Working group on ππ\pi\pi and π\piN interactions - Summary

This is the summary of the working group on $\pi\pi$ and $\pi$N interactions of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997. Each talk is represented by an extended one page abstract. Some additional remarks by the convenors are addedComment: 20 pp, LaTeX2e, uses epsf, 1 fi

pi+- p differential cross sections at low energies

Differential cross sections for pi- p and pi+ p elastic scattering were measured at five energies between 19.9 and 43.3 MeV. The use of the CHAOS magnetic spectrometer at TRIUMF, supplemented by a range telescope for muon background suppression, provided simultaneous coverage of a large part of the full angular range, thus allowing very precise relative cross section measurements. The absolute normalisation was determined with a typical accuracy of 5 %. This was verified in a simultaneous measurement of muon proton elastic scattering. The measured cross sections show some deviations from phase shift analysis predictions, in particular at large angles and low energies. From the new data we determine the real part of the isospin forward scattering amplitude.Comment: 13 pages, 5 figures. To appear in PL

The ALICE experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008

MCP-based detector: some results and perspectives

The timing resolution of photomultiplier tubes (PMT) based on shevron-type microchannel plates (MCP) has been studied inmagnetic fields. The same timingresolution with and without a longitudinal magnetic field up to 2.0 kGwas obtained as = 85 ± 2 ps. It is shown that an increase of timing resolution in this magnetic field does not exceed25 ps (upper limit). The timing resolution of = 31 ± 2 pswas obtained for narrow (10resolution) amplitude spectrumfrom Corone discharge. The counting rate of MCP-based detector was studied in function of the direction of the magnetic field.The spatial and timing resolution for the MCP-based PMT were obtained using laser pulses as well. With laser pulses of 0.3 ns a timing resolution of ≅ 450 ps was obtained. Taking into account the amplitude correction narrows to 140 ps. Using 100 fs-laser with the standard constant fractiondiscriminator gives a timing resolution from 20 to 40 ps depending on the read-out MCP region.The perspectives of using an MCP-based detector for high-energy physics experiments are discussed.Abstract:Summary:We present the results of the systematic in-lab tests of the MCP-based detectors characteristics.Abstract:In the first two tests two conventional PMT 165-2 tubes (produced by St.Petersburg) were used. These photomultipliers contain a photocathode, two microchannel plates in a shevron-type setup and anodes. A special stand was designed and performed for these tests. It consists of a magnet up to 2.0kG, CAMAC electronics and a PC with a set of programmes. The two detectors were placed face-to-face. The Conore discharge placed between the two PMT-MCP detectors was used as a light spark source. The light froma spark comes to both detectors. If a sheet of black paper had been placed between the source and detectors, signals did not exist. Signals from both detectors went to the amplifier-discriminator. Then both of the signals passed to the TDC through the special time expansion block. One signal had been submitted to "start" of TDC, the second one through a delay line had been given to "stop" of TDC. A TDC channel width was 78 ± 2 ps. A special block for an expansion of the timing signal was used. It gives a signal between "stop" and "start" to 100 times longer than in real time. After differentiation, the signals were given to TDC. A precise calibration of the timing track was doen. A 5 ns signal from the generator was divided by two. One had been given to "start" TDC, the second had gone through a 100 ps step delay line and given to "stop". This was a special delay line with an accuracy of 1 ps. The analysis showed that the TDC channel width with using of expansion block was = 0.7 ps and the jitter of all track was = 10.7 ps.As a first step, we wanted to obtain a good timing resolution for the checking of electronics. In this case a narrow (10resolution) amplitude spectrum was used. The timing resolution for one MCP was obtained as = 31 ± 2 ps. For the next step, n amplitude spectrum was used that was closer to a real experimental situation (50 mV - 700 mV). The same timing resolution = 85 ± 2 ps was obtained for both zero magnetic field and up to 2.0 kG magnetic field. We used a longitudinal magnetic field, and the angle between the direction of the magnetic field and the MCP channels was approximately 12 degrees. An estimation of the possible influence of the magnetic fiels was made. It was shown that an increasing of the timing resolution in the magnetic fiels up to 2.0 kG does not exceed 25 ps (upper limit).The next tests were done using a laser. In this case, a one-photon regime was used. A new variant of the read-out was applied. A timing signal was taken from the "input" of the second MCP surface and an amplitude signal was taken from the anode. This makes it possible to combine an adequate amplitude analysis and a high timing resolution in one detector. The timing resolution for the laser impulse of 0.3 ns was obtained as = 450 ps. Taking into account the amplitude correction, the resolution improves to = 140 ps. Using a 100-fs laser with a standard constant fraction discriminator gave a timing resolution better than 40 ps. It is shown that the timing resolution has a dependence on the read-out region. Using a small (3 mm diameter) region gives = 20 ps.The perspectives of using MCP-based detector for high-energy physics experiments are discussed

The He-4(pi+,pi-) reaction at low energies

Using the CHAOS spectrometer at TRIUMF the total cross sections and outgoing pion momentum distributions for the 4He(\u3c0+,\u3c0 12) reaction were measured for \u3c0+ kinetic energies from 70 to 130 MeV. At energies around 100 MeV the total cross sections show an excess by a factor 3 over conventional model calculations which could be ascribed to a contribution from a hypothetical d\u2032 dibaryon

Energy dependence of the He-4(pi+,pi-) total cross-section

The total cross section of the 4He(\u3c0+,\u3c0-) reaction was measured for \u3c0+ kinetic energies ranging from 70 to 130 MeV using the CHAOS spectrometer at TRIUMF and a liquid 4He target. Around T\u3c0=90MeV, total cross sections exceed conventional model predictions by a factor of 3, whereas at T\u3c0=70MeV and for T\u3c0>130MeV the data are consistent with these calculations. An attempt is made to understand this behavior by assuming the production of the hypothetical d\u2032 dibaryon

Search for a bound trineutron with the 3^3He(π−\pi^-,π+\pi^+)nnn reaction

A search for the production of a bound trineutron state has been performed using the reaction $^3$He($\pi^-$,$\pi^+$)nnn at incident pion energies of 65, 75, and 120 MeV. No evidence for the existence of the $^3$n was found, and an upper limit for the production cross section of approximately 30 nb/sr (2$\sigma$ confidence level) was obtained