hibernate hql 时间段查询 报错 ?报错

List orderList = getSession().createQuery("select o.client.name,sum(capital*1.0) from Order o where o.orderDate between "+
helper.getStartTime()+" and "+ helper.getEndTime() +" group by o.client.name")
.setFirstResult(page.getStartIndex())
.setMaxResults(page.getPageSize())
.list();

以上代码报错

org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: Jan near line 1, column 110 [select o.client.name,sum(capital*1.0) from com.brainstrong.crms.domain.Order o where o.orderDate between Mon Jan 01 00:00:00 CST 2007 and Tue Jan 01 00:00:00 CST 2008 group by o.client.name]

怎么解决，在线等。。。急！！！