Accelerator Neutrinos

Abstract:

We have measured the azimuthal angular correlation of bb̄ production, using 86.5pb-1 of data collected by Collider Detector at Fermilab (CDF) in pp̄ collisions at s=1.8TeV during 1994-1995. In high-energy pp̄ collisions, such as at the Tevatron, bb̄ production can be schematically categorized into three mechanisms. The leading-order (LO) process is "flavor creation," where both b and b̄ quarks substantially participate in the hard scattering and result in a distinct back-to-back signal in final state. The "flavor excitation" and the "gluon splitting" processes, which appear at next-leading-order (NLO), are known to make a comparable contribution to total bb̄ cross section, while providing very different opening angle distributions from the LO process. An azimuthal opening angle between bottom and antibottom, Δ, has been used for the correlation measurement to probe the interaction creating bb̄ pairs. The Δ distribution has been obtained from two different methods. One method measures the Δ between bottom hadrons using events with two reconstructed secondary vertex tags. The other method uses bb̄→(J/ ψX)(X′) events, where the charged lepton () is an electron (e) or a muon (μ), to measure Δ between bottom quarks. The bb̄ purity is determined as a function of Δ by fitting the decay length of the J/ψ and the impact parameter of the. Both methods quantify the contribution from higher-order production mechanisms by the fraction of the bb̄ pairs produced in the same azimuthal hemisphere, ftoward. The measured ftoward values are consistent with both parton shower Monte Carlo and NLO QCD predictions. © 2005 The American Physical Society.

Abstract:

We present a search for ZZ and ZW vector boson pair production in pp̄ collisions at s=1.96TeV using the leptonic decay channels ZZ→llνν, ZZ→lll′l′, and ZW→lll′ν. In a data sample corresponding to an integrated luminosity of 194pb-1 collected with the Collider Detector at Fermilab, 3 candidate events are found with an expected background of 1.0±0.2 events. We set a 95% confidence level upper limit of 15.2pb on the cross section for ZZ plus ZW production, compared to the standard model prediction of 5.0±0.4pb. © 2005 The American Physical Society.

Abstract:

Using the data collected with the DO detector at √ s = 1-96 TeV, for integrated luminosities of about 180 pb-1, we have measured the ratio of inclusive cross sections for pp̄ → Z + b jet to pp̄ → Z + jet production. The inclusive Z + b-jet reaction is an important background to searches for the Higgs boson in associated ZH production at the Fermilab Tevatron collider. Our measurement is the first of its kind, and relies on the Z → e+e- and Z → μ+ μ- modes. The combined measurement of the ratio yields 0.021 ± 0.005 for hadronic jets with transverse momenta pT > 20 GeV/c and pseudorapidities |η| < 2.5, consistent with next-to-leading-order predictions of the standard model. © 2005 The American Physical Society.

Abstract:

Using the data collected with the D0 detector at square root(s) = 1.96 TeV, for integrated luminosities of about 180 pb(-1), we have measured the ratio of inclusive cross sections for pp --> Z + b jet to pp --> Z + jet production. The inclusive Z + b-jet reaction is an important background to searches for the Higgs boson in associated ZH production at the Fermilab Tevatron collider. Our measurement is the first of its kind, and relies on the Z --> e+ e- and Z --> mu+ mu- modes. The combined measurement of the ratio yields 0.021+/-0.005 for hadronic jets with transverse momenta pT > 20 GeV/c and pseudorapidities absolute value(eta) < 2.5, consistent with next-to-leading-order predictions of the standard model.