47 research outputs found
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 –> 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 eta eta ` and eta `eta ` channels produced in central pp interactions at 450 GeV/c
The reactions pp –> 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 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 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) –> 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 –> 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–>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