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Register a new userSpin alignment and violation of the OZI rule in exclusive $omega$ and $phi$ production in pp collisions
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Exclusive production of the isoscalar vector mesons $omega$ and $phi$ is measured with a 190 GeV$/c$ proton beam impinging on a liquid hydrogen target. Cross section ratios are determined in three intervals of the Feynman variable $x_{F}$ of the fast proton. A significant violation of the OZI rule is found, confirming earlier findings. Its kinematic dependence on $x_{F}$ and on the invariant mass $M_{pmathrm{V}}$ of the system formed by fast proton $p_mathrm{fast}$ and vector meson $V$ is discussed in terms of diffractive production of $p_mathrm{fast}V$ resonances in competition with central production. The measurement of the spin density matrix element $rho_{00}$ of the vector mesons in different selected reference frames provides another handle to distinguish the contributions of these two major reaction types. Again, dependences of the alignment on $x_{F}$ and on $M_{pmathrm{V}}$ are found. Most of the observations can be traced back to the existence of several excited baryon states contributing to $omega$ production which are absent in the case of the $phi$ meson. Removing the low-mass $M_{pmathrm{V}}$ resonant region, the OZI rule is found to be violated by a factor of eight, independently of $x_mathrm{F}$.
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We investigate the reactions p n -> d omega and p n -> d phi close to the corresponding thresholds. The S-wave amplitudes are calculated within the framework of the two-step model which is described by a triangle graph with pi, rho and omega mesons in the intermediate state. The cross sections of the reactions p n -> d omega and p n -> d phi are predicted to be significantly larger than the cross sections of the corresponding reactions p p -> p p omega and p p -> p p phi at the same values of the c.m. excess energy Q. The ratio of the yields of phi to omega is found to be (30 +/- 7) x 10^-3.
We report the first polarization transfer measurements for exclusive hyperon production reactions. The normal spin transfer coefficient DNN for pp -> p K+ Lambda is large and negative for forward Lambda production at a beam momentum of 3.67 GeV/c, a result qualitatively consistent with expectations for a mechanism dominated by kaon-exchange and rescattering. The sign of DNN is opposite to that observed in the fragmentation regime for inclusive Lambda production at much higher energies.
We report the first measurement of the inclusive jet and the dijet longitudinal double-spin asymmetries, $A_{LL}$, at midrapidity in polarized $pp$ collisions at a center-of-mass energy $sqrt{s} = 510$ GeV. The inclusive jet $A_{LL}$ measurement is sensitive to the gluon helicity distribution down to a gluon momentum fraction of $xapprox 0.015$, while the dijet measurements, separated into four jet-pair topologies, provide constraints on the $x$ dependence of the gluon polarization. Both results are consistent with previous measurements made at $sqrt{s}= 200$ GeV in the overlapping kinematic region, $x > 0.05$, and show good agreement with predictions from recent next-to-leading order global analyses.
The ALICE experiment at the CERN Large Hadron Collider (LHC) will allow the study of resonance production in nucleus-nucleus and proton-proton collisions. This paper presents results based on physics performance studies to discuss prospects in ALICE for $phi$(1020) meson production in pp interactions during the LHC startup.
Using a relativistic effective Lagrangian at the hadronic level, near-threshold $omega$ and $phi$ meson productions in proton proton ($pp$) collisions, $p p to p p omega/phi$, are studied within the distorted wave Born approximation. Both initial and final state $pp$ interactions are included. In addition to total cross section data, both $omega$ and $phi$ angular distribution data are used to constrain further the model parameters. For the $p p to p p omega$ reaction we consider two different possibilities: with and without the inclusion of nucleon resonances. The nucleon resonances are included in a way to be consistent with the $pi^- p to omega n$ reaction. It is shown that the inclusion of nucleon resonances can describe the data better overall than without their inclusion. However, the SATURNE data in the range of excess energies $Q < 31$ MeV are still underestimated by about a factor of two. As for the $p p to p p phi$ reaction it is found that the presently limited available data from DISTO can be reproduced by four sets of values for the vector and tensor $phi NN$ coupling constants. Further measurements of the energy dependence of the total cross section near threshold energies should help to constrain better the $phi NN$ coupling constant.
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