Search results for "meson"

Production of charged pions, kaons, and protons ine+e−annihilations into hadrons ats=10.54  GeV

2013

Inclusive production cross sections of π^±, K^± and p/p per hadronic e^+e^- annihilation event are measured at a center-of-mass energy of 10.54 GeV, using a relatively small sample of very high quality data from the BABAR experiment at the PEP-II B-factory at the SLAC National Accelerator Laboratory. The drift chamber and Cherenkov detector provide clean samples of identified π^±, K^±, and p/p over a wide range of momenta. Since the center-of-mass energy is below the threshold to produce a BB pair, with B a bottom-quark meson, these data represent a pure e^+e^-→qq sample with four quark flavors, and are used to test QCD predictions and hadronization models. Combined with measurements at oth…

Geometric approacch to condensates in halographic QCD

2005

An SU(Nf)xSU(Nf) Yang-Mills theory on an extra-dimensional interval is considered, with appropriate symmetry-breaking boundary conditions on the IR brane. UV-brane to UV-brane correlators at high energies are compared with the OPE of two-point functions of QCD quark currents. Condensates correspond to departure from AdS of the (different) metrics felt by vector and axial combinations, away from the UV brane. Their effect on hadronic observables is studied: the extracted condensates agree with the signs and orders of magnitude expected from QCD.

Heavy quark symmetry at large recoil

1992

Abstract We analyze the large recoil behaviour of heavy meson transition form factors using the Brodsky-Lepage hard scattering formalism. At the leading order of the heavy mass scale the large recoil form factors exhibit a new type of heavy quark symmetry. We discuss next-to-leading mass effects and present explicit 1/MQ expressions for the form factors in the peaking approximation.

Extraction of form Factors from a Four-Dimensional Angular Analysis of B¯→D*ℓ−ν¯ℓ

2019

An angular analysis of the decay B[over ¯]→D^{*}l^{-}ν[over ¯]_{l}, l∈{e,μ}, is reported using the full e^{+}e^{-} collision data set collected by the BABAR experiment at the ϒ(4S) resonance. One B meson from the ϒ(4S)→BB[over ¯] decay is fully reconstructed in a hadronic decay mode, which constrains the kinematics and provides a determination of the neutrino momentum vector. The kinematics of the semileptonic decay is described by the dilepton mass squared, q^{2}, and three angles. The first unbinned fit to the full four-dimensional decay rate in the standard model is performed in the so-called Boyd-Grinstein-Lebed approach, which employs a generic q^{2} parametrization of the underlying f…

Helicity-coupling amplitudes in tensor formalism.

1993

The decay of a particle with spin to two other particles with spin is best described in the helicity formalism. It is the purpose of this paper to show that the helicity-coupling amplitudes, which appear in the angular distributions, can be expressed in terms of the covariant amplitudes in the tensor formalism. This allows for a systematic derivation for the energy dependence of the helicity-coupling amplitudes within the framework of the tensor formalism. The concept of pure intrinsic spin has been developed in the tensor formalism, for decays involving two spins in the final state, in order to bring the formalism to a form comparable to the standard $\ensuremath{\ell}S$-coupling scheme. A…

Transition form factors of theN*(1535)as a dynamically generated resonance

2008

We discuss how electromagnetic properties provide useful tests of the nature of resonances, and we study these properties for the ${N}^{*}(1535)$ that appears dynamically generated from the strong interaction of mesons and baryons. Within this coupled-channels chiral unitary approach, we evaluate the ${A}_{1/2}$ and ${S}_{1/2}$ helicity amplitudes as a function of ${Q}^{2}$ for the electromagnetic ${N}^{*}(1535)\ensuremath{\rightarrow}{\ensuremath{\gamma}}^{*}N$ transition. Within the same formalism we evaluate the cross section for the reactions $\ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\eta}N$. We find a fair agreement for the absolute values of the transition amplitudes, a…

Two-loop calculation of the anomalous dimension of the axial current with static heavy quarks

1992

Abstract A method to perform two-loop calculations in Eichten's effective field theory for heavy quarks is developed. The anomalous dimension of the axial current for static heavy quarks is calculated at two loops. For N = 3, we get γ A (2) = − 1 36 [ 127 2 +28ξ(2)−5N f ] . This result is very important to understand completely the physical significance of the lattice measurement of the decay constant of the B meson. The two-loop correction generated by γ A (2) turns out to be small, less than 1% for four quark flavours, so that the value of the decay constant of the B meson does not need in practice renormalization group improvement. As extra results, the self-energy renormalization consta…

2017

Abstract Exclusive production of ω mesons was studied at the COMPASS experiment by scattering 160 GeV / c muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality 1 ( GeV / c ) 2 Q 2 10 ( GeV / c ) 2 , Bjorken scaling variable 0.003 x Bj 0.3 and transverse momentum squared of the ω meson 0.05 ( GeV / c ) 2 p T 2 0.5 ( GeV / c ) 2 . The measured asymmetries are sensitive to the nucleon helicity-flip Generalised Parton Distributions (GPD) E that are related to the orbital angular momentum of quarks, the chiral-odd GPDs H T that are related to the transversity Parton Distribution Functions, and the si…

Measurement ofKS0andK*0inp+p,d+Au, and Cu + Cu collisions atsNN=200 GeV

2014

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of K-S(0) and K*(0) meson production at midrapidity in p + p, d + Au, and Cu + Cu collisions at root s(NN) = 200 GeV. The K-S(0) and K*(0) mesons are reconstructed via their K-S(0) -> pi(0)(-> gamma gamma) pi(0)(-> gamma gamma) and K*(0) -> K-+/-pi(-/+) decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of K-S(0) and K*(0) mesons in d + Au and Cu + Cu collisions at different centralities. In the d + Au collisions, the nuclear modification factor of K-S(0) and K*(0) mesons is almost constant as a function of transverse momentum a…

Strangeness production inp�p annihilation at rest and the quark ? diquark structure of nucleons

1988

The importance of approximate isospin selection rules observed inN¯ N annihilation at rest into two strange mesons is emphasized. The selection rules are traced back to a symmetry between amplitudes describing annihilation by the flux of quarks. Presumably the symmetry reflects the symmetry of ¯qq annihilation vertices. The relation of the symmetry to a quark — diquark substructure of the nucleon is discussed.