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Jon Pumplin

Publications and source records attributed to Jon Pumplin.

36 records · Page 2Linked to original sources
arXiv2009

Collider Inclusive Jet Data and the Gluon Distribution

Inclusive jet production data are important for constraining the gluon distribution in the global QCD analysis of parton distribution functions. With the addition of recent CDF and D0 Run II jet data, we study a number of issues that play a role in determining the up-to-date gluon distribution and its uncertainty, and produce a new set of parton distributions that make use of that data. We present in detail the general procedures used to study the compatibility between new data sets and the previous body of data used in a global fit. We introduce a new method in which the Hessian matrix for uncertainties is ``rediagonalized'' to obtain eigenvector sets that conveniently characterize the uncertainty of a particular observable.

hep-ph↗
arXiv2009

Data set diagonalization in a global fit

The analysis of data sometimes requires fitting many free parameters in a theory to a large number of data points. Questions naturally arise about the compatibility of specific subsets of the data, such as those from a particular experiment or those based on a particular technique, with the rest of the data. Questions also arise about which theory parameters are determined by specific subsets of the data. I present a method to answer both of these kinds of questions. The method is illustrated by applications to recent work on measuring parton distribution functions.

hep-ph↗
arXiv2005

Uncertainties of the Inclusive Higgs Production Cross Section at the Tevatron and the LHC

We study uncertainties of the predicted inclusive Higgs production cross section due to the uncertainties of parton distribution functions (PDF). Particular attention is given to bbH Yukawa coupling enhanced production mechanisms in beyond SM scenarios, such as MSSM. The PDF uncertainties are determined by the robust Lagrange Multiplier method within the CTEQ global analysis framework. We show that PDF uncertainties dominate over theoretical uncertainties of the perturbative calculation (usually estimated by the scale dependence of the calculated cross sections), except for low Higgs masses at LHC. Thus for the proper interpretation of any Higgs signal, and for better understanding of the underlying electroweak symmetry breaking mechanism, it is important to gain better control of the uncertainties of the PDFs.

hep-ph↗
arXiv2005

Parton Distributions

I present an overview of some current topics in the measurement of Parton Distribution Functions.

hep-ph↗
arXiv2004

Light Gluino Constituents of Hadrons and a Global Analysis of Hadron Scattering Data

Light strongly interacting supersymmetric particles may be treated as partonic constituents of nucleons in high energy scattering processes. We construct parton distribution functions for protons in which a light gluino is included along with standard model quark, antiquark, and gluon constituents. A global analysis is performed of a large set of data from deep-inelastic lepton scattering, massive lepton pair and vector boson production, and hadron jet production at large values of transverse momentum. Constraints are obtained on the allowed range of gluino mass as a function of the value of the strong coupling strength alpha_s(M_Z) determined at the scale of the Z boson mass. We find that gluino masses as small as 10 GeV are admissible provided that alpha_s(M_Z) \ge 0.12. Current hadron scattering data are insensitive to the presence of gluinos heavier than ~ 100 - 150 GeV.

hep-ph↗
arXiv2003

Inclusive Jet Production, Parton Distributions, and the Search for New Physics

Jet production at the Tevatron probes some of the smallest distance scales currently accessible. A gluon distribution that is enhanced at large x compared to previous determinations provides a better description of the Run 1b jet data from both CDF and D0. However, considerable uncertainty still remains regarding the gluon distribution at high x. In this paper, we examine the effects of this uncertainty, and of the remaining uncertainties in the NLO QCD theory, on jet cross section comparisons to Run 1b data. We also calculate the range of contributions still possible from any new physics. Predictions are also made for the expanded kinematic range expected for the ongoing Run 2 at the Tevatron and for the LHC.

hep-ph↗
arXiv1997

Partonometry in W + jet production

QCD predicts soft radiation patterns that are particularly simple for $W+ {jet}$ production. We demonstrate how these patterns can be used to distinguish between the parton-level subprocesses probabilistically on an event-by-event basis. As a test of our method we demonstrate correlations between the soft radiation and the radiation inside the outgoing jet.

hep-ph↗
arXiv1997

Hard underlying event correction to inclusive jet cross sections

Jets observed in hadron-hadron scattering contain a contribution from the underlying event that is produced by spectator interactions taking place incoherently with the major parton-parton collision, due to the extended composite structure of the colliding hadrons. Using a recent measurement of the double parton interaction rate, we calculate that the underlying event may be 2 - 3 times stronger than generally assumed, as a result of semi-hard perturbative multiple-parton interactions. This can have an important influence on the inclusive jet cross section at moderate values of E_T, persisting at the 5 - 10% level to the largest observable E_T. We show how the underlying event can be measured accurately using a generalization of the method first proposed by Marchesini and Webber.

hep-ph↗
arXiv1996

Diffractive Photoproduction of Z0

The two gluon exchange model of the pomeron is used to compute the photoproduction reaction $γp \to Z^0 p$. The predicted cross section is too small to be observed at HERA, but may be detectable at an eventual Next Linear Collider.

hep-ph↗
arXiv1996

Jet Algorithms and Top Quark Mass Measurement

Mass measurements of objects that decay into hadronic jets, such as the top quark, are shown to be improved by using a variant of the $k_t$ jet algorithm in place of standard cone algorithms. The possibility and importance of better estimating the neutrino component in tagged $b$ jets is demonstrated. These techniques will also be useful in the search for Higgs boson $\to b \bar b$.

hep-ph↗
arXiv1995

Improving the Measurement of the Top Quark Mass

Two possible ways to improve the mass resolution for observing hadronic top quark decay $t \to bW \to 3 jets$ are studied: (1) using fixed cones in the rest frames of the $t$ and $W$ to define the decay jets, instead of the traditional cones in the rest frame of the detector; and (2) using the jet angles in the top rest frame to measure $m_t/m_W$. By Monte Carlo simulation, the second method is found to give a useful improvement in the mass resolution. It can be combined with the usual invariant mass method to get an even better mass measurement. The improved resolution can be used to make a more accurate determination of the top quark mass, and to improve the discrimination between $t \bar t$ events and background for studies of the production mechanism.

hep-ph↗
arXiv1995

Two Gluon Exchange Model Predictions for Double Pomeron Jet Production

I extend the two gluon exchange picture of elastic scattering, known as the Low-Nussinov or Subtractive Quark Model, to predict cross sections for double pomeron exchange processes. In particular, I calculate p p-bar to p p-bar q q-bar where the q q-bar partons appear as jets separated from the final p and p-bar by large gaps in rapidity. The predicted cross section is large enough that this process should be observable at the Fermilab Tevatron and at the Large Hadron Collider. It can be distinguished from the background of ordinary jet production by the absence of particles produced in the gap regions.

hep-ph↗
arXiv1994

Measuring Parton Densities in the Pomeron

We present a program to measure the parton densities in the pomeron using diffractive deep inelastic scattering and diffractive photoproduction, and to test the resulting parton densities by applying them to other processes such as the diffractive production of jets in hadron-hadron collisions. Since QCD factorization has been predicted NOT to apply to hard diffractive scattering, this program of fitting and using parton densities might be expected to fail. Its success or failure will provide useful information on the space-time structure of the pomeron.

hep-ph↗
arXiv1994

Multiplicity Distributions and Rapidity Gaps

I examine the phenomenology of particle multiplicity distributions, with special emphasis on the low multiplicities that are a background in the study of rapidity gaps. In particular, I analyze the multiplicity distribution in a rapidity interval between two jets, using the HERWIG QCD simulation with some necessary modifications. The distribution is not of the negative binomial form, and displays an anomalous enhancement at zero multiplicity. Some useful mathematical tools for working with multiplicity distributions are presented. It is demonstrated that ignoring particles with pt<0.2 has theoretical advantages, in addition to being convenient experimentally.

hep-ph↗
arXiv1993

Double Pomeron Opportunities at SQRT(s) = 1.8 Tev

I describe possible ways to discover hard double pomeron exchange (HDPE) with the existing detectors at the Fermilab Tevatron, by using the small-angle ``luminosity'' counters as a veto. Estimates of the cross sections and backgrounds are made. In addition to the intrinsic importance of HDPE, its observation would be useful for calibrating the detectors, and for estimating the ``survival probability'' of rapidity gaps.

hep-ph↗
arXiv1993

Quark-Gluon Jet Differences at LEP

A new method to identify the gluon jet in 3-jet ``{\bf Y}'' decays of $Z^0$ is presented. The method is based on differences in particle multiplicity between quark jets and gluon jets, and is more effective than tagging by leptonic decay. An experimental test of the method and its application to a study of the ``string effect'' are proposed. Various jet-finding schemes for 3-jet events are compared.

hep-ph↗