Σ± p scattering experiment at J-PARC Hadron Experimental Facility

T. Nanamura1,2), K. Miwa3), M. Fujita1), T. K. Harada1,2), S. Hasegawa1), M. Ichikawa1,2),
Y. Ichikawa1), K. Imai1), S. Kajikawa1,3), S. H. Kim1), M. Naruki1,2), H. Sako1), S. Sato1),
H. Tamura1,3), K. Tanida1), T. O. Yamamoto1), and the J-PARC E40 collaboration
1): Hadron Nuclear Physics Gr., JAEA 2): Kyoto Univ. 3): Tohoku Univ.

Nucleons (N), namely, protons (p) and neutrons (n) are themost basic baryons comprising only u and d quarks. Octetbaryons (p, n, Λ, Σ＋, Σ0, Σ-, Ξ0, Ξ-) are extension of nucleonsconsisting of u, d, and s quarks. The latter six baryons include atleast one s quark and are called Hyperons (Y). By investigatinginteractions between octet baryons (BB interaction), the role ofdynamics of quarks and gluons in the short-range nuclear force
can be multi-directionally examined. In particular, it is expectedthat the ΣN interaction is strongly affected by the Pauli principle
at the quark level (quark Pauli effect) [1] and that a larger
repulsive core can be observed in the Σ+p channel than in theNN interaction. A scattering experiment is the most direct
method to investigate BB interactions. However, YN scatteringexperiments have been difficult for a long time due to the short
lifetime of hyperons. Recently, we successfully performed anovel high-statistics Σ±p scattering experiment at J-PARC (JPARC E40 [2]). This experiment aimed at a systematic study ofthe ΣN interaction and the verification of the large predicted
repulsive core in the Σ+p channel.
The experiment was performed at the K1.8 beam line in theJ-PARC Hadron Experimental Facility. A conceptual drawingof the experiment is shown in Fig. 1. A liquid hydrogen target(LH2 target) was used both for the incident Σ± production andfor the Σ±p scattering. Σ±p scattering events can be identified bymeasuring the Σ± momentum, the recoil proton’s kinetic energy
and the proton’s recoil angle.

Σ± momentum vector and the proton direction. This energy isthen compared to the one measured by CATCH. If the detected
proton is really the recoil proton from Σ±p scattering, thecalculated and measured energies should be consistent with eachother. Approximately 4500 Σ-p elastic [4], 2400 Σ+p elastic, and2300 Σ-p→Λn inelastic [5] scattering events were identified.
These numbers are approximately 100 times larger than thoseachieved in past experiments. From this high-statistic data,differential cross sections were obtained. Figure 2 shows theangular distribution of the differential cross sections for Σ-pelastic scattering. The quality of the data has improvedsignificantly. The present data show a forward-peaking angulardistribution in agreement with theoretical predictions, althoughsome small discrepancies can also be seen. The present data inturn constitute a new excellent input which can be used toimprove theoretical models. These systematic studies of the ΣNinteractions will play an important role to establish more
realistic BB interaction models and to constrain the size of therepulsive force owing to the quark Pauli effect.

Fig. 1 Conceptual drawing of the Σ±p scattering experiment. The Σ±pelastic scattering case is drawn.

Fig. 2 Differential cross sections for the Σ-p elastic channel obtained inJ-PARC E40 experiment [4] (black points), grouped into fourgraphs corresponding to different ranges of the Σ- incident
momenta. The error bars and boxes show statistical andsystematic uncertainties. The red points show the previous
experimental data [6]. The pink dotted, blue dot-dashed, andorange solid lines show theoretical predictions; ESC08c [7], fss2[8], and Chiral EFT with shadows representing error bands [9].

Σ± particles were produced via the π±p→K+Σ± reaction
induced by a π± meson beam. By measuring the momenta of thebeam π± and of the outgoing K+ meson using two magnetic
spectrometers, events which resulted in the production of Σ±particles were identified, and the momentum of each Σ± wasdetermined. In total, 1.62×107 Σ- and 4.9 ×107 Σ+ events wereaccumulated. The produced Σ± particles can induce additional
reactions, such as the desired Σ±p scattering. Σ± particles also
decay, such as the Σ-→nπ- decay. Using the CATCH detector
system [3] surrounding the LH2 target, charged particles
involved in these reactions and decays were detected. For eachdetected proton, the direction and kinetic energy could bemeasured.
The Σ±p scattering events were identified by a kinematicalconsistency check. An illustrative example can be taken to be
the case of a Σ±p elastic scattering event, in which a proton wasdetected by CATCH. The kinetic energy of the recoil proton canbe calculated from the kinematics of elastic scattering using theReferences[1] M. Oka and K. Shimizu, and K. Yazaki, Nucl. Phys. A, 464,700 (1987).
[2] K. Miwa et al., J-PARC Proposal P40 (2010).
[3] Y. Akazawa et al., Nucl. Instr. Meth. A1029, 166430 (2022).
[4] K. Miwa et al., Phys. Rev. C, 104, 045204 (2021).
[5] K. Miwa et al., Phys. Rev. Lett., 128, 072501 (2022).
[6] Y. Kondo et al., Nucl. Phys. A 676, 371 (2000).
[7] T. A. Rijken, M. M. Negels, and Y. Yamamoto, Prog. Theor.
Phys. Suppl. 185, 14 (2010).
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[9] J. Haidenbauer et al., Nucl. Phys. A915, 24 (2013).