title: β decay of (38)Ca: sensitive test of isospin symmetry-breaking corrections from mirror superallowed 0+ → 0+ transitions.
abstract: We report the first branching-ratio measurement of the superallowed 0+→0+β transition from Ca38. The result, 0.7728(16), leads to an ft value of 3062.3(68) s with a relative precision of ±0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, Ca38→38mK and K38m→Ar38, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed β decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: H I
authors.initials: HI
authors.lastname: Park
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Hardy
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: V E
authors.initials: VE
authors.lastname: Iacob
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: M
authors.initials: M
authors.lastname: Bencomo
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: V
authors.initials: V
authors.lastname: Horvat
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: N
authors.initials: N
authors.lastname: Nica
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: B T
authors.initials: BT
authors.lastname: Roeder
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: E
authors.initials: E
authors.lastname: Simmons
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: R E
authors.initials: RE
authors.lastname: Tribble
authors.affiliation: Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA.
authors.forename: I S
authors.initials: IS
authors.lastname: Towner