Resolved Photon Contributions Research Articles

Strange quark mass effect in Bs→γγ, γℓℓ¯ decays

In this paper we investigate the next-to-leading power contribution to the ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ and ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\ell}\overline{\ensuremath{\ell}}$ decays from the strange quark mass effect with the dispersion approach which is QCD inspired and more predictive. We present the analytic expression of the quark mass contribution in the ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ and ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\ell}\overline{\ensuremath{\ell}}$ decays, together with a new term that is missed in the previous study. We also evaluate the resolved photon contribution from the A-type amplitude in ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\ell}\overline{\ensuremath{\ell}}$ decay. The numerical results of the strange quark mass contribution to the ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ decay is about 6% relative to the total branching ratio, while it is relatively small in the ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\ell}\overline{\ensuremath{\ell}}$ decay due to the large resonance contribution.

Reevaluating uncertainties in overline{B} → Xsγ decay

The rare decay overline{B} → Xsγ is an important probe of physics beyond the standard model. The largest uncertainty on the total rate and the CP asymmetry arises from resolved photon contributions. These appear first at order 1/mb and are related to operators other than Q7γ in the effective weak Hamiltonian. One of the three leading contributions, {Q}_1^q-{Q}_{7gamma } , is described by a non-local function whose moments are related to HQET parameters. We use recent progress in our knowledge of these parameters to reevaluate the resolved photon contribution to overline{B} → Xsγ total rate and CP asymmetry.

Measurements of isospin asymmetry and difference of directCPasymmetries in inclusiveB→Xsγdecays

We report measurements of isospin asymmetry $\Delta_{0-}$ and difference of direct $CP$ asymmetries $\Delta A_{CP}$ between charged and neutral $B \to X_s \gamma$ decays. This analysis is based on the data sample containing $772 \times 10^6 B\bar{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric $e^+ e^-$ collider. Using a sum-of-exclusive technique with invariant $X_s$ mass up to 2.8~GeV/$c^2$, we obtain $\Delta_{0-} = \bigl[-0.48 \pm 1.49 {\rm (stat.)} \pm 0.97 {\rm (syst.)} \pm 1.15 {(f_{+-}/f_{00})}\bigr]$\% and $\Delta A_{CP} = \bigl[+3.69 \pm 2.65 {\rm (stat.)} \pm 0.76{\rm (syst.)}\bigr]$\%, where the last uncertainty for $\Delta_{0-}$ is due to the uncertainty on the production ratio of $B^+B^-$ to $B^0\bar{B}^0$ in $\Upsilon(4S)$ decays. The measured value of $\Delta_{0-}$ is consistent with zero, allowing us to constrain the resolved photon contribution in the $B \to X_s \gamma$, and improve the branching fraction prediction. The result for $\Delta A_{CP}$ is consistent with the prediction of the SM. We also measure the direct $CP$ asymmetries for charged and neutral $B \to X_s \gamma$ decays. All the measurements are the most precise to date.

Inclusive jet production as a probe of polarized parton distribution functions at a future EIC

We present a detailed phenomenological study of polarized inclusive jet production in electron-proton collisions at a future Electron-Ion Collider (EIC). Our analysis is performed at next-to-leading order in perturbative QCD using the numerical code DISTRESS and includes all relevant partonic channels and resolved photon contributions. We elucidate the role of different kinematic regions in probing different aspects of proton and photon structure. We emphasize the importance of inclusive jet measurements and high collision energies at a future EIC in order to further constrain the polarized gluon distribution of the proton.

Longitudinally polarized photoproduction of heavy flavors at next-to-leading order of QCD

We present a phenomenological study of charm quark photoproduction in longitudinally polarized lepton–hadron collisions at next-to-leading order accuracy of QCD. Our results are based on a recently developed, flexible parton-level Monte Carlo program for spin-dependent heavy flavor hadroproduction, which we extend to deal also with both direct and resolved photon contributions. The subsequent hadronization into charmed mesons is modeled in our calculations, which allows us to compare with data on double-spin asymmetries for D 0 meson production taken by the COMPASS collaboration. In general, next-to-leading order QCD corrections are found to be very significant and do not cancel in spin asymmetries. We elucidate the role of the individual hard scattering subprocesses and determine the range of parton momentum fractions predominantly probed for charm production at COMPASS. Theoretical uncertainties are estimated by varying renormalization and factorization scales and parameters controlling the hadronization of the charm quarks.

Inclusive J/ψ photoproduction and polarization at HERA in the k T -factorization approach

We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k T -factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics.

10.1007/s11448-008-1003-y

Inclusive beauty quark production in photon-photon collisions at CERN LEP2 is considered in the framework of the k T -factorization approach. Both direct and resolved photon contributions are taken into account. The unintegrated gluon distributions in a photon are either obtained from the full Catani-Ciafoloni-Fioyani-Marchesini (CCFM) evolution equation or from the Kimber-Martin-Ryskin prescription. The predicted beauty cross section reasonably agrees with recent experimental data taken by the ALEPH collaboration. It is shown that theoretical and experimental studies of the azimuthal correlations in heavy quark production at high energies can serve as a crucial probe of the unintegrated gluon densities.

Factorization breaking in diffractive photoproduction of dijets-a review

I compare the latest H1 and ZEUS data on diffractive dijet photoproduction with next-to-leading order QCD predictions in order to see whether a rapidity gap survival probability of less than one is supported by the data. I find evidence for this hypothesis when assuming global factorization breaking for both the direct and resolved photon contributions, in which case the suppression factor would have to be strongly E T jet -dependent, and when assuming factorization breaking for the resolved or in addition the related direct initial-state singular contribution only, where it would be independent of E T jet .

Beauty production in two-photon interactions at LEP2: k T factorization versus data

Inclusive beauty quark production in photon-photon collisions at CERN LEP2 is considered in the framework of the k T -factorization approach. Both direct and resolved photon contributions are taken into account. The unintegrated gluon distributions in a photon are either obtained from the full Catani-Ciafoloni-Fioyani-Marchesini (CCFM) evolution equation or from the Kimber-Martin-Ryskin prescription. The predicted beauty cross section reasonably agrees with recent experimental data taken by the ALEPH collaboration. It is shown that theoretical and experimental studies of the azimuthal correlations in heavy quark production at high energies can serve as a crucial probe of the unintegrated gluon densities.

Unintegrated gluon distributions in D*± and dijet associated photoproduction at HERA

We consider the photoproduction of D*± mesons associated with two hadron jets at HERA collider in the framework of the kT-factorization approach. The unintegrated gluon densities in a proton are obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber–Martin–Ryskin prescription. Resolved photon contributions are reproduced by the initial-state gluon radiation. We investigate different production rates and make a comparison with the recent experimental data taken by the ZEUS collaboration. Special attention is given to the specific dijet correlations which can provide unique information about non-collinear gluon evolution dynamics.

HIGGS BOSON PRODUCTION IN γγ COLLISIONS VIA RESOLVED PHOTON CONTRIBUTIONS

We studied single Higgs boson production in γγ collisions proceeding via the hadronic content of the photon. For SM Higgs masses of current theoretical interest, the resolved photon contributions are non-negligible in precision cross section measurements. We found that production of the heavier Higgs bosons H0 and A0 of the MSSM can probe regions of the SUSY parameter space that will complement other measurements. Finally, we showed that associated tH± production in γγ collisions can be used to make an accurate determination of tan β for low and high tan β by precision measurements of the γγ → H±t + X cross section.

Heavy quark and quarkonium production at CERN LEP2: k T-factorization versus data

We present calculations of heavy quark and quarkonium production at CERN LEP2 in the k_T-factorization QCD approach. Both direct and resolved photon contribution are taken into account. The conservative error analisys is performed. The unintegrated gluon distribution in the photon is taken from the full CCFM evolution equation. The traditional color-singlet mechanism to describe non-perturbative transition of heavy quark pair into a final quarkonium is used. Our analisys covers polarization properties of heavy quarkonia at moderate and large transverse momenta. We find that the total and differential open charm production cross sections are consistent with the recent experimental data taken by the L3, OPAL and ALEPH collaborations. At the same time the DELPHI data for the inclusive J/Psi production exceed our predictions but experimental uncertainties are too large to claim a significant inconsistency. The bottom production in photon-photon collisions at CERN LEP2 is hard to explain within the k_T-factorization formalism.

Genuine twist-3 contributions to the generalized parton distributionsfrom instantons

Triple differential dijet cross sections in e^\pm p interactions are presented in the region of photon virtualities 2<Q^2<80GeV^2, inelasticities 0.1<y<0.85, jet transverse energies E_T1>7GeV, E_T2>5GeV, and pseudorapidities -2.5 < eta_1^*, eta_2^* <0. The measurements are made in the gamma^* p centre-of-mass frame, using an integrated luminosity of 57pb^-1. The data are compared with NLO QCD calculations and LO Monte Carlo programs with and without a resolved virtual photon contribution. NLO QCD calculations fail to describe the region of low Q^2 and low jet transverse energies, in contrast to a LO Monte Carlo generator which includes direct and resolved photon interactions with both transversely and longitudinally polarised photons. Initial and final state parton showers are tested as a mechanism for including higher order QCD effects in low E_T jet production.

Measurement of dijet production at low Q 2 at HERA

Triple differential dijet cross sections in e^\pm p interactions are presented in the region of photon virtualities 25GeV, and pseudorapidities -2.5 < eta_1^*, eta_2^* <0. The measurements are made in the gamma^* p centre-of-mass frame, using an integrated luminosity of 57pb^-1. The data are compared with NLO QCD calculations and LO Monte Carlo programs with and without a resolved virtual photon contribution. NLO QCD calculations fail to describe the region of low Q^2 and low jet transverse energies, in contrast to a LO Monte Carlo generator which includes direct and resolved photon interactions with both transversely and longitudinally polarised photons. Initial and final state parton showers are tested as a mechanism for including higher order QCD effects in low E_T jet production.

Resolved photon contributions to Higgs boson production inγγcollisions

We study single Higgs boson production in $\ensuremath{\gamma}\ensuremath{\gamma}$ collisions proceeding via the hadronic content of the photon. These processes complement previous studies of pair and single Higgs boson production at ${e}^{+}{e}^{\ensuremath{-}}$ colliders. For standard model Higgs boson masses of current theoretical interest, the resolved photon contributions are non-negligible in precision cross section measurements. The charged Higgs boson cross sections are not competitive with the $\ensuremath{\gamma}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}{H}^{+}{H}^{\ensuremath{-}}$ process and at best might offer some information about quark-Higgs couplings. Finally, resolved photon production of the heavier Higgs bosons ${H}^{0}$ and ${A}^{0}$ of the MSSM can probe regions of the supersymmetry (SUSY) parameter space that will complement other measurements. This last process shows some promise in SUSY Higgs boson searches and warrants further study.

Color evaporation description of inelastic photoproduction ofJ/ψat DESY HERA

The H1 Collaboration recently reported a new analysis of data on the inelastic photoproduction of $J/\ensuremath{\psi}$ mesons at DESY's HERA ep collider. We show that these new experimental results are well described by the color evaporation model for quarkonium production. Moreover, these new data require the introduction of resolved photon contributions in order to accommodate the results in the kinematic region where the fractional energy carried by the $J/\ensuremath{\psi}$ is small, demonstrating that colored perturbative $c\overline{c}$ states contribute to the production of a color singlet.

Unintegrated gluon in the photon and heavy quark production

The unintegrated gluon density in the photon is determined, using the Kimber-Martin-Ryskin prescription . In addition, a model of the unintegrated gluon is proposed, based on the saturation model extended to the large-x region. These gluon densities are applied to obtain cross sections for charm and bottom production in gamma-p and gamma-gamma collisions using the k_t factorization approach. We investigate both direct and resolved photon contributions and make comparison with the results from the collinear approach and the experimental data. An enhancement of the cross section due to inclusion of non-zero transverse momenta of the gluons is found. The charm production cross section is consistent with the data. The data exceed our conservative estimate for bottom production in gamma-p collisions, but theoretical uncertainties are too large to claim a significant inconsistency. A substantial discrepancy between theory and the experiment is found for gamma gamma -> b bbar X, not being cured by the k_t factorization approach.

Photoproduction of isolated photons at HERA in NLO QCD

The NLO QCD calculation for the photoproduction of an isolated photon with large pT at the HERA ep collider is presented. The single resolved photon contribution and the QCD corrections of order αs to the Born term are consistently included. The sizeable NNLO contributions, the box and the double resolved photon subprocesses, are in addition taken into account. The importance of the isolation cut as well as the influence of other experimental cuts on the pT and ηγ distributions are discussed in detail. Results are compared with experimental data and with different NLO calculations.

Photoproduction of the isolated photon at DESY HERA in next-to-leading order QCD

The NLO QCD calculation for the photoproduction of the isolated photon with a large pT at the HERA ep collider is presented. The single resolved photon contribution and the QCD corrections of order alpha_s to the Born term are consistently included. The NNLO contributions, the box and the double resolved photon subprocesses, are sizeable and are taken into account in addition. The importance of the isolation cut, as well as the influence of other experimental cuts on pT and final photon rapidity distributions are discussed in detail. The investigation of the renormalization scale dependence is performed in order to estimate the size of missing higher order QCD corrections. Results are compared with experimental data and with the prediction of a different NLO calculation.

SINGLE SPARTICLE AND LEPTOQUARK PRODUCTION IN e+e- COLLISIONS UP TO $\sqrt{s} = 202~GeV$ WITH THE DELPHI DETECTOR

Searches for single sparticle productions occuring in R-violating supersymmetry, have been performed, using the data collected by the DELPHI detector at LEP up to [Formula: see text]. In particular, the resonant sneutrino production and subsequent decay to a single chargino or neutralino are studied, and limits on the R-parity violating couplings, at 95% CL, are presented. Relevant aspects on the R-violating squark and on a scalar Leptoquark single production are given. A direct search for the single production of scalar and vector Leptoquarks has been performed and limits are derived on the masses and couplings of the Leptoquark states within two different frameworks, based on the direct (pertubative) and the resolved photon contribution.