By default, the Mac will always mount all non-hidden partitions - so both partitions will automatically mount to both OSes, whichever you boot from, even when each contains a different OS.
You can set each to not mount when the other OS is 'in charge' by tweaking a file known as fstab in each OS separately; but we'll come to that later...
First thing to ensure is that your two partitions have different, recognisable names - it will save a lot of trouble later.
Then you need to get Mavericks onto the new partition.
On first boot after installation it will ask if you wish to Migrate from another machine. That's your time to feed it the Time Machine backup of your MacBook Pro.
By the time it's finished, your Mavericks partition will be a usable 'copy' of your Macbook.
To determine which it will boot into at any given time, you can set that in System Prefs > Startup Disk. That will set the default OS that it will boot into.
To boot into the other on just a single occasion, hold Alt ⌥ at the startup chimes & choose it from the drive icons that will appear [You may also see Recovery at that point too]
Once you are sure that each will boot when requested, then you can set your fstab file to not mount the other drive in each case.
Changing the fstab file to hide a partition is just a 'simple task' of adding one line of text to a text file; one on each boot partition. This 'simple task' is unfortunately complicated by a couple of factors...
Firstly, because you don't 'own' the file the system will try to stop you from writing to it.
To get around this, we drag the file to the desktop & work on the copy that is made there.
It's also in a hidden location, so it's not easy to get to, so we need to start by making it visible...
- Open Terminal [Applications/Utilities]
defaults write com.apple.finder AppleShowAllFiles YES
& hit Enter [You can copy/paste]
Right click the Finder icon in the Dock & select Relaunch. This will make the Finder disappear, then reappear showing all the hidden files [We'll revert this at the end.]
- In Finder, navigate to
*current boot drive*/etc/fstab
etc is an alias, & the fstab file may or may not exist. If it doesn't we can make a new one.
Drag fstab to the desktop, it will make a copy. If no fstab file exists, you can just make a new file from Terminal by typing
& one will appear on the desktop.
- In Terminal - Type
diskutil info *partition name of other partition*
& hit Enter
We are looking for the UUID of the other partition here - the one you want to hide when you are booted into this one, so for instance from Mountain Lion you're looking for
diskutil info Mavericks HD
- Find the line that says Volume UUID & copy the long number that looks like this
20F8C09F-9609-39BD-9C47-D82DCC98ECDE [Ignore the one underneath it that looks similar]
- Open your desktop copy of fstab in TextEdit
- Add a new line to the fstab file like this, but using your copied UUID -
UUID=C126C736-1585-3D12-9CF1-F95EFF0CF744 none hfs rw,noauto
Ignore any existing lines that may be present, just add your new one underneath.
- Fix the ownership on the new version of fstab by typing
sudo chown root:wheel ~/desktop/fstab
Terminal will ask for your password before proceeding.
Delete the existing fstab file from etc/ & then drag the new one into place. Password will be required.
Repeat that process on the other partition, first by finding its own fstab file, then adding to it the UUID of your current boot partition - so each boot drive will hide the other one.
Once completed & satisfied that it actually works, hide the 'invisible' files again -
defaults write com.apple.finder AppleShowAllFiles NO
then relaunch the Finder once more.
If you ever need to see the other partition later, you can always mount it manually from Disk Utility.