Phys.Lett.B

A search is performed for a massive new vector-like quark T, with charge 23 , that is pair produced together with its antiparticle in proton–proton collisions. The data were collected by the CMS experiment at the Large Hadron Collider in 2012 at s=8 TeV and correspond to an integrated luminosity of 19.5 fb−1 . The T quark is assumed to decay into three different final states, bW, tZ, and tH. The search is carried out using events with at least one isolated lepton. No deviations from standard model expectations are observed, and lower limits are set on the T quark mass at 95% confidence level. The lower limit lies between 687 and 782 GeV for all possible values of the branching fractions into the three different final states assuming strong production. These limits are the most stringent constraints to date on the existence of such a quark.

JINST

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011.

JHEP

This paper presents a measurement of the top quark pair ($t\bar{t}$) production charge asymmetry $A_C$ using 4.7 fb−1 of proton-proton collisions at a centre-of-mass energy √s = 7 TeV collected by the ATLAS detector at the LHC. A $t\bar{t}$ enriched sample of events with a single lepton (electron or muon), missing transverse momentum and at least four high transverse momentum jets, of which at least one is tagged as coming from a b–quark, is selected. A likelihood fit is used to reconstruct the $t\bar{t}$ event kinematics. A Bayesian unfolding procedure is employed to estimate $A_C$ at the parton–level. The measured value of the $t\bar{t}$ production charge asymmetry is $A_C$ = 0.006± 0.010, where the uncertainty includes both the statistical and the systematic components. Differential $A_C$ measurements as a function of the invariant mass, the rapidity and the transverse momentum of the $t\bar{t}$-system are also presented. In addition, $A_C$ is measured for a subset of events with large $t\bar{t}$ velocity, where physics beyond the Standard Model could contribute. All measurements are consistent with the Standard Model predictions.

EPJ Web Conf.

The LHC with pp-collisions at √s = 7–14 TeV will obviously supply extra unique information concerning the non-zero intrinsic (or valence-like) heavy quark component of the proton distribution functions component of the proton. On the basis of theoretical study it is demonstrated that investigaton of the intrinsic heavy quark contributions looks very promising at the LHC in processes like pp → γ + c(b) + X.

JHEP

A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 inverse femtobarns. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and b-quark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. Information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models.

JINST

The DarkSide staged program utilizes a two-phase time projection chamber (TPC) with liquid argon as the target material for the scattering of dark matter particles. Efficient background reduction is achieved using low radioactivity underground argon as well as several experimental handles such as pulse shape, ratio of ionization over scintillation signal, 3D event reconstruction, and active neutron and muon vetos. The DarkSide-10 prototype detector has proven high scintillation light yield, which is a particularly important parameter as it sets the energy threshold for the pulse shape discrimination technique. The DarkSide-50 detector system, currently in commissioning phase at the Gran Sasso Underground Laboratory, will reach a sensitivity to dark matter spin-independent scattering cross section of 10−45 cm2 within 3 years of operation.

Phys.Rev.D

We report the results of a search for the neutrinoless double-β decay (0νββ) of Mo100, using the NEMO-3 detector to reconstruct the full topology of the final state events. With an exposure of 34.7  kg·y, no evidence for the 0νββ signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of T1/2(0νββ)>1.1×1024 years (90% C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the nuclear matrix elements this corresponds to an upper limit on the Majorana effective neutrino mass of ⟨mν⟩<0.3–0.9  eV (90% C.L.). Constraints on other lepton number violating mechanisms of 0νββ decays are also given. Searching for high-energy double electron events in all suitable sources of the detector, no event in the energy region [3.2–10] MeV is observed for an exposure of 47  kg·y.

Phys.Rev.Lett.

The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of 7.3σ when compared to 4.92±0.55 expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles θ12, θ23, θ13, a mass difference Δm322 and a CP violating phase δCP. In this neutrino oscillation scenario, assuming |Δm322|=2.4×10−3  eV2, sin2θ23=0.5, and Δm322>0 (Δm322<0), a best-fit value of sin22θ13=0.140−0.032+0.038 (0.170−0.037+0.045) is obtained at δCP=0. When combining the result with the current best knowledge of oscillation parameters including the world average value of θ13 from reactor experiments, some values of δCP are disfavored at the 90% C.L.

JINST

NEXT-MM is a general-purpose high pressure (10 bar,~ 25 l active volume) Xenon-based TPC, read out in chargemode with an 0.8 cm × 0.8 cm-segmented 700 cm2 plane(1152 ch) of the latest microbulk-Micromegas technology. It hasbeen recently commissioned at University of Zaragoza as part of theR&D of the NEXT 0νββ experiment, although theexperiment's first stage is currently being built based on aSiPM/PMT-readout concept relying on electroluminescence. Around 2million events were collected during the last months, stemming fromthe low energy γ-rays emitted by a 241Am source wheninteracting with the Xenon gas (Eγ = 26, 30,59.5 keV). The localized nature of such events around atmosphericpressure, the long drift times, as well as the possibility todetermine their production time from the associated αparticle in coincidence, allow the extraction of primordialproperties of the TPC filling gas, namely the drift velocity,diffusion and attachment coefficients. In this work we focus on thelittle explored combination of Xe and trimethylamine (TMA) forwhich, in particular, such properties are largely unknown. This gasmixture offers potential advantages over pure Xenon when aimed atRare Event Searches, mainly due to its Penning characteristics,wave-length shifting properties and reduced diffusion, and it isbeing actively investigated by our collaboration. The chamber iscurrently operated at 2.7 bar, as an intermediate step towards theenvisaged 10 bar. We report here its performance as well as a firstimplementation of the calibration procedures that have allowed theextension of the previously reported energy resolution to the wholereadout plane (10.6% FWHM@30 keV).

AIP Conf. Proc.

The Majorana Demonstrator neutrinoless double beta-decay experiment is currently under construction at the Sanford Underground Research Facility in South Dakota, USA. An overview and status of the experiment are given.

Phys.Rev.Lett.

A search for forbidden and exotic Z boson decays in the diphoton mass spectrum is presented for the first time in hadron collisions, based on data corresponding to 10.0  fb−1 of integrated luminosity from proton-antiproton collisions at s=1.96  TeV collected by the CDF experiment. No evidence of signal is observed, and 95% credibility level Bayesian upper limits are set on the branching ratios of decays of the Z boson to a photon and neutral pion (which is detected as a photon), a pair of photons, and a pair of neutral pions. The observed branching ratio limits are 2.01×10−5 for Z→π0γ, 1.46×10−5 for Z→γγ, and 1.52×10−5 for Z→π0π0. The Z→π0γ and Z→γγ limits improve the most stringent results from other experiments by factors of 2.6 and 3.6, respectively. The Z→π0π0 branching ratio limit is the first experimental result on this decay.

JINST

A technical description of NEXT-MM and its commissioning andfirst performance is reported. Having an active volume of~ 35 cm drift × 28 cm diameter, it constitutes thelargest Micromegas-read TPC operated in Xenon ever constructed, madeby a sectorial arrangement of the 4 largest single wafersmanufactured with the Microbulk technique to date. It is equippedwith a suitably pixelized readout and with a sufficiently largesensitive volume ( ~ 23 l) so as to contain long ( ~ 20 cm)electron tracks. First results obtained at 1 bar for Xenon andTrymethylamine (Xe-(2%)TMA) mixture are presented. The TPC canaccurately reconstruct extended background tracks. An encouragingfull-width half-maximum of 11.6 % was obtained for ~ 29 keVgammas without resorting to any data post-processing.

Phys.Rev.Lett.

The photoproduction of η mesons off nucleons bound in H2 and H3e has been measured in coincidence with recoil protons and recoil neutrons for incident photon energies from threshold up to 1.4 GeV. The experiments were performed at the Mainz MAMI accelerator, using the Glasgow tagged photon facility. Decay photons from the η→2γ and η→3π0 decays and the recoil nucleons were detected with an almost 4π electromagnetic calorimeter combining the Crystal Ball and TAPS detectors. The data from both targets are of excellent statistical quality and show a narrow structure in the excitation function of γn→nη. The results from the two measurements are consistent, taking into account the expected effects from nuclear Fermi motion. The best estimates for position and intrinsic width of the structure are W=(1670±5)  MeV and Γ=(30±15)  MeV. For the first time precise results for the angular dependence of this structure have been extracted.

Phys. Rev. Lett.

This Letter presents a search for quantum black-hole production using 20.3  fb−1 of data collected with the ATLAS detector in pp collisions at the LHC at s=8  TeV. The quantum black holes are assumed to decay into a final state characterized by a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton+jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black holes with threshold mass above 3.5 TeV is 0.18 fb. This limit constrains the threshold quantum black-hole mass to be above 5.3 TeV in the model considered.

Phys. Rev. D

A measurement of the cross section for the production of isolated prompt photons in pp collisions at a center-of-mass energy $\sqrt{s}$ = 7 TeV is presented. The results are based on an integrated luminosity of 4.6 fb$^{-1}$ collected with the ATLAS detector at the LHC. The cross section is measured as a function of photon pseudorapidity $\eta^\gamma$ and transverse energy $E_T^\gamma$ in the kinematic range 100 < $E_T^\gamma$ < 1000 GeV and in the regions |$\eta^\gamma$| < 1.37 and 1.52 < |$\eta^\gamma$| < 2.37. The results are compared to leading-order parton-shower Monte Carlo models and next-to-leading order perturbative QCD calculations. Next to-leading-order perturbative QCD calculations agree well with the measured cross sections as a function of $E_T^\gamma$ and $\eta^\gamma$.

JINST

This paper summarises the mechanical construction andinstallation of the Tile Calorimeter for the ATLASexperiment at the Large Hadron Collider in CERN, Switzerland. The TileCalorimeter is a sampling calorimeter using scintillator as the sensitivedetector and steel as the absorber and covers the central region of the ATLASexperiment up to pseudorapidities ±1.7. The mechanical construction ofthe Tile Calorimeter occurred over a periodof about 10 years beginning in 1995 with the completionof the Technical Design Report and ending in 2006 with the installationof the final module in the ATLAS cavern. Duringthis period approximately 2600 metric tons of steel were transformedinto a laminated structure to form the absorber of the sampling calorimeter.Following instrumentation and testing, which is described elsewhere, themodules were installed in the ATLAS cavern with a remarkable accuracy fora structure of this size and weight.

Phys.Rev.D

We present a measurement of the W-boson mass, MW, using data corresponding to 2.2  fb−1 of integrated luminosity collected in pp¯ collisions at s=1.96  TeV with the CDF II detector at the Fermilab Tevatron. The selected sample of 470 126 W→eν candidates and 624 708 W→μν candidates yields the measurement MW=80387±12(stat)±15(syst)=80387±19  MeV/c2. This is the most precise single measurement of the W-boson mass to date.

Phys. Lett. B

The transverse spin correlations Ax,x and Ay,y in the n p→dπ0 reaction have been measured for the first time in quasi-free kinematics at the COSY-ANKE facility using a polarised deuteron beam incident on a polarised hydrogen cell target. The results obtained for neutron energies close to 353 MeV and 600 MeV are in good agreement with the partial wave analysis of data on the isospin-related pp→dπ+ reaction, though the present results cover kinematic regions that are largely absent from existing data sets.

JHEP

A measurement of the transverse momentum spectra of jets in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV is reported. Jets are reconstructed from charged particles using the anti-$k_{\rm T}$ jet algorithm with jet resolution parameters $R$ of $0.2$ and $0.3$ in pseudo-rapidity $|\eta|<0.5$. The transverse momentum $p_{\rm T}$ of charged particles is measured down to $0.15$ GeV/$c$ which gives access to the low $p_{\rm T}$ fragments of the jet. Jets found in heavy-ion collisions are corrected event-by-event for average background density and on an inclusive basis (via unfolding) for residual background fluctuations and detector effects. A strong suppression of jet production in central events with respect to peripheral events is observed. The suppression is found to be similar to the suppression of charged hadrons, which suggests that substantial energy is radiated at angles larger than the jet resolution parameter $R=0.3$ considered in the analysis. The fragmentation bias introduced by selecting jets with a high $p_{\rm T}$ leading particle, which rejects jets with a soft fragmentation pattern, has a similar effect on the jet yield for central and peripheral events. The ratio of jet spectra with $R=0.2$ and $R=0.3$ is found to be similar in Pb-Pb and simulated PYTHIA pp events, indicating no strong broadening of the radial jet structure in the reconstructed jets with $R<0.3$.

Phys.Rev.Lett.

Information on the size and shape of the neutron skin on Pb208 is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be cn=6.70±0.03(stat.)  fm and an=0.55±0.01(stat.)-0.03+0.02(sys.)  fm, respectively, corresponding to a neutron skin thickness Δrnp=0.15±0.03(stat.)-0.03+0.01(sys.)  fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of Pb208 has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

Phys.Lett.B

The inclusive J/ψ nuclear modification factor ( RAA ) in Pb–Pb collisions at sNN=2.76 TeV has been measured by ALICE as a function of centrality in the e+e− decay channel at mid-rapidity ( |y|<0.8 ) and as a function of centrality, transverse momentum and rapidity in the μ+μ− decay channel at forward-rapidity ( 2.5