Search results for "detector"
showing 10 items of 3491 documents
Dirac neutrinos from Peccei-Quinn symmetry: a fresh look at the axion
2019
We show that a very simple solution to the strong CP problem naturally leads to Dirac neutrinos. Small effective neutrino masses emerge from a type-I Dirac seesaw mechanism. Neutrino mass limits probe the axion parameters in regions currently inaccessible to conventional searches.
Reloading the Axion in a 3-3-1 setup
2020
We generalize the idea of the axion to an extended electroweak gauge symmetry setup. We propose a minimal axion extension of the Singer-Valle-Schechter (SVS) theory, in which the standard model fits in $\mathrm{SU(3)_L\otimes U(1)_X}$, the number of families results from anomaly cancellation, and the Peccei-Quinn (PQ) solution to the strong-CP problem is implemented. Neutrino masses arise from a type-I Dirac seesaw mechanism, suppressed by the ratio of SVS and PQ scales, suggesting the existence of new physics at a moderate SVS scale. Novel features include an enhanced axion coupling to photons when compared to the DFSZ axion, as well as flavour-changing axion couplings to quarks.
Decoherent neutrino mixing, dark energy, and matter-antimatter asymmetry
2004
A CPT violating decoherence scenario can easily account for all the experimental evidence in the neutrino sector including LSND. In this work it is argued that this framework can also accommodate the Dark Energy content of the Universe, as well as the observed matter-antimatter asymmetry.
Inclusive measurements of the K+- and p / anti-p production in hadronic Z0 decays
1995
This analysis, based on a sample of 170000 hadronic Z0 decays, provides a measurement of the K± and p/View the MathML source differential cross sections which is compared to string- and cluster fragmentation models. The total multiplicities for K± and p/View the MathML source per hadronic event were found to be: NK = 2.26 ± 0.18 and Np = 1.07 ± 0.14. The positions ξ* of the maxima of the differential cross sections as a function of ξ = ln(1/xp) for K± and p/View the MathML source were determined to be 2.63 ± 0.07 and 2.96 ± 0.16 respectively. A comparison of the ξ* values for various identified particles measured at LEP with the prediction of the Modified Leading Logarithm Approximation wit…
Inner detector alignment and top-quark mass measurement with the ATLAS detector
2014
221 páginas. Tesis Doctoral del Departamento de Física Atómica, Molecular y Nuclear de la Universidad de Valencia y del Instituto de Física Corpuscular (IFIC).
A Precise measurement of the partial decay width ratio R(b)**0 = Gamma(b anti-b) / Gamma(had)
1999
The partial decay width of the Z to bb¯ quark pairs has been measured by the DELPHI detector at LEP using data taken in the years 1992 to 1995. Decays of b-hadrons were tagged by several methods using tracks with large impact parameters and/or reconstructed secondary vertices, complemented by event shape variables. Combining these methods in a multivariate analysis the value Γ(Z→bb¯)Γ(Z→had)=0.21634±0.00067(stat)±0.00060(syst) was obtained, where the cc¯ production fraction was fixed to its Standard Model value.
Search for scalar top quark pair production in natural gauge mediated supersymmetry models with the ATLAS detector in pp collisions at √(s)=7 TeV
2012
The results of a search for pair production of the lighter scalar partners of top quarks ((t) over bar (1)) in 2.05 fb(-1) of pp collisions at root s = 7 TeV using the ATLAS experiment at the LHC are reported. Scalar top quarks are searched for in events with two same flavour opposite-sign leptons (e, mu) with invariant mass consistent with the Z boson mass, large missing transverse momentum and jets in the final state. At least one of the jets is identified as originating from a b-quark. No excess over Standard Model expectations is found. The results are interpreted in the framework of R-parity conserving, gauge mediated Supersymmetry breaking 'natural' scenarios, where the neutralino ((c…
Search for charged Higgs bosons decaying via H-+/- -> tau nu in t(t)over-bar events using pp collision data at root s=7 TeV with the ATLAS detector
2012
The results of a search for charged Higgs bosons are presented. The analysis is based on 4.6 fb(-1) of proton-proton collision data at root s = 7TeV collected by the ATLAS experiment at the Large Hadron Collider, using top quark pair events with a tau lepton in the final state. The data are consistent with the expected background from Standard Model processes. Assuming that the branching ratio of the charged Higgs boson to a tau lepton and a neutrino is 100%, this leads to upper limits on the branching ratio of top quark decays to a b quark and a charged Higgs boson between 5% and 1% for charged Higgs boson masses ranging from 90GeV to 160GeV, respectively. In the context of the m(h)(max) s…
A measurement of b+ and b-0 lifetimes using (d)over-bar-l(+) events
1995
A measurement of B meson lifetimes is presented using data collected from 1991 to 1993 by the DELPHI detector at the LEP collider. Samples of events with a D meson and a lepton in the same jet are selected where D¯0ℓ+ and D*ℓ+ events originate mainly from the semileptonic decays of B+ and B0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into D¯∗∗ℓ+v , the following B meson lifetimes and lifetime ratio are measured: τ(B+)=1.61+0.16−0.16(stat.)±0.12(syst.)psτ(B0)=1.61+0.14−0.13(stat.)±0.08(syst.)psτ(B+)/τ(B0)=1.00+0.17−0.15(stat.)±0.10(syst.) and an average lifetime of B+ and B0 mesons is obtained: τ(…
Search for a Supersymmetric Partner to the Top Quark in Final States with Jets and Missing Transverse Momentum at root s=7 TeV with the ATLAS Detector
2012
A search for direct pair production of supersymmetric top squarks ((t) over tilde (1)) is presented, assuming the (t) over tilde (1) decays into a top quark and the lightest supersymmetric particle, (chi) over tilde (0)(1), and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13.5(-3.6)(+3.7) (4.4(-1.3)(+1.7)) events in two signal regions based on integral Ldt = 4.7 fb(-1) of pp collision data taken at root s = 7 TeV with the ATLAS detector at the LHC. An exclusion region in the (t) over tilde (1) versus (chi) over tilde (0)(1) mass plane is evaluated: 370 1) 10) similar to 0 GeV while m((t…