Upper limits on D0-D0 mixing and BB production from muon-nucleon scattering

In deep inelastic interactions of 200 GeV muons with a carbon target, we have found 17 events of the type μ^±N→μ^±μ^?μ^?X (“wrong-sign” dimuons). We derive upper limits of 1.2% (90% CL) on $\text{D}{}^0\text{-}\text{D}{}^0$ transitions (mixing) or, alternatively, of 9 pb (90% CL) cross section for $\text{B}\text{B}$ pair production as possible sources of such events.     

Neutrino production of same-sign dimuons at the Fermilab Tevatron

The rate of neutrino- and antineutrino-induced prompt same-sign dimuon production in steel was measured using a sample of μ^?μ^? events and 25 μ⁺μ⁺ events withP _μ>9 GeV/c, produced in 1.5 millionv _μ and 0.3 million \(\overline {v_\mu }\) induced charged-current events with energies between 30 GeV and 600 GeV. The data were obtained with the Chicago-Columbia-Fermilab-Rochester (CCFR) neutrino detector in the Fermilab Tevatron Quadrupole Triplet Neutrino Beam during experiments E 744 and E 770. After background subtraction, the prompt rate of same-sign dimuon production is (0.53±0.24)×10^?4 perv _μ charged-current event and (0.52±0.33)×10^?4 per \(\overline {v_\mu }\) charged-current event. The kinematic distributions of the same-sign dimuon events after background subtraction are consistent with those of the non-prompt background due to meson decays in the hadron shower of a charged-current event. Calculations ofc \(\bar c\) gluon bremsstrahlung, based on improved measurements of the charm mass parameter and nucleon structure functions by the CCFR collaboration, yield a prompt rate of (0.09±0.39)×10^?4 perv _μ charged-current event. In this case,c \(\bar c\) gluon bremsstrahlung is probably not an observable source of prompt same-sign dimuons.     

On the semileptonic decay of charmed hadrons

The semileptonic and leptonic decay modes of charmed hadrons produced in e⁺e^? collisions above 4 GeV in the cm have been investigated by selecting events with a single electron plus at least two charged tracks. The electron momentum spectrum peaks near 0.5 GeV/c with few events above 0.7 GeV/c. The spectrum excludes large rates for the decays $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}$ and $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{π}$, but is compatible with $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{K}{}^1\text{(892)}$, $\text{D}\text{→}\text{e}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{K}$ or a mixture of both. The semileptonic branching ratio is obtained both by comparing the inclusive electron cross section with the total cross section attributable to charm, and by studying the fraction of events containing a second electron. The semileptonic charm branching ratios obtained are 0.11 ± 0.03 and 0.16 ± 0.06 respectively. A single event with three electrons and hadrons is found, consistent with the estimated background. The 90% confidence upper limit for σ(e⁺e^? → 3e + hadrons) is 0.1 nb.     

Inclusive production of D-mesons in e+e− annihilation at 7 GeV

Inclusive momentum and energy spectra of neutral and charged D-mesons produced in e⁺e^? annihilation at energies near 7 GeV are presented. The slope of the energy spectrum is similar to the charged pion spectrum at the same energy. The inclusive cross section σ(e⁺e^?→ D or $\text{D}$ + anything) at 7 GeV is 4.8±1.3 nb.     

Observation of high transverse momentum electrons at the CERN ISR

A search for high transverse momentum electrons directly produced in proton-proton collisions has been performed at the CERN ISR. The apparatus included a magnetic spectrometer with wire spark chambers, a lead-glass counter array, and a threshold gas ?erenkov counter. At a centre-of-mass energy √s = 52.7 GeV, a signal has been observed in the range $\text{1.6<p}{}_{\mathrm{T}}{}^1\text{<4.7}\text{GeV}\text{/c}$. The signal occurs at a level of approximately 10^?4 of the inclusive pion cross-section.     

A study of high transverse momentum π0's at ISR energies

We present a study of the transverse momentum spectrum of π⁰'s produced at c.m. angles θ = 90° and 53° in pp collisions at √s = 23.6, 30.8, 45.1, 53.2, and 62.9 GeV. The experiment was performed with a lead-glass detector. The data can be described with the usual parametrization $\text{p}{}_{\mathrm{<mtext>T</mtext>}}{}^{\mathrm{?n}}\text{?;(x}{}_{\mathrm{<mtext>T</mtext>}}\text{, θ)}$, with n = 7.2 ± 0.2. Comparison between the 90° and 53° data further indicates no appreciable dependence on θ, at least for x_T < 0.3. Two-particle inclusive cross sections for π⁰'s produced alongside are also presented. They are observed to have a dependence upon the transverse momentum of the dipion similar to that of single-particle cross sections and with the same value of n. Two-photon decays of η mesons are observed between 3 and 4 GeV/c transverse momentum with a production cross section half of that of π⁰.     

Experimental cross section for dimuon production and the Drell-Yan model

We have measured the absolute cross section for dimuon production in hadron collisions at 200 GeV/c in the continuum region M = 4–8.5 GeV. In all the channels studied (pN, $\text{p}$N, π^±N and π^?H₂) the experimental cross section is significantly larger by a factor of 2.3 ± 0.5 than expected from the Drell-Yan model. Furthermore, our proton-nucleon data allow a determination of the nucleon valence structure function which agrees with the deep inelastic lepton scattering data.     

D and D meson production near 4 GeV in e+e− annihilation

We have studied momentum spectra for D⁰ ($\text{D}$⁰) and D^± mesons produced near 4 GeV in e⁺e^? annihilation and find that production is dominated by two-body reactions involving D and D¹ states where the D¹ (charged and neutral) have masses near 2.01 GeV/c². A detailed study of D momentum spectra near E_cm = 4.028 GeV allows determination of masses and branching ratios of D and D¹ states. Lastly we find that events containing a D⁰ meson conserve strangeness, thus establishing upper limits on D⁰-$\text{D}$⁰ mixing and on the effects of charm changing neutral currents.     

Charm dimuons and determination of the strange sea

We re-examine the standard charm model for opposite-sign dimuon events in neutrino-nucleon scattering. Published dimuon rates are shown to be consistent with a simple SU(3) symmetric sea. We discuss the types of correlated studies of different dimuon observables needed to extract unambiguous information on the nucleon's strange sea from upcoming, high statistics data. Our calculations demonstrate the sizeable effects of finite energy resolution and missing final-state energy on predictions of observed dimuon rates, particularly for data obtained from wide-band incident neutrino spectra. We emphasize the crucial role of the non-zero charm mass, not only for the analysis of dimuon events, but also for the interpretation of large-y inclusive $\text{v}\text{N}\text{→}\text{μ}\text{X}$ data.     

Charged pion production in e+e− annihilation at 14, 22 and 34 GeV CM energy

The inclusive production of π^± mesons in e⁺e^? annihilation has been measured at c.m. energies of 14, 22 and 34 GeV for pion momenta between 0.3 ans 10 GeV/c. The fraction of pions among the charged hadrons is above 90% at 0.4 GeV/c and decreases to about 50% at high momenta. The scaled cross sections ($\text{s}\text{β}$) $\text{d}\text{σ}\text{d}\text{x}$ at 14, 22 and 34 GeV as well as the 5.2 GeV data from DASP have a rather similar x dependence. After integration over the x range from 0.2 to 0.6 the cross sections indicate a monotonic decrease with increasing centre-of-mass energy.     

Radiative decays of the Jψ and evidence for a new heavy resonance

The three photon final state produced in e⁺e^? collisions has been measured at the mass of the $\text{J}\text{ψ}$ resonance using the nonmagnetic part of the double arm spectrometer DASP. The decays $\text{J}\text{ψ}\text{→ ηγ, η'γ}$ and π^oγ were observed and their branching ratios are given. A four standard deviation signal was observed in the γγ mass spectrum at a mass of (2.83 ± 0.03) GeV. An upper limit is given for the direct decay $\text{J}\text{ψ}\text{→ 3γ}$.     

Study of neutrino-indiced dimuon events in gargamelle at CERN SPS

This letter reports a study of 117 opposite-sign and 41 like-sign dimuons, in a wide-band neutrino exposure of Gargamelle at CERN SPS. No signal is found in the μ^?μ^? channel. The μ^?μ⁺ channel is found to be dominated by D-meson production and decay. There is evidence in these events for missing energy which may be interpreted as an unseen neutrino. The V⁰ multiplicities, K⁰/event=0.53_?0.20^+0.25and Λ/event=0.03_?0.04^+0.06 show only evidence for charmed meson production. Information on the D-meson fragmentation function is presented. In a specific model, a rate $\text{σ}\text{(μ}{}^{\mathrm{?}}\text{μ}{}^{\mathrm{+}}\text{)}\text{σ(μ}{}^{\mathrm{?}}\text{)}\text{=(0.72±0.14×10}{}^{\mathrm{?2}}$ is found, independent of the energy. An investigation of these events for visible D-decays sets a limit on the life-time τ_D<0.8 ×10^?12s at 90% C.L.     

On the decays π0→νν′

Phenomenological aspects of π⁰→νν′ are considered. From the existing experimental information, we deduce an upper limit $\text{Γ(π}{}^0\text{→νν′)}\text{Γ(π}{}^0\text{→}\text{all}\text{)}\text{< 2.4 × 10}{}^{\mathrm{?5}}\text{(90\%}\text{c.l.}\text{)}$. Possible mechanisms which can give rise to this process are discussed. Branching ratios of the order of 10^?6 for decays into the known neutrinos (ν_e, ν_μ) are found possible. Rates comparable to the experimental limit for decays into final states involving additional neutrinos (massive or massless) cannot be ruled out.     

A study of ππ → KK using an experiment on π−p → KS0KS0n at 8.9 GeV/c

We present an analysis of the K_S⁰K_S⁰ system, based on 6380 events, produced in the reactions π^?p → K_S⁰K_S⁰n. Using a one-pion exchange model with absorption we determine the S- and D-wave amplitudes of ππ → $\text{K}\text{K}$. Several A₂ production amplitudes were also included in the fits and we conclude that an unnatural parity exchange amplitudes which does not interfere with pion exchange, seems to present. A branching ratio $\text{Γ(}\text{f}\text{→}\text{K}\text{K}\text{/ Γ(}\text{f}\text{→ ππ) = 0.029 ± 0.006}$ is determined. With this and other new values of branching ratios we have fitted the 2⁺ → 0^?0^? decay rates of the SU(3) relations resulting in (36.2 ± 1)° for the tensor nonet mixing angle.     

Inclusive π0 production at the CERN p-p̄ collider

Inclusive π⁰ production has been measured at the CERN pp? collider, $\text{s}\text{=540}\text{GeV}$, for 90° production angle and in a range of transverse momenta between 1.5 and 4.5 GeV/c. The invariant production cross section is larger than that measured at $\text{s}\text{= 53}\text{GeV}$ for p-p collisions. The production of μ mesons aand of direct photons is also investigated.     

Observation of wrong-sign tri-muon events in 250 GeV muon-nucleon interactions

Two trimuon events of the type μ⁺N→μ⁺μ⁺μ⁺X and one μ⁺N→μ⁺μ^?μ^?X have been observed in 250 GeV μ⁺ -iron interactions. The expected rate from the decay of hadrons (charm, π, K) is about one event. Other processes that may contribute are both beauty production and charm production with $\text{D}{}^0\text{?}\text{D}{}^0$ mixing. The data give upper limits of 12×10^?36 cm² for the cross section of beauty pair production by muons, and 20% for $\text{D}{}^0\text{?}\text{D}{}^0$ transitions due to mixing, both at 90% confidence level.     

Differential cross-sections for pp → π−π+, K−K+ between 0.8 and 2.4 GeV/c

We present measurements from a spark chamber experiment of the differential cross-sections for $\text{p}$p → π^?π⁺, K^?K⁺ at 20 momenta in the range 0.8–2.4 GeV/c (c.m. energy 2.02 to 2.57 GeV). The c.m. angular range was $\text{?0.95 <}\text{cos}\text{θ}{}^1\text{< 0.95}$. There are about 2000π^?π⁺ events and about 300 K^?K⁺ events at each momentum.     

Inclusive π electroproduction in the deep inelastic region

Using 20.5 GeV electrons on protons, we measured inclusive π⁰'s (of transverse momentum, p_T, from 0 to 1.4 GeV/c) produced by virtual photons of energy, ν, from 4 to 16.5 GeV and four-momentum squared, q², from ?1.8 to ?8.5 (GeV/c)². Comparing with charged pion data, we find , supporting the quark model. Photon knockout of a quark is favored as the interpretation of these data because of scaling in z = E_π/ν and similarity in z-dependence of other pion production data. Consistent with this interpretation are the dependence of 〈p_T〉 on q², the azimuthal dependence, and fits to the constituent interchange model. We also observe a possible p_T^?4 dependence at large |q²| over a limited p_T range.     

Study of longitudinal distributions in the fragmentation regions,using the quark-parton model,in K−p interactions at 70 GeV/c

The study of π^±, π⁰, K⁰ and Λ production in the fragmentation regions (|x|0.2) of K^?p interactions at 70 GeV/c shows that the x-dependence of each invariant cross section is well described by the power law (1?|x|)ⁿ suggested by the dimensional counting rule. Furthermore, pion production is found, both in K^? and proton fragmentation regions, to be very similar to their production in $\text{ν(}\text{ν}\text{)}\text{p}$ interactions as expected from quark-parton models. The quark and diquark fragmentation functions D_u^π, D_uu^π and D_ud^π are extracted from our data.     

Observation of a direct low-mass e+e− continuum in π-p interactions at 16 GeV/c

The production of prompt electron-positron pairs in 16 GeV/c π^-p collisions has been measured using the LASS spectrometer at SLAC. An excess of events is observed above the estimated contribution of direct and Dalitz decays of known resonances in the kinematic range defined by $\text{0.1?χ?0.45, 0?p}{}_{\mathrm{T}}\text{?0.8}\text{GeV}\text{c}$ and $\text{0.2?M(e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{)?0.7}\text{GeV}\text{c}{}^2$. The excess signal decreases slowly with increasing M, but exhibits very steep χ and p_T² dependence.