Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 50 (2017)

Interaction cross section study of the two-neutron halo nucleus 22 C†∗1,∗2∗1,∗2 Y. Kondo∗1,∗2 J.
∗3 A.
∗1,∗2J.J.Gibelin,∗4Y.Togano,
Togano∗1,∗2T. Nakamura,
Nakamura∗1,∗2Y.
T.
Kondo,∗1,∗2J. A.
A. Tostevin,Tostevin,∗3A. T.
T. Saito
Saito,∗1,∗2Gibelin,∗4∗4N.
N.A.
A.Orr,
Orr,∗4
∗4
∗5∗2
∗4∗2
∗2
∗6N. L. Achouri, T. Aumann, H. Baba, F. Delaunay, P. Doornenbal, N. Fukuda, J. Hwang,
N. Inabe,∗2 T. Isobe,∗2 D. Kameda,∗2 D. Kanno,∗1,∗2 S. Kim,∗6 N. Kobayashi,∗1,∗2 T. Kobayashi,∗2,∗7T. Kubo,∗2 S. Leblond,∗4 J. Lee,∗2 F. M. Marqués,∗4 R. Minakata,∗1,∗2 T. Motobayashi,∗2 D. Murai,∗7T. Murakami,∗8 K. Muto,∗6 T. Nakashima,∗1 N. Nakatsuka,∗2,∗8 A. Navin,∗9 S. Nishi,∗1,∗2 S. Ogoshi,∗1,∗2H. Otsu,∗2 H. Sato,∗2 Y. Satou,∗6 Y. Shimizu,∗2 H. Suzuki,∗2 K. Takahashi,∗6 H. Takeda,∗2 S. Takeuchi,∗2R. Tanaka,∗1,∗2 A. G. Tuﬀ,∗10 M. Vandebrouck,∗11 and K. Yoneda∗2To obtain high precision root-mean-squared matter radius r̃m of 22 C, the interaction cross section σI has been measured with a carbon target at235 MeV/nucleon.
Recently the most neutron-rich carbon isotope 22 C
has attracted much attention owing to a possibly
greatly extended two-neutron halo structure, as suggested by a reaction cross section (σR ) study on a proton target at 40 MeV/nucleon.1) r̃m of 5.4 ± 0.9 fm
was deduced from the measured σR = 1.338 ± 0.274 b.
These large uncertainties in σR and the deduced r̃m
do not signiﬁcantly constrain the theoretical models.
A mean-ﬁeld model using an adjusted Skyrme interaction yielded an r̃m of 3.89 fm.2) Three-body models
yielded r̃m in the range of 3.5 ∼ 3.7 fm.3,4) Given thelarge uncertainty in the experimental values of Ref. 1)
and that the theoretical values are within ∼ 2σ of theexperimental value, more deﬁnitive conclusions require
data with higher precision.
A cocktail beam of 19,20,22 C was produced via theprojectile fragmentation of a 345 MeV/nucleon 48 Ca
beam. The 19,20,22 C beams were separated and transported to SAMURAI by BigRIPS. The cocktail beam
impinged on a carbon target with a thickness of
1.789 g/cm2 . The incident particles were identiﬁed
event-by-event by measuring the time of ﬂight, magnetic rigidity, and energy loss with detectors located at
the upstream of the carbon target. The incident angle
and position on the carbon target were measured using two multi-wire drift chambers placed just upstreamof the carbon target. The reaction products from the19,20,22
C + C reactions were identiﬁed using detectors
located at the entrance and exit of the SAMURAI magnet. The detailed experimental setup can be found inRef. 5).

Fig. 1. Mass number dependence of the interaction crosssection obtained in the present study.

The interaction cross sections σI obtained in thepresent study are shown in Fig. 1. The enhancementof σI for 22 C relative to those of 19,20 C is consistent
with a two-neutron halo nature of 22 C.
The present σI of 22 C is analyzed using a four-body(three-body projectile plus target) Glauber reaction
model.4) In the following discussion σI and σR arecompared directly by assuming the inelastic scattering cross section is negligible. From the comparison
with the model calculations and the present σI value,r̃m is deduced to be 3.44 ± 0.08 fm. This deduced r̃mis consistent with the theoretical predictions based on22
C three-body model wave functions,3,6) while it isabout 2σ smaller than the previously reported experimental value (5.4 ± 0.9 fm). More measurements, suchas Coulomb dissociation, will allow for a more detailedstudy of the 22 C structure.

†Condensed from the article in Phys. Lett. B 761, 412 (2016)
Department of Physics, Tokyo Institute of Technology∗2 RIKEN Nishina Center∗3 Department of Physics, University of Surray∗4 LPC-CAEN, ENSICAEN, Université de Caen CNRS/IN2P3∗5 Institut für Kernphysik, Technische Universität Darmstadt∗6 Department of Physics and Astronomy, Seoul National University∗6 Department of Physics, Tohoku Univeristy∗7 Department of Physics, Rikkyo University∗8 Department of Physics, Kyoto University∗9 GANIL, CEA/DSM-CNRS/IN2P3∗10 Department of Physics, University of York∗11 IPN Orsay, Université Paris Sud, IN2P3-CNRS

References∗11) K. Tanaka et al., Phys. Rev. Lett. 104, 062701 (2010).
2) T. Inakura et al., Phys. Rev. C 89, 064316 (2014).
3) W. Horiuchi, Y. Suzuki, Phys. Rev. C 74, 034311(2006).
4) Y. Kucuk, J. A. Tostevin, Phys. Rev. C 89, 034607(2014).
5) T. Kobayashi et al., Nucl. Instr. Meth. B 317, 294(2013).
6) S. N. Ershov et al., Phys. Rev. C 86 034331 (2012).

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