Observation of Polarization in Bottomonium Production at sqrt(s) = 38.8 GeV
/ Authors
C. Brown, T. Awes, M. Beddo, M. Brooks, J. D. Bush, T. Carey, T. Chang, W. Cooper, C. Gagliardi, G. Garvey
and 33 more authors
D. Geesaman, E. Hawker, X. He, L. Isenhower, D. Kaplan, S. Kaufman, P. N. Kirk, D. Koetke, G. Kyle, D. Lee, W. Lee, M. Leitch, N. Makins, P. McGaughey, J. Moss, B. Mueller, P. Nord, V. Papavassiliou, B. Park, J. Peng, G. Petitt, P. Reimer, M. Sadler, W. Sondheim, P. Stankus, T. Thompson, R. Towell, R. Tribble, M. Vasiliev, J. Webb, J. L. Willis, D. Wise, G. Young
/ Abstract
We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at square root of s = 38.8 GeV. The angular distribution of the decay dimuons of the Upsilon(1S) state shows no polarization at small values of the fractional longitudinal momentum x(F) and transverse momentum p(T) but significant positive transverse production polarization for either p(T)>1.8 GeV/c or for x(F)>0.35. The Upsilon(2S+3S) (unresolved) states show a large transverse production polarization at all values of x(F) and p(T) measured. These observations challenge NRQCD calculations of the polarization expected in the hadronic production of bottomonium states.
Journal: Physical Review Letters