PoS

Phys. Rev. D

A search for the standard model Higgs boson produced in association with a vector boson with the decay H→ττ is presented. The data correspond to 20.3  fb-1 of integrated luminosity from proton-proton collisions at s=8  TeV recorded by the ATLAS experiment at the LHC during 2012. The data agree with the background expectation, and 95% confidence-level upper limits are placed on the cross section of this process. The observed (expected) limit, expressed in terms of the signal strength μ=σ/σSM for mH=125  GeV, is μ<5.6 (3.7). The measured value of the signal strength is μ=2.3±1.6.

Phys. Rev. Lett.

We report the first measurement of absolute hadronic branching fractions of Λc+ baryon at the Λc+Λ¯c- production threshold, in the 30 years since the Λc+ discovery. In total, 12 Cabibbo-favored Λc+ hadronic decay modes are analyzed with a double-tag technique, based on a sample of 567  pb-1 of e+e- collisions at s=4.599  GeV recorded with the BESIII detector. A global least-squares fitter is utilized to improve the measured precision. Among the measurements for twelve Λc+ decay modes, the branching fraction for Λc+→pK-π+ is determined to be (5.84±0.27±0.23)%, where the first uncertainty is statistical and the second is systematic. In addition, the measurements of the branching fractions of the other 11 Cabibbo-favored hadronic decay modes are significantly improved.

Nucl. Instrum. Meth. B

One of the possible ways to maintain the micrometer spatial resolution while performing ion beam analysis in the air is to increase the energy of ions. In order to explore capabilities and limitations of this approach, we have tested a range of proton beam energies (2 - 6 MeV) using in-air STIM (Scanning Ion Transmission Microscopy) setup. Measurements of the spatial resolution dependence on proton energy have been compared with SRIM simulation and modelling of proton multiple scattering by different approaches. Results were used to select experimental conditions in which 1 micrometer spatial resolution could be obtained. High resolution in-air microbeam could be applied for IBIC (Ion Beam Induced Charge) tests of large detectors used in nuclear and high energy physics that otherwise can not be tested in relatively small microbeam vacuum chambers.

Phys.Lett.B

This Letter presents evidence for single top-quark production in the s -channel using proton–proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. The analysis is performed on events containing one isolated electron or muon, large missing transverse momentum and exactly two b -tagged jets in the final state. The analysed data set corresponds to an integrated luminosity of 20.3 fb−1 . The signal is extracted using a maximum-likelihood fit of a discriminant which is based on the matrix element method and optimized in order to separate single-top-quark s -channel events from the main background contributions, which are top-quark pair production and W boson production in association with heavy-flavour jets. The measurement leads to an observed signal significance of 3.2 standard deviations and a measured cross-section of σs=4.8±0.8(stat.)−1.3+1.6(syst.) pb , which is consistent with the Standard Model expectation. The expected significance for the analysis is 3.9 standard deviations.

JHEP

A search is presented for a new, light boson with a mass of about 1 GeV and decaying promptly to jets of collimated electrons and/or muons (lepton-jets). The analysis is performed with 20.3 fb$^{−1}$ of data collected by the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a centre-of-mass energy of 8 TeV. Events are required to contain at least two lepton-jets. This study finds no statistically significant deviation from predictions of the Standard Model and places 95% confidence-level upper limits on the contribution of new phenomena beyond the SM, incuding SUSY-portal and Higgs-portal models, on the number of events with lepton-jets.

Phys. Rev. D

We study Λ and Λ¯ production asymmetries in pp¯→Λ(Λ¯)X, pp¯→J/ψΛ(Λ¯)X, and pp¯→μ±Λ(Λ¯)X events recorded by the D0 detector at the Fermilab Tevatron collider at s=1.96  TeV. We find an excess of Λ’s (Λ¯’s) produced in the proton (antiproton) direction. This forward-backward asymmetry is measured as a function of rapidity. We confirm that the Λ¯/Λ production ratio, measured by several experiments with various targets and a wide range of energies, is a universal function of “rapidity loss,” i.e., the rapidity difference of the beam proton and the lambda.

J.Phys.Conf.Ser.

The DarkSide experiment is designed for the direct detection of Dark Matter with a double phase liquid Argon TPC operating underground at Laboratori Nazionali del Gran Sasso. The TPC is placed inside a 30 tons liquid organic scintillator sphere, acting as a neutron veto, which is in turn installed inside a 1 kt water Cherenkov detector. The current detector is running since November 2013 with a 50 kg atmospheric Argon fill and we report here the first null results of a Dark Matter search for a (1422 ± 67) kg.d exposure. This result correspond to a 90% CL upper limit on the WIMP-nucleon cross section of 6.1 × 10(-44) cm(2) (for a WIMP mass of 100 GeV/c(2)) and it's currently the most sensitive limit obtained with an Argon target.

Eur.Phys.J.C

Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, $t\bar{t}$ system and event-level kinematic observables in proton–proton collisions at a centre-of-mass energy of $\sqrt{s}=8\,\mathrm{TeV}$ . The observables have been chosen to emphasize the $t\bar{t}$  production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fb$^{-1}$ , recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. Predictions beyond NLO accuracy improve the agreement with data at high top-quark transverse momenta. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used.

PoS

A Multi Purpose Detector (MPD) is being constructed for the Heavy-Ion Collider at Dubna (NICA). One of the important components of MPD setup is an Electromagnetic Calorimeter, which will operate in the magnetic field of MPD solenoid and provide good energy and space resolution to detect particles in the energy range from ~100 MeV to few GeV. For this purpose the, so-called, “shashlyk” sampling structure with the fiber readout to the silicon Multi Pixel Avalanche Photodetector is used. The genuine design is similar to the one developed by us for COMPASS experiment but a number of important modifications have been introduced to better meet MPD resolution, large volume thermo-stabilization and other requirements. These details are presented in the report along with the beam test results obtained with the MPD/NICA module prototypes.

Astrophys.J.

The lifetime of quasars is fundamental for understanding the growth of supermassive black holes, and is an important ingredient in models of the reionization of the intergalactic medium (IGM). However, despite various attempts to determine quasar lifetimes, current estimates from a variety of methods are uncertain by orders of magnitude. This work combines cosmological hydrodynamical simulations and 1D radiative transfer to investigate the structure and evolution of the He ii Lyα proximity zones around quasars at z ≃ 3–4. We show that the time evolution in the proximity zone can be described by a simple analytical model for the approach of the He ii fraction ${x}_{\mathrm{He}{\rm{II}}}(t)$ to ionization equilibrium, and use this picture to illustrate how the transmission profile depends on the quasar lifetime, quasar UV luminosity, and the ionization state of Helium in the ambient IGM (i.e., the average He ii fraction, or equivalently the metagalactic He ii ionizing background). A significant degeneracy exists between the lifetime and the average He ii fraction, however the latter can be determined from measurements of the He ii Lyα optical depth far from quasars, allowing the lifetime to be measured. We advocate stacking existing He ii quasar spectra at z ∼ 3, and show that the shape of this average proximity zone profile is sensitive to lifetimes as long as ∼30 Myr. At higher redshift z ∼ 4 where the He ii fraction is poorly constrained, degeneracies will make it challenging to determine these parameters independently. Our analytical model for He ii proximity zones should also provide a useful description of the properties of H i proximity zones around quasars at z ≃ 6–7.

Phys.Rev.Lett.

We report evidence for the simultaneous production of J/ψ and ϒ mesons in 8.1  fb-1 of data collected at s=1.96  TeV by the D0 experiment at the Fermilab pp¯ Tevatron Collider. Events with these characteristics are expected to be produced predominantly by gluon-gluon interactions. In this analysis, we extract the effective cross section characterizing the initial parton spatial distribution, σeff=2.2±0.7(stat)±0.9(syst)  mb.

Phys.Part.Nucl.Lett.

The modeling of high energy photons production in collisions of antiproton beam having E$_{beam}$ = 15 GeV with the proton target pp→ γ + {ptX} is done using the event sample simulated by PYTHIA6 generator. Such energy is high enough to consider this collision as a relativistic one and being caused by parton-parton scattering. The distribution of the set of kinematic variables and cuts which can be useful for getting the information about proton structure in the available kinematic region is obtained. The contributions of fake photons which can appear from the hadron decays as well as of the background caused by the minimum bias events and other QCD processes are estimated. The set of cuts which can be useful for separation of signal events containing the direct photons from background events is proposed.

Phys.Lett.B

By analyzing a data set of 2.92 fb−1 of e+e− collision data taken at s=3.773 GeV and 106.41×106 ψ(3686) decays taken at s=3.686 GeV with the BESIII detector at the BEPCII collider, we measure the branching fraction and the partial decay width for ψ(3770)→γχc0 to be B(ψ(3770)→γχc0)=(6.88±0.28±0.67)×10−3 and Γ[ψ(3770)→γχc0]=(187±8±19) keV , respectively. These are the most precise measurements to date.

Phys.Lett.B

A 6.8 nb −1 sample of pp collision data collected under low-luminosity conditions at s=7TeV by the ATLAS detector at the Large Hadron Collider is used to study diffractive dijet production. Events containing at least two jets with pT>20GeV are selected and analysed in terms of variables which discriminate between diffractive and non-diffractive processes. Cross sections are measured differentially in ΔηF , the size of the observable forward region of pseudorapidity which is devoid of hadronic activity, and in an estimator, ξ˜ , of the fractional momentum loss of the proton assuming single diffractive dissociation ( pp→pX ). Model comparisons indicate a dominant non-diffractive contribution up to moderately large ΔηF and small ξ˜ , with a diffractive contribution which is significant at the highest ΔηF and the lowest ξ˜ . The rapidity-gap survival probability is estimated from comparisons of the data in this latter region with predictions based on diffractive parton distribution functions.

10.2172/1251186

This Technical Memorandum (TM) summarizes the Fermilab Test Beam operations for FY 2015. It is one of a series of annual publications intended to gather information in one place. In this case, the information concerns the individual experiments that ran at FTBF and are listed in Table TB‐1. Each experiment section was prepared by the relevant authors, and was edited for inclusion in this summary.

Phys.Procedia

The MAJORANA DEMONSTRATOR will search for neutrinoless-double-beta decay (0 νββ ) in 76Ge, while establishing the feasibility of a future tonne-scale germanium-based 0 νββ experiment, and performing searches for new physics beyond the Standard Model. The experiment, currently under construction at the Sanford Underground Research Facility in Lead, SD, will consist of a pair of modular high-purity germanium detector arrays housed inside of a compact copper, lead, and polyethylene shield. Through a combination of strict materials qualifications and assay, low-background design, and powerful background rejection techniques, the Demonstrator aims to achieve a background rate in the 0 νββ region of interest (ROI) of no more than 3 counts in the 0 νββ -decay ROI per tonne of target isotope per year (cnts/(ROI-t-y)). The current status of the Demonstrator is discussed, as are plans for its completion.

Phys.Procedia

The MAJORANA DEMONSTRATOR will search for the neutrinoless double beta decay ( ββ (0 ν )) of the isotope 76 Ge with a mixed array of enriched and natural germanium detectors. In view of the next generation of tonne-scale germanium-based ββ (0 ν )-decay searches, a major goal of the MAJORANA DEMONSTRATOR is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039-keV Q-value of the 76 Ge ββ (0 ν )-decay. Such a requirement on the background level significantly constrains the design of the readout electronics, which is further driven by noise and energy resolution performances. We present here the low-noise low- background front-end electronics developed for the low-capacitance p-type point contact (P-PC) germanium detectors of the MAJORANA DEMONSTRATOR. This resistive-feedback front-end, specifically designed to have low mass, is fabricated on a radioassayed fused-silica substrate where the feedback resistor consists of a sputtered thin film of high purity amorphous germanium and the feedback capacitor is based on the capacitance between gold conductive traces.

Phys.Procedia

DarkSide-50 is a two phase argon TPC for direct dark matter detection which is installed at the Gran Sasso underground laboratory, Italy. DarkSide-50 has a 50-kg active volume and will make use of underground argon low in 39 Ar. The TPC is installed inside an active neutron veto made with boron-loaded high radiopurity liquid scintillator. The neutron veto is installed inside a 1000 m 3 water Cherenkov muon veto. The DarkSide-50 TPC and cryostat are assembled in two radon-free clean rooms to reduce radioactive contaminants. The overall design aims for a background free exposure after selection cuts are applied. The expected sensitivity for WIMP-nucleon cross section is of the order of 10 −45 cm 2 for WIMP masses around 100 GeV/c 2 . The commissioning and performance of the detector are described. Details of the low-radioactivity underground argon and other unique features of the projects are reported.

Phys.Procedia

The physical characteristics of the multilayer scintillation spectrometer (MSS) for identification and energy measurement of cosmic electrons, positrons and nuclei are considered in this paper. This spectrometer is made on the basis of several plastic scintillator plates with various thick viewed by photomultipliers. Two upper layers are strips of orthogonal scintillators. The nuclei energy measurement range is 3 – 100 MeV/nucleon. Spectrometer is planning for space weather monitoring and investigation of solar-magnetospheric and geophysics effects on satellite. MSS time resolution is about 1 microsecond and it can measure the time profiles of fast processes in the Earth's magnetosphere. Spectrometer experimental characteristics were estimated by means of computer simulation. The ionization loss fluctuations, ion charge exchange during pass through detector and, especially, scintillation quenching effect (Bircs effect) were taken into account in calculations. Multilayer structure of spectrometer allows: 1) Ions mass identification for hydrogen and helium isotopes 2) Ions charge identification without mass identification for nuclei from lithium to oxygen The evaluation of the energy distribution of the nuclei may be obtained as from the analogous information from detectors of the spectrometer and from the estimation of experimental distribution of nuclei ranges in detectors material, based on the results of identification.

Phys.Procedia

The experimental search for the production of heavy lithium isotopes 10-12 Li was carried out in the stopped π - -mesons absorption reactions on the radioactive target 14 C. Study of 10 Li has been performed in the missing mass spectra in 14 С(π - , pt)X and 14 С(π - , dd)X reactions. Three excited states of 10 Li were identified, thus, the broad state with a resonance energy E r = 6.1 ± 0.1 MeV has the highest excitation energy, compared with the previously observed levels. The resonance parameters of three low-lying excited states of 11 Li were determined in the 14 С(π - , pd)X reaction. In the 14 С(π - , pp)X reaction evidence for a 12 Li excited state E r = 4.0 ± 0.2 MeV and Γ = 1.1 ± 0.2 MeV has been found.

Phys.Procedia

Results on the research of spectra and yields of p, d, t formed in the reaction of stopped pion absorption by atomic nuclei are presented. Unique data on charged particle formation on 17 isotopes have been obtained in wide mass range (6 < A < 209). Empirical model is proposed that allows to describe A-dependence of primary proton yields (with 10-15% precision) and to estimate the ratio of the elementary widths of pion absorption on pn and pp pairs R’ = 3.3±0.5.

Phys.Procedia

We present a 1353 days measurement of the geo–neutrino flux in Borexino: the signal was found to be 14.3 ± 4.4 events. This result translates into S geo = (38.8 ± 12.0) TNU when a Th/U fixed chondritic mass ratio of 3.9 is assumed. Furthermore Borexino data are compatible with a mantle geo–neutrino signal of (15.4 ± 12.3) TNU.

Phys.Procedia

Borexino, a large volume liquid scintillator detector installed at Gran Sasso laboratory, demonstrated extraordinary sensitivity with respect to neutrino and antineutrino detection, reporting the best up to date results on low energy solar neutrino fluxes and performing geo-neutrino detection. Energy and position of 1 MeV events in Borexino are recon- structed with a precision of 5% and 14 cm respectively. These performances together with extremely low background provides an excellent opportunity for the study of short distance neutrino oscillations on the eV mass scale with artificial neutrino sources. The possible layouts for 51Cr (monoenergetic neutrino) and 144Ce–144Pr (antineutrino from β-decay) source experiments in Borexino and the expected sensitivity to sterile neutrinos for three possible designs of the experiment are presented.

Eur.Phys.J.A

Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $ \pi^{0}\pi^{0}$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final-state invariant masses up to $ \approx 1550$ MeV), where both reactions are dominated by the $ N(1520)3/2^{-} \rightarrow \Delta(1232)3/2^{+}\pi$ decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an $ N^{\star}\rightarrow N\sigma$ decay for the proton, while the reaction is dominated by a sequential decay via a $ \Delta\pi$ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis.