Angular distributions of leptons from J/ψ’s produced in 920 GeV fixed-target proton-nucleus collisions

Abstract

A study of the angular distributions of leptons from decays of J /ψ's produced in p-C and p-W collisions at √ s = 41.6 GeV has been performed in the J /ψ Feynman-x region −0.34 < x F < 0.14 and for J /ψ transverse momenta up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3 × 10 5 J /ψ's reconstructed in both the e + e − and μ + μ − decay channels, indicate that J /ψ's are produced polarized.

J/ψPolarization inppCollisions ats=7 TeVAbelev1, Quintana2, Adamová3 et al. 2012Phys. Rev. Lett.Self Cite1253530View full textAdd to dashboardCite

“…In this way, we get for all the p t bins values compatible with zero for both CS and HE reference frames. We also note that all the previous experiments assumed ¼ 0 in their analysis, with the exception of HERA-B [23], who measured it in pA collisions at ffiffi ffi s p ¼ 41:6 GeV and found values ranging from 0 to 0.05. Various sources of systematic uncertainty on the measurement of the polarization parameters have been investigated.…”

“…A simultaneous study of the J=c polarization variables in several reference frames, as first carried out in hadroproduction studies by the HERA-B experiment [23], is particularly interesting since consistency checks on the results can be performed, using combinations of the polarization parameters which are frame-invariant. In particular we made use of the invariant F ¼ ð þ 3 Þ=ð1 À Þ [21], performing a simultaneous fit of the j cosj and jj distributions in the two reference systems and further constraining the fit by imposing F to be the same in the CS and HE frames.…”

Angular decay coefficients of J/ψ mesons at forward rapidity from p+p collisions at sAdare1, Aidala2, Ajitanand3 et al. 2017Phys. Rev. D4270View full textAdd to dashboardCite

“…fixed targets by E866/NuSea [13] and HERA-B [14], as well as a collider environment by CDF [15]. The transformation of the measurements depends on the assumption that theẑ-axis of the CS frame is the natural frame, along which the J/ψ spin-alignment is purely longitudinal or transverse.…”

“…The transformation of the measurements depends on the assumption that theẑ-axis of the CS frame is the natural frame, along which the J/ψ spin-alignment is purely longitudinal or transverse. The assumption is based on measurements of the angular distribution for inclusive J/ψ decays from fixed target p + N collisions at HERA-B covering p T < 5 GeV/c and −0.3 < x F < 0.1 [14]. It has been predicted that the natural frame at large p T is near to but not identically along the CSẑ-axis [16].…”

Heavy quarkonium: progress, puzzles, and opportunities

“…Measurements by the CDF [656,658,669], DØ [671], and PHENIX [661][662][663] collaborations were carried out in the helicity frame, while some measurements at fixed-target experiments [727,728] were carried out in the Collins-Soper frame [729]. Recently, the Hera-B collaboration has analyzed quarkonium polarizations [730] not only in the helicity and Collins-Soper frames, but also in the Gottfried-Jackson frame [731], in which the spin-quantization axis is along the direction of the incident beam. In Ref.…”