2,830 research outputs found
Hadronic B Decays to Charmless Final States and to J/psi K*
Preliminary results from the BABAR experiment on charmless B decays to
charged pions or kaons, and the measurement of the B -> J/psi K* decay
amplitudes are presented. The data sample, collected at the asymmetric-energy
B-factory PEP-II at SLAC, comprises a total number of 22.7 million Y(4S)
decays, corresponding to an integrated on-resonance luminosity of approximately
21 fb-1. We measure the following CP-averaged branching fractions:
BR(B -> pi+pi-) = (4.1 +- 1.0(stat) +- 0.7(sys))xE-6 BR(B -> K+pi-) = (16.7
+- 1.6(stat) +1.2-1.7(sys))xE-6
and an upper limit of BR(B -> K+K-) < 2.5xE-6, at 90% confidence limit. The
measurement of the J/psi K* decay amplitudes results in R_\perp = 0.160 +-
0.032(stat) +- 0.036(sys), and reveals a dominant longitudinal component. The
phase of the longitudinal amplitude shows evidence for non-vanishing final
state interaction.Comment: 13 pages, 8 postscript figures, submitted to Proceedings for BCP
Reply to: ''Improved Determination of the CKM Angle alpha from B -> pipi decays''
In reply to hep-ph/0701204 we demonstrate why the arguments made therein do
not address the criticism exposed in hep-ph/0607246 on the fundamental
shortcomings of the Bayesian approach when it comes to the extraction of
parameters of Nature from experimental data. As for the isospin analysis and
the CKM angle alpha it is shown that the use of uniform priors for the observed
quantities in the Explicit Solution parametrization is equivalent to a
frequentist construction resulting from a change of variables, and thus relies
neither on prior PDFs nor on Bayes' theorem. This procedure provides in this
particular case results that are similar to the Confidence Level approach, but
the treatment of mirror solutions remains incorrect and it is far from being
general. In a second part it is shown that important differences subsist
between the Bayesian and frequentist approaches, when following the proposal of
hep-ph/0701204 and inserting additional information on the hadronic amplitudes
beyond isospin invariance. In particular the frequentist result preserves the
exact degeneracy that is expected from the remaining symmetries of the problem
while the Bayesian procedure does not. Moreover, in the Bayesian approach
reducing inference to the 68% or 95% credible interval is a misconception of
the meaning of the posterior PDF, which in turn implies that the significant
dependence of the latter to the chosen parametrization cannot be viewed as a
minor effect, contrary to the claim in hep-ph/0701204.Comment: 5 pages, 1 figure. Fig. 1 corrected (wrong file
Improved Determination of alpha_QED(M_Z^2) and the Anomalous Magnetic Moment of the Muon
We reevaluate the hadronic contribution to the running of the QED fine
structure constant alpha(s) at s = M_Z^2. We use data from e+e- annihilation
and tau decays at low energy and at the qq-bar thresholds, where resonances
occur. Using so-called spectral moments and the Operator Product Expansion
(OPE), it is shown that a reliable theoretical prediction of the hadronic
production rate R(s) is available at relatively low energies. Its application
improves significantly the precision on the hadronic vacuum polarization
contribution. We obtain delta_alpha^had = (277.8 +/- 2.6) x 10^-4 yielding
alpha^-1(M_Z^2) = 128.923 +/- 0.036$. Inserting this value in a global
electroweak fit using current experimental input, we constrain the mass of the
Standard Model Higgs boson to be M_Higgs = (129 +103 -62) GeV. Analogously, we
improve the precision of the hadronic contribution to the anomalous magnetic
moment of the muon for which we obtain a_mu^had = (695.1 +/- 7.5) x 10^-10.Comment: tex, 18 pages and 3 figure
Stau as the Lightest Supersymmetric Particle in R-Parity Violating SUSY Models: Discovery Potential with Early LHC Data
We investigate the discovery potential of the LHC experiments for R-parity
violating supersymmetric models with a stau as the lightest supersymmetric
particle (LSP) in the framework of minimal supergravity. We classify the final
states according to their phenomenology for different R-parity violating decays
of the LSP. We then develop event selection cuts for a specific benchmark
scenario with promising signatures for the first beyond the Standard Model
discoveries at the LHC. For the first time in this model, we perform a detailed
signal over background analysis. We use fast detector simulations to estimate
the discovery significance taking the most important Standard Model backgrounds
into account. Assuming an integrated luminosity of 1 inverse femtobarn at a
center-of-mass energy of 7 TeV, we perform scans in the parameter space around
the benchmark scenario we consider. We then study the feasibility to estimate
the mass of the stau-LSP. We briefly discuss difficulties, which arise in the
identification of hadronic tau decays due to small tau momenta and large
particle multiplicities in our scenarios.Comment: 26 pages, 18 figures, LaTeX; minor changes, final version published
in PR
Weak Phase gamma Using Isospin Analysis and Time Dependent Asymmetry in B_d -> K_s pi^+ pi^-
We present a method for measuring the weak phase gamma using isospin analysis
of three body B decays into K pi pi channels. Differential decay widths and
time dependent asymmetry in B_d -> K_s pi^+pi^- mode needs to be measured into
even isospin pi pi states. The method can be used to extract gamma, as well as,
the size of the electroweak penguin contributions. The technique is free from
assumptions like SU(3) or neglect of any contributions to the decay amplitudes.
By studying different regions of the Dalitz plot, it is possible to reduce the
ambiguity in the value of gamma.Comment: 11 pages, 1 figur
The global electroweak fit at NNLO and prospects for the LHC and ILC
For a long time, global fits of the electroweak sector of the Standard Model
(SM) have been used to exploit measurements of electroweak precision
observables at lepton colliders (LEP, SLC), together with measurements at
hadron colliders (Tevatron, LHC), and accurate theoretical predictions at
multi-loop level, to constrain free parameters of the SM, such as the Higgs and
top masses. Today, all fundamental SM parameters entering these fits are
experimentally determined, including information on the Higgs couplings, and
the global fits are used as powerful tools to assess the validity of the theory
and to constrain scenarios for new physics. Future measurements at the Large
Hadron Collider (LHC) and the International Linear Collider (ILC) promise to
improve the experimental precision of key observables used in the fits. This
paper presents updated electroweak fit results using newest NNLO theoretical
predictions, and prospects for the LHC and ILC. The impact of experimental and
theoretical uncertainties is analysed in detail. We compare constraints from
the electroweak fit on the Higgs couplings with direct LHC measurements, and
examine present and future prospects of these constraints using a model with
modified couplings of the Higgs boson to fermions and bosons.Comment: 26 pages, 9 figure
A population-based approach to background discrimination in particle physics
Background properties in experimental particle physics are typically
estimated using control samples corresponding to large numbers of events. This
can provide precise knowledge of average background distributions, but
typically does not consider the effect of fluctuations in a data set of
interest. A novel approach based on mixture model decomposition is presented as
a way to estimate the effect of fluctuations on the shapes of probability
distributions in a given data set, with a view to improving on the knowledge of
background distributions obtained from control samples. Events are treated as
heterogeneous populations comprising particles originating from different
processes, and individual particles are mapped to a process of interest on a
probabilistic basis. The proposed approach makes it possible to extract from
the data information about the effect of fluctuations that would otherwise be
lost using traditional methods based on high-statistics control samples. A
feasibility study on Monte Carlo is presented, together with a comparison with
existing techniques. Finally, the prospects for the development of tools for
intensive offline analysis of individual events at the Large Hadron Collider
are discussed.Comment: Updated according to the version published in J. Phys.: Conf. Ser.
Minor changes have been made to the text with respect to the published
article with a view to improving readabilit
Catalyst nanoparticle growth dynamics and their influence on product morphology in a CVD process for continuous carbon nanotube synthesis
Extrapolating the properties of individual CNTs into macro-scale CNT materials using a continuous and cost effective process offers enormous potential for a variety of applications. The floating catalyst chemical vapor deposition (FCCVD) method discussed in this paper bridges the gap between generating nano- and macro-scale CNT material and has already been adopted by industry for exploitation. A deep understanding of the phenomena occurring within the FCCVD reactor is thereby key to producing the desired CNT product and successfully scaling up the process further. This paper correlates information on decomposition of reactants, axial catalyst nanoparticle dynamics and the morphology of the resultant CNTs and shows how these are strongly related to the temperature and chemical availability within the reactor. For the first time, in-situ measurements of catalyst particle size distributions coupled with reactant decomposition profiles and a detailed axial SEM study of formed CNT materials reveal specific domains that have important implications for scale-up. A novel observation is the formation, disappearance and reformation of catalyst nanoparticles along the reactor axis, caused by their evaporation and re-condensation and mapping of different CNT morphologies as a result of this process.The authors thank Qflo Ltd for providing funding towards this research, C. Hoecker additionally thanks Churchill College Cambridge for financial support, M. Bajada gratefully acknowledges financial support through the 'Master it! Scholarship Scheme'.This is the accepted manuscript. The final version is available at http://dx.doi.org/10.1016/j.carbon.2015.09.05
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