41 research outputs found

### Standard-model predictions for CP violation in B<sup>0</sup>-meson decay

We examine the present set of constraints on the parameters of the standard model and use the unitarity triangle to present their allowed range. We give the implications of this for CP violation in the B-meson system as a function of top-quark mass, emphasizing what luminosity of an electronpositron collider is needed to guarantee a statistically significant asymmetry in one or more B decay channels.</p

### Search for sterile neutrinos decaying into pions at the LHC

We study the possibility to observe sterile neutrinos with masses in the
range between 5 GeV and 20 GeV at the LHC, using the exclusive semileptonic
modes involving pions, namely W to lepton + N to n pions + lepton+lepton (n =
1, 2, 3). The two pion and three pion modes require extrapolations of form
factors to large time-like $q^2$, which we do using vector dominance models as
well as light front holographic QCD, with remarkable agreement. This mass
region is difficult to explore with inclusive dilepton+dijet modes or trilepton
modes and impossible to explore in rare meson decays. While particle
identification is a real challenge in these modes, vertex displacement due to
the long living neutrino in the above mass range can greatly help reduce
backgrounds. Assuming a sample of $10^9$ W bosons at the end of the LHC Run 2,
these modes could discover a sterile neutrino in the above mass range or
improve the current bounds on the heavy-to-light lepton mixings by an order of
magnitude, $U_{l N}^2 \sim 2 \times 10^{-6}$. Moreover, by studying the equal
sign and opposite sign dileptons, the Majorana or Dirac character of the
sterile neutrino may be revealed.Comment: 18 pages, 4 double figure

### Search for heavy sterile neutrinos in trileptons at the LHC

We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of W$^Â±$ â†’ e$^Â±$ e$^Â±$ Î¼$^\mp$ $\nu$ and Î¼$^Â±$ Î¼$^Â±$ emnplus $\nu$ at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and discrimination limits. Two benchmark points with sterile neutrino mass $m_N$ = 20 GeV and 50 GeV are tested. For an integrated luminosity of 3000 fb$^{âˆ’1}$, sterile neutrinos can be found with 5Ïƒ significance if heavy-to-light neutrino mixings |U$_{Ne} |^2$ ~ |U$_{NÎ¼}|^2$~ 10$^{âˆ’6}$, while Majorana vs. Dirac discrimination can be reached if at least one of the mixings is of order 10$^{âˆ’15}$

### Search for Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC

Heavy sterile neutrinos with masses below $M_W$ can induce trilepton events at the 14 TeV LHC through purely leptonic $W$ decays of $W^\pm \to e^\pm e^\pm \mu^\mp \nu$ and $\mu^\pm \mu^\pm e^\mp \nu$ where the heavy neutrino will be in an intermediate state on its mass shell. Discovery and exclusion limits for the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate Analysis (MVA) methods in this study. We also show that it is possible to discriminate between a Dirac and a Majorana heavy neutrino, even when lepton number conservation cannot be directly tested due to unobservability of the final state neutrino. This discrimination is done by exploiting a combined set of kinematic observables that differ between the Majorana vs. Dirac cases. We find that the MVA method can greatly enhance the discovering and discrimination limits in comparison with the CC method. With an integrated luminosity of 3000 ${\rm fb}^{-1}$, sterile neutrinos can be found with 5$\sigma$ significance if heavy-to-light neutrino mixings $|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-6}$, while the Majorana vs. Dirac type can be distinguished if $|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-5}$ or even $|U_{N\ell}|^2\sim 10^{-6}$ if one of mixing elements can be at least one order of magnitude smaller than the other

### Signatures of Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC

Heavy sterile neutrinos with masses below $M_W$ can induce trilepton events
at the 14 TeV LHC through purely leptonic $W$ decays of $W^\pm \to e^\pm e^\pm
\mu^\mp \nu$ and $\mu^\pm \mu^\pm e^\mp \nu$ where the heavy neutrino will be
in an intermediate state on its mass shell. Discovery and exclusion limits for
the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate
Analysis (MVA) methods in this study. We also show that it is possible to
discriminate between a Dirac and a Majorana heavy neutrino, even when lepton
number conservation cannot be directly tested due to unobservability of the
final state neutrino. This discrimination is done by exploiting a combined set
of kinematic observables that differ between the Majorana vs. Dirac cases. We
find that the MVA method can greatly enhance the discovering and discrimination
limits in comparison with the CC method. For a 14-TeV $pp$ collider with
integrated luminosity of 3000 ${\rm fb}^{-1}$, sterile neutrinos can be found
with 5$\sigma$ significance if heavy-to-light neutrino mixings $|U_{Ne}|^2 \sim
|U_{N\mu}|^2 \sim 10^{-6}$, while the Majorana vs. Dirac type can be
distinguished if $|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-5}$ or even
$|U_{N\ell}|^2\sim 10^{-6}$ if one of the mixing elements is at least an order
of magnitude smaller than the other.Comment: 10 pages, 12 figure

### Search for Heavy Sterile Neutrinos in Trileptons at the LHC

We present a search strategy for both Dirac and Majorana sterile neutrinos
from the purely leptonic decays of $W^\pm \to e^\pm e^\pm \mu^\mp \nu$ and
$\mu^\pm \mu^\pm e^\mp \nu$ at the 14 TeV LHC. The discovery and exclusion
limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and
Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and
Majorana sterile neutrinos by exploiting a set of kinematic observables which
differ between the Dirac and Majorana cases. We find that the MVA method,
compared to the more common CC method, can greatly enhance the discovery and
discrimination limits. Two benchmark points with sterile neutrino mass $m_N =
20$ GeV and 50 GeV are tested. For an integrated luminosity of 3000 ${\rm
fb}^{-1}$, sterile neutrinos can be found with $5 \sigma$ significance if
heavy-to-light neutrino mixings $|U_{Ne}|^2 \sim |U_{N\mu}|^2\sim 10^{-6}$,
while Majorana vs. Dirac discrimination can be reached if at least one of the
mixings is of order $10^{-5}$.Comment: 4 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1703.0193