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

<p>The transverse polarization of <inline-formula><mml:math display="inline"><mml:mi mathvariant="normal">Λ</mml:mi></mml:math></inline-formula> and <inline-formula><mml:math display="inline"><mml:mover accent="true"><mml:mi mathvariant="normal">Λ</mml:mi><mml:mo accent="true" stretchy="false">¯</mml:mo></mml:mover></mml:math></inline-formula> hyperons produced in proton-proton collisions at a center-of-mass energy of 7 TeV is measured. The analysis uses <inline-formula><mml:math display="inline"><mml:mrow><mml:mn>760</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>μ</mml:mi><mml:msup><mml:mrow><mml:mi mathvariant="normal">b</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula> of minimum bias data collected by the ATLAS detector at the LHC in the year 2010. The measured transverse polarization averaged over Feynman <inline-formula><mml:math display="inline"><mml:msub><mml:mi>x</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:msub></mml:math></inline-formula> from <inline-formula><mml:math display="inline"><mml:mn>5</mml:mn><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mn>0</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:msup></mml:math></inline-formula> to 0.01 and transverse momentum <inline-formula><mml:math display="inline"><mml:msub><mml:mi>p</mml:mi><mml:mi mathvariant="normal">T</mml:mi></mml:msub></mml:math></inline-formula> from 0.8 to 15 GeV is <inline-formula><mml:math display="inline"><mml:mrow><mml:mo>-</mml:mo><mml:mn>0.010</mml:mn><mml:mo>±</mml:mo><mml:mn>0.005</mml:mn><mml:mo stretchy="false">(</mml:mo><mml:mtext>stat</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mo>±</mml:mo><mml:mn>0.004</mml:mn><mml:mo stretchy="false">(</mml:mo><mml:mtext>syst</mml:mtext><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math></inline-formula> for <inline-formula><mml:math display="inline"><mml:mi mathvariant="normal">Λ</mml:mi></mml:math></inline-formula> and <inline-formula><mml:math display="inline"><mml:mrow><mml:mn>0.002</mml:mn><mml:mo>±</mml:mo><mml:mn>0.006</mml:mn><mml:mo stretchy="false">(</mml:mo><mml:mtext>stat</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mo>±</mml:mo><mml:mn>0.004</mml:mn><mml:mo stretchy="false">(</mml:mo><mml:mtext>syst</mml:mtext><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math></inline-formula> for <inline-formula><mml:math display="inline"><mml:mover accent="true"><mml:mi mathvariant="normal">Λ</mml:mi><mml:mo accent="true" stretchy="false">¯</mml:mo></mml:mover></mml:math></inline-formula>. It is also measured as a function of <inline-formula><mml:math display="inline"><mml:msub><mml:mi>x</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:msub></mml:math></inline-formula> and <inline-formula><mml:math display="inline"><mml:msub><mml:mi>p</mml:mi><mml:mi mathvariant="normal">T</mml:mi></mml:msub></mml:math></inline-formula>, 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 <inline-formula><mml:math display="inline"><mml:msub><mml:mi>x</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:msub></mml:math></inline-formula> range covered by this measurement.</p>