Missing-mass Experiment Research Articles

Double-diffractive processes in high-resolution missing-mass experiments at the Tevatron

We evaluate, in a model-independent way, the signal-to-background ratio for Higgs -> b bbar detection in exclusive double-diffractive events at the Tevatron and the LHC. For the missing-mass approach to be able to identify the Higgs boson, it will be necessary to use a central jet detector and to tag b quark jets. The signal is predicted to be very small at the Tevatron, but observable at the LHC. However we note that the background, that is double-diffractive dijet production, may serve as a unique gluon factory. We also give estimates for the double-diffractive production of chi_c and chi_b mesons at the Tevatron. We emphasize that a high-resolution missing-mass measurement, on its own, is insufficient to identify rare processes.

Experimental searches for exotic multiquark particles

Experimental searches for "exotic" multiquark hadrons are reported. In a hyperon beam experiment at the Organisation Européenne pour la Recherche Nucléaire-superproton synchrotron (CERN-SPS), evidence was found for narrow states at 3.1 GeV/c2, with charges + 1,0, and −1, decaying into Λ, [Formula: see text], and pions. Similar signals were also seen in a neutron beam experiment at Serpukhov. These states, called U (3100), are tentatively explained as [Formula: see text] systems, i.e., [Formula: see text]. Such states were proposed more than a decade ago. New hyperon beam experiments in preparation at CERN and Fermilab will study these states, provided they exist. The proposed multiquark systems H = uuddss and [Formula: see text] are also discussed. One candidate for the decay H(2175) → Σ−p was observed in a propane buble chamber exposed to a proton beam. At Brookhaven National Laboratory, a missing-mass experiment in a high-intensity K− beam will search for the H, and the new hyperon beam experiments will search for inclusive production of both H and P.

Are the narrow structures recently seen in T=1, B=2 missing mass spectra, dibaryons?

The structures observed in recent missing mass experiments 3He(p, d)X and p( 3He, d)X are discussed and shown to agree to a high accuracy with a rotational like scheme M= M 0+ M 1 J( J+1). An explanation is suggested as to why these structures have not been observed in some other experiments.

A missing-mass spectrometer for momenta below 1.5 GeV/ c

An apparatus consisting of two magnetic spectrometers has been constructed at the CERN Proton Synchrotron (PS) in a missing-mass experiment to identify and select the beam particle and the outgoing one, and to measure their momenta. This paper gives details of the two spectrometers, which are comprised of multiwire proportional chambers, high resolution time-of-flight counters, and aerogel and water Cherenkov detectors.

Silica aerogel Cherenkov counter in a missing-mass experiment K −d → K + + X at 1.4 GeV/ c

Two Cherenkov counters, Č 0 and Č 1, are being used in an experiment to search for dibaryon candidates in the reaction K −d → K + + X at 1.4 GeV/ c. They have useful cross-sections of 10 × 8 cm 2 and 30 × 15 cm 2, respectively. Each counter is a diffusing box surrounding the aerogel sample and can be examined by two photomultipliers. The mean number of photoelectrons collected is equal to 17 in Č 0 and 21 in Č 1 for β = 1 incident particles. Below threshold, the residual scintillation corresponds to 0.12 photoelectrons. The role of each otheter in the trigger logic for the K −d → K + + X experiment is carefully studied.

Search for NarrowN¯NStates near Threshold

A missing-mass experiment in p-bard ..-->.. NX, where X is the system whose mass M/sub X/ is measured, was performed for interactions of antiprotons at rest and in flight below 500 MeV/c. The 4-standard-deviation upper limit for the production of narrow states, in the mass interval M/sub X/=1650--1930 MeV/c/sup 2/, is 2 mb for annihilations in flight and 0.3% of the annihilations at rest.

First measurement of the total width of the η′ (958) meson

In a high-resolution missing mass experiment the total width of the η′ (958) meson has been measured to be 0.28 ± 0.10 MeV. Using the known γγ branching ratio the value Γ( η′ → γγ) = 5.4 ± 2.1 keV is deduced. This is in good agreement with calculations based on fractional charge quarks and a pseudo-scalar mixing angle of 11°.

Study of diffraction dissociation in 19- and 28-GeV/cpdinteractions

The reaction $pd\ensuremath{\rightarrow}{p}_{\mathrm{spec}}p{\ensuremath{\pi}}^{\ensuremath{-}}p$ is studied at 19 and 28 GeV/c with data from the Brookhaven National Laboratory 80-in. deuterium-filled bubble chamber. In addition, a separate study is made of the low-momentum pion spectra in selected low-multiplicity events presumed to be associated with either of two isospin-conjugate modes of deuteron fragmentation by a 28-GeV/c beam proton. Our results from these complementary studies are that low-multiplicity channels are dominantly of a diffractive nature; however, significant differences seen in the mass spectra and angular correlations in the slow $p\ensuremath{\pi}$ between the 19- and 28-GeV/c data indicate that asymptotic behavior has not been reached, as least at 19 GeV/c. Neither $s$- nor $t$-channel helicity conservation is seen in the excitation of the target neutron into a low-mass $p{\ensuremath{\pi}}^{\ensuremath{-}}$ system. The ${N}^{*}(1.4)$ of missing-mass experiments is shown to be a superposition of nucleon-pion and nucleon-two-pion states.

The background in missing mass experiments

We propose a mechanism whereby one can determine the background in missing mass experiments in the resonance region by extending two component duality to absorptive amplitudes with external regeons. It is shown to explain naturally the very different trend of the background in the reactions p + p → p + X and π − + p → p + X at available energies. The implications and limitations of this mechanism for the analysis of the spectrum are discussed.

The production cross section of high-spin resonances in missing mass experiments in the Veneziano model

The generalized Veneziano model is applied to the study of production cross sections of high-spin resonances in missing mass experiments. Explicit calculations for resonances with J⩽21 have been carried out which show that: 1. (i) the production cross section σ decreases rapidly as J increases, the value for J = 20 being merely ∼10 −3 times the values for J = 1; 2. (ii) as a function of s, σ rises slowly from threshold to a maximum, then falls as s further increases. The position of the maximum increases with J (for J = 19, e.g., s max ∼ 100 GeV 2); 3. (iii) the differential cross section dσ dt is almost exponential in t with no dip in the forward direction. Although the results are qualitatively as expected, we have presented graphically in some detail the numerical values in the hope that they may be useful to experimenters planning such experiments.

Diffraction Dissociation and the Production of Baryon Resonances

A model incorporating virtual-meson diffraction scattering followed by a final-state resonant interaction of the meson with an emergent nucleon or isobar is proposed for the production of $I=\frac{1}{2}$ baryon resonances in the reaction $\mathrm{pp}\ensuremath{\rightarrow}p{{N}_{\frac{1}{2}}}^{*}$. Absolute predictions are compared with the experimental data relating to enhancements observed in missing-mass experiments. Agreement is favorable in the case of the ${P}_{11}(1470)$, but otherwise the many resonances predicted by phase-shift analyses complicate the issue and prevent a clear-cut test of the model. The proposed $\ensuremath{\Delta}P={(\ensuremath{-}1)}^{\ensuremath{\Delta}J}$ selection rule is discussed in relation to the large cross section predicted by the model for the "forbidden" ${S}_{11}(1150)$.

Inelastic Shadow Effects in Nuclear Total Cross Sections

We calculate the screening correction in proton-nuclear scattering at energies high enough so that inelastic excitations of the beam proton can contribute coherently. Data from proton-proton missing-mass experiments are used. These inelastic contributions to shadowing further reduce the total cross sections from the sum of single nucleon total cross sections. The effect grows from a very small increase in screening at, say 5 GeV/c, to a significant increase at, say, 15 GeV/c.

Search for the resonance σ +, of mass 960 MeV in the reaction p + p → d + δ +

A missing mass experiment of the reaction p + p → d + δ + shows no evidence for the existence of a boson around 960 MeV.