Search results for "SPECTRA"
showing 10 items of 3542 documents
Observational signatures of Higgs inflation
2016
We investigate the dependency of Higgs inflation on the non-renormalisable matching between the low energy Standard Model limit and the inflationary regime at high energies. We show that for the top mass range $m_t \gtrsim 171.8$ GeV the scenario robustly predicts the spectral index $n_s \simeq 0.97$ and the tensor-to-scalar ratio $r\simeq 0.003$. The matching is however non-trivial, even the best-fit values $m_h=125.09$ GeV and $m_t=173.21$ GeV require a jump $\delta \lambda \sim 0.01$ in the Higgs coupling below the inflationary scale. For $m_t\lesssim 171.8$ GeV, the matching may generate a feature in the inflationary potential. In this case the predicted values of $n_s$ and $r$ vary but…
Axion cold dark matter: Status after Planck and BICEP2
2014
We investigate the axion dark matter scenario (ADM), in which axions account for all of the dark matter in the Universe, in light of the most recent cosmological data. In particular, we use the Planck temperature data, complemented by WMAP E-polarization measurements, as well as the recent BICEP2 observations of B-modes. Baryon Acoustic Oscillation data, including those from the Baryon Oscillation Spectroscopic Survey, are also considered in the numerical analyses. We find that, in the minimal ADM scenario, the full dataset implies that the axion mass m_a = 82.2 pm 1.1 {\mu}eV (corresponding to the Peccei-Quinn symmetry being broken at a scale f_a = (7.54 pm 0.10)*10^10 GeV), or m_a = 76.6 …
Two-particle angular correlations in e(+)e(-) interactions compared with QCD predictions
1998
Two-particle angular correlations in jet cones have been measured in e(+)e(-) annihilation into hadrons at LEP energies (root s = 91 and 183 GeV) and are compared with QCD predictions using the LPHD hypothesis. Two different functions have been tested. While the differentially normalized correlation function shows substantial deviations from the predictions, a globally normalized correlation function agrees well. The size of alpha(s)(eff) land other QCD parameters) and its running with the relevant angular scale, the validity of LPHD, and problems due to non-perturbative effects are discussed critically. (C) 1998 Elsevier Science B.V. All rights reserved.
Unraveling the pattern of the XYZ mesons
2014
We present a plausible mechanism for the origin of the $XYZ$ mesons in the heavy meson spectra within a standard quark-model picture. We discuss the conditions required for the existence of four--quark bound states or resonances contributing to the heavy meson spectra, being either compact or molecular. We concentrate on charmonium and bottomonium spectra, where several new states, difficult to understand as simple quark-antiquark pairs, have been reported by different experimental collaborations. The pivotal role played by entangled meson-meson thresholds is emphasized.
Confronting current NLO parton fragmentation functions with inclusive charged-particle spectra at hadron colliders
2013
The inclusive spectra of charged particles measured at high transverse momenta ($p_T\gtrsim$2GeV/c) in proton-proton and proton-antiproton collisions in the range of center-of-mass energies $\sqrt{s}=200-7000$GeV are compared with next-to-leading order perturbative QCD calculations using seven recent sets of parton-to-hadron fragmentation functions (FFs). Accounting for the uncertainties in the scale choices and in the parton distribution functions, we find that most of the theoretical predictions tend to overpredict the measured LHC and Tevatron cross sections by up to a factor of two. We identify the currently too-hard gluon-to-hadron FFs as the probable source of the problem, and justify…
Measurement of the semileptonic b branching fractions and average b mixing parameter in Z decays
2001
The semileptonic branching fractions for primary and cascade b decays BR(b -> lepton-), BR(b -> c -> lepton+) and BR(b -> cbar -> lepton-) were measured in hadronic Z decays collected by the DELPHI experiment at LEP. The sample was enriched in b decays using the lifetime information and various techniques were used to separate leptons from direct or cascade b decays. By fitting the momentum spectra of di-leptons in opposite jets, the average b mixing parameter chi-bar was also extracted. The following results have been obtained: BR(b -> lepton-) = (10.70 +/- 0.08 (stat) +/- 0.21 (syst)_{+0.44}^{-0.30}(model))% BR(b -> c -> lepton+) = (7.98 +/- 0.22 (stat) +/- 0.21 (s…
Measurement of inclusive pi(0) production in hadronic Z(0) decays
1996
An analysis is presented of inclusive \pi^0 production in Z^0 decays measured with the DELPHI detector. At low energies, \pi^0 decays are reconstructed by \linebreak using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to x_p = 2 \cdot p_{\pi}/\sqrt{s} = 0.75) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for {q\overline q} and {b \bar b} events. The number of \pi^0's per hadronic Z^0 event is N(\pi^0)/ Z_{had}^0 = 9.2 \pm 0.2 \mbox{(stat)} \…
Detailed studies of $^{100}$Mo two-neutrino double beta decay in NEMO-3
2019
The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of $^{100}$Mo to the ground state of $^{100}$Ru, $T_{1/2} = \left[ 6.81 \pm 0.01\,\left(\mbox{stat}\right) ^{+0.38}_{-0.40}\,\left(\mbox{syst}\right) \right] \times10^{18}$ y. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of $5\times10^5$ events and a signal-to-background ratio of ~80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of …
Search for extra dimensions in diphoton events from proton-proton collisions at root s=7 TeV in the ATLAS detector at the LHC
2013
The large difference between the Planck scale and the electroweak scale, known as the hierarchy problem, is addressed in certain models through the postulate of extra spatial dimensions. A search for evidence of extra spatial dimensions in the diphoton channel has been performed using the full set of proton–proton collisions at √s = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. This dataset corresponds to an integrated luminosity of 4.9fb[superscript −1]. The diphoton invariant mass spectrum is observed to be in good agreement with the Standard Model expectation. In the context of the model proposed by Arkani–Hamed, Dimopoulos and Dvali, 95% confidence le…
Effects of dissolved organic matter from a eutrophic lake on the freely dissolved concentrations of emerging organic contaminants
2014
The authors studied the effects of dissolved organic matter (DOM) on the bioavailability of bisphenol A (BPA) and chloramphenicol by measuring the freely dissolved concentrations of the contaminants in solutions containing DOM that had been isolated from a mesocosm in a eutrophic lake. The abundance and aromaticity of the chromophoric DOM increased over the 25-d mesocosm experiment. The BPA freely dissolved concentration was 72.3% lower and the chloramphenicol freely dissolved concentration was 56.2% lower using DOM collected on day 25 than using DOM collected on day 1 of the mesocosm experiment. The freely dissolved concentrations negatively correlated with the ultraviolent absorption coef…