Phys. Rev. D

We present the results of a search for Wprime boson decaying to electron-neutrino pairs in pbarp collisions at a center-of-mass energy of 1.96 TeV, using a data sample corresponding to 205 pb^-1 of integrated luminosity collected by the CDF II detector at Fermilab. We observe no evidence for this decay mode and set limits on the production cross section times branching fraction, assuming the neutrinos from Wprime boson decays to be light. If we assume the manifest left-right symmetric model, we exclude a Wprime boson with mass less than 788 GeV/c^2 at the 95% confidence level.

Phys.Rev.Lett.

We present the first observation of exclusive $e^+e^-$ production in hadron-hadron collisions, using $p\bar{p}$ collision data at \mbox{$\sqrt{s}=1.96$ TeV} taken by the Run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of \mbox{532 pb$^{-1}$}. We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy {$E_T>5$ GeV} and pseudorapidity {$|\eta|<2$}. With these criteria, 16 events are observed compared to a background expectation of {$1.9\pm0.3$} events. These events are consistent in cross section and properties with the QED process \mbox{$p\bar{p} \to p + e^+e^- + \bar{p}$} through two-photon exchange. The measured cross section is \mbox{$1.6^{+0.5}_{-0.3}\mathrm{(stat)}\pm0.3\mathrm{(syst)}$ pb}. This agrees with the theoretical prediction of {$1.71 \pm 0.01$ pb}.

New J.Phys.

The OPERA neutrino detector at the underground Gran Sasso Laboratory (LNGS) was designed to perform the first detection of neutrino oscillations in appearance mode, through the study of nu_mu to nu_tau oscillations. The apparatus consists of a lead/emulsion-film target complemented by electronic detectors. It is placed in the high-energy, long-baseline CERN to LNGS beam (CNGS) 730 km away from the neutrino source. In August 2006 a first run with CNGS neutrinos was successfully conducted. A first sample of neutrino events was collected, statistically consistent with the integrated beam intensity. After a brief description of the beam and of the various sub-detectors, we report on the achievement of this milestone, presenting the first data and some analysis results.

Eur. Phys. J. C

In the reaction e+e- -> WW -> (q_1 qbar_2)(q_3 qbar_4) the usual hadronization models treat the colour singlets q_1 qbar_2 and q_3 qbar_4 coming from two W bosons independently. However, since the final state partons may coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This effect is known as Colour Reconnection. In this article the results of the investigation of Colour Reconnection effects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle flow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its kappa parameter most compatible with the data was found to be: kappa_{SK-I} = 2.2^{+2.5}_{-1.3} corresponding to the probability of reconnection P_{reco} to be in the range 0.31 < P_{reco} < 0.68 at 68% confidence level with its best value at 0.52.

Concepts Phys.

We study the neutrino oscillation problem in the framework of the wave packet formalism. The neutrino state is described by a packet located initially in a region S (source) and detected in another region D at a distance R from S. We examine how the oscillation probability as a function of variable R can be derived from he oscillation probability as a function of time t, the latter being found by using the Schrodinger equation. We justify the known prescription t --> R/c without referring to a specific form of the neutrino wave packet and only assuming the finiteness of its support. The effect of the oscillation damping at large R is revealed. For an illustration, an explicit expression for the damping factor is obtained using Gaussian packet.

Phys. Rev. D

We report a new measurement of the ttbar production cross section in pbarp collisions at a center-of-mass energy of 1.96 TeV using events with one charged lepton (electron or muon), missing transverse energy, and jets. Using 425 pb^{-1} of data collected using the D0 detector at the Fermilab Tevatron Collider, and enhancing the ttbar content of the sample by tagging b jets with a secondary vertex tagging algorithm, the ttbar production cross section is measured to be: 6.6 \pm 0.9 (stat+syst) \pm 0.4 (lum) pb. This cross section is the most precise D0 measurement to date for ttbar production and is in good agreement with standard model expectations.

Phys. Lett. B

A search for the pair production of scalar top quarks, or stops, has been performed in 360 pb-1 of data from p pbar collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron collider. The stop decay mode considered is stop into c chi, where chi is the lightest supersymmetric particle. The topology analyzed therefore consists of a pair of acoplanar heavy-flavor jets with missing transverse energy. The data and standard model expectation are in agreement, and a 95% C.L. exclusion domain in the stop and chi mass plane has been determined, extending the domain excluded by previous experiments.

Mod.Phys.Lett.A

We derive accurately the fermion resonance propagator by means of Dyson summation of the self-energy contribution. It turns out that the relativistic fermion resonance differs essentially from its boson analog.

Phys.Rev.D

We calculate the cross section of charm photoproduction at HERA collider in the framework of the kt-factorization QCD approach. Our analysis cover the inclusive charm production as well as charm and associated jet production processes. Both photon-gluon and gluon-gluon fusion mechanisms are taken into account. The unintegrated gluon densities in a proton and in a photon obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription are used. Our theoretical results are compared with the recent experimental data taken by the H1 and ZEUS collaborations at HERA. Special attention is put on the specific angular correlations which can provide unique information about non-collinear gluon evolution dynamics.

Phys. Rev. C

Mechanisms for the production of $^1S_0$ diproton pairs, ${pp}_s$, in the $pd\to {pp}_s n$ reaction are studied at proton beam energies 0.5 -- 2 GeV in kinematics similar to those of backward elastic $pd$ scattering. This reaction provides valuable information on the short-range $NN$ and $pd$ interactions that is complementary to that investigated in the well known $pd\to dp$ and $dp\to p(0^\circ)X$ processes. The $pd\to {pp}_sn$ reaction is related to the subprocesses $\pi^0 d\to pn$ and $pN\to {pp}_s \pi$ using two different one--pion--exchange (OPE) diagrams. Within both these models a reasonable agreement could be obtained with the data below 1GeV. The similar energy dependence of the $pd\to\{pp\}_s n$ and $pd\to dp$ cross sections and the small ratio of about 1.5% in the production of $\{pp\}_s$ to deuteron final states follow naturally within the OPE models.

Phys.Rev.Lett.

Using 355 pb^-1 of data collected by the CDF II detector in \ppbar collisions at sqrt{s} = 1.96 TeV at the Fermilab Tevatron, we study the fully reconstructed hadronic decays B -> D pi and B -> D pi pi pi. We present the first measurement of the ratio of branching fractions B(Bs -> Ds pi pi pi) / B(Bd -> Dd pi pi pi) = 1.05 pm 0.10 (stat) pm 0.22 (syst). We also update our measurement of B(Bs -> Ds pi) / B(Bd -> Dd pi) to 1.13 pm 0.08 (stat) pm 0.23 (syst) improving the statistical uncertainty by more than a factor of two. We find B(Bs -> Ds pi) = [3.8 pm 0.3 (stat) pm 1.3 (syst)] \times 10^{-3} and B(Bs -> Ds pi pi pi) = [8.4 pm 0.8 (stat) pm 3.2 (syst)] \times 10^{-3}.

Astropart.Phys.

This paper presents our interpretation and understanding of the different backgrounds in the EDELWEISS-I data sets. We analyze in detail the several populations observed, which include gammas, alphas, neutrons, thermal sensor events and surface events, and try to combine all data sets to provide a coherent picture of the nature and localisation of the background sources. In light of this interpretation, we draw conclusions regarding the background suppression scheme for the EDELWEISS-II phase.

Nucl.Phys.A

The charmonium dissociation by mesons in relativistic heavy-ion reactions is analyzed within the Regge approach. It is shown that the inclusion of the initial and final state interactions in the dissociation of J / Ψ to D ¯ ∗ D ∗ close to threshold increases the cross section significantly and can not be neglected in comparison to the total dissociation rate. This is due to resonant D ¯ ∗ − D ∗ interactions in s close to the masses of the Ψ ( 4.04 ) and Ψ ( 4.16 ) mesons. We also investigate thermal effects of the ( c c ¯ ) width for such processes in the medium. All these effects change both the magnitude and the shape of the cross section as a function of s . The results obtained should be applied in the analysis of open and hidden charm production in heavy-ion collisions.

Nucl.Phys.B

New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised 6 LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV / c . Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.

Nucl.Instrum.Meth.A

The Baikal Neutrino Telescope NT200 takes data since April 1998. On April 9th, 2005, the 10 Mton scale detector NT200$+$ was put into operation in Lake Baikal. Selected results obtained during 1998-2002 with the neutrino telescope NT200 are presented.

Phys.Lett.B

We present a measurement of the deuteron spin-dependent structure function g1d based on the data collected by the COMPASS experiment at CERN during the years 2002–2004. The data provide an accurate evaluation for Γ1d , the first moment of g1d(x) , and for the matrix element of the singlet axial current, a0 . The results of QCD fits in the next to leading order (NLO) on all g1 deep inelastic scattering data are also presented. They provide two solutions with the gluon spin distribution function Δ G positive or negative, which describe the data equally well. In both cases, at Q2=3(GeV/c)2 the first moment of ΔG(x) is found to be of the order of 0.2–0.3 in absolute value.

Eur. Phys. J. A

The production of omega-mesons in the pp->pp omega reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92MeV by detecting the two final protons and reconstructing their missing mass. The large multipion background was subtracted using an event-by-event transformation of the proton momenta between the two energies. Differential distributions and total cross sections were obtained after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the predictions of theoretical models. Combined with data on the phi-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka rule violation in the phi/omega production ratio.

Phys. Rev. Lett.

We report a measurement of the Lambda_b lifetime in the exclusive decay Lambda_b --> J/psi Lambda0 in p-pbar collisions at sqrt(s) = 1.96 TeV using an integrated luminosity of 1.0 fb^{-1} of data collected by the CDF II detector at the Fermilab Tevatron. Using fully reconstructed decays, we measure tau(Lambda_b) = 1.593 ^{+0.083}_{-0.078} (stat.) +- 0.033 (syst.) ps. This is the single most precise measurement of tau(Lambda_b) and is 3.2 sigma higher than the current world average.

Phys.Rev.Lett.

This is the version of the Letter entitledObservation of Bs-Bsbar Oscillations that was posted to the arxiv (hep-ex/0609040).We report the observation of Bs-Bsbar oscillations from a time-dependentmeasurement of the Bs-Bsbar oscillation frequency Delta ms.Using a data sample of 1 fb^-1 of p-pbar collisions at sqrt{s}=1.96 TeVcollected with the CDF II detector at the Fermilab Tevatron,we find signals of 5600 fully reconstructed hadronic Bs decays,3100 partially reconstructed hadronic Bs decays, and 61500 partially reconstructed semileptonic Bs decays.We measure the probability as a function of proper decay time that theBs decays with the same, or opposite, flavor as the flavor atproduction, and we find a signal for Bs-Bsbar oscillations.The probability that random fluctuations could produce a comparable signal is 8 X 10^-8, which exceeds 5 sigma significance.We measure Delta ms = 17.77 +- 0.10 (stat) +- 0.07 (syst) ps^-1and extract |Vtd/Vts| = 0.2060 +- 0.0007 (exp) + 0.0081 - 0.0060 (theor).

Phys. Rev. D

We measure the dimuon charge asymmetry A in pp(bar) collisions at a center of mass energy sqrt{s} = 1960 GeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of approximately 1.0 fb-1. Assuming that the asymmetry A is due to asymmetric B^0 <-> B(bar)^0 mixing and decay, we extract the CP-violation parameter of B^0 mixing and decay: Re(epsilon_B^0)(1 + |epsilon_B^0|^2) = A_B^0/4 = -0.0023 +/- 0.0011 (stat) +/- 0.0008 (syst). A_B^0 is the dimuon charge asymmetry from decays of B^0 B(bar)^0 pairs. The general case, with CP violation in both B^0 and B_s^0 systems, is also considered. Finally we obtain the forward-backward asymmetry that quantifies the tendency of mu+ to go in the proton direction and mu- to go in the anti-proton direction. The results are consistent with the standard model and constrain new physics.

Phys.Rev.D

We report on a measurement of the $B^0_d$ mixing frequency and the calibration of an opposite-side flavor tagger in the D{\O}experiment. Various properties associated with the $b$ quark on the opposite side of the reconstructed $B$ meson were combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance was tested with data, using a large sample of reconstructed semileptonic $B \to \mu \dzero X$ and $B \to \mu \dst X$ decays, corresponding to an integrated luminosity of approximately 1 fb$^{-1}$. The events were divided into groups depending on the value of the combined tagging variable, and an independent analysis was performed in each group. Combining the results of these analyses, the overall effective tagging power was found to be eD^2 = (2.48 \pm 0.21 (stat.) ^{+0.08}_{-0.06} (syst.))%. The measured $B^0_d$ mixing frequency dmd = 0.506 \pm 0.020 {\rm (stat) \pm 0.016 (syst) ps}^{-1} is in good agreement with the world average value.

Phys.Rev.D

We present a measurement of the fraction f_+ of right-handed W bosons produced in top quark decays, based on a candidate sample of ttbar events in the l+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb^-1 collected by the DO detector at the Fermilab Tevatron ppbar Collider at sqrt{s}=1.96 TeV. We reconstruct the decay angle theta^* for each lepton. By comparing the \cos\theta^* distribution from the data with those for the expected background and signal for various values of f_+, we find $f_+=0.056 +- 0.080 (stat) +- 0.057 (syst)}. (f_+ < 0.23 at 95% C.L.), consistent with the standard model prediction of f_+=3.6 x10^-4.

Phys.Rev.D

We present a measurement of the top quark mass with the Matrix Element method in the lepton+jets final state. As the energy scale for calorimeter jets represents the dominant source of systematic uncertainty, the Matrix Element likelihood is extended by an additional parameter, which is defined as a global multiplicative factor applied to the standard energy scale. The top quark mass is obtained from a fit that yields the combined statistical and systematic jet energy scale uncertainty. Using a data set of 370 pb-1 taken with the D0 experiment at Run II of the Fermilab Tevatron Collider, the mass of the top quark is measured using topological information to be: mtop(topo) = 169.2 +5.0-7.4 (stat.+JES) +1.5-1.4 (syst.) GeV, and when information about identified $b$ jets is included: mtop(b-tag) = 170.3 +4.1-4.5 (stat.+JES) +1.2-1.8 (syst.) GeV. The measurements yield a jet energy scale consistent with the reference scale.

Phys. Lett. B

We present a measurement of the top quark mass in the dilepton channel based on approximately 370 pb −1 of data collected by the DØ experiment during Run II of the Fermilab Tevatron collider. We employ two different methods to extract the top quark mass. We show that both methods yield consistent results using ensemble tests of events generated with the DØ Monte Carlo simulation. We combine the results from the two methods to obtain a top quark mass mt=178.1±8.2 GeV . The statistical uncertainty is 6.7 GeV and the systematic uncertainty is 4.8 GeV.

Nucl.Phys.A

The double beta decay of 100 Mo to the 0 1 + and 2 1 + excited states of 100 Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of 100 Mo to the excited 0 1 + state is measured to be T 1 / 2 ( 2 ν ) = [ 5.7 −0.9 +1.3 ( stat. ) ± 0.8 ( syst. ) ] × 10 20  y . The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0 1 + state has been found. The corresponding half-life limit is T 1 / 2 ( 0 ν ) ( 0 + → 0 1 + ) > 8.9 × 10 22  y (at 90% C.L.). The search for the double beta decay to the 2 1 + excited state has allowed the determination of limits on the half-life for the two neutrino mode T 1 / 2 ( 2 ν ) ( 0 + → 2 1 + ) > 1.1 × 10 21  y (at 90% C.L.) and for the neutrinoless mode T 1 / 2 ( 0 ν ) ( 0 + → 2 1 + ) > 1.6 × 10 23  y (at 90% C.L.).