jhānas, Zen, and how to practice concentration meditation
A true Jhana master, Venerable Pa Auk Sayadaw:


Breakthrough in
SAMATHA MEDITATION
Knowing and Seeing (4th revised edition)


And if you can purchase this book, I highly recommend it:


Practicing the Jhanas: Traditional Concentration Meditation as Presented by the Venerable Pa Auk Sayadaw


It's written by actual students of the Venerable Pa Auk, who actually succeeded in developing the Jhanas: very clear and concise, with practical advice.