362 research outputs found
Direct Formation of Supermassive Black Holes via Multi-Scale Gas Inflows in Galaxy Mergers
Observations of distant bright quasars suggest that billion solar mass
supermassive black holes (SMBHs) were already in place less than a billion
years after the Big Bang. Models in which light black hole seeds form by the
collapse of primordial metal-free stars cannot explain their rapid appearance
due to inefficient gas accretion. Alternatively, these black holes may form by
direct collapse of gas at the center of protogalaxies. However, this requires
metal-free gas that does not cool efficiently and thus is not turned into
stars, in contrast with the rapid metal enrichment of protogalaxies. Here we
use a numerical simulation to show that mergers between massive protogalaxies
naturally produce the required central gas accumulation with no need to
suppress star formation. Merger-driven gas inflows produce an unstable, massive
nuclear gas disk. Within the disk a second gas inflow accumulates more than 100
million solar masses of gas in a sub-parsec scale cloud in one hundred thousand
years. The cloud undergoes gravitational collapse, which eventually leads to
the formation of a massive black hole. The black hole can grow to a billion
solar masses in less than a billion years by accreting gas from the surrounding
disk.Comment: 26 pages, 4 Figures, submitted to Nature (includes Supplementary
Information
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
Precision Measurement of the Mass of the h_c(1P1) State of Charmonium
A precision measurement of the mass of the h_c(1P1) state of charmonium has
been made using a sample of 24.5 million psi(2S) events produced in e+e-
annihilation at CESR. The reaction used was psi(2S) -> pi0 h_c, pi0 -> gamma
gamma, h_c -> gamma eta_c, and the reaction products were detected in the
CLEO-c detector.
Data have been analyzed both for the inclusive reaction and for the exclusive
reactions in which eta_c decays are reconstructed in fifteen hadronic decay
channels. Consistent results are obtained in the two analyses. The averaged
results of the present measurements are M(h_c)=3525.28+-0.19 (stat)+-0.12(syst)
MeV, and B(psi(2S) -> pi0 h_c)xB(h_c -> gamma eta_c)= (4.19+-0.32+-0.45)x10^-4.
Using the 3PJ centroid mass, Delta M_hf(1P)= - M(h_c) =
+0.02+-0.19+-0.13 MeV.Comment: 9 pages, available through http://www.lns.cornell.edu/public/CLNS/,
submitted to PR
Precision Measurement of B(D+ -> mu+ nu) and the Pseudoscalar Decay Constant fD+
We measure the branching ratio of the purely leptonic decay of the D+ meson
with unprecedented precision as B(D+ -> mu+ nu) = (3.82 +/- 0.32 +/-
0.09)x10^(-4), using 818/pb of data taken on the psi(3770) resonance with the
CLEO-c detector at the CESR collider. We use this determination to derive a
value for the pseudoscalar decay constant fD+, combining with measurements of
the D+ lifetime and assuming |Vcd| = |Vus|. We find fD+ = (205.8 +/- 8.5 +/-
2.5) MeV. The decay rate asymmetry [B(D+ -> mu+ nu)-B(D- -> mu- nu)]/[B(D+ ->
mu+ nu)+B(D- -> mu- nu)] = 0.08 +/- 0.08, consistent with no CP violation. We
also set 90% confidence level upper limits on B(D+ -> tau+ nu) < 1.2x10^(-3)
and B(D+ -> e+ nu) < 8.8x10^(-6).Comment: 24 pages, 11 figures and 6 tables, v2 replaced some figure vertical
axis scales, v3 corrections from PRD revie
J/psi and psi(2S) Radiative Transitions to eta_c
Using 24.5 million psi(2S) decays collected with the CLEO-c detector at CESR
we present the most precise measurements of magnetic dipole transitions in the
charmonium system. We measure B(psi(2S)->gamma eta_c) =
(4.32+/-0.16+/-0.60)x10^-3, B(J/psi->gamma eta_c)/B(psi(2S)->gamma eta_c) =
4.59+/-0.23+/-0.64, and B(J/psi->gamma eta_c) = (1.98+/-0.09+/-0.30)%. We
observe a distortion in the eta_c line shape due to the photon-energy
dependence of the magnetic dipole transition rate. We find that measurements of
the eta_c mass are sensitive to the line shape, suggesting an explanation for
the discrepancy between measurements of the eta_c mass in radiative transitions
and other production mechanisms.Comment: 11 pages, 3 figure
Inclusive chi_bJ(nP) Decays to D0 X
Using Upsilon(2S) and Upsilon(3S) data collected with the CLEO III detector
we have searched for decays of chi_bJ to final states with open charm. We fully
reconstruct D0 mesons with p_D0 > 2.5 GeV/c in three decay modes (K-pi+,
K-pi+pi0, and K-pi-pi+pi+) in coincidence with radiative transition photons
that tag the production of one of the chi_bJ(nP) states. We obtain significant
signals for the two J=1 states. Recent NRQCD calculations of chi_{bJ}(nP) --> c
cbar X depend on one non-perturbative parameter per chi_bJ triplet. The
extrapolation from the observed D0 X rate over a limited momentum range to a
full c cbar X rate also depends on these same parameters. Using our data to fit
for these parameters, we extract results which agree well with NRQCD
predictions, confirming the expectation that charm production is largest for
the J=1 states. In particular, for J=1, our results are consistent with c cbar
g accounting for about one-quarter of all hadronic decays.Comment: Version 2 updates include corrections to important errors in Table V
and VII column headers which summarize results, and additional minor edits.
17 pages, available through http://www.lns.cornell.edu/public/CLNS
Measurement of the Masses and Widths of the Sigma_c^++ and Sigma_c^0 Charmed Baryons
Using data recorded by the CLEO II and CLEO II.V detector configurations at
CESR, we report new measurements of the masses of the Sigma_c^{++} and
Sigma_c^0 charmed baryons, and the first measurements of their intrinsic
widths. We find M(Sigma_c^{++}) - M(Lambda_c^+) = 167.4 +- 0.1 +- 0.2 MeV,
Gamma(Sigma_c^{++}) = 2.3 +- 0.2 +- 0.3 MeV, and M(Sigma_c^0) - M(Lambda_c^+) =
167.2 +- 0.1 +- 0.2 MeV, Gamma(Sigma_c^0) = 2.5 +- 0.2 +- 0.3 MeV, where the
uncertainties are statistical and systematic, respectively.Comment: 9 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, submitted to PRD, Rapid
Communications. Reference [13] correcte
Observation of the Charmed Baryon at CLEO
The CLEO experiment at the CESR collider has used 13.7 fb of data to
search for the production of the (css-ground state) in
collisions at {\rm GeV}. The modes used to
study the are ,
, , , and
. We observe a signal of 40.49.0(stat) events
at a mass of 2694.62.6(stat)1.9(syst) {\rm MeV/}, for all modes
combined.Comment: 10 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Evidence of New States Decaying into
Using 13.7 of data recorded by the CLEO detector at CESR, we report
evidence for two new charmed baryons: one decaying into
with the subsequent decay , and its
isospin partner decaying into followed by
. We measure the following mass differences
for the two states: =318.2+-1.3+-2.9 MeV,
and =324.0+-1.3+-3.0 MeV. We interpret
these new states as the particles, the charmed-strange
analogs of the .Comment: 10 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Search for the Decay
We report on a search for the radiative decay U(1S) -> gamma + eta' in 61.3
pb^-1 of data taken with the CLEO II detector at the Cornell Electron Storage
Ring. Three decay chains were investigated, all involving eta' -> pi+ pi- +
eta, followed by eta -> gamma + gamma, eta -> pi0 + pi0 + pi0, or eta -> pi+ +
pi- + pi0. We find no candidate events in any of the three cases and set a
combined upper limit of 1.6 x 10^-5 at 90% C.L., significantly smaller than the
previous limit. We compare our result to other radiative U(1S) decays, to
radiative J/psi decays, and to theoretical predictions.Comment: 9 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, submitted to PR
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