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Rare B hadron decays provide an excellent test bench for the Standard Model and can probe new physics models. We review the experimental progress of the searches for rare leptonic B decays ($b\rightarrow \ell^+ \ell^-$ and $b\rightarrow s \ell^+ \ell^-$) at LHC and Tevatron experiments.
High Energy Physics explores the most fundamental questions about the nature of the universe, e.g., basic building blocks of matter and energy, existence of the smallest sub-atomic particles, dark matter, dark energy etc. The Large Hadron Collider (LHC) is the most powerful accelerator on earth located near Geneva, Switzerland. It recreates the conditions just after the Big Bang by colliding two proton beams head-on at very high energy every 25-50 nanosecond. With the recent discovery of Higgs boson, the LHC is firmly marching on to explore the TeV energy scale.
This document provides a brief overview of the recently published report on the design of the Large Hadron Electron Collider (LHeC), which comprises its physics programme, accelerator physics, technology and main detector concepts. The LHeC exploits and develops challenging, though principally existing, accelerator and detector technologies. This summary is complemented by brief illustrations of some of the highlights of the physics programme, which relies on a vastly extended kinematic range, luminosity and unprecedented precision in deep inelastic scattering. Illustrations are provided regarding high precision QCD, new physics (Higgs, SUSY) and eletron-ion physics. The LHeC is designed to run synchronously with the LHC in the twenties and to achieve an integrated luminosity of O(100)fb –1 . It will become the cleanest high resolution microscope of mankind and will substantially extend as well as complement the investigation of the physics of the TeV energy scale, which has been enabled by the LHC.
Here, we describe ultrarelativistic heavy ion collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider with a hybrid model using the IP-Glasma model for the earliest stage and viscous hydrodynamics and microscopic transport for the later stages of the collision. We demonstrate that within this framework the bulk viscosity of the plasma plays an important role in describing the experimentally observed radial flow and azimuthal anisotropy simultaneously. Finally, we further investigate the dependence of observables on the temperature below which we employ the microscopic transport description.
Using samples of 102 million Υ(1S) and 158 million Υ(2S) events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to the threebody final states φK + K, ωπ + π - and K *0 (892)K - π + , and to the two-body Vector-Tensor states (φf' 2 (1525), ωf 2 (1270), ρa 2 (1320) and K *0 (892) $\bar{K}$ *0 2 (1430)) and Axial-vector-Pseudoscalar (K1(1270)+K$-$, K 1 (1400) + K - and b 1 (1235) + π - ) states. Signals are observed for the first time in the Υ(1S) → φK + K - , ωπ + π - , K *0 K - π + , K *0 K *0 2 and Υ(2S) → φK + K - , K *0 K - π + decay modes. Branching fractions are determined for all the processes, while 90% confidence level upper limits are established on the branching fractions for the modes with a statistical significance less than 3σ. The ratios of the branching fractions of Υ(2S) and Υ(1S) decays into the same final state are used to test a perturbative QCD prediction for OZI suppressed bottomonium decays.
Study of the hadronic transitions Y(2S) -> (eta, pi(0))Y(1S) at Belle
In this article we report a measurement of the branching fraction ratios R ( D ( * ) ) of B ¯ → D ( * ) τ - ν ¯ τ relative to B ¯ → D ( * ) ℓ - ν ¯ ℓ (where ℓ = e or μ ) using the full Belle data sample of 772 × 10 6 B B ¯ pairs collected at the Υ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. The measured values are R ( D ) = 0.375 ± 0.064 ( stat ) ± 0.026 ( syst ) and R ( D * ) = 0.293 ± 0.038 ( stat ) ± 0.015 ( syst ) . The analysis uses hadronic reconstruction of the tag-side B meson and purely leptonic τ decays. The results are consistent with earlier measurements and do not show a significant deviation from the standard model prediction.
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In this study, we consider a minimal supersymmetric Standard Model scenario in which the only light superparticles are a binolike dark matter candidate and a nearly degenerate slepton. It is notoriously difficult to probe this scenario at the Large Hadron Collider (LHC), because the slepton pair-production process yields a final state with soft leptons and small missing transverse energy. We study this scenario in the region of parameter space where the mass difference between the lightest neutralino and the lightest slepton ( Δ m ) is ≲ 60 GeV , focusing on the process in which an additional radiated jet provides a transverse boost to the slepton pair. We then utilize the angular separation of the leptons from each other and from the missing transverse energy, as well as the angular separation between the jet and the missing transverse energy, to distinguish signal from background events. We also use the reconstructed ditau mass, the cos θ ℓ 1 ℓ 2 * variable, and for larger Δ m , a lower bound on the lepton p T . These cuts can dramatically improve both signal sensitivity and the signal-to-background ratio, permitting discovery at the LHC with reasonable integrated luminosity over the interesting region of parameter space. Using our search strategy the LHC will be able to exclude m μ ˜ ≈ 200 GeV for Δ m ≲ 60 GeV at 1.5 – 3 σ with 1000 fb - 1 of integrated luminosity. Although we focus on a particular model, the results generalize to a variety of scenarios in which the dark matter and a leptonic partner are nearly degenerate in mass, and especially to scenarios featuring a scalar mediator.
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Holographic QCD is an extra-dimensional approach to modeling QCD resonances and their interactions. Holographic models encode information about chiral symmetry breaking, Weinberg sum rules, vector meson dominance, and other phenomenological features of QCD. There are two complementary approaches to holographic model building: a top-down approach which begins with string-theory brane configurations, and a bottom-up approach which is more phenomenological. In this talk I will describe the techniques used to build holographic models of QCD and the tools used to calculate observables in those models.
Yields, correlation shapes, and mean transverse momenta p{sub T} of charged particles associated with intermediate- to high-p{sub T} trigger particles (2.5 < p{sub T} < 10 GeV/c) in d+ Au and Au + Au collisions at {radical}s{sub NN} = 200 GeV are presented. For associated particles at higher p{sub T} {approx}> 2.5 GeV/c, narrow correlation peaks are seen in d + Au and Au + Au, indicating that the main production mechanism is jet fragmentation. At lower associated particle p{sub T} < 2 GeV/c, a large enhancement of the near-({Delta}{phi}{approx}0) and away-side ({Delta}{phi}{approx}{pi}) associated yields is found, together with a strong broadening of the away-side azimuthal distributions in Au + Au collisions compared to d + Au measurements, suggesting that other particle production mechanisms play a role. This is further supported by the observed significant softening of the away-side associated particle yield distribution at {Delta}{phi}{approx}{pi} in central Au + Au collisions.
A search for the pair production of top squarks, each with R -parity-violating decays into two Standard Model quarks, is performed using 17.4 fb -1 of √s=8 TeV proton-proton collision data recorded by the ATLAS experiment at the LHC. Each top squark is assumed to decay to a b- and an s-quark, leading to four quarks in the final state. Background discrimination is achieved with the use of b-tagging and selections on the mass and substructure of large-radius jets, providing sensitivity to top squark masses as low as 100 GeV. Finally, no evidence of an excess beyond the Standard Model background prediction is observed and top squarks decaying to $\overline{b}$$\overline{s}$ are excluded for top squark masses in the range 100 ≤ m $\overline{t}$ ≤ 315 GeV at 95% confidence level.
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