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Behari, S.

Publications and source records attributed to Behari, S..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Search for resonances decaying to top and bottom quarks with the CDF experiment

We report on a search for charged massive resonances decaying to top (t) and bottom (b) quarks in the full data set of proton-antiproton collisions at a center-of-mass energy of √s = 1.96 TeV collected by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.5 fb –1 . No significant excess above the standard model background prediction is observed. We set 95% Bayesian credibility mass-dependent upper limits on the heavy charged-particle production cross section times branching ratio to tb. Using a standard model extension with a W' → tb and left-right-symmetric couplings as a benchmark model, we constrain the W' mass and couplings in the 300–900 GeV/c 2 range. As a result, the limits presented here are the most stringent for a charged resonance with mass in the range 300–600 GeV/c 2 decaying to top and bottom quarks.

Aaltonen, Timo Antero↗
DOE OSTI2015

Measurement of the production and differential cross sections of W⁺W⁻ bosons in association with jets in p p ¯ collisions at s = 1.96 TeV

We present a measurement of the W-boson-pair production cross section in pp¯ collisions at 1.96 TeV center-of-mass energy and the first measurement of the differential cross section as a function of jet multiplicity and leading-jet energy. The W⁺W⁻ cross section is measured in the final state comprising two charged leptons and neutrinos, where either charged lepton can be an electron or a muon. Using data collected by the CDF experiment corresponding to 9.7 fb⁻¹ of integrated luminosity, a total of 3027 collision events consistent with W⁺W⁻ production are observed with an estimated background contribution of 1790 ± 190 events. The measured total cross section is σ(pp¯→ W⁺W⁻) = 14.0 ± 0.6(stat) ⁺1.2 ⁻1.0 (syst) ± 0.8(lumi) pb, consistent with the standard model prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Measurement of central exclusive π⁺ π⁻ production in p p ¯ collisions at √s = 0.9 and 1.96 TeV at CDF

We measure exclusive π⁺ π⁻ production in proton-antiproton collisions at center-of-mass energies √s = 0.9 and 1.96 TeV in the Collider Detector at Fermilab. We select events with two oppositely charged particles, assumed to be pions, with pseudorapidity |η| < 1.3 and with no other particles detected in |η| < 5.9. We require the π⁺ π⁻ system to have rapidity |y| < 1.0. The production mechanism of these events is expected to be dominated by double pomeron exchange, which constrains the quantum numbers of the central state. The data are potentially valuable for isoscalar meson spectroscopy and for understanding the pomeron in a region of transition between nonperturbative and perturbative quantum chromodynamics. The data extend up to dipion mass M(π⁺ π⁻) = 5000 MeV / c² and show resonance structures attributed to f₀ and f₂ (1270) mesons. From the π⁺ π⁻ and K⁺K⁻ spectra, we place upper limits on exclusive χ c0 (3415) production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Constraints on models of the Higgs boson with exotic spin and parity using decays to bottom-antibottom quarks in the full CDF data set

In this study, a search for particles with the same mass and couplings as those of the standard model Higgs boson but different spin and parity quantum numbers is presented. We test two specific alternative Higgs boson hypotheses: a pseudoscalar Higgs boson with spin-parity J P = 0 – and a gravitonlike Higgs boson with J P = 2 + , assuming for both a mass of 125 GeV/c 2 . We search for these exotic states produced in association with a vector boson and decaying into a bottom-antibottom quark pair. The vector boson is reconstructed through its decay into an electron or muon pair, or an electron or muon and a neutrino, or it is inferred from an imbalance in total transverse momentum. We use expected kinematic differences between events containing exotic Higgs bosons and those containing standard model Higgs bosons. The data were collected by the CDF experiment at the Tevatron proton-antiproton collider, operating at a center-of-mass energy of √s = 1.96 TeV, and correspond to an integrated luminosity of 9.45 fb –1 . We exclude deviations from the predictions of the standard model with a Higgs boson of mass 125 GeV/c 2 at the level of 5 standard deviations, assuming signal strengths for exotic boson production equal to the prediction for the standard model Higgs boson, and set upper limits of approximately 30% relative to the standard model rate on the possible rate of production of each exotic state.

Aaltonen, Timo Antero↗
DOE OSTI2014

Measurement of the Single Top Quark Production Cross Section and |𝑉𝑡⁢𝑏| in Events with One Charged Lepton, Large Missing Transverse Energy, and Jets at CDF

We report a measurement of single top quark production in proton-antiproton collisions at a center-of-mass energy of √𝑠 = 1.96 TeV using a data set corresponding to 7.5 fb −1 of integrated luminosity collected by the Collider Detector at Fermilab. We select events consistent with the single top quark decay process 𝑡 →𝑊⁢𝑏 →ℓ⁢𝜈⁢𝑏 by requiring the presence of an electron or muon, a large imbalance of transverse momentum indicating the presence of a neutrino, and two or three jets including at least one originating from a bottom quark. An artificial neural network is used to discriminate the signal from backgrounds. We measure a single top quark production cross section of $3.0⁢4^{+0.57}_{−0.53}$ pb and set a lower limit on the magnitude of the coupling between the top quark and bottom quark |𝑉𝑡⁢𝑏|>0.78 at the 95% credibility level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Measurements of Direct C P -Violating Asymmetries in Charmless Decays of Bottom Baryons

Here, we report final measurements of direct CP-violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using the complete √s = 1.96 TeV proton-antiproton collisions data set, corresponding to 9.3 fb –1 of integrated luminosity, we measure A(Λ 0 b → pπ – ) = +0.06 ± 0.07(stat) ± 0.03(syst) and A(Λ 0 b → pK – ) = –0.10 ± 0.08(stat) ± 0.04(syst), compatible with no asymmetry. In addition we measure the CP-violating asymmetries in B 0 s → K – π + and B 0 → K + π – decays to be A(B 0 s → K – π + ) = +0.22 ± 0.07(stat) ± 0.02(syst) and A(B 0 → K + π – )=–0.083 ± 0.013(stat) ± 0.004(syst), respectively, which are significantly different from zero and consistent with current world averages.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for new physics in trilepton events and limits on the associated chargino-neutralino production at CDF

We perform a search for new physics using final states consisting of three leptons and a large imbalance in transverse momentum resulting from proton-antiproton collisions at 1.96 TeV center-of-mass energy. We use data corresponding to 5.8 fb -1 of integrated luminosity recorded by the CDF II detector at the Tevatron collider. Our main objective is to investigate possible new low-momentum (down to 5 GeV/c) multi-leptonic final states not investigated by LHC experiments. Relative to previous CDF analyses, we expand the geometric and kinematic coverage of electrons and muons and utilize tau leptons that decay hadronically. Inclusion of tau leptons is particularly important for supersymmetry (SUSY) searches. The results are consistent with standard-model predictions. By optimizing our event selection to increase sensitivity to the minimal supergravity (mSUGRA) SUSY model, we set limits on the associated production of chargino and neutralino, the SUSY partners of the electroweak gauge bosons. We exclude cross sections up to 0.1 pb and chargino masses up to 168 GeV/c 2 at 95% CL, for a suited set of mSUGRA parameters. We also exclude a region of the two-dimensional space of the masses of the neutralino and the supersymmetric partner of the tau lepton, not previously excluded at the Tevatron.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for s -Channel Single-Top-Quark Production in Events with Missing Energy Plus Jets in p p ¯ Collisions at s = 1.96 TeV

The first search for single-top-quark production from the exchange of an s -channel virtual W boson using events with an imbalance in the total transverse energy, b -tagged jets, and no identified leptons is presented. Assuming the electroweak production of top quarks of mass 172.5 GeV / c 2 in the s channel, a cross section of 1.1 2 $+ 0.61\atop{- 0.57}$ ( stat + syst ) pb with a significance of 1.9 standard deviations is measured. This measurement is combined with the result obtained from events with an imbalance in total transverse momentum, b -tagged jets, and exactly one identified lepton, yielding a cross section of 1.3 6$+ 0.37\atop{- 0.32}$ ( stat + syst ) pb, with a significance of 4.2 standard deviations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Observation of s -Channel Production of Single Top Quarks at the Tevatron

We report the first observation of single-top-quark production in the s channel through the combination of the CDF and D0 measurements of the cross section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to 9.7 fb-1 per experiment. The measured cross section is $\sigma_s = 1.29^{+0.26}_{-0.24}$ pb. The probability of observing a statistical fluctuation of the background to a cross section of the observed size or larger is $1.8 \times 10^{-10}$, corresponding to a significance of 6.3 standard deviations for the presence of an s-channel contribution to the production of single-top quarks.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

CDF Run II silicon vertex detector annealing study

Between Run II commissioning in early 2001 and the end of operations in September 2011, the Tevatron collider delivered 12~fb$^{-1}$ of $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV to the Collider Detector at Fermilab (CDF). During that time, the CDF silicon vertex detector was subject to radiation doses of up to 12 Mrad. After the end of operations, the silicon detector was annealed for 24 days at $18^{\circ}$C. In this paper, we present a measurement of the change in the bias currents for a subset of sensors during the annealing period. We also introduce a novel method for monitoring the depletion voltage throughout the annealing period. The observed bias current evolution can be characterized by a falling exponential term with time constant $\tau_I=17.88\pm0.36$(stat.)$\pm0.25$(syst.) days. We observe an average decrease of $(27\pm3)\%$ in the depletion voltage, whose evolution can similarly be described by an exponential time constant of $\tau_V=6.21\pm0.21$ days. These results are consistent with the Hamburg model within the measurement uncertainties.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Search for Pair Production of Strongly Interacting Particles Decaying to Pairs of Jets in pp̄ Collisions at √s=1.96 TeV

We present a search for the pair production of a narrow nonstandard-model strongly interacting particle that decays to a pair of quarks or gluons, leading to a final state with four hadronic jets. We consider both nonresonant production via an intermediate gluon as well as resonant production via a distinct nonstandard-model intermediate strongly interacting particle. We use data collected by the CDF experiment in proton-antiproton collisions at √s=1.96 TeV corresponding to an integrated luminosity of 6.6 fb⁻¹. We find the data to be consistent with nonresonant production. We report limits on σ(pp̄→jjjj) as a function of the masses of the hypothetical intermediate particles. Upper limits on the production cross sections for nonstandard-model particles in several resonant and nonresonant processes are also derived.

Aaltonen, T.↗