can a business class passenger use the lounge at LAX?

Only international first class or emerald on an international itinerary.

Business class can access if you also have Oneworld Emerald status. Except if you have Oneworld Emerald via American Airlines. Then you must also be flying international in any class of service.

Business Class passengers can use the One World lounge on Level 5 at LAX Terminal B https://maps.app.goo.gl/KmFaemCYM1RGuD6CA