RHIC and HERA-N center of mass energies. Various scenarios for the polarized gluon distributions are considered and compared, and the possibility of using large p_T processes in polarized pp collision experients to choose between them is analyzed.
A study of the order $α_s^2$ corrections to the Drell Yan (non-singlet) cross section for incoming states of arbitrary longitudinal helicities is presented. The study is performed in the case of the transverse momentum distributions, $(q_T)$, of the lepton pair and extends the calculation of Ellis Martinelli and Petronzio (EMP) to the polarized case. We use the $\bar{MS}$ scheme and the t'Hooft-Veltman regularization for the helicity projectors. From our results one can obtain the bulk of the totally inclusive NNLO cross section for the production of a Drell Yan pair in the non-singlet sector by a simple integration over the heavy photon momentum. We show that in the $\bar{MS}$ helicity is not conserved, unless a finite renormalization is done to reenter into a physical scheme ($\bar{MS}_p$). This aspect of the calculation follows the same trend as in polarized production of single and double photon to $O(α_s^2)$. In the unpolarized limit we reproduce all the results of EMP.
A study of prompt photon plus associated jet production is performed at next-to-leading order (O($αα_s^2$)) in QCD at $\sqrt{S}=200-500$ GeV, appropriate for the RHIC polarized $\vec{p}\vec{p}$ collider experiment. Momentum correlations between the jet and photon are examined and the utility of the process as a method for constraining the size and shape of the polarized gluon density of the proton $ΔG$ is examined.
The cross section for photoproduction of an isolated prompt photon in association with a jet is studied in Next-to-Leading Order. The kinematics are those appropriate for the DESY $ep$ collider HERA. The effects on the cross section of various experimental cuts including isolation cuts on the photon is examined. Comparisons with the ZEUS preliminary data using two parametrizations of the photon structure function is made, and good agreement is found. The data is not yet precise enough to make a distinction between various models for the photon structure function.
The cross section for photoproduction of a prompt photon in association with a jet is studied in Next-to-Leading Order at the DESY $ep$ collider HERA. The effect of various cuts imposed on the cross section by the ZEUS collaboration including isolation cuts on the photon is examined. Comparisons with the ZEUS preliminary data using various parametrizations of the photon structure function is made, and good agreement is found. The preliminary data is not yet precise enough to make a distinction between various models for the photon structure function.
We present the complete $O(α_s^2)$ radiative corrections to the (non singlet) polarized Drell Yan cross section for the production of a lepton pair with a nonzero $q_T$. The helicity of the incoming states is arbitrary. In the case of double photon, results for the longitudinal asymmetries and on the $p_T$ behavior of the cross section are also given (to $O(α_{em}^2α_s )$) in the central rapidity region of the tagged photon.
The cross section for inclusive prompt photon production with polarized hadron beams is calculated at order $αα_s^2$ using the phase space slicing or analytic/Monte Carlo method. Isolation cuts are placed on the photon and the results are compared to a previous fully analytic calculation. Numerical results for the isolated cross section are presented for for $\vec{p}\vec{p}\rightarrow γ+X$ at RHIC center-of-mass energies with plausible isolation parameters using the most modern polarized parton densities evolved in next-to-leading order QCD. The perturbative stability of the asymmetries and scale dependence of the results are briefly discussed.
The cross sections for isolated and non-isolated prompt photon production with unpolarized hadron beams are studied at order $αα_s^2$. Two methods of performing the calculations are compared. One uses purely analytic techniques and the second uses a combination of analytic and Monte Carlo techniques to perform the phase-space integrations. The results of the analytic and Monte Carlo methods are compared both before and after isolation cuts are placed on the photon. Fragmentation contributions are included at next-to-leading order in the analytic case, and the question of the infrared sensitivity of this contribution once isolation is implemented is addressed. Numerical results are presented and compared with the latest CDF data for $p\bar{p} \to γ+X$ using the latest parton densities for the proton.
The two particle inclusive cross section for the reaction $p +\bar{p}\rightarrow γ+ c + X$ is studied in perturbative quantum chromodynamics at order $O(α^2_s)$. Differential distributions are provided for various observables, and a comparison is made with data from the CDF collaboration.
The utility of prompt photon plus associated jet production for constraining the size and shape of the polarized gluon density of the proton $ΔG$ is examined at $\sqrt{S}=40$ GeV, appropriate for the proposed HERA-$\vec{N}$ polarized $\vec{p}\vec{p}$ collider experiment. The calculation is performed at next-to-leading order (O($αα_s^2$)) in QCD. The reliability of the predictions are examined in some detail.
The two particle inclusive cross section for the reaction $p\bar{p}\rightarrow γ+c+X$ is studied in perturbative quantum chromodynamics at order $O(α_s^2)$. Differential distributions are provided for various observables, and a comparison is made with preliminary data from the CDF collaboration.
We present a NLO study of inclusive polarized prompt photon production in a conceivable fixed target $pp$ mode of HERA with longitudinally polarized protons at $\sqrt{s}=39$ GeV. We analyze the sensitivity of the corresponding double spin asymmetry to the proton's polarized gluon distribution $Δg$ and estimate the expected statistical precision in its determination. The main theoretical uncertainties in the predictions are examined.
We present new improved parton distributions for the photon. We fit {\bf all} available data on the photon structure function, $F^γ_{2}(x,Q^2)$, with $Q^2\ge 3$ GeV$^2$, in order to determine the quark distributions. We also pay particular attention to the gluon distribution in the photon, $g^γ(x,Q^2)$, which has been poorly constrained in earlier analyses which only include structure function data. We use large $p_T$ jet production in $γγ$ collisions from TRISTAN to constrain $g^γ$. We also see what information can be gleaned from $γp$ collisions at HERA on $g^γ$ and on the quark distributions at large $x$, where there are no structure function data. We review future prospects of elucidating the parton distributions of the photon.
We study the expectations for prompt photon production rates at HERA in a fully consistent next-to-leading order (NLO) QCD analysis, taking into account the effects of experimental isolation requirements. In particular we examine the sensitivity of the isolated cross section to the photon's gluon content.
We calculate the cross section for inclusive prompt photon production in $γγ$ collisions, i.e. the reaction $e^+e^-\to γγ\to γX$, in next-to-leading order QCD. We show that at LEP2 energies this cross section is measurable and is sensitive to the gluon distribution of the photon, $g^γ$, which is currently very poorly constrained by data.
The two particle inclusive cross section for the reaction $p +\bar{p}\rightarrow γ+ c + X$ is studied in perturbative quantum chromodynamics at order $O(α^2_s)$, for large values of the transverse momentum of the prompt photon and charm quark. Two different techniques are used in performing the phase-space integrals; the first is purely analytical, and the second is a combination of analytic and Monte Carlo integration methods. The second, more versatile technique facilitates imposition of photon isolation restrictions and other selections of relevance in experiments. Differential distributions are provided for various observables, and a comparison is made with preliminary data from the CDF collaboration.
A second order, $O(α^2_s)$, calculation in perturbative quantum chromodynamics of the two particle inclusive cross section is presented for the reaction $p +\bar{p}\rightarrow γ+ c + X$ for large values of the transverse momentum of the prompt photon and charm quark. The combination of analytic and Monte Carlo integration methods used here to perform phase-space integrations facilitates imposition of photon isolation restrictions and other selections of relevance in experiments. Differential distributions are provided for various observables. Positive correlations in rapidity are predicted.