The Underlying Event in Hard Scattering Processes

We study the behavior of the "underlying event" in hard scattering proton-antiproton collisions at 1.8 TeV and compare with the QCD Monte-Carlo models. The "underlying event" is everything except the two outgoing hard scattered "jets" and receives contributions from the "beam-beam remnants" plus initial and final-state radiation. The data indicate that neither ISAJET or HERWIG produce enough charged particles (with PT > 0.5 GeV/c) from the "beam-beam remnant" component and that ISAJET produces too many charged particles from initial-state radiation. PYTHIA which uses multiple parton scattering to enhance the "underlying event" does the best job describing the data.Comment: RevTex4, 18 pages, 29 figures, contribution to Snowmass 200

Searches for Extra Dimensions at the Tevatron

Models in which gravity and/or Standard Model gauge bosons propagate in more than three spatial dimensions have implications that can be tested at current colliders. In this paper, we report on the results from searches for extra dimensions at the two Tevatron experiments, CDF and D0, which utilize up to 200 pb^-1 of proton-antiproton collision data from Run II taken at 1.96 TeV CoM energy, between spring 2002 and fall 2003.Comment: 10 Pages. Proceedings, Hadron Collider Physics (HCP 2004), E. Lansing, Michigan, US

Standard Model Higgs Searches at the Tevatron

We present results from the search for a standard model Higgs boson using data corresponding up to 10 fb-1 of proton-antiproton collision data produced by the Fermilab Tevatron at a center-of-mass energy of 1.96 TeV. The data were recorded by the CDF and D0 Detectors between March 2001 and September of 2011. A broad excess is observed between 105 < mH < 145 GeV/c2 with a global significance of 2.2 standard deviations relative to the background-only hypothesis.Comment: 5 pages, contributed to the Proceedings of the XX International Workshop on Deep-Inelastic Scattering and Related Subjects, March 2012, Bonn, German

The Sources of b-Quarks at the Tevatron and their Correlations

The leading-log order QCD hard scattering Monte-Carlo models of HERWIG, ISAJET, and PYTHIA are used to study the sources of b-quarks at the Tevatron. The reactions responsible for producing b and bbar quarks are separated into three categories; flavor creation, flavor excitation, and parton-shower/fragmentation. Flavor creation corresponds to the production of a b-bbar pair by gluon fusion or by annihilation of light quarks, while flavor excitation corresponds to a b or bbar quark being knocked out of the initial-state by a gluon or a light quark or antiquark. The third source occurs when a b-bbar pair is produced within a parton shower or during the fragmentation process of a gluon or a light quark or antiquark (includes gluon splitting). The QCD Monte-Carlo models indicate that all three sources of b-quarks are important at the Tevatron and when combined they qualitatively describe the inclusive cross-section data. Correlations between the b and bbar quark are very different for the three sources and can be used to isolate the individual contributions.Comment: RevTex4, 14 pages, 20 figures, submitted to Phys. Rev.

Extracting sigma_effective from the CDF gamma+3jets measurement

In their 1997 paper, CDF measured sigma_effective, the normalization factor that relates the cross section for double parton scattering to the product of the inclusive cross sections of the two individual scatters, in a model in which they are assumed to be independent. In his 2007 paper, Treleani pointed out that CDF used a non-standard definition, in which the double parton scattering cross section corresponds to exactly two scatters, rather than the more conventional one in which it is the inclusive two-scatter cross section. He also estimated the correction from one definition to the other, to give a corrected value of sigma_effective. Treleani's form would be correct under the assumption that CDF were able to uniquely identify and count the number of scatters in an event, which is certainly not the case. In this publication we consider CDF's event definition in more detail to provide an improved correction.Comment: 19 page

Photon-jet correlations in pppp and ppˉp \bar p collisions

We compare results of the $k_t$-factorization approach and the next-to-leading order collinear-factorization approach for photon-jet correlations in $pp$ and $p \bar p$ collisions at RHIC and Tevatron energies. We discuss correlations in the azimuthal angle as well as in the two-dimensional space of transverse momentum of photon and jet. Different unintegrated parton distributions (UPDF) are included in the $k_t$-factorization approach. The results depend on UPDFs used. The standard collinear approach gives cross section comparable to the $k_t$-factorization approach. For correlations of the photon and any jet the NLO contributions dominate at relatively small azimuthal angles as well as for asymmetric transverse momenta. For correlations of the photon with the leading jet (the one having the biggest transverse momentum) the NLO approach gives zero contribution at $\phi_{-} < \pi/2$ which opens a possibility to study higher-order terms and/or UPDFs in this region.Comment: 14 pages, 17 figure