1,776 research outputs found
Meson Production in In-In Collisions and the Puzzle
The NA60 experiment measured dimuon production in In-In collisions at 158
AGeV. This paper presents a high statistics measurement of with
the specific objective to provide insight on the puzzle, i.e. the
difference in the inverse slopes and absolute yields measured by NA49 and
NA50 in the kaon and lepton channel, respectively. Transverse momentum
distributions were studied as a function of centrality. The slope parameter
shows a rapid increase with centrality, followed by a saturation. Variations of
with the fit range of the order of 15 MeV were observed, possibly as a
consequence of radial flow. The meson yield normalized to the number of
participants increases with centrality and is consistently higher than the
yield measured by the NA49 experiment at any centrality.Comment: 4 Pages, 2 Figures. Proceedings of the 20 International
Conference on Ultra-Relativistic Nucleus Nucleus Collision
Evidence for radial flow of thermal dileptons in high-energy nuclear collisions
The NA60 experiment at the CERN SPS has studied low-mass dimuon production in
158 AGeV In-In collisions. An excess of pairs above the known meson decays has
been reported before. We now present precision results on the associated
transverse momentum spectra. The slope parameter Teff extracted from the
spectra rises with dimuon mass up to the rho, followed by a sudden decline
above. While the initial rise is consistent with the expectations for radial
flow of a hadronic decay source, the decline signals a transition to an
emission source with much smaller flow. This may well represent the first
direct evidence for thermal radiation of partonic origin in nuclear collisions.Comment: Accepted for publication in Physical Review Letter
Thermal dileptons at SPS energies
Clear signs of excess dileptons above the known sources were found at the SPS
since long. However, a real clarification of these observations was only
recently achieved by NA60, measuring dimuons with unprecedented precision in
158A GeV, In-In collisions. The excess mass spectrum in the region M<1 GeV is
consistent with a dominant contribution from pi+pi- -> rho -> mu+mu-
annihilation. The associated rho spectral function shows a strong broadening,
but essentially no shift in mass. In the region M>1 GeV, the excess is found to
be prompt, not due to enhanced charm production. The inverse slope parameter
Teff associated with the transverse momentum spectra rises with mass up to the
rho, followed by a sudden decline above. While the initial rise, coupled to a
hierarchy in hadron freeze-out, points to radial flow of a hadronic decay
source, the decline above signals a transition to a low-flow source, presumably
of partonic origin. The mass spectra show at low transverse momenta the steep
rise towards low masses characteristic for Planck-like radiation. The
polarization of the excess referred to the Collins Soper frame is found to be
isotropic. All observations are consistent with the interpretation of the
excess as thermal radiation.Comment: Prepared for 20th International Conference on Ultra-Relativistic
Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 4-10
Feb. 200
The insect vector Cacopsylla picta vertically transmits the bacterium ‘Candidatus Phytoplasma mali’ to its progeny
The phloem-sucking psyllid Cacopsylla picta plays an important role in transmitting the bacterium ‘Candidatus Phytoplasma
mali’, the agent associated with apple proliferation disease. The psyllid can ingest ‘Ca. Phytoplasma mali’ from
infected apple trees and spread the bacterium by subsequently feeding on uninfected trees. Until now, this has been the
most important method of ‘Ca. Phytoplasma mali’ transmission. The aim of this study was to investigate whether
infected C. picta are able to transmit ‘Ca. Phytoplasma mali’ directly to their progeny. This method of transmission
would allow the bacteria to bypass a time-consuming reproductive cycle in the host plant. Furthermore, this would
cause a high number of infected F1 individuals in the vector population. To address this question, eggs, nymphs and
adults derived from infected overwintering adults of C. picta were reared on non-infected apple saplings and subsequently
tested for the presence of ‘Ca. Phytoplasma mali’. In this study it was shown for the first time that infected
C. picta individuals transmit ‘Ca. Phytoplasma mali’ to their eggs, nymphs and F1 adults, thus providing the basis for a
more detailed understanding of ‘Ca. Phytoplasma mali’ transmission by C. pict
NA60 results on thermal dimuons
The NA60 experiment at the CERN SPS has measured muon pairs with
unprecedented precision in 158A GeV In-In collisions. A strong excess of pairs
above the known sources is observed in the whole mass region 0.2<M<2.6 GeV. The
mass spectrum for M<1 GeV is consistent with a dominant contribution from
pi+pi- -> rho -> mu+mu- annihilation. The associated rho spectral function
shows a strong broadening, but essentially no shift in mass. For M>1 GeV, the
excess is found to be prompt, not due to enhanced charm production, with
pronounced differences to Drell-Yan pairs. The slope parameter Teff associated
with the transverse momentum spectra rises with mass up to the rho, followed by
a sudden decline above. The rise for M<1 GeV is consistent with radial flow of
a hadronic emission source. The seeming absence of significant flow for M>1 GeV
and its relation to parton-hadron duality is discussed in detail, suggesting a
dominantly partonic emission source in this region. A comparison of the data to
the present status of theoretical modeling is also contained. The accumulated
empirical evidence, including also a Planck-like shape of the mass spectra at
low pT and the lack of polarization, is consistent with a global interpretation
of the excess dimuons as thermal radiation. We conclude with first results on
omega in-medium effects.Comment: 10 pages, 12 figures, submitted to Eur. Phys. J.
Study of the electromagnetic transition form-factors in \eta -> \mu^+\mu^-\gamma and \omega -> \mu^+\mu^-\pi^0 decays with NA60
The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158A
GeV In-In collisions. The mass and pT spectra associated with peripheral
collisions can quantitatively be described by the known neutral meson decays.
The high data quality has allowed to remeasure the electromagnetic transition
form factors of the Dalitz decays \eta -> \mu^+\mu^-\gamma and \omega ->
\mu^+\mu^-\pi^0. Using the usual pole approximation F =
(1-M_{\mu\mu}^{2}/\Lambda^{2})^{-1} for the form factors, we find \Lambda^{-2}
(in GeV^{-2}) to be 1.95+-0.17(stat.)+-0.05(syst.) for the \eta and
2.24+-0.06(stat.)+-0.02(syst.) for the \omega. While the values agree with
previous results from the Lepton-G experiment, the errors are greatly improved,
confirming now on the level of 10\sigma the strong enhancement of the \omega
form factor beyond the expectation from vector meson dominance. An improved
value of the branching ratio BR(\omega -> \mu^+\mu^-\pi^0) =
[1.73+-0.25(stat.)+-0.14(syst.)]*10^{-4} has been obtained as a byproduct.Comment: Submitted to Phys. Lett.
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
A note on comonotonicity and positivity of the control components of decoupled quadratic FBSDE
In this small note we are concerned with the solution of Forward-Backward
Stochastic Differential Equations (FBSDE) with drivers that grow quadratically
in the control component (quadratic growth FBSDE or qgFBSDE). The main theorem
is a comparison result that allows comparing componentwise the signs of the
control processes of two different qgFBSDE. As a byproduct one obtains
conditions that allow establishing the positivity of the control process.Comment: accepted for publicatio
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at , 2.76 and 7 TeV
Measurements of the sphericity of primary charged particles in minimum bias
proton--proton collisions at , 2.76 and 7 TeV with the ALICE
detector at the LHC are presented. The observable is linearized to be collinear
safe and is measured in the plane perpendicular to the beam direction using
primary charged tracks with GeV/c in . The
mean sphericity as a function of the charged particle multiplicity at
mid-rapidity () is reported for events with different
scales ("soft" and "hard") defined by the transverse momentum of the leading
particle. In addition, the mean charged particle transverse momentum versus
multiplicity is presented for the different event classes, and the sphericity
distributions in bins of multiplicity are presented. The data are compared with
calculations of standard Monte Carlo event generators. The transverse
sphericity is found to grow with multiplicity at all collision energies, with a
steeper rise at low , whereas the event generators show the
opposite tendency. The combined study of the sphericity and the mean with multiplicity indicates that most of the tested event generators
produce events with higher multiplicity by generating more back-to-back jets
resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with
tune PERUGIA-2011 exhibits a noticeable improvement in describing the data,
compared to the other tested generators.Comment: 21 pages, 9 captioned figures, 3 tables, authors from page 16,
published version, figures from
http://aliceinfo.cern.ch/ArtSubmission/node/308
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