Top Quark Charge Asymmetry: Searching for Light Axigluons in top pair + jet Production at the LHC

We investigate the discovery potential of light color-octet bosons in the mass range of 100 - 400 GeV in exclusive top-pair plus jet production at the LHC. We study the impact of such bosons on the incline, the energy and the rapidity asymmetries. We show that light axigluons with large couplings to quarks can be discovered at the LHC with a luminosity of a few inverse fb. Almost all of the considered axigluon parameter space can be probed using the already available 2011/2012 LHC data. In a small-coupling scenario, axigluons could be discovered using the charge asymmetry with 65 inverse fb at the LHC and a center of mass energy of 14 TeV. We furthermore show that top pair+jet production could reveal the existence of scenarios where axigluons couple with a different strength to up- and down-type quarks.Comment: 25 pages, 11 figures, 1 tabl

Top-Quark Charge Asymmetry with a Jet Handle

Pairs of top and antitop quarks are produced at the LHC to a large extent in association with a hard jet. We investigate the charge asymmetry in top pair + jet production in quantum chromodynamics (QCD) and with additional massive color-octet vector bosons. The total charge asymmetry at the LHC is suppressed by the large charge-symmetric background from gluon-gluon fusion. We show to what extent the asymmetry can be enhanced by suitable phase space cuts and, in particular, elaborate on the kinematics of the hard jet in the top pair + jet final state. We demonstrate that in QCD, the asymmetry amounts to -1.5% for central jets without an excessive reduction of the cross section. By applying additional kinematical cuts, the asymmetry can be enhanced to -4%, but at the cost of a strong reduction of the cross section. Massive color-octet states can generate sizeable effects in top pair + jet production, both on the charge asymmetry and on the cross section. The charge asymmetry probes both vector and axial-vector couplings to quarks. We show that massive color octets can generate asymmetries up to +-10% for moderate and up to +-30% for strong kinematical cuts to be used in experimental analyses at the LHC. Jet kinematics can be used to obtain further information about the nature of the couplings and thereby to discriminate between different models.Comment: 29 pages, 12 figure

Lepton-mass effects in the decays H→ZZ∗→ℓ+ℓ−τ+τ−H \to ZZ^{\ast} \to \ell^{+} \ell^{-} \tau^{+} \tau^{-} and H→WW∗→ℓντντH \to WW^{\ast} \to \ell \nu \tau \nu_{\tau}

We consider lepton-mass effects in the cascade decays $H\to Z(\to \ell^{+} \ell^{-})+Z^{\ast}(\to \tau^{+}\tau^{-})$ and $H\to W^{-}(\to \ell^{-}\bar \nu_{\ell})+W^{+\ast}(\to \tau^{+}\nu_{\tau})$. Since the scale of the problem is set by the off-shellness $q^{2}$ of the respective gauge bosons in the limits $(m_{\ell}+m_{\ell'})^{2} \le q^{2} \le (m_{H}-m_{W,Z})^{2}$ and not by $m_{W,Z}^{2}$, lepton-mass effects are non-negligible for the $\tau$ modes in particular close to the threshold of the off-shell decays. Lepton-mass effects show up e.g.\ in the three-fold joint angular decay distribution for the decays. Nonzero lepton masses lead to leptonic helicity-flip contributions which in turn can generate novel angular dependencies in the respective three-fold angular decay distributions. Lepton-mass effects are more pronounced in the $H \to Z(\to \ell\ell)Z^{\ast}(\to\tau\tau)$ mode which, in part, is due to the fact that the ratio of lepton helicity flip/nonflip contributions in the decay $Z^{\ast} \to \ell^{+}\ell^{-}$ is four times larger than in the decay $W^{+\ast}\to \ell^{+}\nu$. We also briefly consider the corresponding off-shell -- off-shell decays $H\to Z^{\ast}(\to \ell^{+}\ell^{-})+Z^{\ast}(\to \tau^{+}\tau^{-})$ and $H\to W^{-\ast}(\to \ell^{-}\bar \nu_{\ell})+W^{+\ast}(\to \tau^{+}\nu_{\tau})$.Comment: 45 pages, 9 figures and 6 tables, published versio

MSSM corrections to the top-antitop quark forward-backward asymmetry at the Tevatron

We study the effects of the complete supersymmetric QCD and electroweak one-loop corrections to the ttbar forward-backward asymmetry at the Fermilab Tevatron collider. We work in the complex Minimal Supersymmetric Standard Model (MSSM), only restricted by the condition of minimal flavor violation (MFV). We perform a comprehensive scan over the relevant parameter space of the complex MFV-MSSM and determine the maximal possible contributions of these MSSM loop corrections to the forward-backward asymmetry in the ttbar center-of-mass frame.Comment: 25 pages, 9 figure

q_T Uncertainties for W and Z Production

Analysis of semi-inclusive DIS hadroproduction suggests broadening of transverse momentum distributions at small x below 1E-3 ~ 1E-2 which can be modeled in the Collins-Soper-Sterman formalism by a modification of impact parameter dependent parton densities. We investigate these consequences for the production of electroweak bosons at the Tevatron and the LHC. If substantial small-x broadening is observed in forward Z boson production in the Tevatron Run-2, it will strongly affect the predicted q_T distributions for W and Z boson production at the LHC.Comment: 4 pages, 2 figures; contribution to the XIII International Workshop on Deep Inelastic Scattering (DIS 2005

Determining the CP parity of Higgs bosons at the LHC in the τ\tau to 1-prong decay channels

We propose a method for determining the CP nature of a neutral Higgs boson or spin-zero resonance $\phi$ at the CERN Large Hadron Collider (LHC) in its $\phi\to\tau^{-}\tau^{+}$ decay channel. The method can be applied to any 1-prong $\tau$-decay mode, which comprise the majority of the $\tau$-lepton decays. The proposed observables allow to discriminate between pure scalar and pseudoscalar Higgs-boson states and/or between a CP-conserving and CP-violating Higgs sector. We show for the decays $\tau\to\pi\nu_{\tau}$ that the method maintains its discriminating power when measurement uncertainties are taken into account. The method will be applicable also at a future linear $e^{+}e^{-}$ collider.Comment: Latex, 15 pages, 6 figure