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

• Main Author: ATLAS collaboration (2875 authors)
• Publication Date: 2015
• Other Authors: Aguilar-Saavedra, Juan Antonio, Amor Dos Santos, Susana Patricia, Anjos, Nuno, Araque, Juan Pedro, Cantrill, Robert, Carvalho, João, Castro, Nuno Filipe, Conde Muiño, Patricia, Da Cunha Sargedas De Sousa, Mario Jose, Fiolhais, Miguel, Galhardo, Bruno, Gomes, Agostinho, Gonçalo, Ricardo, Jorge, Pedro, Lopes, Lourenco, Machado Miguens, Joana, Maio, Amélia, Maneira, José, Onofre, António, Palma, Alberto, Pedro, Rute, Pina, João Antonio, Pinto, Belmiro, Santos, Helena, Saraiva, João, Silva, José, Tavares Delgado, Ademar, Veloso, Filipe, Wolters, Helmut
• Format: Article
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://dx.doi.org/10.1103/PhysRevD.91.032004; http://hdl.handle.net/10400.26/26741

<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>