122356247
Automatic analysis of the emulsion chamber using the image scanner applied to the Tibet hybrid experiment
A new method of emulsion chamber analysis by using an image scanner is developed in order to process a large number of X-ray films used in the Tibet hybrid experiment which is carried out to observe primary proton spectrum in the PeV region. The experimental procedure in this method consists of multiple steps of processing the image of the X-ray films, i.e. the detection of cascade showers induced by high-energy γ-rays, the noise reduction, the spatial reconstruction of γ-families and their energy determination. The quality of the results obtained by the new method is compared with that obtained by the current manual method or Monte Carlo simulations. It is shown that sufficiently high quality of the emulsion chamber analysis is realized by the automatic method both in energy and geometrical resolution.
108549890
A fast Time‐of‐Flight detector also used as a tracker
We present a possible scheme for a fast Time‐of‐Flight detector which could also serve as part of the charged particle tracking system. The detector consists of scintillating fibers read out by newly developed microchannel plate photomultipliers. The performance of the detector in the experimental environment of the τ/charm factory was investigated by a detailed Monte Carlo simulation. The time and space resolutions of the detector are expected to be about 92 ps and 140 μm, respectively.
15875750
The use of RPC in the ARGO-YBJ project
We present the ARGO-YBJ experiment, a full coverage detector placed at high altitude (∼4300 m a.s.l.) that exploits the RPC technique. Results of a test experiment performed at Yanbajing site, with a full coverage RPC carpet of 50 m2 are also presented.
121510906
Results from the ARGO-YBJ test experiment
Abstract A resistive plate counters (RPCs) carpet of ∼50 m 2 has been put in operation in the Yangbajing Laboratory (Tibet, P.R. China) at 4300 m a.s.l., in order to study the RPCs performance at high altitude and the detector capability of imaging the EAS disc. This test has been performed in view of an enlarged use of RPCs for the ARGO-YBJ experiment. This experiment will be devoted to a wide range of fundamental issues in cosmic rays and astroparticle physics, including in particular γ-ray astronomy and γ-ray bursts physics at energies ⩾100 GeV. In this paper we present and discuss the procedures adopted to calibrate the detector and reconstruct the shower direction. Results concerning many shower features as the angular distribution, the density spectrum, the time profile of the shower front, are found well consistent with the expectation.
14865448
Performance of the RPCs for the ARGO detector operated at the YangBaJing laboratory (4300 m a.s.l.)
Bakelite RPCs, assembled according to the ARGO design, have been operated in the high altitude Laboratory of YBJ using dedicated electronics to pick-up the streamer signal. Here we report on the results concerning absorbed current, single counting rate, efficiency and time resolution. Environmental data concerning the operating temperature inside the ARGO experimental hall are also reported.
118885684
Double inflation and the low CMB quadrupole
Recent released WMAP data show a low value of quadrupole in the CMB temperature fluctuations, which confirms the early observations by COBE. In this Letter we consider a model of two inflatons with different masses, V(01, 02) V (phi(1),phi(2)) = 1/2m(1)(2)phi(1)(2)+1/2m(2)(2)phi(2)(2), m(1) > m(2) and study its effects on CMB of suppressing the primordial power spectrum P(k) at small k. Inflation is driven in this model firstly by the heavier inflaton phi(1), then the lighter field phi(2). But there is no interruption in between. We numerically calculate the scalar and tensor power spectra with mode by mode integrations, then fit the model to WMAP temperature correlations TT and the TE temperature-polarization spectra. Our results show that with m(1) similar to 10(14) GeV and m(2) similar to 10(13) GeV, this model solves the problems of flatness, etc. and the CMB quadrupole predicted can be much lower than the standard power-law ACDM model. (C) 2003 Elsevier B.V. All rights reserved.
119233801
Neutrino mass hierarchy from nuclear reactor experiments
Ten years from now reactor neutrino experiments will attempt to determine which neutrino mass eigenstate is the most massive. In this paper we present the results of more than seven million detailed simulations of such experiments, studying the dependence of the probability of successfully determining the mass hierarchy upon the analysis method, the neutrino mass matrix parameters, reactor flux models, geoneutrinos and, in particular, combinations of baselines. We show that a recently reported spurious dependence of the data analysis upon the high energy tail of the reactor spectrum can be removed by using a weighted Fourier transform. We determine the optimal baselines and corresponding detector locations. For most values of the CP-violating, leptonic Dirac phase delta, a degeneracy prevents NO nu A and T2K from determining either delta or the hierarchy. We determine the confidence with which a reactor experiment can determine the hierarchy, breaking the degeneracy.
119337025
DARK MATTER AND COSMIC STRINGS IN PARTICLE MODELS
In this talk, I will discuss the mechanism of nonthermal production of the neutralino cold dark matter from the decay of cosmic strings and the embedded defects, the $\pi$ and $\eta^\prime$ strings in the strong interaction sector of the standard model.
118356430
Probing CPT violation with CMB polarization measurements
The electrodynamics modified by the Chern-Simons term Lcs similar to p(mu)A(nu)(F) over tilde (mu nu) with a non-vanishing p(mu) violates the Charge-Parity-Time Reversal symmetry (CPT) and rotates the linear polarizations of the propagating Cosmic Microwave Background (CMB) photons. In this Letter we measure the rotation angle Delta alpha by performing a global analysis on the current CMB polarization measurements from the five-year Wilkinson Microwave Anisotropy Probe (WMAP5), BOOMERanG 2003 (B03), BICEP and QUaD using a Markov Chain Monte Carlo method. Neglecting the systematic errors of these experiments, we find that the results from WMAP5, B03 and BICEP all are consistent and their combination gives Delta alpha = -2.62 +/- 0.87 deg (68% C.L.), indicating a 3 sigma detection of the CPT violation. The QUaD data alone gives Delta alpha = 0.59 +/- 0.42 deg (68% C.L.) which has an opposite sign for the central value and smaller error bar compared to that obtained from WMAP5, B03 and BICEP. When combining all the polarization data together, we find Delta alpha = 0.09 +/- 0.36 deg (68% C.L.) which significantly improves the previous constraint on Delta alpha and test the validity of the fundamental CPT symmetry at a higher level. (C) 2010 Elsevier B.V. All rights reserved.
119454485
Dark energy constraints from the cosmic age and supernova
Using the low limit of cosmic ages from globular cluster and the white dwarfs: t(0) > 12 Gyr, together with recent new high redshift supernova observations from the HST/GOODS program and previous supernova data, we give a considerable estimation of the equation of state for dark energy, with uniform priors as weak as 0.2 < Omega(m) < 0.4 or 0.1 < Omega(m)h(2) < 0.16. We find cosmic age limit plays a significant role in lowering the upper bound on the variation amplitude of dark energy equation of state. We propose in this Letter a new scenario of dark energy dubbed quintom, which gives rise to the equation of state larger than -1 in the past and less than -1 today, satisfying current observations. In addition we have also considered the implications of recent X-ray gas mass fraction data on dark energy, which favors a negative running of the equation of state. (C) 2004 Elsevier B.V. All rights reserved.