Showing papers by "Andre Sopczak published in 2008"
CERN1, Durham University2, University of Colorado Boulder3, Tel Aviv University4, Indian Institute of Science5, Stanford University6, University of Vienna7, Daresbury Laboratory8, University of Liverpool9, University of Freiburg10, University of Bonn11, University of Würzburg12, Fermilab13, Uppsala University14, Waseda University15, University of Warsaw16, RWTH Aachen University17, Cornell University18, University of Southampton19, Heidelberg University20, Nagoya University21, KEK22, University of Bergen23, Istituto Nazionale di Fisica Nucleare24, Spanish National Research Council25, University of Zurich26, Physical Research Laboratory27, Lancaster University28, University of Mainz29, University of California, Berkeley30, Max Planck Society31, University of Kansas32, University of Paris33
TL;DR: In this paper, the International Linear Collider (ILC) is used for discovering physics beyond the Standard Model and for unraveling the structure of the underlying physics, and the physics return can be maximized by the use of polarized beams.
248 citations
TL;DR: In this article, a measurement of the inclusive jet cross section in p (p) over bar collisions at a center-of-mass energy root s = 1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0: 70 fb(-1).
Abstract: We report on a measurement of the inclusive jet cross section in p (p) over bar collisions at a center-of-mass energy root s = 1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0: 70 fb(-1). The data cover jet transverse momenta from 50 to 600 GeV and jet rapidities in the range -2.4 to 2.4. Detailed studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented, and the cross section measurements are found to be in good agreement with next-to-leading order QCD calculations.
246 citations
TL;DR: In this paper, the authors obtained the width difference between the B-s(0) light and heavy mass eigenstates, Delta Gamma(s)=0.19 +/- 0.07(stat), and the CP-violating phase, phi(s)=-0.57(-0.30)(+0.24) ps(-1), and -1.20
Abstract: From an analysis of the flavor-tagged decay B-s(0)-> J/psi phi we obtain the width difference between the B-s(0) light and heavy mass eigenstates, Delta Gamma(s)=0.19 +/- 0.07(stat)(-0.01)(+0.02)(syst) ps(-1), and the CP-violating phase, phi(s)=-0.57(-0.30)(+0.24)(stat)(-0.02)(+0.08)(syst). The allowed 90% CL intervals of Delta Gamma(s) and phi(s) are 0.06
184 citations
TL;DR: The first measurement of the integrated forward-backward charge asymmetry in top-quark-top-antiquark pair (t (t) over bar) production in proton-antiproton (p (p)over bar) collisions in the lepton+jets final state was presented in this article.
Abstract: We present the first measurement of the integrated forward-backward charge asymmetry in top-quark-top-antiquark pair (t (t) over bar) production in proton-antiproton (p (p) over bar) collisions in the lepton+jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming t (t) over bar +X production and decay, a sample of 0.9 fb(-1) of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on t (t) over bar +X production via a Z' resonance.
181 citations
TL;DR: The first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron ppbar collider has been presented in this paper, where a binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single-top quark production of 4.7 +-1.3 pb.
Abstract: We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron ppbar collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top quark partner that is always produced from strong coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top quark production has been searched for in ever larger datasets. In this analysis, we select events from a 0.9 fb-1 dataset that have an electron or muon and missing transverse energy from the decay of a W boson from the top quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a b hadron decay. The selected events are mostly backgrounds such as W+jets and ttbar events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top quark production of 4.7 +- 1.3 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top quark production.
122 citations
TL;DR: In this paper, the shape of the Z/gamma* boson transverse momentum (q(T)) distribution in p (p) over bar -> Z/Gamma(*)-> e(+)e(-)+X events at a center-of-mass energy of 1.96 TeV using 0.98 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron collider.
Abstract: We present a measurement of the shape of the Z/gamma* boson transverse momentum (q(T)) distribution in p (p) over bar -> Z/gamma(*)-> e(+)e(-)+X events at a center-of-mass energy of 1.96 TeV using 0.98 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron collider. The data are found to be consistent with the resummation prediction at low q(T), but above the perturbative QCD calculation in the region of q(T)> 30 GeV/c. Using events with q(T)< 30 GeV/c, we extract the value of g(2), one of the nonperturbative parameters for the resummation calculation. Data at large boson rapidity y are compared with the prediction of resummation and with alternative models that employ a resummed form factor with modifications in the small Bjorken x region of the proton wave function.
120 citations
TL;DR: In this paper, a data sample corresponding to an integrated luminosity of 2.1 fb-1 collected by the D0 detector at the Fermilab Tevatron Collider was analyzed to search for squarks and gluinos produced in ppbar collisions at a center-of-mass energy of 1.96 TeV.
119 citations
TL;DR: A fully reconstructed B-c -> J/psi pi signal was observed with the D0 detector at the Fermilab Tevatron p (p) over bar collider using 1.3 fb(-1) of integrated luminosity as mentioned in this paper.
Abstract: A fully reconstructed B-c -> J/psi pi signal is observed with the D0 detector at the Fermilab Tevatron p (p) over bar collider using 1.3 fb(-1) of integrated luminosity. The signal consists of 54 +/- 12 candidates with a significance that exceeds 5 standard deviations, and confirms earlier observations of this decay. The measured mass of the B-c meson is 6300 +/- 14(stat)+/- 5(syst) MeV/c(2).
97 citations
TL;DR: In this paper, the doubly strange b baryon Omega(b) signal was observed at the Fermilab Tevatron Collider with a mass of 6.165 +/- 0.4 sigma.
Abstract: We report the observation of the doubly strange b baryon Omega(-)(b) in the decay channel Omega(-)(b) -> J/psi Omega(-), with J/psi -> mu(+)mu(-) and Omega(-) -> Lambda K- -> (p pi(-))K-, in p (p) over bar collisions at root s = 1.96 TeV. Using approximately 1.3 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider, we observe 17.8 +/- 4.9(stat) +/- 0.8(syst) Omega(-)(b) signal events at a mass of 6.165 +/- 0.010(stat) +/- 0.013(syst) GeV. The significance of the observed signal is 5.4 sigma, corresponding to a probability of 6.7 x 10(-8) of it arising from a background fluctuation.
83 citations
TL;DR: The direct observation of the excited L=1 state B_(s2)(*) in fully reconstructed decays to B+K-.
Abstract: We report the direct observation of the excited L=1 state B-s2* in fully reconstructed decays to B+K-. The mass of the B-s2* meson is measured to be 5839.6 +/- 1.1(stat)+/- 0.7(syst) MeV/c(2), and its production rate relative to the B+ meson is measured to be [1.15 +/- 0.23(stat)+/- 0.13(syst)]%.
81 citations
TL;DR: In this paper, a measurement of the muon charge asymmetry from W boson decays using 0.3 fb(-1) of data collected at root s = 1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron (p) over bar Collider.
Abstract: We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb(-1) of data collected at root s =1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron (p) over bar Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.
TL;DR: In this paper, a search for the pair production of scalar top quarks was conducted using 995 pb$^{-1}$ of data collected in $p\bar{p}$ collisions with the D0 detector at the Fermilab Tevatron Collider at 1.96$ TeV.
TL;DR: This Letter describes the search for a new heavy charged gauge boson W' decaying into an electron and a neutrino, and sets an upper limit on sigma_(W') x B(W')-->e nu, which significantly improves upon previous limits and is the most stringent to date.
Abstract: This Letter describes the search for a new heavy charged gauge boson W' decaying into an electron and a neutrino. The data were collected with the D0 detector at the Fermilab Tevatron proton-antiproton Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of about 1 inverse femtobarn. Lacking any significant excess in the data in comparison with known processes, an upper limit is set on the production cross section times branching fraction, and a W' boson with mass below 1.00 TeV can be excluded at the 95% C.L., assuming standard-model-like couplings to fermions. This result significantly improves upon previous limits, and is the most stringent to date.
TL;DR: In this paper, the fundamental mass scale was reduced from 884 GeV to 778 GeV for 2 to 8 extra dimensions in the Kaluza-Klein graviton production with a photon and missing transverse energy.
Abstract: We report on a search for large extra dimensions in a data sample of approximately 1 fb^{-1} of p pbar collisions at sqrt(s) = 1.96 TeV. We investigate Kaluza-Klein graviton production with a photon and missing transverse energy in the final state. At the 95% C.L. we set limits on the fundamental mass scale M_{D} from 884 GeV to 778 GeV for 2 to 8 extra dimensions.
TL;DR: In this paper, the electron charge asymmetry in ppbar-W+X->enu+X events at the center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider was measured as a function of the electron transverse momentum and pseudorapidity.
Abstract: We present a measurement of the electron charge asymmetry in ppbar->W+X->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.
TL;DR: In this article, the authors search for a heavy W'gauge boson that decays to third generation quarks in 0: 9 fb(-1) of p (p) over bar collisions at root s = 1: 96 TeV, collected with the D0 detector at the Fermilab Tevatron collider.
Abstract: We search for the production of a heavy W ' gauge boson that decays to third generation quarks in 0: 9 fb(-1) of p (p) over bar collisions at root s = 1: 96 TeV, collected with the D0 detector at the Fermilab Tevatron collider. We find no significant excess in the final-state invariant mass distribution and set upper limits on the production cross section times branching fraction. For a left-handed W ' boson with SM couplings, we set a lower mass limit of 731 GeV. For right-handed W ' bosons, we set lower mass limits of 739 GeV if the W ' boson decays to both leptons and quarks and 768 GeV if the W ' boson decays only to quarks. We also set limits on the coupling of the W ' boson to fermions as a function of its mass.
TL;DR: In this article, the authors measured the polarization of the production cross section of the Fermilab Tevatron Collider using a 1.3 $ fb$^{-1}$ data sample collected by the D0 experiment.
Abstract: We present a study of the polarization of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states using a $1.3 $ fb$^{-1}$ data sample collected by the D0 experiment in 2002--2006 during Run II of the Fermilab Tevatron Collider. We measure the polarization parameter $\alpha=(\sigma_{T}-2\sigma_{L})/(\sigma_{T}+2\sigma_{L})$, where $\sigma_{T}$ and $\sigma_{L}$ are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum ($p_{T}^{\Upsilon}$) for the $\Upsilon(1S)$ and $\Upsilon(2S)$. Significant $p_{T}^{\Upsilon}$-dependent longitudinal polarization is observed for the $\Upsilon(1S)$. A comparison with theoretical models is presented.
TL;DR: In this paper, a search for a narrow-width heavy resonance decaying into top quark pairs X->ttbar in ppbar collisions at sqrt{s}=1.96TeV using approximately 0.9fb^-1 of data collected with the D0 detector at the Fermilab Tevatron Collider is presented.
TL;DR: In this paper, the effect of the heavy b-quark mass on the two, three and four-jet rates was studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995.
Abstract: The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of b-quark jets and light quark jets (l = uds) in events with n = 2, 3, and 4 jets, together with the ratio of two and four-jet rates of b-quarks with respect to light-quarks, R_n^bl, have been measured with a double-tag technique using the CAMBRIDGE jet-clustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the four-jet observable R_4^bl, a measurement of the b-quark mass using massive leading-order calculations gives: m_b(M_Z) = 3.76 +/- 0.32 (stat) +/- 0.17 (syst) +/- 0.22 (had) +/- 0.90 (theo) GeV/c^2 . This result is compatible with previous three-jet determinations at the M_Z energy scale and with low energy mass measurements evolved to the M_Z scale using QCD Renormalisation Group Equations.
TL;DR: The first model-independent measurement of the helicity of W bosons produced in top quark decays is presented, based on a 1 fb(-1) sample of candidate tt events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron Collider.
Abstract: We present the first model-independent measurement of the helicity of $W$ bosons produced in top quark decays, based on a 1 fb$^{-1}$ sample of candidate $t\bar{t}$ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. We reconstruct the angle $\theta^*$ between the momenta of the down-type fermion and the top quark in the $W$ boson rest frame for each top quark decay. A fit of the resulting \costheta distribution finds that the fraction of longitudinal $W$ bosons $f_0 = 0.425 \pm 0.166 \hbox{(stat.)} \pm 0.102 \hbox{(syst.)}$ and the fraction of right-handed $W$ bosons $f_+ = 0.119 \pm 0.090 \hbox{(stat.)} \pm 0.053 \hbox{(syst.)}$, which is consistent at the 30% C.L. with the standard model.
TL;DR: In this article, the authors presented new measurements of differential cross sections for Z/gamma*(->mumu)+jet+X production in a 1 fb-1 data sample collected with the D0 detector in proton anti-proton collisions at sqrt{s}=1.96 TeV.
TL;DR: The first simultaneous measurement of the ratio of branching fractions in the lepton plus jets channel was presented in this article, with q being a d, s, or b quark, and sigma(t (t) over bar) = 8.18(-0.84) + 0.50(lumi) pb, in agreement with the standard model prediction.
Abstract: We present the first simultaneous measurement of the ratio of branching fractions, R = B(t --> Wb)/B(t --> Wq), with q being a d, s, or b quark, and the top-quark pair production cross section sigma(t (t) over bar) in the lepton plus jets channel using 0.9 fb(-1) of p (p) over bar collision data at root s = 1.96 TeV collected with the D0 detector. We extract R and sigma(t (t) over bar) by analyzing samples of events with 0, 1, and >= 2 identified b jets. We measure R = 0.97(-0.08)(+0.09) (stat + syst) and sigma(t (t) over bar) = 8.18(-0.84)(+0.90) (stat + syst) +/- 0.50(lumi) pb, in agreement with the standard model prediction.
TL;DR: In this article, a search for the pair production of the lightest supersymmetric partner of the top quark, t ˜ 1, using a data set corresponding to an integrated luminosity of 1 fb −1 collected by the DO detector at a p p ¯ center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider was performed in the electron plus muon and dielectron final states.
TL;DR: In this paper, a measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996-2000).
Abstract: A measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996-2000). The data sample has an integrated luminosity of 660 pb^-1 and was collected over a range of centre-of-mass energies from 161 to 209 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W- -> lvqq and W+W- -> qqqq channels. The W mass result for the combined data set is M_W = 80.336 +/- 0.055 (Stat.) +/- 0.028 (Syst.) +/- 0.025 (FSI) +/- 0.009 (LEP) GeV/c^2, where FSI represents the uncertainty due to final state interaction effects in the qqqq channel, and LEP represents that arising from the knowledge of the collision energy of the accelerator. The combined value for the W width is Gamma_W = 2.404 +/- 0.140 (Stat.) +/- 0.077 (Syst.) +/- 0.065 (FSI) GeV/c^2. These results supersede all values previously published by the DELPHI collaboration. This paper is dedicated to the memory of Carlo Caso.
TL;DR: In this article, the results of a search for pair production of doubly-charged Higgs bosons via ppbar to H^{++}H^{--}X to mu+mu^+mu+mu-mu^-mu-X at sqrt{s} = 1.96 TeV were reported.
Abstract: We report the results of a search for pair production of doubly-charged Higgs bosons via ppbar to H^{++}H^{--}X to mu^+mu^+mu^-mu^-X at sqrt{s} = 1.96 TeV. We use a dataset corresponding to an integrated luminosity of 1.1 fb^{-1} collected from 2002 to 2006 by the D0 detector at the Fermilab Tevatron Collider. In the absence of an excess above the standard model background, lower mass limits of M(H^{pmpm}_L) > 150 GeV/c^2 and M(H^{pmpm}_R) > 127 GeV/c^2 at 95% C.L. are set, respectively, for left-handed and right-handed doubly-charged Higgs bosons assuming a 100% branching ratio into muons.
TL;DR: In this paper, the authors present a study of events with Z bosons and jets produced at the Fermilab Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV.
TL;DR: This Letter reports on a search for long-lived particles that decay into final states with two electrons or photons, and interprets this search as a quasi model-independent limit on their production cross section, as well as a limit on a long- lived fourth generation quark.
Abstract: In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, such as hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.
TL;DR: In this paper, a determination of the single W Spin Density Matrix (SDM) elements in the reaction e+e- -> W+W- -> l nu q qbar (l=e/mu) is reported at center-of-mass energies between 189 and 209 GeV.
Abstract: A determination of the single W Spin Density Matrix (SDM) elements in the reaction e+e- -> W+W- -> l nu q qbar (l=e/mu) is reported at centre-of-mass energies between 189 and 209 GeV. The data sample used corresponds to an integrated luminosity of 520 pb^{-1} taken by DELPHI between 1998 and 2000. The single W SDM elements, rho_{tau tau'}^{W+-} (tau,tau' = +/-1 or 0), are determined as a function of the W- production angle with respect to the e- beam direction and are obtained from measurements of the W decay products by the application of suitable projection operators, Lambda_{tau tau'}, which assume the V-A coupling of the W boson to fermions. The measured SDM elements are used to obtain the fraction of longitudinally polarised Ws, with the result: sigma_L/sigma_tot = 24.9 +/- 4.5(stat) +/- 2.2(syst) % at a mean energy of 198 GeV. The SDM elements are also used to determine the Triple Gauge Couplings Delta g_1^Z, Delta kappa_gamma, lambda_gamma and g_4^Z, ~kappa_Z and ~lambda_Z. For the CP-violating couplings the results of single parameter fits are: g_4^Z = -0.39 +0.19 -0.20 ~kappa_Z = -0.09 +0.08 -0.05 ~lambda_Z = -0.08 +/- 0.07 . The errors are a combination of statistical and systematic errors. All results are consistent with the Standard Model.
TL;DR: In this paper, the fraction of W + c-jets events produced with net charm quantum number 11, denoted W+ c-jet, in p collisions at root s = 1.96 TeV using approximately 1 fb(-1) of data collected by the DO detector at the Fermilab Tevatron Collider.
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TL;DR: The report of the Working Group on Higgs Bosons for the Workshop, ''Physics at TeV Colliders'', Les Houches, France, 11-29 June, 2007 as discussed by the authors
Abstract: Report of the Working Group on Higgs Bosons for the Workshop, ``Physics at TeV Colliders'', Les Houches, France, 11-29 June, 2007.