116437401
COMPASS RESULTS ON GLUON POLARISATION FROM HIGH PT HADRON PAIRS
AbstractOne of the goals of the COMPASS experiment is the determination of the gluonpolarisation ∆G/G, for a deep understanding of the spin structure of the nucleon.In DIS the gluon polarisation can be measured via the Photon-Gluon-Fusion (PGF)process, identiﬁed by open charm production or by selecting high p T hadron pairsin the ﬁnal state. The data used for this work were collected by the COMPASSexperiment during the years 2002-2004, using a 160 GeV naturally polarised positivemuon beam scattering on a polarised nucleon target. A new preliminary result of thegluon polarisation ∆G/G from high p T hadron pairs in events with Q 2 > 1 (GeV/c) 2 is presented. In order to extract ∆G/G, this analysis takes into account the leadingprocess γq contribution together with the PGF and QCD Compton processes. Anew weighted method based on a neural network approach is used. A preliminary∆G/G result for events from quasi-real photoproduction (Q 2 < 1 (GeV/c) 2 ) is alsopresented. 1 Introduction
125350297
COMPASS results on gluon polarisation
118204757
Gluon polarisation from high transverse momentum hadron pairs production (COMPASS)
A new preliminary result of a gluon polarisation \Delta G/G obtained selecting high transverse momentum hadron pairs in DIS events with Q^2>1 (GeV/c)^2 is presented. Data has been collected by COMPASS at CERN during the 2002-2004 years. In the extraction of $\Delta G/G$ contributions coming from the leading order $\gamma q$ and QCD processes are taken into account. A new weighting method based on a neural network approach is used. Also a preliminary result of \Delta G/G for events with Q^2<1 (GeV/c)^2 is presented.
117242696
Measurement of The Gluon Polarisation Through High $p_T$ Hadron Production in COMPASS
One of the missing keys in the present understanding of the spin structure of the nucleon is the contribution from the gluons: the so called gluon polarisation. This quantity can be determined in DIS through the Photon-Gluon Fusion (PGF) process, in which two analysis methods may be used: (i) identifying open charm events or (ii) selecting events with high pT hadrons. The data used in the present work were collected by the COMPASS Experiment, where a naturally polarised muon beam of 160 GeV, impinging on a polarised nucleon fixed target, is used. The results for the gluon polarisation from high pT are presented. The gluon polarisation result for high pT hadrons is divided, for the first time, into three independent xG bins at leading order (LO). A new weighted method based on a neural network approach is used.
121546704
Experimental Program of the Future COMPASS-II Experiment at CERN
Over the last decade the COMPASS experiment has successfully obtained precise results on nucleon structure and hadron spectroscopy, with statistical errors much lower than previously reported. Recently, the new COMPASS-II program, focused on the study of a more complete nucleon description, was approved by CERN. The goal of the program is to access the nucleon structure beyond the collinear approxi-mation, including the quark intrinsic transverse momentum distributions, which are described by the Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs) and by Generalised Parton Distributions (GPDs). The COMPASS collaboration proposes to measure the TMD PDFs, for the first time, via the polarised Drell-Yan process. The results will be complementary to those already obtained in polarised Semi-Inclusive Deep Inelastic Scattering (SIDIS). The GPDs can be accessed using deeply virtual Compton scattering and hard exclusive meson production using an unpolarised hydrogen target in a kinematic region not yet covered by any existing experiment. Also unpolarised SIDIS will be studied, by improving the knowledge of the strange quark PDF and obtaining the kaon fragmentation functions. Another topic covered in this COMPASS-II program is the measurement of the pion and kaon polarisabilities using the Primakoff reaction, which corresponds to a test of the chiral perturbative theory.
49553651
THE HABITABLE ZONE OF EARTH-LIKE PLANETS WITH DIFFERENT LEVELS OF ATMOSPHERIC PRESSURE
As a contribution to the study of the habitability of extrasolar planets, we implemented a one-dimensional energy balance model (EBM), the simplest seasonal model of planetary climate, with new prescriptions for most physical quantities. Here we apply our EBM to investigate the surface habitability of planets with an Earth-like atmospheric composition but different levels of surface pressure. The habitability, defined as the mean fraction of the planet's surface on which liquid water could exist, is estimated from the pressure-dependent liquid water temperature range, taking into account seasonal and latitudinal variations of surface temperature. By running several thousands of EBM simulations we generated a map of the habitable zone (HZ) in the plane of the orbital semi-major axis, a, and surface pressure, p, for planets in circular orbits around a Sun-like star. As pressure increases, the HZ becomes broader, with an increase of 0.25 AU in its radial extent from p = 1/3 to 3 bar. At low pressure, the habitability is low and varies with a; at high pressure, the habitability is high and relatively constant inside the HZ. We interpret these results in terms of the pressure dependence of the greenhouse effect, the efficiency of horizontal heat transport, and the extent of the liquid water temperature range. Within the limits discussed in the paper, the results can be extended to planets in eccentric orbits around non-solar-type stars. The main characteristics of the pressure-dependent HZ are modestly affected by variations of planetary properties, particularly at high pressure.
6720121
A Physical Model for the Coevolution of QSOs and Their Spheroidal Hosts
We present a physically motivated model for the early coevolution of massive spheroidal galaxies and active nuclei at their centers. Within dark matter halos, forming at the rate predicted by the canonical hierarchical clustering scenario, the gas evolution is controlled by gravity, radiative cooling, and heating by feedback from supernovae and from the growing active nucleus. Supernova heating is increasingly effective with decreasing binding energy in slowing down the star formation and in driving gas outflows. The more massive protogalaxies virializing at earlier times are thus the sites of the faster star formation. The correspondingly higher radiation drag fastens the angular momentum loss by the gas, resulting in a larger accretion rate onto the central black hole. In turn, the kinetic energy carried by outflows driven by active nuclei can unbind the residual gas, thus halting both the star formation and the black hole growth, in a time again shorter for larger halos. For the most massive galaxies the gas unbinding time is short enough for the bulk of the star formation to be completed before Type Ia supernovae can substantially increase the Fe abundance of the interstellar medium, thus accounting for the α-enhancement seen in the largest galaxies. The feedback from supernovae and from the active nucleus also determines the relationship between the black hole mass and the mass, or the velocity dispersion, of the host galaxy, as well as the black hole mass function. In both cases the model predictions are in excellent agreement with the observational data. Coupling the model with GRASIL (Silva et al. 1998), the code computing in a self-consistent way the chemical and spectrophotometric evolution of galaxies over a very wide wavelength interval, we have obtained predictions in excellent agreement with observations for a number of observables that proved to be extremely challenging for all the current semianalytic models, including the submillimeter counts and the corresponding redshift distributions, and the epoch-dependent K-band luminosity function of spheroidal galaxies.
18857754
Early-Type Galaxies in the Hubble Deep Field: The Star Formation History*
We have investigated the properties of a complete K-band selected sample of 35 elliptical and S0 galaxies brighter than K = 20.15 mag in the Hubble deep field, as representative of the field galaxy population. This sample has been derived from deep K-band image by the KPNO-IRIM camera, by applying a rigorous morphological classification scheme based on quantitative analyses of the surface brightness profiles. The completeness of the sample is proved by a careful evaluation of all biasing effects inherent in the automated selection procedure. Fifteen objects have spectroscopic redshifts, while for the remaining 20 a photometric redshift is estimated from a seven-color broadband spectrum (including four HST and three near-IR bands). This data set, based on public archives from HST and from deep observations at Kitt Peak and Hawaii, is unique for its morphological information and for its photometric and spectroscopic coverage. The broadband spectra of the sample galaxies, together with a few basic assumptions about the IMF and the stellar evolutionary paths, allow us to date their dominant stellar populations. The majority of bright early-type galaxies in this field are found at redshifts z 1.3 to display colors indicative of a fairly wide range of ages (typically 1.5 to 3 Gyr). Because of the different cosmological timescales, the star formation history depends to some extent on the assumed value for the cosmological deceleration parameter: we find that the major episodes of star formation (SF) building up typical M galaxies have taken place during a wide redshift interval 1 1.3, which should be detectable during the luminous star formation phase expected to happen at these redshifts. Obvious solutions are (1) that the merging events triggering the SF imply strongly perturbed morphologies that prevent selecting them by our morphological classification filter, or (2) that a dust-polluted interstellar medium (ISM) obscures the (either continuous or episodic) events of star formation, after which gas consumption (or a galactic wind) cleans up the galaxy. We conclude that the likely solution is a combination thereof, i.e., a set of dust-enshrouded merging-driven starbursts occurring during the first few gigayears of the galaxy's lifetime. While our main conclusions are moderately dependent on the assumed value of q0, an open universe is favored in our analysis by the match of the K-band local luminosity functions with the observed numbers of faint distant galaxies. Two sources of uncertainty in our analysis, i.e., the possible presence of a background cluster or group at z ~ 1 in the HDF (possibly contaminating the z distribution) and the lack of a complete spectroscopic identification, are shown unlikely to affect our main results. In any case, they will be reduced soon by new observations in the southern HDF and by deep spectroscopic surveys with large telescopes.
18550190
Evaluating and improving semi-analytic modelling of dust in galaxies based on radiative transfer calculations
The treatment of dust attenuation is crucial in order to compare the predictions of galaxy formation models with multiwavelength observations. Most past studies have used either simple analytic prescriptions or full radiative transfer (RT) calculations. Here, we couple star formation histories and morphologies predicted by the semi-analytic galaxy formation model MORGANA with RT calculations from the spectrophotometric and dust code GRASIL to create a library of galaxy spectral energy distributions from the UV/optical through the far-infrared, and compare the predictions of the RT calculations with analytic prescriptions. We consider a low- and high-redshift sample, as well as an additional library constructed with empirical, noncosmological star formation histories and simple (pure bulge or disc) morphologies. Based on these libraries, we derive fitting formulae for the effective dust optical depth as a function of galaxy physical properties such as metallicity, gas mass and radius. We show that such fitting formulae can predict the V-band optical depth with a scatter smaller than 0.4 dex for both the low- and high-redshift samples, but there is a large galaxy-to-galaxy scatter in the shapes of attenuation curves, probably due to geometrical variations, which our simple recipe does not capture well. However, our new recipe provides a better approximation to the GRASIL results at optical wavelength than standard analytic prescriptions from the literature, particularly at high redshift.
210001150
Bridging the cosmic infrared background to the X-ray background