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.

Phys. Lett. B

The results of a search for new physics in final states with jets, either photons or leptons, and low missing transverse momentum are reported. The study is based on a sample of proton–proton collisions collected at a center-of-mass energy s=8 TeV with the CMS detector in 2012. The integrated luminosity of the sample is 19.7 fb −1 . Many models of new physics predict the production of events with jets, electroweak gauge bosons, and little or no missing transverse momentum. Examples include stealth models of supersymmetry (SUSY), which predict a hidden sector at the electroweak energy scale in which SUSY is approximately conserved. The data are used to search for stealth SUSY signatures in final states with either two photons or an oppositely charged electron and muon. No excess is observed with respect to the standard model expectation, and the results are used to set limits on squark pair production in the stealth SUSY framework.

JHEP

Searches for heavy long-lived charged particles are performed using a data sample of 19.1 fb$^{−1}$ from proton-proton collisions at a centre-of-mass energy of $ \sqrt{s}=8 $ TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for tan β between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. R-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector, and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer.

Phys. Atom. Nucl.

In this paper we present a description of the universal approach for analytic calculations for a certain class of J functions for six topologies of the boxes for the process ud → WA. These functions J arise at the reduction of the infrared divergent box diagrams. The standard Passarino–Veltman reduction of the four-point box diagram with an internal photon line connecting two external lines on the mass shell leads to infrared-divergent and mass-singular D$_{0}$ functions. In the system SANC a systematic procedure is adopted to separate both types of singularities into the simplest objects, namely C$_{0}$ functions. The functions J, in turn, are represented as certain linear combinations of the standard D$_{0}$ and C$_{0}$ functions. The subtracted J functions are free of both types of singularities and are expressed as explicit and compact linear combinations of dilogarithm functions. We present extensive comparisons of numerical results of SANC with those obtained with the aid of the LoopTools package.

Phys. Lett. B

The difference in total widths between the Bc+ and B+ mesons is measured using a data sample corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton–proton collisions at the LHC. Through the study of the time evolution of Bc+→J/ψπ+ and B+→J/ψK+ decays, the width difference is measured to be ΔΓ≡ΓBc+−ΓB+=4.46±0.14±0.07 mm−1c, where the first uncertainty is statistical and the second systematic. The known lifetime of the B+ meson is used to convert this to a precise measurement of the Bc+ lifetime, τBc+=513.4±11.0±5.7 fs, where the first uncertainty is statistical and the second is systematic.

Phys. Rev. D

A search is performed for long-lived particles that decay into final states that include a pair of electrons or a pair of muons. The experimental signature is a distinctive topology consisting of a pair of charged leptons originating from a displaced secondary vertex. Events corresponding to an integrated luminosity of 19.6 (20.5)  fb-1 in the electron (muon) channel were collected with the CMS detector at the CERN LHC in proton-proton collisions at s=8  TeV. No significant excess is observed above standard model expectations. Upper limits on the product of the cross section and branching fraction of such a signal are presented as a function of the long-lived particle’s mean proper decay length. The limits are presented in an approximately model-independent way, allowing them to be applied to a wide class of models yielding the above topology. Over much of the investigated parameter space, the limits obtained are the most stringent to date. In the specific case of a model in which a Higgs boson in the mass range 125–1000  GeV/c2 decays into a pair of long-lived neutral bosons in the mass range 20–350  GeV/c2, each of which can then decay to dileptons, the upper limits obtained are typically in the range 0.2–10 fb for mean proper decay lengths of the long-lived particles in the range 0.01–100 cm. In the case of the lowest Higgs mass considered (125  GeV/c2), the limits are in the range 2–50 fb. These limits are sensitive to Higgs boson branching fractions as low as 10-4.

PTEP

We have observed a “$K^{-}pp$”-like structure in the $d(\pi ^{+ },K^{+ })$ reaction at 1.69 GeV$/c$. In this reaction, a $\Lambda (1405)$ hyperon resonance is expected to be produced as a doorway to form $K^{-}pp$ through the $\Lambda ^{\ast }p\rightarrow K^{-}pp$ process. However, most of the $\Lambda (1405)$ produced would escape from the deuteron without secondary reactions. Therefore, coincidence of high-momentum ($>$250 MeV$/c$) proton(s) at large emission angles ($39^\circ \lt \theta _{\rm lab.} \lt 122^\circ$) was requested to enhance the signal-to-background ratio. A broad enhancement in the proton coincidence spectra is observed around the missing mass of 2.27 GeV$/c^2$, which corresponds to the $K^{-}pp$ binding energy of 95 ${}^{+18}_{-17}$ (stat.) ${}^{+30}_{-21}$ (syst.) MeV and the width of 162 ${}^{+87}_{-45}$ (stat.) ${}^{+66}_{-78}$ (syst.) MeV.

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. Rev. D

A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of 18.5  fb-1. No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, H, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral X particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For X with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically 0.5–200  fb. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of 2–40  cm, the upper limits on the cross section are typically 0.5–3  fb. The above limits are the most stringent on these channels to date.

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.

Chin.Phys.C

Using data samples collected at center-of-mass energies of √s = 4.009, 4.230, 4.260, and 4.360 GeV with the BESIII detector operating at the BEPCII collider, we perform a search for the process e(+)e(−) → γχ(c)J (J=0, 1, 2) and find evidence for e(+)e(−) → γχ(c1) and e(+)e(−) → γχ(c2) with statistical significances of 3.0σ and 3.4σ, respectively. The Born cross sections σ(B)(e(+)e(−) → γχ(c)J), as well as their upper limits at the 90% confidence level (C.L.) are determined at each center-of-mass energy.

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. D

This paper reports a measurement by the T2K experiment of the νμ charged current quasielastic (CCQE) cross section on a carbon target with the off-axis detector based on the observed distribution of muon momentum (pμ) and angle with respect to the incident neutrino beam (θμ). The flux-integrated CCQE cross section was measured to be ⟨σ⟩=(0.83±0.12)×10-38  cm2. The energy dependence of the CCQE cross section is also reported. The axial mass, MAQE, of the dipole axial form factor was extracted assuming the Smith-Moniz CCQE model with a relativistic Fermi gas nuclear model. Using the absolute (shape-only) pμ-cosθμ distribution, the effective MAQE parameter was measured to be 1.26-0.18+0.21  GeV/c2 (1.43-0.22+0.28  GeV/c2).

JHEP

A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. Disappearing tracks are identified as those with little or no associated calorimeter energy deposits and with missing hits in the outer layers of the tracker. The search uses proton-proton collision data recorded at $ \sqrt{s}=8 $ TeV that corresponds to an integrated luminosity of 19.5 fb$^{−1}$. The results of the search are interpreted in the context of the anomaly-mediated supersymmetry breaking (AMSB) model. The number of observed events is in agreement with the background expectation, and limits are set on the cross section of direct electroweak chargino production in terms of the chargino mass and mean proper lifetime. At 95% confidence level, AMSB models with a chargino mass less than 260 GeV, corresponding to a mean proper lifetime of 0.2 ns, are excluded.

Phys. Lett. B

The first measurement of the cross section ratio $\sigma_\mathrm{ t \bar{t} b \bar{b}} / \sigma_\mathrm{ t \bar{t} jj }$ is presented using a data sample corresponding to an integrated luminosity of 19.6 fb$^{-1}$ collected in pp collisions at $\sqrt{s}$ = 8 TeV with the CMS detector at the LHC. Events with two leptons ($\mathrm{e}$ or $\mu$) and four reconstructed jets, including two identified as b quark jets, in the final state are selected. The ratio is determined for a minimum jet transverse momentum $p_\mathrm{T}$ of both 20 and 40 GeV/$c$. The measured ratio is 0.022 $\pm$ 0.003 (stat) $\pm$ 0.005 (syst) for $p_\mathrm{T}$ greater than 20 GeV/$c$. The absolute cross sections $\sigma_\mathrm{ t \bar{t} b \bar{b}}$ and $\sigma_\mathrm{ t \bar{t} jj }$ are also measured. The measured ratio for $p_\mathrm{T}$ greater than 40 GeV/$c$ is compatible with a theoretical quantum chromodynamics calculation at next-to-leading order.

Phys. Rev. Lett.

Two structures are observed close to the kinematic threshold in the Ξb0π- mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0  fb-1, recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content bds are expected in this mass region: the spin-parity JP=(1/2)+ and JP=(3/2)+ states, denoted Ξb′- and Ξb*-. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be m(Ξb′-)-m(Ξb0)-m(π-)=3.653±0.018±0.006  MeV/c2, m(Ξb*-)-m(Ξb0)-m(π-)=23.96±0.12±0.06  MeV/c2, Γ(Ξb*-)=1.65±0.31±0.10  MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of Γ(Ξb′-)<0.08  MeV at 95% confidence level. Relative production rates of these states are also reported.

Phys. Rev. D

The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at center-of-mass energy s=7  TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the midrapidity region using the sequential recombination kT and anti-kT as well as the SISCone jet finding algorithms with several resolution parameters in the range R=0.2–0.6. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum (pT) interval 20