According to the Hanafi school of thought if a man touches a woman, his wuduu does not break.
They base their opinion on the following hadith
The Prophet (sallallaahu alayhi wa sallam) kissed one of his wives and went out for saying prayer. He did not perform ablution. 'Urwah said: I said to her: Who is she except you! Thereupon she laughed. Abu Dawud said: The same version has been reported through a different chain of narrators.
[Sunan Abi Dawud]
Urwah narrated from Aishah that:
"The Prophet kissed one of his wives, then he went to the prayer and did not perform Wudu." He (Urwah) said: "I said 'Who was it except you?'" [He said:] "So she laughed."
The majority hold the opinion that if a man touches a woman, his Wuduu breaks. This is when there is no separator between them. If they touch without a separator, the Wuduu of both breaks.
They base their opinion on the following Verse of the Qur'aan
O you who have believed, do not approach prayer while you are intoxicated until you know what you are saying or in a state of janabah, except those passing through [a place of prayer], until you have washed [your whole body]. And if you are ill or on a journey or one of you comes from the place of relieving himself or you have touched women and find no water, then seek clean earth and wipe over your faces and your hands [with it]. Indeed, Allah is ever Pardoning and Forgiving.
The Hanafis contend that touch in this Verse means sexual intercourse as Ibn Abbaas (may Allaah be pleased with him) has said.
Kuwaiti Encyclopedia of Fiqh
Volume 16 Page 237-239