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S. Abachi

Publications and source records attributed to S. Abachi.

At least 19 recordsLinked to original sources
arXiv2025

Space-time Areas and Hadronization Studies

Space-time area laws play a fundamental role in modeling strongly interacting phenomena, such as in relativistic string models, QCD on the lattice, and in hadronization modeling. For the latter, an exact expression for relevant space-time areas related to the final state hadronic events for hadrons of any mass is calculated. Usage of this expression in the UCLA hadronization model helps validate its space-time area law (STAL) principle and unifies the treatment of heavy and light hadrons via a single fragmentation function.

hep-ph↗
arXiv1997

Measurement of the Top Quark Pair Production Cross Section in pbarp Collisions

We present a measurement of the ttbar production cross section in ppbar collisions at root(s) = 1.8TeV by the D0 experiment at the Fermilab Tevatron. The measurement is based on data from an integrated luminosity of approximately 125 pb^-1 accumulated during the 1992-1996 collider run. We observe 39 ttbar candidate events in the dilepton and lepton+jets decay channels with an expected background of 13.7+-2.2 events. For a top quark mass of 173.3GeV/c^2, we measure the ttbar production cross section to be 5.5+-1.8 pb.

hep-ex↗
arXiv1997

Direct Measurement of the Top Quark Mass

We measure the top quark mass m_t using t tbar pairs produced in the D0 detector by root(s) = 1.8 TeV p pbar collisions in a 125 pb^-1 exposure at the Fermilab Tevatron. We make a two constraint fit to m_t in t tbar --> b W^+ bbar W^- final states with one W decaying to q qbar and the other to e nu or mu nu. Events are binned in fit mass versus a measure of probability for events to be signal rather than background. Likelihood fits to the data yield m_t = 173.3 +- 5.6 (stat) +- 6.2 (syst) GeV/c^2.

hep-ex↗
arXiv1997

Study of the ZZγand ZγγCouplings in Z(νν)γProduction

We have measured the ZZ-gamma and Z-gamma-gamma couplings by studying p-bar p -> (missing ET) gamma + X events at sqrt(s)=1.8 TeV with the D0 detector at the Fermilab Tevatron Collider. This first study of hadronic Z-gamma production in the neutrino decay channel gives the most stringent limits on anomalous couplings available. A fit to the transverse energy spectrum of the photon in the candidate event sample, based on a data set corresponding to an integrated luminosity of 13.1 pb^(-1), yields 95% CL limits on the anomalous CP-conserving ZZ-gamma couplings of |h^Z_(30)|<0.9, |h^Z_(40)|<0.21, for a form-factor scale Lambda = 500 GeV. Combining these results with our previous measurement using Z -> ee and mu-mu yields the limits:|h^Z_(30)|<0.8, |h^Z_(40)|<0.19 (Lambda = 500 GeV) and |h^Z_(30)|<0.4, |h^Z_(40)|<0.06 (Lambda = 750 GeV).

hep-ex↗
arXiv1996

Search for Top Squark Pair Production in the Dielectron Channel

This report describes the first search for top squark pair production in the channel stop_1 stopbar_1 -> b bbar chargino_1 chargino_1 -> ee+jets+MEt using 74.9 +- 8.9 pb^-1 of data collected using the D0 detector. A 95% confidence level upper limit on sigma*B is presented. The limit is above the theoretical expectation for sigma*B for this process, but does show the sensitivity of the current D0 data set to a particular topology for new physics.

hep-ex↗
arXiv1996

Search for Diphoton Events with Large Missing Transverse Energy in proton-antiproton collisions at sqrt(s) = 1.8 TeV

A search for signals of new physics has been carried out in the channel p pbar -> gamma gamma + ETmiss. This signature is expected in various recently proposed supersymmetric (SUSY) models. We observe 842 events with two photons having transverse momentum ET(g) > 12 GeV and pseudorapidity |eta(g)| < 1.1. Of these, none have missing transverse energy (ETmiss) in excess of 25 GeV. The distribution of ETmiss is consistent with that of the expected background. We therefore set limits on production cross sections for selectron, sneutrino and neutralino pairs, decaying into photons. The limits range from about 400 fb to 1 pb depending on the sparticle masses. A general limit of 185 fb (95% C.L.) is set on sigma.B(pbar p -> gamma gamma ETmiss + X) where ET(g) > 12 GeV, |eta(g)| < 1.1, and ETmiss > 25 GeV.

hep-ex↗
arXiv1996

Limits on Anomalous $WWγ$ Couplings from $p\bar{p} \to W γ+ X$ Events at $\sqrt{s}=1.8$ TeV

We have measured the $WWγ$ gauge boson coupling parameters using $p\bar{p}\to \ellνγ+X$ ($\ell=e,μ$) events at $\sqrt{s}=1.8$ TeV. The data, corresponding to an integrated luminosity of 89.1 pb^{-1}, were collected using the D0 detector at the Fermilab Tevatron Collider. The measured cross section times branching ratio for $p\bar{p} \to Wγ+X$ with $p_T^γ$ > 10 GeV/c and $R_{\ellγ} > 0.7$ is ${11.8}^{+1.7}_{-1.6} \pm 2.0$ pb, in agreement with the Standard Model prediction. The one degree of freedom 95% confidence level limits on individual CP-conserving parameters are $-0.98<Δκ<1.01$ and $-0.33<λ<0.31$. Similar limits are set on the CP}violating coupling parameters.

hep-ex↗
arXiv1996

Search for Anomalous WW and WZ Production in ppbar Collisions at sqrt(s) = 1.8 TeV

We present results from a search for anomalous WW and WZ production in ppbar collisions at sqrt(s) = 1.8 TeV. We used ppbar->evjjX events observed during the 1992-1993 run of the Fermilab Tevatron collider, corresponding to an integrated luminosity of 13.7 +- 0.7 pb^-1. A fit to the transverse momentum spectrum of the W boson yields direct limits on the CP-conserving anomalous WWgamma and WWZ coupling parameters of -0.9 < delta kappa < 1.1 (with lambda = 0) and -0.6 < lambda < 0.7 (with delta kappa = 0) at the 95% confidence level, for a form factor scale Lambda = 1.5 TeV, assuming that the WWgamma and WWZ coupling parameters are equal.

hep-ex↗
arXiv1996

The Isolated Photon Cross Section in the Central and Forward Rapidity Regions in p-pbar Collisions at sqrt(s) = 1.8 TeV

A measurement of the cross section for production of single, isolated photons is reported for transverse energies in the range of 10-125 GeV, for two regions of pseudorapidity, |η|<0.9 and 1.6<|η|<2.5. The data represent 12.9 pb-1 of integrated luminosity accumulated in p-pbar collisions at sqrt{s} = 1.8 TeV and recorded with the D0 detector at the Fermilab Tevatron Collider.

hep-ex↗
arXiv1995

Search for Right-Handed $W$ Bosons and Heavy $W^\prime$ in $p\bar p$ Collisions at $\sqrt{s} =$1.8 TeV

We report on a search for right-handed $W$ bosons ($W_R$). We used data collected with the DØ detector at the Fermilab Tevatron $p\bar p$ collider at $\sqrt{s}=$1.8 TeV to search for $W_R$ decays into an electron and a massive right-handed neutrino $W_R^\pm \to e^\pm N_R$. Using the inclusive electron data, we set mass limits independent of the $N_R$ decay: $m_{W_R}>650$ GeV/c$^2$ and $m_{W_R}>720$ GeV/c$^2$ at the 95% confidence level, valid for $m_{N_R}<{1/2}m_{W_R}$ and $m_{N_R} \ll m_{W_R}$ respectively. The latter also represents a new lower limit on the mass of a heavy left-handed $W$ boson ($W^\prime$) decaying into $e ν$. In addition, limits on $m_{W_R}$ valid for larger values of the $N_R$ mass are obtained assuming that $N_R$ decays to an electron and two jets.

hep-ex↗
arXiv1995

Search for $\widetilde{W}_1\widetilde{Z}_2$ Production via Trilepton Final States in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV

We have searched for associated production of the lightest chargino, $\widetilde{W}_1$, and next-to-lightest neutralino, $\widetilde{Z}_2$, of the Minimal Supersymmetric Standard Model in $p\bar{p}$ collisions at \mbox{$\sqrt{s}$ = 1.8 TeV} using the \D0 detector at the Fermilab Tevatron collider. Data corresponding to an integrated luminosity of 12.5$\pm 0.7$ \ipb were examined for events containing three isolated leptons. No evidence for $\widetilde{W}_1\widetilde{Z}_2$ pair production was found. Limits on $σ(\widetilde{W}_1\widetilde{Z}_2)$Br$(\widetilde{W}_1\to lν\widetilde{Z}_1)$Br$(\widetilde{Z}_2\to l\bar{l}\widetilde{Z}_1)$ are presented.

hep-ex↗
arXiv1995

Jet Production via Strongly-Interacting Color-Singlet Exchange in $p\bar{p}$ Collisions

A study of the particle multiplicity between jets with large rapidity separation has been performed using the DØdetector at the Fermilab Tevatron $p\bar{p}$ Collider operating at $\sqrt{s}=1.8$ TeV. A significant excess of low-multiplicity events is observed above the expectation for color-exchange processes. The measured fractional excess is $1.07 \pm 0.10({\rm stat})^{+ 0.25}_{- 0.13}({\rm syst})%$, which is consistent with a strongly-interacting color-singlet (colorless) exchange process and cannot be explained by electroweak exchange alone. A lower limit of 0.80% (95% C.L.) is obtained on the fraction of dijet events with color-singlet exchange, independent of the rapidity gap survival probability.

hep-ex↗
arXiv1995

Studies of Topological Distributions of the Three- and Four-Jet Events in $\pp$ Collisions at $\sqrt{s}=1800$ GeV with the DØDetector

The global topologies of inclusive three-- and four--jet events produced in $\pp$ interactions are described. The three-- and four--jet events are selected from data recorded by the DØdetector at the Tevatron Collider operating at a center--of--mass energy of $\sqrt{s} = 1800$ GeV. The measured, normalized distributions of various topological variables are compared with parton--level predictions of tree--level QCD calculations. The parton--level QCD calculations are found to be in good agreement with the data. The studies also show that the topological distributions of the different subprocesses involving different numbers of quarks are very similar and reproduce the measured distributions well. The parton shower Monte Carlo generators provide a less satisfactory description of the topologies of the three-- and four--jet events.

hep-ex↗
arXiv1995

Tests of QCD in W and Z Production at Tevatron

We present measurements of the production cross sections times leptonic branching fractions and the transverse momentum distributions of $W$ and $Z$ bosons in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV using data collected with the DØdetector at the Fermilab Tevatron $p\bar{p}$ collider. A preliminary measurement of the $W$ charge asymmetry is also presented.

hep-ex↗
arXiv1995

Second Generation Leptoquark Search in p\bar{p} Collisions at $\sqrt{s}$ = 1.8 TeV

We report on a search for second generation leptoquarks with the DØ detector at the Fermilab Tevatron $p\bar{p}$ collider at $\sqrt{s}$ = 1.8 TeV. This search is based on 12.7 pb$^{-1}$ of data. Second generation leptoquarks are assumed to be produced in pairs and to decay into a muon and quark with branching ratio $β$ or to neutrino and quark with branching ratio $(1-β)$. We obtain cross section times branching ratio limits as a function of leptoquark mass and set a lower limit on the leptoquark mass of 111 GeV/c$^{2}$ for $β= 1 $ and 89 GeV/c$^{2}$ for $β= 0.5 $ at the 95%\ confidence level.

hep-ex↗
arXiv1995

Measurement of the $WWγ$ gauge boson couplings in $p\bar{p}$ Collisions at $\sqrt{s}=1.8$ TeV

The $WWγ$ gauge boson couplings were measured using $p\bar{p}\to \ellνγ+X$ ($\ell=e,μ$) events at $\sqrt{s}=1.8$ TeV observed with the {DØ} detector at the Fermilab Tevatron Collider. The signal, obtained from the data corresponding to an integrated luminosity of $13.8 {\rm pb}^{-1}$, agrees well with the Standard Model prediction. A fit to the photon transverse energy spectrum yields limits at the 95% confidence level on the CP--conserving anomalous coupling parameters of $-1.6<Δκ<1.8$ ($λ$ = 0) and $-0.6<λ<0.6$ ($Δκ$ = 0).

hep-ex↗
arXiv1995

Search for $W$ boson pair production in $p\bar{p}$ collisions at $\sqrt{s}~=~1.8~$~TeV

The results of a search for $W$ boson pair production in $p\bar{p}$ collisions at $\sqrt{s}=1.8$ TeV with subsequent decay to dilepton ($eμ, ee $, and $μμ$) channels are presented. One event is observed with an expected background of $0.56\pm0.13$ events with an integrated luminosity of approximately 14 pb$^{-1}$. %$13.9\pm1.7$ pb$^{-1}$. Assuming equal strengths for the $WWZ$ and $WWγ$ gauge boson coupling parameters $κ$ and $λ$, limits on the CP-conserving anomalous coupling constants are $-2.6<Δκ<2.8$ and $-2.2<λ<2.2$ at the 95% confidence level.

hep-ex↗