Peter Renton
The central value and theoretical uncertainties on the cross section ratio sigma_W/sigma_Z at the Tevatron are evaluated using the NNLO calculations and the latest MSTW PDFs. The partial width, total width and branching ratios of the W boson in the Standard Model, in the light of the latest electroweak calculations, are also updated.
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We review the modelling of multiple interactions in the event generator Herwig++ and study implications of recent tuning efforts to Tevatron and LHC data. It is often said that measurements of the effective cross section for double-parton scattering, sigma_effective, are in contradiction with models of the final state of multi-parton interactions, but we show that the Herwig++ model is consistent with both and gives stable predictions for underlying event observables at 14 TeV.
We present updated predictions for the total cross section for Higgs boson production through gluon fusion at hadron colliders. In addition to renormalization-group improvement at next-to-next-to-next-to-leading logarithmic accuracy, we incorporate the two-loop electroweak corrections, which leads to the most precise predictions at present. Numerical results are given for Higgs masses between 115 GeV and 200 GeV at the Tevatron with \sqrt{s}=1.96 TeV and the LHC with \sqrt{s}=7-14 TeV.
We present updated predictions for the total production cross section of top-quark pairs at the Tevatron and at the LHC, and, at the LHC, of heavy-quark pairs with mass in the range 0.5-2 TeV. For t\bar{t} production at the LHC we also present results at \sqrt{S}= 10 TeV, in view of the expected accelerator conditions during the forthcoming 2008 run. Our results are accurate at the level of next-to-leading order in alpha_s, and of next-to-leading threshold logarithms (NLO+NLL). We adopt the most recent parametrizations of parton distribution functions, and compute the corresponding uncertainti…
Following the nonrelativistic QCD factorization scheme, by taking latest available measurement on $χ_b(3P)$ into consideration, we present an updated study on the yield and polarization of $Υ(1S,2S,3S)$ hadroproduction, and the fractions of $χ_b(mP)$ feed-down in $Υ(nS)$ production at QCD next-to-leading order. In the fitting, three schemes are applied with different choice of $χ_b(mP)$ feed-down ratios and NRQCD factorization scale. The results can explain the measurements on yield very well as in our previous work. The polarization puzzle to $Υ(3S)$ is now solved by considering the $χ_b(3P)$…
Expecting the forthcoming experiment at the upgraded Fermilab Tevatron, we calculated CP-violating polarization asymmetry of t t-bar, A_{CP}= [sigma(p p-bar --> t(-) t-bar(-) X) - sigma(p p-bar --> t(+) t-bar(+) X)]/ sigma(p p-bar --> t t-bar X), due to possible anomalous chromomagnetic (kappa) and chromoelectric (tilde{kappa}) couplings of the gluon to the top quark. Since kappa and tilde{kappa} are sensitive to a contribution from new physics beyond standard model, this observable is useful to search for a signal of new physics. It was seen that the magnitude of A_{CP} depends only on Im(til…
We present an updated analysis of meson-baryon sigma terms in the perturbative chiral quark model, which is based on effective chiral Lagrangian. The new feature concerns the inclusion of excited states in the quark propagator. Its influence on meson loops is shown to lead in particular for the pion-nucleon sigma term to an enhancement relevant for the current evaluation of this quantity. We also determine various flavor combinations of the scalar nucleon form factors and their respective low-momentum transfer limits.
We present updated predictions for the total cross section for Higgs boson production by gluon--gluon fusion in hadron collisions. Our calculation includes the most advanced theoretical information available at present for this observable: soft-gluon resummation up to next-to-next-to-leading logarithmic accuracy, the exact treatment of the bottom-quark contribution up to next-to-leading order, and two-loop electroweak effects. We adopt the most recent parametrization of parton distribution functions at next-to-next-to-leading order, and we evaluate the corresponding uncertainties. In compariso…
Recent CDF and D0 measurements of the top quark forward-backward asymmetry at the Tevatron present deviations between 1-sigma and 2-sigma from QCD predictions and a cut M_inv > 450 GeV on the events increases this deviation to 3.4 sigma in the CDF measurement. The inclusion of electroweak contributions of order alpha^2 and order alpha alphas^2 enlarges the theoretical prediction from QCD by a factor ~ 1.2 and diminishes the observed deviations. The calculation method is shortly discussed and numerical results are compared to the experimental data.
Updated Standard Model Higgs boson search results from the Tevatron experiments are presented. We focus on the updated CDF MET+bb result, where a significant shift in observed limits is explained. For the Tevatron combinations, upper limits at 95% credibility level and best-fit values for the Higgs boson cross section times branching ratio are presented. We also place constraints on the Higgs couplings to fermions and electroweak vector bosons. All results are consistent with the existence of a Standard Model Higgs boson with a mass of 125 GeV/c2, and with the Standard-Model predictions associ…
Preliminary results obtained by the CDF and D0 Collaborations on the Standard Model Higgs searches at the Tevatron Run II are discussed. The data that correspond to an integrated luminosity of > 150/pb are compared to theoretical expectations. Various final states involving the W and Z bosons production are examined, and new limits are set on the sigma[W(->enu/munu)H(->bb)] and sigma[H(->WW(*))] cross sections.
We present predictions for the total ttbar production cross section sigma_ttbar at the Tevatron and LHC, which include the resummation of soft logarithms and Coulomb singularities through next-to-next-to-leading logarithmic order, and ttbar bound-state contributions. Resummation effects amount to about 8 % of the next-to-leading order result at Tevatron and about 3 % at LHC with 7 TeV centre-of-mass energy. They lead to a significant reduction of the theoretical uncertainty. With m_t=173.3 GeV, we find sigma_ttbar=7.22^{+0.31+0.71}_{-0.47-0.55} pb at Tevatron and sigma_ttbar=162.6^{+7.4+15.4}_…
The top quark forward-backward asymmetry A_{FB}^t measured at the Tevatron is above the Standard Model prediction by more than 2-sigma deviation, which might be a harbinger for new physics. In this work we examine the contribution to A_{FB}^t in two different new physics models: one is the minimal supersymmetric model without R-parity (RPV-MSSM) which contributes to A_{FB}^t via sparticle-mediated t-channel process d d_bar-> t t_bar; the other is the third-generation enhanced left-right model (LR model) which contributes to A_{FB}^t via Z'-mediated t-channel or s-channel processes. We find tha…
We present updated predictions for Higgs boson production at the Tevatron and the LHC and we review their corresponding uncertainties. We report on a study of the impact of QCD radiative corrections on the Higgs boson search at the Tevatron.
We propose to use rich informations on the pp, pbar p total cross sections sigma below N=10 GeV in order to predict the total cross section and rho ratio at very high energies. Using the FESR as a constraint for high energy parameters, we search for the simultaneous best fit to the data points of sigma and rho ratio up to some energy (e.g., ISR, Tevatron) to determine the high-energy parameters. We then predict sigma and rho in the LHC and high-energy cosmic-ray regions. Using the data up to sqrt s =1.8 TeV(Tevatron), we predict sigma(pp) and rho(pp) at the LHC energy(sqrt s = 14 TeV) as 106.3…
The sensitivity of Standard Model Higgs boson searches at the Tevatron experiments with a mass 135<MH<190 GeV using the channel H->WW->ll+MET (l=e,mu) is discussed. Three new event selections involving Higgs in association with one or two high PT hadronic jets are discussed. Using Leading Order Matrix Elements and a conservative cut-based analysis a 95% confidence level exclusion on sigmaxBR(H->WW), 1.6 times larger than that predicted by the Standard Model for MH=165 GeV, may be achieved with 5fb-1 of integrated luminosity. By combining these three event selections with the existing analysis,…
The single diffractive production of the standard model Higgs boson is computed using the diffractive factorization formalism, taking into account a parametrization for the Pomeron structure function provided by the H1 Collaboration. We compute the cross sections at next-to-leading order accuracy for the gluon fusion process, which includes QCD and electroweak corrections. The gap survival probability ($<\!|S|^2\!>$) is also introduced to account for the rescattering corrections due to spectator particles present in the interaction, and to this end we compare two different models for the survi…
We investigate the prospects for heavy charged Higgs boson production through the mechanisms pp-bar(pp)->tbH+ +X at the upgraded Fermilab Tevatron and at the upcoming LHC collider at CERN respectively. We focus on the MSSM case at high values of tan[beta]> m_top/m_bot and include the leading SUSY quantum corrections. A detailed study is performed for all important production modes and basic background processes for the "ttbb" signature. At the upgraded Tevatron a charged Higgs signal is potentially viable in the 220-250 GeV range or excluded at 95%CL up to 300 GeV. At the LHC, a H+ of mass up …
We propose that the 3.2 sigma excess at ~150 GeV in the dijet mass spectrum of W + jets reported by CDF is the technipion $π_T$ of low-scale technicolor. Its relatively large cross section is due to production of a narrow $Wjj$ resonance, the technirho, which decays to W + $π_T$. We discuss ways to enhance and strengthen the technicolor hypothesis and suggest companion searches at the Tevatron and LHC.
Based on duality, we previously proposed to use rich informations on pi p total cross sections below N=10GeV in addition to high-energy data in order to discriminate whether these cross sections increase like log nu or log2 nu at high energies. We then arrived at the conclusion that our analysis prefers the log2 nu behaviours. Using the FESR as a constraint for high energy parameters also for the pp, pbar p scattering, we search for the simultaneous best fit to the data points of sigma(tot) and rho ratio up to some energy (e.g., ISR, Tevatron) to determine the high-energy parameters. We then p…
This report presents the theoretical analysis relevant for Higgs physics at the upgraded Tevatron collider and documents the Higgs Working Group simulations to estimate the discovery reach in Run 2 for the Standard Model and MSSM Higgs bosons. Based on a simple detector simulation, we have determined the integrated luminosity necessary to discover the SM Higgs in the mass range 100-190 GeV. The first phase of the Run 2 Higgs search, with a total integrated luminosity of 2 fb-1 per detector, will provide a 95% CL exclusion sensitivity comparable to that expected at the end of the LEP2 run. With…
We describe the the improved properties of the NMHDECAY program, that is designed to compute Higgs and sparticle masses and Higgs decay widths in the NMSSM. In the version 2.0, Higgs decays into squarks and sleptons are included, accompagnied by a calculation of the squark, gluino and slepton spectrum and tests against constraints from LEP and the Tevatron. Further radiative corrections are included in the Higgs mass calculation. A link to MicrOMEGAs allows to compute the dark matter relic density, and a rough (lowest order) calculation of the BR(s -> b gamma) is performed.
The ALLM parameterization of sigma_{tot}(gamma* p) has been updated by using all published F_2 data to determine its parameters. The fit yields a chi^2/ndf of 0.97 for the 1356 data points. The updated ALLM parameterization, ALLM97, gives a good description of all the available data in the whole x and Q^2 range studied so far (3\times10^{-6} < x < 0.85, 0 \le Q^2 < 5000 GeV^2).
We examine the prospects of detecting the light Higgs h^0 of the Constrained MSSM at the Tevatron. To this end we explore the CMSSM parameter space with μ>0, using a Markov Chain Monte Carlo technique, and apply all relevant collider and cosmological constraints including their uncertainties, as well as those of the Standard Model parameters. Taking 50 GeV < m_{1/2}, m_0 < 4 TeV, |A_0| < 7 TeV and 2 < tan(beta) < 62 as flat priors and using the formalism of Bayesian statistics we find that the 68% posterior probability region for the h^0 mass lies between 115.4 GeV and 120.4 GeV. Otherwise, h^…
We consider the transverse-momentum (q_T) distribution of Standard Model Higgs bosons produced by gluon fusion in hadron collisions. At small q_T (q_T<<m_H, m_H being the mass of the Higgs boson), we resum the logarithmically-enhanced contributions due to multiple soft-gluon emission to all order in QCD perturbation theory. At intermediate and large values of q_T (q_T <~m_H), we consistently combine resummation with the known fixed-order results. We use the most advanced perturbative information that is available at present: next-to-next-to-leading logarithmic resummation combined with the nex…
We discuss the observability of the lightest neutral Higgs boson in the constrained MSSM (CMSSM), with universal soft supersymmetry-breaking parameters, at hadron colliders such as the Tevatron and the LHC. We take account of the constraints on parameter space provided by LEP, the measured rate of b to s gamma decay, the cosmological relic density Omega h^2, and the recent measurement of g_mu - 2. We normalize products of the expected CMSSM Higgs production cross sections and decay branching ratios (sigma B)_CMSSM relative to those expected for a Standard Model Higgs boson of the same mass. In…
The production of new spin-1 chiral bosons at the hadron colliders, the Fermilab Tevatron and the CERN LHC, is considered. The masses of the chiral bosons can be determined on the basis of experimental data of precise low-energy experiments, which already indicate indirectly their existence. They can explain, for example, the serious 4.5 sigma discrepancy between the measured and the predicted two pion branching ratio of the tau decay and the sign of the 3.3 sigma deviation of the muon (g-2) theoretical prediction from the experimental value. Quantitative evaluations of the various differentia…
We present numerical calculations of the production cross section of a heavy Z' resonance in hadron-hadron collisions with subsequent decay into top-antitop pairs. In particular, we consider the leptophobic topcolor Z' discussed under Model IV of hep-ph/9911288 which has predicted cross sections large enough to be experimentally accessible at the Fermilab Tevatron and the Large Hadron Collider at CERN. This article presents an updated calculation valid for the Tevatron and all proposed LHC collision energies. Cross sections are presented for various Z' widths, in p-pbar collisions at \sqrt{s}=…
We perform a comprehensive statistical analysis of the standard model (SM) with three and four generations using the latest Higgs search results from LHC and Tevatron, the electroweak precision observables (EWPOs) measured at LEP and SLD and the latest determinations of M_W, m_t and alpha_s. For the three-generation case we analyse the tensions in the electroweak fit by removing individual observables from the fit and comparing their predicted values with the measured ones. In particular, we discuss the impact of the Higgs search results on the deviations of the EWPOs from their best-fit value…
In a recent paper, we updated the theoretical predictions for the production cross sections of the Standard Model Higgs boson at the Tevatron and estimated the various uncertainties affecting these predictions. We found that there is a large theoretical uncertainty, of order 40%, on the cross section for the main production channel, gluon-gluon fusion into a Higgs boson. Since then, a note from the Higgs working groups of the CDF and D0 collaborations criticizing our modeling of the $gg\to H$ cross section has appeared. In this addendum, we answer to this criticism point by point and, in parti…
A canonical signature of the Minimal Supersymmetric Standard Model (MSSM) is the presence of a neutral Higgs boson with mass bounded from above by about 135 GeV and Standard Model (SM)-like couplings to the electroweak gauge bosons. In this note we investigate the reach of the Tevatron collider for the MSSM Higgs sector parameter space associated with a variety of high-scale minimal models of supersymmetry (SUSY)-breaking, including the Constrained MSSM (CMSSM), minimal Gauge Mediated SUSY-breaking (mGMSB), and minimal Anomaly Mediated SUSY-breaking (mAMSB). We find that the Tevatron can provi…
The discovery potential of the Tevatron CDF for the rare B-decay B_s --> mu^+ mu^- is analysed. We find that with an integrated luminosity of 2 fb^(-1), and using CDF as the example detector, a 5 sigma combined discovery reach of the Tevatron is possible if the Branching ratio for B_s --> mu^+ mu^- is (1.7 +- 0.46) \times 10^(-7). Such a possible signal for the decay B_s --> mu^+ mu^- will invite large tan(beta) values and set an upper bound on the heaviest mass of the MSSM Higgs sector in a complete analogy to the upper bound of the lightest observable supersymmetric particle set from the exc…
We re-examine the bounds on supersymmetric particle masses in light of the new E821 data on the muon anomalous magnetic moment and the revised theoretical calculations of its hadronic contributions. The current experimental excess is either 1.5 sigma or 3.2 sigma depending on whether e+e- or tau-decay data are used in the theoretical calculations for the leading order hadronic processes. Neither result is compelling evidence for new physics. However, if one interprets the excess as coming from supersymmetry, one can obtain upper mass bounds on many of the particles of the minimal supersymmetri…
Expanded and updated version of a talk originally presented at ``IVth Int. Symp. on Pion--Nucleon Physics and the Structure of the Nucleon'', Bad Honnef, 9--13 September 1991, originally published in $πN$ Newletter 6 (1992) 21--32. Table of contents: 1. Introduction. 2. $σ$--terms and ``measurements'' of the strange--quark scalar density of the nucleon. 3. Methods of extrapolation to $q^2 = t = ω^2 = 0$: a subjective review: 3.1. The ``improved'' Altarelli--Cabibbo--Maiani method. 3.2. The Fubini--Furlan analysis of meson-nucleus scattering lengths. 3.2. The ``unitarized'' version of the Cheng…
Searches for the Minimal Supersymmetric Standard Model (MSSM) Higgs bosons are among the most promising channels for exploring new physics at the Tevatron. In particular, interesting regions of large $\tan β$ and small $m_A$ are probed by searches for heavy neutral Higgs bosons, A and H, when they decay to $τ^+ τ^-$ and $b\bar{b}$. At the same time, direct searches for dark matter, such as CDMS, attempt to observe neutralino dark matter particles scattering elastically off nuclei. This can occur through t-channel Higgs exchange, which has a large cross section in the case of large $\tan β$ and…
We present an update of the Standard Model fit to electroweak precision data. We include newest experimental results on the top quark mass, the W mass and width, and the Higgs boson mass bounds from LEP, Tevatron and the LHC. We also include a new determination of the electromagnetic coupling strength at the Z pole. We find for the Higgs boson mass (91 +30 -23) GeV and (120 +12 -5) GeV when not including and including the direct Higgs searches, respectively. From the latter fit we indirectly determine the W mass to be (80.360 +0.014 -0.013) GeV. We exploit the data to determine experimental co…
We determine the dominant missing Standard Model (SM) contribution to the top quark pair forward-backward asymmetry at the Tevatron. Contrary to past expectations, we find a large, around 27%, shift relative to the well-known value of the inclusive asymmetry in next-to-leading order (NLO) QCD. Combining all known Standard Model corrections, we find that AFB^{SM} = 0.095 +- 0.007. This value is in agreement with the latest D0 measurement [V. M. Abazov et al. (D0 Collaboration), Phys. Rev. D 90, 072011 (2014)] AFB^{D0} = 0.106+- 0.03 and about 1.5 sigma below that of CDF [T. Aaltonen et al. (CDF…
A simple explanation of the W+dijet excess recently reported by the CDF collaboration involves the introduction of a new gauge boson with sizable couplings to quarks, but with no or highly suppressed couplings to leptons. Anomaly-free theories which include such a leptophobic gauge boson must also include additional particle content, which may include a stable and otherwise viable candidate for dark matter. Based on the couplings and mass of the Z' required to generate the CDF excess, we predict such a dark matter candidate to possess an elastic scattering cross section with nucleons on the or…
A number of candidate theories beyond the standard model (SM) predict new scalar bosons below the TeV region. Among these, the radion, which is predicted in the Randall-Sundrum model, and the dilaton, which is predicted in spontaneous scale symmetry breaking, have very similar couplings to those of the SM Higgs boson, and it is very difficult to differentiate these three spin-0 particles in the expected signals of the Higgs boson at the LHC and Tevatron. We demonstrate that the observation of the ratio sigma(gamma gamma)/sigma(WW) gives a simple and decisive way, independently of the values of…
Measurements of the top quark forward-backward asymmetry performed at the Tevatron suggest that new-physics may be playing a role in t-tbar production. To better understand the source of the asymmetry, recent proposals have called for a measurement of the bottom and charm forward-backward asymmetries at the Tevatron, using jets with embedded muons. Here we propose a corresponding measurement of the bottom quark forward-central asymmetry designed to look for similar effects in the b-sector at ATLAS and CMS. We construct a set of cuts designed to enhance sensitivity to this asymmetry, and test o…
An updated global analysis within the Standard Model (SM) of all relevant electroweak precision and Higgs boson search data is presented with special emphasis on the implications for the Higgs boson mass, M_H. Included are, in particular, the most recent results on the top quark and W boson masses, updated and significantly shifted constraints on the strong coupling constant, alpha_s, from tau decays and other low energy measurements such as from atomic parity violation and neutrino deep inelastic scattering. The latest results from searches for Higgs production and decay at the Tevatron are i…
The Higgs boson was postulated in 1964, and phenomenological studies of its possible production and decays started in the early 1970s, followed by studies of its possible production in electron-positron, antiproton-proton and proton-proton collisions, in particular. Until recently, the most sensitive searches for the Higgs boson were at LEP between 1989 and 2000, which were complemented by searches at the Fermilab Tevatron. Then the LHC experiments ATLAS and CMS entered the hunt, announcing on July 4, 2012 the discovery of a "Higgs-like" particle with a mass of about 125~GeV. This identificati…
The pion-nucleon sigma term ($σ_{πN}$) is an observable of fundamental importance because embodies information about the internal scalar structure of the nucleon. Nowadays this quantity has triggered renewed interest because it is a key input for a reliable estimation of the dark matter-nucleon spin independent elastic scattering cross section. In this proceeding we present how this quantity can be reliably extracted by employing only experimental information with the use covariant baryon chiral perturbation theory. We also contrast our extraction with updated phenomenology related to $σ_{πN}$…
Searches for the Standard Model Higgs boson by the four LEP experiments found excess events in two mass ranges: a 2.3 sigma excess around 98 GeV, and an 1.7 sigma excess around 115 GeV. The latter has been discussed widely in the literature, but the former has attracted little attention so far. In this paper I explore the possibility of explaining the excess near 98 GeV through production of the lighter CP--even Higgs boson in the Minimal Supersymmetric Standard Model (MSSM). It is shown that this allows to simultaneously explain the excess near 115 GeV through the production of the heavier CP…
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