Charge asymmetry in W + jets production at the LHC

The charge asymmetry in W + jets production at the LHC can serve to calibrate the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying particular attention to the uncertainty in the prediction from higher-order perturbative corrections and uncertainties in parton distribution functions. We show that these uncertainties are generally of order a few percent, making the experimental measurement of the charge asymmetry ratio a particularly useful diagnostic tool for New Physics contributions.Comment: 13 pages, 7 figures. Reference added. Slightly modified tex

Use of W-Boson Longitudinal-Transverse Interference in Top Quark Spin-Correlation Functions: II

This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of top-antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production contributions are included for the charged-lepton-plus-jets reaction p p or p bar{p} --> t bar{t} --> (W^+ b)(W^- bar{b}) --> (l^{+} nu b)(W^- bar{b}). There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of, or for measurement of a possible non-trivial phase between the two dominant helicity amplitudes for t --> W^{+} b decay. There is an analogous function and tests for bar{t} --> W^{-} bar{b} decay. This signature requires use of the (t bar{t}) c.m.-energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar-angle of W-boson emission in the anti-top (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude phase convention of Jacob & Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal-transverse interference effect.Comment: Continuation of hep-ph/0506240 to include gluon-production contribution; 3 "postscript" figures. Equation numbers as in published-on-line EPJ

Squark Mixing in Electron-Positron Reactions

Squark mixing plays a large role in the phenomenology of the minimal supersymmetric standard model, determining the mass of the lightest Higgs boson and the electroweak interactions of the squarks themselves. We examine how mixing may be investigated in high energy $e^+ e^-$ reactions, both at LEP-II and the proposed linear collider. In particular, off-diagonal production of one lighter and one heavier squark allows one to measure the squark mixing angle, and would allow one to test the mass relations for the light Higgs boson. In some cases off-diagonal production may provide the best prospects to discover supersymmetry. In the context of the light bottom squark scenario, we show that existing data from LEP-II should show definitive evidence for the heavier bottom squark provided that its mass $m_{\tilde{b}_2} \le 120$ GeV.Comment: 22 pages, latex, 6 figure

Soft gluons and superleading logarithms in QCD

After a brief introduction to the physics of soft gluons in QCD we present a surprising prediction. Dijet production in hadron-hadron collisions provides the paradigm, i.e. h_1 +h_2 \to jj+X. In particular, we look at the case where there is a restriction placed on the emission of any further jets in the region in between the primary (highest p_T) dijets. Logarithms in the ratio of the jet scale to the veto scale can be summed to all orders in the strong coupling. Surprisingly, factorization of collinear emissions fails at scales above the veto scale and triggers the appearance of double logarithms in the hard sub-process. The effect appears first at fourth order relative to the leading order prediction and is subleading in the number of colours.Comment: Talk presented at the workshop "New Trends in HERA Physics", Ringberg Castle, Tegernsee, 5-10 October 200

W^+W^+ plus dijet production in the POWHEGBOX

We present an implementation of the calculation of the production of W^+W^+ plus two jets at hadron colliders, at next-to-leading order (NLO) in QCD, in the POWHEG framework, which is a method that allows the interfacing of NLO calculations to shower Monte Carlo programs. This is the first 2 -> 4 process to be described to NLO accuracy within a shower Monte Carlo framework. The implementation was built within the POWHEGBOX package. We discuss a few technical improvements that were needed in the POWHEGBOX to deal with the computer intensive nature of the NLO calculation, and argue that further improvements are possible, so that the method can match the complexity that is reached today in NLO calculations. We have interfaced our POWHEG implementation with PYTHIA and HERWIG, and present some phenomenological results, discussing similarities and differences between the pure NLO and the POWHEG+PYTHIA calculation both for inclusive and more exclusive distributions. We have made the relevant code available at the POWHEGBOX web site.Comment: 16 pages, 5 figure

The Pomeron In Exclusive Vector Meson Production

An earlier developed model for vector meson photoproduction, based on a dipole Pomeron exchange, is extended to electroproduction. Universality of the non linear Pomeron trajectory is tested by fitting the model to ZEUS and H1 data as well as to CDF data on $\bar pp$ elastic scattering.Comment: 12 pages, 13 figure

Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation

The transverse momentum $Q_T$ distribution is computed for inclusive Higgs boson production at the energy of the CERN Large Hadron Collider. We focus on the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and incorporate contributions from the quark-gluon and quark-antiquark channels. Using an impact-parameter $b$-space formalism, we include all-orders resummation of large logarithms associated with emission of soft gluons. Our resummed results merge smoothly at large $Q_T$ with the fixed-order expectations in perturbative quantum chromodynamics, as they should, with no need for a matching procedure. They show a high degree of stability with respect to variation of parameters associated with the non-perturbative input at low $Q_T$. We provide distributions $d\sigma/dy dQ_T$ for Higgs boson masses from $M_Z$ to 200 GeV. The average transverse momentum at zero rapidity $y$ grows approximately linearly with mass of the Higgs boson over the range $M_Z < m_h \simeq 0.18 m_h + 18$~GeV. We provide analogous results for $Z$ boson production, for which we compute $\simeq 25$ GeV. The harder transverse momentum distribution for the Higgs boson arises because there is more soft gluon radiation in Higgs boson production than in $Z$ production.Comment: 42 pages, latex, 26 figures. All figures replaced. Some changes in wording. Published in Phys. Rev. D67, 034026 (2003

Thickness Estimation of Epitaxial Graphene on SiC using Attenuation of Substrate Raman Intensity

A simple, non-invasive method using Raman spectroscopy for the estimation of the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is presented, enabling simultaneous determination of thickness, grain size and disorder using the spectra. The attenuation of the substrate Raman signal due to the graphene overlayer is found to be dependent on the graphene film thickness deduced from X-ray photoelectron spectroscopy and transmission electron microscopy of the surfaces. We explain this dependence using an absorbing overlayer model. This method can be used for mapping graphene thickness over a region and is capable of estimating thickness of multilayer graphene films beyond that possible by XPS and Auger electron spectroscopy (AES).Comment: 14 pages, 9 figure

Likelihood Functions for Supersymmetric Observables in Frequentist Analyses of the CMSSM and NUHM1

On the basis of frequentist analyses of experimental constraints from electroweak precision data, g-2, B physics and cosmological data, we investigate the parameters of the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking mass parameters, and a model with common non-universal Higgs masses (NUHM1). We present chi^2 likelihood functions for the masses of supersymmetric particles and Higgs bosons, as well as b to s gamma, b to mu mu and the spin-independent dark matter scattering cross section. In the CMSSM we find preferences for sparticle masses that are relatively light. In the NUHM1 the best-fit values for many sparticle masses are even slightly smaller, but with greater uncertainties. The likelihood functions for most sparticle masses are cut off sharply at small masses, in particular by the LEP Higgs mass constraint. Both in the CMSSM and the NUHM1, the coannihilation region is favoured over the focus-point region at about the 3-sigma level, largely but not exclusively because of g-2. Many sparticle masses are highly correlated in both the CMSSM and NUHM1, and most of the regions preferred at the 95% C.L. are accessible to early LHC running. Some slepton and chargino/neutralino masses should be in reach at the ILC. The masses of the heavier Higgs bosons should be accessible at the LHC and the ILC in portions of the preferred regions in the (M_A, tan beta) plane. In the CMSSM, the likelihood function for b to mu mu is peaked close to the Standard Model value, but much larger values are possible in the NUHM1. We find that values of the DM cross section > 10^{-10} pb are preferred in both the CMSSM and the NUHM1. We study the effects of dropping the g-2, b to s gamma, relic density and M_h constraints.Comment: 34 pages, 24 figure

How much energy do closed timelike curves in 2+1 spacetimes need?

By noticing that, in open 2+1 gravity, polarized surfaces cannot converge in the presence of timelike total energy momentum (except for a rotation of 2 pi), we give a simple argument which shows that, quite generally, closed timelike curves cannot exist in the presence of such energy condition.Comment: 3 pages, with no figures. Accepted in PRD as Rapid Communicatio