119241450
Edge Charge Asymmetry in Top Pair Production at the LHC
In this brief report, we propose a new definition of charge asymmetry in top pair production at the LHC, namely the edge charge asymmetry (ECA). ECA utilizes the information of drifting direction only for single top (or anti-top) with hadronically decay. Therefore ECA can be free from the uncertainty arising from the missing neutrino in the tt̄ event reconstruction. Moreover rapidity Y of top (or anti-top) is required to be greater than a critical value YC in order to suppress the symmetric tt̄ events mainly due to the gluongluon fusion process. In this paper ECA is calculated up to next-to-leading order QCD in the standard model and the choice of the optimal YC is investigated. ∗ E-mail:homenature@pku.edu.cn † E-mail:wangyk@pku.edu.cn ‡ E-mail:zhongqiu zhou@pku.edu.cn § E-mail:shzhu@pku.edu.cn
119282423
New color-octet axial vector boson revisited
In this paper we reexamine how to utilize the previous proposed color-octet axial-vector boson Z(C) to explain the 3: 4 sigma anomaly of t (t) over bar forward-backward (FB) asymmetry A(FB) for m(t (t) over bar) > 450 GeV observed by CDF. Our numerical results indicate that the best-fit parameters are g(A)(q) = 0: 07, g(A)(Q) 3, and M(C) 440 GeV, which are obtained by fitting the mass dependent AFB and total cross section data provided by a recent CDF measurement. Here g(A)(q) (g(A)(Q)) and MC are the axial couplings among Z(C) with the first two (the third) generation quarks, and Z(C) mass, respectively. We also calculate one-side forward-backward asymmetry AOFB for top and bottom quark pair production at the LHC, focusing on the new contributions from Z(C). Our studies show that AOFB can be utilized to measure the properties of new particle Z(C).
118863203
One-side forward-backward asymmetry in top quark pair production at the CERN Large Hadron Collider
Both D0 and CDF at Tevatron reported the measurements of forward-backward asymmetry in top pair production, which showed possible deviation from the standard model QCD prediction. In this paper, we explore how to examine the same higher-order QCD effects at the more powerful Large Hadron Collider.
118431292
One-side forward-backward asymmetry at the LHC
Forward-backward asymmetry AFB is an essential observable to study the nature of coupling in the standard model and physics beyond the standard model, as shown at LEP and Tevatron. As a proton-proton collider, the LHC does not have the preferred direction contrary to her counterpart, namely, LEP and Tevatron. Therefore AFB is not applicable at the LHC. However for the proton the momentum of valence quark is usually larger than that of the sea quark. Utilizing this feature we have defined a so-called one-side forward-backward asymmetry AOFB for the top quark pair production at LHC in the previous work. In this paper we extend our studies to the charged leptons and bottom quarks as the final states. Our numerical results show that at the LHC AOFB can be utilized to study the nature of the couplings once enough events are collected.
118168382
First observation of the isospin violating decay $J/\psi\rightarrow \Lambda\bar{\Sigma}^{0}+c.c.$
Using a sample of $(225.2\pm 2.8)\times 10^6$ $J/\psi$ events collected with the BESIII detector, we present results of a study of $J/\psi\rightarrow \gamma\Lambda\bar{\Lambda}$ and report the first observation of the isospin violating decay $J/\psi\rightarrow\Lambda\bar{\Sigma}^{0}+c.c.$, in which $\bar{\Sigma}^{0}$ decays to $\gamma \bar{\Lambda}$. The measured branching fractions are $\mathcal{B}(J/\psi\rightarrow\bar{\Lambda}\Sigma^{0}$) = $(1.46\pm0.11\pm0.12) \times10^{-5}$ and $\mathcal{B}(J/\psi\rightarrow\Lambda\bar{\Sigma^{0}}$) = $(1.37\pm0.12\pm0.11) \times10^{-5}$. We search for $\Lambda(1520) \rightarrow \gamma \Lambda$ decay, and find no evident signal, and an upper limit for the product branching fraction $\mathcal{B}(J/\psi\rightarrow\Lambda\bar{\Lambda}(1520)+c.c.)\times \mathcal{B}(\Lambda(1520)\rightarrow\gamma\Lambda)<4.1 \times10^{-6}$ is set at the 90% confidence level. We also report the observation of $\eta_{c}\rightarrow\Lambda\bar{\Lambda}$ in $J/\psi \rightarrow \gamma \eta_{c}$, $\eta_{c}\rightarrow\Lambda\bar{\Lambda}$ and measure the branching fraction $\mathcal{B}(\eta_{c}\rightarrow\Lambda\bar{\Lambda}) =(1.16\pm0.12 (stat)\pm0.19(syst)\pm0.28(PDG))\times10^{-3}$.
118521922
Implications of LHCb measurements and future prospects
During 2011 the LHCb experiment at CERN collected 1.0 fb−1 of $\sqrt{s} = 7\mbox{~TeV}$pp collisions. Due to the large heavy quark production cross-sections, these data provide unprecedented samples of heavy flavoured hadrons. The first results from LHCb have made a significant impact on the flavour physics landscape and have definitively proved the concept of a dedicated experiment in the forward region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.
42445249
Hadron collider signatures for new interactions of top and bottom quarks
One of the main goals for hadron colliders is the study of the properties of the third generation quarks. We study the signatures for new TeV resonances that couple to top or bottom quarks both at the Tevatron Run II and at the CERN LHC. We find that in the simplest production processes of Drell-Yan type at the Tevatron, the signals are overwhelmed by QCD backgrounds. We also find that it is possible to study these resonances when they are produced in association with a pair of heavy quarks or in association with a single top at the LHC. In particular, with an integrated luminosity of 300 fb(-1) at the LHC, it is possible to probe resonance masses up to around 2 TeV.
119253997
Constraints on flavor-changing neutral-current $Htq$ couplings from the signal of $tH$ associated production with QCD next-to-leading order accuracy at the LHC
We study a generic Higgs boson and a top quark associated production via model-independent flavor-changing neutral-current couplings at the LHC, including complete QCD next-to-leading order (NLO) corrections to the production and decay of the top quark and the Higgs boson. We find that QCD NLO corrections can increase the total production cross sections by about 48.9% and 57.9% for the Htu and Htc coupling induced processes at the LHC, respectively. After kinematic cuts are imposed on the decay products of the top quark and the Higgs boson, the QCD NLO corrections are reduced to 11% for the Htu coupling induced process and almost vanish for the Htc coupling induced process. Moreover, QCD NLO corrections reduce the dependence of the total cross sections on the renormalization and factorization scales. We also discuss signals of the
119239060
Hidden conformal symmetry of the Kerr-Newman black hole
We investigate the hidden conformal symmetry of the 4-dimensional non-extremal Kerr-Newman (KN) black hole with the idea of the near-region Kerr/CFT correspondence proposed by Castro, Maloney and Strominger in arXiv:1004.0996[hep-th]. The near-region KN black hole is dual to a 2D CFT with left and right temperatures TL = (2M2 − Q2)/(4πJ) and $ {T_R} = {{{\sqrt {{{M^4} - {J^2} - {M^2}{Q^2}}} }} \left/ {{\left( {2\pi J} \right)}} \right.} $. Furthermore, we reproduce the microscopic entropy of the KN black hole via the Cardy formula, which is in agreement with the macroscopic Bekenstein-Hawking entropy and precisely match the absorption cross section of a near-region scalar field in the KN black hole with the finite-temperature absorption cross section for a 2D CFT.