H. Becker

Diffractive Production of Strange Mesons at 63-{GeV}

Abstract Nearly 200 000 examples of the diffractive process K − p → K − π − π + p at 63 GeV have been obtained using a two magnet spectrometer equipped with Cerenkov counters for secondary particle identification. In addition some 2000 examples of the process K − p → ω K − p have been obtained. The K ππ data have been subjected to partial-wave analysis. The dominant J P = 1 + system couples to K ∗ π , in both S and D waves, ϱ K, κπ and e K. The data confirm the existence of two J P = 1 + Q mesons and their masses, widths and branching ratios are given. The ifωK data show that the couplings of the Q mesons to ω K are approximately equal to the couplings to ϱ 0 K. The two 1 + nonets expected in the quark model are discussed in the light of this and other recent experiments. There is strong evidence for a broad J P = 0 − resonance at about 1.46 GeV. At higher masses, structure in the J P = 2 − partial waves establishes the existence of at least one J P = 2 − L meson.

Diffractive production of 3π states at 63 and 94 GeV

Diffractive production of the 3π system has been studied at 63 and 94 GeV using a two magnet spectrometer with high, uniform acceptance. The total number of events used in the analysis is ∼600 000. The A2 meson is shown to be diffractively produced. The existence of a resonant component in both the 1+ and 2− enhancements is established and resonance parameters for the corresponding A1 and A3 mesons are given. There are several indications in the data of states which would correspond to radial excitations in the quark model.

A model-independent partial-wave analysis of the π+π− system produced at low four-momentum transfer in the reaction π−p ↑ → π+π−n at 17.2 GeV/c

Abstract The π + π − partial waves are studied up to the F-wave in the mass region from 580 to 1780 MeV/ c 2 at low four-momentum transfer. The study is based on a previous hydrogen target experiment and a more recent polarized target experiment. Using the results of both experiments for 0.01 ⩽ | t | ⩽ 0.20 GeV 2 / c 2 , a partial-wave analysis is performed in each mass bin ( Δm = 40 MeV/ c 2 ) independently. For the first time a model-independent analysis has been possible, which enables us to check the assumptions made in previous studies. In general we find a unique solution determining the exact intensity of each partial wave. The uniqueness of our solution is related to the Barrelet zeros being real in the mass region where their imaginary part were supposed to produce ambiguities. We observe a non-π exchange contribution even in the helicity m = 0 amplitudes.

Measurement of the mass and width of the charmed meson D∗+ (2010)

Abstract Using a high-resolution silicon vertex detector we have observed a very clean signal of 127 D∗+. After a careful study of the experimental resolution of our apparatus we have measured m( D ∗++ )−m( D 0 ) = 145.39±0.06±0.03 MeV . We have also obtained a 90% CL upper limit to γ(D∗+) of 131 keV.

Experimental determination of the normalization for (α, t) reactions and comparison with the theoretical normalization factor

Abstract The reaction 205Tl(α,t) 206Pb(g.s.) has been measured between 20 and 25 MeV α-energy, i.e. below and near the Coulomb barrier. It was possible to calculate the absolute experimental cross sections using a DWBA code with finite-range corrections provided that the (t+p) relative motion in the projectile is described by a Hulthen potential with β α = 1.55 ± 0.14 . This leads to an experimental normalization of D 0 exp (α, t ) = −(272 ± 14) MeV · fm 3 2 , where the errors are due to uncertainties in the proton bound state potential parameters. A calculation of the theoretical normalization using only known properties of the α-particle leads to β α = 1.57 ± 0.02 and D 0 th (α, t ) = −(269 ± 2) MeV · fm 3 2 . Using this value we deduce a proton bound state potential for the lead region of Woods-Saxon type with r0 = 1.27 fm and a = 0.71 fm. A possible extension of the general results of this analysis to all transfer reactions from projectiles with A ≦ 4 is discussed.

Inclusive φ-meson production in 93 and 63 GeV hadron interactions

Abstract The inclusive reactions h+p→φ+X, (h=π±,,K±,p±), are studied for 0⪅xF⪅0.3 and p⊥ ⩽ 1 GeV at 93 and and 63 GeV incident momentum. Differential cross sections dσ/dp⊥2 anddσ/dxF are presented and are compared with predictions of the naive parton model.

The design, construction and performance of the ALEPH silicon vertex detector

Abstract The ALEPH silicon vertex detector is the first detector operating in a colliding beam environment that uses silicon strip detectors which provide readout on both sides and hence a three-dimensional point measurement for the trajectory of charged particles. The detector system was commissioned successfully at the e+e− collider LEP at the research centre CERN, Switzerland, during the year 1991 while taking data at the Z0 resonance. The achieved spatial resolution of the complete 73 728 channel device (intrinsic plus alignment) is 12 μm in the r-f view and 12 μm in the z view. The design and construction of the entire detector system are discussed in detail and the experience gained in running the detector will be described with special emphasis on the uses of this novel tracking device for the physics of short-lived heavy particles produced in the decays of the Z0 resonance.

A supersonic jet gas target for γ-ray spectroscopy measurements☆

Abstract A five-stage differentially pumped and recirculating gas target system of the supersonic jet type has been developed for γ-ray spectroscopy measurements. The features of this jet system are described.

Production of the charmed baryon Λ+c in π−Cu and K−Cu interactions at 230 GeV

Abstract We present results from the NA32 experiment at CERN on the production characteristics of the charmed baryon Λ + c in 230 GeV π − Cu and K − Cu interactions. A high resolution vertex detector consisting of change-coupled devices and silicon microstrip detectors allowed the selection of a very clean sample of 154 Λ + c → pK − π + (and charge conjugate) decays. Results on differential and integrated cross sections are given.

Measurement of the lifetime of the charmed baryon Λc

Abstract We present results on a sample of Λc decays obtained in the NA32 experiment in 1985 using charge-coupled devices for vertex reconstruction and a trigger on Λc→pK−π+ (and charge conjugate). We observe a distinct peak at the Λc mass on zero background. The lifetime of the Λc is determined to be (1.4±0.30.5±0.3)x10−13 s based on a sample of 14 events.