Belle Back for Autumn

The KEKB accelerator was fired up again after the summer shutdown at 09:00 on September 19. There were problems with the injection system of the HER (high energy ring), which meant we couldn’t get enough electrons stored in the rings for collision for the first 24 hours or so, although it looks a bit better now. The LER (low energy ring, positron) beam seems to be working normally. Collisions started at about 19:30 last night, and we started taking data at 22:43 after a few hours of tuning.

The graph below shows the recent performance of the KEKB accelerator. The horizontal axis represents time and shows the last 24 hours. The yellow line in the third graph from the top shows the instantaneous luminosity (collisions per second), and is currently about 8.145 /nb/s, compared to our world record of 16.517 /nb/s. It will hopefully climb fairly quickly over the next couple of days. The dark green line (right axis) in the same graph shows the integrated luminosity -- which corresponds to the total amount of data recorded -- for the runs so far. You can see the text "Collision Tuning" at the top of the graph, which indicates that the accelerator experts are still trying to figure out the best way to get the two beams to collide with each other. Things don't always work exactly the same after a long shutdown as they did before, so it takes a while to make sure both beams are stable and on target so that we can get as much data as possible out of the machine.

I'm amazed at how easily they have managed to bring everything back online after having people down there fiddling with it for the last two months or so. I have shifts in another three weeks or so, so hopefully it will all be back to normal by then.