using WP_Query doesn't work on category page

On my product category template (mp_category.php) I have the following:

$new = new WP_Query("showposts=4&product_category=bath&post_type=product");
if ($new->have_posts()) : while ($new->have_posts()) : $new->the_post();

But nothing appears.

Removing the '&product_category=bath' part of the argument shows ALL products (not just ones in the bath category). Also, when I click on the View link for my product categories, nothing displays. Can you offer any help on this mystery?