Outbursts of EX Hydrae Revisited

We present optical spectroscopy of EX Hya during its 1991 outburst. This outburst is characterised by strong irradiation of the front face of the secondary star by the white dwarf, an overflowing stream which is seen strongly in HeII and by a dip in the light curves, which extends from 0.1-0.6 in the binary and spin phases. Strong irradiation of the accretion curtain and that of the inner regions of the disc led to strong emission of HeII and to the suppression of the Hg and Hb emission. Disc overflow was observed in quiescence in earlier studies, where the overflow stream material was modulated at high velocities close to 1000 km/s. In outburst, the overflowing material is modulated at even higher velocities (~1500 km/s). These are streaming velocities down the field lines close to the white dwarf. Evidence for material collecting near the outer edge of the disc and corotating with the accretion curtain was observed. In decline, this material and the accretion curtain obscured almost all the emission near binary phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse minimum. This has provided additional evidence for an extended accretion curtain, and for the corotation of material with the accretion curtain at the outer edge of the disc. From these observations we suggest that a mechanism similar to that of Spruit & Taam, where outbursts result due to the storage and release of matter outside the magnetosphere, triggers the outbursts of EX Hya. This is followed by the irradiation of the secondary star due to accretion induced radiation.Comment: 12 pages, 14 figures, 1 table. Figures 6, 7, 8 and 11 at low resolution. Paper accepted by the Monthly Notices of the Royal Astronomical Societ

The masses of the cataclysmic variables AC Cancri and V363 Aurigae

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variables AC Cnc and V363 Aur (= Lanning 10). There is evidence of irradiation on the inner hemisphere of the secondary star in both systems, which we correct for using a model that reproduces the observations remarkably well. We find the radial velocity of the secondary star in AC Cnc to be KR= 176 ± 3 km s−1 and its rotational velocity to be v sin i= 135 ± 3 km s−1. From these parameters we obtain masses of M1= 0.76 ± 0.03 M⊙ for the white-dwarf primary and M2= 0.77 ± 0.05 M⊙ for the K2 ± 1V secondary star, giving a mass ratio of q= 1.02 ± 0.04. We measure the radial and rotational velocities of the G7 ± 2V secondary star in V363 Aur to be KR= 168 ± 5 km s−1 and v sin i= 143 ± 5 km s−1, respectively. The component masses of V363 Aur are M1= 0.90 ± 0.06 M⊙ and M2= 1.06 ± 0.11 M⊙, giving a mass ratio of q= 1.17 ± 0.07. The mass ratios for AC Cnc and V363 Aur fall within the theoretical limits for dynamically and thermally stable mass transfer. Both systems are similar to the SW Sex stars, exhibiting single-peaked emission lines with transient absorption features, high-velocity S-wave components and phase-offsets in their radial-velocity curves. The Balmer lines in V363 Aur show a rapid increase in flux around phase 0 followed by a rapid decrease, which we attribute to the eclipse of an optically thick region at the centre of the disc. This model could also account for the behaviour of other SW Sex stars where the Balmer lines show only a shallow eclipse compared to the continuum

The component masses of the cataclysmic variable V347 Puppis

We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of KR= 198 ± 5 km s−1. The rotational velocity of the secondary star in V347 Pup is found to be v sin i= 131 ± 5 km s−1 and the system inclination is i= 840 ± 23. From these parameters we obtain masses of M1= 0.63 ± 0.04 M⊙ for the white dwarf primary and M2= 0.52 ± 0.06 M⊙ for the M0.5V secondary star, giving a mass ratio of q= 0.83 ± 0.05. On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc

Study of the B +→ J / ψ Λ ¯ p decay in proton-proton collisions at √s = 8 TeV

A study of the B +→ J / ψ Λ ¯ p decay using proton-proton collision data collected at s = 8 TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.6 fb−1, is presented. The ratio of branching fractions B(B+→J/ψΛ¯p)/B(B+→J/ψK∗(892)+) is measured to be (1.054 ± 0.057(stat) ± 0.035(syst) ± 0.011(B))%, where the last uncertainty reflects the uncertainties in the world-average branching fractions of Λ ¯ and K*(892) + decays to reconstructed final states. The invariant mass distributions of the J / ψ Λ ¯ , J/ψp, and Λ ¯ p systems produced in the B +→ J / ψ Λ¯ p decay are investigated and found to be inconsistent with the pure phase space hypothesis. The analysis is extended by using a model-independent angular amplitude analysis, which shows that the observed invariant mass distributions are consistent with the contributions from excited kaons decaying to the Λ ¯ p system. [Figure not available: see fulltext.

Measurement of the top quark Yukawa coupling from t t kinematic distributions in the lepton+jets final state in proton-proton collisions at s =13 TeV MEASUREMENT of the TOP QUARK YUKAWA COUPLING from ... SIRUNYAN et al.

Results are presented for an extraction of the top quark Yukawa coupling from top quark-antiquark (tt) kinematic distributions in the lepton plus jets final state in proton-proton collisions, based on data collected by the CMS experiment at the LHC at s=13 TeV, corresponding to an integrated luminosity of 35.8 fb-1. Corrections from weak boson exchange, including Higgs bosons, between the top quarks can produce large distortions of differential distributions near the energy threshold of tt production. Therefore, precise measurements of these distributions are sensitive to the Yukawa coupling. Top quark events are reconstructed with at least three jets in the final state, and a novel technique is introduced to reconstruct the tt system for events with one missing jet. This technique enhances the experimental sensitivity in the low invariant mass region, Mtt. The data yields in Mtt, the rapidity difference |yt-yt|, and the number of reconstructed jets are compared with distributions representing different Yukawa couplings. These comparisons are used to measure the ratio of the top quark Yukawa coupling to its standard model predicted value to be 1.07-0.43+0.34 with an upper limit of 1.67 at the 95% confidence level

Search for new neutral Higgs bosons through the H → ZA→ ℓ+ℓ−b b ¯ process in pp collisions at √s = 13 TeV

This paper reports on a search for an extension to the scalar sector of the standard model, where a new CP-even (odd) boson decays to a Z boson and a lighter CP-odd (even) boson, and the latter further decays to a b quark pair. The Z boson is reconstructed via its decays to electron or muon pairs. The analysed data were recorded in proton-proton collisions at a center-of-mass energy s = 13 TeV, collected by the CMS experiment at the LHC during 2016, corresponding to an integrated luminosity of 35.9 fb−1. Data and predictions from the standard model are in agreement within the uncertainties. Upper limits at 95% confidence level are set on the production cross section times branching fraction, with masses of the new bosons up to 1000 GeV. The results are interpreted in the context of the two-Higgs-doublet model. [Figure not available: see fulltext.]