26,892,986 research outputs found
Observation of the TeV gamma-ray source MGRO J1908+06 with ARGO-YBJ
The extended gamma ray source MGRO J1908+06, discovered by the Milagro air
shower detector in 2007, has been observed for about 4 years by the ARGO-YBJ
experiment at TeV energies, with a statistical significance of 6.2 standard
deviations. The peak of the signal is found at a position consistent with the
pulsar PSR J1907+0602. Parametrizing the source shape with a two-dimensional
Gauss function we estimate an extension \sigma = 0.49 \pm 0.22 degrees,
consistent with a previous measurement by the Cherenkov Array H.E.S.S.. The
observed energy spectrum is dN/dE = 6.1 \pm 1.4 \times 10^-13 (E/4 TeV)^{-2.54
\pm 0.36} photons cm^-2 s^-1 TeV^-1, in the energy range 1-20 TeV. The measured
gamma ray flux is consistent with the results of the Milagro detector, but is
2-3 times larger than the flux previously derived by H.E.S.S. at energies of a
few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable
excess rate observed by ARGO-YBJ along 4 years of data taking support the
identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula
of PSR J1907+0602, with an integrated luminosity above 1 TeV about 1.8 times
the Crab Nebula luminosity.Comment: 6 pages, accepted for pubblication by ApJ. Replaced to correct the
author lis
Probing dense and hot matter with low-mass dileptons and photons
Results on low-mass dileptons, covering the very broad energy range from the
BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by
the intriguing results obtained so far and the prospects for addressing them in
the near future with the second generation of experiments, in particular HADES,
NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference,
Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published
in Eur. Phys. J. C. The orginal version is available at www.springerlink.co
Near-threshold production of omega mesons in the pn -> d omega reaction
The first measurement of the p n -> d omega total cross section has been
achieved at mean excess energies of Q = 28 and 57 MeV by using a deuterium
cluster-jet target. The momentum of the fast deuteron was measured in the ANKE
spectrometer at COSY-Juelich and that of the slow "spectator" proton p(sp) from
the p d -> p(sp) d omega reaction in a silicon telescope placed close to the
target. The cross sections lie above those measured for p p -> p p omega but
seem to be below theoretical predictions.Comment: 7 pages, 8 figures; second approach to describe the background has
been added; results changed insignificantly, EPJ in pres
Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at TeV
Inclusive transverse momentum spectra of primary charged particles in Pb-Pb
collisions at = 2.76 TeV have been measured by the ALICE
Collaboration at the LHC. The data are presented for central and peripheral
collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross
section. The measured charged particle spectra in and GeV/ are compared to the expectation in pp collisions at the same
, scaled by the number of underlying nucleon-nucleon
collisions. The comparison is expressed in terms of the nuclear modification
factor . The result indicates only weak medium effects ( 0.7) in peripheral collisions. In central collisions,
reaches a minimum of about 0.14 at -7GeV/ and increases
significantly at larger . The measured suppression of high- particles is stronger than that observed at lower collision energies,
indicating that a very dense medium is formed in central Pb-Pb collisions at
the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98
The Experimental Status of the Standard Electroweak Model at the End of the LEP-SLC Era
A method is proposed to calculate the confidence level for agreement of data
with the Standard Model (SM) by combining information from direct and indirect
Higgs Boson searches. Good agreement with the SM is found for
GeV using the observables most sensitive to : and . In
particular, quantum corrections, as predicted by the SM, are observed with a
statistical significance of forty-four standard deviations. However, apparent
deviations from the SM of 3.7 and 2.8 are found for the Z and right-handed Zb couplings respectively. The
maximum confidence level for agreement with the SM of the entire data set
considered is for GeV. The reason why
confidence levels about an order of magnitude higher than this have been
claimed for global fits to similar data sets is explained.Comment: 47 pages, 8 figures, 24 tables. An in-depth study of statistical
issues related to the comparison of precision EW data to the S
Electric dipole moments of charged leptons in the split fermion scenario in the two Higgs doublet model
We predict the charged lepton electric dipole moments in the split fermion
scenario in the framework of the two Higgs doublet model. We observe that the
numerical value of the muon (tau) electric dipole moment is at the order of the
magnitude of () and there is an enhancement
in the case of two extra dimensions, especially for the tau lepton electric
dipole moment.Comment: 17 pages, 5 figure
Quantifying bid-ask spreads in the Chinese stock market using limit-order book data: Intraday pattern, probability distribution, long memory, and multifractal nature
The statistical properties of the bid-ask spread of a frequently traded
Chinese stock listed on the Shenzhen Stock Exchange are investigated using the
limit-order book data. Three different definitions of spread are considered
based on the time right before transactions, the time whenever the highest
buying price or the lowest selling price changes, and a fixed time interval.
The results are qualitatively similar no matter linear prices or logarithmic
prices are used. The average spread exhibits evident intraday patterns
consisting of a big L-shape in morning transactions and a small L-shape in the
afternoon. The distributions of the spread with different definitions decay as
power laws. The tail exponents of spreads at transaction level are well within
the interval and that of average spreads are well in line with the
inverse cubic law for different time intervals. Based on the detrended
fluctuation analysis, we found the evidence of long memory in the bid-ask
spread time series for all three definitions, even after the removal of the
intraday pattern. Using the classical box-counting approach for multifractal
analysis, we show that the time series of bid-ask spread does not possess
multifractal nature.Comment: 8 EPJ pages including 7 eps figure
Identification of the TeV Gamma-ray Source ARGO J2031+4157 with the Cygnus Cocoon
The extended TeV gamma-ray source ARGO J2031+4157 (or MGRO J2031+41) is
positionally consistent with the Cygnus Cocoon discovered by -LAT at GeV
energies in the Cygnus superbubble. Reanalyzing the ARGO-YBJ data collected
from November 2007 to January 2013, the angular extension and energy spectrum
of ARGO J2031+4157 are evaluated. After subtracting the contribution of the
overlapping TeV sources, the ARGO-YBJ excess map is fitted with a
two-dimensional Gaussian function in a square region of , finding a source extension =
1.80.5. The observed differential energy spectrum is
photons cm
s TeV, in the energy range 0.2-10 TeV. The angular extension is
consistent with that of the Cygnus Cocoon as measured by -LAT, and the
spectrum also shows a good connection with the one measured in the 1-100 GeV
energy range. These features suggest to identify ARGO J2031+4157 as the
counterpart of the Cygnus Cocoon at TeV energies. The Cygnus Cocoon, located in
the star-forming region of Cygnus X, is interpreted as a cocoon of freshly
accelerated cosmic rays related to the Cygnus superbubble. The spectral
similarity with Supernova Remnants indicates that the particle acceleration
inside a superbubble is similar to that in a SNR. The spectral measurements
from 1 GeV to 10 TeV allows for the first time to determine the possible
spectrum slope of the underlying particle distribution. A hadronic model is
adopted to explain the spectral energy distribution.Comment: 16 pages, 3 figures, has been accepted by ApJ for publicatio
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at = 2.76 TeV
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb
collisions at TeV at the Large Hadron Collider is
presented. We observe a growing trend with energy now not only for the
longitudinal and the outward but also for the sideward pion source radius. The
pion homogeneity volume and the decoupling time are significantly larger than
those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/388
Generalised Thurston-Bennequin invariants for real algebraic surface singularities
A generalised Thurston-Bennequin invariant for a Q-singularity of a real
algebraic variety is defined as a linking form on the homologies of the real
link of the singularity. The main goal of this paper is to present a method to
calculate the linking form in terms of the very good resolution graph of a real
normal unibranch surface singularity. For such singularities, the value of the
linking form is the Thurston-Bennequin number of the real link of the
singularity. As a special case of unibranch surface singularities, the
behaviour of the linking form is investigated on the Brieskorn double points
x^m+y^n\pm z^2=0.Comment: 22 pages, TeX, 12 figure
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