14,481 research outputs found
Recent results on Top quark Physics with the ATLAS and CMS experiments
An overview of the most recent results on top quark physics obtained using
proton-proton collision data collected with the ATLAS and the CMS experiments
at 7 TeV center-of-mass energy is given. Measurements for inclusive and
differential top quark pair or single top quark production in different final
states are reviewed. Top properties such as W helicity in top decays, electric
charge, charge asymmetry and spin correlations of top quark pairs, among others
have also been measured by the LHC experiments. All the measurements are found
to be consistent with the Standard Model predictions with a good level of
accuracy. The latest results in the measurement of the top quark mass at the
LHC are also presented and discussed.Comment: Contribution to the proceedings the 47th Rencontres de Moriond
Electroweak session 201
INFN What Next: Ultra-relativistic Heavy-Ion Collisions
This document was prepared by the community that is active in Italy, within
INFN (Istituto Nazionale di Fisica Nucleare), in the field of
ultra-relativistic heavy-ion collisions. The experimental study of the phase
diagram of strongly-interacting matter and of the Quark-Gluon Plasma (QGP)
deconfined state will proceed, in the next 10-15 years, along two directions:
the high-energy regime at RHIC and at the LHC, and the low-energy regime at
FAIR, NICA, SPS and RHIC. The Italian community is strongly involved in the
present and future programme of the ALICE experiment, the upgrade of which will
open, in the 2020s, a new phase of high-precision characterisation of the QGP
properties at the LHC. As a complement of this main activity, there is a
growing interest in a possible future experiment at the SPS, which would target
the search for the onset of deconfinement using dimuon measurements. On a
longer timescale, the community looks with interest at the ongoing studies and
discussions on a possible fixed-target programme using the LHC ion beams and on
the Future Circular Collider.Comment: 99 pages, 56 figure
Pseudoscalar top-Higgs coupling: Exploration of -odd observables to resolve the sign ambiguity
We present a collection of -odd observables for the process
that
are linearly dependent on the scalar () and pseudoscalar
() top-Higgs coupling and hence sensitive to the
corresponding relative sign. The proposed observables are based on triple
product (TP) correlations that we extract from the expression for the
differential cross section in terms of the spin vectors of the top and antitop
quarks. In order to explore other possibilities, we progressively modify these
TPs, first by combining them, and then by replacing the spin vectors by the
lepton momenta or the and momenta by their visible parts. We
generate Monte Carlo data sets for several benchmark scenarios, including the
Standard Model (, ) and two scenarios with
mixed properties (, ).
Assuming an integrated luminosity that is consistent with that envisioned for
the High Luminosity Large Hadron Collider, using Monte Carlo-truth and taking
into account only statistical uncertainties, we find that the most promising
observable can disentangle the "-mixed" scenarios with an
effective separation of . In the case of observables that do not
require the reconstruction of the and momenta, the power of
discrimination is up to for the same number of events. We also
show that the most promising observables can still disentangle the
-mixed scenarios when the number of events is reduced to values
consistent with expectations for the Large Hadron Collider in the near term.Comment: 28 pages, 7 figures. Published versio
Discovery and characterisation of detached M-dwarf eclipsing binaries in the WFCAM Transit Survey
We report the discovery of 16 detached M-dwarf eclipsing binaries with J<16
mag and provide a detailed characterisation of three of them, using
high-precision infrared light curves from the WFCAM Transit Survey (WTS). Such
systems provide the most accurate and model-independent method for measuring
the fundamental parameters of these poorly understood yet numerous stars, which
currently lack sufficient observations to precisely calibrate stellar evolution
models. We fully solve for the masses and radii of three of the systems,
finding orbital periods in the range 1.5<P<4.9 days, with masses spanning
0.35-0.50 Msun and radii between 0.38-0.50 Rsun, with uncertainties of
~3.5-6.4% in mass and ~2.7-5.5% in radius. Close-companions in short-period
binaries are expected to be tidally-locked into fast rotational velocities,
resulting in high levels of magnetic activity. This is predicted to inflate
their radii by inhibiting convective flow and increasing star spot coverage.
The radii of the WTS systems are inflated above model predictions by ~3-12%, in
agreement with the observed trend, despite an expected lower systematic
contribution from star spots signals at infrared wavelengths. We searched for
correlation between the orbital period and radius inflation by combining our
results with all existing M-dwarf radius measurements of comparable precision,
but we found no statistically significant evidence for a decrease in radius
inflation for longer period, less active systems. Radius inflation continues to
exists in non-synchronised systems indicating that the problem remains even for
very low activity M-dwarfs. Resolving this issue is vital not only for
understanding the most populous stars in the Universe, but also for
characterising their planetary companions, which hold the best prospects for
finding Earth-like planets in the traditional habitable zone.Comment: 30 pages, 14 figures, 16 tables, Accepted for publication in MNRA
Young Suns Exoplanet Survey: Detection of a wide-orbit planetary-mass companion to a solar-type Sco-Cen member
The Young Suns Exoplanet Survey consists of a homogeneous sample of 70 young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association with an average age of 15 ± 3âMyr. We report the detection of a co-moving companion around the K3IV star TYC 8998-760-1 (2MASSJ13251211â6456207) that is located at a distance of 94.6 ± 0.3âpc using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER constrain the mass of the star to 1.00±0.02Mâ and an age of 16.7±1.4 Myr. The companion TYC 8998-760-1 b is detected at a projected separation of 1.71âł, which implies a projected physical separation of 162âau. Photometric measurements ranging from Y to M band provide a mass estimate of 14±3 M_(jup) by comparison to BT-Settl and AMES-dusty isochrones, corresponding to a mass ratio of q = 0.013 ± 0.003 with respect to the primary. We rule out additional companions to TYC 8998-760-1 that are more massive than 12 M_(jup) and farther than 12âau away from the host. Future polarimetric and spectroscopic observations of this system with ground and space based observatories will facilitate testing of formation and evolution scenarios shaping the architecture of the circumstellar environment around this âyoung Sunâ
Study of intermediate velocity products in the Ar+Ni collisions between 52 and 95 A.MeV
Intermediate velocity products in Ar+Ni collisions from 52 to 95 A.MeV are
studied in an experiment performed at the GANIL facility with the 4
multidetector INDRA. It is shown that these emissions cannot be explained by
statistical decays of the quasi-projectile and the quasi-target in complete
equilibrium. Three methods are used to isolate and characterize intermediate
velocity products. The total mass of these products increases with the violence
of the collision and reaches a large fraction of the system mass in mid-central
collisions. This mass is found independent of the incident energy, but strongly
dependent on the geometry of the collision. Finally it is shown that the
kinematical characteristics of intermediate velocity products are weakly
dependent on the experimental impact parameter, but strongly dependent on the
incident energy. The observed trends are consistent with a
participant-spectator like scenario or with neck emissions and/or break-up.Comment: 37 pages, 13 figure
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