NEW GAMS RESULTS ON MESON SPECTROSCOPY

Results on meson spectroscopy obtained in 1993 by the GAMS Collaboration are presented. Model-independent measurements of the omega --> etagamma decay branching ratio, as well as the observation of the X(1740) state in the K(s)0K(s)0 decay mode, are considered. The results on the partial-wave analysis of the omegapi0 and pi0pi0 systems produced at small momentum transfer in pi-p charge-exchange reactions are discussed. The experiments on resonant etaeta-system production on a central region of the pp interaction are also discussed

GAMS RESULTS ON THE OMEGA-PI(0) SYSTEM

The first results on the omega-pi-0 system produced in the charge-exchange reaction of pi--p scattering at 38 GeV/c and 100 GeV/c are presented. The omega-pi-0 mass spectrum shows, alongside with the well-known b1(0) (1235) and rho-3(0) (1690) mesons, a new neutral state with mass 2200 +/- 20 MeV and width 260 +/- 50 MeV. This meson, X(2200), is produced like rho-3 through one-pion exchange. X(2200) is a candidate for the 1-- multiplet, and its possible interpretation is a 2(3)D1 excitation of the rho-0. Its production cross section at 3 S GeV/c is equal to sigma(pi--p --> Xn) . BR (X --> omega-pi-0) = 120 +/- 25 nb. Cross sections for b1 and rho-3 have also been measured. The energy dependences have been determined

Study of the pi(0)pi(0) system in pp central collisions at 450 GeV/c

The effective mass spectrum of pi(0) pairs produced in pp central collisions (pp --> pf pi(0) pi(0)p(s)) at 450 GeV/c, root s = 29 GeV, below 1 GeV differs from that observed in peripheral charge exchange reactions, In particular, there is a large number of events between pi pi-threshold and 1 GeV, that interfere with f(0)(980) destructively. The possible existence of a broad S-wave state is suggested. (C) 1997 Published by Elsevier Science B.V

A kinematical selection of glueball candidates in central production

A study of central meson production as a function of the difference in transverse momentum (dP(T)) of the exchanged particles shows that undisputed <q(q)over bar> mesons are suppressed at small dP(T) whereas the glueball candidates are enhanced. (C)1997 Elsevier Science B.V

Multiplicity dependence of pion, kaon, proton and lambda production in p–Pb collisions at √sNN = 5.02 TeV

Inthis Letter, comprehensive results on π±,K±,K0S, p(pbar) and Λ(Λbar) production at mid-rapidity (0< yCMS < 0.5) in p–Pb collisions at √sNN = 5.02 TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb–Pb collisions at the LHC. The measured pT distributions are compared to d–Au, Au–Au and Pb–Pb results at lower energy and with predictions based on QCD-inspired and hydrodynamic models

Production of omega mesons in pp collisions at s=7 TeV

The invariant differential cross section of inclusive omega (782) meson production at midrapidity (|y| pi+pi-pi 0 decay channel. The measured omega production cross section is compared to various calculations: PYTHIA 8.2 Monash 2013 describes the data, while PYTHIA 8.2 Tune 4C overestimates the data by about 50%. A recent NLO calculation, which includes a model describing the fragmentation of the whole vector-meson nonet, describes the data within uncertainties below 6 GeV/c, while it overestimates the data by up to 50% for higher pT. The omega/pi 0 ratio is in agreement with previous measurements at lower collision energies and the PYTHIA calculations. In addition, the measurement is compatible with transverse mass scaling within the measured pT range and the ratio is constant with C omega/pi 0=0.67 +/- 0.03(stat) +/- 0.04(sys) above a transverse momentum of 2.5 GeV/c

First proton-proton collisions at the LHC as observed with the ALICE detector: Measurement of the charged-particle pseudorapidity density at √s = 900 GeV

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|<0.5, we obtain dNch/dη=3. 10±0. 13(stat.)±0. 22(syst.) for all inelastic interactions, and dNch/dη=3.51±0. 15(stat.)±0. 25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN SppS̄ collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase