Studies of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>C</mml:mi> <mml:mi>P</mml:mi> <mml:mi>T</mml:mi> </mml:mrow> </mml:math> symmetry in positronium decays with the 192 plastic strip J-PET detector

A direct test of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>C</a:mi> <a:mi>P</a:mi> <a:mi>T</a:mi> </a:mrow> </a:math> symmetry is performed for the electromagnetic decays of ortho-positronium using the Jagiellonian positron emission tomograph (J-PET). We present the precise measurement of the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>C</c:mi> <c:mi>P</c:mi> <c:mi>T</c:mi> </c:math> -sensitive angular correlation entailing the positronium spin and the momenta of its annihilation photons, surpassing previous studies utilizing the same detection system. Positrons originating from a <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mrow> <e:mmultiscripts> <e:mrow> <e:mi>Na</e:mi> </e:mrow> <e:mprescripts/> <e:none/> <e:mrow> <e:mn>22</e:mn> </e:mrow> </e:mmultiscripts> </e:mrow> </e:math> source are emitted from the detector’s center and subsequently form positronium atoms within the spherical chamber covered with porous material. Reconstruction of annihilation locations using the 192-strip J-PET detector makes it possible to determine the positronium emission direction, which defines the quantization axis along which positronium is polarized, without the application of external magnetic fields. The measurements were performed in total for 356 days resulting in an identification of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mrow> <g:mn>47.8</g:mn> <g:mo>×</g:mo> <g:msup> <g:mrow> <g:mn>10</g:mn> </g:mrow> <g:mrow> <g:mn>6</g:mn> </g:mrow> </g:msup> </g:mrow> </g:math> events with ortho-positronium decays into three photons. The results are consistent with the exactness of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>C</i:mi> <i:mi>P</i:mi> <i:mi>T</i:mi> </i:math> symmetry with measured asymmetry amplitude <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mrow> <k:mo>−</k:mo> <k:mn>0.00029</k:mn> <k:mo>±</k:mo> <k:mn>0.00022</k:mn> </k:mrow> </k:math> (stat.) and with statistical error four times smaller than the previous best measurement.