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We take the recently published data of twin kHz quasi-period oscillations(QPOs) in neutron star (NS) lowmass X-ray binaries (LMXBs) as the samples, andinvestigate the morphology of the samples, which focuses on the quality factor,peak frequency of kHz QPOs, and try to infer their physical mechanism. Wenotice that: (1) The quality factors of upper kHz QPOs are low (2 ~ 20 ingeneral) and increase with the kHz QPO peak frequencies for both Z and Atollsources. (2) The distribution of quality factor versus frequency for the lowerkHz QPOs are quite different between Z and Atoll sources. For most Z sourcesamples, the quality factors of lower kHz QPOs are low (usually lower than 15)and rise steadily with the peak frequencies except for Sco X-1, which dropabruptly at the frequency of about 750 Hz. While for most Atoll sources, thequality factors of lower kHz QPOs are very high (from 2 to 200) and usuallyhave a rising part, a maximum and an abrupt drop. (3) There are three Atollsources (4U 1728-34, 4U 1636-53 and 4U 1608-52) of displaying very high qualityfactors for lower kHz QPOs. These three sources have been detected with thespin frequencies and sidebands, in which the source with higher spin frequencypresents higher quality factor of lower kHz QPOs and lower difference betweensideband frequency and lower kHz QPO frequency.

Morphological analysis on the coherence of kHz QPOs