Observation of Electromagnetic Dalitz decays J/ψ\to P e^+e^-

Based on a sample of (225.3\pm2.8)\times 10^{6} J/\psi events collected with the BESIII detector, the electromagnetic Dalitz decays of J/\psi \to P e^+e^-(P=\eta'/\eta/\pi^0) are studied. By reconstructing the pseudoscalar mesons in various decay modes, the decays J/\psi \to \eta' e^+e^-, J/\psi \to \eta e^+e^- and J/\psi \to \pi^0 e^+e^- are observed for the first time. The branching fractions are determined to be \mathcal{B}(J/\psi\to \eta' e^+e^-) = (5.81\pm0.16\pm0.31)\times10^{-5}, \mathcal{B}(J/\psi\to \eta e^+e^-) = (1.16\pm0.07\pm0.06)\times10^{-5}, and \mathcal{B}(J/\psi\to \pi^0 e^+e^-)=(7.56\pm1.32\pm0.50)\times10^{-7}, where the first errors are statistical and the second ones systematic

Charge and frequency resolved isochronous mass spectrometry and the mass of 51 Co

Revolution frequency measurements of individual ions in storage rings require sophisticated timing detectors. One of common approaches for such detectors is the detection of secondary electrons released from a thin foil due to penetration of the stored ions. A new method based on the analysis of intensities of secondary electrons was developed which enables determination of the charge of each ion simultaneously with the measurement of its revolution frequency. Although the mass-over-charge ratios of 51 Co 27+ and 34 Ar 18+ ions are almost identical, and therefore, the ions cannot be resolved in a storage ring, by applying the new method the mass excess of the short-lived 51 Co is determined for the first time to be <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">ME</mi></mrow><mo stretchy="false">(</mo><mmultiscripts><mrow><mi mathvariant="normal">Co</mi></mrow><mprescripts/><none/><mrow><mn>51</mn></mrow></mmultiscripts><mo stretchy="false">)</mo><mo>=</mo><mo>−</mo><mn>27</mn><mspace width="0.2em"/><mn>342</mn><mo stretchy="false">(</mo><mn>48</mn><mo stretchy="false">)</mo><mtext> keV</mtext></math> . Shell-model calculations in the fp -shell nuclei compared to the new data indicate the need to include isospin-nonconserving forces

Search for B decays to final states with the η c meson

We report a search for B decays to selected final states with the η c meson: B ± → K ± η c π + π − , B ± → K ± η c ω , B ± → K ± η c η and B ± → K ± η c π 0 . The analysis is based on 772 × 10 6 B B ¯ $$B\overline{B}$$ pairs collected at the Υ(4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. We set 90% confidence level upper limits on the branching fractions of the studied B decay modes, independent of intermediate resonances, in the range (0 . 6–5 . 3) × 10 −4 . We also search for molecular-state candidates in the D 0 D ¯ ∗ 0 − D ¯ 0 D ∗ 0 , D 0 D ¯ 0 + D ¯ 0 D 0 $${D}^0{\overline{D}}^{\ast 0}-{\overline{D}}^0{D}^{\ast 0},{D}^0{\overline{D}}^0+{\overline{D}}^0{D}^0$$ and D ∗ 0 D ¯ ∗ 0 + D ¯ ∗ 0 D ∗ 0 $${D}^{\ast 0}{\overline{D}}^{\ast 0}+{\overline{D}}^{\ast 0}{D}^{\ast 0}$$ combinations, neutral partners of the Z (3900) ± and Z (4020) ± , and a poorly understood state X (3915) as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range (0 . 6–6 . 9) × 10 −5

Measurement of branching fractions for B J / K decays and search for a narrow resonance in the J / final state

We report an observation of the and decays using pairs collected at the resonance with the Belle detector at the KEKB asymmetric-energy collider. We obtain the branching fractions and . We search for a new narrow charmonium(-like) state in the mass spectrum and find no significant excess. We set upper limits on the product of branching fractions, , at where a -odd partner of may exist, at and assuming their known mass and width, and over a range from 3.8 to . The obtained upper limits at 90 confidence level for , , and are , , and , respectively

First results from the DarkSide-50 dark matter experiment at Laboratori Nazionali del Gran Sasso

We report the first results of DarkSide-50, a direct search for dark matter operating in the underground Laboratori Nazionali del Gran Sasso (LNGS) and searching for the rare nuclear recoils possibly induced by weakly interacting massive particles (WIMPs). The dark matter detector is a Liquid Argon Time Projection Chamber with a (46.4±0.7) kg active mass, operated inside a 30 t organic liquid scintillator neutron veto, which is in turn installed at the center of a 1 kt water Cherenkov veto for the residual flux of cosmic rays. We report here the null results of a dark matter search for a (1422±67) kgd exposure with an atmospheric argon fill. This is the most sensitive dark matter search performed with an argon target, corresponding to a 90% CL upper limit on the WIMP-nucleon spin-independent cross section of 6.1×10−44 cm2 for a WIMP mass of 100 Gev/c2

Bose–Einstein correlations in hadron-pairs from lepto-production on nuclei ranging from hydrogen to xenon

Bose–Einstein correlations of like-sign charged hadrons produced in deep-inelastic electron and positron scattering are studied in the HERMES experiment using nuclear targets of 1 H, 2 H, 3 He, 4 He, N, Ne, Kr, and Xe. A Gaussian approach is used to parametrize a two-particle correlation function determined from events with at least two charged hadrons of the same sign charge. This correlation function is compared to two different empirical distributions that do not include the Bose–Einstein correlations. One distribution is derived from unlike-sign hadron pairs, and the second is derived from mixing like-sign pairs from different events. The extraction procedure used simulations incorporating the experimental setup in order to correct the results for spectrometer acceptance effects, and was tested using the distribution of unlike-sign hadron pairs. Clear signals of Bose–Einstein correlations for all target nuclei without a significant variation with the nuclear target mass are found. Also, no evidence for a dependence on the invariant mass W of the photon-nucleon system is found when the results are compared to those of previous experiments

The DarkSide Multiton Detector for the Direct Dark Matter Search

Although the existence of dark matter is supported by many evidences, based on astrophysical measurements, its nature is still completely unknown. One major candidate is represented by weakly interacting massive particles (WIMPs), which could in principle be detected through their collisions with ordinary nuclei in a sensitive target, producing observable low-energy (<100 keV) nuclear recoils. The DarkSide program aims at the WIPMs detection using a liquid argon time projection chamber (LAr-TPC). In this paper we quickly review the DarkSide program focusing in particular on the next generation experiment DarkSide-G2, a 3.6-ton LAr-TPC. The different detector components are described as well as the improvements needed to scale the detector from DarkSide-50 (50 kg LAr-TPC) up to DarkSide-G2. Finally, the preliminary results on background suppression and expected sensitivity are presented

Spin density matrix elements in exclusive ω electroproduction on 1 H and 2 H targets at 27.5 GeV beam energy

Exclusive electroproduction of <math><mi mathvariant="italic">ω</mi></math> mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of <math><mrow><msup><mi>Q</mi><mn>2</mn></msup><mo>&gt;</mo><mn>1.0</mn></mrow></math>  GeV <math><msup><mrow/><mn>2</mn></msup></math> , 3.0 GeV  <math><mrow><mo>&lt;</mo><mi>W</mi><mo>&lt;</mo></mrow></math>  6.3 GeV, and <math><mrow><mo>-</mo><msup><mi>t</mi><mo>′</mo></msup><mo>&lt;</mo><mn>0.2</mn></mrow></math>  GeV <math><msup><mrow/><mn>2</mn></msup></math> . Results on the angular distribution of the <math><mi mathvariant="italic">ω</mi></math> meson, including its decay products, are presented. The data were accumulated with the HERMES forward spectrometer during the 1996–2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of <math><msup><mi>Q</mi><mn>2</mn></msup></math> or <math><mrow><mo>-</mo><msup><mi>t</mi><mo>′</mo></msup></mrow></math> . Violation of <math><mi>s</mi></math> -channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse <math><mi mathvariant="italic">ω</mi></math> production by longitudinal and transverse virtual photons, <math><mrow><msubsup><mi mathvariant="italic">γ</mi><mi>L</mi><mrow><mrow/><mo>∗</mo></mrow></msubsup><mo stretchy="false">→</mo><msub><mi mathvariant="italic">ω</mi><mi>T</mi></msub></mrow></math> and <math><mrow><msubsup><mi mathvariant="italic">γ</mi><mi>T</mi><mrow><mrow/><mo>∗</mo></mrow></msubsup><mo stretchy="false">→</mo><msub><mi mathvariant="italic">ω</mi><mi>T</mi></msub></mrow></math> , is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the <math><mrow><msubsup><mi mathvariant="italic">γ</mi><mi>T</mi><mo>∗</mo></msubsup><mo stretchy="false">→</mo><msub><mi mathvariant="italic">ω</mi><mi>T</mi></msub></mrow></math> transition dominates over the two natural-parity-exchange amplitudes describing the <math><mrow><msubsup><mi mathvariant="italic">γ</mi><mi>L</mi><mo>∗</mo></msubsup><mo stretchy="false">→</mo><msub><mi mathvariant="italic">ω</mi><mi>L</mi></msub></mrow></math> and <math><mrow><msubsup><mi mathvariant="italic">γ</mi><mi>T</mi><mo>∗</mo></msubsup><mo stretchy="false">→</mo><msub><mi mathvariant="italic">ω</mi><mi>T</mi></msub></mrow></math> transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity

Search for exclusive photoproduction of Zc± (3900) at COMPASS

A search for the exclusive production of the Zc±(3900) hadron by virtual photons has been performed in the channel Zc±(3900)→J/ψπ± . The data cover the range from 7 GeV to 19 GeV in the centre-of-mass energy of the photon–nucleon system. The full set of the COMPASS data set collected with a muon beam between 2002 and 2011 has been used. An upper limit for the ratio BR(Zc±(3900)→J/ψπ±)×σγN→Zc±(3900)N/σγN→J/ψN of 3.7×10−3 has been established at the confidence level of 90%

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise