arXiv subjects

Stephen J. Parke

Publications and source records attributed to Stephen J. Parke.

46 records · Page 3Linked to original sources

arXiv2010

Summary report of MINSIS workshop in Madrid

Recent developments on tau detection technologies and the construction of high intensity neutrino beams open the possibility of a high precision search for non-standard μ - τ flavour transition with neutrinos at short distances. The MINSIS - Main Injector Non-Standard Interaction Search- is a proposal under discussion to realize such precision measurement. This document contains the proceedings of the workshop which took place on 10-11 December 2009 in Madrid to discuss both the physics reach as well as the experimental requirements for this proposal.

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arXiv2010

Interpretation of MINOS data in terms of non-standard neutrino interactions

The MINOS experiment at Fermilab has recently reported a tension between the oscillation results for neutrinos and anti-neutrinos. We show that this tension, if it persists, can be understood in the framework of non-standard neutrino interactions (NSI). While neutral current NSI (non-standard matter effects) are disfavored by atmospheric neutrinos, a new charged current coupling between tau neutrinos and nucleons can fit the MINOS data without violating other constraints. In particular, we show that loop-level contributions to flavor-violating tau decays are sufficiently suppressed. However, conflicts with existing bounds could arise once the effective theory considered here is embedded into a complete renormalizable model. We predict the future sensitivity of the T2K and NOvA experiments to the NSI parameter region favored by the MINOS fit, and show that both experiments are excellent tools to test the NSI interpretation of the MINOS data.

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arXiv2010

Spin Correlation Effects in Top Quark Pair Production

An analysis of the spin correlation effects in top quark pair production at hadron colliders is presented with special emphasis for the Large Hadron Collider (LHC). At the LHC top quark pair production is dominated by gluon-gluon fusion. For gluon-gluon fusion at high energies the production is dominated by unlike helicity gluon fusion which has the same spin correlations as quark-antiquark annihilation. At low energies the production is dominated by like helicity gluon fusion which imparts very strong azimuthal correlations on the di-lepton decay products in top quark pair decay. This production process is studied in detail and this suggest a new way to look for spin correlations in top quark pair production at the LHC.

hep-ph↗

arXiv2010

Spin Correlation Effects in Top Quark Pair Production at the LHC

At a 14 TeV proton-proton collider, the Large Hadron Collider (LHC), we show that top quark pair production is dominated at low invariant mass by the fusion of two like-helicity gluons, producing top quark pairs in the left-left or right-right helicity configurations. Whereas, at higher invariant mass the production is dominated by the fusion of unlike-helicity gluons, producing top quark pairs in the up-down or down-up off-diagonal configurations, identical to top quark pair production via quark-antiquark annihilation. We study in detail the low invariant mass region, and show that the spin correlations can be easily observed in this region by looking at the distribution of the difference in the azimuthal angles, Delta-phi, of the dileptons decay products of the top quarks in the laboratory frame. Due to the large cross section for top pair production at the LHC, even with a cut requiring that the invariant mass of the top quark pair be less than 400 GeV, the approximate yield would be 10^4 di-lepton (e, mu) events per fb^{-1} before detector efficiencies are applied. Therefore, there is ample statistics to form the Delta-phi distribution of the dilepton events, even with the invariant mass restriction. We also discuss possibilities for observing these spin correlations in the lepton plus jets channel.

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arXiv2008

CP Violation in the Neutrino Sector

This talk will address how various experiments will address the following issues: the $ν_e$ flavor content of the 3rd neutrino mass eigenstates, $\sin^2 θ_{13}$, the mass ordering of the neutrinos, ${\rm sign}(δm^2_{31})$ and whether CP is violated in the neutrino sector, $\sin δ\neq 0$.

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arXiv2005

Multi-Parton Amplitudes in Gauge Theories

In this report we review recent developments in perturbation theory methods for gauge theories. We present techniques and results that are useful in the calculation of cross sections for processes with many final state partons which have applications in the study of multi-jet phenomena in high-energy Colliders.

hep-th↗

arXiv2001

On the Normalization of the Neutrino-Deuteron Cross Section

As is well-known, comparison of the solar neutrino fluxes measured in SuperKamiokande (SK) by $ν+ e^- \to ν+ e^-$ and in the Sudbury Neutrino Observatory (SNO) by $ν_e + d \to e^- + p + p$ can provide a ``smoking gun'' signature for neutrino oscillations as the solution to the solar neutrino puzzle. This occurs because SK has some sensitivity to all active neutrino flavors whereas SNO can isolate electron neutrinos. This comparison depends crucially on the normalization and uncertainty of the theoretical charged-current neutrino-deuteron cross section. We address a number of effects which are significant enough to change the interpretation of the SK--SNO comparison.

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arXiv2001

Optimizing T-violating Effects for Neutrino Oscillations in Matter

Matter effects may strongly enhance the Jarlskog factor J in T and CP-violating three-neutrino oscillation probabilities. However, we show that when J is enhanced, the same matter effects suppress the oscillating factors and increase the oscillation length. The net result is that there is no large enhancement in measurable probabilities for earth-bound experiments using neutrino parameters suggested by current experiments. We show that by an appropriate choice of the experimental parameters, neutrino energy and travel length, the T-violating probability can be enhanced by matter effects over their vacuum values by 50%. Our approach is analytical, allowing considerable insight into the underlying physics.

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arXiv1999

Cross Section for Topcolor Z' decaying to top-antitop

We present a calculation of the cross section for the process p pbar -> Zt' -> t tbar, the production of a Topcolor Z' with subsequent decay to top quark pairs in proton anti-proton collisions at 1.8 TeV. Variations of the cross section with varying assumptions about the model, the resonance width, the parton distributions and the renormalization scale are presented.

hep-ph↗

arXiv1993

Top Production: Sensitivity to New Physics

The production cross--section and distributions of the top quark are sensitive to new physics, e.g., the $t\overline{t}$ system can be a probe of new resonances or gauge bosons that are strongly coupled to the top quark, in analogy to Drell--Yan production. The existence of such new physics is expected in dynamical electroweak symmetry breaking schemes, and associated with the large mass of the top quark. The total top production cross--section can be more than doubled, and distributions significantly distorted with a chosen scale of new physics of $\sim 1 $ TeV in the vector color singlet or octet $s$--channel. New resonance physics is most readily discernible in the high--$p_T$ distributions of the single top quark and of the $W$ boson.

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