This is not currently supported in 2.x, at least not directly.
You might want to subscribe yourself on the existing enhancement request: 109918: Ant task to download an artifact or log for a build.

For now, what I recommend is publishing the artifacts you want to preserve on some other server, then use curl or a remote file copy to retrieve them later.
The link can be published to the build result downloads page, as if it was a file, using the artifactLinkPublisher Ant task.

It's also possible to list and retrieve contents via the (internal) REST interface used to drive the web UI. For example:
{yourJazzRepo}/resource/virtual/build/result/{buildResultUUID}/contributions?type=com.ibm.team.build.common.model.IBuildResultContribution.artifact&_prettyPrint=true

Where the {buildResultUUID} can be obtained from the last segment of Copy URL on the build result in the RTC client. For logs, change .artifact to .log.

But this interface is internal, and may change in the future. We are working on a more well-defined REST API, an implementation of the OSLC Automation API, in 3.0. See 73070: RESTful API for Build, to support C/ALM integration scenarios and its child items.

Regards,
Nick