Charged hadron multiplicities and inclusive π− distributions in inelastic ep scattering

Electroproduction of hadrons is studied in the kinematic region W < 2.8 GeV and 0.3 < Q² < 1.4 GeV² using the DESY streamer chamber. Prong cross sections, charged-particle multiplicities and inclusive π^? distributions are presented. The average charged multiplicity is found to be independent of Q² in the Q² range studied here; however it is lower than in photoproduction. The fraction of forward π^? is found to be significantly less in electroproduction than in photoproduction. The 〈p_⊥²〉 for inclusive π^? is, for all x values, similar to that found in photoproduction.     

Laser desorption fast gas chromatography–Mass spectrometry in supersonic molecular beams

A novel method for fast analysis is presented. It is based on laser desorption injection followed by fast gas chromatography-mass spectrometry (GC-MS) in supersonic molecular beams. The sample was placed in an open air or purged laser desorption compartment, held at atmospheric pressure and near room temperature conditions. Desorption was performed with a XeCl Excimer pulsed laser with pulse energy of typically 3 mJ on the surface. About 20 pulses at 50 Hz were applied for sample injection, resulting in about 0.4 s injection time and one or a few micrograms sample vapor or small particles. The laser desorbed sample was further thermally vaporized at a heated frit glass filter located at the fast GC inlet. Ultrafast GC separation and quantification was achieved with a 50-cm-long megabore column operated with a high carrier gas flow rate of up to 240 mL/min. The high carrier gas flow rate provided effective and efficient entrainment of the laser desorbed species in the sweeping gas. Following the fast GC separation, the sample was analyzed by mass spectrometry in supersonic molecular beams. Both electron ionization and hyperthermal surface ionization were employed for enhanced selectivity and sensitivity. Typical laser desorption analysis time was under 10 s. The laser desorption fast GC-MS was studied and demonstrated with the following sample/matrices combinations, all without sample preparation or extraction: (a) traces of dioctylphthalate plasticizer oil on stainless steel surface and the efficiency of its cleaning; (b) the detection of methylparathion and aldicarb pesticides on orange leaves; (c) water surface analysis for the presence of methylparathion pesticide; (d) caffeine analysis in regular and decaffeinated coffee powder; (e) paracetamol and codeine drug analysis in pain relieving drug tablets; (f) caffeine trace analysis in raw urine; (g) blood analysis for the presence of 1 ppm lidocaine drug. The features and advantages of the laser desorption fast GC-MS are demonstrated and discussed.     

A study of theKπ system in the reactionK^ - p \to \bar K^0 \pi ^ - p at 8.25 GeV/c

The production ofK ^* resonances has been studied in the reaction \(K^ - p \to \bar K^0 \pi ^ - p\) at 8.25 GeV/c. The data comes from a high statistics bubble chamber experiment (180 events/μb). Masses, widths and production cross-sections have been determined for the first threeK ^*'s. The contributions from natural and unnatural parity exchange have been obtained for theK ^*(890) and theK ^*(1420). A partial wave analysis of theK π system from threshold to 1.9 GeV provides evidence for a 0⁺ enhancement near 1.4 GeV which could be interpreted as the κ(1350).     

A partial wave analysis of thef′ region in the reactionK^ - p \to K\bar K\Lambda ^0 at 8.25 GeV/c

A partial wave analysis of theK \(\bar K\) system produced by 8.25 GeV/cK ^? mesons in the reaction \(K^ - p \to K\bar K\Lambda ^{ 0} \) has been performed, taking into account the information provided by the Λ⁰ decay. Thef′ region is dominated byD ₀ ^(?) andD ₁ ⁽⁺⁾ waves. We see no evidence for the production of new 0⁺⁺ states in the mass region 1.05 to 1.75 GeV.     

The reactionsK − p→π ∓ Σ(1385)± at 8.25 GeV/c

The reactionsK ^? p→π ^? Σ(1385)^± are studied at an incident laboratory momentum of 8.25 GeV/c using data from a high statistics (?180 events/μb) bubble chamber experiment. In the case of the reactionK ^? p→π ^? Σ(1385)⁺ an amplitude analysis is performed and the complete Σ(1385)⁺ spin density matrix is extracted as a function oft′. The results are compared with the predictions of the additive quark model. In the case of the reactionK ^? p→π ⁺ Σ(1385)^? the cross-sections for forward and backward production are determined.     

Hadron production by virtual photons in the quark fragmentation region

We have measured the inclusive electroproduction of positive and negative hadrons in the quark fragmentation region using the streamer chamber at DESY. Data are presented in terms of the variable z_p = p/v in the kinematic region 1.8 < W < 2.8 GeV and 0.3 < Q² < 1.4 GeV². The positive hadron distributions contain a strong proton component. After subtraction of the proton component and elastic rho events, the distribution (1/σ_tot) dσ/dz_p for positive and negative hadrons agrees well with the corresponding distribution from e⁺e^? annihilation (DORIS data). This behaviour supports the validity of the quark-parton model at surprisingly low Q² and W.     

Rho production by virtual photons

The reaction γ_Vp → pπ⁺π^? was studied in the W, Q² region 1.3–2.8 GeV, 0.3–1.4 GeV² using the streamer chamber at DESY. A detailed analysis of rho production viaγ_Vp→?⁰p is presented. Near threshold rho production has peripheral and non-peripheral contributions of comparable magnitude. At higher energies (W > 2 GeV) the peripheral component is dominant. The Q² dependence of σ(γ_Vp→?⁰p) follows that of the rho propagator as predicted by VDM. The slope of dσ/dt at 〈Q²〉 = 0.4 and 0.8 GeV² is within errors equal to its value at Q² = 0. The overall shape of the ?⁰ is t dependent as in photoproduction, but is independent of Q². The decay angular distribution shows that longitudinal rhos dominate in the threshold region. At higher energies transverse rhos are dominant. Rho production by transverse photons proceeds almost exclusively by natural parity exchange, σ_T^N ? (0.83 ± 0.06) σ_T for 2.2 < W < 2.8 GeV. The s-channel helicity-flip amplitudes are small compared to non-flip amplitudes. The ratio R = σ_L/σ_T was determined assuming s-channel helicity conservation. We find R = ξ²Q²/M_?² with ξ² ≈ 0.4 for 〈W〉 = 2.45 GeV. Interference between rho production amplitudes from longitudinal and transverse photons is observed. With increasing energy the phase between the two amplitudes decreases. The observed features of rho electroproduction are consistent with a dominantly diffractive production mechanism for W > 2 GeV.