The production cross sections for the Λ, Σ0, Ξ−, Σ0 (1385), Ξ0 (1530) and Ω− hyperons have been measured, both in the continuum and in direct ϒ decays. Baryon rates in direct ϒ decays are enhanced by a factor of 2.5 or more compared to the continuum. Such a large baryon enhancement cannot be explained by standard fragmentation models. The strangeness suppression for baryons and mesons turns out to be the same. A strong suppression of spin 3/2 states is observed.
We report the first observation of an orbitally excited baryon, the Λ(1520), in quark and gluon fragmentation. The production rate is found to be (1.15±0.21±0.16)×10 −2 and (0.80±0.17 −0.13 +0.10 )×10 −2 Λ (1520) hyperons per event in direct ϒ decays and in the continuum, respectively. In contrast to the observed situation for ground state baryons, the production of the Λ(1520) in direct ϒ decays shows little or no enhancement with respect to continuum production.
We report on a high precision measurement of ϕ-meson production in continuum events and in direct decays of the Υ(1S)- and Υ(2S)-mesons. The ratio of the total production rate of ϕ-mesons in direct Υ(1S)- and Υ(2S)-decays over that in continuum events is 1.32±0.08±0.09 and 1.07±0.13±0.11 respectively. This is compatible with the corresponding ratio obtained for lighter mesons, but is appreciably smaller than the relative baryon production rate.
We report on a high statistics study of π0 and η production in continuum events and in direct decays of the Γ(1S) and Γ(2S) resonances. The measured production rates per event are\(\left\langle {n_{\pi ^0 } } \right\rangle\)=3.22 ± 0.07 ± 0.31 (3.97 ± 0.23 ± 0.38) and 〈nη〉=0.19 ± 0.04 ± 0.04 (0.40 ± 0.14 ± 0.09) for continuum events (direct Γ(1S) decays).
Using the ARGUS detector at thee+e− storage ring DORIS II, we have investigated inclusive production of π±,K±,Ks0 and\(\bar p\) in multihadron events at 9.98 GeV and in direct decays of the ϒ(1S) meson, i.e. from quark and gluon fragmentation. The most pronounced difference is the rate of baryon production. The Lund Monte Carlo program gives a reasonable qualitative description, although it cannot reproduce our data in detail.
A measurement of inclusive ZZ production cross section and constraints on anomalous triple gauge couplings in proton-proton collisions at sqrt(s) = 8 TeV are presented. A data sample, corresponding to an integrated luminosity of 19.6 inverse femtobarns was collected with the CMS experiment at the LHC. The measurements are performed in the leptonic decay modes ZZ to lll'l', where l = e, mu and l' = e, mu, tau. The measured total cross section, sigma(pp to ZZ) = 7.7 +/- 0.5 (stat.) +0.5-0.4 (syst.) +/- 0.4 (theo.) +/- 0.2 (lum.) pb for both Z bosons produced in the mass range 60 < m[Z] < 120 GeV, is consistent with standard model predictions. Differential cross sections are measured and well described by the theoretical predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ gamma couplings at the 95% confidence level: -0.004 < f[4,Z] < 0.004, -0.004 < f[5,Z] < 0.004, -0.005 < f[4,gamma] < 0.005, and -0.005 < f[5,gamma] < 0.005.
We compared the multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale Qjet which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Qjet for pizero, eta and Kzero was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of eta meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, C=2.27+-0.20(stat+syst),is about one standard deviation higher than the perturbative prediction.
In this paper, results are presented from a study of the hadronic final states in e+e− annihilation at 29 GeV. The data were obtained with the High Resolution Spectrometer (HRS) at the SLAC PEP e+e− colliding-beam facility. The results are based on 6342 selected events corresponding to an integrated luminosity of 19.6 pb−1. The distributions of the events in sphericity (S), thrust (T), and aplanarity (A) are given and compared to other e+e− data in the same energy range. We measure 〈S〉=0.130±0.003±0.010 and 〈1-T〉=0.100±0.002. The sphericity distribution is compared to sphericity measurements made for beam jets in hadronic collisions as well as jets studied in neutrino scattering. The data sample is further reduced to 4371 events with the two-jet selections, S≤0.25 and A≤0.1. The single-particle distributions in the longitudinal and transverse directions are given. For low values of the momentum fraction (z=2p/W), the invariant distribution shows a maximum at z∼0.06, consistent with a QCD expectation. The data at high Feynman x (xF) show distribution consistent with being dominated by a (1-xf)2 variation for the leading quark-meson transition. The rapidity distribution shows a shallow central minimum with a height (1/NevdNh/dY‖Y=0=2.3±0.02±0.07. The mean charged multiplicity is measured to be 〈nch〉=13.1±0.05±0.6. The mean transverse momentum relative to the thrust axis 〈pT〉 rises as a function of z to a value of 0.70±0.02 GeV/c for z≳0.3. The distributions are compared to those measured in other reactions.
Data from the high-resolution spectrometer at PEP have been used to study the inclusive production of φ mesons and F± mesons decaying into φπ±. Fragmentation functions and cross sections are presented and compared to existing data. The total φ cross section at 29 GeV is 40±6 pb. The observed F signal in the region z>0.4, given the assumption that R(F)[R(F)+R(D)]=0.15, corresponds to an F→φπ branching ratio of (3.3±1.1)%. The measured F mass is 1963±3±3 MeV/c2.
Data from the High Resolution Spectrometer at the SLAC storage ring PEP have been used to study the inclusive production of baryons and mesons. Time-of-flight measurements are used to identify the charged hadrons. Neutral hadrons are identified from effective-mass peaks associated with their decay into two charged particles. Cross sections and other inclusive production characteristics are presented for π±, K±, and K0 (K¯0) mesons, and for the baryons (antibaryons) p (p¯) and Λ (Λ¯). The ratio of the inclusive cross section to the point cross section for the K0 and K¯0 mesons is R(K0,K¯0)=6.15±0.13±0.25, and for Λ and Λ¯, R(Λ,Λ¯)=0.846±0.036±0.085. The neutral-hadron differential cross sections are compared with the predictions of the Lund string model.
η production has been investigated by the Mark II collaboration at the SLAC e+e− storage ring PEP. η particles are reconstructed by their γγ decay mode. The η fragmentation function has been measured and found to be in good agreement with the Lund-model prediction. η′ production has been measured for the first time in high-energy e+e− annihilation. There is evidence at the 3σ level for Ds± decay into ηπ± and η′π±.
This paper presents measurements of the inclusive production cross sections of Λ baryons in e+e− annihilations at s=29 GeV. The data sample corresponds to an integrated luminosity of 256 pb−1 collected with the High-Resolution Spectrometer at the SLAC storage ring PEP. Comparisons are made to the predictions of the Lund model. The data are well described with use of a strange-diquark suppression parameter, (usud)(sd), of 0.89 ± 0.10−0.16+0.56, and the measured Λc→Λ+X branching ratio of (23 ± 10)%.
The inclusive production cross sections of η′ (958) andfo (975) mesons are measured ine+e− annihilation in the nonresonant continuum around\(\sqrt s= 10\) GeV and in decays of the υ resonances using the ARGUS detector. For η′ (958) mesons, a production ratio of η′ (958)/ηdir=0.35±0.24, with ηdir=η−BR(η′→ηX)·η′, is determined in direct υ(1S) decays, which can be partially explained by the pseudoscalar singlet/octet mixing. Forfo(975) production, we obtain a production ratio offo(975)/p(770)°=0.17±0.030 in direct υ(1S) decays. In its production features, thefo(975) behaves like an ordinary meson, though aK\(\bar K\) molecule nature cannot be excluded. The substantial production yield of thefo(975) meson demonstrates the important effect of feeddown from mesons beyond the basic multiples on pseudoscalar and vector meson production.
Measurements of inclusive differential cross sections for charged pion and kaon production in electron-positron annihilation have been carried out at a center-of-mass energy of Q = 10.52 GeV. The measurements were performed with the Belle detector at the KEKB electron-positron collider using a data sample containing 113 million e+e- -> qqbar events, where q={u,d,s,c}. We present charge-integrated differential cross sections d\sigma_h+-/dz for h+- = pi+-, K+- as a function of the relative hadron energy z = 2*E_h / sqrt{s} from 0.2 to 0.98. The combined statistical and systematic uncertainties for pi+- (K+-) are 4% (4%) at z ~ 0.6 and 15% (24%) at z ~ 0.9. The cross sections are the first measurements of the z-dependence of pion and kaon production for z > 0.7 as well as the first precision cross section measurements at a center-of-mass energy far below the Z^0 resonance used by the experiments at LEP and SLC.
The inclusive production of D^{*+-}(2010) mesons in deep-inelastic scattering is studied with the H1 detector at HERA. In the kinematic region 1<Q^2<100 GeV^2 and 0.05<y<0.7 an e^+p cross section for inclusive D^(*+-) meson production of 8.50+- 0.42 (stat.)^(+1.21)_(-1.00) (syst.) nb is measured in the visible range p_(tD^*)>1.5 GeV and |\eta_(D^*)|<1.5. Single and double differential inclusive D^(*+-) meson cross sections are compared to perturbative QCD calculations in two different evolution schemes. The charm contribution to the proton structure, F_2^c(x,Q^2), is determined by extrapolating the visible charm cross section to the full phase space. This contribution is found to rise from about 10% at Q^2 = 1.5 GeV^2 to more than 25% at Q^2 = 60 GeV^2 corresponding to x values ranging from 5*10^(-5) to 3*10^(-3)$.
The production of $K^*+(892)$, $K^{*0}+(892)$, $\rho^{0}(770)$ and $\omega(783)$ vector mesons in $q\bar{q}$ events as well as in the gluonic $\Upsilon(1S)$ decays and $\Upsilon(4S) \to B\bar{B}$ decays has been studied using the ARGUS detector. Combining these results with data on pseudoscalar meson, $\phi$ meson and baryon production collected with the same detector allow comprehensive studies of quark and gluon fragmentation. Model independent information on $s$ quark and vector meson suppression $(s/u = 0.37 \pm 0.04, V/(V+P)_{\pi} = 0.21 \pm 0.04$ and $V/( V+ P)_K = 0.34 \pm 0.03))$ are derived. The data are compared with predictions from the models Jetset 7.3 and UCLA 7.31.
H1 and ZEUS have published single-differential cross sections for inclusive D^{*\pm}-meson production in deep-inelastic ep scattering at HERA from their respective final data sets. These cross sections are combined in the common visible phase-space region of photon virtuality Q2 > 5 GeV2, electron inelasticity 0.02 < y < 0.7 and the D^{*\pm} meson's transverse momentum pT (D^*) > 1.5 GeV and pseudorapidity |eta(D^*)| < 1.5. The combination procedure takes into account all correlations, yielding significantly reduced experimental uncertainties. Double-differential cross sections d2s /dQ2dy are combined with earlier D^{*\pm} data, extending the kinematic range down to Q2 > 1.5 GeV2. Perturbative next-to-leadingorder QCD predictions are compared to the results.
The cross section of the diffractive process e^+p -> e^+Xp is measured at a centre-of-mass energy of 318 GeV, where the system X contains at least two jets and the leading final state proton p is detected in the H1 Very Forward Proton Spectrometer. The measurement is performed in photoproduction with photon virtualities Q^2 <2 GeV^2 and in deep-inelastic scattering with 4 GeV^2<Q^2<80 GeV^2. The results are compared to next-to-leading order QCD calculations based on diffractive parton distribution functions as extracted from measurements of inclusive cross sections in diffractive deep-inelastic scattering.
Inclusive π±, K± and\((p,\bar p)\) differential cross-sections in hadronic decays of the Z have been measured as a function ofz=Phadron/Pbeam, the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified by their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, ξ*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD.
This analysis, based on a sample of 170000 hadronic Z0 decays, provides a measurement of the K ± and p/ p differential cross sections which is compared to string- and cluster fragmentation models. The total multiplicities for K ± and p/ p per hadronic event were found to be: NK = 2.26 ± 0.18 and N p = 1.07 ± 0.14. The positions ξ * of the maxima of the differential cross sections as a function of ξ = ln(1/ x p ) for K ± and p/ p were determined to be 2.63 ± 0.07 and 2.96 ± 0.16 respectively. A comparison of the ξ * values for various identified particles measured at LEP with the prediction of the Modified Leading Logarithm Approximation with Local Parton Hadron Duality model has been performed. The measured ξ * position as a function of the hadron mass, after corrections due to particle decays, is in agreement with the model calculation.
Inclusive D* production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D* meson is investigated. The analysis covers values of photon virtuality 2< Q^2 <=100 GeV^2 and of inelasticity 0.05<= y <= 0.7. Differential cross sections are measured as a function of Q^2 and x and of various D* meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon-gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the k_T-unintegrated gluon distribution of the proton.
The production of the charmed meson state D*+ has been observed in e+e− annihilation at 29 GeV. The fragmentation function for charmed quarks appears to be peaked about z=0.5.
The production of charmed D* mesons in e+e− annihilations at a center-of-mass energy of 29 GeV has been studied using the time-projection-chamber (TPC) detector at the SLAC storage ring PEP. The production cross section, fragmentation function, and forward-backward asymmetry due to electroweak effects are measured, and a limit on D0-D¯0 mixing is determined.
We report measurements of π±K±, and p, p¯ inclusive cross sections and fractions in e+e− annihilation at s=29 GeV, for the momentum interval 0.01<z=ppbeam<0.90. The analysis is based on approximately 70 pb−1 of data collected with the TPC2γ detector facility at the SLAC storage ring PEP. Detector upgrades result in significantly improved momentum coverage and precision of the data, compared to previous measurements.
The jet fragmentation function and transverse profile for jets with 25 GeV < ptJet < 500 GeV and etaJet<1.2 produced in proton-proton collisions with a center-of-mass energy of 7 TeV are presented. The measurement is performed using data with an integrated luminosity of 36 pb^-1. Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. None of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the measurement.