Search results for "38"
showing 10 items of 1730 documents
Detecting the long-distance structure of the X(3872)
2014
We study the X(3872)-->D^0 \bar D^0 \pi^0 decay within a D \bar D^* molecular picture for the X(3872) state. This decay mode is more sensitive to the long-distance structure of the X(3872) resonance than its J/\psi\pi\pi and J/\psi3\pi decays, which are mainly controlled by the details of the X(3872) wave function at short distances. We show that the D^0 \bar D^0 final state interaction can be important, and that a precise measurement of this partial decay width can provide valuable information on the interaction strength between the D^{(*)} \bar D^{(*)} charm mesons.
Observation of charmonium pairs produced exclusively in $pp$ collisions
2014
A search is performed for the central exclusive production of pairs of charmonia produced in proton-proton collisions. Using data corresponding to an integrated luminosity of $3{\rm\ fb}^{-1}$ collected at centre-of-mass energies of 7 and 8 TeV, $J/\psi J/\psi$ and $J/\psi\psi(2S)$ pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges $(-3.5,-1.5)$ and $(1.5,5.0)$. Searches are also performed for pairs of P-wave charmonia and limits are set on their production. The cross-sections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measu…
Observation of Exclusive Dijet Production at the Fermilab Tevatron p-pbar Collider
2007
We present the first observation and cross section measurement of exclusive dijet production in pbar-p interactions, pbar + p --> pbar + dijet + p. Using a data sample of 310 pb-1 collected by the Run II Collider Detector at Fermilab at sqrt{s}=1.96 TeV, exclusive cross sections for events with two jets of transverse energy ET >= 10 GeV have been measured as a function of minimum ET(jet). The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of 200 pb-1 of b-tagged jet events, where exclusi…
A time-of-flight correction procedure for fast-timing data of recoils with varying implantation positions at a spectrometer focal plane
2019
Abstract Fast-timing measurements at the focal plane of a separator can suffer from poor timing resolution. This is due to the variations in time-of-flight (ToF) for photons travelling to a given detector, which arise from the changes in the implantation positions of the recoil nuclei emitting the γ rays of interest. In order to minimise these effects on timing measurements, a procedure is presented that improves fast-timing data by performing ToF corrections on an event-by-event basis. This method was used to correct data collected with an array of eight LaBr 3 detectors, which detected γ rays from spatially distributed 138Gd recoil-implants at the focal plane of the Recoil-Ion-Transport-U…
Search for right-handed W bosons in top quark decay
2005
We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $\theta^*$ for each event. By comparing the $\cos\theta^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This …
An improved limit for Γee of X(3872) and Γee measurement of ψ(3686)
2015
Using the data sets taken at center-of-mass energies above 4 GeV by the BESIII detector at the BEPCII storage ring, we search for the reaction e+eââγISRX(3872)âγISRÏ+ÏâJ/Ï via the Initial State Radiation technique. The production of a resonance with quantum numbers JPC=1++ such as the X(3872) via single photon e+eâ annihilation is forbidden, but is allowed by a next-to-leading order box diagram. We do not observe a significant signal of X(3872) , and therefore give an upper limit for the electronic width times the branching fraction ÎeeX(3872)B(X(3872)âÏ+ÏâJ/Ï)<0.13 eV at the 90% confidence level. This measurement improves upon existing limits by a factor of 46. U…
Measurements of Sigma(+) and Sigma(-) time-like electromagnetic form factors for center-of-mass energies from 2.3864 to 3.0200 GeV
2021
Physics letters / B 814, 136110 (2021). doi:10.1016/j.physletb.2021.136110
Quantum numbers of theX(3872)state and orbital angular momentum in itsρ0J/ψdecay
2015
Angular correlations in B+→X(3872)K+ decays, with X(3872)→ρ0J/ψ, ρ0→π+π− and J/ψ→μ+μ−, are used to measure orbital angular momentum contributions and to determine the JPC value of the X(3872) meson. The data correspond to an integrated luminosity of 3.0 fb−1 of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be JPC=1++. The X(3872) is found to decay predominantly through S wave and an upper limit of 4% at 95% C.L. is set on the fraction of D wave.
Study of theB−→J/ψK−π+π−decay and measurement of theB−→X(3872)K−branching fraction
2005
The authors study the decay B{sup -} {yields} J/{psi}K{sup -}{pi}{sup +}{pi}{sup -} using 117 million B{bar B} events collected at the {Upsilon}(4S) resonance with the BaBar detector at the PEP-II e{sup +}e{sup -} asymmetric-energy storage ring. They measure the branching fractions {Beta}(B{sup -} {yields} J/{psi}K{sup -} {pi}{sup +}{pi}{sup -}) = (116 {+-} 7(stat.) {+-} 9(syst.)) x 10{sup -5} and {Beta}(B{sup -} {yields} X(3872)K{sup -}) x {Beta}(X(3872) {yields} J/{psi}{pi}{sup +}{pi}{sup -}) = (1.28 {+-} 0.41) x 10{sup -5} and find the mass of the X(3872) to be 3873.4 {+-} 1.4MeV/c{sup 2}. They search for the h{sub c} narrow state in the decay B{sup -} {yields} h{sub c} K{sup -}, h{sub c…
DirectX(3872)production ine+e−collisions
2014
Abstract Direct production of the charmonium-like state X ( 3872 ) in e + e − collisions is considered in the framework of the vector meson dominance model. An order-of-magnitude estimate for the width Γ ( X → e + e − ) is found to be ≳0.03 eV. The same approach applied to the χ c 1 charmonium decay predicts the corresponding width of the order 0.1 eV in agreement with earlier estimates. Experimental perspectives for the direct production of the 1 + + charmonia in e + e − collisions are briefly discussed.