123119837
Time projection chambers for the T2K near detectors
The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector located 295 km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator–bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker are used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/NOMAD dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system.
16373353
Mass limit for the lightest neutralino
AbstractIndirect limits on the mass of the lightest neutralino are derived from the results of searches for charginos, neutralinos, and sleptons performed with data taken by the ALEPH Collaboration at centre-of-mass energies near the Z peak and at 130 and 136 GeV. Within the context of the Minimal Supersymmetric Standard Model and when
$$M_{\tilde \nu } \geqslant 200 GeV/c^2 $$
, the boundMx> 12.8 GeV/c2 at the 95% confidence level applies for any tanβ. The impact of lighter sneutrinos is presented in the framework of SUSY grand unified theories; a massless neutralino is allowed only for a narrow range of tanβ,μ, and the scalar mass parameterm0. Finally, by including Higgs mass constraints and requiring that radiative electroweak symmetry breaking occur, more stringent bounds onMx as a function of tanβ are derived.
121018557
Measurement of triple gauge-boson couplings at 172 GeV
The triple gauge-boson couplings, αWΦ, αW and αBΦ, have been measured using 34 semileptonically and 54 hadronically decaying W+W− candidate events. The events were selected in the data recorded during 1996 with the ALEPH detector at 172 GeV, corresponding to an integrated luminosity of 10.65 pb−1. The triple gauge-boson couplings have been measured using optimal observables constructed from kinematic information of W+W− events. The results are in agreement with the Standard Model expectation.
125825698
Improved measurement of the $\bar{B}^0$ and $B^{-}$ meson lifetimes
110110190
Architecture of the HERA-B data acquisition system
The HERA-B experiment was dedicated for the measurement of CP-violation in decays of neutral B-mesons and for investigating the physics of charmed particles. One of the experimental requirements is a highly selective on-line filtering of data due to high interaction rates and a low signal-to-background ratio. This demands a hierarchical trigger and a high bandwidth data acquisition system. The challenge for the DAQ system is a readout free of deadtime, which requires an unprecedent speed of storing and processing the data. In this paper we will outline the general architecture and hardware implementation of the HERA-B DAQ.
120102665
Search for neutrino-induced charged current coherent pion production with carbon in a 1.3 GeV wide band muon neutrino beam
The search for charged-current coherent pion production induced by neutrinos with a mean energy of 1.3 GeV is discussed. The data are collected with a fully active scintillator detector in the K2K long-baseline neutrino oscillation experiment. No evidence for coherent pion production is observed and an upper limit of 0.60 × 10−2 is set on the cross section ratio of coherent pion production to the total charged current interaction at the 90% confidence level.
117442387
Star Formation and Molecular Gas in AGN
We present initial results from a survey of nearby AGN using the near infrared adaptive optics integral field spectrograph SINFONI. These data enable us to probe the distribution and kinematics of the gas and stars at spatial resolutions as small as 0.085arcsec, corresponding in some cases to less than 10pc. In this contribution we present results concerning (1) the molecular gas in the nucleus of NGC1068 and its relation to the obscuring torus; and (2) the stars which exist on spatial scales of a few tens of parsecs around the AGN, the evidence for their remarkably young age and extreme intensities, and their relation to the AGN.
118466336
Precise measurement of the radial baryon acoustic oscillation scales in galaxy redshift surveys
In this paper we present a new method to extract cosmological parameters using the radial scale of the Baryon Acoustic Oscillations as a standard ruler in deep galaxy surveys. The method consists in an empirical parametrization of the radial 2-point correlation function, which provides a robust and precise extraction of the sound horizon scale. Moreover, it uses data from galaxy surveys in a manner that is fully cosmology independent and therefore, unbiased. A study of the main systematic errors and the validation of the method in cosmological simulations are also presented, showing that the measurement is limited only by cosmic variance. We then study the full information contained in the Baryon Acoustic Oscillations, obtaining that the combination of the radial and angular determinations of this scale is a very sensitive probe of cosmological parameters, able to set strong constraints on the dark energy properties, even without combining it with any other probe.
118846693
Measuring the transition to homogeneity with photometric redshift surveys
We study the possibility of detecting the transition to homogeneity using photometric redshift catalogs. Our method is based on measuring the fractality of the projected galaxy distribution, using angular distances, and relies only on observable quantites. It thus provides a way to test the Cosmological Principle in a model-independent unbiased way. We have tested our method on dierent synthetic inhomogeneous catalogs, and shown that it is capable of discriminating some fractal models with relatively large fractal dimensions, in spite of the loss of information due to the radial projection. We have also studied the inuence of the redshift bin width, photometric redshift errors, bias, non-linear clustering, and surveyed area, on the angular homogeneity index H2( ) in a CDM cosmology. The level to which an upcoming galaxy survey will be able to constrain the transition to homogeneity will depend mainly on the total surveyed area and the compactness of the surveyed region. In particular, a Dark Energy Survey (DES)-like survey should be able to easily discriminate certain fractal models with fractal dimensions as large as D2 = 2:95. We believe that this method will have relevant applications for upcoming large photometric redshift surveys, such as DES or the Large Synoptic Survey Telescope (LSST).
18485124
SINFONI adaptive optics integral field spectroscopy of the Circinus Galaxy
Aims. We investigate the star formation activity and the gas and stellar dynamics on scales of a few parsecs in the nucleus of the Circinus Galaxy. Methods. Using the adaptive optics near infrared integral field spectrometer SINFONI on the VLT, we have obtained observations of the Circinus galaxy on scales of a few parsecs and at a spectral resolution of 70 km s −1 FWHM. The physical properties of the nucleus are analyzed by means of line and velocity maps extracted from the SINFONI datacube. Starburst models are constrained using the Brγ flux, stellar continuum (as traced via the CO absorption bandheads longward of 2.3 µm), and radio continuum. Results. The similarity of the morphologies of the H2 1−0S (1) 2.12 µ ma nd Brγ 2.17 µm lines to the stellar continuum and also their kinematics, suggest a common origin in star formation. Within 8 pc of the AGN we find there has been a recent starburst in the last 100 Myr, which currently accounts for 1.4% of the galaxy’s bolometric luminosity. The similarity of the spatial scales over which the stars and gas exist indicates that this star formation is occuring within the torus; and comparison of the gas column density through the torus to the maximum possible optical depth to the stars implies the torus is a clumpy medium. The coronal lines show asymmetric profiles with a spatially compact narrow component and a spatially extended blue wing. These characteristics are consistent with some of the emission arising in clouds gravitationally bound to the AGN, and some outflowing in cloudlets which have been eroded away from the bound clouds.
15076787
MOLECULAR GAS STREAMERS FEEDING AND OBSCURING THE ACTIVE NUCLEUS OF NGC 1068
We report the first direct observations of neutral, molecular gas streaming in the nucleus of NGC 1068 on scales of <30 pc using SINFONI near-infrared integral field spectroscopy. At a resolution of 0075, the flux map of 2.12 μm 1-0 S(1) molecular hydrogen emission around the nucleus in the central arcsec reveals two prominent linear structures leading to the active galactic nucleus from the north and south. The kinematics of the gas in these features are dominated by noncircular motions and indicate that material streams toward the nucleus on highly elliptical or parabolic trajectories, whose orientations are compatible with that of the disk plane of the galaxy. We interpret the data as evidence for fueling of gas to the central region. The radial transport rate from ~30 pc to a few parsecs from the nucleus is ~15 M ☉ yr–1. One of the infalling clouds lies directly in front of the central engine. We interpret it as a tidally disrupted streamer that forms the optically thick outer part of an amorphous clumpy molecular/dusty structure which contributes to the nuclear obscuration.