698 research outputs found
Analysis and correction of the magnetic field effects in the Hybrid Photo-Detectors of the RICH2 Ring Imaging Cherenkov detector of LHCb
The Ring Imaging Cherenkov detectors of the LHCb experiment at the Large
Hadron Collider at CERN are equipped with Hybrid Photo-Detectors. These vacuum
photo-detectors are affected by the stray magnetic field of the LHCb magnet,
which degrades their imaging properties. This effect increases the error on the
Cherenkov angle measurement and would reduce the particle identification
capabilities of LHCb. A system has been developed for the RICH2 Ring Imaging
Cherenkov detector to perform a detailed characterisation of the magnetic
distortion effects. It is described, along with the methods implemented to
correct for these effects, restoring the optimal resolution.Comment: 16 pages, 11 figure
The Semileptonic to Decays in QCD Sum Rules
We analyze the semileptonic rare decays of meson to and
axial vector mesons. The
decays are significant flavor changing neutral current decays of the meson.
These decays are sensitive to the new physics beyond SM, since these processes
are forbidden at tree level at SM. These decays occurring at the quark level
via transition, also provide new opportunities for
calculating the CKM matrix elements and . In this study, the
transition form factors of the decays
are calculated using three-point QCD sum rules approach. The resulting form
factors are used to estimate the branching fractions of these decays.Comment: 18 pages, 7 figures, version to appear in JP
The UTfit Collaboration Report on the Status of the Unitarity Triangle beyond the Standard Model I. Model-independent Analysis and Minimal Flavour Violation
Starting from a (new physics independent) tree level determination of rhobar
and etabar, we perform the Unitarity Triangle analysis in general extensions of
the Standard Model with arbitrary new physics contributions to loop-mediated
processes. Using a simple parameterization, we determine the allowed ranges of
non-standard contributions to |Delta F|=2 processes. Remarkably, the recent
measurements from B factories allow us to determine with good precision the
shape of the Unitarity Triangle even in the presence of new physics, and to
derive stringent constraints on non-standard contributions to |Delta F|=2
processes. Since the present experimental constraints favour models with
Minimal Flavour Violation, we present the determination of the Universal
Unitarity Triangle that can be defined in this class of extensions of the
Standard Model. Finally, we perform a combined fit of the Unitarity Triangle
and of new physics contributions in Minimal Flavour Violation, reaching a
sensitivity to a new physics scale of about 5 TeV. We also extrapolate all
these analyses into a "year 2010" scenario for experimental and theoretical
inputs in the flavour sector. All the results presented in this paper are also
available at the URL http://www.utfit.org, where they are continuously updated.Comment: 29 pages, 56 figure
Present and Future CP Measurements
We review theoretical and experimental results on CP violation summarizing
the discussions in the working group on CP violation at the UK phenomenology
workshop 2000 in Durham.Comment: 104 pages, Latex, to appear in Journal of Physics
From Little Bangs to the Big Bang
The `Little Bangs' made in particle collider experiments reproduce the
conditions in the Big Bang when the age of the Universe was a fraction of a
second. It is thought that matter was generated, the structures in the Universe
were formed and cold dark matter froze out during this very early epoch when
the equation of state of the Universe was dominated by the quark-gluon plasma
(QGP). Future Little Bangs may reveal the mechanism of matter generation and
the nature of cold dark matter. Knowledge of the QGP will be an essential
ingredient in quantitative understanding of the very early Universe.Comment: Invited Plenary Talk at the International Conference on the Physics
and Astrophysics of the Quark-Gluon Plasma, Kolkata, Feb. 2005: 13 pages, 11
figures, uses IoP style files (included
Angular analysis of B --> V (--> P_1 P_2) l^+ l^- decays
The angular analysis of exclusive rare B-meson decays via intermediate vector
mesons V into 4-body final states of two pseudo-scalars P_1, P_2 and a pair of
light leptons l = e, mu offers a large set of observables. They can be used to
test the electroweak short-distance couplings in the Standard Model and to
search for New Physics. The two kinematic regions of low and high dilepton mass
depend on short-distance physics in complementary ways and can be expanded in
powers of Lambda_QCD/m_b. These expansions guide towards suitable combinations
of observables allowing to i) reduce the hadronic uncertainties in the
extraction of the short-distance couplings or ii) test the lattice QCD (B -> V)
form factors in short-distance independent combinations. Several such
possibilities of CP-averaged and CP-asymmetric (T-even and T-odd) quantities
are presented for B_d^0 --> K^*0 (-> K pi) l^+ l^- and time-integrated
CP-asymmetries without tagging for (anti-B_s, B_s) --> phi (--> K^- K^+) l^+
l^- decays in view of the latest B-factory and CDF results and the forthcoming
LHCb measurements.Comment: 9 pages, 4 figures; Talk given at Discrete '10: Symposium on
Prospects in the Physics of Discrete Symmetries, Rome, Italy, 6-11 Dec 201
Radiation damage in the LHCb vertex locator
The LHCb Vertex Locator (VELO) is a silicon strip detector designed to reconstruct charged particle trajectories and vertices produced at the LHCb interaction region. During the first two years of data collection, the 84 VELO sensors have been exposed to a range of fluences up to a maximum value of approximately 45 Ă 1012 1 MeV neutron equivalent (1 MeV neq). At the operational sensor temperature of approximately â7 °C, the average rate of sensor current increase is 18 ÎŒA per fbâ1, in excellent agreement with predictions. The silicon effective bandgap has been determined using current versus temperature scan data after irradiation, with an average value of Eg = 1.16±0.03±0.04 eV obtained. The first observation of n+-on-n sensor type inversion at the LHC has been made, occurring at a fluence of around 15 Ă 1012 of 1 MeV neq. The only n+-on-p sensors in use at the LHC have also been studied. With an initial fluence of approximately 3 Ă 1012 1 MeV neq, a decrease in the Effective Depletion Voltage (EDV) of around 25 V is observed. Following this initial decrease, the EDV increases at a comparable rate to the type inverted n+-on-n type sensors, with rates of (1.43±0.16) Ă 10â12 V/ 1 MeV neq and (1.35±0.25) Ă 10â12 V/ 1 MeV neq measured for n+-on-p and n+-on-n type sensors, respectively. A reduction in the charge collection efficiency due to an unexpected effect involving the second metal layer readout lines is observed
Nuclear model developments in FLUKA for present and future applications
The FLUKAS code [1â3] is used in research laboratories all around the world for challenging applications spanning a very wide range of energies, projectiles and targets. FLUKAS is also extensively used for in hadrontherapy research studies and clinical planning systems. In this paper some of the recent developments in the FLUKAS nuclear physics models of relevance for very different application fields including medical physics are presented. A few examples are shown demonstrating the effectiveness of the upgraded code
Search for CP violation in D+âÏÏ+ and D+sâK0SÏ+ decays
A search for CP violation in D + â ÏÏ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fbâ1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (â0.04 ± 0.14 ± 0.14)% for candidates with K â K + mass within 20 MeV/c 2 of the Ï meson mass. A search for a CP -violating asymmetry that varies across the Ï mass region of the D + â K â K + Ï + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+sâK0SÏ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%
Measurements of the branching fractions of the decays B°s â Dâs K± and B°s â DÂŻsÏ+
The decay mode B°s â Dâs K± allows for one of the theoretically cleanest measurements of the CKM angle Îł through the study of time-dependent CP violation. This paper reports a measurement of its branching fraction relative to the Cabibbo-favoured mode B°s â DÂŻsÏ+ based on a data sample corresponding to 0.37 fbÂŻÂč of proton-proton collisions at âs = 7TeV collected in 2011 with the LHCb detector. In addition, the ratio of B meson production fractions fs/fd, determined from semileptonic decays, together with the known branching fraction of the control channel B°s â DÂŻsÏ+ is used to perform an absolute measurement of the branching fractions: B(B°s â DÂŻsÏ+) = (2.95 ± 0.05 ± 0.17 -0.22 +0.18) Ă 10ÂŻÂł ; B(B°s â Dâs K±) = (1.90 ± 0.12 ± 0.13 -0.14 +0.12) Ă 10ÂŻ4 ; where the first uncertainty is statistical, the second the experimental systematic uncertainty, and the third the uncertainty due to f s/f
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