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).

Results of a search for supersymmetry via direct production of third-generation squarks are reported, using 20.3 fb −1 of proton-proton collision data at ffiffi ffi s p ¼ 8 TeV recorded by the ATLAS experiment at the LHC in 2012. Two different analysis strategies based on monojetlike and c-tagged event selections are carried out to optimize the sensitivity for direct top squark-pair production in the decay channel to a charm quark and the lightest neutralino (t 1 → c þχ 0 1 ) across the top squark-neutralino mass parameter space. No excess above the Standard Model background expectation is observed. The results are interpreted in the context of direct pair production of top squarks and presented in terms of exclusion limits in the (m~t 1 , m~χ0 1 ) parameter space. A top squark of mass up to about 240 GeV is excluded at 95% confidence level for arbitrary neutralino masses, within the kinematic boundaries. Top squark masses up to 270 GeV are excluded for a neutralino mass of 200 GeV. In a scenario where the top squark and the lightest neutralino are nearly degenerate in mass, top squark masses up to 260 GeV are excluded. The results from the monojetlike analysis are also interpreted in terms of compressed scenarios for top squark-pair production in the decay channelt 1 → b þ ff 0 þχ 0 1 and sbottom pair production withb 1 → b þχ 0 1 , leading to a similar exclusion for nearly mass-degenerate third-generation squarks and the lightest neutralino. The results in this paper significantly extend previous results at colliders.

No abstract

We propose a new dynamics of the electroweak symmetry breaking in a classically scale invariant version of the standard model. The scale invariance is broken by the condensations of additional fermions under a strong coupling dynamics. The electroweak symmetry breaking is triggered by negative mass squared of the elementary Higgs doublet, which is dynamically generated through the bosonic seesaw mechanism. We introduce a real pseudo-scalar singlet field interacting with additional fermions and Higgs doublet in order to avoid massless Nambu-Goldstone bosons from the chiral symmetry breaking in a strong coupling sector. We investigate the mass spectra and decay rates of these pseudo-Nambu-Goldstone bosons, and show they can decay fast enough without cosmological problems. We further evaluate the energy dependences of the couplings between elementary fields perturbatively, and find that our model is the first one which realizes the flatland scenario with the dimensional transmutation by the strong coupling dynamics. Similarly to the conventional flatland model with Coleman-Weinberg mechanism, the electroweak vacuum in our model is meta-stable.The origin of the electroweak symmetry breaking (EWSB) remains a mystery. In the standard model (SM), the EWSB requires a negative mass squared for the Higgs doublet scalar field, whose magnitude is set by hand. We expect a fundamental theory which naturally gives the negative mass squared with the suitable value. In a model of supersymmetric extension of the SM, the EWSB can be realized by so-called radiative breaking [2]. However, the supersymmetry breaking scale must be high because of no signal of super-particle at any experiments so far. In technicolor (TC) model [1], the Higgs doublet field is no longer an elementary scalar field, and the EWSB is triggered by the techni-fermion condensation under strongly coupled TC gauge interaction. However, the naive TC model, which is just scale up of QCD, has already been excluded by the electroweak precision measurements.Recently, there are a lot of studies of other possibilities to solve the gauge hierarchy problem by imposing a classically scale invariance with an additional U(1) gauge symmetry [3]- [26]. From the viewpoint of Bardeen's argument [27], we can only focus on logarithmic divergences, and the scale invariance protects large Higgs mass corrections. Under the classically scale invariance in terms of the cutoff regularization, the quadratic divergence itself can be subtracted by a boundary condition of the UV complete theory [8]. Once we subtract the quadratic divergence from the theory, it never appears in the observables. In the model with an additional U(1) gauge symmetry, the scale invariance is broken by the Coleman-Weinberg mechanism [28], and if the breaking scale is not so far from the electroweak (EW) scale, there is no gauge hierarchy problem. On the other hand, a strong coupling dynamics can also realize such an EWSB with classically scale invariance [29,30], where an additional singlet scalar mediates dimensio...