Production of the charmonium states {chi}{sub c1} and {chi}{sub c2} in proton nucleus interactions at {radical}(s)=41.6 GeV
- Max-Planck-Institut fuer Physik, Werner-Heisenberg-Institut, D-80805 Muenchen (Germany)
- Institut fuer Physik, Universitaet Dortmund, D-44221 Dortmund (Germany)
- Max-Planck-Institut fuer Kernphysik, D-69117 Heidelberg (Germany)
A measurement of the ratio R{sub {chi}{sub c}}=({chi}{sub c}{yields}J/{psi}+{gamma})/J/{psi} in pC, pTi, and pW interactions at 920 GeV/c ({radical}(s)=41.6 GeV) in the Feynman-x range -0.35<x{sub F}{sup J/{psi}}<0.15 is presented. Both {mu}{sup +}{mu}{sup -} and e{sup +}e{sup -} J/{psi} decay channels are observed with an overall statistics of about 15 000 {chi}{sub c} events, which is by far the largest available sample in pA collisions. The result is R{sub {chi}{sub c}}=0.188{+-}0.013{sub st}(+0.024/-0.022){sub sys} averaged over the different materials, when no J/{psi} and {chi}{sub c} polarizations are considered. The {chi}{sub c1} to {chi}{sub c2} production ratio R{sub 12}=R{sub {chi}{sub c}}{sub 1}/R{sub {chi}{sub c}}{sub 2} is measured to be 1.02{+-}0.40, leading to a cross section ratio ({sigma}({chi}{sub c1})/{sigma}({chi}{sub c2}))=0.57{+-}0.23. The dependence of R{sub {chi}{sub c}} on the Feynman-x of the J/{psi}, x{sub F}{sup J/{psi}}, and its transverse momentum, p{sub T}{sup J/{psi}}, is studied, as well as its dependence on the atomic number, A, of the target. For the first time, an extensive study of possible biases on R{sub {chi}{sub c}} and R{sub 12} due to the dependence of acceptance on the polarization states of J/{psi} and {chi}{sub c} is performed. By varying the polarization parameter, {lambda}{sub obs}, of all produced J/{psi}'s by two sigma around the value measured by HERA-B, and considering the maximum variation due to the possible {chi}{sub c1} and {chi}{sub c2} polarizations, it is shown that R{sub {chi}{sub c}} could change by a factor between 1.02 and 1.21 and R{sub 12} by a factor between 0.89 and 1.16.
- OSTI ID:
- 21254666
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 79, Issue 1; Other Information: DOI: 10.1103/PhysRevD.79.012001; (c) 2009 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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