H. Miettinen

A new multivariate technique for top quark search

Abstract We present a new multivariate event classifier, the PDE classifier, which can be used to identify rare signals in the presence of large backgrounds. The classifier is based on a discriminant function which uses kernel density estimates of the signal and background event densities. The PDE method offers the flexibility of a neural network but is conceptually simpler, theoretically better understood, and easier to optimize in practice. The technique is tested on Monte Carlo data using processes t t → e + E t + jets as signal and W + jets → e + Et + jets as background. The performance of the PDE classifier is similar to that of a neural network. Both methods outperform conventional analysis.

Measurement of the spin parameters A and Ann in pp elastic scattering in the 1–3 GeV/c region☆

Abstract We have measured the asymmetry parameter A and the spin correlation parameter A nn in pp elastic scattering, using the Argonne ZGS polarized proton beam and a polarized proton target. Angular distributions of A and A nn for | t | ≳ 0.2 (GeV/ c ) 2 were obtained at eight momenta between 1.10 and 2 if 2.75 GeV/ c . We find significant structure in both the energy and t -dependence of A nn at these energies. At p lab ≈ 1.34 GeV/ c A nn reaches a very large value of about 0.8–0.9 near θ cm = 90°.

Evidence for multiple scattering of high energy partons in nuclei

Abstract New experimental information is presented about the effect of a nucleus on partons which have undergone a hard scatter. We have observed clear dijet events from 400 GeV / c p-nucleus interactions and compared them to dijets from pp interactions. Our results show that the angular width of the individual jets is only slightly affected by the presence of the nucleus, but the acoplanarity of the jet pairs is sharply increased.

Modular TPCs for relativistic heavy-ion experiments☆

Abstract A description is given of a TPC system that operates in a relativistic heavy-ion beam and yields good track reconstruction efficiency in very-high-multiplicity events. The mechanical construction of the chamber is discussed. A set of custom hybrid circuits are used to build a very compact, cost-effective electronics system mounted directly on the chamber. Results from running in test beams and from preliminary experimental runs are given.

alphaPDE: A New multivariate technique for parameter estimation

Abstract We present α → PDE, a new multivariate analysis technique for parameter estimation. The method is based on a direct construction of joint probability densities of known variables and the parameters to be estimated. We show how posterior densities and best-value estimates are then obtained for the parameters of interest by a straightforward manipulation of these densities. The method is essentially non-parametric and allows for an intuitive graphical interpretation. We illustrate the method by outlining how it can be used to estimate the mass of the top quark, and we explain how the method is applied to an ensemble of events containing background.

Jet production from nuclei at 400 GeV/c

Abstract Results are presented from a calorimeter study on the production of jets in large- E T proton-nucleus collisions at 400 GeV/c. Jet-like large- p T events from eight nuclear targets are seen with a special jet trigger. As previously observed, the cross section for such events increases slightly faster than the atomic number, much like in the production of large- p T single hadrons. Data on energy flows and multiplicities suggest that a heavy nucleus does not significantly widen the angular distribution of the beam remmants. In the central region the particle flow in hard nuclear collisions is similar to that in soft nuclear collisions.

Hadron-nucleus scattering as a function of nuclear size☆

Abstract High-energy hadron-nucleus collisions, when viewed in terms of nuclear size, exhibit a remarkable simplicity. The data suggest that nuclear matter is extremely opaque to hadrons, and that fast-forward hadrons ( x ≳0.3) arise solely from peripheral collisions. This picture naturally explains why the production ratios of different hadron species are target independent at large x .

Measurement of the single-jet invariant cross section at Fermilab

Abstract In an experiment performed at Fermilab we have studied the production of high pt hadron jets from 400 GeV/c pp interactions. A large solid-angle, towered calorimeter was used to trigger and reconstruct the jet events. We report results for inclusive single-jet production and compare those results with QCD predictions and results obtained at the ISR and the SPS Collider.

Energy dependence of Ann(90°) in pp elastic scattering from 1.10 to 2.75 GeV/c

We have measured the spin correlation parameter Ann in pp elastic scattering near ΘCM=90° from 1.10 to 2.75 GeV/c. We find that Ann(90°) has a pronounced peak at Plab≂1.34 GeV/c, reaching a value of about 0.8–0.9.

Search for QGP signals at AGS with a TPC spectrometer, and comparison of our event generator predictions for plasma model and cascade interactions

We have developed and successfully tested a TPC Magnetic Spectrometer to search for QGP signals produced by ion beams at AGS. We also developed a cascade and plasma event generator the predictions of which are used to illustrate how our technique can detect possible plasma signals.