B--Physics in Hadron Colliders

The possibility of exploring the systematics of the spectroscopy, strong dynamics, and the weak and rare decay modes of b--quark systems at hadron colliders such as Fermilab, LHC and SSC, is discussed. A copious yield of $10^{10}$ detected $B$--mesons is readily accessible in a dedicated Fermilab program, and implies a vast array of accessible decay modes, including second order weak processes and $CP$--violation, which will be unavailable elsewhere until the commissioning of LHC or SSC. Kinematic and flavor tagging, utilizing the ``daughter pions'' from resonances, is expected to play a major role in semileptonic weak decay studies and the search for $CP$--violation. Plenary talk, Workshop on $B$ Physics at Hadron Accelerators, Snowmass, Colorado, June 25, 1993; Invited Lecture, TASI, Boulder, Colorado, June 18, 1993.Comment: Fermilab-Pub-93/256-T, 23 pages, Latex file, (171 blocks) 3 figures (charm.eps, beaut.eps, phase.eps

Reconstruction of semileptonically decaying beauty hadrons produced in high energy pp collisions

It is well known that in $b$ hadron decays with a single unreconstructible final state particle, the decay kinematics can be solved up to a quadratic ambiguity, without any knowledge of the $b$ hadron momentum. We present a method to infer the momenta of $b$ hadrons produced in hadron collider experiments using information from their reconstructed flight vectors. Our method is strictly agnostic to the decay itself, which implies that it can be validated with control samples of topologically similar decays to fully reconstructible final states. A multivariate regression algorithm based on the flight information provides a $b$ hadron momentum estimate with a resolution of around 60% which is sufficient to select the correct solution to the quadratic equation in around 70% of cases. This will improve the ability of hadron collider experiments to make differential decay rate measurements with semileptonic $b$ hadron decays.Comment: 18 pages, 17 figures. Updated version to be published in JHE

Data driving the top quark forward--backward asymmetry with a lepton-based handle

We propose that, within the standard model, the correlation between the $t\bar{t}$ forward--backward asymmetry $A_{t\bar t}$ and the corresponding lepton-based asymmetry $A_l$ -- at the differential level -- is strong and rather clean both theoretically and experimentally. Hence a combined measurement of the two distributions as a function of the lepton $p_T$, a direct and experimentally clean observable, would lead to a potentially unbiased and normalization-free test of the standard model prediction. To check the robustness of our proposal we study how the correlation is affected by mis-measurement of the $t\bar t$ system transverse momenta, acceptance cuts, scale dependence and compare the results of MCFM, POWHEG (with & without PYTHIA showering), and SHERPA's CSSHOWER in first-emission mode. We find that the shape of the relative differential distribution $A_{l} (p^{l}_{T}) [A_{t\bar{t}} (p^l_T)]$ is only moderately distorted hence supporting the usefulness of our proposal. Beyond the first emission, we find that the correlation is not accurately captured by lowest-order treatment. We also briefly consider other differential variables such as the system transverse mass and the canonical $t\bar t$ invariant mass. Finally, we study new physics scenarios where the correlation is significantly distorted and therefore can be more readily constrained or discovered using our method.Comment: 27 pages, 12 figure

Constraining new resonant physics with top spin polarisation information

We provide a comprehensive analysis of the power of including top quark-polarisation information to kinematically challenging $t\bar t$ resonance searches, for which ATLAS and CMS start losing sensitivity. Following the general modeling and analysis strategies pursued by the experiments, we analyse the semi-leptonic and the di-lepton $t\bar t$ channels and show that including polarisation information can lead to large improvements in the limit setting procedures with large data sets. This will allow us to set limits for parameter choices where sensitivity from $m(t\bar t)$ is not sufficient. This highlights the importance of spin observables as part of a more comprehensive set of observables to gain sensitivity to BSM resonance searches.Comment: 13 pages, 11 figure

MT2M_{T2} as a probe of CP phase in h→ττh \rightarrow \tau \tau at the LHC

We propose to utilize the transverse mass variable $M_{T2}$ and it's descendant $M_{2Cons}$ for constraining the CP admixture of the tau lepton Yukawa coupling at the LHC. We have considered the tau lepton pair produced from the Higgs boson with each tau decays to a charged pion and a neutrino, $\tau^{\pm} \rightarrow \pi^{\pm} \nu_{\tau}$. Recently, for this channel, the LHC has employed the impact parameter method to measure the CP mixing angle of tau lepton Yukawa coupling with large uncertainty. The observables we propose here can be measured in the lab frame without the impact parameter measurement and in turn, give a complementary probe of the CP admixture of tau lepton Yukawa. The CP mixing angle, with our method, can be constrained up to 17$^{\circ}$ (7$^{\circ}$) with 300 (3000) $fb^{-1}$ of integrated luminosity at the 14 LHC.Comment: 14 pages, 4 figure

Gauge-mediated supersymmetry breaking with generalized messenger sector at LHC

We consider the generalized gauge mediated supersymmetry breaking (GMSB) models with the messenger elds which do not form the complete multiplets of SU(5) GUT symmetry. Such a situation may happen in the anomalous U(1) GUT scenario because the mass spectrum of the superheavy particle does not respect SU(5) GUT symmetry, although the success of the gauge coupling uni cation can be explained. In this paper, we assume that one pair of the messenger elds gives the dominant contribution, and the LHC signature for the two possible messengers, X + X and Q + Q, are examined. We investigate the possibility to measure the deviation from the usual GUT relation of the gaugino masses which is one of the most important features of these scenarios. 1

Measuring superparticle masses at hadron collider using the transverse mass kink

We present a detailed study of the collider observable $m_{T2}$ applied for pair-produced superparticles decaying to visible particles and a pair of invisible lightest supersymmetric particles (LSPs). Analytic expressions of the maximum of $m_{T2}$ over all events ($m_{T2}^{\rm max}$) are derived. It is noticed that if the decay product of each superparticle involves more than one visible particles, $m_{T2}^{\rm max}$ being a function of the {\it trial} LSP mass ${m}_\chi$ has a kink structure at ${m}_\chi=$ true LSP mass, which can be used to determine the mother superparticle mass and the LSP mass simultaneously. To see how well $m_{T2}^{\rm max}$ can be constructed from collider data, a Monte-Carlo analysis of the gluino $m_{T2}$ is performed for some superparticle spectra.Comment: Typos corrected. A few references added. Figures update