  We present NMR measurements of a strong-leg spin-1/2 Heisenberg
antiferromagnetic ladder compound (C7H10N)2CuBr4 under magnetic fields up to 15
T in the temperature range from 1.2 K down to 50 mK. From the splitting of NMR
lines we determine the phase boundary and the order parameter of the
low-temperature (3-dimensional) long-range-ordered phase. In the
Tomonaga-Luttinger regime above the ordered phase, NMR relaxation reflects
characteristic power-law decay of spin correlation functions as 1/T1
T^(1/2K-1), which allows us to determine the interaction parameter K as a
function of field. We find that field-dependent K varies within the 1<K<2 range
which signifies attractive interaction between the spinless fermions in the
Tomonaga-Luttinger liquid.
