Measurement of polarization observables of the associated strangeness production in proton proton interactions

Abstract

Abstract. The Λ polarization, the analyzing power, and the Λ spin transfer coefficient of the reaction pp Ñ pK`Λ were measured at beam momenta of 2.70 GeV/c and 2.95 GeV/c corresponding to excess energies of 122 MeV and 204 MeV. While the analyzing power and the spin transfer coefficient do not change significantly with the excess energy, the Λ polarization varies strongly and changes its sign. As this is the first measurement of polarization observables below an excess energy of 200 MeV, the change of the sign of the Λ polarization was not observed before. The high statistics of the data (« 200 k events for each momentum) enables detailed studies of the dependence of the Λ polarization and the analyzing power on the center of mass momentum of the particles. The results of the spin transfer coefficient are in qualitative agreement with the DISTO experiment. The Λ polarization data of 2.95 GeV/c are only conform with the DISTO experiment, while both the 2.70 GeV/c and 2.95 GeV/c data differ strongly from all previous measurements, whether exclusive or inclusive.

The legacy of the experimental hadron physics programme at COSY

“…The azimuthal symmetry of the COST-TOF detector minimizes many systematic uncertainties in measurements involving polarized particles. Figure 65 shows several measurements carried out at 2.7 and 2.95 GeV/c in the pp → K + Λp reaction [222]. Though all the events were fully reconstructed, only observables associated with the direction of the Λ are shown here.…”

“…65. COSY-TOF measurements of the pp → K + Λp reaction at a beam momentum of 2.7 GeV/c (red downwardpointing triangles) and 2.95 GeV/c (blue upward-pointing triangles) [222]. Shown are the Λ polarization, the proton analyzing power with respect to the Λ direction, and the transverse spin-transfer coefficient DNN between the incident polarized proton and the produced Λ.…”

“…Although close to threshold the pp → K + pΛ reaction is dominated by the excitation of the N * isobar S 11 (1650), it is only through the study of the different angular distributions away from threshold that one can confirm the importance of the higher N * . Such angular distributions could only be measured at COSY with the help of the TOF detector [218,26,27], and this is also true for the associated spin dependence [222]. 7.…”

Measurement of Bell-type inequalities and quantum entanglement from $Λ$-hyperon spin correlations at high energy colliders

“…Illustration of double Λ polarization; here â ( b) denotes the momentum direction of ΛA (ΛB) daughter particle in the ΛA (ΛB) rest frame. spins are measured in terms of their polarization, where the decay kinematics on an event-averaged basis reflects their spin projections [71][72][73][74][75][76][77][78][79][80][81][82][83][84]. The CHSH inequality and entanglement measures can be extracted from the correlation of their relative spin projections, illustrated in Fig.…”

Determination of the spin tripletpΛscattering length from the final state interaction in thep⃗p→pK+Hauenstein1, Clement2, Kilian3 et al. 2017Phys. Rev. CSelf Cite

“…the Λ polarization, in order to put further constraints on the production mechanism of associated strangeness as well as on the creation of pΛ spin triplet states. These results are published in [24] but further theoretical considerations are necessary to set other constraints.…”