F. Fabbri

The multiplicities of charged secondaries in proton-proton collisions were determined using the split-field-magnet detector at the CERN Intersecting Storage Rings (ISR). Measurements are presented on multiplicity distributions both for inelastic and non-single-diffractive events at four different energies √s=30.4, 44.5, 52.6, and 62.2 GeV. The results reported here represent the first high-statistics measurement of charged multiplicity distributions at ISR energies with a magnetic detector covering nearly the full solid angle.Received 23 March 1984DOI:https://doi.org/10.1103/PhysRevD.30.528©1984 American Physical Society

We report the direct observation of muon neutrino interactions with the SND@LHC detector at the Large Hadron Collider. A dataset of proton-proton collisions at sqrt[s]=13.6 TeV collected by SND@LHC in 2022 is used, corresponding to an integrated luminosity of 36.8 fb^{-1}. The search is based on information from the active electronic components of the SND@LHC detector, which covers the pseudorapidity region of 7.2<η<8.4, inaccessible to the other experiments at the collider. Muon neutrino candidates are identified through their charged-current interaction topology, with a track propagating through the entire length of the muon detector. After selection cuts, 8 ν_{μ} interaction candidate events remain with an estimated background of 0.086 events, yielding a significance of about 7 standard deviations for the observed ν_{μ} signal.

The magnetic spectrometer and charged particle tracking system used in Fermilab experiment 687 to study the photoproduction and decay of charm particles are described in detail. The photons are produced by a wideband electron beam which can operate at energies up to 600 GeV/c. The spectrometer consists of a high resolution silicon microstrip detector, a large aperture dipole magnet, proportional chambers, a second large aperture dipole, and more proportional chambers. Three multi-cell threshold Cherenkov counters provide charged particle identification. The tracking system is capable of resolving the secondary decay vertices of charm and beauty mesons and baryons from the primary interaction vertex. It also determines the invariant mass of the multibody final states of particles containing heavy quarks with excellent resolution. The particle identification system allows one to identify kaons and protons present in these final states clearly. This collection of detectors produces very clean signals for charm particles and permits one to make many cross checks of the apparatus. The performance is illustrated for a variety of charm signals. Of particular interest is a description of the tracking through the silicon microstrip detector and its use in isolating downstream decay vertices. Two complementary approaches to the reconstruction of secondary decay vertices are presented and insight is gained by comparing their strengths and weaknesses.

Using data from the FOCUS experiment we analyze the D+π− and D0π+ invariant mass distributions. We measure the D2∗0 mass MD2∗0=(2464.5±1.1±1.9)MeV/c2 and width ΓD2∗0=(38.7±5.3±2.9)MeV/c2, and the D2∗+ mass MD2∗+=(2467.6±1.5±0.76)MeV/c2 and width ΓD2∗+=(34.1±6.5±4.2)MeV/c2. We find evidence for broad structures over background in both the neutral and charged final state. If each is interpreted as evidence for a single L=1, jq=1/2 excited charm meson resonance, the masses and widths are M1/20=(2407±21±35)MeV/c2, Γ1/20=(240±55±59)MeV/c2, and M1/2+=(2403±14±35)MeV/c2, Γ1/2+=(283±24±34)MeV/c2, respectively.

Chiral symmetry and its spontaneous breaking play an important role both in the light hadron and heavy hadron systems. The chiral perturbation theory (χPT) is the low energy effective field theory of the Quantum Chromodynamics. In this work, we shall review the investigations on the chiral corrections to the properties of the heavy mesons and baryons within the framework of χPT. We will also review the scatterings of the light pseudoscalar mesons and heavy hadrons, through which many new resonances such as the Ds0∗(2317) could be understood.Moreover, many new hadron states were observed experimentally in the past decades. A large group of these states is near-threshold resonances, such as the charged charmoniumlike Zc and Zcs states, bottomoniumlike Zb states, hidden-charm pentaquark Pc and Pcs states and the doubly charmed Tcc state, etc. They are very good candidates of the loosely bound molecular states composed of a pair of charmed (bottom) hadrons, which are very similar to the loosely bound deuteron. The modern nuclear force was built upon the chiral effective field theory (χEFT), which is the extension of the χPT to the systems with two matter fields. The long-range and medium-long-range interactions between two nucleons arise from the single- and double-pion exchange respectively, which are well constrained by the chiral symmetry and its spontaneous breaking. The short-distance interactions can be described by the low energy constants. Such a framework works very well for the nucleon–nucleon scattering and nuclei. In this work, we will perform an extensive review of the progress on the heavy hadronic molecular states within the framework of χEFT. We shall emphasize that the same chiral dynamics not only govern the nuclei and forms the deuteron, but also dictates the shallow bound states or resonances composed of two heavy hadrons.

We have measured the differential cross section for ¯pp and pp elastic scattering at √s=53 GeV in the interval 0.5<|t|<4.0 (GeV/c)2 at the CERN intersecting storage rings using the split-field magnet detector. The shape of the differential cross section differs significantly between ¯pp and pp scattering in the region 1.1<|t|<1.5 (GeV/c)2, with ¯pp data showing a less pronounced dip structure than pp data.Received 1 February 1985DOI:https://doi.org/10.1103/PhysRevLett.54.2180©1985 American Physical Society

We have measured the differential cross section for pp and p̄p elastic scattering at √s = 31, 53 and 62 GeV in the interval 0.05 < |t| < 0.85 GeV2 at the CERN ISR using the Split Field Magnet detector. At 53 and 62 GeV, for 0.17 < |t| < 0.85 GeV2 both pp and p̄p data show simple exponential behaviour in t; at √s = 31 GeV the data for 0.05 < |t| < 0.85 GeV2 are consistent with a change in slope near |t| = 0.15 GeV2.

A study of b quark hadronisation is presented using inclusively reconstructed B hadrons in about four million hadronic Z decays recorded in 1992-2000 with the OPAL detector at LEP. The data are compared to different theoretical models, and fragmentation function parameters of these models are fitted. The average scaled energy of weakly decaying B hadrons is determined to be <xe>=0.7193+-0.0016(stat)+0.0036-0.0031(syst)

The Search for Hidden Particles (SHiP) Collaboration has shown that the CERN SPS accelerator with its 400 GeV/c proton beam offers a unique opportunity to explore the Hidden Sector [1–3]. The proposed experiment is an intensity frontier experiment which is capable of searching for hidden particles through both visible decays and through scattering signatures from recoil of electrons or nuclei. The high-intensity experimental facility developed by the SHiP Collaboration is based on a number of key features and developments which provide the possibility of probing a large part of the parameter space for a wide range of models with light long-lived super-weakly interacting particles with masses up to (10) GeV/c2 in an environment of extremely clean background conditions. This paper describes the proposal for the experimental facility together with the most important feasibility studies. The paper focuses on the challenging new ideas behind the beam extraction and beam delivery, the proton beam dump, and the suppression of beam-induced background.

Using a high statistics sample of photoproduced charm particles from the FOCUS experiment at Fermilab, we compare the lifetimes of neutral D mesons decaying via D0 to K- pi+ and K- K+ to measure the lifetime differences between CP even and CP odd final states. These measurements bear on the phenomenology of D0 - D0bar mixing. If the D0 to K-pi+ is an equal mixture of CP even and CP odd eigenstates, we measure yCP = 0.0342 \pm 0.0139 \pm 0.0074.

Photonic events with large missing energy have been observed in $\rm e^+e^-$ collisions at a centre-of-mass energy of 189 GeV using the OPAL detector at LEP. Results are presented for event topologies consistent with a single photon or with an acoplanar photon pair. Cross-section measurements are performed within the kinematic acceptance of each selection, and the number of light neutrino species is measured. Cross-section results are compared with the expectations from the Standard Model process $\mathrme^+\mathrme^-\to \nu\overline{\nu}$ + photon(s). No evidence is observed for new physics contributions to these final states. Upper limits on $\sigma(\mathrme^+\mathrme^-\to\mathrm{X}\mathrm{Y})\cdot\mathrm{BR}(\mathrm{X}\to\mathrm{Y}\gamma)$ and $\sigma(\mathrme^+\mathrme^-\to\mathrm{XX})\cdot\mathrm{BR}^2(\mathrm{X}\to\mathrm{Y}\gamma)$ are derived for the case of stable and invisible $\mathrm{Y}$ . These limits apply to single and pair production of excited neutrinos ( $\mathrm{X} = \nu^*, \mathrm{Y} = \nu$ ), to neutralino production ( $\mathrm{X}={{{\tilde{\chi}}^{0}}_{2}}, \mathrm{Y}={{{\tilde{\chi}}^{0}}_{1}}$ ) and to supersymmetric models in which $\mathrm{X} ={{{\tilde{\chi}}^{0}}_{1}}$ and $\mathrm{Y}={\tilde{\mathrm{G}}}$ is a light gravitino. The case of macroscopic decay lengths of particle X is considered for $\mathrme^+\mathrme^- \to \mathrm{XX}$ , $\rm X \to Y \gamma$ , when $M_{\mathrm Y}\approx 0$ . The single-photon results are also used to place upper limits on superlight gravitino pair production as well as graviton-photon production in the context of theories with additional space dimensions.

Evidence is presented for kinematic and charge correlations of B mesons with charged pions and kaons. Using a new technique, a sample of over 80 000 partially reconstructed B mesons is obtained in 3.5·106 hadronic Z0 decays recorded using the OPAL detector at LEP. The invariant mass distributions of B+π− and B+K− combinations show enhancements consistent with the decays of P-wave resonances of a b antiquark and a light quark. We observe an excess of 1738±195 B+π− pairs with invariant masses in the range 5.60-5.85 GeV and an excess of 149±31 B+K− pairs with invariant masses in the range 5.80–6.00 GeV. Labeling the observed enhancements generically as B** we find $$\begin{gathered} \frac{{BR(Z^0 \to \bar b \to B^{**0} \to B^{(*) + } \pi ^ - )}}{{BR(Z^0 \to \bar b \to B^ + )}} = 0.18 \pm 0.04, \hfill \\ \frac{{BR(Z^0 \to \bar b \to B_s^{**0} \to B^{(*) + } K^ - )}}{{BR(Z^0 \to \bar b \to B^ + )}} = 0.026 \pm 0.008, \hfill \\ \end{gathered} $$ where B(*)+ indicates the sum of B+ and B*+ and the errors include statistical and systematic contributions. From a study of π-B charge-flavor correlations we conclude that the production flavor of a B meson can be tagged with the charge of a pion in an appropriately chosen kinematic region, and that the performance of this flavor tag compares favorably in the $$Z^0 \to q\bar q$$ environment with lepton-based tags.

Using a large sample of charm semileptonic decays collected by the FOCUS photoproduction experiment at Fermilab, we present evidence for a small, even spin K−π+ amplitude that interferes with the dominant K̄∗0 component in the D+→K−π+μ+ν final state. Although this interference significantly distorts the D+→K−π+μ+ν decay angular distributions, the new amplitude creates only a very small distortion to the observed kaon pion mass distribution when integrated over the other kinematic variables describing the decay. Our data can be described by K̄∗0 interference with either a constant amplitude or broad spin zero resonance.

Analysis of three D → Kππ Dalitz plots is presented using data collected by the Fermilab high energy photoproduction experiment E687. Our data are fit to a model consisting of a sum of Breit-Wigner amplitudes for the intermediate two-body resonant decay modes and a constant term for the nonresonant contribution. We extract branching fractions and relative phases and compare them to the results obtained in other experiments. Although this model qualitatively reproduces many features of our data, statistically significant discrepancies are observed in some of our fits.

Quark and gluon jets in e+e− three-jet events at LEP are identified using lepton tagging of quark jets, through observation of semi-leptonic charm and bottom quark decays. Events with a symmetry under transposition of the energies and directions of a quark and gluon jet are selected: these quark and gluon jets have essentially the same energy and event environment and as a consequence their properties can be compared directly. The energy of the jets which are studied is about 24.5 GeV. In the cores of the jets, gluon jets are found to yield a softer particle energy spectrum than quark jets. Gluon jets are observed to be broader than quark jets, as seen from the shape of their particle momentum spectra both in and out of the three-jet event plane. The greater width of gluon jets relative to quark jets is also visible from the shapes of their multiplicity distributions. Little difference is observed, however, between the mean value of particle multiplicity for the two jet types.

Additive manufacturing of metal parts in the motorsport industry is becoming a decisive technology for producing lightweight and rigid parts, with increasing applications as the costs decrease. Among the available metal alloys, AlSi10Mg is one of the most widely used. In this paper, the corrosion resistance of additively manufactured AlSi10Mg is compared with that of other traditionally manufactured aluminium alloys widespread in the automotive industry. Several potentially corrosive agents, typical of vehicle applications, were used: salty water, motor oil, suspension oil, cooling fluid and gasoline. Corrosion tests were conducted at both room temperature and 90 °C. The effects of heat and surface treatments were evaluated separately. The samples were visually inspected and weighed to evaluate the corrosion rate with the aid of SEM and EDS analysis. Additively manufactured AlSi10Mg generally showed better corrosion resistance in the stress-relieved condition as compared to the T6-treated state, with slightly better results for the polished samples. Motor oil, suspension oil, cooling fluid and gasoline did not significantly corrode the specimens, except for the T6-treated AlSi10Mg samples at 90 °C. However, the corrosion rate was always higher than traditionally manufactured aluminium alloys tested for comparison.

A search for single top quark production via flavour changing neutral currents (FCNC) was performed with data collected by the OPAL detector at the e+e− collider LEP. Approximately 600 pb−1 of data collected at s=189–209 GeV were used to search for the FCNC process e+e−→tc(u)→bWc(u). This analysis is sensitive to the leptonic and the hadronic decay modes of the W boson. No evidence for a FCNC process is observed. Upper limits at the 95% confidence level on the single top production cross-section as a function of the centre-of-mass energy are derived. Limits on the anomalous coupling parameters κγ and κZ are determined from these results.

A search for stable and long-lived massive particles of electric charge |Q/e|=1 or fractional charges of 2/3, 4/3, and 5/3 is reported using data collected by the OPAL detector at LEP, at centre-of-mass energies from 130 to 209 GeV. These particles are assumed to be pair-produced in e+e− collisions and not to interact strongly. No evidence for the production of these particles was observed. Model-independent upper limits on the production cross-section between 0.005 and 0.028 pb have been derived for scalar and spin-1/2 particles with charge ±1. Within the framework of the Constrained Minimal Supersymmetric Standard Model (CMSSM), this implies a lower limit of 98.0 (98.5) GeV on the mass of long-lived right- (left-)handed scalar muons and scalar taus. Long-lived charged heavy leptons and charginos are excluded for masses below 102.0 GeV. For particles with fractional charge ±2/3, ±4/3 and ±5/3, the upper limit on the production cross-section varies between 0.005 and 0.020 pb. All mass and cross-section limits are derived at the 95% confidence level and are valid for particles with lifetimes longer than 10−6 s.

A search for pair-produced doubly charged Higgs bosons has been performed using data samples corresponding to an integrated luminosity of about 614 pb−1 collected with the OPAL detector at LEP at centre-of-mass energies between 189 GeV and 209 GeV. No evidence for a signal has been observed. A mass limit of 98.5 GeV/c2 at the 95% confidence level has been set for the doubly charged Higgs particle in left–right symmetric models. This is the first search for doubly charged Higgs bosons at centre-of-mass energies larger than 91 GeV.

We describe the algorithm used to identify charged tracks in the fixed-target charm-photoproduction experiment FOCUS.

Using a large sample of D0→K−μ+ν and D0→π−μ+ν decays collected by the FOCUS photoproduction experiment at Fermilab, we present new measurements of the q2 dependence for the f+(q2) form factor. These measured f+(q2) form factors are fit to common parameterizations such as the pole dominance form and compared to recent unquenched Lattice QCD calculations. We find mpole=1.93±0.05±0.03GeV/c2 for D0→K−μ+ν and mpole=1.91−0.15+0.30±0.07GeV/c2 for D0→π−μ+ν and f−(K)(0)/f+(K)(0)=−1.7−1.4+1.5±0.3.

We observe an increase of the average transverse momentum with the multiplicity of the charged particles produced in the central rapidity region of proton-proton collisions at ISR energies. The increase is smaller than that observed at the CERN proton-antiproton collider. The magnitude of the effect is the same for negative and positive particles.

We report on a search for new quarks in hadronic Z° decays. From the event shape analysis of a data sample containing 2185 multihadronic annihilation events, we observe no evidence for the top or b' quarks. We derive limits for the top and b' quark masses under the assumption of various possible standard model and non-standard model decay schemes. Our search is sensitive to quark masses larger than 23 GeV/c2; it yields the following lower limits at a 95% confidence level: 44.5 GeV/c2 for the top quark mass and 45.2 GeV/c2 for the b′ quark mass.

The capture cross sections of 93Nb, 103Rh, and 181Ta were measured in the 10- to 70-keV neutron energy range, using 197Au as a standard. Most of the data points were obtained with a total uncertainty of ∼4%. This was possible because the calculation of capture gamma-ray spectra allowed reducing the most severe systematic uncertainties involved. Hauser-Feshbach calculations were performed that yielded not only the neutron cross sections of the isotopes considered up to 4-MeV neutron energy but also partial capture cross sections and capture gamma-ray spectra. For these calculations a consistent set of input parameters was determined from available experimental information or from model-guided systematics. The influence of these parameters on the results is discussed.

The neutron capture widths of s-wave resonances in 56Fe (27.7 keV), 58Ni (15.4 keV), and 60Ni (12.5 keV) have been determined using a setup completely different from previous experiments. A pulsed 3-MV Van de Graaff accelerator and a kinematically collimated neutron beam, produced via the 7Li(p, n) reaction, were used in the experiments. Capture gamma rays were observed by three Moxon-Rae detectors with graphite, bismuth-graphite, and bismuth converters, respectively. The samples were positioned at a neutron flight path of only 9 cm. Thus, events due to capture of resonance-scattered neutrons in the detectors or in surrounding materials are completely discriminated by their additional time of flight. The high neutron flux at the sample position allowed the use of very thin samples (0.15 to 0.45 mm), avoiding large multiple scattering corrections. The data obtained with the individual detectors were corrected for the efficiency of the respective converter materials. For that purpose, detailed theoretical calculations of the capture gamma-ray spectra of the measured isotopes and of gold, which was used as a standard, were performed. The final results are Γγ(27.7 keV, 56Fe) = 1.06 ± 0.05 eV; Γγ(15.4 keV, 58Ni) = 1.53 ± 0.10 eV; and Γγ(12.5 keV, 60Ni) = 2.92 ± 0.19 eV. The accuracy obtained with the present experimental method represents an improvement by a factor 3 to 6 compared to previous experiments. The investigated s-wave resonances contribute 10 to 40% to the total capture rate of the respective isotopes in a typical fast reactor.

Using data from FOCUS (E831) experiment at Fermilab, we present a model independent partial-wave analysis of the K−π+ S-wave amplitude from the decay D+→K−π+π+. The S-wave is a generic complex function to be determined directly from the data fit. The P- and D-waves are parameterized by a sum of Breit–Wigner amplitudes. The measurement of the S-wave amplitude covers the whole elastic range of the K−π+ system.

Amplitude analyses of the D+ and Ds+ → K+K−π+ Dalitz plots are presented using data collected by the Fermilab high energy photoproduction experiment E687. Our data are fit to a model consisting of a sum of Breit-Wigner amplitudes for the intermediate two-body resonant decay modes. We extract decay fractions and relative phases. These results are used to infer new branching ratios for D+ → K+K−π+ inclusive as well as the Φπ+ and K∗(892)0K+ channels.

From the observed yield and properties of isolated energetic photons in the reaction e+e−→Z0→hadrons+γ measured with the OPAL detector at LEP, evidence for final state radiation from primary quarks is obtained. Combined with the measurement of the total hadronic width of the Z0, the observed rate allows the extraction of the electroweak coupling constants of up and down type quarks: ν132 + a132 = 1.24±0.47 and ν232 + a232 = 1.72±0.70 No evidence for additional photon production from anomalous decays of the Z0 or from decays of new particles is found. This measurement limits the contribution to the total Z0 width from such sources to be less than 8.2 MeV at the 95% confidence level.

Quark and gluon in 3-jet events from hadronic Z0 decays are identified through use of the semi-leptonic decays of charm and bottom quarks. This tagging method allows geometrically symmetric or transposed configurations of the quark and gluon jets to be selected, permitting a study of the asymmetry in the population of particles in the regions between jets, commonly called the string effect, which avoids restrictions present in previous studies. In particular, our demonstration of a population asymmetry is performed without use of a model. Our results imply that dynamical differences exist between quarks and gluons or between quark-antiquark and quark-gluon jet systems with respect to their particle production properties.

The average transverse momentum and the size of the particle emitting source (measured via Bose-Einstein correlations) have been studied as functions of the charged particle density in the central region inp-p interactions at $$\sqrt s $$ =62, 44 and 31 GeV. Both the average transverse momentum and the source size increase with increasing density at all three energies. This effect, very weak at $$\sqrt s $$ =31 GeV, becomes stronger with increasing energy.

The relative yield of high transverse momentum protons measured inpp interctions at the CERN ISR is calculated in the framework of simple parton models. Whereas models based exclusively on quark and gluon scattering fail to describe the data, the hypothesis of diquark scattering provides a quantitative understanding of the measured dependences on transverse momentum, polar angle, and centre-of-mass energy. Different assumptions on diquark structure functions are tested.

The ratios of high pT charged kaon to pion production cross sections at √s = 45 and 62 GeV are presented. The values of the K±π± ratios are essentially independent of both √s and xT = 2pT√s and are compatible with a strangeness suppression factor λ = 0.55. By contrast, the K−π− values fall with xT suggesting a gluonic origin of K−. QCD calculations agrees with the measurements.

.Using the OPAL detector at LEP, the running of the effective QED coupling α(t) is measured for space-like momentum transfer from the angular distribution of small-angle Bhabha scattering. In an almost ideal QED framework, with very favourable experimental conditions, we obtain: \( \Delta \alpha {\left( { - 6.07\;{\text{GeV}}^{2} } \right)} - \Delta \alpha {\left( { - 1.81\;{\text{GeV}}^{2} } \right)} = {\left( {440 \pm 58 \pm 43 \pm 30} \right)} \times 10^{{ - 5}} ,\) where the first error is statistical, the second is the experimental systematic and the third is the theoretical uncertainty. This agrees with current evaluations of α(t). The null hypothesis that α remains constant within the above interval of -t is excluded with a significance above 5σ. Similarly, our results are inconsistent at the level of 3σ with the hypothesis that only leptonic loops contribute to the running. This is currently the most significant direct measurement where the running α(t) is probed differentially within the measured t range.

An amplitude analysis of the D+, Ds+ → π−π+π+ Dalitz plots is presented using data collected by the Fermilab high-energy photoproduction experiment E687. The data are fitted to a model consisting of a sum of relativistic Breit-Wigner amplitudes for the intermediate two-body resonant decay modes plus a flat non-resonant contribution. From the fit we derive decay fractions and relative phases. We also present measurements of Γ(D+→π−π+π+)Γ(D+→K−π+π+) and Γ(Ds+→π−π+π+)Γ(Ds+→K−K+π+).

We measure the mass of the τ to be 1775.1±1.6(mcnstat.)±1.0(mcnsys.) MeV using τ from Z0 decays. To test CPT invariance we compare the masses of the positively and negatively charged τ. The relative mass difference is found to be smaller than 3.0×10−3 at the 90% confidence level.

The magnitude of the Cabibbo-Kobayashi-Maskawa matrix element Vcb has been measured using B̄0→D∗+ℓ−ν̄ decays recorded on the Z0 peak using the OPAL detector at LEP. The D∗+→D0π+ decays were reconstructed both in the particular decay modes D0→K−π+ and D0→K−π+π0 and via an inclusive technique. The product of |Vcb| and the decay form factor of the B̄0→D∗+ℓ−ν̄ transition at zero recoil F(1) was measured to be F(1)|Vcb|=(37.1±1.0±2.0)×10−3, where the uncertainties are statistical and systematic respectively. By using Heavy Quark Effective Theory calculations for F(1), a value of|Vcb|=(40.7±1.1±2.2±1.6)×10−3was obtained, where the third error is due to theoretical uncertainties in the value of F(1). The branching ratio Br(B̄0→D∗+ℓ−ν̄) was also measured to be (5.26±0.20±0.46)%.

Using data from the FOCUS (E831) experiment, we have searched for T violation in charm meson decays using the four-body decay channels $D^0 \to K^-K^+\pi^-\pi^+$, $D^+ \to K^0_SK^+\pi^-\pi^+$, and $D^+_s \to K^0_SK^+\pi^-\pi^+$. The T violation asymmetry is obtained using triple-product correlations and assuming the validity of the CPT theorem. We find the asymmetry values to be $A_Tviol (D^0) = 0.010 \pm 0.057(stat.) \pm 0.037(syst.)$, $A_Tviol (D^+) = 0.023 \pm 0.062(stat.) \pm 0.022(syst.)$, and $A_Tviol (D^+_s) = -0.036 \pm 0.067(stat.) \pm 0.023(syst.)$. Each measurement is consistent with no T violation. New measurements of the CP asymmetries for some of these decay modes are also presented.

Using a large sample of D+ to K- pi+ mu+ nu decays collected by the FOCUS photoproduction experiment at Fermilab, we present new measurements of two semileptonic form factor ratios: rv and r2. We find rv = 1.504 \pm 0.057 \pm 0.039 and r2 = 0.875 \pm 0.049 \pm 0.064. Our form factor results include the effects of the s-wave interference discussed in a previous paper.

Data are presented on Pomeron-Pomeron interactions which produce a centralπ + π − system in proton-proton collisions at $$\sqrt s = 62 GeV$$ at the CERN Intersecting Storage Rings. This process may favor the production of gluonic bound states. A partial-wave analysis of theπ + π − system shows evidence for the production of the statesf 0(975),f 0(1400), andf 2(1270). The fitted mass for thef 2(1270) is about 50 MeV below the world average. In addition, the production mechanism for thef 2(1270) is uniquely different from that for the other final states in that there is a correlation between the outgoing protons. this is consistent with a picture of two-gluon exchange with thef 2(1270) produced by gluon fusion, and could indicate that thef 2(1270) has a glueball component.

We present a Kπ mass spectrum analysis of the four-body semileptonic charm decay D+→K−π+μ+ν in the range of 0.65GeV/c2<mKπ<1.5GeV/c2. We observe a non-resonant contribution of 5.30±0.74−0.96+0.99% with respect to the total D+→K−π+μ+ν decay. For the K∗(892)0 resonance, we obtain a mass of 895.41±0.32−0.43+0.35MeV/c2, a width of 47.79±0.86−1.06+1.32MeV/c2, and a Blatt–Weisskopf damping factor parameter of 3.96±0.54−0.90+1.31GeV−1. We also report 90% CL upper limits of 4% and 0.64% for the branching ratios Γ(D+→K¯∗(1680)0μ+ν)Γ(D+→K−π+μ+ν) and Γ(D+→K¯0∗(1430)0μ+ν)Γ(D+→K−π+μ+ν), respectively.

We describe a silicon microstrip detector interleaved with segments of a beryllium oxide target which was used in the FOCUS photoproduction experiment at Fermilab. The detector was designed to improve the vertex resolution and to enhance the reconstruction efficiency of short-lived charm particles.

Abstract Measurements are presented of inclusive distributions in pp and p p interactions at √s = 53 GeV. The data were obtained at the CERN ISR using the Split Field Magnet spectrometer with a minimum bias trigger. The inclusive distributions are analyzed as functions of the transverse momentum, the rapidity and the Feynman-x variable.

We present an analysis of the decay D0→K+π− based on FOCUS data. From a sample of 234 signal events, we find a branching ratio of Γ(D0→K+π−)Γ(D0→K−π+)=(0.429−0.061+0.063±0.027)% under the assumptions of no mixing and no CP violation. Allowing for CP violation, we find a branching ratio of (0.429±0.063±0.028)% and a CP asymmetry of 0.18±0.14±0.04. The branching ratio for the case of mixing with no CP violation is (0.381−0.163+0.167±0.092)%. We also present limits on charm mixing.

The Compact Muon Solenoid (CMS) experiment prepares its Phase-2 upgrade for the high-luminosity era of the LHC operation (HL-LHC). Due to the increase of occupancy, trigger latency and rates, the full electronics of the CMS Drift Tube (DT) chambers will need to be replaced. In the new design, the time bin for the digitization of the chamber signals will be of around 1 ns, and the totality of the signals will be forwarded asynchronously to the service cavern at full resolution. The new backend system will be in charge of building the trigger primitives of each chamber. These trigger primitives contain the information at chamber level about the muon candidates position, direction, and collision time, and are used as input in the L1 CMS trigger. The added functionalities will improve the robustness of the system against ageing. An algorithm based on analytical solutions for reconstructing the DT trigger primitives, called Analytical Method, has been implemented both as a software C++ emulator and in firmware. Its performance has been estimated using the software emulator with simulated and real data samples, and through hardware implementation tests. Measured efficiencies are 96 to 98% for all qualities and time and spatial resolutions are close to the ultimate performance of the DT chambers. A prototype chain of the HL-LHC electronics using the Analytical Method for trigger primitive generation has been installed during Long Shutdown 2 of the LHC and operated in CMS cosmic data taking campaigns in 2020 and 2021. Results from this validation step, the so-called Slice Test, are presented.

Abstract The Scattering and Neutrino Detector at the LHC (SND@LHC) started taking data at the beginning of Run 3 of the LHC. The experiment is designed to perform measurements with neutrinos produced in proton-proton collisions at the LHC in an energy range between 100 GeV and 1 TeV. It covers a previously unexplored pseudo-rapidity range of $$7.2&lt;\eta &lt;8.4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>7.2</mml:mn> <mml:mo>&lt;</mml:mo> <mml:mi>η</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mn>8.4</mml:mn> </mml:mrow> </mml:math> . The detector is located 480 m downstream of the ATLAS interaction point in the TI18 tunnel. It comprises a veto system, a target consisting of tungsten plates interleaved with nuclear emulsion and scintillating fiber (SciFi) trackers, followed by a muon detector (UpStream, US and DownStream, DS). In this article we report the measurement of the muon flux in three subdetectors: the emulsion, the SciFi trackers and the DownStream Muon detector. The muon flux per integrated luminosity through an 18 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> 18 cm $$^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>2</mml:mn> </mml:msup> </mml:math> area in the emulsion is: $$\begin{aligned} 1.5 \pm 0.1(\text {stat}) \times 10^4\,\text {fb/cm}^{2}. \end{aligned}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtable> <mml:mtr> <mml:mtd> <mml:mrow> <mml:mn>1.5</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.1</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>stat</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> <mml:mspace /> <mml:msup> <mml:mtext>fb/cm</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> <mml:mo>.</mml:mo> </mml:mrow> </mml:mtd> </mml:mtr> </mml:mtable> </mml:mrow> </mml:math> The muon flux per integrated luminosity through a 31 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> 31 cm $$^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>2</mml:mn> </mml:msup> </mml:math> area in the centre of the SciFi is: $$\begin{aligned} 2.06\pm 0.01(\text {stat})\pm 0.12(\text {sys}) \times 10^{4} \text {fb/cm}^{2} \end{aligned}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtable> <mml:mtr> <mml:mtd> <mml:mrow> <mml:mn>2.06</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>stat</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>±</mml:mo> <mml:mn>0.12</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>sys</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> <mml:msup> <mml:mtext>fb/cm</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:mtd> </mml:mtr> </mml:mtable> </mml:mrow> </mml:math> The muon flux per integrated luminosity through a 52 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> 52 cm $$^{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>2</mml:mn> </mml:msup> </mml:math> area in the centre of the downstream muon system is: $$\begin{aligned} 2.35\pm 0.01(\text {stat})\pm 0.10(\text {sys}) \times 10^{4}\,\text {fb/cm}^{2} \end{aligned}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mtable> <mml:mtr> <mml:mtd> <mml:mrow> <mml:mn>2.35</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>stat</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>±</mml:mo> <mml:mn>0.10</mml:mn> <mml:mrow> <mml:mo>(</mml:mo> <mml:mtext>sys</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> <mml:mspace /> <mml:msup> <mml:mtext>fb/cm</mml:mtext> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:mtd> </mml:mtr> </mml:mtable> </mml:mrow> </mml:math> The total relative uncertainty of the measurements by the electronic detectors is 6 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> for the SciFi and 4 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> for the DS measurement. The Monte Carlo simulation prediction of these fluxes is 20–25 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> lower than the measured values.

Cross-sections for hadronic and leptonic two-fermion events, and leptonic forward-backward asymmetries, have been measured in e+e− collisions at a centre-of-mass energy of 161 GeV, using the OPAL detector at LEP. Results are presented both including and excluding the dominant production of radiative γZ0 events. We have measured Rb, the ratio of the number of bb to all multihadronic events at 161 GeV, and compared it to the result obtained at 130–136 GeV. All results agree well with the Standard Model expectations. In a model-independent fit to the Z0 lineshape, the data presented here give an improved precision on the γZ0-interference term. The data have also been used to obtain new limits on extensions of the Standard Model described by effective four-fermion contact interactions.

New measurements are presented of the photon structure function F2γ(x,Q2) at four values of Q2 between 9 and 59 GeV2 based on data collected with the OPAL detector at centre-of-mass energies of 161–172 GeV, with a total integrated luminosity of 18.1 pb−1. The evolution of F2γ with Q2 in bins of x is determined in the Q2 range from 1.86 to 135 GeV2 using data taken at centre-of-mass energies of 91 GeV and 161–172 GeV. F2γ is observed to increase with Q2 with a slope of α−1dF2γdlnQ2 = 0.10−0.03+0.05 measured in the range 0.1 < x < 0.6.

This paper presents updated measurements of the lifetimes of the Bs0 meson and the Λb0 baryon using 4.4 million hadronic Z0 decays recorded by the OPAL detector at LEP from 1990 to 1995. A sample of Bs0 decays is obtained using Ds−ℓ+ combinations, where the Ds− is fully reconstructed in the φπ−, K∗0K− and K−K0S decay channels and partially reconstructed in the φℓ−ν̄X decay mode. A sample of Λb0 decays is obtained using Λc+ℓ− combinations, where the Λc+ is fully reconstructed in its decay to a pK−π+ final state and partially reconstructed in the Λℓ+νX decay channel. From 172±28 Ds−ℓ+ combinations attributed to Bs0 decays, the measured lifetime is τ(Bs0)=1.50+0.16−0.15±0.04ps, where the errors are statistical and systematic, respectively. From the 129±25 Λc+ℓ− combinations attributed to Λb0 decays, the measured lifetime is τ(Λb0)=1.29+0.24−0.22±0.06ps, where the errors are statistical and systematic, respectively.

Helicity density matrix elements for inclusive K∗(892)0 mesons from hadronic Z0 decays have been measured over the full range of K∗ 0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum xp values above 0.3, with the matrix element ϱ00 rising to 0.66 ± 0.11 for xp > 0.7. The values of the real part of the off-diagonal element ϱ1 - 1 are negative at large xp, with a weighted average value of −0.09 ± 0.03 for xp > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq system from the Z0 decay. All other helicity density matrix elements measured are consistent with zero over the entire xp range. The K∗ 0 fragmentation function has also been measured and the total rate determined to be 0.74 ± 0.02 ± 0.02 K∗(892)0 mesons per hadronic Z0 decay.

A factorial moment analysis has been performed on the differential multiplicity distributions of hadronic final states of the Z0 recorded with the OPAL detector at LEP. The moments of the one-dimensional rapidity and the two-dimensional rapidity versus azimuthal angle distributions are found to exhibit “intermittent” behaviour attributable to the jet structure of the events. The moments are reproduced by both parton shower and matrix element QCD based hadronisation models. No evidence for fluctuations beyond those attributable to jet structure is observed.

A search for decays of the Bc meson was performed using data collected from 1990–1995 with the OPAL detector on or near the Z0 peak at LEP. The decay channels Bc+→J/ψπ+, Bc+→J/ψa1+ and Bc+→J/ψℓ+ν were investigated, where ℓ denotes an electron or a muon. Two candidates are observed in the mode Bc+→J/ψπ+, with an estimated background of (0.63±0.20) events. The weighted mean of the masses of the two candidates is (6.32±0.06) GeV/c2, which is consistent with the predicted mass of the Bc meson. One candidate event is observed in the mode Bc+→J/ψℓ+ν, with an estimated background of (0.82±0.19) events. No candidate events are observed in the Bc+→J/ψa1+ decay mode, with an estimated background of (1.10±0.22) events. Upper bounds at the 90% confidence level are set on the production rates for these processes.

A search was performed for charginos with masses close to the mass of the lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209 GeV recorded by the OPAL detector at LEP. Events were selected if they had an observed high-energy photon from initial state radiation, reducing the dominant background from two-photon scattering to a negligible level. No significant excess over Standard Model expectations has been observed in the analysed data set corresponding to an integrated luminosity of 570pb-1. Upper limits were derived on the chargino pair-productin cross-section, and lower limits on the chargino mass were derived in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated Supersymmetry breaking scenarios.

Using data from FOCUS (E831) experiment at Fermilab, we present a model independent partial-wave analysis of the K−π+ S-wave amplitude from the decay D+→K−π+π+. The S-wave is a generic complex function to be determined directly from the data fit. The P- and D-waves are parameterized by a sum of Breit–Wigner amplitudes. The measurement of the S-wave amplitude covers the whole elastic range of the K−π+ system.

A high statistics sample of photoproduced charm particles from the FOCUS (E831) experiment at Fermilab has been used to search for CP violation in the Cabibbo suppressed decay modes D+→K−K+π+, D0→K−K+ and D0→π−π+. We have measured the following CP asymmetry parameters: ACP(K−K+π+)=+0.006±0.011±0.005, ACP(K−K+)=−0.001±0.022±0.015 and ACP(π−π+)=+0.048±0.039±0.025 where the first error is statistical and the second error is systematic. These asymmetries are consistent with zero with smaller errors than previous measurements.

A high-statistics sample of photoproduced charm from the FOCUS experiment has been used to search for direct CP violation in the decay rates for D+-->K(S)pi+ and D+-->K(S)K+. We have measured the following asymmetry parameters relative to D+-->K-pi+pi+: A(CP)(K(S)pi+) = (-1.6+/-1.5+/-0.9)%, A(CP)(K(S)K+) = (+6.9+/-6.0+/-1.5)%, and A(CP)(K(S)K+) = (+7.1+/-6.1+/-1.2)% relative to D+-->K(S)pi+. We have also measured the relative branching ratios and found Gamma(D+-->K(0)pi+)/Gamma(D+-->K-pi+pi+) = (30.60+/-0.46+/-0.32)%, Gamma(D+-->K(0)K+)/Gamma(D+-->K-pi+pi+) = (6.04+/-0.35+/-0.30)%, and Gamma(D+-->K(0)K+)/Gamma(D+-->K(0)pi+) = (19.96+/-1.19+/-0.96)%.

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement for the branching ratios of the Cabibbo-suppressed decay modes D0→π−π+ and D0→K−K+. We measured: Γ(D0→K−K+)/Γ(D0→π−π+)=2.81±0.10(stat)±0.06(syst), Γ(D0→K−K+)/Γ(D0→K−π+)=0.0993±0.0014(stat)±0.0014(syst), and Γ(D0→π−π+)/Γ(D0→K−π+)=0.0353±0.0012(stat)±0.0006(syst). These values have been combined with other experimental data to extract the ratios of isospin amplitudes and the phase shifts for the D→KK and D→ππ decay channels.

We review genetic programming principles, their application to FOCUS data samples, and use the method to study the doubly Cabibbo suppressed decay D+ -> K+ pi+ pi- relative to its Cabibbo favored counterpart, D+ -> K- pi+ pi+. We find that this technique is able to improve upon more traditional analysis methods. To our knowledge, this is the first application of the genetic programming technique to High Energy Physics data.

Data are presented for the exclusive reaction pp → pp π+ π− at $$\sqrt s = 62GeV$$ with two leading protons at large Feynman-x and a centrally produced π+;π− system. In this kinematical configuration one expects a substantial contribution from Double Pomeron Exchange, which is a potential source of glueballs. The experiment was performed at the CERN ISR using the Split Field Magnet spectrometer. In the mass range between 1,000 and 1,700 MeV/c2 the invariant mass distribution for the central π+;π− system exhibits a very significant signal for thef 0(1270) and no other obvious resonant states.

A new experimental method has been used to determine the isomeric ratio (IR) in neutron capture of 241Am in a differential experiment. Thin 241Am samples have been activated with subthermal monoenergetic neutrons of 14.75 meV and quasi-monoenergetic neutrons of ∼30 keV. The decay of the 242Am nuclei produced has been determined by observing the emitted beta spectrum in a mini-orange spectrometer. The measurements have been performed relative to gold. The ratio R1 = σγ (241Am→ 242gAm)/σγ(Au) was found to be R1 = 5.79 ± 0.33 at 14.75 meV and R1 = 2.73 ± 0.16 at ∼30 keV. The corresponding IRs, σγ(241Am→ 242gAm)/σγ(Am), are 0.92. ± 0.06 at 14.75 meV and 0.65 ± 0.05 at ∼30 keV.Detailed theoretical calculations of the total capture cross section, the IR, and the capture gamma-ray spectra were performed in the energy range from 1 to 1000 keV taking advantage of recently available information on the discrete level scheme of 242Am. With the present knowledge on the level scheme of 242Am, it seems to be difficult to reproduce the strong energy dependence of IR as indicated by the experimental results.

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement of the weak decay-asymmetry parameter αΛc in Λc+→Λπ+ decay. Comparing particle with antiparticle decays, we obtain the first measurement of the CP violation parameter A≡αΛc+αΛ¯cαΛc−αΛ¯c. We obtain αΛc=−0.78±0.16±0.19 and A=−0.07±0.19±0.24 where errors are statistical and systematic.

We report a study of forward-backward multiplicity correlations and a measurement of the dependence on charged multiplicity of the mean transverse momentum of charged hadrons, measured with respect to the thrust axis. The study was performed on a high statistics sample of Z0 decays to multihadronic final states collected by the OPAL Collaboration at LEP. The positive forward-backward multiplicity correlation observed in our inclusive sample can be understood in terms of a superposition of distinct event topologies characterized by a different amount of hard gluon radiation (2-, 3- and 4-jet events) and with different mean multiplicities. The residual positive correlation that we see in a clean 2-jet sample can be interpreted in terms of fragmentation properties of different quark flavours and of the production and decay of resonances. We have compared the observed effects with the predictions of QCD-based parton shower models. The data are well described by the Jetset 7.3 Monte Carlo, while Herwig 5.5 does not satisfactorily reproduce the measured correlations. Hard gluon radiation is also shown to be responsible for the observed increase of about 40% in the mean transverse momentum of produced charged hadrons in the multiplicity range from 10 to 30. The comparison with the results obtained in an analysis of a sample enriched in Z0 → bb̄ events, shows that the presence of heavy flavours does not contribute significantly to the observed effect.

We present evidence for the Ωc0 in a new decay mode Ωc0 → Σ+K−K−π+, for which we find 42.5 ± 8.8 events with a mass of 2699.9 ± 1.5 ± 2.5 MeV/c2. The data are from Fermilab high energy photoproduction experiment E687.

We report the measurement of masses and widths of the following L=1 charm mesons by the E687 Collaboration at Fermilab: a ${\mathit{D}}_{2}^{\mathrm{*}0}$ state of mass (width) 2453\ifmmode\pm\else\textpm\fi{}3\ifmmode\pm\else\textpm\fi{}2 (25\ifmmode\pm\else\textpm\fi{}10\ifmmode\pm\else\textpm\fi{}5) MeV/${\mathit{c}}^{2}$ decaying to ${\mathit{D}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$, a ${\mathit{D}}_{2}^{\mathrm{*}+}$ state of mass (width) 2453\ifmmode\pm\else\textpm\fi{}3\ifmmode\pm\else\textpm\fi{}2 (23\ifmmode\pm\else\textpm\fi{}9\ifmmode\pm\else\textpm\fi{}5) MeV/${\mathit{c}}^{2}$ decaying to ${\mathit{D}}^{0}$${\mathrm{\ensuremath{\pi}}}^{+}$, a ${\mathit{D}}_{1}^{0}$ state of mass (width) 2422\ifmmode\pm\else\textpm\fi{}2\ifmmode\pm\else\textpm\fi{}2 (15\ifmmode\pm\else\textpm\fi{}8\ifmmode\pm\else\textpm\fi{}4) MeV/${\mathit{c}}^{2}$ decaying to ${\mathit{D}}^{\mathrm{*}+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$, and a ${\mathit{D}}_{\mathit{s}1}^{+}$ state of mass 2535.0\ifmmode\pm\else\textpm\fi{}0.6\ifmmode\pm\else\textpm\fi{}1.0 MeV/${\mathit{c}}^{2}$ and width 3.2 MeV/${\mathit{c}}^{2}$ at 90% confidence level, decaying to ${\mathit{D}}^{\mathrm{*}+}$${\mathit{K}}_{\mathit{s}}^{0}$ and ${\mathit{D}}^{\mathrm{*}0}$${\mathit{K}}^{+}$.

We report evidence of a narrow resonance at a mass of 2705.9 ± 3.3 ± 2.0 MeV/c2 in the final state Ω−π+ and the charge conjugate. The mass and width support the interpretation of a weakly decaying doubly strange charmed baryon, the Ωc0. Limits on the relative branching ratios for Ωc0→Ω−K−π+π+ and Ωc0→Ω−π−π+π+ are also presented.

A search for charginos and neutralinos, predicted by supersymmetric theories, has been performed using a data sample of 2.6 pb−1 at a centre-of-mass energy of S=130 GeV and 2.6 pb−1 at 136 GeV collected with the OPAL detector at LEP during November 1995. No candidate events were observed. The 95% C.L. lower limit on the lightest chargino mass in the Minimal Supersymmetric Standard Model is 65.4 GeV if the universal scalar mass m0 is greater than 1 TeV, and 58.7 GeV for the smallest m0 compatible with slepton and sneutrino mass limits obtained at centre-of-mass energies near the Z peak. These limits were obtained under the conditions that the lightest chargino is heavier than the lightest neutralino by more than 10 GeV and tan β is larger than 1.5. The results of a model independent search for charginos and neutralinos are also given.

We describe the various techniques developed in the Fermilab Wideband Experiments, E687 and FOCUS, to reconstruct long-lived states. The techniques all involve modifications to standard tracking techniques and are useful to report for future experiments.

The 40 MHz bunched muon beam set up at CERN was used in May 2003 to make a full test of the drift tubes local muon trigger. The main goal of the test was to prove that the integration of the various devices located on a muon chamber was adequately done both on the hardware and software side of the system. Furthermore the test provided complete information about the general performance of the trigger algorithms in terms of efficiency and noise. Data were collected with the default configuration of the trigger devices and with several alternative configurations at various angles of incidence of the beam. Tests on noise suppression and di-muon trigger capability were performed.

.A search for pair-produced leptoquarks is performed using \(\mbox{e}^ + \mbox{e}^-\) collision events collected by the OPAL detector at LEP at centre-of-mass energies between 189 and 209 GeV. The data sample corresponds to a total integrated luminosity of 596 pb-1. The leptoquarks are assumed to be produced via couplings to the photon and the Z0. For a given search channel only leptoquark decays involving a single lepton generation are considered. No evidence for leptoquark pair production is observed. Lower limits on masses for scalar and vector leptoquarks are calculated. The results improve most of the LEP limits derived from previous searches for the pair production process by 10-25 GeV, depending on the leptoquark quantum numbers.

A search for minimal standard model (MSM) and minimal supersymmetric model (MSSM), Higgs bosons with masses larger than 3 GeV/c2 has been performed by the OPAL collaboration one + e − data from LEP corresponding to an integrated luminosity of 1.24 pb−1. The limits for MSM Higgs bosons have been obtained using the channelsZ 0→Z 0* H 0,Z 0*→(v $$\bar v$$ ore + e − or µ+, µ−. The search for MSSM Higgs bosons has been performed using the channelsZ 0→Z 0* H 0,v $$\bar v$$ ore + e − or µ+µ−),h 0 →q $$\bar q$$ andZ 0→h 0 A 0,h 0 A 0→(4 jet orτ + τ −→ or 4τ), whereh 0 andA 0 are the two lightest neutral MSSM Higgs bosons. No Higgs boson signal has been observed. The MSM Higgs boson is excluded in the mass range 3 GeV < $$m_{H^0 }$$ <25.3 GeV/c2 at the 95% confidence level; limits on the masses of the two lightest neutral MSSM Higgs bosons are obtained forh 0 mases up to 40.5 GeV/c2.

We analyse the variation of the average transverse momentum, 〈pT〉, with the multiplicity of charged particles produced in pp, p̄p, dd and αα collisions at ISR energies. An increase of 〈pT〉 with increasing particle density p=ΔnΔy for charged particles produced in the central region is observed. The energy dependence of this effect and its dependence on the type of colliding particles are discussed.

The multiplicity distributions of charged secondaries in proton-proton interactions at $$\sqrt s = 31$$ , 44 and 62 GeV have been measured with high statistics using the split field magnet (SFM) detector at the CERN ISR. The multiplicity distributions for narrow bins in rapidity depend on the rapidity variable. The validity of KNO scaling is discussed. The negative binomial function fits well the charged and negative multiplicity data for full phase space and for central rapidity windows. The energy and the rapidity dependence of the negative binomial parameters, $$\bar n$$ andk, are presented. We also analyse their implications for a cascade model in terms of the average number of «clans» and of the average number of particles per «clan».

Bose-Einstein correlations between two equal charge pions were measured in pp and pp collisions at s = 63 GeV. The data were recorded at the CERN-ISR with the split field magnet detector (SFM) using minimum bias triggers. The second-order interference is used to determine the size and the degree of coherence of the pion source in pp and [ovbar|p]p collisions. They are found to be equal within errors.

We present evidence for fluctuations of the average transverse momentum in pp, pα and αα collisions at ISR energies. In thermodynamical models, this is interpreted as fluctuations in the temperature of hadronic interactions. We find that the effect does not depend on the energy of the collision, however, the fluctuations are smaller for αp and αα reactions than for pp interactions.

Deep inelastic electron-photon scattering is studied using e+e− data collected by the OPAL detector at centre-of-mass energies s=MZ0. The photon structure function F2γ(x,Q2) is explored in a Q2 range of 1.1 to 6.6 GeV2 at lower x values than ever before. To probe this kinematic region events are selected with a beam electron scattered into one of the OPAL luminosity calorimeters at scattering angles between 27 and 55 mrad. A measurement is presented of the photon structure function F2γ(x,Q2) at 〈Q2〉 = 1.86 GeV2 and 3.76 GeV2 in five logarithmic x bins from 0.0025 to 0.2.

We report measurements of charm particle production asymmetries from the Fermilab photoproduction experiment E687. An asymmetry in the rate of production of charm versus anticharm particles is expected to arise primarily from fragmentation effects. We observe statistically significant asymmetries in the photoproduction of D+, D∗+ and D0 mesons and find small (but statistically weak) asymmetries in the production of the Ds+ meson and the Λc+ baryon. Our inclusive photoproduction asymmetries are compared to predictions from nonperturbative models of charm quark fragmentation.

Measurements are presented of the inclusive cross section for K∗(892)± production in hadronic decays of the Z0 using a sample of about half a million events recorded with the OPAL experiment at LEP. Charged K∗ mesons are reconstructed in the decay channel K0Sπ±. A mean rate of 0.72±0.02±0.08 K∗ mesons per hadronic event is found. Comparison of the results with predictions of the JETSET and HERWIG models shows that JETSET overestimates the K∗± production cross section while HERWIG is consistent with the data.

.Gluon jets with a mean energy of 22 GeV and purity of 95% are selected from hadronic Z0 decay events produced in e + e- annihilations. A subsample of these jets is identified which exhibits a large gap in the rapidity distribution of particles within the jet. After imposing the requirement of a rapidity gap, the gluon jet purity is 86%. These jets are observed to demonstrate a high degree of sensitivity to the presence of color reconnection, i.e. higher order QCD processes affecting the underlying color structure. We use our data to test three QCD models which include a simulation of color reconnection: one in the Ariadne Monte Carlo, one in the Herwig Monte Carlo, and the other by Rathsman in the Pythia Monte Carlo. We find the Rathsman and Ariadne color reconnection models can describe our gluon jet measurements only if very large values are used for the cutoff parameters which serve to terminate the parton showers, and that the description of inclusive Z0 data is significantly degraded in this case. We conclude that color reconnection as implemented by these two models is disfavored. The signal from the Herwig color reconnection model is less clear and we do not obtain a definite conclusion concerning this model. In a separate study, we follow recent theoretical suggestions and search for glueball-like objects in the leading part of the gluon jets. No clear evidence is observed for these objects.

Data are presented for the first time on inclusive Pomeron-Pomeron interactions which produce a central systemX (composed mainly of multimeson states) in proton-proton collisions at $$\sqrt s $$ at the CERN ISR. The systemX has a Feynman-x distribution which is sharply peaked atx f=0, is inconsistent with any significant contributions from Reggeon exchange processes, and has an invariant mass dependence in good agreement with the predicted formM −2 . Kaon production is about 15% of pion production, nearly independent ofM x, while proton-antiproton production averages about 5% of pion production and increases withM x. The structure of the central systemX develops into a jetlike shape, asM x increases, as would be expected from a model of Pomeron fragmentation. The shape of thex f(π) distribution in the center of mass of theX system (although not proving existence) is consistent with asoft partonic substructure of the Pomeron.

The Extreme Energy Events Project has been designed to join the scientific interest of a cosmic rays physics experiment with the enormous didactic potentiality deriving from letting it be carried out by high school students and teachers. After the initial phase, the experiment is starting to take data continuously, and the first interesting physics results have been obtained, demonstrating the validity of the idea of running a real physics investigation in these peculiar conditions. Here an overview of its structure and status is presented, together with some studies about detector performance and first physics results.

We present measurements of the hadronic photon structure functionF 2 (x), in twoQ 2 ranges with mean values of 5.9 GeV2 and 14.7 GeV2. The data were taken by the OPAL experiment at LEP, with $$\sqrt s$$ close to theZ 0 mass and correspond to an integratede + e − luminosity of 44.8 pb−1. In the context of a QCD-based model we find the quark transverse momentum cutoff separating the vector meson dominance (VMD) and perturbative QCD regions to be 0.27±0.10 GeV. We confirm that there is a significant pointlike component of the photon when the probe photon hasQ 2>4 GeV2. Our measurements extend to lower values ofx than any previous experiment, and no increase ofF 2 (x) is observed.

Measurements have been made in the OPAL experiment at LEP of the inclusive production of strange vector φ(1020) and K*(892)0 mesons, and the tensor meson K 2 * (1430)0. The overall production rates per hadronic Z0 decay have been determined to be 0.100±0.004stat.±0.007syst. φ(1020) mesons, 0.74±0.03stat.±0.03syst. K*(892)0 mesons and (forx E <0.3) 0.19±0.04stat.±0.06syst. K 2 * (1430)0 mesons. The measurements for the vector states update previously published results based on lower statistics, while the K 2 * (1430)0 rate represents the first direct measurement of a strange tensor state in Z0 decay. For the vector states, both the overall production rates and normalised differential cross sections, with respect to the scaled energy variablex E , have been compared to JETSET and HERWIG predictions. The peak positions in the ζ=ln(1/x p ) distributions have been measured and compared to measurements of other hadron states.

A search for the Minimal Standard Model Higgs boson (H0) has been performed with data from e+e− collisions collected by the OPAL detector at LEP. The search was made for events of the types e+e−→(e+e−,μ+μ− or νν)H0, H0→qq̄ and was based on approximately 78 pb−1 of data taken at center-of-mass energies between 88 and 95 GeV in the years 1990–1993. The present study, combined with previous OPAL publications, excludes the existence of a Minimal Standard Model Higgs boson with mass below 56.9 GeV at the 95% confidence level.

We present a measurement of the forward-backward charge asymmetry in hadronic decays of the Z0 using data collected with the OPAL detector at LEP. The forward-backward charge asymmetry was measured using a weight function method which gave the number of forward events on a statistical basis. In a data sample of 448 942 hadronic Z0 decays, we have observed a charge asymmetry of Ah = 0.040±0.004 (stat.)±0.006 (syst.)±0.002 (B0B0mix.), taking into account the effect of B0B0 mixing. In the framework of the standard model, this asymmetry corresponds to an effective weak mixing angle averaged over five quark flavours of sin2θW = 0.2321 ± 0.0017 (stat.) ± 0.0027 (syst.) ± 0.0009 (B0B0mix.). The result agrees with the value obtained from the Z0 line shape and lepton pair forward-backward asymmetry.

The perturbative QCD approach to multiparticle production predicts a characteristic suppression of particle multiplicity in a heavy quark jet as compared to a light quark jet. In the Modified Leading Logarithmic Approximation (MLLA) the multiplicity difference \delta_{Q\ell} between heavy and light quark jets is derived in terms of a few other experimentally measured quantities. The earlier prediction for b-quarks needs revision in the light of new experimental results and the improvement in the understanding of the experimental data. We now find \delta_{b\ell}=4.4\pm0.4. The updated MLLA results on \delta_{b\ell} and \delta_{c\ell} are compared with the present data from e^+e^- annihilation. Their expected energy independence is confirmed within the energy range between 29 and 200 GeV; the absolute values are now in better agreement with experiment than in the previous analysis, and the remaining difference can be attributed largely to next-to-MLLA contributions, an important subset of which are identified and evaluated.

Using a high statistics sample of photo-produced charm particles from the FOCUS experiment at Fermilab, we report on the measurement of the ratio of semileptonic rates \Gamma(D+ > ANTI-K pi mu+ nu)/\Gamma(D+ > ANTI-K0 mu+ nu)= 0.625 +/- 0.045 +/- 0.034. Allowing for the K pi S-wave interference measured previously by FOCUS, we extract the vector to pseudoscalar ratio \Gamma(D+ > ANTI-K*0 mu+ nu)/\Gamma(D+ > ANTI-K0 mu+ nu)= 0.594 +/- 0.043 +/- 0.033 and the ratio \Gamma(D+ > ANTI-K0 mu+ nu)/\Gamma(D+ > K- pi+ pi+)= 1.019 +/- 0.076 +/- 0.065. Our results show a lower ratio for \Gamma(D > K* \ell nu})/\Gamma(D > K \ell nu) than has been reported recently and indicate the current world average branching fractions for the decays D+ >ANTI-K0(mu+, e+) nu are low. Using the PDG world average for B(D+ > K- pi+ pi+) we extract B(D+ > ANIT-K0 mu+ nu)=(9.27 +/- 0.69 +/- 0.59 +/- 0.61)%.

Measurements are presented of two-particle rapidity correlations in pp and pp at √s = 53 GeV. The data were recorded at the CERN-ISR using the Split Field Magnet spectrometer with a minimum bias trigger. Short range correlations in normal inelastic events with measured charged multiplicities nch ⩾ 4 are observed of pairs for charged particles in all charge combinations. Within the experimental errors no differences are observed between the analogous correlations in pp and pp interactions.

Due to its large volume (18 m3)the Resistive Plate Chamber (RPC) detector of the Compact Muon Solenoid (CMS) experiment at the LHC proton collider (CERN, Switzerland) will employ a gas re-circulation system. Since the mixture composition and quality are crucial issues for the detector operation, CMS-RPC will use an online gas analysis and monitoring system. An overview of both the CMS-RPC gas system and gas monitoring system is given and the project parameters are described.

The Search for Hidden Particles (SHiP) experiment proposal at CERN demands a dedicated dipole magnet for its scattering and neutrino detector. This requires a very large volume to be uniformly magnetized at B > 1.2 T, with constraints regarding the inner instrumented volume as well as the external region, where no massive structures are allowed and only an extremely low stray field is admitted. In this paper we report the main technical challenges and the relevant design options providing a comprehensive design for the magnet of the SHiP Scattering and Neutrino Detector.

The Pixel Luminosity Telescope is a silicon pixel detector dedicated to luminosity measurement at the CMS experiment at the LHC. It is located approximately 1.75 m from the interaction point and arranged into 16 "telescopes", with eight telescopes installed around the beam pipe at either end of the detector and each telescope composed of three individual silicon sensor planes. The per-bunch instantaneous luminosity is measured by counting events where all three planes in the telescope register a hit, using a special readout at the full LHC bunch-crossing rate of 40 MHz. The full pixel information is read out at a lower rate and can be used to determine calibrations, corrections, and systematic uncertainties for the online and offline measurements. This paper details the commissioning, operational history, and performance of the detector during Run 2 (2015-18) of the LHC, as well as preparations for Run 3, which will begin in 2022.

Using a large sample of photoproduced charm mesons from the FOCUS experiment at Fermilab (FNAL-E831), we observe the decay D0-->K+pi- with a signal yield of 149+/-31 events compared to a similarly cut sample consisting of 36 760+/-195 D0-->K-pi+ events. We use the observed ratio of D0-->K+pi- to D0-->K-pi+ (0.404+/-0.085+/-0.025)% to obtain a relationship between the D0 mixing and doubly Cabibbo suppressed decay parameters.

We search for lepton flavour violating events (eμ, eτ and μτ) that could be directly produced in e+e− annihilations, using the full available data sample collected with the OPAL detector at centre-of-mass energies between 189 GeV and 209 GeV. In general, the Standard Model expectations describe the data well for all the channels and at each s. A single eμ event is observed where according to our Monte Carlo simulations only 0.019 events are expected from Standard Model processes. We obtain the first limits on the cross-sections σ(e+e−→eμ, eτ and μτ) as a function of s at LEP2 energies.

Charged multiplicity and π0 cross sections for π−p inelastic interactions at 70 GeV/c are presented. The data were obtained from an exposure of the BEBC bubble chamber equipped with a track sensitive target (TST) to an unseparated negative beam at the CERN SPS. About 10 000 events were used for the charged multiplicity study, and about 2000 Dalitz pairs for the π0 production analysis. A total of 12 e+e− pairs with a mass higher than the π0 mass were found and analysed in terms of η or ω Dalitz pairs or decay pairs of vector mesons. Comparisons with data at other energies are made in terms of charged prong, π0 cross sections, and of multiplicity parameters. The moments of longitudinal and transverse momentum distributions of theπ0 are determined and compared to the predictions of quark counting rule models.

Using data collected by the fixed target Fermilab experiment FOCUS, we present several first measurements for the semileptonic decay D0→K¯0π−μ+ν. Using a model that includes a K¯0π− s-wave component, we measure the form factor ratios to be rv=1.71±0.68±0.34 and r2=0.91±0.37±0.10 and the s-wave amplitude to be A=0.35±0.22±0.05GeV−1. Finally, we measure the vector semileptonic branching ratio Γ(D0→K*(892)−μ+ν)Γ(D0→K¯0π−π+)=0.337±0.034±0.013.

A study of Bose–Einstein correlations in pairs of identically charged pions produced in e+e- annihilations at the Z0 peak has been performed for the first time assuming a non-static emitting source. The results are based on the high statistics data obtained with the OPAL detector at LEP. The correlation functions have been analyzed in intervals of the average pair transverse momentum and of the pair rapidity, in order to study possible correlations between the pion production points and their momenta (position–momentum correlations). The Yano–Koonin and the Bertsch–Pratt parameterizations have been fitted to the measured correlation functions to estimate the geometrical parameters of the source as well as the velocity of the source elements with respect to the overall centre-of-mass frame. The source rapidity is found to scale approximately with the pair rapidity, and both the longitudinal and transverse source dimensions are found to decrease for increasing average pair transverse momenta.

The OPAL detector at LEP is used to measure the branching ratio of theZ 0 into invisible particles by measuring the cross section of single photon events ine + e − collisions at centre-of-mass energies near theZ 0 resonance. In a data sample of 5.3 pb−1, we observe 73 events with single photons depositing more than 1.5 GeV in the electromagnetic calorimeter, with an expected background of 8±2 events not associated with invisibleZ 0 decay. With this data we determine theZ 0 invisible width to be 0.50±0.07±0.03 GeV, where the first error is statistical and the second systematic. This corresponds to 3.0±0.4±0.2 light neutrino generations in the Standard Model.