Uncertainty In Luminosity Research Articles

The HERBAL Model: A Hierarchical Errors-in-variables Bayesian Lognormal Hurdle Model for Galactic Globular Cluster Populations

Galaxy stellar mass is known to be monotonically related to the size of the galaxy’s globular cluster (GC) population for Milky Way sized and larger galaxies. However, the relation becomes ambiguous for dwarf galaxies, where there is some evidence for a downturn in GC population size at low galaxy masses. Smaller dwarfs are increasingly likely to have no GCs, and these zeros cannot be easily incorporated into linear models. We introduce the Hierarchical Errors-in-variables ERrors-in-variables BAyesian Lognormal hurdle (HERBAL) model to represent the relationship between dwarf galaxies and their GC populations, and apply it to the sample of Local Group galaxies, where the luminosity range coverage is maximal. This bimodal model accurately represents the two populations of dwarf galaxies: those that have GCs and those that do not. Our model thoroughly accounts for all uncertainties, including measurement uncertainty, uncertainty in luminosity to stellar mass conversions, and intrinsic scatter. The hierarchical nature of our Bayesian model also allows us to estimate galaxy masses and individual mass-to-light ratios from luminosity data within the model. We find that 50% of galaxies are expected to host GC populations at a stellar mass of , and that the expected mass of GC populations remains linear down to the smallest galaxies. Our hierarchical model recovers an accurate estimate of the Milky Way stellar mass. Under our assumed error model, we find a nonzero intrinsic scatter of (95% credible interval) that should be accounted for in future models.

The fast beam condition monitor as standalone luminometer of the CMS experiment at the HL-LHC

For the Phase-2 CMS upgrade for the High-Luminosity LHC, a luminosity uncertainty of 1% is targeted. To achieve this goal, measurements from multiple luminometers with orthogonal systematics are required. A standalone luminometer, the Fast Beam Condition Monitor (FBCM) is being designed for the online bunch-by-bunch luminosity measurement. The sampling time resolution of ∼0.7 ns also enables the measurement of beam-induced backgrounds. In this paper, the hardware architecture and the readout protocol of the FBCM are described. The expected performance with a simple behavioral model of the front-end comprising a constant fraction discriminator is discussed, although the final implementation in the ASIC is still under discussion. Simulation results show that the FBCM will provide the required statistical uncertainty and deviation from linearity by employing 336 silicon-pad sensors, each with an area of about 3 mm2. In addition, the front-end with sensitivity to as low as 6000 electrons will satisfy the longevity constraints for an exposure of 1 MeV neutron equivalent fluence of 3.5 × 1015 per cm2.

Van der Meer scan luminosity measurement and beam\u2013beam correction

The main method for calibrating the luminosity at Large Hadron Collider (LHC) is van der Meer scan where the beams are swept transversely across each other. This beautiful method was invented in 1968. Despite the honourable age, it remains the preferable tool at hadron colliders. It delivers the lowest calibration systematics, which still often dominates the overall luminosity uncertainty at LHC experiments. Various details of the method are discussed in the paper. One of the main factors limiting proton–proton van der Meer scan accuracy is the beam–beam electromagnetic interaction. It modifies the shapes of the colliding bunches and biases the measured luminosity. In the first years of operation, four main LHC experiments did not attempt to correct the bias because of its complexity. In 2012 a correction method was proposed and then subsequently used by all experiments. It was based, however, on a simplified linear approximation of the beam–beam force and, therefore, had limited accuracy. In this paper, a new simulation is presented, which takes into account the exact non-linear force. Depending on the beam parameters, the results of the new and old methods differ by sim 1%. This needs to be propagated to all LHC cross-section measurements after 2012. The new simulation is going to be used at LHC in future luminosity calibrations.

Measurement of Z \u2192 \u03c4+\u03c4\u2212 production in proton-proton collisions at sqrt{mathrm{s}}=8 TeV

A measurement of Z → τ+τ− production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb−1, from pp collisions at sqrt{s}=8 TeV collected by the LHCb experiment. The τ+τ− candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for Z bosons with invariant mass between 60 and 120 GeV/c2, which decay to tau leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be {sigma}_{pp}{{}_{to Zto {tau}^{+}}}_{tau^{-}}=95.8 pm 2.1 pm 4.6 pm 0.2 pm 1.1 pb, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for Z → τ+τ− to Z → μ+μ− (Z → e+e−), determined to be 1.01 ± 0.05 (1.02 ± 0.06), is consistent with the lepton-universality hypothesis in Z decays.

R-Process nucleosynthesis from three-dimensional jet-driven core-collapse supernovae with magnetic misalignments

We investigate $r$-process nucleosynthesis in three-dimensional general relativistic magnetohydrodynamic simulations of jet-driven supernovae resulting from rapidly rotating, strongly magnetized core-collapse. We explore the effect of misaligning the pre-collapse magnetic field with respect to the rotation axis by performing four simulations: one aligned model and models with 15, 30, and 45 degree misalignments. The simulations we present employ a microphysical finite-temperature equation of state and a leakage scheme that captures the overall energetics and lepton number exchange due to post-bounce neutrino emission and absorption. We track the thermodynamic properties of the ejected material with Lagrangian tracer particles and analyse its composition with the nuclear reaction network SkyNet. By using different neutrino luminosities in post-processing the tracer data with SkyNet, we constrain the impact of uncertainties in neutrino luminosities. We find that, for the aligned model considered here, the use of an approximate leakage scheme results in neutrino luminosity uncertainties corresponding to a factor of 100-1000 uncertainty in the abundance of third peak $r$-process elements. Our results show that for misalignments of 30 degrees or less, $r$-process elements are robustly produced as long as neutrino luminosities are reasonably low ($\lesssim 5 \times 10^{52}$ erg s$^{-1}$). For a more extreme misalignment of 45 degrees, we find the production of $r$-process elements beyond the second peak significantly reduced. We conclude that robust $r$-process nucleosynthesis in magnetorotational supernovae requires a progenitor stellar core with a large poloidal magnetic field component that is at least moderately (within $\sim 30$ degrees) aligned with the rotation axis.

Fundamental parameters and infrared excesses of Tycho–Gaia stars

Effective temperatures and luminosities are calculated for 1,475,921 Tycho-2 and 107,145 Hipparcos stars, based on distances from Gaia Data Release 1. Parameters are derived by comparing multi-wavelength archival photometry to BT-Settl model atmospheres. The 1-sigma uncertainties for the Tycho-2 and Hipparcos stars are +/-137 K and +/-125 K in temperature and +/-35 per cent and +/-19 per cent in luminosity. The luminosity uncertainty is dominated by that of the Gaia parallax. Evidence for infrared excess between 4.6 and 25 microns is found for 4256 stars, of which 1883 are strong candidates. These include asymptotic giant branch (AGB) stars, Cepheids, Herbig Ae/Be stars, young stellar objects, and other sources. We briefly demonstrate the capabilities of this dataset by exploring local interstellar extinction, the onset of dust production in AGB stars, the age and metallicity gradients of the solar neighbourhood and structure within the Gould Belt. We close by discussing the potential impact of future Gaia data releases.

Luminosity determination in pp collisions at [Formula: see text] = 8 TeV using the ATLAS detector at the LHC.

The luminosity determination for the ATLAS detector at the LHC during pp collisions at sqrt{s} = 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of delta mathcal{L}/ mathcal{L} = pm 1.9% is obtained for the 22.7,mathrm {fb}^{-1} of pp collision data delivered to ATLAS at sqrt{s} = 8 TeV in 2012.

How similar are the properties of quasars with nearly identical ultraviolet spectra?

The spectrum of a quasar contains important information about its properties. Thus, it can be expected that two quasars with similar spectra will have similar properties, but just how similar has not before been quantified. Here we compare the ultraviolet spectra of a sample of 5553 quasars from Data Release 7 of the Sloan Digital Sky Survey, focusing on the $1350$ \AA \ $\leq \lambda \leq 2900$ \AA \ rest-frame region which contains prominent emission lines from \SiIV, O IV], \CIV, \CIII, and \MgII\ species. We use principal component analysis to determine the dominant components of spectral variation, as well as to quantitatively measure spectral similarity. As suggested by both the Baldwin effect and modified Baldwin effect, quasars with similar spectra have similar properties: bolometric luminosity, Eddington fraction, and black hole mass. The latter two quantities are calculated from the luminosity in conjunction with spectral features, and the variation between quasars with virtually identical spectra (which we call doppelg\"angers) is driven by the variance in the luminosity plus measurement uncertainties. In the doppelgangers the luminosity differences show 1$\sigma$ uncertainties of 57\% (or 0.63 magnitudes) and $\sim$70\% 1$\sigma$ uncertainties for mass and Eddington fraction. Much of the difference in luminosities may be attributable to time lags between the spectral lines and the continuum. Furthermore, we find that suggestions that the mostly highly accreting quasars should be better standard candles than other quasars are not bourne out for doppelgangers. Finally, we discuss the implications for using quasars as cosmological probes and the nature of the first two spectral principal components.

RESOLVING THE ACTIVE GALACTIC NUCLEUS AND HOST EMISSION IN THE MID-INFRARED USING A MODEL-INDEPENDENT SPECTRAL DECOMPOSITION

We present results on the spectral decomposition of 118 Spitzer Infrared Spectrograph (IRS) spectra from local active galactic nuclei (AGN) using a large set of Spitzer/IRS spectra as templates. The templates are themselves IRS spectra from extreme cases where a single physical component (stellar, interstellar, or AGN) completely dominates the integrated mid-infrared emission. We show that a linear combination of one template for each physical component reproduces the observed IRS spectra of AGN hosts with unprecedented fidelity for a template fitting method, with no need to model extinction separately. We use full probability distribution functions to estimate expectation values and uncertainties for observables, and find that the decomposition results are robust against degeneracies. Furthermore, we compare the AGN spectra derived from the spectral decomposition with sub-arcsecond resolution nuclear photometry and spectroscopy from ground-based observations. We find that the AGN component derived from the decomposition closely matches the nuclear spectrum, with a 1-sigma dispersion of 0.12 dex in luminosity and typical uncertainties of ~0.19 in the spectral index and ~0.1 in the silicate strength. We conclude that the emission from the host galaxy can be reliably removed from the IRS spectra of AGN. This allows for unbiased studies of the AGN emission in intermediate and high redshift galaxies -currently inaccesible to ground-based observations- with archival Spitzer/IRS data and in the future with the Mid-InfraRed Instrument of the James Webb Space Telescope. The decomposition code and templates are available at http://www.denebola.org/ahc/deblendIRS.

Six faint gamma-ray pulsars seen with theFermiLarge Area Telescope

Context: GeV gamma-ray pulsations from over 140 pulsars have been characterized using the Fermi Large Area Telescope, enabling improved understanding of the emission regions within the neutron star magnetospheres, and the contributions of pulsars to high energy electrons and diffuse gamma rays in the Milky Way. The first gamma-ray pulsars to be detected were the most intense and/or those with narrow pulses. Aims: As the Fermi mission progresses, progressively fainter objects can be studied. In addition to more distant pulsars (thus probing a larger volume of the Galaxy), or ones in high background regions (thus improving the sampling uniformity across the Galactic plane), we detect pulsars with broader pulses or lower luminosity. Adding pulsars to our catalog with inclination angles that are rare in the observed sample, and/or with lower spindown power, will reduce the bias in the currently known gamma-ray pulsar population. Methods: We use rotation ephemerides derived from radio observations to phase-fold gamma rays recorded by the Fermi Large Area Telescope, to then determine the pulse profile properties. Spectral analysis provides the luminosities and, when the signal-to-noise ratio allows, the cutoff energies. We constrain the pulsar distances by different means in order to minimize the luminosity uncertainties. Results: We present six new gamma-ray pulsars with an eclectic mix of properties. Three are young, and three are recycled. They include the farthest, the lowest power, two of the highest duty-cycle pulsars seen, and only the fourth young gamma-ray pulsar with a radio interpulse. We discuss the biases existing in the current gamma-ray pulsar catalog, and steps to be taken to mitigate the bias.

Improved luminosity determination in pp collisions at [Formula: see text] using the ATLAS detector at the LHC.

The luminosity calibration for the ATLAS detector at the LHC during pp collisions at sqrt{s} = 7~mathrm{TeV} in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at sqrt{s} = 7~mathrm{TeV}. A luminosity uncertainty of deltamathcal{L}/ mathcal{L} = pm 3.5~% is obtained for the 47 pb−1 of data delivered to ATLAS in 2010, and an uncertainty of deltamathcal{L}/ mathcal{L} = pm1.8~% is obtained for the 5.5 fb−1 delivered in 2011.

A study of the Z production cross-section in pp collisions at $ \sqrt{s}=7\,\mathrm{TeV} $ using tau final states

Abstract A measurement of the inclusive Z → ττ cross-section in pp collisions at $ \sqrt{s}=7\,\mathrm{TeV} $ is presented based on a dataset of 1.0 fb−1 collected by the LHCb detector. Candidates for Z → τ τ decays are identified through reconstructed final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. The production cross-section for Z bosons, with invariant mass between 60 and 120 GeV/c 2, which decay to τ leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5, is measured to be σ pp→Z→ττ = 71.4 ± 3.5 ± 2.8 ± 2.5 pb; the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the integrated luminosity. The ratio of the cross-sections for Z → τ τ to Z → μμ is determined to be 0.93 ± 0.09, where the uncertainty is the combination of statistical, systematic, and luminosity uncertainties of the two measurements.

PDF dependence of Higgs cross sections at the Tevatron and LHC: response to recent criticism

We respond to some criticism questioning the validity of the current Standard Model Higgs exclusion limits at the Tevatron, due to the significant dependence of the dominant production cross section from gluon-gluon fusion on the choice of parton distribution functions (PDFs) and the strong coupling (α S ). We demonstrate the ability of the Tevatron jet data to discriminate between different high-x gluon distributions, performing a detailed quantitative comparison to show that fits not explicitly including these data fail to give a good description. In this context we emphasise the importance of the consistent treatment of luminosity uncertainties. We comment on the values of α S obtained from fitting deep-inelastic scattering data, particularly the fixed-target NMC data, and we show that jet data are needed for stability. We conclude that the Higgs cross-section uncertainties due to PDFs and α S currently used by the Tevatron and LHC experiments are not significantly underestimated, contrary to some recent claims.

Measuring the Higgs-vector boson couplings at lineare+e−collider

We estimate the accuracy with which the coefficient of the $CP$ even dimension-six operators involving Higgs and two vector bosons ($HVV$) can be measured at linear ${e}^{+}{e}^{\ensuremath{-}}$ colliders. Using the optimal observables method for the kinematic distributions, our analysis is based on the five different processes. First is the $WW$ fusion process in the $t$-channel (${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}{\ensuremath{\nu}}_{e}H$), where we use the rapidity $y$ and the transverse momentum ${p}_{\mathrm{T}}$ of the Higgs boson as observables. Second is the $ZH$ pair production process in the $s$ channel, where we use the scattering angle of the $Z$ and the $Z$ decay angular distributions, reproducing the results of the previous studies. Third is the $t$-channel $ZZ$, fusion processes (${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}H$), where we use the energy and angular distributions of the tagged ${e}^{+}$ and ${e}^{\ensuremath{-}}$. In the fourth, we consider the rapidity distribution of the untagged ${e}^{+}{e}^{\ensuremath{-}}H$ events, which can be approximated well as the $\ensuremath{\gamma}\ensuremath{\gamma}$ fusion of the bremsstrahlung photons from ${e}^{+}$ and ${e}^{\ensuremath{-}}$ beams. As the last process, we consider the single-tagged ${e}^{+}{e}^{\ensuremath{-}}H$ events, which probe the $\ensuremath{\gamma}{e}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}H{e}^{\ifmmode\pm\else\textpm\fi{}}$ process. All the results are presented in such a way that statistical errors of the constraints on the effective couplings and their correlations are read off when all of them are allowed to vary simultaneously, for each of the above processes, for ${m}_{H}=120\text{ }\text{ }\mathrm{GeV}$, at $\sqrt{s}=250\text{ }\text{ }\mathrm{GeV}$, 350 GeV, 500 GeV, and 1 TeV, with and without ${e}^{\ensuremath{-}}$ beam polarization of 80%. We find, for instance, that the $HZZ$ and $HWW$ couplings can be measured with 0.6% and 0.9% accuracy, respectively, for the integrated luminosity of $L=100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ at $\sqrt{s}=250\text{ }\text{ }\mathrm{GeV}$, 350 GeV, and $L=500\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ at $\sqrt{s}=500\text{ }\text{ }\mathrm{GeV}$, 1 TeV, for the luminosity uncertainty of 1% at each energy. We find that the luminosity uncertainty affects only one combination of the nonstandard couplings, which are proportional to the standard $HWW$ and $HZZ$ couplings, while it does not affect the errors of the other independent combinations of the couplings. As a consequence, we observe that a few combinations of the eight dimension-six operators can be constrained as accurately as the two operators, which have been constrained by the precision measurements of the $Z$ and $W$ boson properties.

α Centauri AB

Detailed models of α Centauri A and B based on the Hipparcos, Yale, and Soderhjelm parallaxes are compared. The consequences of the uncertainty in mass, luminosity, surface temperature, and composition on the structure and the p-mode pulsation spectrum of the models are presented. All of the models were constructed using the most current stellar structure physics available to us, including helium and heavy-element diffusion, OPAL (Lawrence Livermore Opacity Library) equation of state, and OPAL and Alexander opacities. Self-consistent models of α Cen A and B that satisfy the observational constraints have an initial helium mass fraction YZAMS=~0.28. The age of the system depends critically on whether or not α Cen A has a convective core. If it does (our best model), then α Cen AB is ~7.6 Gyr old, and if it does not, then the binary system is ~6.8 Gyr old. Both ages and YZAMS are accurate to ±~10% owing to observational uncertainties. The Galactic enrichment parameter (ΔY/ΔZ) for our best model pair is less than 1. Pulsation analyses of our best models yield an average large and small spacing of 101±3 μHz and 4.6±0.4 μHz, respectively, for α Cen A, and 173±6 μHz and 15±1 μHz for α Cen B. Some methodologies that use p-mode frequency observations to constrain the system further are outlined. We include a simple test to determine whether or not α Cen A has a convective core and introduce a method to use the small frequency spacing to determine the age of system, overcoming the limitation that it is also sensitive to composition.