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We investigate the correlation between the frequencies of the twin kilohertzquasi-periodic oscillations (kHz QPOs) and the neutron star (NS) spins in lowmass X-ray binaries (LMXBs), based on the data sets of 12 sources withsimultaneously detected twin kHz QPOs and NS spins, and find that the histogramof the ratio between the frequency difference of twin kHz QPOs ({\Delta}{\nu} ={\nu}2 - {\nu}1) and NS spin {\nu}s shows a non-uniform distribution with a gapat {\Delta}{\nu}/{\nu}s ~ 0.65. We try to classify the 12 sources into twocategories according to this gap: (I) The slow rotators with <{\nu}s> ~ 311 Hz,XTE J1807.4-294, 4U 1915-05, IGR J17191-2821, 4U 1702-43, 4U 1728-34 and 4U0614+09 follow a relation {\Delta}{\nu}/{\nu}s > 0.65; (II) The fast rotatorswith <{\nu}s> ~ 546 Hz, SAX J1808.4-3658, KS 1731-260, Aql X-1, 4U 1636-53, SAXJ1750.8-2900 and 4U 1608-52 satisfy the relation {\Delta}{\nu}/{\nu}s < 0.65.However, the linear fittings of {\Delta}{\nu} versus {\nu}s relations of group(I) and (II) are unsatisfactory to ensure any certain correlations. We suggestthat this phenomenon may arise from the fact that most measured kHz QPOs andspins satisfy the conditions of 1.1 {\nu}s < {\nu}2 < 1300Hz and {\Delta}{\nu}decreasing with {\nu}2. Apparently, the diversified distribution of{\Delta}{\nu}/{\nu}s refutes the simple beat-frequency model, and thestatistical correlations between the twin kHz QPOs and NS spins may arise fromthe magnetosphere-disk boundary environments, e.g., co-rotation radius and NSradius, that modulate the occurrences of X-ray signals. Furthermore, we alsofind that the distribution of the ratio of {\nu}2 to {\nu}1 clusters around thevalue of <{\nu}2/{\nu}1> ~ 3 : 2, which shows no obvious correlation with NSspins.

Correlations between the frequencies of twin kHz QPOs and spins of neutron stars in LMXBs