Sun Hongkai 孙宏开, Katia Chirkova 齐卡佳, and Liu Guangkun 刘光坤. Baima yu yanjiu 白马语研究 (Study of the Baima Language). Beijing: Minzu Chubanshe, 2007. ISBN: 9787105084012.
This book is part of the series Zhongguo xin faxian yuyan yanjiu congshu 中国新发现语言研究丛书 (Studies of Newly Discovered Languages of China). It covers Baima phonology, vocabulary, grammar, and so on, and it contains several short Baima stories with Chinese translations.
More information about the book is available here (in Chinese).