It's a SFF-8784 Edge connector (see the photo below - connector in in the bottom middle of the photo). FWIW, HD - WD5000MPCK - is supposed to be 5mm thick but there's apparently lots of room in the computer for a 7mm drive. FWIW, the drive is supposed to have 6 Gb/sec connector speed.
Below is the EFF-8784 connector:
Below is the standard SATA connector cable for the computer
Disclaimer: I actually haven't opened the laptop yet (requires Torx bits that I dn't have with me) but a drive scan tells me it is the WD drive (the same computer model can also come with a Seagate drive, with a standard SATA connector - a MB to HD connector makes the difference but Lenovo doesn't sell the cable).