Measurement of the transverse polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons produced in proton-proton collisions at $\sqrt{s}=7$ TeV using the ATLAS detector

Abstract

The transverse polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons produced in proton-proton collisions at a center-of-mass energy of 7 TeV is measured. The analysis uses 760 $\mu$b${}^{-1}$ of minimum bias data collected by the ATLAS detector at the LHC in the year 2010. The measured transverse polarization averaged over Feynman $x_{\mathrm{F}}$ from $5\times 10^{-5}$ to 0.01 and transverse momentum $p_{\mathrm{T}}$ from 0.8 to 15 GeV is $-0.010\pm 0.005(\mathrm{stat})\pm 0.004(\mathrm{syst})$ for $\Lambda$ and $0.002\pm 0.006(\mathrm{stat})\pm 0.004(\mathrm{syst})$ for $\bar{\Lambda }$. It is also measured as a function of $x_{\mathrm{F}}$ and $p_{\mathrm{T}}$, but no significant dependence on these variables is observed. Prior to this measurement, the polarization was measured at fixed-target experiments with center-of-mass energies up to about 40 GeV. The ATLAS results are compatible with the extrapolation of a fit from previous measurements to the $x_{\mathrm{F}}$ range covered by this mesurement.

10 pages plus author list + cover pages (23 pages total), 8 figures, 3 tables, published version, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2011-45/

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