We present a measurement of two-particle angular correlations in proton-proton collisions at sqrt(s) = 900 GeV and 7 TeV. The collision events were collected during 2009 and 2010 with the ATLAS detector at the Large Hadron Collider using a single-arm minimum bias trigger. Correlations are measured for charged particles produced in the kinematic range of transverse momentum pT > 100 MeV and pseudorapidity |eta| < 2.5. A complex structure in pseudorapidity and azimuth is observed at both collision energies. Results are compared to Pythia 8 and Herwig++ as well as to the AMBT2B, DW and Perugia 2011 tunes of Pythia 6. The data are not satisfactorily described by any of these models.
Corrected two particle RCORR distribution as a function of Delta(ETARAP) obtained by integrating the foreground and background distributions over Delta(PHI) between 0 and PI.
Corrected two particle RCORR distribution as a function of Delta(ETARAP) obtained by integrating the foreground and background distributions over Delta(PHI) between 0 and PI/2.
Corrected two particle RCORR distribution as a function of Delta(ETARAP) obtained by integrating the foreground and background distributions over Delta(PHI) between PI/2 and PI.
We present measurements of the process $p\bar{p} \to WZ+X \to \ell^{\prime} \nu_{\ell^{\prime}} \ell \bar{\ell}$ at $\sqrt{s}=1.96$ TeV, where $\ell$ and $\ell^{\prime}$ are electrons or muons. Using 1 fb$^{-1}$ of data from the D0 experiment, we observe 13 candidates with an expected background of $4.5\pm0.6$ events and measure a cross section $\sigma(WZ)=2.7^{+1.7}_{-1.3}$ pb. From the number of observed events and the $Z$ boson transverse momentum distribution, we limit the trilinear $WWZ$ gauge couplings to $-0.17 \le \lambda_Z \le 0.21$ $(\Delta \kappa_Z = 0)$ at the 95% C.L. for a form factor scale $\Lambda=2$ TeV. Further, assuming that $\Delta g^Z_1 = \Delta\kappa_Z$, we find $-0.12 \le \Delta\kappa_Z \le 0.29$ $(\lambda_Z=0)$ at the 95% C.L. These are the most restrictive limits on the $WWZ$ couplings available to date.
Measured WZ cross section.
We present a measurement of the shape of the boson rapidity distribution for $p\bar{p}\to Z / \gamma^* \to e^+e^- + X$ events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71 < M_ee < 111 GeV and uses 0.4 $fb^{-1}$ of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of NNLO QCD are found to agree well with the data over the full rapidity range.
Normalized rapidity distribution.
Details of systematic errors.
Using 7.3 pb-1 of ppbar collisions collected by the D0 detector at the Fermilab Tevatron, we measure the distribution of the variable \phistar, which probes the same physical effects as the Z/gamma* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. A QCD prediction is found to describe the general features of the \phistar distribution, but is unable to describe its detailed shape or dependence on boson rapidity. A prediction that includes a broadening of transverse momentum for small values of the parton momentum fraction is strongly disfavored.
The measured PHI* distributions for the dielectron events corrected back to the particle level. The distributions are normalised to unity inidividually for each abs(yrap) bin and channel.
The measured PHI* distributions for the dimuon events corrected back to the particle level. The distributions are normalised to unity inidividually for each abs(yrap) bin and channel.
We present a new measurement of the Z/gamma* transverse momentum distribution in the range 0 - 330GeV, in proton-antiproton collisions at sqrt{s}=1.96 TeV. The measurement uses 0.97 fb-1 of integrated luminosity recorded by the D0 experiment and is the first using the Z/gamma*->mu+mu- + X channel at this center-of-mass energy. This is also the first measurement of the Z/gamma* transverse momentum distribution that presents the result at the level of particles entering the detector, minimizing dependence on theoretical models. As any momentum of the Z/gamma* in the plane transverse to the incoming beams must be balanced by some recoiling system, primarily the result of QCD radiation in the initial state, this variable is an excellent probe of the underlying process. Tests of the predictions of QCD calculations and current event generators show they have varied success in describing the data. Using this measurement as an input to theoretical predictions will allow for a better description of hadron collider data and hence it will increase experimental sensitivity to rare signals.
Normalized differential cross section.
Absolute differential cross section produced by multiplying by the measuredtotal cross section (118 pb).
We present the first measurements at a hadron collider of differential cross sections for Z+jet+X production in delta phi(Z, jet), |delta y(Z, jet)| and |y_boost(Z, jet)|. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.
Differential cross section in bins of PHI(P=3)-PHI(P=4) for Z/GAMMA* transverse momentum > 25 GeV.
Differential cross section in bins of PHI(P=3)-PHI(P=4) for Z/GAMMA* transverse momentum > 45 GeV.
Differential cross section in bins of ABS(YRAP(P=3)-YRAP(P=4)) for Z/GAMMA* transverse momentum > 25 GeV.
We report a new measurement of the cross section for the production of isolated photons, with transverse energies (ET) above 10 GeV and pseudorapidities |eta| < 2.5, in p pbar collisions at sqrt{s} = 1.8 TeV. The results are based on a data sample of 107.6 pb-1 recorded during 1992--1995 with the D0 detector at the Fermilab Tevatron collider. The background, predominantly from jets which fragment to neutral mesons, was estimated using the longitudinal shower shape of photon candidates in the calorimeter. The measured cross section is in good agreement with the next-to-leading order (NLO) QCD calculation for ET > 36 GeV.
The measured isolated photon cross sections. The first error contains the statistics and uncorrelated systematic uncertainties, the DSYS error is the correlated systematic uncertainty.
The measured isolated photon cross sections. The first error contains the statistics and uncorrelated systematic uncertainties, the DSYS error is the correlated systematic uncertainty.
Evidence of anomalous WW and WZ production was sought in pbar{p} collisions at a center-of-mass energy of sqrt(s) = 1.8 TeV. The final states $WW (WZ) to mu-nu-jet-jet + X, WZ to mu-nu-e-e + X and WZ to e-nu-e-e + X were studied using a data sample corresponding to an integrated luminosity of approximately 90 pb-1. No evidence of anomalous diboson production was found. Limits were set on anomalous WWgamma and WWZ couplings and were combined with our previous results. The combined 95% confidence level anomalous coupling limits for Lambda=2 TeV are -0.25 LE Delta-kappa LE 0.39 (lambda=0) and -0.18 LE lambda LE 0.19 (Delta \kappa = 0), assuming the WWgamma couplings are equal to the WWZ couplings.
CONST(NAME=SCALE) is the model parameter, used in the modification of the couplings as follows: g = g0/(1 + M(gamma Z)**2/CONST(NAME=SCALE)**2)**n. KAPPA_GZ means KAPPA_GAMMA = KAPPA_Z. LAMBDA_GZ means LAMBDA_GAMMA = LAMBDA_Z.
CONST(NAME=SCALE) is the model parameter, used in the modification of the couplings as follows: g = g0/(1 + M(gamma Z)**2/CONST(NAME=SCALE)**2)**n.
DO has measured the inclusive production cross section of W and Z bosons in a sample of 13 pb$^{-1}$ of data collected at the Fermilab Tevatron. The cross sections, multiplied by their leptonic branching fractions, for production in pbar-p collisions at sqrt{s}=1.8 TeV are sigma_W*B(W->e nu) = 2.36+-0.02+-0.08+-0.13 nb, sigma_W*B(W->mu nu) = 2.09+-0.06+-0.22+-0.11 nb, sigma_Z*B(Z->e+ e-) = 0.218+-0.008+-0.008+-0.012 nb, and sigma_Z*B(Z->mu+ mu-) = 0.178+-0.022+-0.021+-0.009 nb, where the first uncertainty is statistical and the second systematic; the third reflects the uncertainty in the integrated luminosity. For the combined electron and muon analyses, we find sigma_W*B(W->l mu)/sigma_Z*B(Z->l+ l-) = 10.90+-0.52. Assuming standard model couplings, we use this result to determine the width of the W boson, and obtain Gamma(W) = 2.044+-0.097 GeV.
No description provided.
Combined electron and muon analysis.
We present a measurement of the differential cross section as a function of transverse momentum of the Z boson in ppbar collisions at sqrt{s}=1.8 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider during 1994--1996. We find good agreement between our data and the NNLO resummation prediction and extract values of the non-perturbative parameters for the resummed prediction from a fit to the differential cross section.
Differential cross section in the electron channel. The errors contain both statistical and systematic error excluding the overall normalization error.