30 Search Results

We present a measurement of the cross section and transverse single-spin asymmetry (A_N) for η mesons at large pseudorapidity from √s=200 GeV p^↑+p collisions. The measured cross section for 0.5_T<5.0 GeV/c and 3.0<|η|<3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries A_N have been measured as a function of Feynman-x (x_F) from 0.2<|x_F|<0.7, as well as transverse momentum (p_T) from 1.0_T<4.5 GeV/c. The asymmetry averaged over positive x_F is (A_N) = 0.061±0.014. The results are consistent with prior transverse single-spin measurements of forward η and π⁰ mesons at various energies in overlapping x_F ranges. Comparison of different particlemore » species can help to determine the origin of the large observed asymmetries in p^↑+p collisions.« less

We present a spectrum of highly excited charmonium mesons up to around 4.5 GeV calculated using dynamical lattice QCD. Employing novel computational techniques and the variational method with a large basis of carefully constructed operators, we extract and reliably identify the continuum spin of an extensive set of excited states, states with exotic quantum numbers (0^+-, 1^-+, 2^+-) and states with high spin. Calculations are performed on two lattice volumes with pion mass ? 400 MeV and the mass determinations have high statistical precision even for excited states. We discuss the results in light of experimental observations, identify the lightestmore » 'supermultiplet' of hybrid mesons and comment on the phenomenological implications of the spectrum of exotic mesons.« less

Motivated by the desire to construct meson-meson operators of definite relative momentum in order to study resonances in lattice QCD, we present a set of single-meson interpolating fields at non-zero momentum that respect the reduced symmetry of a cubic lattice in a finite cubic volume. These operators follow from the subduction of operators of definite helicity into irreducible representations of the appropriate little groups. We show their effectiveness in explicit computations where we find that the spectrum of states interpolated by these operators is close to diagonal in helicity, admitting a description in terms of single-meson states of identified J^PC.more » Lastly, the variationally determined optimal superpositions of the operators for each state give rapid relaxation in Euclidean time to that state, ideal for the construction of meson-meson operators and for the evaluation of matrix elements at finite momentum.« less

In this study, a unitary coupled-channels model is presented for investigating the decays of heavy mesons and excited meson states into three light pseudoscalar mesons. The model accounts for the three-mesons final state interactions in the decay processes, as required by both the three-body and two-body unitarity conditions. In the absence of the Z-diagram mechanisms that are necessary consequences of the three-body unitarity, our decay amplitudes are reduced to a form similar to those used in the so-called isobar-model analysis. We apply our coupled-channels model to the three-pions decays of α₁(1260), π₂(1670), π₂(2100), and D⁰ mesons, and show that themore » Z-diagram mechanisms can contribute to the calculated Dalitz plot distributions by as much as 30% in magnitudes in the regions where f₀(600), ρ(770), and f₂(1270) dominate the distributions. Also, by fitting to the same Dalitz plot distributions, we demonstrate that the decay amplitudes obtained with the unitary model and the isobar model can be rather different, particularly in the phase that plays a crucial role in extracting the CKM CP-violating phase from the data of B meson decays. Our results indicate that the commonly used isobar model analysis must be extended to account for the final state interactions required by the three-body unitarity to reanalyze the three-mesons decays of heavy mesons, thereby exploring hybrid or exotic mesons, and signatures of physics beyond the standard model.« less

The production of mesons containing strange quarks ($$K^0_S$$, Φ) and both singly and doubly strange baryons ($$Λ, \overline Λ$$, and $$\Xi^– + \overline {\Xi}^+$$) are measured at mid-rapidity in pp collisions at $$\sqrt{s}$$ = 0.9 TeV with the $$\hbox{ALICE}$$ experiment at the $$\hbox{LHC}$$. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (d$$N$$ / d$$y$$) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields ($$\langle$$ d$$N$$ / d$$y\rangle$$) of $0.184 ± 0.002(stat.) ± 0.006(syst.)$ for $$K^0_S$$ and $0.021 ± 0.004(stat.) ±more » 0.003(syst.)$ for Φ. For baryons, we find ($$\langle$$ d$$N$$ / d$$y\rangle$$) = $0.048 ± 0.001(stat.)± 0.004(syst.)$ for $$Λ$$, $0.047 ± 0.002(stat.) ± 0.005(syst.)$ for $$\overline Λ$$ and $0.0101 ± 0.0020(stat.) ± 0.0009(syst.)$ for $$\Xi^– + \overline {\Xi}^+$$. The results are also compared with predictions for identified particle spectra from $$\hbox{QCD}$$-inspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions.« less

In this report, we measure the differential cross section on $$\phi$$-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, $K^+$ and $K^-$ near the theoretical production threshold of 1.57 GeV. Moreover, the extracted differential cross sections $$\frac{d\sigma}{dt}$$ for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. Ultimately, this experiment establishes a baseline for a future experimental search for an exotic $$\phi$$-N bound statemore » from heavier nuclear targets utilizing subthreshold/near-threshold production of $$\phi$$ mesons.« less

We measured the production of Φ mesons in the collisions of 2.83 GeV protons with C, Cu, Ag, and Au at forward angles via the Φ → K⁺K^- decay using the COSY-ANKE magnetic spectrometer. The Φ meson production cross section follows a target mass dependence of A^0.56±0.02 in the momentum region of 0.6-1.6 GeV/c. Moreover, the comparison of the data with model calculations suggests that the in-medium Φ width is about an order of magnitude larger than its free value.

Here, high-statistics measurements of differential cross sections and recoil polarizations for the reaction $$\gamma p \rightarrow K^+ \Sigma^0$$ have been obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass energies ($$\sqrt{s}$$) from 1.69 to 2.84 GeV, with an extensive coverage in the $K^+$ production angle. Independent measurements were made using the $$K^{+}p\pi^{-}$$($$\gamma$$) and $$K^{+}p$$($$\pi^-,\gamma$$) final-state topologies, and were found to exhibit good agreement. Our differential cross sections show good agreement with earlier CLAS, SAPHIR and LEPS results, while offering better statistical precision and a 300-MeV increase in $$\sqrt{s}$$ coverage. Above $$\sqrt{s} \approx 2.5$$ GeV, $$t$$- and $$u$$-channel Reggemore » scaling behavior can be seen at forward- and backward-angles, respectively. Our recoil polarization ($$P_\Sigma$$) measurements represent a substantial increase in kinematic coverage and enhanced precision over previous world data. At forward angles we find that $$P_\Sigma$$ is of the same magnitude but opposite sign as $$P_\Lambda$$, in agreement with the static SU(6) quark model prediction of $$P_\Sigma \approx -P_\Lambda$$. This expectation is violated in some mid- and backward-angle kinematic regimes, where $$P_\Sigma$$ and $$P_\Lambda$$ are of similar magnitudes but also have the same signs. In conjunction with several other meson photoproduction results recently published by CLAS, the present data will help constrain the partial wave analyses being performed to search for missing baryon resonances.« less

The development of a dynamical model for investigating the nucleon resonances using the reactions of meson production from $$\pi N$$, $$\gamma N$$, $N(e,e')$, and $$N(\nu,{\it l})$$ reactions is reviewed. The results for the $$\Delta$$ (1232) state are summarized and discussed. The progress in investigating higher mass nucleon resonances is reported.

Here, we present the first observation of the baryon decay $$Λ^{0}_{b}$$ → $$Λ^{+}_{c}$$$$⁢π^-$ followed by $$Λ^{+}_{c}$$ → $pK^-$$⁢π^+$ in 106 $$pb^{-1}$$ $$p\overline{p}$$ collisions at $$\sqrt{s}$$ =1.96 TeV in the CDF experiment. In order to reduce systematic error, the measured rate for $$Λ^{0}_{b}$$ decay is normalized to the kinematically similar meson decay $$\overline{B}$$$$^0$ → $D^+⁢π^-$ followed by $D^+$ → $π^+K^-⁢π^+$. We report the ratio of production cross sections ($$σ$$) times the ratio of branching fractions ($$\mathscr{B}$$) for the momentum region integrated above $$p_t$$ > 6 GeV/c and pseudorapidity range |$$η$$| < 1.3: $$σ$$⁡($$p\overline{p}$$ → $$Λ^{0}_{b}$$$$X$)/$$σ$$⁡($$p\overline{p}$$ → $$\overline{B}$$$$^0$$X$$) × $$\mathscr{B}$$⁡($$Λ^{0}_{b}$$ → $$Λ^{+}_{c}$$$$⁢π^-$)/$$\mathscr{B}$$⁡($$\overline{B}$$$$^0$more » → $D^+⁢π^-$)=0.82±0.08⁢(stat)±0.11⁢(syst)±0.22⁢[$$\mathscr{B}$$($$Λ^{+}_{c}$$ → $pK^-$$⁢π^+$)].« less