Measurement of the CP-violating weak phase φs and the decay width difference δΓc using the Bs 0→J/ψφ(1020) decay channel in pp collisions at √ s=8 TeV

The CP-violating weak phase ϕsϕs of the View the MathML sourceBs0 meson and the decay width difference ΔΓsΔΓs of the View the MathML sourceBs0 light and heavy mass eigenstates are measured with the CMS detector at the LHC using a data sample of View the MathML sourceBs0→J/ψϕ(1020)→μ+μ−K+K− decays. The analysed data set corresponds to an integrated luminosity of View the MathML source19.7fb−1 collected in pp collisions at a centre-of-mass energy of View the MathML source8TeV. A total of 49 200 reconstructed View the MathML sourceBs0 decays are used to extract the values of ϕsϕs and ΔΓsΔΓs by performing a time-dependent and flavour-tagged angular analysis of the μ+μ−K+K−μ+μ−K+K− final state. The weak phase is measured to be View the MathML sourceϕs=−0.075±0.097(stat)±0.031(syst) rad, and the decay width difference is View the MathML sourceΔΓs=0.095±0.013(stat)±0.007(syst) ps−1

Contrasting H-mode behaviour with deuterium fuelling and nitrogen seeding in the all-carbon and metallic versions of JET

The former all-carbon wall on JET has been replaced with beryllium in the main torus and tungsten in the divertor to mimic the surface materials envisaged for ITER. Comparisons are presented between type I H-mode characteristics in each design by examining respective scans over deuterium fuelling and impurity seeding, required to ameliorate exhaust loads both in JET at full capability and in ITER. Attention is focused upon a common high-triangularity, single-null divertor configuration at 2.5 MA, q 95 ≈ 3.5 yielding the most robust all-C performance. Contrasting results between the alternative linings are found firstly in unseeded plasmas, for which purity is improved and intrinsic radiation reduced in the ITER-like wall (ILW) but normalized energy confinement is ≈30% lower than in all-C counterparts, owing to a commensurately lower (electron) pedestal temperature. Divertor recycling is also radically altered, with slower, inboard/outboard asymmetric transients at ELMs and spontaneous oscillations in between them. Secondly, nitrogen seeding elicits opposite responses in the ILW to all-C experience, tending to raise plasma density, reduce ELM frequency, and above all to recover (electron) pedestal pressure, hence global confinement, almost back to previous levels. A hitherto unrecognized role of light impurities in pedestal stability and dynamics is consequently suggested. Thirdly, while heat loads on the divertor outboard target between ELMs are successfully reduced in proportion to the radiative cooling and ELM frequency effects of N in both wall environments, more surprisingly, average power ejected by ELMs also declines in the same proportion for the ILW. Detachment between transients is simultaneously promoted. Finally, inter-ELM W sources in the ILW divertor tend to fall with N input, although core accumulation possibly due to increased particle confinement still leads to significantly less steady conditions than in all-C plasmas. This limitation of ILW H-modes so far will be readdressed in future campaigns to continue progress towards a fully integrated scenario suitable for D T experiments on JET and for ‘baseline’ operation on ITER. The diverse changes in behaviour between all-C and ILW contexts demonstrate essentially the strong impact which boundary conditions and intrinsic impurities can have on tokamak-plasma states