CERN Accelerating science

(Color online) Schematic layout of the NA61/SHINE experiment at the CERN SPS (horizontal cut, not to scale). The orientation of the \NASixtyOne coordinate system is shown on the picture. The nominal beam direction is along the $z$ axis. The magnetic field bends charged particle trajectories in the $x$-$z$ plane. The electron drift direction in the TPCs is along the $y$ (vertical) axis.

(Color online) \textit{Left:} The $\Lambda$\pim invariant mass spectrum of \Xim candidates for rapidity $\y$ between -0.25 and 0.25 and transverse momentum \pt from 0.4 to 0.6~\GeVc. Magenta line represents the fitted Lorentzian function and blue one shows the fitted background, black line represents their sum. The vertical solid gray line shows the nominal PDG $\Xi$ mass, dashed lines show the integration range used. \textit{Right:} Analogous $\overline{\Lambda}$\pip invariant mass spectrum of \Xip candidates.

(Color online) \textit{Left:} The $\Lambda$\pim invariant mass spectrum of \Xim candidates for rapidity $\y$ between -0.25 and 0.25 and transverse momentum \pt from 0.4 to 0.6~\GeVc. Magenta line represents the fitted Lorentzian function and blue one shows the fitted background, black line represents their sum. The vertical solid gray line shows the nominal PDG $\Xi$ mass, dashed lines show the integration range used. \textit{Right:} Analogous $\overline{\Lambda}$\pip invariant mass spectrum of \Xip candidates.

(Color online) Measured lifetime ratio $\tau/\tau_{PDG}$ for $\Xim$ (blue squares) and $\Xip$ (red circles) as a function of center of mass rapidity. Only statistical uncertainties are shown.

(Color online) Transverse momentum spectra in rapidity slices of $\Xim$ (\textit{left}) and $\Xip$ (\textit{right}) produced in inelastic \pp interactions at 158~\GeVc. Rapidity values given in the legends correspond to the middle of the corresponding interval. Statistical uncertainties are smaller than the marker size, shaded bands show systematic uncertainties. Spectra are scaled by the given factors for better separation.

(Color online) Transverse momentum spectra in rapidity slices of $\Xim$ (\textit{left}) and $\Xip$ (\textit{right}) produced in inelastic \pp interactions at 158~\GeVc. Rapidity values given in the legends correspond to the middle of the corresponding interval. Statistical uncertainties are smaller than the marker size, shaded bands show systematic uncertainties. Spectra are scaled by the given factors for better separation.

(Color online) Rapidity spectra of $\Xim$ (blue squares) and $\Xip$ (red circles) produced in inelastic \pp interactions at 158~\GeVc. Statistical uncertainties are smaller than the marker size, shaded bands correspond to systematic uncertainties of the measurements. Curves depict Gaussian fits used to determine total mean multiplicities.

(Color online) Mid-rapidity densities (dn/d\y) of $\Xim$ (full symbols) and $\Xip$ (open symbols) measured in inelastic \pp interactions as a function of centre-of-mass energy $\sqrt{s_{NN}}$. The systematic and statistical uncertainties are smaller than the symbol size. The data are compared to results from STAR at the BNL RHIC measured at $\sqrt{s_{NN}}$ = 200~\GeV~\cite{Abelev:2006cs}, from ALICE at CERN LHC measured at $\sqrt{s_{NN}}$ = 0.9, 7 and 13~\TeV~\cite{Aamodt:2011zza, Abelev:2012jp, Acharya:2019kyh} and from CMS at the CERN LHC measured at $\sqrt{s_{NN}}$ = 0.9 and 7~\TeV~\cite{Khachatryan:2011tm}.

(Color online) The strangeness enhancement $E$ at the mid-rapidity as a function of average number of wounded nucleons $\left$ calculated as a ratio of rapidity density for $\Xim$ production (\textit{left}) and $\Xip$ production (\textit{right}) in nucleus-nucleus interactions per $\left$ divided by the corresponding value for \pp interactions (see Eq.~\ref{eq:enhancment}). Red circles – NA49 Pb+Pb at 158\AGeV~\cite{Anticic:2009ie}, blue squares - NA57 \textit{p}+Be, \textit{p}+Pb and Pb-Pb at the same center-of-mass energy $\sqrt{s_{NN}}$ = 17.3~\GeV~\cite{Antinori:2006ij}, magenta triangles - STAR Au+Au at $\sqrt{s_{NN}}$ = 200~\GeV~\cite{Abelev:2007xp}, gray diamonds - ALICE Pb+Pb at $\sqrt{s_{NN}}$ = 2.76~\TeV~\cite{ABELEV:2013zaa}. The systematic errors are represented by shaded boxes.

(Color online) The strangeness enhancement $E$ at the mid-rapidity as a function of average number of wounded nucleons $\left$ calculated as a ratio of rapidity density for $\Xim$ production (\textit{left}) and $\Xip$ production (\textit{right}) in nucleus-nucleus interactions per $\left$ divided by the corresponding value for \pp interactions (see Eq.~\ref{eq:enhancment}). Red circles – NA49 Pb+Pb at 158\AGeV~\cite{Anticic:2009ie}, blue squares - NA57 \textit{p}+Be, \textit{p}+Pb and Pb-Pb at the same center-of-mass energy $\sqrt{s_{NN}}$ = 17.3~\GeV~\cite{Antinori:2006ij}, magenta triangles - STAR Au+Au at $\sqrt{s_{NN}}$ = 200~\GeV~\cite{Abelev:2007xp}, gray diamonds - ALICE Pb+Pb at $\sqrt{s_{NN}}$ = 2.76~\TeV~\cite{ABELEV:2013zaa}. The systematic errors are represented by shaded boxes.

(Color online) Transverse momentum spectra at mid-rapidity of $\Xim$ (\textit{left}) and $\Xip$ (\textit{right}) produced in inelastic \pp interactions at 158~\GeVc. Rapidity range is included in the legends. Shaded bands show systematic uncertainties. \Urqmd 3.4~\cite{Bass:1998ca,Bleicher:1999xi}, \Epos~1.99~\cite{Werner:2008zza}, \Ampt~1.26~\cite{PhysRevC.72.064901, PhysRevC.90.014904, PhysRevC.61.067901}, \SmashModel~1.6~\cite{Mohs:2019iee, Weil:2016zrk, dmytro_oliinychenko_2019_3485108} and \PHSD~\cite{Cassing:2009vt, Cassing:2008sv} predictions are shown as magenta, blue, black, gray and green lines, respectively.

(Color online) Transverse momentum spectra at mid-rapidity of $\Xim$ (\textit{left}) and $\Xip$ (\textit{right}) produced in inelastic \pp interactions at 158~\GeVc. Rapidity range is included in the legends. Shaded bands show systematic uncertainties. \Urqmd 3.4~\cite{Bass:1998ca,Bleicher:1999xi}, \Epos~1.99~\cite{Werner:2008zza}, \Ampt~1.26~\cite{PhysRevC.72.064901, PhysRevC.90.014904, PhysRevC.61.067901}, \SmashModel~1.6~\cite{Mohs:2019iee, Weil:2016zrk, dmytro_oliinychenko_2019_3485108} and \PHSD~\cite{Cassing:2009vt, Cassing:2008sv} predictions are shown as magenta, blue, black, gray and green lines, respectively.

(Color online) Rapidity spectra of $\Xim$ (\textit{left}), $\Xip$ (\textit{middle}) and $\Xip/\Xim$ ratio (\textit{right}) measured in inelastic \pp interactions at 158~\GeVc. Shaded bands show systematic uncertainties. \Urqmd 3.4~\cite{Bass:1998ca,Bleicher:1999xi}, \Epos~1.99~\cite{Werner:2008zza}, \Ampt~1.26~\cite{PhysRevC.72.064901, PhysRevC.90.014904, PhysRevC.61.067901}, \SmashModel~1.6~\cite{Mohs:2019iee, Weil:2016zrk, dmytro_oliinychenko_2019_3485108} and \PHSD~\cite{Cassing:2009vt, Cassing:2008sv} predictions are shown as magenta, blue, black, gray and green lines, respectively.

(Color online) Rapidity spectra of $\Xim$ (\textit{left}), $\Xip$ (\textit{middle}) and $\Xip/\Xim$ ratio (\textit{right}) measured in inelastic \pp interactions at 158~\GeVc. Shaded bands show systematic uncertainties. \Urqmd 3.4~\cite{Bass:1998ca,Bleicher:1999xi}, \Epos~1.99~\cite{Werner:2008zza}, \Ampt~1.26~\cite{PhysRevC.72.064901, PhysRevC.90.014904, PhysRevC.61.067901}, \SmashModel~1.6~\cite{Mohs:2019iee, Weil:2016zrk, dmytro_oliinychenko_2019_3485108} and \PHSD~\cite{Cassing:2009vt, Cassing:2008sv} predictions are shown as magenta, blue, black, gray and green lines, respectively.

(Color online) Rapidity spectra of $\Xim$ (\textit{left}), $\Xip$ (\textit{middle}) and $\Xip/\Xim$ ratio (\textit{right}) measured in inelastic \pp interactions at 158~\GeVc. Shaded bands show systematic uncertainties. \Urqmd 3.4~\cite{Bass:1998ca,Bleicher:1999xi}, \Epos~1.99~\cite{Werner:2008zza}, \Ampt~1.26~\cite{PhysRevC.72.064901, PhysRevC.90.014904, PhysRevC.61.067901}, \SmashModel~1.6~\cite{Mohs:2019iee, Weil:2016zrk, dmytro_oliinychenko_2019_3485108} and \PHSD~\cite{Cassing:2009vt, Cassing:2008sv} predictions are shown as magenta, blue, black, gray and green lines, respectively.