121910914
A GeSi active target for the measurement of short lifetimes
Abstract A new GeSi active target is presently used in the NA1 experiment at CERN to study photoproduction of charmed particles and to measure their lifetimes. Some general comments on the active target technique are made.
108986863
Performance measurements of histe-V VLPC photon detectors for E835 at FNAL
A set of 144 VLPC chips has been used by experiment E835 at FNAL for the readout of its scintillating fiber detector. During the data taking, the fibers have been exposed to rates up to 2.5×104 mips/sec, corresponding to 3.5×106 photons/sec on each VLPC pixel surface. This paper reports about a study on rate dependence of gain and quantum efficiency throughout the run, as well as VLPC failure statistics during operation. No significant aging effects are observed. A review about the overall system performance is given.
123064237
The charged trigger of the experiment E835 at Fermilab
Abstract Fermilab experiment E835 studies the charmonium states primarily through their electromagnetic decays. A kinematical charged trigger has been designed to select the electromagnetic final states e + e − and e + e − X and the hadronic decay c c → φφ →4 K ± . A detailed description of the charged trigger is presented here. The design, its implementation and the performances are given.
119936495
Hadronic Physics with Antiprotons at FAIR
The physics program of the future FAIR facility covers a wide range of topics that address central issues of strong interactions and QCD. The antiproton beam of unprecedented quality in the momentum range from 1 GeV/c to 15 GeV/c will allow to make high precision, high statistics measurements, from charmonium spectroscopy to the search for exotic hadrons and the study of nucleon structure, from the study of in-medium modifications of hadron masses to the physics of hypernuclei. These topics form the scientific program of the PANDA experiment. In addition to that the possibility to polarize antiprotons will provide the possibility to perform new, unique measurements of single- and double-spin observables, which are part of the experimental program of PAX.
125782352
Experimental Study of the Strong Interaction at FAIR
The physics program of the future FAIR facility covers a wide range of topics that address central issues of strong interactions and QCD. The antiproton beam of unprecedented quality in the momentum range from 1 GeV/c to 15 GeV/c will allow to make high precision, high statistics measurements, from charmonium spectroscopy to the search for exotic hadrons and the study of nucleon structure, from the study of in-medium modification s of hadron masses to the physics of hypernuclei. In addition to that the possibility to polarize antiprotons will provide access to a wealth of singleand double-spin observables, opening up the possibility to perform new, unique measurements, like the transversity distribution of the valence quarks in the proton, new measurements of singlespin asymmetries and the first determination of the relative phase of the electric and magnetic form factors of the proton in the time-like region. In this paper we will discuss the experimental program of the PANDA and PAX experiments, which will address these fundamental issues at FAIR.
121711542
Drift chambers with controlled charge collection geometry for the NA34/Helios experiment
We report on the design and performance of a set of drift chambers for the NA34/HELIOS experiment at the CERN-SPS. The chambers are operated with CO2 at low drift velocity and have a field geometry allowing a controllable track sample length and isochronous charge collection. In beam tests using a silicon microstrip hodoscope as external track reference, we measure a two-track separation of 600 μm and, at a drift velocity of 8.9 μm/ns, an absolute single track percision of 60 μ on average the total drift distance of 20 mm. The influence of the track sample length on the chamber performance is studied and a value of 2.5–3.0 mm is found as an optimum.
55221673
EVOLUTION OF BRIGHTEST CLUSTER GALAXY STRUCTURAL PARAMETERS IN THE LAST ∼6 Gyr: FEEDBACK PROCESSES VERSUS MERGER EVENTS
We present results on the evolution of the structural parameters of two samples of brightest cluster galaxies (BCGs) in the last 6 Gyr. The nearby sample of BCGs consists of 69 galaxies from the WINGS survey spanning a redshift range of 0.04 < z < 0.07. The intermediate-redshift (0.3 < z < 0.6) sample is formed by 20 BCGs extracted from the Hubble Space Telescope archive. Both samples have similar spatial resolution and their host clusters have similar X-ray luminosities. We report an increase in the size of the BCGs from intermediate to local redshift. However, we do not detect any variation in the Sersic shape parameter in both samples. These results prove to be robust since the observed tendencies are model independent. We also obtain significant correlations between some of the BCG parameters and the main properties of the host clusters. More luminous, larger, and centrally located BCGs are located in more massive and dominant galaxy clusters. These facts indicate that the host galaxy cluster has played an important role in the formation of their BCGs. We discuss the possible mechanisms that can explain the observed evolution of the structural parameters of the BCGs. We conclude that the main mechanisms that can explain the increase in size and the non-evolution in the Sersic shape parameter of the BCGs in the last 6 Gyr are feedback processes. This result disagrees with semi-analytical simulation results supporting the idea that merging processes are the main mechanism responsible for the evolution of the BCGs up until the present epoch.
11244261
Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of H emission line of a sample of 111 spiral galaxies with recognizable and well defined spiral morphology and with a well determined environmental status, ranging from isolation to non-disruptive interaction with satellites or companions. The form and properties of the rotation curves are considered as a function of the isolation degree, morphological type and luminosity. The line ratios are used to estimate the metallicity of all the detected HII regions, thus producing a composite metallicity profile for dierent types of spirals. We have found that isolated galaxies tend to be of later types and lower luminosity than the interacting galaxies. The outer parts of the rotation curves of isolated galaxies tend to be flatter than in interacting galaxies, but they show similar relations between global parameters. The scatter of the Tully-Fisher relation defined by isolated galaxies is significantly lower than that of interacting galaxies. The (NII)/H ratios, used as a metallicity indicator, show a clear trend between Z and morphological type, t, with earlier spirals showing higher ratios; this trend is tighter when instead of t the gradient of the inner rotation curve, G, is used; no trend is found with the change in interaction status. The Z-gradient of the disks depends on the type, being almost flat for early spirals, and increasing for later types. The (NII)/H ratios measured for disk HII regions of interacting galaxies are higher than for normal/isolated objects, even if all the galaxy families present similar distributions of H Equivalent Width.
10342067
THE VISIBLE ENVIRONMENT OF POLAR RING GALAXIES
A statistical study of the environment around Polar Ring Galaxies is presented. Two kinds of search are performed: 1) a study of the concentration and diameters of all the objects surrounding the Polar Rings, within a search eld 5 times the ring diameter. New magnitudes for polar ring galaxies are pre- sented. 2) a search, in a wider eld, for galaxies of similar size that may have encountered the polar ring host galaxy in a time of the order of 1 Gyr. Differently from the results of similar searches in the elds of active galaxies, the environment of the Polar Ring Galaxies seems to be similar to that of normal galax- ies. This result may give support to the models suggesting long timesforformationandevolutionoftherings.Iftheringsareold (and stable or in equilibrium), no traces of the past interaction are expected in their surroundings. In addition, the formation of massive polar rings, too big to derive from the ingestion of a present-day dwarf galaxy, may be easily placed in epochs with a higher number of gas-rich galaxies.
118464591
A new photometric investigation of the double-ringed galaxy ESO 474—G26: unveiling the formation scenario
We present a detailed photometric study of the peculiar double-ringed galaxy ESO 474−G26. Near-infrared (NIR) and optical data have been used, with the main goal of constraining the formation history of ESO 474−G26. NIR photometry is fundamental in this kind of study, because it gives better constraints on the spectral energy distribution (SED) and traces the older stellar population of the galaxy well. This galaxy presents a very complex structure with two almost orthogonal rings, one in the equatorial and another in the polar plane, around an elliptical-like object. Due to the peculiar morphology of ESO 474−G26, we used both NIR images (J and K bands) to derive accurate analysis of the stellar light distribution and optical images (in the B, V and R bands) to derive colour profiles and colour maps to study the structure of the rings. The observational characteristics of ESO 474−G26 are typical of galaxies that have experienced some kind of interaction during their evolution. We investigated two alternatives: a merging process and an accretion event.
119467863
Properties of Isolated Disk Galaxies
We present a new sample of northern isolated galaxies, which are defined by the physical criterion that they were not affected by other galaxies in their evolution during the last few Gyr. To find them we used the logarithmic ratio, f , between inner and tidal forces acting upon the candidate galaxy by a possible perturber. The analysis of the distribution of the f -values for the galaxies in the Coma cluster lead us to adopt the criterion f ≤− 4.5 for isolated galaxies. The candidates were chosen from the CfA catalog of galaxies within the volume defined bycz ≤ 5000 km s −1 , galactic latitude higher than 40 ◦ and declination ≥−2.5 ◦ . The selection of the sample, based on redshift values (when available), magnitudes and sizes of the candidate galaxies and possible perturbers present in the same field is discussed. The final list of selected isolated galaxies includes 203 objects from the initial 1706. The list contains only truly isolated galaxies in the sense defined, but it is by no means complete, since all the galaxies with possible companions under the f -criterion but with unknown redshift were discarded. We also selected a sample of perturbed galaxies comprised of all the disk galaxies from the initial list with companions (with known redshift) satisfying f ≥− 2a nd∆(cz) ≤ 500 km s −1 ; a total of 130 objects. The statistical comparison of both samples shows significant differences in morphology, sizes, masses, luminosities and color indices. Confirming previous results, we found that late spiral, Sc-type galaxies are, in particular, more frequent among isolated galaxies, whereas Lenticular galaxies are more abundant among perturbed galaxies. Isolated systems appear to be smaller, less luminous and bluer than interacting objects. We also found that bars are twice as frequent among perturbed galaxies compared to isolated galaxies, in particular for early Spirals and Lenticulars. The perturbed galaxies have higher LFIR/LB and Mmol/LB ratios, but the atomic gas content is similar for the two samples. The analysis of the luminosity-size and mass-luminosity relations shows similar trends for both families, the main difference being the almost total absence of big, bright and massive galaxies among the family of isolated systems, together with the almost total absence of small, faint and low mass galaxies among the perturbed systems. All these aspects indicate that the evolution induced by interactions with neighbors would proceed from late, small, faint and low mass Spirals to earlier, bigger, more luminous and more massive spiral and lenticular galaxies, producing at the same time a larger fraction of barred galaxies but preserving the same relations between global parameters. The properties we found for our sample of isolated galaxies appear similar to those of high redshift galaxies, suggesting that the present-day isolated galaxies could be quietly evolved, unused building blocks surviving in low density environments.