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The European Physical Journal C
ISSN: 1434-6044 (printed version)
ISSN: 1434-6052 (electronic version)
Abstract Volume 2 Issue 3 (1998) pp 539-544
DOI 10.1007/s100529800709
theoretical physics:
Off-diagonal helicity density matrix elements for vector mesons produced at LEP
M. Anselmino (1), M. Bertini (1)(2), F. Murgia (3), P. Quintairos (1)(4)
(1) Dipartimento di Fisica Teorica, Università di Torino and INFN, Sezione di Torino, Via P. Giuria 1, I-10125 Torino, Italy
(2) Institut de Physique Nucléaire de Lyon 43 Bvd. du 11 Novembre 1918, F-69622 Villeurbanne Cedex
(3) INFN, Sezione di Cagliari, Via A. Negri 18, I-09127 Cagliari, Italy
(4) Centro Brasileiro de Pesquisas Físicas R. Dr. Xavier Sigaud 150, 22290-180, Rio de Janeiro, Brazil
Received: 15 May 1997 / Published online: 20 February 1998
Abstract. Final state $q\bar q$ interactions may give origin to non-zero values of the off-diagonal element $\rho_{1,-1}$ of the helicity density matrix of vector mesons produced in $e^+ e^-$ annihilations, as confirmed by recent OPAL data on $\phi$ and $D^*$'s. Predictions are given for $\rho_{1,-1}$ of several mesons produced at large $z$ and small $p_T$, i.e. collinear with the parent jet; the values obtained for $\phi$ and $D^*$ are in agreement with data. The fragmentation functions of quarks and gluons into photons are studied beyond the Leading Logarithm approximation. We address the nature of the initial conditions of the evolution equation solutions and study problems related to factorization scheme invariance. The possibility of measuring these distributions in LEP experiments is discussed, and a comparison with existing data is made.
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Online publication: April 25, 1998
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