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.

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.

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.

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$$^\circ$$.

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.

Eur. Phys. J. A

The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$ , are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined.

PoS

The orbital NUCLEON detector was launched at 26 December 2014 for 5 years of data taken. The experiment is designed to measure cosmic ray energy spectrum and charge composition at 100 GeV – 1000 TeV and Z = 1- 30 respectively. The NUCLEON apparatus structure, methods of primary cosmic ray charge and ener gy measurements are described. Preliminary results of the measurements of the cosmic nuclei energy spectra and the charge composition are presented from the first year and a half of data taking from orbit .

Phys. Lett. B

A search is presented for narrow resonances decaying to dijet final states in proton–proton collisions at s=13TeV using data corresponding to an integrated luminosity of 12.9 fb −1 . The dijet mass spectrum is well described by a smooth parameterization and no significant evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.4 TeV, scalar diquarks below 6.9 TeV, axigluons and colorons below 5.5 TeV, excited quarks below 5.4 TeV, color-octet scalars below 3.0 TeV, W′ bosons below 2.7 TeV, Z′ bosons below 2.1 TeV and between 2.3 and 2.6 TeV, and RS gravitons below 1.9 TeV. These extend previous limits in the dijet channel. Vector and axial-vector mediators in a simplified model of interactions between quarks and dark matter are excluded below 2.0 TeV. The first limits in the dijet channel on dark matter mediators are presented as functions of dark matter mass and are compared to the exclusions of dark matter in direct detection experiments.

JHEP

The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward (−4.46 < y$_{cms}$ < −2.96) and forward (2.03 < y$_{cms}$ < 3.53) rapidity regions, corresponding to Pb-going and p-going directions, respectively. The Z-boson production cross section, with dimuon invariant mass of 60 < m$_{μμ}$ < 120 GeV/c$^{2}$ and muon transverse momentum (p$_{T}^{μ}$ ) larger than 20 GeV/c, is measured. The production cross section and charge asymmetry of muons from W-boson decays with p$_{T}^{μ}$ > 10 GeV/c are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties.

Phys. Rev. Lett.

We report the first direct measurement of decays of the Λc+ baryon involving the neutron. The analysis is performed using 567  pb-1 of e+e- collision data collected at s=4.599  GeV with the BESIII detector at the BEPCII collider. We observe the decay Λc+→nKS0π+ and measure the absolute branching fraction to be B(Λc+→nKS0π+)=[1.82±0.23(stat)±0.11(syst)]%. A comparison to B[Λc+→p(K¯π)0] provides an important test of isospin symmetry and final state interactions.

Phys. Part. Nucl. Lett.

In April 2015, the first cluster of Baikal-GVD was deployed in Lake Baikal and put into operation. It comprises eight strings. Each string consists of 24 optical modules. An optical module is a detection element of Baikal-GVD, it includes a Hamamatsu R7081-100 photomultiplier tube with a high quantum sensitivity. We describe the design of the optical module, the front-end electronics, and the laboratory characterization and calibration.

JINST

This paper describes the design, fabrication, commissioning and use of a CALibration source Insertion System (CALIS) in the DarkSide-50 direct dark matter search experiment. CALIS deploys radioactive sources into the liquid scintillator veto to characterize the detector response and detection efficiency of the DarkSide-50 Liquid Argon Time Projection Chamber, and the surrounding 30 t organic liquid scintillator neutron veto. It was commissioned in September 2014 and has been used successfully in several gamma and neutron source campaigns since then. A description of the hardware and an excerpt of calibration analysis results are given below.

Phys.Part.Nucl.

We discuss neutrinos originating from dark matter in the Galactic Center and present sensitivity of Baikal Gigaton Volume Detector to this signal.

Phys. Part. Nucl.

The objective of the Baikal-GVD project is the construction of a km$^{3}$-scale neutrino telescope in Lake Baikal. The Gigaton Volume Detector consists of a large three-dimensional array of photo-multiplier tubes. The first GVD-cluster has been deployed and commissioned in April 2015. The data acquisition system (DAQ) of the detector takes care of the digitization of the photo-multiplier tube signals, data transmission, filtering and storage. The design and the implementation of the data acquisition system are described.

Zh.Eksp.Teor.Fiz.

Using a modification of the Shapiro approach, we introduce the two-parameter family of conductance distributions W(g), defined by simple differential equations, which are in the one-to-one correspondence with conductance distributions for quasi-one-dimensional systems of size L$^{d}^{–1}$ × L$_{z}$ , characterizing by parameters L/ξ and L$_{z}$ /L (ξ is the correlation length, d is the dimension of space). This family contains the Gaussian and log-normal distributions, typical for the metallic and localized phases. For a certain choice of parameters, we reproduce the results for the cumulants of conductance in the space dimension d = 2 + ϵ obtained in the framework of the σ-model approach. The universal property of distributions is existence of two asymptotic regimes, log-normal for small g and exponential for large g. In the metallic phase they refer to remote tails, in the critical region they determine practically all distribution, in the localized phase the former asymptotics forces out the latter. A singularity at g = 1, discovered in numerical experiments, is admissible in the framework of their calculational scheme, but related with a deficient definition of conductance. Apart of this singularity, the critical distribution for d = 3 is well described by the present theory. One-parameter scaling for the whole distribution takes place under condition, that two independent parameters characterizing this distribution are functions of the ratio L/ξ.

JHEP

The spectra of charged particles produced within the pseudorapidity window |η| < 1 at $ \sqrt{s_{\mathrm{N}\,\mathrm{N}}}=5.02 $ TeV are measured using 404 μb$^{−1}$ of PbPb and 27.4 pb$^{−1}$ of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < p$_{T}$ < 400 GeV in pp and 0.7 < p$_{T}$ < 400 GeV in PbPb collisions. The corresponding nuclear modification factor, R$_{AA}$, is measured in bins of collision centrality. The R$_{AA}$ in the 5% most central collisions shows a maximal suppression by a factor of 7-8 in the p$_{T}$ region of 6-9 GeV. This dip is followed by an increase, which continues up to the highest p$_{T}$ measured, and approaches unity in the vicinity of p$_{T}$ = 200 GeV. The R$_{AA}$ is compared to theoretical predictions and earlier experimental results at lower collision energies. The newly measured pp spectrum is combined with the pPb spectrum previously published by the CMS collaboration to construct the pPb nuclear modification factor, R$_{pA}$, up to 120 GeV. For p$_{T}$ > 20 GeV, R$_{pA}$ exhibits weak momentum dependence and shows a moderate enhancement above unity.