Summary
Active deep‐sea hydrothermal vents are areas of intense mixing and severe thermal and chemical gradients, fostering a biotope rich in novel hyperthermophilic microorganisms and metabolic ...pathways. The goal of this study was to identify the earliest archaeal colonizers of nascent hydrothermal chimneys, organisms that may be previously uncharacterized as they are quickly replaced by a more stable climax community. During expeditions in 2001 and 2002 to the hydrothermal vents of the East Pacific Rise (EPR) (9°50′N, 104°17′W), we removed actively venting chimneys and in their place deployed mineral chambers and sampling units that promoted the growth of new, natural hydrothermal chimneys and allowed their collection within hours of formation. These samples were compared with those collected from established hydrothermal chimneys from EPR and Guaymas Basin vent sites. Using molecular and phylogenetic analysis of the 16S rDNA, we show here that at high temperatures, early colonization of a natural chimney is dominated by members of the archaeal genus Ignicoccus and its symbiont, Nanoarchaeum. We have identified 19 unique sequences closely related to the nanoarchaeal group, and five archaeal sequences that group closely with Ignicoccus. These organisms were found to colonize a natural, high temperature protochimney and vent‐like mineral assemblages deployed over high temperature outflows within 92 h. When compared phylogenetically, several of these colonizing organisms form a unique clade independent of those found in mature chimneys and low‐temperature mineral chamber samples. As a model ecosystem, the identification of pioneering consortia in deep‐sea hydrothermal vents may help advance the understanding of how early microbial life forms gained a foothold in hydrothermal systems on early Earth and potentially on other planetary bodies.
Spin precession of channeled particles in bent crystals has been observed for the first time. Polarized Sigmasup + were channeled using bent Si crystals. These crystals provided an effective magnetic ...field of 45 T which resulted in a measured spin precession of 60plus minus17degree. This agrees with the prediction of 62plus minus2degree using the world average of Sigmasup + magnetic moment measurements. This new technique gives a Sigmasup + magnetic moment of (2.40plus minus0.46plus minus0.40)musub ital N, where the quoted uncertainties are statistical and systematic, respectively. We see no evidence of depolarization in the channeling process.
The transverse momentum spectra of charged particles have been measured in pp and PbPb collisions at \(\sqrt{s_{NN}}=2.76~\mathrm{TeV}\) by the CMS experiment at the LHC. In the transverse momentum ...range pT=5–10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 7 compared to the pp yield scaled by the number of incoherent nucleon–nucleon collisions. At higher pT, this suppression is significantly reduced, approaching roughly a factor of 2 for particles with pT in the range pT=40–100 GeV/c.
Measurements of the differential production cross sections dσ/dpTB and dσ/dyB for B0 mesons produced in pp collisions at sqrts = 7 TeV are presented. The data set used was collected by the CMS ...experiment at the LHC and corresponds to an integrated luminosity of 40 pb-1. The production cross section is measured from B0 meson decays reconstructed in the exclusive final state J/ψKS0, with the subsequent decays J/ψ → μ + μ - and KS0 → π+}π-. The total cross section for pTB>5 GeV and |yB|<2.2 is measured to be 33.2 ± 2.5 ± 3.5 μb, where the first uncertainty is statistical and the second is systematic.
A search for supersymmetry in the context of general gauge-mediated breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is ...presented. The data sample corresponds to an integrated luminosity of 36 pb(-1) recorded by the CMS experiment at the LHC. The search is performed by using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for general gauge-mediated supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squark, gluino, and neutralino masses, excluding supersymmetry parameter space that was inaccessible to previous experiments.
The Σ− mean squared charge radius has been measured in the space-like Q2 range 0.035–0.105 GeV2/c2 by elastic scattering of a Σ− beam off atomic electrons. The measurement was performed with the ...SELEX (E781) spectrometer using the Fermilab hyperon beam at a mean energy of 610 GeV/c.
We obtain 〈r2ch〉Σ−=(0.61±0.12(stat.)±0.09(syst.)) fm2. The proton and π− charge radii were measured as well and are consistent with results of other experiments. Our result agrees with the recently measured strong interaction radius of the Σ−.
Nuclear dependence of charm production Blanco-Covarrubias, A.; Engelfried, J.; Akgun, U. ...
The European physical journal. C, Particles and fields,
12/2009, Letnik:
64, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Using data taken by SELEX during the 1996–1997 fixed target run at Fermilab, we study the production of charmed hadrons on copper and carbon targets with
Σ
−
,
p
,
π
−
, and
π
+
beams. Parametrizing ...the dependence of the inclusive production cross section on the atomic number
A
as
A
α
, we determine
α
for
D
+
,
D
0
,
D
s
+
,
D
+
(2010),
Λ
c
+
, and their respective anti-particles, as a function of their transverse momentum
p
t
and scaled longitudinal momentum
x
F
. Within our statistics there is no dependence of
α
on
x
F
for any charm species for the interval 0.1<
x
F
<1.0. The average value of
α
for charm production by pion beams is
α
meson
=0.850±0.028. This is somewhat larger than the corresponding average
α
baryon
=0.755±0.016 for charm production by baryon beams (
Σ
−
,
p
).
We report the first observation of two Cabibbo-suppressed decay modes, Ξc+→Σ+π−π+ and Ξc+→Σ−π+π+. We observe 59±14 over a background of 87, and 22±8 over a background of 13 events, respectively, for ...the signals. The data were accumulated using the SELEX spectrometer during the 1996–1997 fixed target run at Fermilab, chiefly from a 600GeV/cΣ− beam. The branching ratios of the decays relative to the Cabibbo-favored Ξc+→Ξ−π+π+ are measured to be B(Ξc+→Σ+π−π+)/B(Ξc+→Ξ−π+π+)=0.48±0.20, and B(Ξc+→Σ−π+π+)/B(Ξc+→Ξ−π+π+)=0.18±0.09, respectively. We also report branching ratios for the same decay modes of the Λc+ relative to Λc+→pK−π+.
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