ABSTRACT
Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earth's) and lies projected at ~0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planet's temperature is much lower, <60 Kelvin, because the host star is only 0.10 to 0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host itself orbits a slightly more massive companion with projected separation of 10 to 15 AU. This detection is consistent with such systems being very common. Straightforward modification of current microlensing search strategies could increase sensitivity to planets in binary systems. With more detections, such binary-star planetary systems could constrain models of planet formation and evolution.
ABSTRACT
We have observed exclusive γγ production in proton-antiproton collisions at âs=1.96 TeV, using data from 1.11±0.07 fb(-1) integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy E(T)>2.5 GeV and pseudorapidity |η|<1.0, with no other particles detected in -7.4<η<+7.4. The two showers have similar E(T) and azimuthal angle separation Δφ~π; 34 events have two charged particle tracks, consistent with the QED process pp¯âp+e(+)e(-)+p¯ by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive π(0)π(0) is consistent with zero and is <15 at 95% C.L. The cross section for pp¯âp+γγ+p¯ with |η(γ)|<1.0 and E(T)(γ)>2.5 GeV is 2.48(-0.35)(+0.40)(stat)(-0.51)(+0.40)(syst) pb.
ABSTRACT
Most known extrasolar planets (exoplanets) have been discovered using the radial velocity or transit methods. Both are biased towards planets that are relatively close to their parent stars, and studies find that around 17-30% (refs 4, 5) of solar-like stars host a planet. Gravitational microlensing, on the other hand, probes planets that are further away from their stars. Recently, a population of planets that are unbound or very far from their stars was discovered by microlensing. These planets are at least as numerous as the stars in the Milky Way. Here we report a statistical analysis of microlensing data (gathered in 2002-07) that reveals the fraction of bound planets 0.5-10 AU (Sun-Earth distance) from their stars. We find that 17(+6)(-9)% of stars host Jupiter-mass planets (0.3-10 M(J), where M(J) = 318 M(â) and M(â) is Earth's mass). Cool Neptunes (10-30 M(â)) and super-Earths (5-10 M(â)) are even more common: their respective abundances per star are 52(+22)(-29)% and 62(+35)(-37)%. We conclude that stars are orbited by planets as a rule, rather than the exception.
ABSTRACT
This Letter presents a search for exclusive Z boson production in proton-antiproton collisions at sqrt[s]=1.96 TeV, using the CDF II detector. No exclusive Z-->l;{+}l;{-} candidates are observed and the first upper limit on the exclusive Z cross section in hadron collisions is found to be sigma_{excl}(Z)<0.96 pb at 95% confidence level. In addition, eight candidate exclusive dilepton events from the process pp[over ]-->pgammagammap[over ]-->pl;{+}l;{-}p[over ] are observed, and a measurement of the cross section for M_{ll}>40 GeV/c;{2} and |eta_{l}|<4 is found to be sigma=0.24_{-0.10};{+0.13} pb, which is consistent with the standard model prediction.
ABSTRACT
In CDF we have observed the reactions p + p[over] --> p + X + p[over], with X being a centrally produced J/psi, psi(2S), or chi_{c0}, and gammagamma-->micro;{+}micro;{-} in pp[over] collisions at sqrt[s] = 1.96 TeV. The event signature requires two oppositely charged central muons, and either no other particles or one additional photon detected. Exclusive vector meson production is as expected for elastic photoproduction, gamma + p --> J/psi(psi(2S)) + p, observed here for the first time in hadron-hadron collisions. We also observe exclusive chi_{c0} --> J/psi + gamma. The cross sections dsigma/dy|_{y = 0} for J/psi, psi(2S), and chi_{c0} are 3.92 +/- 0.25(stat) +/- 0.52(syst) nb, 0.53 +/- 0.09(stat) +/- 0.10(syst) nb, and 76 +/- 10(stat) +/- 10(syst) nb, respectively, and the continuum is consistent with QED. We put an upper limit on the cross section for Odderon exchange in exclusive J/psi production.
ABSTRACT
We report a measurement of the top-quark mass M_{t} in the dilepton decay channel tt[over ] --> bl;{'+} nu_{l};{'}b[over ]l;{-}nu[over ]_{l}. Events are selected with a neural network which has been directly optimized for statistical precision in top-quark mass using neuroevolution, a technique modeled on biological evolution. The top-quark mass is extracted from per-event probability densities that are formed by the convolution of leading order matrix elements and detector resolution functions. The joint probability is the product of the probability densities from 344 candidate events in 2.0 fb;{-1} of pp[over ] collisions collected with the CDF II detector, yielding a measurement of M_{t} = 171.2 +/- 2.7(stat) +/- 2.9(syst) GeV / c;{2}.
ABSTRACT
We report a measurement of resonance parameters of the orbitally excited (L=1) narrow B0 mesons in decays to B;{(*)+}pi;{-} using 1.7 fb;{-1} of data collected by the CDF II detector at the Fermilab Tevatron. The mass and width of the B_{2};{*0} state are measured to be m(B_{2};{*0})=5740.2_{-1.8};{+1.7}(stat)-0.8+0.9(syst) MeV/c;{2} and Gamma(B_{2};{*0})=22.7_{-3.2};{+3.8}(stat)-10.2+3.2(syst) MeV/c;{2}. The mass difference between the B_{2};{*0} and B10 states is measured to be 14.9_{-2.5};{+2.2}(stat)-1.4+1.2(syst) MeV/c;{2}, resulting in a B10 mass of 5725.3_{-2.2};{+1.6}(stat)-1.5+1.4(syst) MeV/c;{2}. This is currently the most precise measurement of the masses of these states and the first measurement of the B_{2};{*0} width.
ABSTRACT
We report on a search for inclusive production of squarks and gluinos in pp[over ] collisions at sqrt[s]=1.96 TeV, in events with large missing transverse energy and multiple jets of hadrons in the final state. The study uses a CDF Run II data sample corresponding to 2 fb(-1) of integrated luminosity. The data are in good agreement with the standard model predictions, giving no evidence for any squark or gluino component. In an R-parity conserving minimal supergravity scenario with A(0)=0, mu<0, and tanbeta=5, 95% C.L. upper limits on the production cross sections in the range between 0.1 and 1 pb are obtained, depending on the squark and gluino masses considered. For gluino masses below 280 GeV/c(2), arbitrarily large squark masses are excluded at the 95% C.L., while for mass degenerate gluinos and squarks, masses below 392 GeV/c(2) are excluded at the 95% C.L.
ABSTRACT
We present a search for a Higgs boson decaying to two W bosons in pp[over ] collisions at sqrt[s]=1.96 TeV center-of-mass energy. The data sample corresponds to an integrated luminosity of 3.0 fb;(-1) collected with the CDF II detector. We find no evidence for production of a Higgs boson with mass between 110 and 200 GeV/c;(2), and determine upper limits on the production cross section. For the mass of 160 GeV/c;(2), where the analysis is most sensitive, the observed (expected) limit is 0.7 pb (0.9 pb) at 95% Bayesian credibility level which is 1.7 (2.2) times the standard model cross section.
ABSTRACT
A search for high-mass resonances in the e+e- final state is presented based on 2.5 fb(-1) of sqrt[s]=1.96 TeV pp collision data from the CDF II detector at the Fermilab Tevatron. The largest excess over the standard model prediction is at an e+e- invariant mass of 240 GeV/c2. The probability of observing such an excess arising from fluctuations in the standard model anywhere in the mass range of 150-1000 GeV/c2 is 0.6% (equivalent to 2.5sigma). We exclude the standard model coupling Z' and the Randall-Sundrum graviton for k/MPl=0.1 with masses below 963 and 848 GeV/c2 at the 95% credibility level, respectively.