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Register a new userPrecision Measurements of the Stop Quark Mass at the ILC
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Most supersymmetric models predict new particles within the reach of the next generation of colliders. For an understanding of the model structure and the mechanism(s) of electroweak symmetry breaking, it is important to know the masses of the new particles precisely. The measurement of the mass of the scalar partner of the top quark (stop) at an e+e- collider is studied. A relatively light stop is motivated by attempts to explain electroweak baryogenesis and can play an important role in dark matter annihilation. A method is presented which makes use of cross-section measurements near the pair-production threshold as well as at higher center-of-mass energies. It is shown that this method does not only increase the statistical precision, but also reduces the influence of systematic uncertainties, which can be important. Numerical results are presented, based on a realistic event simulation, for two signal selection strategies: using conventional selection cuts, and using an Iterative Discriminant Analysis (IDA). While the analysis of stops is particularly challenging due to the possibility of stop hadronization and fragmentation, the general procedure could be applied to many precision mass measurements.
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We present a precision measurement of the top-quark mass using the full sample of Tevatron $sqrt{s}=1.96$ TeV proton-antiproton collisions collected by the CDF II detector, corresponding to an integrated luminosity of 8.7 $fb^{-1}$. Using a sample of $tbar{t}$ candidate events decaying into the lepton+jets channel, we obtain distributions of the top-quark masses and the invariant mass of two jets from the $W$ boson decays from data. We then compare these distributions to templates derived from signal and background samples to extract the top-quark mass and the energy scale of the calorimeter jets with {it in situ} calibration. The likelihood fit of the templates from signal and background events to the data yields the single most-precise measurement of the top-quark mass, $mtop = 172.85 $pm$ 0.71 (stat) $pm$ 0.85 (syst) GeV/c^{2}.$
This note presents an analysis of the potential of future high-energy electron-positron colliders to measure the $b$-quark mass. We perform a full-simulation study of the measurement of the ratio of the three-jet rates in events with $bbar{b}(g)$ and $qbar{q}(g)$ production, $R_{3}^{bl}$, and assess the dominant uncertainties, including theory and experimental systematic uncertainties. We find that the ILC Higgs factory stage, with an integrated luminosity of 2 ab$^{-1}$ at $sqrt{s}=$ 250 GeV can measure the $b-$quark $bar{MS}$ mass at a scale of 250 GeV ($m_b(250~$GeV$)$) with a precision of 1 GeV. From this result we extrapolate the potential of the GigaZ run running at $sqrt{s}= m_Z$. We expect $m_b(m_Z)$ can be determined with an 0.12 GeV uncertainty, exceeding the precision of the LEP and SLD measurements by a factor $sim$3.
We present measurements of the top quark mass based on 3.6 fb^-1 of data collected by the D0 experiment during Run II of the Fermilab Tevatron collider. We present results in the dilepton and lepton+jets final states. We also present the measurement of the mass difference between t and tbar quarks observed in lepton+jets final states of ttbar events in 1 fb^-1 of data.
The discovery of the stop - the Supersymmetric partner of the top quark - is a key goal of the physics program enabled by the Large Hadron Collider. Although much of the accessible parameter space has already been probed, all current searches assume the top mass is known. This is relevant for the stealth stop regime, which is characterized by decay kinematics that force the final state top quark off its mass shell; such decays would contaminate the top mass measurements. We investigate the resulting bias imparted to the template method based ATLAS approach. A careful recasting of these results shows that effect can be as large as 2.0 GeV, comparable to the current quoted uncertainty on the top mass. Thus, a robust exploration of the stealth stop splinter requires the simultaneous consideration of the impact on the top mass. Additionally, we explore the robustness of the template technique, and point out a simple strategy for improving the methodology implemented for the semi-leptonic channel.
In these proceedings a novel approach to deal with the beam-induced effects in luminosity measurement is presented. Based on the relativistic kinematics of the collision frame of the Bhabha process, the beam-beam related uncertainties can be reduced to the permille level independently of a precision with which the beam parameters are known. Specific event selection combined with the corrective methods we introduce, leads to the systematic uncertainty from the beam-induced effects to be at a few permille level in the peak region above the 80% of the nominal centre-of-mass energies at ILC.
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