2,562 research outputs found
Bottom Production
We review the prospects for bottom production physics at the LHC.Comment: 74 pages, Latex, 71 figures, to appear in the Report of the ``1999
CERN Workshop on SM physics (and more) at the LHC'', P. Nason, G. Ridolfi, O.
Schneider G.F. Tartarelli, P. Vikas (conveners
Probing EWSB Naturalness in Unified SUSY Models with Dark Matter
We have studied Electroweak Symmetry Breaking (EWSB) fine-tuning in the
context of two unified Supersymmetry scenarios: the Constrained Minimal
Supersymmetric Model (CMSSM) and models with Non-Universal Higgs Masses (NUHM),
in light of current and upcoming direct detection dark matter experiments. We
consider both those models that satisfy a one-sided bound on the relic density
of neutralinos, , and also the subset that satisfy
the two-sided bound in which the relic density is within the 2 sigma best fit
of WMAP7 + BAO + H0 data. We find that current direct detection searches for
dark matter probe the least fine-tuned regions of parameter-space, or
equivalently those of lowest Higgs mass parameter , and will tend to probe
progressively more and more fine-tuned models, though the trend is more
pronounced in the CMSSM than in the NUHM. Additionally, we examine several
subsets of model points, categorized by common mass hierarchies; M_{\chi_0}
\sim M_{\chi^\pm}, M_{\chi_0} \sim M_{\stau}, M_{\chi_0} \sim M_{\stop_1}, the
light and heavy Higgs poles, and any additional models classified as "other";
the relevance of these mass hierarchies is their connection to the preferred
neutralino annihilation channel that determines the relic abundance. For each
of these subsets of models we investigated the degree of fine-tuning and
discoverability in current and next generation direct detection experiments.Comment: 26 pages, 10 figures. v2: references added. v3: matches published
versio
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ âJ/ÏK
+, B0 âJ/ÏK
â0 and B0 âD
ââ
Ό
+
ΜΌ decay
modes with 0.37 fbâ1 of data collected in pp collisions
at
â
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ â J/ÏK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
Supersymmetric Benchmarks with Non-Universal Scalar Masses or Gravitino Dark Matter
We propose and examine a new set of benchmark supersymmetric scenarios, some
of which have non-universal Higgs scalar masses (NUHM) and others have
gravitino dark matter (GDM). The scalar masses in these models are either
considerably larger or smaller than the narrow range allowed for the same
gaugino mass m_{1/2} in the constrained MSSM (CMSSM) with universal scalar
masses m_0 and neutralino dark matter. The NUHM and GDM models with larger m_0
may have large branching ratios for Higgs and/or production in the cascade
decays of heavier sparticles, whose detection we discuss. The phenomenology of
the GDM models depends on the nature of the next-to-lightest supersymmetric
particle (NLSP), which has a lifetime exceeding 10^4 seconds in the proposed
benchmark scenarios. In one GDM scenario the NLSP is the lightest neutralino
\chi, and the supersymmetric collider signatures are similar to those in
previous CMSSM benchmarks, but with a distinctive spectrum. In the other GDM
scenarios based on minimal supergravity (mSUGRA), the NLSP is the lighter stau
slepton {\tilde \tau}_1, with a lifetime between ~ 10^4 and 3 X 10^6 seconds.
Every supersymmetric cascade would end in a {\tilde \tau}_1, which would have a
distinctive time-of-flight signature. Slow-moving {\tilde \tau}_1's might be
trapped in a collider detector or outside it, and the preferred detection
strategy would depend on the {\tilde \tau}_1 lifetime. We discuss the extent to
which these mSUGRA GDM scenarios could be distinguished from gauge-mediated
models.Comment: 52 pages LaTeX, 13 figure
Differential branching fraction and angular analysis of the decay B0âKâ0ÎŒ+ÎŒâ
The angular distribution and differential branching fraction of the decay B 0â K â0 ÎŒ + ÎŒ â are studied using a data sample, collected by the LHCb experiment in pp collisions at sâ=7 TeV, corresponding to an integrated luminosity of 1.0 fbâ1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Measurement of charged particle multiplicities in collisions at TeV in the forward region
The charged particle production in proton-proton collisions is studied with
the LHCb detector at a centre-of-mass energy of TeV in different
intervals of pseudorapidity . The charged particles are reconstructed
close to the interaction region in the vertex detector, which provides high
reconstruction efficiency in the ranges and
. The data were taken with a minimum bias trigger, only requiring
one or more reconstructed tracks in the vertex detector. By selecting an event
sample with at least one track with a transverse momentum greater than 1 GeV/c
a hard QCD subsample is investigated. Several event generators are compared
with the data; none are able to describe fully the multiplicity distributions
or the charged particle density distribution as a function of . In
general, the models underestimate the charged particle production
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
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