12 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 Spin Structure of the Nucleon
We present an overview of recent experimental and theoretical advances in our
understanding of the spin structure of protons and neutrons.Comment: 84 pages, 29 figure
Bessel-Weighted Asymmetries in Semi Inclusive Deep Inelastic Scattering
The concept of weighted asymmetries is revisited for semi-inclusive deep
inelastic scattering. We consider the cross section in Fourier space, conjugate
to the outgoing hadron's transverse momentum, where convolutions of transverse
momentum dependent parton distribution functions and fragmentation functions
become simple products. Individual asymmetric terms in the cross section can be
projected out by means of a generalized set of weights involving Bessel
functions. Advantages of employing these Bessel weights are that they suppress
(divergent) contributions from high transverse momentum and that soft factors
cancel in (Bessel-) weighted asymmetries. Also, the resulting compact
expressions immediately connect to previous work on evolution equations for
transverse momentum dependent parton distribution and fragmentation functions
and to quantities accessible in lattice QCD. Bessel weighted asymmetries are
thus model independent observables that augment the description and our
understanding of correlations of spin and momentum in nucleon structure.Comment: Matches published version, JHEP style, 36 pages and 2 figures, minor
correction
Measurement of the spin structure of the deuteron in the DIS region
Ageev ES, Alexakhin VY, Alexandrov Y, et al. Measurement of the spin structure of the deuteron in the DIS region. Phys.Lett. B. 2005;612(3-4):154-164.We present a new measurement of the longitudinal spin asymmetry Ad and the spin-dependent structure function g(1)(d) of the deuteron in the range 1 < Q(2) < 100 GeV2 and 0.004 < x < 0.7. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised (LiD)-Li-6 target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004 < x < 0.03. (c) 2005 Elsevier B.V. All rights reserved
Epidemiological applications of long-term stress in daily life.
The gluon polarisation in the nucleon has been determined by detecting charm production via D0 meson decay to charged K and \u3c0 in polarised muon scattering off a longitudinally polarised deuteron target. The data were taken by the COMPASS Collaboration at CERN between 2002 and 2006 and correspond to an integrated luminosity of 2.8 fb 121. The dominant underlying process of charm production is the photon\u2013gluon fusion to a_(c barc) pair. A leading order QCD approach gives an average gluon polarisation of _x= 120.49\ub10.27(stat)\ub10.11(syst) at a scale \u3bc^2 4813 (GeV/c)^2 and at an average gluon momentum fraction 480.11. The longitudinal cross-section asymmetry for D0 production is presented in bins of the transverse momentum and the energy of the D0 meson