arXiv subjects

Zack Sullivan

Publications and source records attributed to Zack Sullivan.

41 records · Page 3Linked to original sources

arXiv2004

Lower limits on R-parity-violating couplings in supersymmetric models with light squarks

We interpret the results of searches for strongly interacting massive particles to place absolute lower limits on R-parity-violating couplings for squarks with mass (m_\tilde{q}) below 100 GeV. Recent searches for anomalous isotopes require that there be a baryon-number-violating or lepton-number-violating coupling larger than 10^{-22} -- 10^{-21} if m_\tilde{q} > 18 GeV. Using data from searches for stable particles at the CERN Large Electron Positron collider (LEP) we demonstrate that this lower limit increases by 14 orders of magnitude, to an R-parity-violating coupling larger than 10^{-8} -- 10^{-7} for any squarks of mass less than 90 GeV. In the presence of an R-parity-violating coupling of this magnitude, neutralinos cannot explain the dark matter density in the Universe.

hep-ph↗

arXiv2004

Faster Parton Distribution Evaluation in Monte Carlos

I recommend a few trivial changes to the routines that evaluate CTEQ parton distribution functions. These changes allow modern compilers to optimize the evaluation routines, while having no quantitative effect on the results. Computation time is reduced by a factor of 2 in matrix-element calculations, and by 1.3-1.5 in the showering Monte Carlo event generators with fast detector effects included. The results suggest that additional time should be invested in optimizing these routines.

hep-ph↗

arXiv2003

How to rule out Little Higgs (and constrain many other models) at the LHC

In this talk I describe how to discover or rule out the existence of W^{prime} bosons at the CERN Large Hadron Collider as a function of arbitrary couplings and W^{prime} masses. If W^{prime} bosons are not found, I demonstrate the 95% confidence-level exclusions that can be reached for several classes of models. In particular, W^{prime} bosons in the entire reasonable parameter space of Little Higgs models can be discovered or excluded in 1 year at the LHC.

hep-ph↗

arXiv2002

Fully differential W' production and decay at next-to-leading order in QCD

We present the fully differential production and decay of a W' boson, with arbitrary vector and axial-vector couplings, to any final state at next-to-leading order in QCD. We demonstrate a complete factorization of couplings at next-to-leading order in both the partial width of the W' boson, and in the full two-to-two cross section. We provide numerical predictions for the contribution of a W' boson to single-top-quark production, and separate results based on whether the mass of the right-handed neutrino (nu_R) is light enough for the leptonic decay channel to be open. The single-top-quark analysis will allow for an improved direct W' mass limit of 525-550 GeV using data from run I of the Fermilab Tevatron. We propose a modified tolerance method for estimating parton distribution function uncertainties in cross sections.

hep-ph↗

arXiv1997

Supersymmetric QCD correction to top-quark production at the Tevatron

We calculate the supersymmetric QCD correction to top-quark production at the Fermilab Tevatron, allowing for arbitrary left-right mixing of the squarks. We find that the correction is significant for several combinations of gluino and squark masses, e.g. +33% for m_{\tilde g}=200 GeV, m_{\tilde t} = m_{\tilde q} =75 GeV.

hep-ph↗