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Studying the Underlying Event in Drell-Yan and High Transverse Momentum Jet Production at the Tevatron

Description: We study the underlying event in proton-antiproton collisions by examining the behavior of charged particles (transverse momentum p{sub T} > 0.5 GeV/c, pseudorapidity |{eta}| < 1) produced in association with large transverse momentum jets ({approx}2.2 fb{sup -1}) or with Drell-Yan lepton-pairs ({approx}2.7 fb{sup -1}) in the Z-boson mass region (70 < M(pair) < 110 GeV/c{sup 2}) as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton-pair (in Drell-Yan production) or the leading jet (in high-p{sub T} jet production) in each event to define three regions of {eta}-{phi} space; toward, away, and transverse, where {phi} is the azimuthal scattering angle. For Drell-Yan production (excluding the leptons) both the toward and transverse regions are very sensitive to the underlying event. In high-p{sub T} jet production the transverse region is very sensitive to the underlying event and is separated into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte-Carlo models. The goal of this analysis is to provide data that can be used to test and improve the QCD Monte-Carlo models of the underlying event that are used to simulate hadron-hadron collisions.
Date: March 1, 2010
Creator: ,; Aaltonen, T.; Adelman, J.; Gonzalez, B.Alvarez; Amerio, S.; Amidei, D. et al.
Partner: UNT Libraries Government Documents Department

Search for a heavy particle decaying to a top quark and a light quark in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

Description: We present a search for a new heavy particle M produced in association with a top quark, p{bar p} {yields} t(M {yields} {bar t}q) or p{bar p} {yields} {bar t}({bar M} {yields} t{bar q}), where q stands for up quarks and down quarks. Such a particle may explain the recent anomalous measurements of top-quark forward-backward asymmetry. If the light-flavor quark (q) is reconstructed as a jet (j), this gives a {bar t}+j or t+j resonance in t{bar t}+jet events, a previously unexplored experimental signature. In a sample of events with exactly one lepton, missing transverse momentum and at least five jets, corresponding to an integrated luminosity of 8.7 fb{sup -1} collected by the CDF II detector, we find the data to be consistent with the standard model. We set cross-section upper limits on the production (p{bar p} {yields} Mt or {bar M} {bar t}) at 95% confidence level from 0.61 pb to 0.02 pb for M masses ranging from 200 GeV/c{sup 2} to 800 GeV/c{sup 2}, respectively.
Date: March 1, 2012
Creator: Aaltonen, T.; Adelman, J.; Alvarez Gonzalez, B.; Amerio, S.; Amidei, D.; Anastassov, A. et al.
Partner: UNT Libraries Government Documents Department

An additional study of multi-muon events produced in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

Description: We present one additional study of multi-muon events produced at the Fermilab Tevatron collider and recorded by the CDF II detector. We use a data set acquired with a dedicated dimuon trigger and corresponding to an integrated luminosity of 3.9 fb{sup -1}. We investigate the distribution of the azimuthal angle between the two trigger muons in events containing at least four additional muon candidates to test the compatibility of these events with originating from known QCD processes. We find that this distribution is markedly different from what is expected from such QCD processes and this observation strongly disfavours the possibility that multi-muon events result from an underestimate of the rate of misidentified muons in ordinary QCD events.
Date: November 1, 2011
Creator: Aaltonen, T.; Alvarez Gonzalez, B.; Amerio, S.; Amidei, D.; Anastassov, A.; Annovi, A. et al.
Partner: UNT Libraries Government Documents Department

Search for high-mass resonances decaying into $ZZ$ in p$\bar{p}$ collisions at $\sqrt{s}=1.96$\,TeV

Description: The authors search for high-mass resonances decaying into Z boson pairs using data corresponding to 6 fb{sup -1} collected by the CDF experiment in p{bar p} collisions at {radical}s = 1.96 TeV. The search is performed in three distinct final states: ZZ {yields} {ell}{sup +}{ell}{sup -}{ell}{sup +}{ell}{sup -}, ZZ {yields} {ell}{sup +}{ell}{sup -}{nu}{nu}, and ZZ {yields} {ell}{sup +}{ell}{sup -}jj. For a Randall-Sundrum graviton G*, the 95% CL upper limits on the production cross section times branching ratio to ZZ, {sigma}(p{bar p} {yields} G* {yields} ZZ), vary between 0.26 pb and 0.045 pb in the mass range 300 < M{sub G*} < 1000 GeV/c{sup 2}.
Date: November 1, 2011
Creator: Aaltonen, T.; Alvarez Gonzalez, B.; Amerio, S.; Amidei, D.; Anastassov, A.; Annovi, A. et al.
Partner: UNT Libraries Government Documents Department

Observation of the $\Xi_b^0$ Baryon

Description: The observation of the bottom, strange baryon {Xi}{sup 0}{sub b} through the decay chain {Xi}{sup 0}{sub b} {yields} {Xi}{sup +}{sub c} {pi}{sup -}, where {Xi}{sup +}{sub c} {yields} {Xi}{sup -} {pi}{sup +} {pi}{sup +}, {Xi}{sup -} {yields} {Lambda} {yields} p {pi}{sup -}, is reported using data corresponding to an integrated luminosity of 4.2 ft{sup -1} from p{anti p} collisions at {radical}{ovr s} = 1.96 TeV recorded with the Collider Detector at Fermilab. A signal of 25.3{sup +5.6}{sub -5.4} candidates is observed whose probability of arising from a background fluctuation is 3.6 x 10{sup -12}, corresponding to 6.8 Gaussian standard deviations. The {Xi}{sup 0}{sub b} mass is measured to be 5787.8 {+-} 5.0(stat) {+-} 1.3(syst) MeV/c{sup 2}. In addition, the {Xi}{sup -}{sub b} is observed through the process {Xi}{sup -}{sub b} {yields} {Xi}{sup 0}{sub c} {pi}{sup -}, where {Xi}{sup 0}{sub c} {yields} {Xi}{sup -} {pi}{sup +}, {Xi}{sup -} {yields} {Lambda} {pi}{sup -}, and {Lambda} {yields} p {pi}{sup -}.
Date: July 1, 2011
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Alvarez Gonzalez, B.; Phys., /Oviedo U. /Cantabria Inst. of; Amerio, S.; /INFN, Padua et al.
Partner: UNT Libraries Government Documents Department

Search for a Heavy Top-Like Quark in $p\bar{p}$ Collisions at ${\surd}s = 1.96$~TeV

Description: We present the results of a search for pair production of a heavy top-like (t') quark decaying to W q final states using data corresponding to an integrated luminosity of 5.6 fb{sup -1} collected by the CDF II detector in p{anti p} collisions at {radical}{ovr s} = 1.96 TeV. We perform parallel searches for t' {yields} W b and t' {yields} W q (where q is a generic down-type quark) in events containing a lepton and four or more jets. By performing a fit to the two-dimensional distribution of total transverse energy versus reconstructed t' quark mass, we set upper limits on the t'{anti t}' production cross section and exclude a standard model fourth-generation t' quark decaying to W b (W q) with mass below 358 (340) GeV/c{sup 2} at 95% CL.
Date: July 1, 2011
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Alvarez Gonzalez, B.; Phys., /Oviedo U. /Cantabria Inst. of; Amerio, S.; /INFN, Padua et al.
Partner: UNT Libraries Government Documents Department

Search for the Rare Radiative Decay: $W\rightarrow\pi\gamma$ in $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV

Description: We present a search for the rare radiative decay W{sup {+-}} {yields} {pi}{sup {+-}}{gamma} using data corresponding to an integrated luminosity of 4.3 fb{sup -1} of proton-antiproton collisions at a center of mass energy of 1.96 TeV collected by the CDF experiment at Fermilab. As no statistically significant signal is observed, we set a 95% confidence level upper limit on the relative branching fraction {Gamma}(W{sup {+-}} {yields} {pi}{sup {+-}}{gamma})/{Gamma}(W{sup {+-}} {yields} e{sup {+-}}{nu}) at 6.4 x 10{sup -5}, a factor of 10 improvement over the previous limit.
Date: April 1, 2011
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Alvarez Gonzalez, B.; Phys., /Oviedo U. /Cantabria Inst. of; Amerio, S.; /INFN, Padua et al.
Partner: UNT Libraries Government Documents Department

Search for the supersymmetric partner of the top quark in ppbar collisions at sqrt(s) = 1.96 TeV

Description: We present a search for the lightest supersymmetric partner of the top quark in proton-antiproton collisions at a center-of-mass energy {radical}s = 1.96 TeV. This search was conducted within the framework of the R-parity conserving minimal supersymmetric extension of the standard model, assuming the stop decays dominantly to a lepton, a sneutrino, and a bottom quark. We searched for events with two oppositely-charged leptons, at least one jet, and missing transverse energy in a data sample corresponding to an integrated luminosity of 1 fb{sup -1} collected by the CDF experiment. No significant evidence of a stop quark signal was found. Exclusion limits at 95% confidence level in the stop quark versus sneutrino mass plane are set. Stop quark masses up to 180 GeV/c{sup 2} are excluded for sneutrino masses around 45 GeV/c{sup 2}, and sneutrino masses up to 116 GeV/c{sup 2} are excluded for stop quark masses around 150 GeV/c{sup 2}.
Date: September 1, 2010
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Alvarez Gonzalez, B.; Phys., /Oviedo U. /Cantabria Inst. of; Amerio, S.; /INFN, Padua et al.
Partner: UNT Libraries Government Documents Department

Color coherence in p pbar collisions at squareroot s = 1.8 TeV

Description: We report on two preliminary studies of color coherence effects on {ital p}{ital {anti p}} collisions based on data collected by the D{null} detector during the 1992-1993 and 1994-1995 runs at the Fermilab Tevatron collider at a center of mass energy {radical}s = 1. 8 TeV. Demonstration of initial-to-final state color interference effects is done in a higher energy region by measuring spatial correlations between the softer third jet and the second leading- {ital E}{sub {ital T}} jet in multi-jet events and in a lower energy regime by examining particle distribution patterns in W+Jet events. The data are compared to Monte Carlo simulations with different color coherence implementations and the predictions of an NLO parton level calculation.
Date: September 1, 1996
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

The dijet mass spectrum and angular distributions with the D0 detector

Description: We present preliminary results from an analysis of dijet data collected during the 1994-95 Tevatron Collider run with an integrated luminosity of 91 pb{sup -1}. Measurements of dijet mass spectra and dijet angular distributions in {anti p}p collisions at {radical}s- = 1.8 TeV are compared with next-to-leading order QCD theory.
Date: July 1, 1996
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Diphoton production in p{bar p} collisions at {radical}s = 1.8 TeV

Description: We present measurements of the inclusive {gamma}{gamma} cross section (as a function of invariant mass and photon {epsilon}{sub {tau}}), in p{bar p} collisions at {radical}s = 1.8 TeV, made using the D0 detector at the Fermilab Tevatron collider. The next is leading order (NLO) QCD prediction is found to be in good agreement with the data. The effects of invariant mass and diphoton balance cuts, which test the next-to-leading order contributions to the cross section, are investigated. We also compare the distribution of {kappa}{sub {tau}} between samples of diphotons and highly electromagnetic jets, and find that the NLO QCD prediction models the shape of the {gamma}{gamma} {kappa}{sub {tau}} distribution quite well.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Direct photon measurements by the D{O} experiment

Description: We report a measurement of the cross section for production of isolated photons with transverse energy E{sub T} > 12 GeV in the central (absolute value of {eta} < 0.9) and forward (1.6 < absolute value of {eta} < 2.5) rapidity regions for {bar p}p collisions at center of mass energy {radical}s = 1.8 TeV, using an integrated luminosity of 13 pb{sup {minus}1}. The cross section is compared with a next-to-leading order (NLO) QCD calculation. We also present preliminary measurements of the center of mass scattering angle distribution and of the correlations between the rapidity of the photon and that of the leading jet in the event.
Date: July 1, 1996
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Inclusive muon and b quark production cross sections in p{bar p} collisions at {radical}s = 1.8 TeV

Description: We report on the measurement of inclusive muon and b quark production by the D0 collaboration in p{bar p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron Collider. The results represent a refined analysis of the previously published 1992--93 data. We measure the muon cross section due to b quark decays over the kinematic range 4 < p{sub T}{sup {mu}} < 30 GeV/c and {vert_bar}y{sup {mu}}{vert_bar} < 0.8. The extracted b quark production cross section is consistent with next to leading order QCD predictions within theoretical and experimental errors. The improved inclusive b quark production cross section is 6.9 {plus_minus}0.1(stat) {plus_minus} 2.2(syst) {mu}b for p{sub T}{sup {mu}} > 6 GeV/c and {vert_bar}y{sup b}{vert_bar} < 1.0.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

J/{psi} production in p{anti p} collisions at {radical}s = 1.8 TeV

Description: The authors have studied J/{psi} production in p{anti p} collisions at {radical}s = 1.8 TeV with the D0 detector at Fermilab, using a {mu}{sup +}{mu}{sup {minus}} data sample corresponding to an integrated luminosity of 13 pb{sup {minus}1}. They have measured the inclusive J/{psi} production cross section as a function of J/{psi} transverse momentum p{sub T}. For the kinematic range p{sub T} > 8 GeV/c and {vert_bar}{eta}{vert_bar} < 0.6 they obtain Br(J/{psi} {yields} {mu}{sup +}{mu}{sup {minus}}) {center_dot} {sigma}(p{anti p} {yields} J/{psi} + X) = 1.93 {+-} 0.16(stat) {+-} 0.43(syst) nb. Using the muon impact parameter they have estimated the fraction of J/{psi} mesons coming from B meson decays to be f{sub b} = 0.35 {+-} 0.09 (stat) {+-} 0.10 (syst) and inferred the inclusive b production cross section. From the information on the event topology a fraction of non-isolated J/{psi} events has been measured to be f{sub non-isol} = 0.64 {+-} 0.09(stat) {+-} 0.06(syst). They have also obtained the fraction of events resulting from radiative decays of {chi}{sub c} states as f{sub {chi}} = 0.30 {+-} 0.07(stat) {+-} 0.07(syst). They discuss the implications of the measurements for charmonium production processes.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Limits on the anomalous ZZ{gamma} and Z{gamma}{gamma} couplings in p{anti p} collisions at {radical}s = 1.8 TeV

Description: The authors performed a direct search for the anomalous ZZ{gamma} and Z{gamma}{gamma} couplings by studying p{anti p} {yields} {ell}{ell}{gamma} + X, ({ell} = e, {mu}) events at {radical}s = 1.8 TeV with the D0 detector at the Fermilab Tevatron Collider. A fit to the transverse energy spectrum of the photon in the signal events, based on the data set corresponding to an integrated luminosity of 14.3 pb{sup {minus}1} (13.7 pb{sup {minus}1}) for the electron (muon) channel, yields the following 95% confidence level limits on the anomalous CP-conserving ZZ{gamma} couplings: {vert_bar}h{sub 30}{sup Z}{vert_bar} < 1.8 (h{sub 40}{sup Z} = 0), and {vert_bar}h{sub 40}{sup Z}{vert_bar} < 0.5 (h{sub 30}{sup Z} = 0), for a form-factor scale {Lambda} = 500 GeV. Limits for the Z{gamma}{gamma} couplings and CP-violating couplings are also discussed.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Measurement of B{sup 0} {minus} {bar B}{sup 0} mixing using dimuons at D0

Description: The D0 experiment at Fermilab has determined the B{sup 0} {minus} B{sup 0} mixing probability x using dimuon events produced in p{bar p} collisions at {radical}s = 1.8 TeV. Using a sample of 172 dimuon events, we have determined the time and flavor averaged mixing probability x to be 0.09 {plus_minus} 0.04(stat){plus_minus}0.03(sys) [preliminary] in agreement with the present world average.
Date: July 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Measurement of inclusive triple differential dijet cross section, d{sup 3}{sigma}/dE{sub T}d{eta}{sub 1}d{eta}{sub 2} in p{bar p} collisions at {radical}s = 1.8 TeV

Description: Measurement of the inclusive triple differential dijet cross section, d{sup 3}{sigma}/dE{sub T}d{sub {eta}1}d{sub {eta}2}, at a center of mass energy {radical}s = 1.8 TeV with the D0 detector during the 1992--1993 run. The sensitivity of this measurement to different parton distribution functions is explored. A comparison of the data to NLO theory using different parton distributions functions indicates the need for a smaller gluon content in the x range accessible at the Tevatron than is predicted by current parton distribution sets.
Date: July 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Rapidity correlations between high p{sub T} intermediate vector bosons and jets in {bar p}p collisions at {radical}s = 1.8 TeV

Description: D{O} has used W {yields} e{nu} and Z {yields} e{sup +}e{sup -} events produced in association with a high p{sub T}, jet to examine the effects of strong radiative corrections. We have compared the primary jet pseudorapidity distribution, as a function of reconstructed W or Z boson rapidity to leading order (LO) and Next-to-Leading order (NLO) QCD Monte Carlo generators, as well as a model based on extended color dipoles. We find that the primary jet is more central than either LO or NLO expectations. None of the Monte Carlo programs does a good job of predicting the shape of the jet distributions as a function of intermediate vector bosons rapidity.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Rapidity dependence of the inclusive J/{Psi} production in p{bar p} collisions at {radical}s = 1.8 TeV

Description: We have studied J/{psi} production in p{bar p} collisions at {radical}s = 1.8 TeV with the D0 detector at Fermilab, using a {mu}{sup +}{mu}{sup {minus}} data sample collected during the 1994--1995 collider run. We have measured the inclusive J/{psi} production cross section as a function of the J/{psi} transverse momentum, p{sub T}{sup J/{psi}}, in the central and forward rapidity regions. The cross section d{sigma}/dp{sub T}{sup J/{psi}} for {vert_bar}{eta}{sup J/{psi}}{vert_bar}<0.6 covers the p{sub T}{sup J/{psi}} range from 8 to 20 GeV/c. The new measurements are in a good agreement with the CDF and earlier D0 results. The cross section d{sigma}/dp{sub T}{sup J/{psi}} for 2.6 <{vert_bar}{eta}{sup J/{psi}}{vert_bar}<3.4 covers the p{sub T}{sup J/{psi}} range from 3 to 12 GeV/c. We combine the measurements in the two {vert_bar}{eta}{sup J/{psi}}{vert_bar} regions to calculate d{sigma}/d{eta}{sup J/{psi}} for p{sub T}{sup J/{psi}} > 8 GeV/c. The data are compared with the next-to-leading (NLO) QCD calculations, which take into account different J/{psi} production mechanisms.
Date: November 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Rapidity gaps between jets at D{O}

Description: We present studies of jet production via color-singlet events with low particle multiplicity between the jets. A preliminary study of the multiplicity in other regions of the color singlet events and the dependence of color-singlet exchange on jet transverse energy is also presented.
Date: July 1, 1996
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Rapidity gaps between jets at D0

Description: Results are presented from an analysis of the particle multiplicity distribution between high transverse energy jets produced at the Fermilab Tevatron p{bar p} Collider at {radical}s = 1.8 Tev. Using the D0 detector, we examine the particle multiplicity distribution between the two highest transverse energy jets. For events with large rapidity separation, we observed a significant excess of events at low tagged-particle multiplicity which is consistent with a strongly interacting color-singlet exchange process.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Results from a search for a neutral Scalar produced in association with a W boson in p pbar collisions at squareroot s = 1.8 TeV

Description: This paper presents a search for production of a hypothetical heavy particle {ital X} in association with a {ital W} boson. For the search presented here, the kinematics and acceptance are modelled under the assumption that the {ital X} particle has the spin and decay properties of the standard model Higgs boson with the modification that only {ital X} {r_arrow} {ital b}{ital {anti b}} decays are allowed. The {ital W} is required to decay via either the electron or muon mode. The complete D{null} 1992-1995 data set is used. This sample has an integrated luminosity of 100 pb{sup -1} and was taken at a center of mass energy of 1.8 TeV. Limits are placed on the number of associated production events and the production cross section.
Date: August 1, 1996
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Search for anomalous WW and WZ production at D0

Description: We present a preliminary result from a search for anomalous WW and WZ production in p{bar p} collisions at {radical}s = 1.8 TeV using p{bar p} {yields} e{nu}jj events observed during the 1992-1993 run of the Fermilab Tevatron collider. A fit to the p{sub T} spectrum of W(e{nu}) yields direct limits on the CP-conserving anomalous WW{gamma} and WWZ coupling parameters of -0.89 < {Delta}{kappa} < 1.07 ({lambda} = 0) and -0.66 < {lambda} < 0.67 ({Delta}{kappa} = 0) at the 95% confidence level, assuming that the WWZ coupling parameters are equal to the WW{gamma} coupling parameters, and a form factor scale {Lambda} = 1.5 TeV.
Date: July 1, 1995
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department