Eur. Phys. J. C

This paper presents the performance of the ATLAS muon reconstruction during the LHC run with pp$collisions at$\sqrt{s}=7$–8 TeV in 2011–2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of${J/\psi \rightarrow \mu \mu }$,$Z \rightarrow \mu \mu $and${\Upsilon \rightarrow \mu \mu }$decays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon$|\eta |<2.7$and$5 \lesssim p_{\mathrm{T}}\lesssim 100$GeV) the efficiency is above$99\,\%$and is measured with per-mille precision. The momentum resolution ranges from$1.7\,\%$at central rapidity and for transverse momentum$p_{\mathrm{T}}\simeq 10$GeV, to$4\,\%$at large rapidity and$p_{\mathrm{T}}\simeq 100$GeV. The momentum scale is known with an uncertainty of$0.05\,\%$to$0.2\,\%$depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.$

J. Phys. Conf. Ser.

The HERAFitter project was established to increase applicability of the QCD analysis in the hadron collider experiments. The framework may be used to extract parton density functions from a variety of experimental measurements and to assess the impact of new data on the parton density determination. It may also be employed to perform data consistency checks and to test theoretical models. This short article covers a poster contribution on the BEACH2014 conference held at the Birmingham University.

Eur. Phys. J. C

A search for heavy, right-handed neutrinos, \mathrm {N}_{\ell }$($\ell = \mathrm {e}, \mu $), and right-handed$\mathrm {W}_{\mathrm {R}}$bosons, which arise in the left-right symmetric extensions of the standard model, has been performed by the CMS experiment. The search was based on a sample of two lepton plus two jet events collected in proton–proton collisions at a center-of-mass energy of 8$\,\text {TeV}$corresponding to an integrated luminosity of 19.7$\mathrm{fb}^{-1}$. For models with strict left-right symmetry, and assuming only one$\mathrm {N}_{\ell }$flavor contributes significantly to the$\mathrm {W}_{\mathrm {R}}$decay width, the region in the two-dimensional$(M_{\mathrm {W\mathrm {R}}}, M_{\mathrm {N\ell }})$mass plane excluded at a 95$M_{\mathrm {W\mathrm {R}}} = 3.0\,\text {TeV} $and covers a large range of neutrino masses below the$\mathrm {W}_{\mathrm {R}}$boson mass, depending on the value of$M_{\mathrm {W\mathrm {R}}}$. This search significantly extends the$(M_{\mathrm {W\mathrm {R}}}, M_{\mathrm {N\ell }})$exclusion region beyond previous results.$

Eur. Phys. J. A

The helicity dependences of the differential cross sections for the semi-inclusive γ^{3}$He → π$^{0}$X and γ$^{3}$He → π$^{±}$X reactions have been measured for the first time in the energy region 200 < E$_{γ}$450 MeV. The experiment was performed at the tagged photon beam facility of the MAMI accelerator in Mainz using a longitudinally polarised high-pressure$^{3}$He gas target. Hadronic products were measured with the large-acceptance Crystal Ball detector complemented with additional devices for charged-particle tracking and identification. Unpolarised differential cross sections and their helicity dependence are compared with theoretical calculations using the Fix-Arenhövel model. The effect of the intermediate excitation of the Δ(1232) resonance can be clearly seen from this comparison, especially for the polarised case, where nuclear effects are relatively small. The model provides a better theoretical description of the unpolarised charged pion photoproduction data than the neutral pion channel. It does significantly better in describing the helicity-dependent data in both channels. These comparisons provide new information on the mechanisms involved in pion photoproduction on$^{3}$He and suggest that a polarised$^{3}$He target can provide valuable information on the corresponding polarised quasi-free neutron reactions.$

Phys.Part.Nucl.Lett.

This paper presents numerical simulations and experimental results related to the effect of imperfections of the radial component of a magnetic field on the beam dynamics in the medical cyclotron C235-V3 of the Dimitrovgrad Proton Therapy Center. These imperfections in the region of the minimal axial betatron frequency lead to a transformation of coherent motion of the center of gravity of the beam to the incoherent motion of separate particles. The radial component increases the axial size of the beam by a factor of 2 at a radius of 20 cm, which produces additional losses of protons. To reduce undesirable actions of the radial component on the axial motion, the magnetic system in the central region has been optimized using two procedures: the positioning of shim correctors on sectors and selecting a special asymmetric arrangement of the upper and lower central plugs. This led to a twofold reduction in the axial size of the beam and a decrease in proton losses. Eventually, the beam transmission in C235-V3 has been increased to 72% without a limiting aperture diaphragm, which is commonly used in cyclotrons of this type. This makes it possible to reduce the irradiation dose of machine elements and increase the beam current at a deflector entrance of the cyclotron C235-V3 by a factor of 1.5 when compared to a serial C235 cyclotron.

Bull. Russ. Acad. Sci. Phys.

Three narrow (Γ ≤ 0.5 MeV) low-lying states of^{7}$He with excitation energies of 3.2(1) MeV, 4.9(2) MeV and 6.65(15) MeV are observed simultaneously for the first time in reactions of the absorption of stopped π$^{−}$-mesons$^{11}$B(π$^{−}$,pt)$^{7}$He and$^{11}$B(π$^{−}$,dd)$^{7}$He. No indications of the existence of a level in the area of E$_{x}$∼ 1 MeV are found. Highly excited$^{7}$He states with parameters E$_{x}$= 19.6(3) MeV, Γ = 1.7(4) MeV and E$_{x}$= 25.2(6) MeV, Γ= 4.8(9) MeV are observed.$

Bull. Russ. Acad. Sci. Phys.

Experimental results are presented for the spectra and yields of t and^{3}$He produced by nuclei in the reaction of stopped pion absorption. Contributions from different processes in the formation of particles are determined using a phenomenological model. The ratio of t and$^{3}$He yields agrees with the hypothesis of particle formation during the pre-equilibrium stage in the process of deuteron pick-up by primary nucleons on the surface of a nucleus.$

Phys.Part.Nucl.Lett.

The scientific design of a 14-MeV H^{−}$compact superconducting cyclotron for producing of the$^{18}$F and$^{13}$N isotopes has been developed. Main requirements to the facility as a medical accelerator are met in the design. In particular, the main requirement for the cyclotron was the smallest possible size due to the superconducting magnet. The calculations show that the proposed cyclotron allows extracted beam intensity over 500 μA. To increase system reliability and production rates, an external H$^{−}$ion source is applied. The choice of the cyclotron concept, design of the structure elements, calculation of the electromagnetic fields and beam dynamics from the ion source to the extraction system were performed.$

Phys.Rev.Lett.

A search for excited states of the Bc± meson is performed using 4.9  fb-1 of 7 TeV and 19.2  fb-1 of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay Bc±→J/ψπ±. The state appears in the m(Bc±π+π-)-m(Bc±)-2m(π±) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842±4±5  MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the Bc± meson, Bc±(2S).

JHEP

The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with proton-proton collision data at \sqrt{s} $= 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20 fb$^{−1}$. The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay modes considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a W boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the W bosons or the top quarks are off-shell. Decay modes involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between 210 and 640 GeV decaying directly to a top quark and a massless LSP is excluded at 95$

Phys.Rev.D

Searches for supersymmetry (SUSY) are presented based on the electroweak pair production of neutralinos and charginos, leading to decay channels with Higgs, Z, and W bosons and undetected lightest SUSY particles (LSPs). The data sample corresponds to an integrated luminosity of about 19.5  fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV collected in 2012 with the CMS detector at the LHC. The main emphasis is neutralino pair production in which each neutralino decays either to a Higgs boson (h) and an LSP or to a Z boson and an LSP, leading to hh, hZ, and ZZ states with missing transverse energy (ETmiss). A second aspect is chargino-neutralino pair production, leading to hW states with ETmiss. The decays of a Higgs boson to a bottom-quark pair, to a photon pair, and to final states with leptons are considered in conjunction with hadronic and leptonic decay modes of the Z and W bosons. No evidence is found for supersymmetric particles, and 95% confidence level upper limits are evaluated for the respective pair production cross sections and for neutralino and chargino mass values.

Phys. Rev. Lett.

We present a measurement of the CP-violating weak mixing phase ϕs using the decay B¯s0→Ds+Ds- in a data sample corresponding to 3.0 fb-1 of integrated luminosity collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not use the constraint |λ|=1 to allow for the presence of CP violation in decay, yields ϕs=0.02±0.17(stat)±0.02(syst)  rad, |λ|=0.91-0.15+0.18(stat)±0.02(syst). This result is consistent with the standard model expectation.

Phys. Lett. B

This Letter presents a search at the LHC for s -channel single top-quark production in proton–proton collisions at a centre-of-mass energy of 8 TeV. The analyzed data set was recorded by the ATLAS detector and corresponds to an integrated luminosity of 20.3 fb −1 . Selected events contain one charged lepton, large missing transverse momentum and exactly two b -tagged jets. A multivariate event classifier based on boosted decision trees is developed to discriminate s -channel single top-quark events from the main background contributions. The signal extraction is based on a binned maximum-likelihood fit of the output classifier distribution. The analysis leads to an upper limit on the s -channel single top-quark production cross-section of 14.6 pb at the 95% confidence level. The fit gives a cross-section of σs=5.0±4.3 pb , consistent with the Standard Model expectation.