The new ATLAS luminosity monitor has many innovative aspects implemented. Its photomultipliers tubes are used as detector elements by using the Cherenkov light produced by charged particles above threshold crossing the quartz windows. The analog shaping of the readout chain has been improved, in order to cope with the 25 ns bunch spacing of the LHC machine. The main readout card is a quite general processing unit based on 12 bit -320 MS/s Flash ADC and on FPGAs, delivering the processed data to 1.3 Gb/s optical links. The article will describe all these aspects and will outline future perspectives of the card for next generation high energy physics experiments.

The main luminosity monitor of the ATLAS experiment consists of an array of Cherenkov counters. The intrinsically fast response of the detector and its readout electronics makes it ideal for measuring the number of interactions per LHC bunch crossing, and for providing an interaction trigger to the ATLAS experiment. The detector already took some data during the first beam interactions produced by the LHC. An original method to derive the detector response with an analytical approach is presented here.

An isochronous system is introduced by modifying the Nth ODE of the stationary Burgers hierarchy, and then, by investigating its behaviour near its equilibria, neat Diophantine relations are identified, involving (well-known) polynomials of arbitrary degree having integer zeros, or equivalently matrices the determinants of which yield such polynomials. The basic idea to arrive at such relations is not new, but the specific application reported in this paper is new, and it is likely to open the way to several analogous new findings.

A recent technique to identify solvable many-body problems in two-dimensional space yields, via a new twist, new many-body problems of “goldfish” type. Some of these models are isochronous, namely their generic solutions are completely periodic with a fixed period (independent of the initial data). The investigation of the behavior of some of these isochronous systems in the vicinity of their equilibrium configurations yields some amusing diophantine relations.

The relation between the branching ratios and direct CP asymmetries of B → Kπ decays and the angle γ of the CKM unitarity triangle is studied numerically in the general framework of the SU(3) approach, with minimal assumptions about the parameters not fixed by flavor-symmetry arguments. Experimental and theoretical uncertainties are subjected to a statistical treatment according to the Bayesian method. In this context, the experimental limits recently obtained by CLEO, BaBar and Belle for the direct CP asymmetries are translated into the bound |γ - 90°| > 21° at the 95% C.L. A detailed analysis is carried out to evaluate the conditions under which measurements of the CP averaged branching ratios may place a significant constraint on γ. Predictions for the ratios of charged (R c ) and neutral (R n ) B → Kπ decays are also presented.

The matrix equation Ü=2U3+AU+UA is integrable (here U=U(t) is a n×n-matrix, with n an arbitrary positive integer, and A is an arbitrary constant n×n-matrix). The matrix evolution equation Ü=U2+a is also integrable (a arbitrary scalar constant). The matrix evolution equation Ü=f(U), where fU is an arbitrary function of U (and of no other matrix, so that the commutator U,fU vanishes) possesses at least n2−n (scalar) constants of motion. Lax pairs are exhibited for all these second-order n×n-matrix evolution ODEs.

The reaction p̄p→K+K−π0 was analysed for antiproton annihilations at rest at three hydrogen target densities. A strong dependence of the p̄p→φπ0 yield on the quantum numbers of the initial state is observed. The branching ratio of the φπ0 channel from the 3S1 initial state is more than 15 times larger than the one from the 1P1 state. A large apparent violation of the OZI rule for tensor meson production from p̄p-annihilations from the P-waves (1+++2++) is observed: Rexp(f′2π0/f2π0)=(149±20)·10−3, significantly exceeding the OZI-rule prediction R=16·10−3.

The results of the spin-parity analysis of pp → 2π+2π− annihilations at very low momentum p (≈ 50 MeV/c) are reported. To describe the data the production of the ϱ, f2, a2 and a1 mesons and the presence of the ππ interaction in S-wave (the σ term) in the final state are necessary. The best fit solution requires also the presence of a ϱ′ state of mass and width M = 1.282 ± 0.037, Γ = 0.236 ± 0.036 GeV/c2 and of a heavy pion π(1300) of mass and width M = 1.275 ± 0.015, Γ = 0.218 ± 0.100 GeV/c2. The measured fraction of the annihilation cross section into 2π+2π− is (7.61 ± 0.35) · 10−2.

The study of the K±Kmiss0π∓π+π− channel (7016 events), from pp annihilations in a gaseous hydrogen target at NTP, with the OBELIX spectrometer at LEAR (CERN), is presented. A spin-parity analysis provides evidence for two axial vectors, one in the low KKπ mass region, the well established f1(1285), decaying to a0(980)π, the second, the 1++ component of the old puzzling El, the f1(1420), decaying mainly to K∗K, seen for the first time in pp annihilation at rest. The analysis confirms the dominant production of the pseudoscalar η(1405), decaying mainly to (Kπ)SK, and the existence of a second pseudoscalar in the same mass region, the η(1460), decaying mainly to K∗K.

Antinucleon-nucleus annihilations into two-body final states containing only one or no meson are unusual annihilations (Pontecorvo reactions), practically unexplored experimentally, with the exception of the channel p d → π− p, for which only two low-statistics measurements exist. Their physical interest lies in the possibility of exploring small-distance nuclear dynamics, in which an important role can be played by non-nucleonic degrees of freedom. A new measurement of the p d → π− p reaction rate at rest, performed with the OBELIX spectrometer at LEAR, with the best statistics up to now and a careful evaluation of systematic effects is reported, together with a critical analysis of the existing theoretical models. The measured branching ratio, which confirms the previous results, can represent a reference point for the studies in the field.

The use of low-density hydrogen targets is demonstrated experimentally to be a new way of selecting protonium (pp atom) annihilations with initial angular momentum L = 1. The mean value and the width of the time distributions which occur between protonium formation and annihilation have been measured at room temperature at 8.2, 4.1, 2.1 mbar. They are (110±10; 45±5), (145±15; 82±9) and (210±25;125±9) ns, respectively.

The technique of producing trapezoidal signals by means of a modified version of the DL-RC filter, which proved to work successfully when applied to gamma spectroscopy with large volume germanium detectors [1], has been extended to particle spectroscopy. The trapezoidal pulses, synthesized for particle energy measurements, have a flat top of 70 ns and a total duration of 270 ns. A fast stretcher was designed in order to properly process these short signals. A description of the trapezoidal DL-RC shaper, as well as of the fast linear gate and stretcher is given.

The relationship between the algebra of finite-dimensional matrices acting as raising and lowering operators on a given set of vectors and the operators of multiplication by a variable ξ and of differentiation with respect to ξ are tersely reviewed. A number of matrix formulae implied by this relationship is reported and the possibility to implement them in explicit form is highlighted by referring to a remarkably neat construction of matrices of ordern, defined explicitly in terms ofn arbitrary numbers and satisfying the algebra of raising and lowering operators.