Q.new red tip photinia
I just planted several new photinia and on one of them the leaves are turning brown. We had a freeze recently. Did it kill the plant? I live in zone 8.

Most Photinia are listed as hardy in zones 8 - 10.
Your new bush very well could have been touched by the freeze.
Make sure you are watering well, daily for the first 2 weeks, then you can cut back.
You can prune away the dead material and wait and see.
Here are some links to refresh you on the care requirements.
https://www.gardeningknowhow.com/ornamental/shrubs/photinia/growing-red-tip-photinia.htm
https://www.gardeningknowhow.com/ornamental/shrubs/photinia/red-tip-photinia-fertilizer.htm