Parameters for the Linear Collider: An update

This column is written by Barry Barish, director of the Global Design Effort for the International Linear Collider.

Barry Barish

As we explore the possible trade-offs to make the ILC Reference Design as cost effective as possible, we have needed sharper definitions for some of the stated parameters, making us consider alternatives. With this in mind, the International Linear Collider Steering Committee (ILCSC) reconvened their parameters subcommittee who wrote the original parameters report that dictates the scientific requirements and hence the design for the ILC. In August, I wrote about this ILCSC action, gave the motivation and charge to the committee, and anticipated that a parameters update would be the result. The parameters subcommittee has now issued its update. This revised document is very timely for us as we take the final decisions before freezing the Reference Design Report.

The ILCSC parameters subcommittee is global in nature, having members from Asia (Sachio Komamiya and Dongchul Son), from Europe (Rolf Heuer (chair) and Francois Richard) and from the Americas (Paul Grannis and Mark Oreglia). Overall, the updated report is consistent with the original and contains some clarifications, but no major changes. From our side, the Reference Design Report (RDR) that we are producing is consistent with this parameters report.

The update reaffirms that the baseline maximum centre-of-mass energy should be 500 GeV. In addition, it provides some necessary guidance to clarify exactly what that implies for the machine design. In particular the report states that "removing safety margins in the energy reach is acceptable but should be recoverable without extra construction. The maximum luminosity is not needed at the top energy (500 GeV), however, 500 GeV should be reachable assuming nominal gradient." We are in the process of analyzing what margin to provide in the RDR, but in any case, we intend to follow the key point in this recommendation -- allow for the provision of full luminosity at the top energy. This means extra un-instrumented tunnel length, providing the margin needed, will be incorporated into the baseline.

It won't be empty long

Dear FT:

Many of us from Fermilab's CMS Physics Center are at CERN this week, attending a major CMS meeting. As you know, CMS started lowering its first detectors into the underground cavern, some 300 feet below the ground (see Photo of the Day, Friday, December 1).

Boaz Klima and I were given a tour of the CMS cavern and we had a chance to take a photograph in front of a large piece of the CMS detector--the muon endcap system (called "YE+3" in the CMS lingo). The detector cavern will soon be filled with other parts of the CMS detector. This photo offers a unique view of how it looks before the entire detector is lowered into its final position to take data next year.

Best regards,
Greg Landsberg
Brown University, CMS

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