Gil Fronsdal provides a good introduction to calm and tranquility that you can find on the Insight Meditation Center website: Tranquility
Jack Kornfield describes the relationship between tranquility and happiness in an article that you can find here: Happiness and Tranquility
Sounds True has produced an e-book on the factors of awakening that is an excerpt from Joseph Goldstein’s great book, “Mindfulness“. It’s called the “7 Treasures of Awakening” and is currently available for 79 cents from Sounds True on their website: Seven Treasures of Awakening