Eur.Phys.J.C

During 2015 the ATLAS experiment recorded $3.8\,{\mathrm{fb}}^{-1}$ of proton–proton collision data at a centre-of-mass energy of $13\,{\mathrm{TeV}}$ . The ATLAS trigger system is a crucial component of the experiment, responsible for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton–proton collision data.

EPJ Web Conf.

First results of the ATLAS experiment at LHC on quarkonium and heavy flavour meson production in proton-proton collisions at 13 TeV are presented. A brief summary of the results obtained at 7-8 TeV is also reported. Comparison of the data cross sections with various theoretical predictions is discussed.

JHEP

The results of a first search for CP violation in the production and decay of top quark-antiquark ( $ t\overline{t} $ ) pairs are presented. The search is based on asymmetries in T-odd, triple-product correlation observables, where T is the time-reversal operator. The analysis uses a sample of proton-proton collisions at $ \sqrt{s}=8 $ TeV collected by the CMS experiment, corresponding to an integrated luminosity of 19.7 fb$^{−1}$. Events are selected having one electron or muon and at least four jets. The T-odd observables are measured using four-momentum vectors associated with $ t\overline{t} $ production and decay. The measured asymmetries exhibit no evidence for CP-violating effects, consistent with the expectation from the standard model.

JHEP

A search for the rare two-body charmless baryonic decay $ {B}^{+}\to p\overline{\varLambda} $ is performed with pp collision data, corresponding to an integrated luminosity of 3 fb$^{−1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of $ {B}^{+}\to p\overline{\varLambda} $ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the B$^{+}$ → K$_{S}^{0}$ π$^{+}$ decay for normalisation, is $ \mathrm{\mathcal{B}}\left({B}^{+}\to p\overline{\varLambda}\right)=\left(2.{4}_{-0.8}^{+1.0}\pm 0.3\right)\times 1{0}^{-7}, $ where the first uncertainty is statistical and the second systematic.

JHEP

A search for the non-resonant decays B$_{s}^{0}$  → μ$^{+}$ μ$^{−}$ μ$^{+}$ μ$^{−}$ and B$^{0}$ → μ$^{+}$ μ$^{−}$ μ$^{+}$ μ$^{−}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of 1 and 2 fb$^{−1}$ collected at centre-of-mass energies of 7 and 8 TeV, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at 95% confidence level are determined to be $ \mathrm{\mathcal{B}}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}{\mu}^{+}{\mu}^{-}\right)<2.5\times 1{0}^{-9}, $ $ \mathrm{\mathcal{B}}\left({B}^0\to {\mu}^{+}{\mu}^{-}{\mu}^{+}{\mu}^{-}\right)<6.9\times 1{0}^{-10}. $

Phys.Rev.C

An influence of the phonon-phonon coupling (PPC) on the β-decay half-lives and multi-neutron emission probabilities is analyzed within the microscopic model based on the Skyrme interaction with tensor components included. The finite-rank separable approximation is used in order to handle large two-quasiparticle spaces. The even-even nuclei near the r-process paths at N=82 are studied. The characteristics of ground states, 2+ excitations, and β-decay strength of the neutron-rich Cd isotopes are treated in detail. It is shown that a strong redistribution of the Gamow-Teller strength due to the PPC is mostly sensitive to the multi-neutron emission probability of the Cd isotopes.

J.Phys.Conf.Ser.

The SANC system is used for systematic calculations of various processes within the Standard Model in the one-loop approximation. QED, electroweak, and QCD corrections are computed to a number of processes being of interest for modern and future high-energy experiments. Several applications for the LHC physics program are presented. Development of the system and the general problems and perspectives for future improvement of the theoretical precision are discussed.

J.Phys.Conf.Ser.

The ATLAS EventIndex is a data catalogue system that stores event-related metadata for all (real and simulated) ATLAS events, on all processing stages. As it consists of different components that depend on other applications (such as distributed storage, and different sources of information) we need to monitor the conditions of many heterogeneous subsystems, to make sure everything is working correctly. This paper describes how we gather information about the EventIndex components and related subsystems: the Producer-Consumer architecture for data collection, health parameters from the servers that run EventIndex components, EventIndex web interface status, and the Hadoop infrastructure that stores EventIndex data. This information is collected, processed, and then displayed using CERN service monitoring software based on the Kibana analytic and visualization package, provided by CERN IT Department. EventIndex monitoring is used both by the EventIndex team and ATLAS Distributed Computing shifts crew.

J.Phys.Conf.Ser.

The ATLAS EventIndex is the catalogue of the event-related metadata for the information collected from the ATLAS detector. The basic unit of this information is the event record, containing the event identification parameters, pointers to the files containing this event as well as trigger decision information. The main use case for the EventIndex is event picking, as well as data consistency checks for large production campaigns. The EventIndex employs the Hadoop platform for data storage and handling, as well as a messaging system for the collection of information. The information for the EventIndex is collected both at Tier-0, when the data are first produced, and from the Grid, when various types of derived data are produced. The EventIndex uses various types of auxiliary information from other ATLAS sources for data collection and processing: trigger tables from the condition metadata database (COMA), dataset information from the data catalogue AMI and the Rucio data management system and information on production jobs from the ATLAS production system. The ATLAS production system is also used for the collection of event information from the Grid jobs. EventIndex developments started in 2012 and in the middle of 2015 the system was commissioned and started collecting event metadata, as a part of ATLAS Distributed Computing operations.

Nucl.Phys.B

The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb−1 . Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.

JHEP

A search for heavy resonances that decay to tau lepton pairs is performed using proton-proton collisions at $\sqrt{s} = 13$ TeV. The data were collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 2.2 inverse femtobarns. The observations are in agreement with standard model predictions. An upper limit at 95% confidence level on the product of the production cross section and branching fraction into tau lepton pairs is calculated as a function of the resonance mass. For the sequential standard model, the presence of Z' bosons decaying into tau lepton pairs is excluded for Z' masses below 2.1 TeV, extending previous limits for this final state. For the topcolor-assisted technicolor model, which predicts Z bosons that preferentially couple to third-generation fermions, Z' masses below 1.7 TeV are excluded, representing the most stringent limit to date.

Phys. Lett. B

The results of a search for new physics in final states with photons and missing transverse energy are reported. The study is based on a sample of proton–proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 fb −1 . Final states with two photons and significant missing transverse energy are used to search for supersymmetric particles in models of supersymmetry (SUSY) with general gauge-mediated (GGM) supersymmetry breaking. No excess is observed with respect to the standard model expectation, and the results are used to set limits on gluino pair production and squark pair production in the GGM SUSY framework. Gluino masses below 1.65 TeV and squark masses below 1.37 TeV are excluded at a 95% confidence level.

Eur.Phys.J.C

Measurements of the associated production of a Z boson with at least one jet originating from a b quark in proton-proton collisions at $\sqrt{s} =$ 8 TeV are presented. Differential cross sections are measured with data collected by the CMS experiment corresponding to an integrated luminosity of 19.8 inverse femtobarns. Z bosons are reconstructed through their decays to electrons and muons. Cross sections are measured as a function of observables characterizing the kinematics of the b jet and the Z boson. Ratios of differential cross sections for the associated production with at least one b jet to the associated production with any jet are also presented. The production of a Z boson with two b jets is investigated, and differential cross sections are measured for the dijet system. Results are compared to theoretical predictions, testing two different flavour schemes for the choice of initial-state partons.

Astropart.Phys.

Internal contaminations of 238 U, 235 U and 232 Th in the bulk of high purity germanium detectors are potential backgrounds for experiments searching for neutrinoless double beta decay of 76 Ge. The data from Gerda Phase I have been analyzed for alpha events from the decay chain of these contaminations by looking for full decay chains and for time correlations between successive decays in the same detector. No candidate events for a full chain have been found. Upper limits on the activities in the range of a few nBq/kg for 226 Ra, 227 Ac and 228 Th, the long-lived daughter nuclides of 238 U, 235 U and 232 Th, respectively, have been derived. With these upper limits a background index in the energy region of interest from 226 Ra and 228 Th contamination is estimated which satisfies the prerequisites of a future ton scale germanium double beta decay experiment.

PTEP

Hyper-Kamiokande consists of two identical water-Cherenkov detectors of total 520 kt, with the first one in Japan at 295 km from the J-PARC neutrino beam with 2.5$$^\circ$$ off-axis angles (OAAs), and the second one possibly in Korea at a later stage. Having the second detector in Korea would benefit almost all areas of neutrino oscillation physics, mainly due to longer baselines. There are several candidate sites in Korea with baselines of 1000–1300 km and OAAs of 1$$^\circ$$–3$$^\circ$$.

Phys. Rev. D

Measurements of charm mixing and CP violation parameters from the decay-time-dependent ratio of D0→K+π- to D0→K-π+ decay rates and the charge-conjugate ratio are reported. The analysis uses B¯→D*+μ-X, and charge-conjugate decays, where D*+→D0π+, and D0→K∓π±. The pp collision data are recorded by the LHCb experiment at center-of-mass energies s=7 and 8 TeV, corresponding to an integrated luminosity of 3  fb-1. The data are analyzed under three hypotheses: (i) mixing assuming CP symmetry, (ii) mixing assuming no direct CP violation in the Cabibbo-favored or doubly Cabibbo-suppressed decay amplitudes, and (iii) mixing allowing either direct CP violation and/or CP violation in the superpositions of flavor eigenstates defining the mass eigenstates. The data are also combined with those from a previous LHCb study of D0→Kπ decays from a disjoint set of D*+ candidates produced directly in pp collisions. In all cases, the data are consistent with the hypothesis of CP symmetry.

Eur.Phys.J.C

Two searches for new phenomena in final states containing a same-flavour opposite-sign lepton (electron or muon) pair, jets, and large missing transverse momentum are presented. These searches make use of proton–proton collision data, collected during 2015 and 2016 at a centre-of-mass energy $\sqrt{s}=13$   $\text {TeV}$ by the ATLAS detector at the large hadron collider, which correspond to an integrated luminosity of $14.7~\mathrm {fb}^{-1}$ . Both searches target the pair production of supersymmetric particles, squarks or gluinos, which decay to final states containing a same-flavour opposite-sign lepton pair via one of two mechanisms: a leptonically decaying Z boson in the final state, leading to a peak in the dilepton invariant-mass distribution around the Z boson mass, and decays of neutralinos (e.g. $\tilde{\chi }_2^0 \rightarrow \ell ^+\ell ^- \tilde{\chi }_1^0$ ), yielding a kinematic endpoint in the dilepton invariant-mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.70  $\text {TeV}$ (980  $\text {GeV}$ ).

Astrophys.J.

Despite decades of effort, the timing and duration of He II reionization, as well as its morphology and the properties of the quasars believed to drive it, are still not well constrained. In this paper we present a new method to study both He II reionization and quasars via the thermal proximity effect -- the photoelectric heating of the intergalactic medium around quasars when their hard radiation doubly ionizes helium. We post-process a SPH simulation with 1D radiative calculations, and study how the thermal proximity effect depends on the amount of singly ionized helium, $x_{\rm HeII,0}$, which prevailed in the IGM before the quasar turned on, and the characteristic lifetime $t_{\rm Q}$ for which quasars shine. We find that the amplitude of the temperature boost in the quasar environment depends on $x_{\rm HeII,0}$, with a characteristic value of $\Delta T \simeq 10^4\,{\rm K}$ for an initially singly ionized IGM ($x_{\rm HeII,0} = 1.0$), whereas the size of the thermal proximity zone is sensitive to quasar lifetime $t_{\rm Q}$, with typical sizes of ~100 cMpc for luminous quasars shining for $t_{\rm Q}=10^8$ yr. This temperature boost is manifest as a change in the thermal broadening of H I absorption lines near the quasar. We introduce a new method based on measuring the Ly$\alpha$ forest power spectrum as a function of distance from the quasar, and conduct Bayesian MCMC analysis to demonstrate that the thermal proximity effect should be easily detectable. For a mock dataset of 50 quasars at z~4, we predict that one can measure $x_{\rm HeII,0}$ to a precision $\approx 0.04$, and $t_{\rm Q}$ to a precision of $\approx 0.1$ dex. By applying our formalism to existing high-resolution Ly$\alpha$ forest spectra of quasars at $3.1 \lesssim z \lesssim 5.0$, one should be able to detect the thermal proximity effect, and reconstruct the full reionization history of He II.

PoS

The Low Energy QCD allows to calculate the ππ and π K scattering lengths with high precision. There are accurate relations between these scattering lengths and π + π − , π − K + , π + K − atoms lifetimes. The experiment on the first observation of π − K + and π + K − atoms is described. The atoms were generated in Nickel and Platinum targets hit by the PS CERN proton beam with momentum of 24 GeV/ c . Moving in the target, part of atoms break up producing characteristic π K pairs (atomic pairs) with small relative momentum Q in their c.m.s. In the experiment, we detected n A = 349 ± 62 (5.6 standard deviations) π − K + and π + K − atomic pairs. The main part of π K pairs are produced in free state. The majority of such particles are generated directly or from short-lived sources as ρ , ω and similar resonances. The electromagnetic interactions in the final state create Coulomb pairs with a known sharp dependence on Q . This effect allows to evaluate the number of these Coulomb pairs. There is a precise ratio ( ∼ 1%) between the number of π − K + ( π + K − ) Coulomb pairs with small Q and the number of produced π − K + ( π + K − ) atoms. Using this ratio, we obtained the numbers of generated π − K + and π + K − atoms. The atom breakup probability in a target P br = n A / N A depends on the atom lifetime. Using such dependences for the Ni and Pt targets, known with a precision about 1%, the π K atom lifetime was measured and from this value the π K scattering lengths were evaluated. The presented analysis shows that the π − K + and π + K − atoms production in the p-nucleus inter- actions increases by 16 and 38 times respectively if the proton momentum is increased from 24 GeV/ c up to 450 GeV/ c .

Phys.Rev.C

The Dalitz decay π0→e+e−γ has been measured in the γp→π0p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the π0 electromagnetic transition form factor, aπ=0.030±0.010tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of aπ is lower than in previous results based on the π0→e+e−γ decay.

Phys.Lett.B

By analyzing 2.93fb−1 of data taken at the ψ(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+→KS0KS0K+ , D+→KS0KS0π+ , D0→KS0KS0 and D0→KS0KS0KS0 . They are determined to be B(D+→KS0KS0K+)=(2.54±0.05stat.±0.12sys.)×10−3 , B(D+→KS0KS0π+)=(2.70±0.05stat.±0.12sys.)×10−3 , B(D0→KS0KS0)=(1.67±0.11stat.±0.11sys.)×10−4 and B(D0→KS0KS0KS0)=(7.21±0.33stat.±0.44sys.)×10−4 , where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.

Phys. Lett. B

We report the first measurement of the absolute branching fraction for Λc+→Λμ+νμ . This measurement is based on a sample of e+e− annihilation data produced at a center-of-mass energy s=4.6 GeV , collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb−1 . The branching fraction is determined to be B(Λc+→Λμ+νμ)=(3.49±0.46(stat)±0.27(syst))% . In addition, we calculate the ratio B(Λc+→Λμ+νμ)/B(Λc+→Λe+νe) to be 0.96±0.16(stat)±0.04(syst) .

PoS

DarkSide-50 is a direct dark matter search experiment operating underground at Laboratori Nazionali del Gran Sasso. It is based on a Time Projection Chamber (TPC) that contains 50 kg of liquid argon; the TPC cryostat sits inside an active neutron veto based on a boron-loaded organic scintillator, which is in turn installed inside a water Cherenkov muon veto. The experiment started acquiring data in Nov 2013 filled with atmospheric argon. In April 2015 it commissioned the low-radioactivity argon from underground sources and has been running in a stable manner since then. We report the current status of the detector and the latest results, including the measurement of the radioactivity of the underground argon and the most sensitive dark matter search performed with an argon target.

PoS

The GERmanium Detector Array (G ERDA ) experiment, located at the Gran Sasso underground laboratory in Italy, is built for the search of 0 νβ β decay in 76 Ge. G ERDA operates bare high purity germanium detectors submersed in liquid Argon (LAr). Phase I of the experiment was completed reaching an exposure of about 21 kg · yr with a background level of 10 − 2 cts/(keV · kg · yr) . GERDA Phase I set a limit on the 0 νβ β decay of 76 Ge of T 0 ν 1 / 2 > 2 . 1 · 10 25 yr. In Phase II 35 kg of germa- nium detectors enriched in 76 Ge are operated to reach an exposure of 100 kg · yr. The design goal is to reduce the background by one order of magnitude to reach the sensitivity for T 0 ν 1 / 2 = O ( 10 26 ) yr. The Phase II setup comprises thirty newly produced Broad Energy Germanium (BEGe) de- tectors. They contribute to the background reduction with better energy resolution and enhanced pulse shape discrimination. To achieve the necessary background reduction, the setup was com- plemented with LAr veto. The hardware upgrade for Phase II was finished and all detectors were deployed in December 2015. We present the first results of Phase II with 10.8 kg · yr exposure reached in June 2016.

Eur. Phys. J. C

The cross section of top quark-antiquark pair production in proton-proton collisions at $\sqrt{s} = 13$ TeV is measured by the CMS experiment at the LHC, using data corresponding to an integrated luminosity of 2.2 inverse femtobarns. The measurement is performed by analyzing events in which the final state includes one electron, one muon, and two or more jets, at least one of which is identified as originating from hadronization of a b quark. The measured cross section is 792 $\pm$ 8 (stat) $\pm$ 37 (syst) $\pm$ 21 (lumi) pb, in agreement with the expectation from the standard model.