[100727] A rich harvest of data from the LHC

姫海棠 果

http://cdsweb.cern.ch/record/1277714

After mastering operation with nominal bunch intensities in June, the number of nominal intensity bunches injected into the machine has been carefully increased over the last 3 weeks, and is presently 12 per beam. This achievement has allowed the LHC experiments to record more than 250 nb-1 of integrated luminosity, most of it in recent physics fills. This represents a rich harvest of data that the experiments are now analysing with a view to presenting their latest physics results at the ICHEP conference in Paris from 22 to 28 July. You can follow the event by watching the live webcast or by reading the blog.




The graph shows the loss of four bunches (red, green, pink, and blue in order of time). Other bunches were not affected, as indicated with the cyan trace. The cause and cure of the losses is under investigation.

Operation with many nominal bunches is a major technical achievement which the operations teams have obtained this week. The total number of particles per beam in the LHC has now exceeded the threshold of 1012, a critical value whose achievement required the meticulous setting-up of many accelerator systems.

The particle bunches are injected into the LHC from the SPS accelerator. Until this week the operations teams had kept the injection scheme simple, taking just one bunch per SPS cycle. Now that the number of bunches injected is increasing, the time needed to fill the LHC is becoming uncomfortably long. So this week, for the first time, the teams have commissioned multi-bunch injection and have succeeded in injecting more than one bunch for each SPS particle acceleration cycle, thus considerably reducing the time needed to fill the LHC.

Once the colliding beams are injected into the LHC, it is now possible to maintain them for many hours. However, some instabilities are being observed with high intensity bunches in the machine. These instabilities, still under study, can result in beam loss (see picture), which in turn causes a reduction in luminosity for physics. Understanding and preventing these sudden losses is one of the main priorities for the coming weeks.

The long hours of stable operation at high intensity and high energy have provided the experiments with a rich harvest of data. The LHCf experiment, one of the three smaller experiments at the LHC, has already completed its run for 2010 (more information on this will be published in the next issue of the Bulletin), while the other experiments are preparing to present their latest physics results at the ICHEP conference in Paris.