title: Experimental evidence of core modification in the near drip-line nucleus 23O.
abstract: The longitudinal momentum (P(axially)) distributions of one- and two-neutron removal fragments ((21,22)O) of 23O from the reaction with a C target at 72 A MeV have been measured for the first time using a new direct time-of-flight method with nearly full acceptance for the breakup fragments. The unexpectedly narrow width of 21O ( 115 +/- 34 MeV/c in FWHM) is consistent with two neutrons occupying the 2s(1/2) orbital in 23O. This indicates modification of core (22O) structure for neutron halo-like sd shell nuclei near the drip line. This also suggests the lowering of the s orbital providing a justification for the N = 16 magic number.
authors.affiliation: RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Rituparna
authors.initials: R
authors.lastname: Kanungo
authors.forename: Masami
authors.initials: M
authors.lastname: Chiba
authors.forename: Naohito
authors.initials: N
authors.lastname: Iwasa
authors.forename: Shunji
authors.initials: S
authors.lastname: Nishimura
authors.forename: Akira
authors.initials: A
authors.lastname: Ozawa
authors.forename: Chhanda
authors.initials: C
authors.lastname: Samanta
authors.forename: Toshimi
authors.initials: T
authors.lastname: Suda
authors.forename: Takeshi
authors.initials: T
authors.lastname: Suzuki
authors.forename: Takayuki
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Tao
authors.initials: T
authors.lastname: Zheng
authors.forename: Isao
authors.initials: I
authors.lastname: Tanihata