Production of π0 mesons and charged hadrons in\bar v neon and ν neon charged current interactions

The average multiplicities of charged hadrons and of π⁺, π^? and π⁰ mesons, produced in \(\bar v\) Ne and νNe charged current interactions in the forward and backward hemispheres of theW ^±-nucleon center of mass system, are studied with data from BEBC. The dependence of the multiplicities on the hadronic mass (W) and on the laboratory rapidity (y _Lab) and the energy fraction (z) of the pion is also investigated. Special care is taken to determine the π⁰ multiplicity accurately. The ratio of average π multiplicities \(\frac{{2\left\langle {n_{\pi ^O } } \right\rangle }}{{[\left\langle {n_{\pi ^ + } } \right\rangle + \left\langle {n_{\pi ^ - } } \right\rangle ]}}\) is consistent with 1. In the backward hemisphere \(\left\langle {n_{\pi ^O } } \right\rangle \) is positively correlated with the charged multiplicity. This correlation, as well as differences in multiplicities between \(\mathop v\limits^{( - )} \) and \(\mathop v\limits^{( - )} \) , \(\mathop v\limits^{( - )} \) scattering, is attributed to reinteractions inside the neon nucleus of the hadrons produced in the initial \(\mathop v\limits^{( - )} \) interaction.     

Inclusive π 0 and KS 0 production in two-photon collisions at LEP

The reactions e⁺e⁻→e⁺e⁻ π ⁰ X and e⁺e⁻→e⁺e⁻K_S ⁰ X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Inclusive differential cross sections are measured as a function of the particle transverse momentum p _t and the pseudo-rapidity. For p _t ⩽1.5 GeV, the π ⁰ and K_S ⁰ differential cross sections are described by an exponential, typical of soft hadronic processes. For p _t ⩾1.5 GeV, the cross sections show the presence of perturbative QCD processes, described by a power-law. The data are compared to Monte Carlo predictions and to NLO QCD calculations.     

Role of the Λ(1600) in the ${K}^{-}p \rightarrow {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction

Role of the Λ(1600) is studied in the ${K}^{-}p\to {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction by using the effective Lagrangian approach near the threshold. We perform a calculation for the total and differential cross sections by considering the contributions from the Λ(1600) and Λ(1670) intermediate resonances decaying into ${\pi }^{0}{{\rm{\Sigma }}}^{* 0}(1385)$ with ${{\rm{\Sigma }}}^{* 0}(1385)$ decaying into ${\pi }^{0}{\rm{\Lambda }}$. Additionally, the non-resonance process from u-channel nucleon pole is also taken into account. With our model parameters, the current experimental data on the total cross sections of the ${K}^{-}p\to {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction can be well reproduced. It is shown that we really need the contribution from the Λ(1600) with spin-parity ${J}^{P}=1/{2}^{+}$, and that these measurements can be used to determine some of the properties of the Λ(1600) resonance. Furthermore, we also plot the π⁰Λ invariant mass distributions which could be tested by the future experimental measurements.     

On production of η′ mesons in pp collisions close to threshold

The near threshold behaviour of the reaction cross section for pp→ppη^′, recently measured in experiments at COSY and SATURNE, is analyzed. The interaction in the pp as well as in the η^′ p final states is taken into account. The suppression of the total cross section for this process at excess energies Q < 3 MeV observed in these experiments is interpreted as an evidence for a strong repulsive η^′ p interaction. Received: 26 May 1999 / Revised version: 8 July 1999     

Regularity and Existence of Global Solutions to the Ericksen–Leslie System in {\mathbb{R}^2}

In this paper, we first establish the regularity theorem for suitable weak solutions to the Ericksen–Leslie system in \({\mathbb{R}^2}\) . Building on such a regularity, we then establish the existence of a global weak solution to the Ericksen–Leslie system in \({\mathbb{R}^2}\) for any initial data in the energy space, under the physical constraints on the Leslie coefficients ensuring the dissipation of energy of the system, which is smooth away from at most finitely many times. This extends earlier works by Lin et al. (Arch Ration Mech Anal 197:297–336, 2010) on a simplified nematic liquid crystal flow to the general Ericksen–Leslie system.     

Combined analysis of near-threshold production of ω and φ mesons in nucleon-nucleon collisions within an effective meson-nucleon model

Vector meson ( V = ,) production in near-threshold elementary nucleon-nucleon collisions ppppV, pnpnV and pndV is studied within an effective meson-nucleon theory. It is shown that a set of effective parameters can be established to describe fairly well the available experimental data of angular distributions and the energy dependence of the total cross-sections without explicit implementation of the Okubo-Zweig-Iizuka rule violation. Isospin effects are considered in detail and compared with experimental data whenever available.     

Transverse momentum of charged hadrons produced in ν and\bar v deuterium charged current interactions

The transverse momentum properties of charged hadrons produced in charged current ν and \(\bar v\) deuterium interactions are studied. The variation of <P _t ² > withW ²,Q ²,x _F andz ² is analyzed. A study of transverse momentum balance shows that soft gluon emission and some quark primordial transverse momentum with <k _t ² >?(0.4 GeV/c)² are needed to balance highp _t particles. Distributions ofp _tin andP _tout in and out of the event plane are presented. A three jet structure is observed for events withW ²>50 (GeV²) and with a highp _t track, which is compatible with models taking into account hard gluon emission.     

Inclusive ρ0(770) meson production invp and\bar vp charged current interactions

Using data obtained with the bubble chamber BEBC at CERN, the inclusive ρ⁰ (770) meson production in νp and \(\bar vp\) charged current reactions is studied. The average ρ⁰ multiplicity is measured as a function of the event variablesE _ν ,W ²,Q ²,x _Bj , and the charged multiplicity. The differentialx _F ,y ^*,z andp _T ² distributions of the ρ⁰ are presented as well as the averagep _T ² as a function ofW ² andx _F . The ρ⁰/π⁰ ratio and the fractions of the π^± originating from ρ⁰ decays are given as functions ofx _F . The results are compared to the predictions of fragmentation models. A particular version of the Lund model predicts ρ⁰ multiplicities which are generally too high, although it qualitatively reproduces many aspects of the data. The ρ⁰ multiplicities predicted by a semi-empirical model (Wells model) are in quantitative agreement with the measurements.     

Inclusive production of vector mesons in π+ p interactions at 250 GeV/c

We report on a study of ρ⁰, ρ⁺, ω, \(\bar K^{*0} (892)\) andK ^*0 (892) inclusive production in π⁺ p interactions at 250 GeV/c, for ρ⁺, \(\bar K^{*0} (892)\) for the first time in a π⁺ p experiment. The data are compared withK ⁺ p data in the same experiment, with results of other experiments and with quark-parton models. Interesting differences are found between ρ^+,0 and ω production.     

Study of the production of Λ_b~0 band ~0 hadrons in pp collisions and first measurement of the Λ_b~0→J/ψpK~- branching fraction

The product of the A_b~0(B~0) differential production cross-section and the branching fraction of the decay A_b~0→J/ψpK~-(B~0→J/ψK~*(892)~0) is measured as a function of the beauty hadron transverse momentum,p_T,and rapidity,y.The kinematic region of the measurements is p_T 20 GeV/c and 2.0y4.5.The measurements use a data sample corresponding to an integrated luminosity of 3fb~(-1) collected by the LHCb detector in pp collisions at centre-of-mass energies s~(1/2)=7 TeV in 2011 and s~(1/2)= 8TeV in 2012.Based on previous LHCb results of the fragmentation fraction ratio,f_∧_b~0/f_d,the branching fraction of the decay ∧_b~0→J/ψpK~- is measured to be B(∧_b~0→J/ψpK~-)=(3.17±0.04±0.07±0.34_(-0.28)~(+0.45)×10~(-4)where the first uncertainty is statistical,the second is systematic,the third is due to the uncertainty on the branching fraction of the decay B~0→J/ψK~*(892)~0,and the fourth is due to the knowledge of f_∧_b~0/f_d.The sum of the asymmetries in the production and decay between A_b and A_b~0 is also measured as a function of p_T and y.The previously published branching fraction of A_b~0→J/φpπ~-,relative to that of A_b~0→J/ψpK~-,is updated.The branching fractions of∧_b~0→P_c~+(→J/ψp)K~- are determined.     

Anisotropic emission of charged mesons and structure characteristic of emission source in heavy ion collisions at 1-2A GeV

Angular distributions of pious and kaons produced in heavy ion collisions at the low-energy end of high energies （1-2 A GeV） have been investigated by using a multisource ideal gas model. The model covers the expansions and movements of the emission sources, and it is related to the collective flows. By using the analytic expression and the Monte Carlo method, the azimuthal and polar angle distributions of mesons are calculated by the model and compared with the experimental data of the KaoS Collaboration.     

Inclusive production of charged pions, kaons and protons in υ(4S) decays

Using the detector ARGUS at thee ⁺ e ^– storage ring DORIS II, we have investigated inclusive momentum spectra of charged pions, kaons, and protons from decays of the (4S) meson. The kaon spectra have been measured in two independent ways, by coherently exploiting the detector's particle identification capabilities, and by detecting decays in-flight. The extracted mean multiplicities for charged hadrons are 7.17±0.05±0.14 pions, 1.56±0.03±0.05 kaons and 0.110±0.010±0.007 protons per (4S) decay, where pions and protons fromK _s ^o and decays have been subtracted.Supported in part by the Institute of Physics, University of Lund, Sweden     

Measurement of $D_s ^+$ meson production in Z decays and of the ${⋏r B}_s ^0$ lifetime

$D_s ^+$ mesons produced in Z⁰ → bb? events were separated from the Z⁰ → cc? component using a lifetime tag. Using a sample of 1.5 million hadronic Z decays collected with the Aleph detector the ${?r B}_s ^0$ and $D_s ^+$ yields have been measured: $$?trix {B(b?ghtarrow {?r B}_s ^0)B({?r B}_s ^0?ghtarrow D_s ^+)=0.088pm 0.020(? stat.)? pm 0.020(? syst.)? B(c?ghtarrow D_s ^+)=0.128pm 0.019(? stat.)_{-0.016} ^{+0.019}(? syst.)}$$ The ${?r B}_s ^0$ lifetime was measured in a ${?r B}_s ^0$ enriched sample reconstructing the decay length from the vertex of the $D_s ^+$ with a hadron from the ${?r B}_s ^0$ decay. The result obtained is: $${?u_B}_s=1.61_{-0.29} ^{+0.30}(? stat.)_{-0.16} ^{+0.18}(? syst.) {? ps.}$$     

Single-spin asymmetry for charged hadrons produced in proton-nucleus collisions at 40 GeV for c.m. production angles in the range 40°–79°

The transverse single-spin asymmetry for charged hadrons (π ^±, K ^±, p, $\bar p$ ) produced in proton-nucleus collisions was measured for c.m. production angles in the range 40°–79°. The measurements were performed with the FODS-2 setup by using a 40-GeV polarized proton beam originating from the accelerator of the Institute for High Energy Physics (Protvino) and hitting carbon and copper nuclear targets. The data in question were obtained in the polarized-proton-fragmentation region (0.0 < x _F < 0.7, 0.6 < p T < 2.5 GeV/c). In agreement with data obtained at other energies, the single-spin asymmetry for π ^± mesons is significant at high x _F. For the first time, a sizable analyzing power, which changes sign at x _F = 0.43, is observed for protons. The dependence of the analyzing power on the target-nucleus mass is insignificant.