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.
We report on measurements of the inclusive production rate of Sigma+ and Sigma0 baryons in hadronic Z decays collected with the L3 detector at LEP. The Sigma+ baryons are detected through the decay Sigma+ -> p pi0, while the Sigma0 baryons are detected via the decay mode Sigma0 -> Lambda gamma. The average numbers of Sigma+ and Sigma0 per hadronic Z decay are measured to be: < N_Sigma+ > + < N_Sigma+~ > = 0.114 +/- 0.011 (stat) +/- 0.009 (syst), < N_Sigma0 > + < N_Sigma0~ > = 0.095 +/- 0.015 (stat) +/- 0.013 (syst). These rates are found to be higher than the predictions from Monte Carlo hadronization models and analytical parameterizations of strange baryon production.
Deep--inelastic scattering events with a leading baryon have been detected by the H1 experiment at HERA using a forward proton spectrometer and a forward neutron calorimeter. Semi--inclusive cross sections have been measured in the kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T <= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV, or a neutron with energy E' >= 160 GeV. The measurements are used to test production models and factorization hypotheses. A Regge model of leading baryon production which consists of pion, pomeron and secondary reggeon exchanges gives an acceptable description of both semi-inclusive cross sections in the region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading neutron data are used to estimate for the first time the structure function of the pion at small Bjorken--x.
Strange baryon and in particular multi-strange baryon production is suggested to be a useful probe in the search for quark gluon plasma formation in heavy ion collisions. We have measured the (Ω − + Ω + ) (Ξ − + Ξ + ) production ratio to be 0.8±0.4 at central rapidity and ϱ T > 1.6 GeV/c.
The $p_{\rm T}$-differential cross sections of prompt charm-strange baryons $\Xi^0_{\rm c}$ and $\Xi^+_{\rm c}$ were measured at midrapidity ($|y| < 0.5$) in proton$-$proton (pp) collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV with the ALICE detector at the LHC. The $\Xi^0_{\rm c}$ baryon was reconstructed via both the semileptonic decay ($\Xi^{-}{\rm e^{+}}\nu_{\rm e}$) and the hadronic decay ($\Xi^{-}{\rm \pi^{+}}$) channels. The $\Xi^+_{\rm c}$ baryon was reconstructed via the hadronic decay ($\Xi^{-}\pi^{+}\pi^{+}$) channel. The branching-fraction ratio $\rm {\rm BR}(\Xi_c^0\rightarrow \Xi^-e^+\nu_e)/\rm {\rm BR}(\Xi_c^0\rightarrow \Xi^{-}\pi^+)=$ 1.38 $\pm$ 0.14 (stat) $\pm$ 0.22 (syst) was measured with a total uncertainty reduced by a factor of about 3 with respect to the current world average reported by the Particle Data Group. The transverse momentum ($p_{\rm T}$) dependence of the $\Xi^0_{\rm c}$- and $\Xi^+_{\rm c}$-baryon production relative to the ${\rm D^0}$-meson and to the $\Sigma^{0,+,++}_{\rm c}$- and $\Lambda^+_{\rm c}$-baryon production are reported. The baryon-to-meson ratio increases towards low $p_{\rm T}$ up to a value of approximately 0.3. The measurements are compared with various models that take different hadronisation mechanisms into consideration. The results provide stringent constraints to these theoretical calculations and additional evidence that different processes are involved in charm hadronisation in electron$-$positron ($\rm e^+e^-$) and hadronic collisions.
The $p_{\rm T}-$ integrated cross section of prompt $\Xi^{0}_{\rm c}-$baryon production in pp collisions at 13 TeV for $|y| < 0.5$.
The $p_{\rm T}-$ integrated cross section of prompt $\Xi^{0}_{\rm c}-$baryon production in pp collisions at 13 TeV for $|y| < 0.5$.
The $p_{\rm T}-$ integrated cross section of prompt $\Xi^{+}_{\rm c}-$baryon production in pp collisions at 13 TeV for $|y| < 0.5$.
The Large Hadron Collider forward (LHCf) experiment is designed to use the LHC to verify the hadronic-interaction models used in cosmic-ray physics. Forward baryon production is one of the crucial points to understand the development of cosmic-ray showers. We report the neutron-energy spectra for LHC $\sqrt{s}$ = 7 TeV proton--proton collisions with the pseudo-rapidity $\eta$ ranging from 8.81 to 8.99, from 8.99 to 9.22, and from 10.76 to infinity. The measured energy spectra obtained from the two independent calorimeters of Arm1 and Arm2 show the same characteristic feature before unfolding the difference in the detector responses. We unfolded the measured spectra by using the multidimensional unfolding method based on Bayesian theory, and the unfolded spectra were compared with current hadronic-interaction models. The QGSJET II-03 model predicts a high neutron production rate at the highest pseudo-rapidity range similar to our results and the DPMJET 3.04 model describes our results well at the lower pseudo-rapidity ranges. However no model perfectly explains the experimental results in the whole pseudo-rapidity range. The experimental data indicate the most abundant neutron production rate relative to the photon production, which does not agree with predictions of the models.
We report the first measurement of strange ($\Lambda$) and anti-strange ($\bar{\Lambda}$) baryon production from $\sqrt{s_{_{NN}}}=130$ GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Rapidity density and transverse mass distributions at mid-rapidity are presented as a function of centrality. The yield of $\Lambda$ and $\bar{\Lambda}$ hyperons is found to be approximately proportional to the number of negative hadrons. The production of $\bar{\Lambda}$ hyperons relative to negative hadrons increases very rapidly with transverse momentum. The magnitude of the increase cannot be described by existing hadronic string fragmentation models.
PHENIX has measured the centrality dependence of mid-rapidity pion, kaon and proton transverse momentum distributions in d+Au and p+p collisions at sqrt(s_NN) = 200 GeV. The p+p data provide a reference for nuclear effects in d+Au and previously measured Au+Au collisions. Hadron production is enhanced in d+Au, relative to independent nucleon-nucleon scattering, as was observed in lower energy collisions. The nuclear modification factor for (anti) protons is larger than that for pions. The difference increases with centrality, but is not sufficient to account for the abundance of baryon production observed in central Au+Au collisions at RHIC. The centrality dependence in d+Au shows that the nuclear modification factor increases gradually with the number of collisions suffered by each participant nucleon. We also present comparisons with lower energy data as well as with parton recombination and other theoretical models of nuclear effects on particle production.
The differential cross sections of $\Lambda_\mathrm{c}^+$ baryon production are measured via the exclusive decay channel $\Lambda_\mathrm{c}^+ \to $pK$^-\pi^+$, as a function of transverse momentum ($p_\mathrm{T}$) in proton-proton (pp) and lead-lead (PbPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV with the CMS detector at the LHC. The measurement is performed within the $\Lambda_\mathrm{c}^+$ rapidity interval $|y|<$1.0 in the $p_\mathrm{T}$ range of 5-20 GeV/$c$ in pp and 10-20 GeV/$c$ in PbPb collisions. The observed yields of $\Lambda_\mathrm{c}^+$ for $p_\mathrm{T}$ of 10-20 GeV/$c$ suggest a possible suppression in central PbPb collisions compared to pp collisions. The $\Lambda_\mathrm{c}^+/$D$^0$ production ratio in pp collisions is compared to theoretical models. In PbPb collisions, this ratio is consistent with the result from pp collisions in their common $p_\mathrm{T}$ range.
We report results from a search for neutrino-induced neutral current (NC) resonant $\Delta$(1232) baryon production followed by $\Delta$ radiative decay, with a $\langle0.8\rangle$~GeV neutrino beam. Data corresponding to MicroBooNE's first three years of operations (6.80$\times$10$^{20}$ protons on target) are used to select single-photon events with one or zero protons and without charged leptons in the final state ($1\gamma1p$ and $1\gamma0p$, respectively). The background is constrained via an in-situ high-purity measurement of NC $\pi^0$ events, made possible via dedicated $2\gamma1p$ and $2\gamma0p$ selections. A total of 16 and 153 events are observed for the $1\gamma1p$ and $1\gamma0p$ selections, respectively, compared to a constrained background prediction of $20.5 \pm 3.65 \text{(sys.)} $ and $145.1 \pm 13.8 \text{(sys.)} $ events. The data lead to a bound on an anomalous enhancement of the normalization of NC $\Delta$ radiative decay of less than $2.3$ times the predicted nominal rate for this process at the 90% confidence level (CL). The measurement disfavors a candidate photon interpretation of the MiniBooNE low-energy excess as a factor of $3.18$ times the nominal NC $\Delta$ radiative decay rate at the 94.8% CL, in favor of the nominal prediction, and represents a greater than $50$-fold improvement over the world's best limit on single-photon production in NC interactions in the sub-GeV neutrino energy range