A comparative study of the D0 neural-network analysis of the top quark non-leptonic decay channel

A simpler neural-network approach is presented for the analysis of the top quark non-leptonic decay channel in events of the D0 Collaboration. Results for the top quark signal are comparable to those found by the D0 Collaboration by a more elaborate handling of the event information used as input to the neural network.Comment: 5 pages, 1 figur

Interannual variability of winter precipitation in the European Alps: relations with the North Atlantic Oscillation.

Abstract. The European Alps rely on winter precipitation for various needs in terms of hydropower and other water uses. Major European rivers originate from the Alps and depend on winter precipitation and the consequent spring snow melt for their summer base flows. Understanding the fluctuations in winter rainfall in this region is crucially important to the study of changes in hydrologic regime in river basins, as well as to the management of their water resources. Despite the recognized relevance of winter precipitation to the water resources of the Alps and surrounding regions, the magnitude and mechanistic explanation of interannual precipitation variability in the Alpine region remains unclear and poorly investigated. Here we use gridded precipitation data from the CRU TS 1.2 to study the interannual variability of winter alpine precipitation. We found that the Alps are the region with the highest interannual variability in winter precipitation in Europe. This variability cannot be explained by large scale climate patterns such as the Arctic Oscillation (AO), North Atlantic Oscillation (NAO) or the East Atlantic/West Russia (EA/WR), even though regions below and above the Alps demonstrate connections with these patterns. Significant trends were detected only in small regions located in the Eastern part of the Alps

The assembly of massive galaxies from NIR observations of the Hubble Deep Field South

We use a deep K(AB)<25 galaxy sample in the Hubble Deep Field South to trace the evolution of the cosmological stellar mass density from z~ 0.5 to z~3. We find clear evidence for a decrease of the average stellar mass density at high redshift, 2<z<3.2, that is 15^{+25}_{-5}% of the local value, two times higher than what observed in the Hubble Deep Field North. To take into account for the selection effects, we define a homogeneous subsample of galaxies with 10^{10}M_\odot \leq M_* \leq 10^{11}M_\odot: in this sample, the mass density at z>2 is 20^{+20}_{-5} % of the local value. In the mass--limited subsample at z>2, the fraction of passively fading galaxies is at most 25%, although they can contribute up to about 40% of the stellar mass density. On the other hand, star--forming galaxies at z>2 form stars with an average specific rate at least ~4 x10^{-10} yr$^{-1}$, 3 times higher than the z<~1 value. This implies that UV bright star--forming galaxies are substancial contributors to the rise of the stellar mass density with cosmic time. Although these results are globally consistent with $\Lambda$--CDM scenarios, the present rendition of semi analytic models fails to match the stellar mass density produced by more massive galaxies present at z>2.Comment: Accepted for publication on ApJLetter

The evolution of the galaxy luminosity function in the rest frame blue band up to z=3.5

We present an estimate of the cosmological evolution of the field galaxy luminosity function (LF) in the rest frame 4400 Angstrom B -band up to redshift z=3.5. To this purpose, we use a composite sample of 1541 I--selected galaxies selected down to I_(AB)=27.2 and 138 galaxies selected down to K_(AB)=25 from ground-based and HST multicolor surveys, most notably the new deep JHK images in the Hubble Deep Field South (HDF-S) taken with the ISAAC instrument at the ESO-VLT telescope. About 21% of the sample has spectroscopic redshifts, and the remaining fraction well calibrated photometric redshifts. The resulting blue LF shows little density evolution at the faint end with respect to the local values, while at the bright end (M_B(AB)<-20) a brightening increasing with redshift is apparent with respect to the local LF. Hierarchical CDM models overpredict the number of faint galaxies by about a factor 3 at z=1. At the bright end the predicted LFs are in reasonable agreement only at low and intermediate redshifts (z=1), but fail to reproduce the pronounced brightening observed in the high redshift (z=2-3) LF. This brightening could mark the epoch where a major star formation activity is present in the galaxy evolution.Comment: 14 pages, 2 figures, Astrophysical Journal Letters, in pres

Strongly star-forming rotating disks in a complex merging system at z = 4,7 as revealed by ALMA

We performed a kinematical analysis of the [CII] line emission of the BR 1202-0725 system at z~4,7 using ALMA observations. The most prominent sources of this system are a quasar and a submillimeter galaxy, separated by a projected distance of about 24 kpc and characterized by very high SFR, higher than 1000 Msun/yr. However, the ALMA observations reveal that these galaxies apparently have undisturbed rotating disks, which is at variance with the commonly accepted scenario in which strong star formation activity is induced by a major merger. We also detected faint components which, after spectral deblending, were spatially resolved from the main QSO and SMG emissions. The relative velocities and positions of these components are compatible with orbital motions within the gravitational potentials generated by the QSO host galaxy and the SMG, suggesting that they are smaller galaxies in interaction or gas clouds in accretion flows of tidal streams. We did not find any clear spectral evidence for outflows caused by AGN or stellar feedback. This suggests that the high star formation rates might be induced by interactions or minor mergers with these companions, which do not affect the large-scale kinematics of the disks, however. Our kinematical analysis also indicates that the QSO and the SMG have similar Mdyn, mostly in the form of molecular gas, and that the QSO host galaxy and the SMG are seen close to face-on with slightly different disk inclinations: the QSO host galaxy is seen almost face-on (i~15), while the SMG is seen at higher inclinations (i~25). Finally, the ratio between the black hole mass of the QSO, obtained from XShooter spectroscopy, and the Mdyn of the host galaxy is similar to value found in very massive local galaxies, suggesting that the evolution of black hole galaxy relations is probably better studied with dynamical than with stellar host galaxy masses.Comment: Accepted for publication in Astronomy and Astrophysic

Fluctuations and Entropy Indices of QCD Parton Showers

The branching processes in parton showers are studied in perturbative QCD for both quark and gluon jets. The emphasis is on the nature of fluctuations of both the parton multiplicities and the spatial patterns of the final states. Effective measures of such fluctuations are calculated from the data obtained by Monte Carlo simulations. The entropy indices are used to characterize chaoticity. Both running and fixed couplings are considered. The fixed coupling case is used to study the onset of chaos. Implications of the results are discussed.Comment: 8 pages, LaTex, 12 figures in a single postscript file, submitted to Phys. Rev. D. Hard copy sent upon request to [email protected]

Calculating Dilepton Rates from Monte Carlo Simulations of Parton Production

To calculate dilepton rates in a Monte Carlo simulation of ultrarelativistic heavy ion collisions, one usually scales the number of similar QCD processes by a ratio of the corresponding differential probabilities. We derive the formula for such a ratio especially for dilepton bremsstrahlung processes. We also discuss the non-triviality of including higher order corrections to direct Drell-Yan process. The resultant mass spectra from our Monte Carlo simulation are consistent with the semi-analytical calculation using dilepton fragmentation functions.Comment: 14 pages in RevTex, 3 figures in uuencoded files, LBL-3466

Isoscalar resonances with J^{PC}=1^{--} in e^+e^-annihilation

The analysis of the vector isoscalar excitations in the energy range between 1 and 2 GeV of the $e^+e^-$ annihilation is presented for the final states $\pi^+\pi^-\pi^0$, $\omega\pi^+\pi^-$, $K^+K^-$, $K^0_SK^\pm\pi^\mp$ and $K^{\ast0}K^-\pi^++ c.c$. The effects of both the resonance mixing and the successive opening of multiparticle channels, with the energy dependent partial widths, are taken into account. The work extends our previous analysis hep-ph/9609216 of the vector isovector excitations and is aimed to compare the existing data with the predictions of the $q\bar q$ model. It is shown that this hypothesis does not contradict the data.Comment: 16 pages, revtex, 6 ps figures. Clarifying remarks, a table, and references are added. Accepted in Phys. Rev.