Hello, thank you very much for this tip.
I tried to follow your instructions but it doesn't work. I think I haven't understood how the raw template works:
If I test this link directly in my browser ($url = JURI::base().'index.php?option=com_cck&view=list&search=list_b&task=search&id_a='.$id ) it displays correctly my list b. But if I add '&tmpl=raw' the page is blank and the content is empty.
Of course I put the raw.php file in the templateS directory.
Thank you for your help