Future Colliders

Abstract:

This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4:7 fb–1of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at √s = 7 TeV. Final states containing one or two isolated leptons (electrons or muons) and jets are considered. Two measurements of αℓP, the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a CP conserving or a maximally CP violating production process. The measurements obtained, αℓPCPC=–0.035 ± 0.014(stat) ± 0:037(syst) and αℓPCPV= 0.020 ± 0:016(stat)+0.013–0.017(syst), are in good agreement with the standard model prediction of negligible top quark polarization.

Abstract:

Characteristics of multi-particle production in proton-proton collisions at √s = 7 TeV are studied as a function of the charged-particle multiplicity, N ch. The produced particles are separated into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity {pipe}η{pipe}<2.4 and transverse momentum p T>0.25 GeV/c. Jets are reconstructed from charged-particles only and required to have p T>5 GeV/c. The distributions of jet p T, average p T of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of N ch and compared to the predictions of the pythia and herwig event generators. Predictions without multi-parton interactions fail completely to describe the N ch-dependence observed in the data. For increasing N ch, pythia systematically predicts higher jet rates and harder p T spectra than seen in the data, whereas herwig shows the opposite trends. At the highest multiplicity, the data-model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients. © 2013 CERN for the benefit of the CMS collaboration.

Abstract:

We report on recent measurements made at FACET by the E-203 collaboration to test a longitudinal bunch profile monitor based on Coherent Smith-Purcell radiation. The capacity of this monitor to resolve sub-picosecond bunches will be shown as well as a comparison of profile reconstructed for different data sets. We also present recent electromagnetic simulations of the interactions between the beam and the grating as well as the expected resolution of such monitor with a "notch collimator".

Abstract:

The potential of Coherent Smith-Purcell radiation as a longitudinal bunch profile monitor has already been demonstrated and has recently been extended to the sub-picosecond range. As a critical step toward the construction of a single shot bunch profile monitor using Coherent Smith-Purcell radiation it is important to measure very accurately the distribution of such radiation. Optimum background suppression techniques need to be found and relatively cheap detectors suitable for the far infra-red need to be qualified. To perform these tasks a test stand has been installed at the end of the linac of the synchrotron SOLEIL. This test stand and the first results from its commissioning will be presented here.

Abstract:

This paper presents a search for the pair production of top squarks in events with a single isolated electron or muon, jets, large missing transverse momentum, and large transverse mass. The data sample corresponds to an integrated luminosity of 19.5 fb-1 of pp collisions collected in 2012 by the CMS experiment at the LHC at a center-of-mass energy of √s = 8 TeV. No significant excess in data is observed above the expectation from standard model processes. The results are interpreted in the context of supersymmetric models with pair production of top squarks that decay either to a top quark and a neutralino or to a bottom quark and a chargino. For small mass values of the lightest supersymmetric particle, top-squark mass values up to around 650 GeV are excluded. © 2013 CERN for the benefit of the CMS collaboration.