The great accelerator
in the sky

Cosmic rays have many origins, including active black hole (artist's rendetion upper left). Particles accelerated across the universe slam into the Earth, forming cosmic ray muons like the one shown passing through the CMS detector (lower right). These cosmic ray muons are invaluable tools for understanding a detector in its early stages.

Editor's note: This is the first in a three-part series that describes the science done with data using cosmic rays in the CMS experiment.

A long time ago, perhaps in a galaxy far, far, away, a star died, swallowed by a nearby ravenous black hole. This cosmic calamity tore the star apart, dragging most of it down into oblivion. But as the hot gas that composed the star spiraled downward, it encountered strong magnetic fields that rescued some of it and blasted it across the cosmos. As the relatively small surviving amount of now-ionized gas spread throughout the universe, each bit of plasma became more and more isolated - a single proton, a cosmic Flying Dutchman, doomed to travel alone forever. This and other ways of forming cosmic rays works like a giant accelerator, supplying particles that allow physicists to test their detectors.

A few of these cosmic rays happen to hit Earth. These particles hit atoms in the atmosphere and each collision results in more particles, which in turn hit more atoms. The single proton becomes hundreds or thousands of muons slicing downward toward the planet's surface, penetrating deeply into the Earth. Particle physicists are concerned mostly with these muons, some of which encounter a particle detector called CMS.

The same properties that allow muons to penetrate hundreds of feet of rock allow them to traverse CMS, leaving distinct signatures in the detector. The muons can penetrate all detector systems and interact in predictable ways.

The CMS detector consists of 100 million detector elements. Each piece is carefully crafted and placed as accurately as possible. However, getting perfect knowledge of the position of each piece is a challenge. That is where muons from cosmic rays can help.

By knowing muon behavior and seeing these particles' signatures in the detector, CMS physicists can calibrate their system. By exploiting the huge data set, which consists of more than 1 billion muons, physicists can really investigate their equipment's performance. With help from the great accelerator in the sky, CMS physicists are ready for beam.

— Don Lincoln

Graduate students and postdocs play a pivotal role in the commissioning of any detector. These young physicists have been heavily involved in understanding CMS' muon detection system.

Jim Pivarski of Texas A&M University was recently awarded a CMS Achievement Award for leadership in the alignment of the muon detector systems using beam data taken during the brief running period last fall.

East gate Q&A

Editor's Note: The east gate will begin closing from 1 to 5 a.m. in mid- to late-November, as Fermilab Today reported in September. That article prompted questions from readers, which were answered in a followup Q&A. Fermilab Today staff consulted FESS management and the project's manager for answers to additional frequently asked questions. Those questions and answers are below.

Q: When will the new gate go into operation?
A: Sometime in mid- to late November.

Q: During what hours will it be closed?
A: From 1- 5 a.m.

Q: Why are we making the change?
A: When the Department of Energy took over Fermilab's Safeguards and Security contract, the funds for the contract were moved out of the laboratory's high energy physics budget and into a separate safeguards and Security budget. Congress has provided a limited amount of funding for Safeguard and Security activities. With inflation the costs have risen, but the budget has not.

To meet Department of Energy targets for small business contracts, in 2007 DOE took over the contract for laboratory security from Fermilab, deducting that cost from Fermilab's budget. Now DOE must make cuts in guards' hours to stay within the fixed Safeguards and Security operating budget. Besides closing the east gate between 1 - 5 a.m., DOE will also reduce the hours of guard staffing at the Wilson Hall front desk.

Q: How much will the gate and associated construction cost?
A: The gate is budgeted at $472,000 from Safety and Security capital funding.

Q: What is the total cost per hour of a guard?
A: About $27.

Q: How does this make economic sense?
A: The cost of the gate is paid from a different source from the guards' wages. The cost of the gate is paid from DOE's Safeguards and Security capital budget, not from its operating budget.

Q: Will essential personnel (experts called in for accelerator repairs, for example) on laboratory business be able to enter the East gate during the hours it is closed?
A: That is the laboratory's goal. Part of the contract for the new gate includes technology to operate it remotely, either from the Communications Center or by a hand-held device. If these systems and the gate can be shown to work reliably, essential personnel on laboratory business will be able to employ these devices to enter the gate during the hours it is closed.

Q: What about emergency vehicles?
A: Emergency vehicles have electronic devices (like the ones that turn traffic lights green) that can open the gate. If the gate system fails, emergency personnel may use more drastic means of opening the gate.

Q: If the gates can be opened reliably electronically, why not eliminate guards and use only automatic gates at all hours?
A: The Fermilab site is open to the public. With automatic gates, neighbors and visitors would not be able to enter. Besides checking ID's, guards at the gates greet visitors, provide information and answer questions.