RHIC Detector Technical Advisory Committee

Report of the Meeting of January 26-27, 1996
PHENIX Muon Arms Review

TAC Members Present: Donald Geesaman (ANL), Tom Ludlam (BNL,Chair), Michael Zeller (Yale)

Consultants: David Hedin (Northern Illinois), Venetios Polychronakos (13NL)

Also Attending: Dennis Kovar (DOE-NP), Satoshi Ozaki (BNL), Alan Stevens (BNL), James Yeck (DOE-BG)

I. Summary and Major Conclusions

The purpose of this review was to provide an assessment of the readiness of the two PHENIX muon arms to begin a full-scale fabrication effort, beyond the approved RHIC construction baseline. The North Muon Arm has been a part of the PHENIX design from the outset, and is seen by the collaboration as essential to the heavy ion research program. The steel structure for this arm is part of the on-going, approved PHENIX baseline construction. The South Muon Arm, funded by RIKEN, is new, and is specifically aimed at enhancing the PHENIX capability for spin physics measurements with polarized protons in RHIC (although it too can play a significant role in the heavy ion program).

At this time DOE, with the concurrence of NSAC, has approved Additional Experimental Equipment (AEE) funds to implement the North Muon Arm instrumentation. The first of these funds have become available, and a preliminary funding profile has been worked out. A formal agreement with RIKEN has been signed for the RXIC spin initiative, and Japanese funds to begin work on the South Muon Arm are now also available. Therefore, this Committee has been asked to address the following specific issues:

Are the designs of the muon arms technically feasible, and capable of meeting the physics requirements outlined by PHENIX for the heavy ion and spin physics programs?
Are the funding resources, manpower, and the work plan presented by PHENIX consistent with a successful completion of these projects, without adverse effect on the construction, cornmissioning, and initial operation of the baseline detector?

The review agenda is given as an appendix to this report.

In answer to question l, the Committee finds that the designs for the muon arms, and the plans for their construction, installation and operation are technically feasible and, except for some detailed concerns mentioned below, are well matched to the physics measurements described by the PHENIX collaboration.

Turning to the second question, the committee was very impressed by the quality of the team assembled to construct the muon system. They have the high level of physics dedication and technical expertise required to bring this project to a very successful completion. In particular, they have considerable expertise in all areas where issues remain.

We think it is quite likely that the funding scenario for the muon system may be slower than the collaboration would desire. While the collaboration should certainly strive for operation of the muon system at RHIC turn-on, we believe PHENIX needs to make credible contingency plans for alternative funding profiles which would bring the muon arms into operation somewhat later. The committee is convinced that this is possible and that the final performance of the muon system would not suffer. This is not a statement of scientific or technical priority relative to the base detector; it is a recognition of acknowledged uncertainties in the long term plan for the DOE-supported AEE funding.

The Committee's detailed findings and recommendations are discussed in the following sections.

II. Physics Capability/Technical Design

The physics case for muon detection at RHIC is extremely compelling for both the heavy ion program and the spin program. The large acceptance for vector mesons makes this a capacity that is very desirable at RHIC turn-on, even at low luminosity. The committee is convinced that this design presented at this review is technically feasible and essentially capable of meeting the physics goals of PHENIX for the heavy ion and spin programs. The dominant technical constraints are:

The 100 micron tracking chamber resolution required to achieve , ' separation.
The 100 MeV/c2 mass resolution required for , ' separation. This is dominated by the multiple scattering in the initial hadron absorbers.
The limits background hits and tracks place on the muon trigger and track reconstruction efficiency.

In the committee's opinion, the 100 micron design goal for the cathode strip readout is challenging and may be difficult to achieve. We would recommend the coarse cathode strips be replaced with fine strips to provide an effective 40% improvement in resolution if needed. The decision to implement this higher resolution readout in the electronics could be made at a later date. Since the design is pushing the state of the art for these chambers, it is essential that more realistic simulations of the cathode strip readout should be pursued, including the detailed stripanode geometry.

Constraints on the detector associated with mass resolution and background limitations appear to be reasonably well understood in the present design. However, the collaboration needs to continually upgrade and monitor their detector simulations in regard to these issues as final engineering choices are made. It was clear that this has not happened over the past two years. In particular, the background radiation environment may be affected by design detail. We note that the current design for the South arm has less absorber thereby improving the mass resolution near the Psi , Psi '.

In terms of the installation of the muon arm components, and the impact on the overall schedule for PHENIX, it is clear that the design of the "removable" shield wall, and the time scales and effort needed to effect its removal to install large equipment after the initial operation of PHENIX, is an important consideration in the plans for implementing the muon arms. At present the design for this shield wall does not exist, and it is clear that this must be developed as quickly as possible.

III. Cost/Schedule

The time schedule for the electronics is very tight and the Oak Ridge group is heavily committed. We consider the amplifier-shaper of the cathode strip chambers to be a challenging design for 100 micron resolution with the large chamber capacitances. The full chain tests, which we see as the most important milestone, occur quite late in the schedule. The collaboration must be prepared to make serious use of the prototyping results, both to learn more about the performance of the technology and to develop strategies if prototype performance is not consistent with expectations. PHENIX management must remain abreast of the prototyping results to carefully weigh the cost/ schedule trade-offs. We believe in this case it is important to test the performance of chamber elements which are constructed with the final fabrication techniques and materials in a high-intensity test beam.

The chamber installation and repair scenarios are still far too sketchy. A significant factor in this is that there is no design for the Hall shield wall. It is imperative for the entire experiment endgame procedure and repair strategy that the shield wall design, including the installation, removal plan and capability of partial section removal, be completed as soon as possible.

In general, the committee thought the mechanical costs seemed to be on a reasonably sound basis. We considered the electronics costs to be more uncertain due to the aggressive schedules, challenging technical issues, and because final design choices have not been made in some instances. With respect to the last item, we note that the current electronics for the Iarocci tubes includes digitizing the pulse heights as an aid in monitoring the chambers' performance. The committee did not feel that this was critical, and eliminating this digitization would both simplify and reduce the cost of the electronics. However, the time available in this review did not permit an indepth evaluation of the cost estimates. We therefore recommend that:

The collaboration and RHIC management should immediately go over the cost estimate in some detail.
The muon system cost estimate should be a priority item at the next TAC review of PHENIX which is scheduled for this spring.

Appendix I

PHENIX Muon Arm Review Agenda
Brookhaven National Laboratory


8:45 a.m.	Committee executive session		(30)
9:15	Progress of Muon Activities - Overview	G. Young	(30)
9:45	Physics Program for Muon Arms	P. McGaughey	(30)
l0:15	Magnets &Absorbers	J. Thomas	(30)
10:45	Break		(15)
11:00	Tracking Chamber	D. Lee	(30)
11:30	MuID Detectors/Electronics	K. Read	(30)
12:00 p.m.	Activities in Japan	N. Saito	(30)
12:30	Lunch		(l 30)
2:00	Alignment and Performance Simulations	M. Brooks	(30)
2:30	Overview of Muon Arms Funding & Schedule	W. Kinnison	(l :00)
3:30	Integration	P. Kroon	(30)
4:00	Break		(15)
4:15	Impact on PHENIX Baseline Construction	S. Aronson	(30)
4:45	Japanese Commitments	H. En'yo	(20)
5:05	LANL Commitments	P.Barnes	(10)
5:15	ORNL Commitments	G. Young	(10)
5:25	Summary of Muon Arms	W. Kinnison	(15)
5:40	Committee executive session
8:00	Committee dinner

8:30 a.m.	Committee executive session		( 1 30)

l0:00	Report Writing		(1:30)
11:30	Closeout
12:00 p.m.	Adjourn