Phys.Rev.Lett.

We present a search for high-mass neutral resonances using dimuon data corresponding to an integrated luminosity of 2.3 fb$^{-1}$ collected in {$p\bar p$} collisions at {$\sqrt{s}$ = 1.96 TeV} by the CDF II detector at the Fermilab Tevatron. No significant excess above the standard model expectation is observed in the dimuon invariant-mass spectrum. We set 95% confidence level upper limits on $\sigma \cdot BR (p \bar{p} \to X \to \mu \bar{\mu})$, where $X$ is a boson with spin 0, 1, or 2. Using these cross section limits, we determine lower mass limits on sneutrinos in R-parity-violating supersymmetric models, $Z'$ bosons, and Kaluza-Klein gravitons in the Randall-Sundrum model.

Phys. Lett. B

Fully reconstructed tt¯→W+bW−b¯→ℓνqq¯′bb¯ events are used to determine the fractions of right-handed ( f+ ) and longitudinally polarized ( f0 ) W bosons produced in top-quark decays. The helicity fractions are sensitive to the couplings and the Dirac structure of the Wtb vertex. This Letter reports measurements of the W -boson helicity fractions from two different methods using data corresponding to an integrated luminosity of 1.9fb−1 of pp¯ collisions at a center-of-mass energy of 1.96 TeV collected by the CDF II detector operating at the Fermilab Tevatron. Combining the results from the two methods, we find f0=0.62±0.10(stat)±0.05(syst) under the assumption that f+=0 , and f+=−0.04±0.04(stat)±0.03(syst) with f0 fixed to the theoretically expected value of 0.70. Model-independent fits are also performed and simultaneously determine f0=0.66±0.16(stat)±0.05(syst) and f+=−0.03±0.06(stat)±0.03(syst) . All these results are consistent with standard model expectations.

Phys.Rev.D

We present a measurement of the top quark mass in the all-hadronic channel (\tt $\to$ \bb$q_{1}\bar{q_{2}}q_{3}\bar{q_{4}}$) using 943 pb$^{-1}$ of \ppbar collisions at $\sqrt {s} = 1.96$ TeV collected at the CDF II detector at Fermilab (CDF). We apply the standard model production and decay matrix-element (ME) to $\ttbar$ candidate events. We calculate per-event probability densities according to the ME calculation and construct template models of signal and background. The scale of the jet energy is calibrated using additional templates formed with the invariant mass of pairs of jets. These templates form an overall likelihood function that depends on the top quark mass and on the jet energy scale (JES). We estimate both by maximizing this function. Given 72 observed events, we measure a top quark mass of 171.1 $\pm$ 3.7 (stat.+JES) $\pm$ 2.1 (syst.) GeV/$c^{2}$. The combined uncertainty on the top quark mass is 4.3 GeV/$c^{2}$.

Phys.Rev.Lett.

We report on a search for inclusive production of squarks and gluinos in ppbar collisions at sqrt{s}=1.96 TeV, in events with large missing transverse energy and multiple jets of hadrons in the final state. The study uses a CDF Run II data sample corresponding to 2 fb-1 of integrated luminosity. The data are in good agreement with the standard model predictions, giving no evidence for any squark or gluino component. In an R-parity conserving minimal supergravity scenario with A_0 = 0, mu < 0 and tanbeta = 5, 95% C.L. upper limits on the production cross sections in the range between 0.1 pb and 1 pb are obtained, depending on the squark and gluino masses considered. For gluino masses below 280 GeV/c2, arbitrarily large squark masses are excluded at the 95%C.L., while for mass degenerate gluinos and squarks, masses below 392 GeV/c2 are excluded at the 95% C.L.

Phys.Rev.Lett.

We present a measurement of the transverse momentum with respect to the jet axis ($k_{T}$) of particles in jets produced in $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV. Results are obtained for charged particles within a cone of opening angle 0.5 radians around the jet axis in events with dijet invariant masses between 66 and 737 GeV/c$^{2}$. The experimental data are compared to theoretical predictions obtained for fragmentation partons within the framework of resummed perturbative QCD using the modified leading log and next-to-modified leading log approximations. The comparison shows that trends in data are successfully described by the theoretical predictions, indicating that the perturbative QCD stage of jet fragmentation is dominant in shaping basic jet characteristics.

Eur.Phys.J.C

Measurements are presented of R_b, the ratio of the b bbar cross-section to the q qbar cross-section in e+e- collisions, and the forward-backward asymmetry A^b_FB at twelve energy points in the range sqrt(s) = 130-207 GeV. These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.

Phys. Rev. Lett.

The first search in ppbar collisions at sqrt(s)=1.96 GeV for the production of neutral Higgs bosons in association with bottom quarks and decaying in two tau leptons is presented. The cross section for this process is enhanced in many extensions of the Standard Model (SM), such as its minimal supersymmetric extension (MSSM) at large tan(beta). The data, corresponding to an integrated luminosity of 328 pb-1, were collected with the D0 detector at the Fermilab Tevatron Collider. An upper limit is set on the production cross section of neutral Higgs bosons in the mass range of 90 to 150 GeV, and this limit is used to exclude part of the MSSM parameter space.

Phys.Lett.B

We report results of 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 DØ detector at a pp¯ center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. Both scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino. The search is performed in the electron plus muon and dielectron final states. The signal topology consists of two isolated leptons, missing transverse energy, and jets. We find no evidence for this process and exclude regions of parameter space in the framework of the minimal supersymmetric standard model.

Phys. Rev. Lett.

We search for the semi-inclusive process B_s^0 --> D_s^(*)D_s^(*) using 2.8 fb^-1 of ppbar collisions at s^(1/2) = 1.96 TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We observe 26.6 +/- 8.4 signal events with a significance above background of 3.2 standard deviations yielding a branching ratio of Br(B_s^0 --> D_s^(*)D_s^(*)) = 0.035 +/- 0.010(stat) +/- 0.011(syst). Under certain theoretical assumptions, these double-charm final states saturate CP-even eigenstates in the B_s^0 decays resulting in a width difference of Delta_Gamma_s^CP/Gamma_s = 0.072 +/- 0.021(stat) +/- 0.022(syst). This corresponds to the first evidence for a width difference in the B_s^0 system.

AIP Conf.Proc.

We study the production of prompt photons at high energy in the framework of the kT—factorization approach. The amplitude for production of a single photon associated with quark pair in the fusion of two off‐shell gluons is calculated. Theoretical results are compared with the Tevatron data.

J.Phys.G

In the framework of the kt-factorization approach, we study the production of prompt photons and electroweak gauge bosons in high energy proton-(anti)proton collisions at modern colliders. Our consideration is based on the amplitude for the production of a single photon or W/Z boson associated with a quark pair in the fusion of two off-shell gluons. The quark component is taken into account separately using the quark-gluon scaterring and quark-antiquark annihilation QCD subprocesses. Special attention is put on the contributions from the quarks involved into the earlier steps of the evolution cascade. Using the Kimber-Martin-Ryskin formalism, we simulate this component and demonstrate that it plays an important role at both the Tevatron and LHC energies. Our theoretical results are compared with recent experimental data taken by the D0 and CDF collaborations at the Tevatron.

Eur.Phys.J.D

We consider the possibility of experimental verification of vacuum e^+e^- pair creation at the focus of two counter-propagating optical laser beams with intensities 10^{20}-10^{22} W/cm^2, achievable with present-day petawatt lasers, and approaching the Schwinger limit: 10^{29} W/cm^2 to be reached at ELI. Our approach is based on the collisionless kinetic equation for the evolution of the e^+ and e^- distribution functions governed by a non-Markovian source term for pair production. As possible experimental signals of vacuum pair production we consider e^+e^- annihilation into gamma-pairs and the refraction of a high-frequency probe laser beam by the produced e^+e^- plasma. We discuss the dependence of the dynamical pair production process on laser wavelength, with special emphasis on applications in the X-ray domain (X-FEL), as well as the prospects for \mu^+\mu^- and \pi^+\pi^- pair creation at high-intensity lasers. We investigate perspectives for using high-intensity lasers as ``boosters'' of ion beams in the few-GeV per nucleon range, which is relevant, e.g., to the exploration of the QCD phase transition in laboratory experiments.

AIP Conf. Proc.

The existing models of baryons usually predict considerably more resonance (three or more in number) than it was found by investigation of elastic pion‐nucleon scattering. This disagreement invites further investigation of the pion‐nucleon interaction and among other things the measurement of spin rotation parameters A and R in the elastic pion‐nucleon scattering. Recent experiments of the PNPI and PNPI‐ITEP collaborations resolved a part of twofold ambiguities of the existing partial wave analyses (PWA). These results were used in the last PWA of the George Washington University group SP06. The proposal for the additional spin rotation parameters A and R measurement in the resonance region is motivated. Such additional measurements are necessary to resolve remaining twofold ambiguities of the existing PWAs.

Hyperfine Interact.

We have analyzed data of the DISTO experiment on the exclusive pp → K +  Λp process at Tp = 2.85 GeV to search for

Phys.Rev.Lett.

A search for high-mass resonances in the $e^+e^-$ final state is presented based on 2.5 fb$^{-1}$ of $\sqrt{s}=$1.96 TeV $p\bar{p}$ collision data from the CDF II detector at the Fermilab Tevatron. The largest excess over the standard model prediction is at an $e^+e^-$ invariant mass of 240 GeV/$c^2$. The probability of observing such an excess arising from fluctuations in the standard model anywhere in the mass range of 150--1,000 GeV/$c^2$ is 0.6% (equivalent to 2.5 $\sigma$). We exclude the standard model coupling $Z'$ and the Randall-Sundrum graviton for $k/\overline{M}_{Pl}=0.1$ with masses below 963 and 848 GeV/$c^2$ at the 95% credibility level, respectively.

Phys.Rev.D

The analysis uses data from an integrated luminosity of approximately 172 pb-1 of ppbar collisions at sqrt(s)=1.96 TeV, collected with the CDF II detector at the Fermilab Tevatron. The Lambda_b and B0 relative branching fractions are measured to be: B(Lambda_b to Lambda_c+ mu nu)/B(Lambda_b to Lambda_c+ pi) = 16.6 +- 3.0 (stat) +- 1.0 (syst) +2.6 -3.4 (PDG) +- 0.3 (EBR), B(B0 to D+ mu nu)/B(B0 to D+ pi) = 9.9 +- 1.0 (stat) +- 0.6 (syst) +- 0.4 (PDG) +- 0.5 (EBR), B(B0 to D*+ mu nu)/B(B0 to D*+ pi) = 16.5 +- 2.3 (stat) +- 0.6 (syst) +- 0.5 (PDG) +- 0.8 (EBR) This article also presents measurements of the branching fractions of four new Lambda_b semileptonic decays: Lambda_b to Lambda_c(2595)+ mu nu, Lambda_b to Lambda_c(2625)+ mu nu, Lambda_b to Sigma_c(2455)0 pi mu nu, Lambda_b to Sigma_c(2455)++ pi mu nu, relative to the branching fraction of the Lambda_b to Lambda_c mu nu decay. Finally, the transverse-momentum distribution of Lambda_b baryons produced in p-pbar collisions is measured and found to be significantly different from that of B0 mesons.

Phys. Rev. D

A search for new physics using three-lepton (trilepton) data collected with the CDF II detector and corresponding to an integrated luminosity of 976 pb-1 is presented. The standard model predicts a low rate of trilepton events, which makes some supersymmetric processes, such as chargino-neutralino production, measurable in this channel. The mu+mu+l signature is investigated, where l is an electron or a muon, with the additional requirement of large missing transverse energy. In this analysis, the lepton transverse momenta with respect to the beam direction (pT) are as low as 5 GeV/c, a selection that improves the sensitivity to particles which are light as well as to ones which result in leptonically decaying tau leptons. At the same time, this low-p_T selection presents additional challenges due to the non-negligible heavy-quark background at low lepton momenta. This background is measured with an innovative technique using experimental data. Several dimuon and trilepton control regions are investigated, and good agreement between experimental results and standard-model predictions is observed. In the signal region, we observe one three-muon event and expect 0.4+/-0.1 mu+mu+l events

Phys.Rev.Lett.

We present measurements of the linear polarization amplitudes and the strong relative phases that describe the flavor-untagged decays $B_{d}^{0}\to J/\psi K^{*0}$ and $B_{s}^{0}\to J/\psi\phi$ in the transversity basis. We also measure the mean lifetime $\bar{\tau}_{s}$ of the $B_{s}^{0}$ mass eigenstates and the lifetime ratio $\bar{\tau}_{s}/\tau_{d}$. The analyses are based on approximately 2.8 fb$^{-1}$ of data recorded with the D0 detector. From our measurements of the angular parameters we conclude that there is no evidence for a deviation from flavor SU(3) symmetry for these decays and that the factorization assumption is not valid for the $B_{d}^{0}\to J/\psi K^{*0}$ decay.

Phys. Rev. Lett.

We present the first evidence of WW+WZ production with lepton+jets final states at a hadron collider. The data correspond to 1.07 inverse femtobarns of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider in proton-antiproton collisions at sqrt(s)=1.96 TeV. The observed cross section for WW+WZ production is 20.2 +/- 4.5 pb, consistent with the SM prediction of 16.1 +/- 0.9 pb. The probability for background fluctuations to produce an excess equal to or larger than that observed is estimated to be 5.4e-6, corresponding to a significance of 4.4 standard deviations.

Eur. Phys. J. A

The asymmetry parameter P was measured for the elastic pion-proton scattering in the very backward angular region of theta_cm ~ 150-170^o at several pion beam energies in the invariant mass range containing most of the pion-proton resonances. The general goal of the experimental program was to provide new data for partial wave analyses in order to resolve their uncertainties in the baryon resonance region to allow the unambiguous baryon spectrum reconstructions. Until recently the parameter P was not measured in the examined domain that might be explained by the extremely low cross section. At the same time the predictions of various partial wave analyses are far from agreement in some kinematic areas and specifically those areas were chosen for the measurements where the disagreement is most pronouncing. The experiment was performed at the ITEP U-10 proton synchrotron, Moscow, by the ITEP-PNPI collaboration in the latest 5 years.

arXiv

The GERmanium Detector Array, GERDA, will search for neutrinoless double beta decay in ^76Ge at the National Gran Sasso Laboratory of the INFN. Bare high-purity germanium detectors enriched in ^76Ge will be submerged in liquid argon serving simultaneously as a shield against external radioactivity and as a cooling medium. In GERDA Phase-I, reprocessed enriched-Ge detectors, which were previously operated by the Heidelberg-Moscow and IGEX collaborations, will be redeployed. Before operating the enriched detectors, tests are performed with non-enriched bare HPGe detectors in the GERDA underground Detector Laboratory to test the Phase-I detector assembly, the detector handling protocols, the refurbishment technology and to study the long-term stability in liquid argon. The leakage currents in liquid argon and liquid nitrogen have been extensively studied under varying gamma irradiation conditions. In total three non-enriched high-purity p-type prototype germanium detectors have been operated successfully. The detector performance is stable over the long-term measurements. For the first time, performance of bare high-purity germanium detectors in liquid argon is reported.

10.1109/NSSMIC.2008.4774923

The transition from a proportional to a self quenching streamer mode, as a function of track length and angle, was investigated in a single wire chamber filled with either pure DME or isobutane. The chamber was irradiated with ^241Am alpha particles. An investigation of multistreamer events in the DME due to alpha particles entering the chamber at 20° with track length 4 mm gave an estimate of a dead zone, defined as the product of dead length and dead time, to be less than 0.1 μs⋅cm. This value is 3 orders of magnitude less than those observed by other groups for noble gases based mixtures. No second streamers were observed with pure isobutane for the similar tracks.

10.1109/NSSMIC.2008.4774571

A new detector system was proposed for the measurement of the double differential cross section (DDX) data on proton-actinide reactions in the 600-MeV region. The detector system is the combination of pulse height measurement and TOF measurement. In the pulse height measurement, conventional ΔE-E method was used with a plastic scintillator and an inorganic crystal. The TOF measurement was done by using two plastic scintillators. The result of the preliminary experiment carried out using 230 MeV/u helium beam is reported.

10.1109/NSSMIC.2008.4774741

The TGV II (Telescope Germanium Vertical) facility is a low background spectrometer operated in Modane Underground Laboratory (France). It aims at the study of double beta electron capture of ^106Cd. The spectrometer is composed of 32 HPGe planar detectors (total mass of Ge ∼3 kg) interleaved with thin-foil samples made of enriched ^106Cd. In 2007 the Phase I of the experiment (1 year measurement) was finished and the new limit on half-life for two-neutrino double electron capture (g.s. → g.s.) of ^106Cd was obtained as 3.2 × 10^20 years. This limit is significantly higher (by almost three orders of magnitude) than those already published. From December 2007 the Phase II of the experiment continues with more enriched material (13.6 grams instead of 8 grams) and with significantly suppressed background of the cryostat.

Phys. Rev. C

The half-life for double beta decay of 150-Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of 150-Nd the half-life for 2nubb decay is measured to be T_1/2^2nu = (9.11+0.25_-0.22}(stat.) +- 0.63 (syst.)) x 10^18 years. The observed limit on the half-life for neutrinoless double beta decay is found to be T_1/2^{0nu} > 1.8 x 10^22 years at 90 % Confidence Level. This translates into a limit on the effective Majorana neutrino mass of <4.0-6.3 eV if the nuclear deformation is taken into account. We also set limits on models involving Majoron emission, right-handed currents and transitions to excited states.