The production of strange particles in π + d interactions has been examined at 4 GeV/ c where no previous data exist. Careful attention has been given to the resolution of ambiguities and to corrections for losses in a total sample of about 22 000 events which have been used to determine channel cross sections. Where they can be checked, the cross sections fit well into the observed variation of existing cross sections at higher and at lower energies.
No description provided.
Production of multi-strange baryons and antibaryons is expected to be a useful indicator in the search for Quark-Gluon Plasma formation. Production of Ξ − and Ξ − has been observed for the first time in ultra-relativistic heavy ion interactions by the WA85 Experiment. We describe the procedure used to select these cascade candidates and show that Ξ − and Ξ − decays can be identified. Preliminary ratios of Ξ/Ξ production in sulphur-tungsten and proton-tungsten interactions are also presented.
PRODUCTION AT CENTRAL RAPIDITY. 123 XI- AND 53 XIBAR+ CANDIDATES.
PRODUCTION AT CENTRAL RAPIDITY. 82 XI- AND 22 XIBAR+ CANDIDATES.
A partial wave analysis of the reaction π + n → π + π − π 0 p yields an A 0 2 production cross section of 225 ± 30μb for momentum transfer squared < 1 (GeV/ c ) 2 ; the differential cross-section and density matrix are presented and compared with ω 0 production in the light of theoretical models.
The reaction π + n → ω 0 p has been studied at 4 GeV/ c giving a total cross section of 313 ± 26 μ b. The sample of about 3500 ω 0 events produced in the forward direction has been used to determine the differential cross section and the spin density matrix elements. The effective trajectory for unnatural parity exchange has been determined by a comparison of ϱ 00 d σ /d t at different energies. A comparison of ϱ 00 d σ /d t has been made with the similar data for ϱ 0 production in this experiment allowing π-B exchange degeneracy and ϱ-ω interference to be investigated. These methods result in an unnatural trajectory consistent with that expected for the B-meson. A further study of ϱ-ω interference has been made by comparing the reactions π + n → ω 0 p and π − p → ω 0 n at similar energies. Our results on ω and ϱ production are combined with data on K ∗0 and K ∗0 production at 4 GeV/ c and an SU(3) sum rule relating the production of these four mesons is shown to be satisfied.
Production and decay properties of the B-meson are studied in the reactions π±p→B±p at 11 GeV/c. Values for mass, width, total and differential cross-sections and spin density matrix elements are given. The spin and parity, and the helicity states in the B→πω decay, are analysed.
A search for the production of three massive vector bosons in proton--proton collisions is performed using data at $\sqrt{s}=13\,TeV$ recorded with the ATLAS detector at the Large Hadron Collider in the years 2015--2017, corresponding to an integrated luminosity of $79.8\,\text{fb}^{-1}$. Events with two same-sign leptons $\ell$ (electrons or muons) and at least two reconstructed jets are selected to search for $WWW\to\ell\nu\ell\nu qq$. Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for $WWW\to\ell\nu\ell\nu\ell\nu$, while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for $WWZ\to\ell\nu qq \ell\ell$. Finally, events with four leptons are analysed to search for $WWZ\to\ell\nu\ell\nu\ell\ell$ and $WZZ\to qq \ell\ell\ell\ell$. Evidence for the joint production of three massive vector bosons is observed with a significance of 4.0 standard deviations, where the expectation is 3.1 standard deviations.
For the reaction π + p → ωΔ ++ data on the total cross section ( σ = 61 ± 12 μ b), differential cross sections, spin density matrix elements and statistical tensor elements are given. We observe natural and unnatural parity exchange contributions to the total cross section. We note that the value of ϱ 00 is not zero and in the helicity frame exhibits a dip at t ≈ −0.25 (GeV/ c ) 2 . A qualitative theoretical discussion of our results is presented.
The production of a $W$ boson in association with a single charm quark is studied using 140 $\mathrm{fb}^{-1}$ of $\sqrt{s} = 13\,\mathrm{TeV}$ proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The charm quark is tagged by a charmed hadron, reconstructed with a secondary-vertex fit. The $W$ boson is reconstructed from an electron/muon decay and the missing transverse momentum. The mesons reconstructed are $D^{\pm} \to K^\mp \pi^\pm \pi^\pm$ and $D^{*\pm} \to D^{0} \pi^\pm \to (K^\mp \pi^\pm) \pi^\pm$, where $p_{\text{T}}(e, \mu) > 30\,\mathrm{GeV}$, $|\eta(e, \mu)| < 2.5$, $p_{\text{T}}(D) > 8\,\mathrm{GeV}$, and $|\eta(D)| < 2.2$. The integrated and normalized differential cross-sections as a function of the pseudorapidity of the lepton from the $W$ boson decay, and of the transverse momentum of the meson, are extracted from the data using a profile likelihood fit. The measured fiducial cross-sections are $\sigma^{\mathrm{OS-SS}}_{\mathrm{fid}}(W^{-}{+}D^{+}) = 50.2\pm0.2\,\mathrm{(stat.)}\,^{+2.4}_{-2.3}\,\mathrm{(syst.)}\,\mathrm{pb}$, $\sigma^{\mathrm{OS-SS}}_{\mathrm{fid}}(W^{+}{+}D^{-}) = 48.5\pm0.2\,\mathrm{(stat.)}\,^{+2.3}_{-2.2}\,\mathrm{(syst.)}\,\mathrm{pb}$, $\sigma^{\mathrm{OS-SS}}_{\mathrm{fid}}(W^{-}{+}D^{*+}) = 51.1\pm0.4\,\mathrm{(stat.)}\,^{+1.9}_{-1.8}\,\mathrm{(syst.)}\,\mathrm{pb}$, and $\sigma^{\mathrm{OS-SS}}_{\mathrm{fid}}(W^{+}{+}D^{*-}) = 50.0\pm0.4\,\mathrm{(stat.)}\,^{+1.9}_{-1.8}\,\mathrm{(syst.)}\,\mathrm{pb}$. Results are compared with the predictions of next-to-leading-order quantum chromodynamics calculations performed using state-of-the-art parton distribution functions. The ratio of charm to anti-charm production cross-sections is studied to probe the $s$-$\bar{s}$ quark asymmetry and is found to be $R_c^\pm = 0.971\pm0.006\,\mathrm{(stat.)}\pm0.011\,\mathrm{(syst.)}$.
Measured fiducial cross-sections times the single-lepton-flavor W boson branching ratio.
Measured cross section ratios for the W+D production. The $R_{c}(D^{(*)})$ observable is obtained by combining the individual measurements of $R_{c}(D^{+})$ and $R_{c}(D^{*+})$ as explained in the text. The displayed cross sections are integrated over each differential bin.
Measured $p_{\mathrm{T}}(D^{+})$ differential fiducial cross-section times the single-lepton-flavor W boson branching ratio in the $W^{-}+D^{+}$ channel. The last $p_{\mathrm{T}}$ bin has no upper bound. The displayed cross sections are integrated over each differential bin.
This Letter describes a model-independent search for the production of new resonances in photon + jet events using 20 inverse fb of proton--proton LHC data recorded with the ATLAS detector at a centre-of-mass energy of sqrt(s) = 8 TeV. The photon + jet mass distribution is compared to a background model fit from data; no significant deviation from the background-only hypothesis is found. Limits are set at 95% credibility level on generic Gaussian-shaped signals and two benchmark phenomena beyond the Standard Model: non-thermal quantum black holes and excited quarks. Non-thermal quantum black holes are excluded below masses of 4.6 TeV and excited quarks are excluded below masses of 3.5 TeV.
Invariant mass of the photon+jet pair for events passing the final selections. The number of observed events and the fit background estimates are given in each bin, where the fit estimates are rounded to the nearest integer.
The 95% CL upper limits on SIG*BR*A*EPSILON for a hypothetical signal with a Gaussian-shaped M(GAMMA JET) distribution as a function of the signal mass M(G) for four values of the relative width SIGMA(G) / M(G).
Acceptance (A), efficiency (EPSILON), cross-section (SIG) and limits in number of events for the quantum black hole (QBH) benchmark model, as a function of the threshold mass M(th). Uncertainties on the cross section are on the order of 1%. The limits include statistical uncertainties only. Expected limits include the 68% uncertainty band. Acceptance was calculated using parton-level quantities by imposing criteria that apply directly to kinematic selections (photon/jet |eta|, photon/jet transverse momentum, Delta(eta), Delta(R)). All other selections, which in general correspond to event and object quality criteria, were used to calculate the efficiency based on the events included in the acceptance.
Searches for heavy long-lived charged particles are performed using a data sample of 19.8 fb$^{-1}$ from proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for $\tan\beta$ between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. $R$-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer.
Cross-section upper limits as a function of the $\tilde{\tau}_1$ mass for direct $\tilde{\tau}_1$ production and three values of $\tan\beta$. Expected limits for $\tan\beta=10$ with $\pm 1\sigma$ and $\pm 2\sigma$ uncertainties observed limits for three values of $\tan\beta$ and theoretical cross-section prediction for $\tan\beta=10$ with $\pm 1\sigma$ band.
Cross-section upper limits as a function of the $\tilde{\chi}_1$ mass for $\tilde{\tau}_1$ sleptons resulting from the decay of directly produced charginos and neutralinos in GMSB. Observed limits, expected limits for $\tan\beta=10$ with $\pm 1\sigma$ and $\pm 2\sigma$ uncertainties and theoretical cross-section prediction (dominated by $\tilde{\chi}^0_1 \tilde{\chi}^+_1$ production) with $\pm 1\sigma$ uncertainty. Depending on the hypothesis and to a small extent on $\tan\beta$, in these models, the chargino mass is 210 to 260 GeV higher than the neutralino mass.
Cross-section upper limits for various chargino masses in stable-chargino models. Expected limit with $\pm 1\sigma$ and $\pm 2\sigma$ uncertainties, observed limit and theoretical cross-section prediction with $\pm 1\sigma$ uncertainties.
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