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STAR Newsletter #89

February 2002
Star Home Page
Editor: Howard Matis

Contents

  1. Spokesman's Column
  2. STAR Operations
  3. STAR Council
  4. Detectors and Subsystems
  5. Period Coordinators Report
  6. Physics Working Groups (protected area) No contributions this month
  7. People: Comings and Goings
  8. Announcements and Notes
  9. Employment Opportunities

Spokesman's Column (Tim Hallman)

No contribution this month.

STAR Operations (Bill Christie)

No contribution this month.

STAR Council (Jay Marx)

February 8, 2002 marked a landmark meeting of the STAR Council. In addition to the first election of a STAR Spokesperson, Council representatives from almost all STAR institutions participated in very active discussions on a number of issues that will have a considerable influence on the future of the STAR Collaboration and on how the Council itself does business. In this article I will try to give both a flavor of the discussions that took place and an indication of the important decisions that were taken.

Following the introduction of members including the new representatives of the junior members of the Collaboration, the initial order of business under the new Collaboration Bylaws that were adopted last November was for the Council to conduct the Collaboration's first Spokesperson election. On the first ballot the Council elected Tim Hallman as STAR Spokesperson for a three-year term.

The Council congratulated Tim on his election and welcomed Tim in his new role as STAR Spokesman. The Council unanimously expressed its thanks and deep appreciation to outgoing Spokesperson John Harris for his effective leadership of the Collaboration since its formation and throughout the design and construction of the experiment and the initial data taking and physics program and for his many seminal contributions to STAR.

Personally, I want to express my profound thanks and gratitude to John for all he has done to bring STAR to where we are now producing important and exciting physics results in just a short time after the first collisions at RHIC. He and I have worked closely together for many years and it has been a real pleasure. And I know that John will continue to make important contributions to STAR and to our physics.

I also want the Collaboration to know that I have complete confidence that Tim will continue the high level of leadership that this Collaboration has come to expect from our Spokesperson. Tim and I are committed to continue to work together as we have in the past to do all we can for the benefit of the Collaboration and to enhance our physics productivity. The Council will be working with Tim in a constructive way to achieve these goals. I urge all of you to join me in rallying behind Tim and giving him your complete support.

Following the election the Council discussed a proposal to establish a STAR Advisory Board to advise both the Spokesperson and the Council on issues of major importance to the Collaboration. The Council voted to charter the STAR Advisory Board for a 1-year period after which the Council will evaluate the benefits of the Board and decide whether it should continue and in what form.

The working philosophy behind the Advisory Board is that it collectively has broad scientific judgment, technical expertise and realistic knowledge of the status, capabilities and available resources of the experiment and of the Collaboration. The Board is advisory to both the Council and Spokesperson, based on in-depth study of issues of major importance to the Collaboration. It is proactive with mandated periodic (every two months) meetings with the agenda set by the Spokesperson in consultation with the Council Chair. Meetings at shorter intervals to discuss specific issues will be called as needed and minutes from the meetings of the Advisory Board will be made available to the Collaboration except for special circumstances requiring executive sessions.

The STAR Advisory Board will consist of up to 12 STAR members, including the Spokesperson, Deputy Spokespersons, Council Chair, Deputy Council Chair and Physics Analysis Coordinator. The Council will elect six additional members: three from the collaboration at large, one from the STAR Operations Group and two from the ranks of the Physics Working Group Convenors. Should the board's charter be extended beyond a year, the latter six elected members of the Advisory Board will serve staggered two-year terms. The Council Chair will receive nominations for these seats from Council representatives and so I encourage you to suggest the names of collaborators who would be effective members of the Board to your Council representative.

As you may know, the Council has expressed its intention to become more active in the affairs of the Collaboration than in the past. The Council chair proposed that the Council establish working committees of the Council in a number of areas that are germane to the Council's role in the Collaboration. After much discussion the Council charged the chair to draft working descriptions for several committees in consultation with the Spokesperson. Some committees would have membership drawn from the Collaboration at-large in addition to having strong representation from the Council. Based on these descriptions the Council will consider whether to establish these committees with a decision taken by E-mail vote.

If these Council committees are established, and after consultation with Council representatives and the Spokesperson, the Council chair will propose their membership for approval by the Council. The Council Committees that are being considered are a publications committee, a talks committee (this would be derivative of the existing talks committee), a service work committee, a collaboration resources committee, and a committee to help develop the physics vision of STAR for the intermediate and longer range future.

The Council then discussed the broad issues related to service work in the Collaboration. An important part of this discussion was a presentation of the views of the junior members of the Collaboration. In particular, the willingness and even enthusiasm of the junior members of the Collaboration for contributing in this area, the importance of all Collaborators doing so, and the value of providing an environment that motivates such contributions were emphasized.

The Council recognizes the essential need for adequate service work and shift work by the Collaboration so that the experiment can be successful. The Council views the STAR institutions as the basic unit for assigning and evaluating such contributions and it is on this basis that a Council service committee would monitor and enable service work by the Collaboration.

After lunch the Council heard a presentation by Tom Ludlam that described the activities and time-scale for STAR to participate in both R & D and proposals for upgrades related to Brookhaven's desire to increase the RHIC luminosity by an order of magnitude utilizing electron cooling of the heavy ion beams. The Brookhaven plan aims to begin construction of both the accelerator and detector upgrades in fiscal year 2005. Several Council members expressed the view that this date is very optimistic in light of the priorities set by the recent NSAC Long Range Plan for Nuclear Physics. Two key near-term activities will be a STAR workshop to further the process of framing a compelling physics vision as a basis for upgrading STAR and the submission of proposals to Brookhaven for detector R & D aimed at the detector upgrades. The Council reiterated the importance of the Collaboration pursuing more immediate upgrade opportunities and that the funding is expected to be available to begin such upgrades in the next year or so, independent of the funding for the luminosity upgrade. The Council then approved the Council chair's request to select (with the Council's approval) an interim Deputy Council chair for the one-year period until the election of a Deputy Chair under the new Bylaws.

This was followed by a far ranging discussion by the Council about how the Collaboration can best organized itself to analyze the data and produce physics output. The value of the physics working group structure was discussed as well as some of the problems that have arisen. This discussion provided important input to Tim Hallman as he considers these issues. .

After a coffee break the minutes from the December 7, 2001 meeting were approved. Minutes from the Council meetings can be accessed from the STAR web site under "STAR Council".

Hans Georg Ritter, the STAR Shift Coordinator then presented a report about his experiences as shift coordinator and his suggestions for solving some of the problems related to providing adequate coverage for shifts during the run. .

Finally, the Council discussed and approved a change to the Bylaws requiring an affirmative vote of 75% of the Council for new groups to join the Collaboration.

As Council chair I want to emphasize how pleased I am with the new activist spirit in the Council. I am convinced that the result will be a more effective Collaboration and an increased responsiveness to the needs for improvement in how we go about our business of doing physics at RHIC.

Detectors and Subsystems

FTPC (from Volker Eckardt)

After the problem with the CO2 gas was understood and solved, the FTPC worked smoothly. All the data taken starting from early November to the end of the run are good and stable. We believe that the gas problem was caused by contaminated gas cylinders provided by the vendor. All of the time, the newly installed drift velocity monitor worked and delivered important calibration data.

Significant progress was also made with the reconstruction of event and laser tracks. A first production run of 80k minimum bias events was performed and showed good symmetric behavior between both sides. This analysis gave us our first physics distributions.

Finally, I would like to thank all my colleagues and specially the detector operators who helped take care of the FTPC during this long run.

Slow Controls (from Mike Cherney)

No news from slow controls this month.

EMC (from Alexandre Suaide)

No contribution this month.

TPC (from Blair Stringfellow)

The TPC completed the recent run in good shape. We used the shutdown between AuAu and pp running to replace two RDOs on the west side. At the end of the run all RDOs were functioning. For the entire run, since the beginning of July, the TPC took data with minimal trouble.

Over the long shutdown, we have two major projects:

The only down note is that one section of an outer sector (1/4 of the sector) no longer holds HV. All tests indicate that the problem is inside the TPC, possibly on the high voltage distribution board. We have no plans at this time to remove and repair this sector.

Level 3 Trigger (from the commissioning contingent)

No contribution this month.

Endcap EMC (from Will Jacobs)

No contribution this month.

RICH

No contribution this month.

TOFp - (Bill Llope and F. Geurts)

In our last contribution, we described the successful repair of the FEE comparators. Soon after these repairs were done, problems began with the LV power supply for the pVPDs. On Oct. 20, we swapped the power supply. Unfortunately the FEE fuse of the east pVPD blew. For more than two weeks TOFp ran in a single pVPD mode requiring only a 2-out-of-3 coincidence on the west pVPD. The analysis of this data will require the primary vertex from tracking to do the timing analyses, but otherwise we don't expect the performance to be significantly degraded.

On Nov. 8 we were able to replace the east FEE and switched back to the original 2-out-of-3 mode for east and west coincidences. Throughout the remainder of the run, there was a usual assortment of failures in only a handful of channels (FEE board fuse, timing channel of one slat, HV cells). For the 20 GeV run on Nov. 25-26, TOFp collected data without any modifications to its 200 GeV set-up.

For the p+p run, no specific run plan for TOFp existed other than providing a pre-trigger to the RICH. Some estimates predicted the pVPD triggering efficiency would be < 1 % per p+p event. Without a start signal from the pVPD the TOFp tray will not run either. The RICH detector overlaps with the lowest rapidity 30% of the TOFp tray. The discriminated signals of those 13 TOFp slats are provided as an OR-ed signal to the RICH logic. We kept the local DAQ running and left TOFp in the STAR data stream during the full p+p run. A much looser pvpd trigger condition was used in the p+p running.

Based on a preliminary analysis of our local p+p data (all TOFp data is stored for 1 out of 10 STAR events to a local disk), this trigger turns out to be 60% efficient. In fact in 13% of the STAR triggers, there are east-west coincidences which allow one to measure the z-position of the p+p vertex. A better start timing resolution is possible, when more than one pVPD channel fires in a given event.

During last year's Au+Au and p+p run, the TOFp system collected roughly 2.8M central and 1.47 minimum bias Au+Au events at 200 GeV, 72k central and 216k minimum bias Au+Au events at 20 GeV, and approximately 21M p+p events at 200 GeV. The TOFp systems did not miss a single event in the p+p run and performed without any problems or hassles to the shift crews.

More analysis is under way in which we work to understand the timing offsets and many other corrections. At the last collaboration meeting, we showed some of our preliminary results on the tracking & extrapolation algorithm and how it successfully reproduces slat propagation times, which we measured earlier on the bench. While the raw data together with the TPC track information comes more and more available, we can impose stricter cuts and determine other corrections (e.g. start time, slewing, timing offsets, more accurate propagation times, etc.) more accurately.

Period Coordinator Reports

Harold Spinka (December 31 - January 11 )

SUMMARY: The pp run had some successes and some problems during the past two weeks. Since the start of the pp run, approximately 12 M min bias events have been collected. The FPD and BEMC have been commissioned, and both have collected some data. However, the beam polarization has been low, and production polarized data have not been collected yet.

RHIC: Beam was delivered to STAR (as measured from the time it was cogged or steered until we were asked to power down) about 155 hours, or roughly 49% of the available time. The luminosity rose to over 10^30 at the start of fills, with a typical average of 5*10^29. The integrated luminosity delivered to STAR from the beginning of the pp run is on the order of 240 nb^-1 or 0.24 pb^-1, using the STAR calibration for the BBC's; van der Meer scans suggest this calibration may be low by ~20%. The interaction diamond has been approximately constant with a standard deviation of about 80 cm. An attempt to rebucket the bunches worked only marginally and has been abandoned for further running this year.

There were many short accesses - I lost track of the total time involved for these. Some accesses were mandated by work on the Westinghouse MG set, needed to operate the AGS.

At the beginning of this period, the focus of the accelerator work was to increase the luminosity. A significant change was noted early, and continued improvements have occurred. However, some of this came at the price of shorter beam lifetimes, more background in all the detectors in RHIC, and in time spent developing new tunes. The polarization also dropped! The focus then shifted to improving polarization and maintaining the present luminosity at the planning meeting on Wednesday, Jan. 9. The flattop asymmetry in the yellow ring (of importance to the FPD measurements) returned to previous levels, but the inferred polarization remains generally below 20%.

The phase-locked loop (PLL) on the accelerator tune has received a lot of priority and effort, and it was recently decided to concentrate on its use for down ramping. The down ramping is needed to attempt a measurement of the RHIC polarimeter analyzing power at flattop. Only one down ramp was attempted, and resulted in a RHIC magnet quench. More studies are planned.

STAR: Most of the detectors operated well during the period. There were the usual number of minor trips, but no major breakdowns. The magnetic field was reversed, causing a problem with an SVT power supply; this has been remedied. One magnet trip occurred and there was a delayed alarm from the slow controls. The SVT was operated again after a couple days "warm-up".

The FPD was fully commissioned and operated for systematic studies while awaiting higher beam polarizations. The scalers have been implemented and tested. A total of ~1.1 M triggers have been collected, all with low polarizations, which will be used to study systematic errors in these spin measurements.

The BEMC trigger and ADCs are now both operational, and some test runs with the BEMC trigger have occurred. However, only a part of the presently implemented system is operational due to problems with the high voltage for some phototubes. "High" or "hot" towers have been masked off in the trigger.

It was decided not to use the CTB trigger at present because of the weak correlation between summed CTB signals and the number of tracks in the pp event. This decision may be revisited if new evidence becomes available.

STAR was operated and collecting data for roughly 70% of the available time, with an additional 5% in various downtime (DAQ or L3 problems usually). The remainder of the time was to bring the detectors and magnet up at the start of the store, to start and stop runs, and to change triggers. The shift crews and on-call experts deserve our thanks for keeping this "lost" time to a minimum.

Based on a projection to the end of the pp run, we will be close to the goal of 20 M min bias events. It is unclear whether the RHIC polarization will be high enough to make a good FPD spin measurement, however.

Les Bland (January 12-24)

STAR operations: No major problems were encountered in the last two weeks of the run. Most of the data acquired in this period include all of the detector subsystems. There were two major achievements during this period:

The success in commissioning the high-tower trigger, combined with the excellent progress made earlier in the proton run towards the goal of recording 20M minimum-bias triggers, prompted a shift in emphasis for the data collection at the end of the run. Most of the data collected in this period used a trigger mix emphasizing rare triggers. The trigger mix included a prescaled minimum bias data sample, a BEMC high-tower trigger requiring more than ~2 GeV energy deposition in a single BEMC tower, and events with large energy deposition in the forward pi0 detector (FPD). The typical event rate for this trigger mix was ~20 Hz at a luminosity of ~10^30 cm^-2s^-1. The system live time averaged 70%, as required to have good efficiency for rare triggers.

As noted in the summary of RHIC operations below, stable beam operations required that all of the data collected in this period were obtained with a single magnetic field setting (full field, polarity A).

Details of the runs taken during this period are given in the table below. An overall summary of the triggers recorded in this period is:

Trigger Trigger Word Total Number of Events
Minimum Bias 0x2000 3,500,000
BEMC high tower 0x2003 670,000
FPD (including BBC condition) 0x2004 2,200,000

Of order 10^9 counts were recorded by the STAR scaler system in the last ~5 days of the run. This data sample provides great statistical precision to look for small spin effects at the trigger level, and also provides important systematic error checks.

In addition to the primary data collection, addressing both primary objectives of obtaining a pp reference data set for the heavy-ion physics program and spin asymmetries from polarized proton collisions, several special runs were also completed, including:

Several (generally minor) problems were encountered in this period:

As an overall summary, the STAR detector systems worked quite well throughout the polarized proton run. A significant fraction of STAR's physics goals will most likely be met from the data obtained.

RHIC operations: For this period, the luminosity and up time of the collider was generally good. For the entire period, the average luminosity was 0.6x10^30 cm^-2s^-1. My count of total fill time used for STAR physics runs was 144 hours, of the total possible 288 hours from 12-23 January, corresponding to a 50% up time for the collider. Excluding the begin-of-fill calibration runs (pedestal runs, etc.), STAR recorded physics data for 93 of these 144 hours. The integrated luminosity seen by STAR during data recording was 0.2 pb^-1 in this period, spread over 24 different fills of the collider.

In general, the Yellow ring performed more stably than the Blue throughout this period. Typical stores resulted in much shorter beam lifetime in Blue. At the C-A meetings, this phenomenon was attributed to beam emittance effects (an asymmetry in beam size resulted in the `big beam' continuing to increase in size; an unstable situation).

More attention was paid to polarization by C-A throughout this period. Significant efforts were expended to try and improve the polarization from the AGS. No substantive improvement was achieved, with the beam polarization at extraction averaging 25%. The low polarization was attributed mostly to the smaller acceleration rate in the AGS, due to the forced utilization of the Westinghouse motor generator. The polarization in the Yellow ring, as measured by the Coulomb-nuclear interference (CNI) polarimeter at 12 o'clock, averaged ~15% at 100 GeV/c through this period. The polarization was generally much more stable in the Yellow ring than the Blue, except for a 1-day period around 19 January, when tuning adjustments were made to compensate for a change in the PHOBOS magnet polarity. The polarization in the Blue ring was generally lower, and had much larger fill-to-fill variations.

The conversion from measured CNI polarimeter spin asymmetries to beam polarization at 100 GeV/c is based on the assumption that the analyzing power for p+12C elastic scattering does not substantially change between RHIC injection energies, where a calibration has been measured, to 100 GeV/c.

Several attempts were made to commission a deceleration of the RHIC beams. The motivation was to calibrate the effective analyzing power of the CNI polarimeter at 100 GeV/c using a method where the beam polarization was measured at injection energy, once again after the beams were ramped to full energy, and once more after the beams were ramped back to injection energy. If the asymmetries are the same before and after the ramp, then the effective analyzing power of the CNI polarimeter can be deduced at 100 GeV/c. Smaller measured asymmetries following the down-ramp would imply polarization loss, either on the up- or the down-ramp. Difficulties in controlling the beam chromaticities resulted in consistent beam loss at gamma=50 during the down ramp. This was attributed to lack of detailed knowledge of the hysteresis loop traversed in the down ramp. Measurements of this part of the hysteresis curve will be required before down ramps can be successful in next year's run. Deceleration of the beam will remain the primary method of determining the beam polarization at the flat top, until a polarization calibration planned with a polarized atomic hydrogen gas jet can be performed.

A final note on the CNI polarimeter should be mentioned. Data analysis performed during the run by Hal Spinka, Jeff Wood and Bernard Surrow, revealed several apparent systematic errors with the CNI polarimeter. Careful offline analysis of this data will be required to provide reliable spin asymmetries that can be used for normalizing spin asymmetries measured at STAR and by the other experiments.

In addition to the down ramps, a means of rapid polarization reversal of the bunches stored in RHIC was developed. This so-called `spin flipper', makes use of an AC dipole to induce a resonance. As the AC dipole frequency is varied across this resonance, the beam polarization flips its sign. The AC dipole can also be used to establish the `spin tune' of the RHIC rings. This provides a diagnostic of the operation of the helical dipole magnets (Siberian snakes). At least one successful spin flip was made during the RHIC AC dipole commissioning at the end-of-store machine development time.

RHIC fill #2267 on 19 January was a 6-bunch store. This was a test for the pp2pp experiment. STAR data was collected with a minimum bias trigger during this store (runs 3019040-45). The last day of the run was devoted to the pp2pp experiment. Low intensity beams were ramped with the beta* being increased from its injection value of 3m to 10m. This beta* value was required by the pp2pp experiment to look for proton-proton elastic.

Physics Working Groups - (See the protected area)

No contribution this month.

This section contains summaries of the status of the physics working groups. These articles are in a protected area for STAR collaboration members only. This link uses the standard STAR account and password for physics results. If you do not have this information, please contact your council representative.

People

Announcements and Notes

NIM Articles Available for Preview by Jim Thomas

I am pleased to announce that the NIM articles dedicated to the detectors at RHIC are nearly complete. As you may know, we are preparing a volume with Tom Ludlam and Satoshi Ozaki as the general editors, and I am the STAR editor. The volume will contain contributions from all four experiments plus the accelerator team. The volume will be over 600 pages long and the STAR contributions will occupy over 200 of these pages. Since this is a writing effort that involves many people, we have to wait for everyone to finish writing before we can submit the volume to NIM A and the most recent estimate from PHENIX is that they will complete their final article by February 15th. So I have been encouraging our authors to finish 10 minutes before they do! I believe the articles will be ready to go to the publishers before the next edition of the Newsletter hits the newsstands. You can see from the enclosed web reference that we are essentially ready to go. We have a few details to clean up and we have to choose a small number figures to be printed in color. Apart from this modest amount of work, we are ready to go. Please have a look. Your comments are welcome and they should be sent directly to the principal authors or to me.

STAR Junior Council by Kai Schweda

During the last week of January, the STAR-juniors elected three new representatives by an E-mail vote. These representatives are Mercedes Lopez Noriega (OSU), Zhangbu Xu (BNL) and Kai Schweda (LBNL). They will represent us in the council meeting for the next two years. We thank the former representatives Lee Barnby (Kent State), Manuel Calderon de la Barca Sanchez (BNL) and Frank Laue (BNL) for doing an outstanding job in the past 18 months. They represented our interests in the council meetings and organized the traditional barbecue during collaboration meetings.

Minutes from the STAR-juniors meeting on February 6 are below:

During the recent collaboration meeting at BNL, the STAR Juniors held their meeting on Feb. 6. 51 out of 109 STAR-juniors attended. In a constructive and fruitful discussion, the topic of service work was addressed. Unanimously, the STAR-juniors feel that service work is useful and necessary to keep the collaboration going. Furthermore, it provides the opportunity for young people to educate themselves on a topic they find interesting and which later might help in finding jobs in industry. People who are doing service work should be given more credit, e.g. by sending them to conferences where they can give physics talks. These conclusions were then reported at the council meeting. We thank Liz Mogavero and the STAR management for providing excellent food and beverages at the STAR junior meeting.

It should be emphasized that within the STAR-juniors (who comprise a quarter of the whole collaboration), we have an enthusiastic atmosphere of collegiality and even friendship. This makes working together much more effective and spending time together a lot of fun.

Employment Opportunities

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