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D. A. Ross

Publications and source records attributed to D. A. Ross.

At least 37 records · Page 2Linked to original sources
arXiv2007

MSSM Effects in Top-antitop Production at the LHC

We report on a calculation of the effects of supersymmetry on the cross-section for top-antitop production at LHC. A numerical study is carried out for the ten benchmarks of the Snowmass accord. It is found that the higher order effects involving supersymmetric particles in internal loops can be as high as 6%, both for the cross-section and the (parity even) helicity asymmetry, for one particular benchmark. For other benchmarks smaller but nonetheless observable corrections are found.

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arXiv2006

Weak corrections and high $E_T$ jets at Tevatron

We calculate one-loop (purely) Weak (W) corrections of ${\cal O}(α_{\mathrm{S}}^2α_{\mathrm{W}})$ to the partonic cross section of two jets at Tevatron and prove that they can be larger than the tree-level ${\cal O}(α_{\mathrm{S}}α_{\mathrm{EW}})$ and ${\cal O}(α_{\mathrm{EW}}^2)$ Electro-Weak (EW) ones. At high transverse energy of the jets, all such corrections may lead to detectable effects of, e.g., -10% or so, with respect to the leading-order (LO) QCD term of ${\cal O}(α_{\mathrm{S}}^2)$, for the highest value so far probed by Run 2, depending on the factorisation/renormalisation scale. Besides, they increase significantly with jet transverse energy. Hence, our results show that EW corrections may be needed to fit the Standard Model (SM) to present and future Tevatron jet data.

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arXiv2006

Weak corrections to four-parton processes

We report on a calculation of the `mixed' strong and (purely) weak corrections through the order $α_{\mathrm{S}}^2α_{\mathrm{W}}$ to parton-parton processes in all possible channels at hadron colliders entering the single jet inclusive cross section. At both Tevatron and LHC, such effects are always negligible (below permille level) in the total integrated cross section whilst they become sizable in differential rates. Specifically, if such corrections are defined with respect to the full leading-order result of ${\cal O}(α_{\mathrm{S}}^2 +α_{\mathrm{S}}α_{\mathrm{EW}}+α_{\mathrm{EW}}^2)$, we find that, at the FNAL accelerator, they can reach the -5% benchmark in the jet transverse energy (at the kinematical limit of the machine, rendering their detection quite difficult). At the CERN collider, in the same observable, they exceed the -10% level already at 1 TeV and can reach -40% at 4 TeV, kinematic regions where such corrections will be comfortably observable for standard luminosity. In addition, such corrections are somewhat sensitive to the factorisation/renormalisation scale choice.

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arXiv2006

Weak effects in proton beam asymmetries at polarised RHIC and beyond

We report on a calculation of the full one-loop weak corrections through the order $α_{\mathrm{S}}^2α_{\mathrm{W}}$ to parton-parton scattering in all possible channels at the Relativistic Heavy Ion Collider (RHIC) running with polarised $pp$ beams (RHIC-Spin). This study extends the analysis previously carried out for the case of $2\to2$ subprocesses with two external gluons, by including all possible four-quark modes with and without an external gluon. The additional contributions due to the new four-quarks processes are extremely large, of order 50 to 100% (of either sign), not only in the case of parity-violating beam asymmetries but also for the parity-conserving ones and (although to a more limited extent) the total cross section. Such ${\cal O}(α_{\mathrm{S}}^2α_{\mathrm{W}})$ effects on the CP-violating observables would be an astounding 5 times larger for the case of the LHC with polarised beams -- which has been discussed as one of the possible upgrades of the CERN machine -- whereas they would be much reduced for the case of the CP-conserving ones as well as the cross section.

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arXiv2006

Les Houches Physics at TeV Colliders 2005, Standard Model and Higgs working group: Summary report

This Report summarises the activities of the "SM and Higgs" working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. On the one hand, we performed a variety of experimental and theoretical studies on standard candles (such as W, Z, and ttbar production), treating them either as proper signals of known physics, or as backgrounds to unknown physics; we also addressed issues relevant to those non-perturbative or semi-perturbative ingredients, such as Parton Density Functions and Underlying Events, whose understanding will be crucial for a proper simulation of the actual events taking place in the detectors. On the other hand, several channels for the production of the Higgs, or involving the Higgs, have been considered in some detail. The report is structured into four main parts. The first one deals with Standard Model physics, except the Higgs. A variety of arguments are treated here, from full simulation of processes constituting a background to Higgs production, to studies of uncertainties due to PDFs and to extrapolations of models for underlying events, from small-$x$ issues to electroweak corrections which may play a role in vector boson physics. The second part of the report treats Higgs physics from the point of view of the signal. In the third part, reviews are presented on the current status of multi-leg, next-to-leading order and of next-to-next-to-leading order QCD computations. Finally, the fourth part deals with the use of Monte Carlos for simulation of LHC physics.

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arXiv2005

One-loop weak corrections to $γ/Z$ hadro-production at finite transverse momentum

We illustrate the effects of one-loop weak corrections onto the production of neutral gauge bosons of the Standard Model at RHIC-Spin, Tevatron and LHC, in presence of quark/gluon radiation from the initial state. We find such effects to be rather large, up to ${\cal O}(10-20%)$ in typical observables at all such colliders, where the cross section is measurable, thus advocating their inclusion in precision analyses

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arXiv2004

Weak Corrections to Hadronic Observables

We illustrate one-loop weak corrections to three-jet production in $e^+e^-$ at $\sqrt{s}=M_Z$, to the production of a $Z$ or $γ$ in association with a hard jet at hadron colliders and to the production cross section of two $b$-jets at Tevatron and Large Hadron Collider (LHC).

hep-ph↗
arXiv2004

One-loop weak corrections to three-jet observables at the Z pole

We briefly illustrate the impact of the genuinely weak one-loop virtual terms of the ${\cal O}(α_{\rm S}α_{\rm EW}^3)$ factorisable corrections to the three-jet cross section at $\sqrt s=M_Z$. Their importance for the measurement of $α_{\rm S}$ at GigaZ luminosities is emphasised

hep-ph↗
arXiv2004

Les Houches 'Physics at Tev Colliders 2003' QCD/SM Working Group: Summary Report

This report documents the results obtained by the Working Group on Quantum Chromodynamics and the Standard Model for the Workshop `Physics at TeV Colliders'', Les Houches, France, 26 May - 6 June 2003. After a Monte Guide description, the first contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is then followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop.

hep-ph↗
arXiv2003

One-loop weak corrections to the $b\bar b$ cross section at TeV energy hadron colliders

We investigate one-loop weak corrections to the production cross section of two $b$-jets at Tevatron and Large Hadron Collider (LHC). We establish that they are small at inclusive level but dominant in exclusive observables that have a non-trivial dependence on the helicity structure of the hard subprocesses. Such effects can serve as a test of the Standard Model (SM) and, conversely, they should be taken into account in future experimental analyses aiming at extracting possible signals of new physics.

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arXiv2003

Weak Corrections to Three-Jet Production in Electron-Positron Annihilations: 1) The Factorisable Contributions

We report on the calculation of the factorisable one-loop weak-interaction corrections to the initial and final states for three-jet observables in electron-positron annihilations. We show that such corrections are of a few percent at $\sqrt s=M_Z$. Hence, while their impact is not dramatic in the context of LEP1 and SLC, where the total error on the measured value of $α_{\mathrm{S}}$ is larger, at a future Linear Collider, running at the $Z$ mass peak (e.g., GigaZ), they ought to be taken into account in the experimental fits, as here the uncertainty on the value of the strong coupling constant is expected to be at the 0.1% level or even smaller. The calculation has been performed using helicity amplitudes so that it can be applied to the case of polarised beams.

hep-ph↗
arXiv2002

Chargino Pair Production at One-loop

We use the quantum corrected chargino production cross section, including information on the beam polarization and chargino helicities, to estimate the precision achievable at a 1 TeV, 500 ${\mathrm fb}^{-1}$ Linear Collider on the determination of fundamental supersymmetric parameters from measurements of light chargino mass and production cross sections. We show that to get meaningful results higher order corrections should be included.

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arXiv2002

Power corrections in deep inelastic structure functions at large Bjorken x

We study power corrections to the spin-averaged structure functions F_2 and F_L in the semi-inclusive region. The dramatic breakdown of the operator product expansion at large Bjorken x due to the formation of a narrow jet with invariant mass W (W^2=Q^2(1-x)/x) calls for an alternative approach. Our main conjecture is that the dominant contribution at each twist is the one which mixes under renormalization with the leading twist (ultraviolet dominance). At twist two the dominant perturbative corrections at large x due to soft and collinear radiation can be factorized into a jet function. From the ultraviolet dominance conjecture it follows that the twist two parton distribution as well as the jet function actually factorize to any order in the twist expansion. This factorization suggests that non-perturbative corrections ~1/W^{2n} exponentiate together with the leading twist. We verify explicitly, at the level of a single dressed gluon, the cancellation between ambiguities due to infrared renormalons in the twist-two coefficient functions and those due to the ultraviolet divergence of twist-four matrix elements. Independently of the renormalon analysis, we show that the dominant contribution to twist four at large x is associated with a twist-two like configuration: the final states are identical to those of twist two, whereas the initial states differ just by additional partons carrying small momentum fractions. This picture is consistent with the ultraviolet dominance conjecture.

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arXiv2001

Higgs mass bounds in a Triplet Model

We perform a global fit to high energy precision electroweak data in a Higgs model containing the usual isospin doublet plus a real isospin triplet. The analysis is performed in terms of the oblique parameters S, T and U and we show that the mass of the lightest Higgs boson can be as large as 2 TeV.

hep-ph↗
arXiv2001

Prototype Graphs for radiative Corrections to Polarized Chargino or Neutralino Production in Electron-Positron Annihilation

We present the contributions from all types of one-loop corrections to the scattering amplitude for the pair production of polarized charginos or neutralinos from polarized electron-positron annihilation. The contributions are classified in terms of ``prototypes'' distinguished by the number of particles inside the loops and their spins. The results are quoted in terms of the Veltman-Passarino functions in terms of general couplings and internal masses. The results can therefore be applied to any supersymmetric extension of the Standard Model or indeed to any polarized fermion pair production process in electron-positron annihilation.

hep-ph↗
arXiv2000

Solving the BFKL Equation with Running Coupling

We describe a formalism for solving the BFKL equation with a coupling that runs for momenta above a certain infrared cutoff. By suitably choosing matching conditions proper account is taken of the fact that the BFKL diffusion implies that the solution in the infrared (fixed coupling) regime depends upon the solution in the ultraviolet (running coupling) regime and vice versa. Expanding the BFKL kernel to a given order in the ratio of the transverse momenta allows arbitrary accuracy to be achieved.

hep-ph↗
arXiv2000

Photon Structure Functions Beyind the SUSY Threshold

We evolve virtual photon parton densities up to the SUSY threshold and higher using coupled inhomogeneous DGLAP differential equations. Reliable input parameterizations were available from the c-quark threshold. Limited $P^2$ ( target photon virtuality ) dependence is observed. The difference to the photon structure function is shown to be significant with the introduction of SUSY dependent splitting functions. A negligible difference is observed by letting the gluino mass enter after the squark mass. An effort is made to include the squark threshold effect in such a way that both the renormalization group equations are satisfied and the perturbative calculation is reproduced.

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