Observation of a J^PC = 1-+ exotic resonance in diffractive dissociation of 190 GeV/c pi- into pi- pi- pi+

The COMPASS experiment at the CERN SPS has studied the diffractive dissociation of negative pions into the pi- pi- pi+ final state using a 190 GeV/c pion beam hitting a lead target. A partial wave analysis has been performed on a sample of 420000 events taken at values of the squared 4-momentum transfer t' between 0.1 and 1 GeV^2/c^2. The well-known resonances a1(1260), a2(1320), and pi2(1670) are clearly observed. In addition, the data show a significant natural parity exchange production of a resonance with spin-exotic quantum numbers J^PC = 1-+ at 1.66 GeV/c^2 decaying to rho pi. The resonant nature of this wave is evident from the mass-dependent phase differences to the J^PC = 2-+ and 1++ waves. From a mass-dependent fit a resonance mass of 1660 +- 10+0-64 MeV/c^2 and a width of 269+-21+42-64 MeV/c^2 is deduced.Comment: 7 page, 3 figures; version 2 gives some more details, data unchanged; version 3 updated authors, text shortened, data unchange

The Polarised Valence Quark Distribution from semi-inclusive DIS

The semi-inclusive difference asymmetry A^{h^{+}-h^{-}} for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised ^6LiD target and cover the range 0.006 < x < 0.7 and 1 < Q^2 < 100 (GeV/c)^2. In leading order QCD (LO) the asymmetry A_d^{h^{+}-h^{-}} measures the valence quark polarisation and provides an evaluation of the first moment of Delta u_v + Delta d_v which is found to be equal to 0.40 +- 0.07 (stat.) +- 0.05 (syst.) over the measured range of x at Q^2 = 10 (GeV/c)^2. When combined with the first moment of g_1^d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Delta u-bar = - Delta d-bar at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Delta u-bar = Delta d-bar = Delta s-bar = Delta s.Comment: 7 pages, 3 figures, COMPASS, revised: details added, author list update

A spin analysis of the 4 pi channels produced in central pp interactions at 450 GeV/c

The reactions pp –&gt; p(f)(X-0)p(s), where X-0 is observed decaying to pi(0)pi(0)pi(0)pi(0), pi(+)pi(-)pi(+)pi(-) and pi(+)pi(-)pi(0)pi(0), have been studied at 450 GeV/c. There is evidence for an a(2)(1320)pi decay mode of the eta(2)(1645) and eta(2)(1870) in the pi(+)pi(-)pi(0)pi(0) and pi(+)pi(-)pi(+)pi(-) find states. The f(2)(1950) is consistent with being a single resonance with a dominant f(2)(1270)pi pi decay mode. The f(0)(1370) is found to decay dominantly to rho rho while the f(0)(1500) is found to decay to rho rho and sigma sigma. (C) 2000 Published by Elsevier Science B.V. All rights reserved

A study of the f(0)(1370), f(0)(1500), f(0)(2000) and f(2)(1950) observed in the centrally produced 4 pi final states

{The production and decay properties of the f(0)(1370), f(0)(1500), f(0)(2000) and f(2)(1950) have been studied in central pp interactions at 450 GeV/c. The dP(T), phi and \textbackslash{}t\textbackslash{} distributions of these resonances are presented. For the J= 0 states, the f(0)(1370) and f(0)(2000) have similar dP(T) and phi dependences. These are different to the dP(T) and phi dependences of the f(0)(980), f(0)(1500) and f(0)(1710). For the J = 2 states the f(2)(1950) has different dependences to the f(2)(1270) and f(2)(1520). This shows that the dP(T) and phi dependences are not just J phenomena. (C) 2000 Published by Elsevier Science B,V. All rights reserved.

A study of the eta eta ` and eta `eta ` channels produced in central pp interactions at 450 GeV/c

The reactions pp –&gt; p(f)(X-0)p(s), where X-0 is observed decaying to eta eta’ and eta’eta’, have been studied at 450 GeV/c. This is the first time that these channels have been observed in central production and only the second time that the eta’eta’ channel has been observed in any production mechanism. In the eta eta’ channel there is evidence for the f(0)(1500) and a peak at 1.95 GeV. The eta’eta’ channel shows a peak at threshold which is compatible with having J(PC) = 2(++) and spin projection J(Z) = 0. (C) 2000 Published by Elsevier Science B.V. All rights reserved

A search for charmonium states produced in central pp interactions at 450 GeV/c

A search for centrally produced charmonium states has been presented. There is no significant evidence for any charmonium production. An upper limit of 2 nb is found for the cross section of chi(c) production using the decay chi(c)(1P) –&gt; J/psi gamma. (C) 2000 Elsevier Science B.V. All rights reserved

A study of the eta pi(+) pi(-) channel produced in central pp interactions at 450 GeV/c

The reaction pp –&gt; p(f)(eta pi(+)pi(-))p(s) has been studied at 450 GeV/c. There is clear evidence for an a(2)(1320)pi decay mode of the eta(2)(1645) and eta(2)(1870). In addition, there is evidence for an a(0)(980)pi decay mode of both resonances and an f(2)(1270)eta decay mode of the eta(2)(1870). No evidence is found for a J(PC) = 2(++)a(2)(1320)pi wave. (C) 2000 Published by Elsevier Science B.V. All rights reserved

Experimental evidence for a vector-like behaviour of Pomeron exchange

Evidence is presented that the Pomeron acts as a non-conserved vector current. A study has been made of the azimuthal angle phi, which is defined as the angle between the p(T) vectors of the two outgoing protons, in the reaction pp–&gt;pp(X-0) for those resonances (X-0) which are compatible with being produced by double Pomeron exchange. These distributions have been compared with a moder which describes the Pomeron as a non-conserved vector current and a qualitative agreement is found. In addition, when one of the particles exchanged is known to have spin 0, namely pi-Pomeron exchange, the phi distribution is flat. (C) 1999 Elsevier Science B.V. All rights reserved