arXiv subjects

Gregory Mahlon

Publications and source records attributed to Gregory Mahlon.

26 records · Page 2Linked to original sources

arXiv1997

Recognizing Superpartners at LEP

There is a class of supersymmetric models which is well-motivated by hints of evidence for SUSY and consistent with all existing data. It is important to study the predictions of these models. They are characterized by M(N3) > M(C1) > M(snu) > M(N1) (where Ni and Ci are neutralino and chargino mass eigenstates), |mu| ~< M1 ~< M2 ~= M(Z), mu < 0, and tan(beta) near 1. Their LEP signatures are mostly unusual. Most produced superpartners are invisible! A good signature is two photons plus large missing energy. There are also excess events at large recoil mass in the single photon plus nothing channel. We list the main signatures for charginos, stops, etc., which are also likely to be unconventional. This class of models will be definitively tested at LEP194 with 100 pb^{-1} per detector, and almost definitively tested at LEP184.

hep-ph↗

arXiv1997

Improved Spin Basis for Angular Correlation Studies in Single Top Quark Production at the Tevatron

We show in single top quark production that the spin of the top quark is correlated with the direction of the d-type quark in the event. For single top production in the W* channel, the d-type quark comes dominantly from the antiproton at the Tevatron, whereas for the W-gluon fusion channel the spectator jet is the d-type quark the majority of the time at this machine. Our results are that 98% of the top quarks from the W* process have their spins in the antiproton direction, and 96% of the top quarks in the W-gluon fusion process have their spins in the spectator jet direction. We also compare with the more traditional, but less effective, helicity basis. The direction of the top quark spin is reflected in angular correlations in its decay products.

hep-ph↗

arXiv1996

Searching for a Light Stop at the Tevatron

We describe a method to help the search for a light stop squark [M(stop) + M(LSP) < M(top)] at the Fermilab Tevatron. Traditional search methods rely upon a series of stringent background-reducing cuts which, unfortunately, leave very few signal events given the present data set. To avoid this difficulty, we instead suggest using a milder set of cuts, combined with a "superweight," whose purpose is to discriminate between signal and background events. The superweight consists of a sum of terms, each of which are either zero or one. The terms are assigned event-by-event depending upon the values of various observables. We suggest a method for choosing the observables as well as the criteria used to assign the values such that the superweight is "large" for the supersymmetric signal and "small" for the standard model background. For illustration, we mainly consider the detection of stops coming from top decay, making our analysis especially relevant to the W+2 jets top sample.

hep-ph↗

arXiv1996

How to Search for a Light Stop at the Tevatron

We describe a method for searching for a light stop squark [M(stop)+M(LSP)<M(t)] at the Fermilab Tevatron. Traditional searches rely upon stringent background-reducing cuts which, unfortunately, leave very few signal events given the present data set. To avoid this difficulty, we suggest using a milder set of cuts, combined with a ``superweight,'' whose purpose is to discriminate between signal and background. The superweight consists of a sum of terms (each of which are either zero or one) assigned event-by-event depending upon the values of various observables. By construction, the superweight ``large'' for the signal and ``small'' for the background. We apply this method to the detection of stops coming from top decay. It is straightforward to adapt our method to other processes.

hep-ph↗

arXiv1995

Angular Correlations in Top Quark Pair Production and Decay at Hadron Colliders

We show how to observe sizable angular correlations between the decay products of the top quark and those of the anti-top quark in top quark pair production and decay at hadron colliders. These correlations result from the large asymmetry in the rate for producing like-spin versus unlike-spin top quark pairs provided the appropriate spin axes are used. The effects of new physics at production or decay on these correlations are briefly discussed.

hep-ph↗

arXiv1994

Use of Recursion Relations to Compute One-Loop Helicity Amplitudes

We illustrate the use of recursion relations in the computation of certain one-loop helicity amplitudes containing an arbitrary number of gauge bosons. After a brief review of the recursion relations themselves, we discuss the resolution of the apparent conflict between the spinor helicity method used to solve the recursion relations and the dimensional regulator used in the loop integrals. We then outline the procedure for constructing loop amplitudes, and present two examples of results obtained in this manner.

hep-ph↗

arXiv1993

Multigluon Helicity Amplitudes Involving a Quark Loop

We apply the solution to the recursion relation for the double-off-shell quark current to the problem of computing one loop amplitudes with an arbitrary number of gluons. We are able to compute amplitudes for photon-gluon scattering, electron-positron annihilation to gluons, and gluon-gluon scattering via a quark loop in the case of like-helicity gluons. In addition, we present the result for the one-loop gluon-gluon scattering amplitude when one of the gluons has opposite helicity from the others.

hep-ph↗

arXiv1993

One Loop Multiphoton Helicity Amplitudes

We use the solutions to the recursion relations for double-off-shell fermion currents to compute helicity amplitudes for $n$-photon scattering and electron-positron annihilation to photons in the massless limit of QED. The form of these solutions is simple enough to allow {\it all}\ of the integrations to be performed explicitly. For $n$-photon scattering, we find that unless $n=4$, the amplitudes for the helicity configurations (+++...+) and (-++...+) vanish to one-loop order.

hep-ph↗