781 research outputs found

### Lepton flavour violation in future linear colliders in the long-lived stau NLSP scenario

We analyze the prospects of observing lepton flavour violation in future e-e-
and e+e- linear colliders in scenarios where the gravitino is the lightest
supersymmetric particle, and the stau is the next-to-lightest supersymmetric
particle. The signals consist of multilepton final states with two heavily
ionizing charged tracks produced by the long-lived staus. The Standard Model
backgrounds are very small and the supersymmetric backgrounds can be kept well
under control by the use of suitable kinematical cuts. We discuss in particular
the potential of the projected International Linear Collider to discover lepton
flavour violation in this class of scenarios, and we compare the estimated
sensitivity with the constraints stemming from the non-observation of rare
decays.Comment: 30 pages, 12 figures. Discussion extended to include the efficiency
of identifying long-lived staus, references added. To appear in JHE

### Combined CDF and D0 Upper Limits on Standard Model Higgs-Boson Production with 2.1 - 5.4 fb-1 of Data

We combine results from CDF and D0 on direct searches for a standard model
(SM) Higgs boson (H) in ppbar collisions at the Fermilab Tevatron at
sqrt(s)=1.96 TeV. Compared to the previous Tevatron Higgs search combination
more data have been added and some previously used channels have been
reanalyzed to gain sensitivity. We use the latest parton distribution functions
and gg->H theoretical cross sections when comparing our limits to the SM
predictions. With 2.0-4.8 fb-1 of data analyzed at CDF, and 2.1-5.4 fb-1 at D0,
the 95% C.L. upper limits on Higgs boson production are a factor of 2.70 (0.94)
times the SM cross section for a Higgs boson mass of m_H=115 (165) GeV/c^2. The
corresponding median upper limits expected in the absence of Higgs boson
production are 1.78 (0.89). The mass range excluded at 95% C.L. for a SM Higgs
is 163<m_H<166 GeV/c^2, with an expected exclusion of 159<m_H<168 GeV/c^2.Comment: 30 pages, five figures. Results prepared for the HCP 2009 conference,
November 16-20, in Evian, Franc

### Probing Lepton Flavor Violation Signal Induced by R-violating Minimal Supersymmetric Standard Model at a Linear Collider

The lepton-flavor violation (LFV) effect at an $e^+e^-$ linear collider (LC),
in the frame of R-parity violating minimal supersymmetric standard model is
studied. We take the R-parity violating processes $e^+e^-\to e^{\mp}\mu^{\pm}$
as signal, and define the summation of the two processes as ``experiment''
observable. We find that the cross-section summation can reach
$\cal{O}$$(10^1)fb$ in the parameter space without sneutrino resonance
effect($\sqrt{s} \sim m_{\tilde{\nu}}$). The summation treatment manifests
uniform differential distribution on $\cos\theta$, where $\theta$ denotes the
polar angles of both outgoing $e^+/e^-$ respectively to incoming electron beam
in two signal processes. The uniform feature together with $e\mu$ collinearity
would help to reduce the SM background dramatically. Consequently we conclude
that at a $500 GeV$ LC with $480 fb^{-1}$ annual luminosity, it's either
possible to detect the distinctive R-violating LFV $e\mu$ signal, or exclude
sneutrino to $m_{\tilde{\nu}}>1.1 TeV$ at 95% CL in the machine's biennial
runtime interval.Comment: 14 pages, 9 figure

### Analysis strategy for the SM Higgs boson search in the four-lepton final state in CMS

The current status of the searches for the SM Higgs boson in the
$H$$\rightarrow$$ZZ^{(*)}$$\rightarrow$$4\ell$ decay channel with the CMS
experiment is presented. The selection cuts for suppressing the backgrounds
while keeping very high signal efficiencies are described, along with the
data-driven algorithms implemented to estimate the background yields and the
systematic uncertainties. With an integrated luminosity of $1.66
\mathrm{fb}^{-1}$, upper limits at 95% CL on the SM-like Higgs cross section
$\times$ branching ratio exclude cross sections from about one to two times the
expected value from the Standard Model in the range $150 < m_{H} < 420
\mathrm{GeV}$. No evidence for the existence of the SM Higgs boson has been
found so far.Comment: "Presented at the 2011 Hadron Collider Physics symposium (HCP-2011),
Paris, France, November 14-18 2011, 3 pages, 5 figures.

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