STAR Newsletter #84 September 2001
	Star Home Page			Editor: Howard Matis

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RICH

No contribution this month.

Period Coordinator Reports

The main focus of STAR during these two weeks was the commissioning of the STAR trigger. The trigger developments included:

Killer bits The fast detectors in the trigger are the ZDCs and the CTB. Both suffer from the problem that the signals ring. Thus a valid event can fire the discriminators for several crossings after an event takes place. This ringing confuses the scale downs and causes gaps in the TPC timing in multiples of the RHIC clock. To prevent this problem, after a trigger takes place, the following 10 RHIC clock ticks are killed by the trigger. This method was tested and checked exhaustively and shown to work properly. The resulting dead time can be calculated and a correction can be applied for absolute cross section measurements. At the design luminosity for the heavy ion program, this correction will be on the order of 1 part in 1000. (1 microsecond compared to 1 millisecond)

Prescales We implemented and checked the trigger prescales. We did the check by running a minimum bias trigger along with a central trigger with a prescale factor of 4:1. The central trigger was based on the CTB total signal which was not calibrated so the resulting data cannot be analyzed. The prescale factors were analyzed offline and worked as expected.

Minimum bias trigger The minimum bias trigger is based on the zero degree calorimeters (ZDC), east and west. The gains on the signals from the ZDCs are set so that the single neutron peak is well above the pedestal. The threshold for triggering on each ZDC is set above the pedestal and as far below the single neutron peak as practical. Several runs were taken to verify the pedestal, offset, gain, and threshold of the ZDC. The threshold is set 2.5 sigma below the peak value.

Z vertex trigger at level 0 The minimum bias trigger is composed of a coincidence between the ADC values of the east and west ZDCs. In addition, a timing signal is produced between each ZDC and the RHIC clock. These analog signals are digitized and the difference between the two values is proportional to the Z vertex position. This difference is used to trigger on events with Z vertices within ± 25 of the center of STAR. The standard minimum bias trigger will be a coincidence between the two ZDCs and a timing signal with ±25 cm. To allow the extraction of absolute cross sections by providing a measurement of the interaction diamond, a scaled down trigger comprised of a ZDC coincidence with the timing signal outside the ± 25 cm range will also be collected.

We have a plan to verify the operation of this trigger that will be carried out when the beam returns. In addition, the bunch crossing timing signals of the blue and yellow rings will be added to the minimum bias trigger.

Interleaved triggers for the TPC and SVT We have set up interleaving of laser events with data events for the TPC. This method required that the killer bits work properly. We also implemented and check an interleaved charge injection pulser for the SVT interspersed with data events. Thus the calibration of the TPC and SVT can be monitored throughout the run.

Central trigger Considerable effort was invested in the calibration of the CTB slats. The CTB slat calibration was done by using minimum bias events analyzed off line. Events with low to medium multiplicity were selected and slats were analyzed with one and only one minimum ionizing particle (mip) hitting the center of the slat. The CTB voltages were adjusted to put the mip peak at an ADC value of 5. Last year's voltages could not be used because we are now running full field and the pulse height of the CTB pmt's is strongly affected by the higher field. Currently, we think we are one iteration from having the CTB calibrated and being able to trigger on central collisions.

Once the calibration is complete, we need to choose the threshold for central collisions. We cannot choose the threshold so high that we select events that are so central that the ZDC cannot fire. John Harris had requested a 5% central trigger cut but we must be sure that we are not biasing our data by setting the central threshold too high. The current opinion is that we will run again with a 15% central trigger.

Production running with the central trigger must include the ZDC Z vertex trigger at level 0. Presumably the central trigger must also include scaled triggers not in the Z vertex range.

Peripheral collisions trigger The main effort here has been to set up the multiwire counter (MWC) of the TPC to be part of the trigger at level 0. The problem was that the signals from the MWC do not all fall in the same RHIC clock tick. Because the level 0 trigger can only trigger on information in one crossing, an effort was made to adjust the thresholds of the MWC to improve its efficiency without increasing its noise. Delay was added to the level 0 trigger to allow the digitization of the MWC to be complete before the trigger decision was made. This action added three RHIC clock ticks to the STAR level 0 trigger timing, effectively reducing the size of the TPC at large |Z| values by a few cm.

The plan for the peripheral collisions trigger is to install completely new trigger software incorporating all of the previous work on min bias and central triggers. The CTB total signal will be scaled down to free up bits that need to be used in the peripheral trigger.

Final trigger plan The final trigger will include minimum bias, central, and peripheral triggers with and without Z vertex. These triggers will include interspersed laser triggers for the TPC and charge injection for the SVT. The job of the Collaboration will be to verify that these triggers are robust and that the resulting data are analyzable.

RHIC STATUS

The first week (August 26- September 1) RHIC provided useful beam on the level of 30%. The RHIC goal to lengthen stores led to a 12 hour store (one time).

RHIC studies of longitudinal profile using 200MHz RF were continued, as well as tests of switching between running of heavy ions and slow extracted protons. The latest results show that this switch can be completed in 30 min. During the week of September 2 - September 9 there was practically no data taking. We have had beam stored and cogged a few times, but it died usually with a quentch fault in 15-20 minutes. The RHIC goal for the coming week(s) is to improve machine stability and work on understanding of process of de-bunching (loss is significantly different in short time intervals (1-2 hour) in both rings; rapid de-bunching occurs mainly in blue).

There were three scheduled down times: two access periods (to work on EMC and TOF) and one due to a DOE visit to STAR. There were two incidents (5 days apart, first at 1:30 am on August 29) where the STAR detector was blasted off with radiation. The big background current went up in all detectors 10-20 times normal levels. The RHIC ZDC signal dropped from 130 to 20 in 5 min. The first time beam recovered (by itself ?), the second time an immediate dump followed. Almost all our detectors tripped instantly. In both cases, beam loss monitors did not register losses. Other experiments were not affected. There is a plan to install a chipmunk detector in the STAR area to help with diagnostics. This needs to be followed up.

Phobos reported another (similar) blast last week. This one triggered alarms in the MCR. Fortunately Phobos detectors did not have HV on due to some other work in progress.

At the 9 am meeting (September 10) Tom Kirk said that the RHIC DOE review (last week) concluded the following:

start-up of RHIC is as expected for a machine of such complexity

RHIC plan of addressing (attacking ?) problems is very good

STAR STATUS

These two weeks were devoted to defining the production trigger for this year's run. The STAR Trigger Board made the following decisions (See Star Trigger Board Summary Minutes of 9/6/01 for details):

Minimum Bias Set - includes the following three triggers

Hadronic MB (all detectors read out

UPC MB (all detectors except SVT in data set)

HiMult (all detectors in data set)

Central Set - includes the following two triggers

Hadronic Central

HiMULT (all detectors in data set)

The Minimum Bias Set trigger was implemented, and all 3 components were tested separately (but without the SVT). The Production MinBias trigger was not, however, tested in its final version (all components of mixed trigger together). It is ready and waiting for beam. There was a problem with > 33K CTB part of the ProductionMinBias trigger. This was solved by swapping the Layer2 CTB-MWC DSM Board. The new DSM board seems to work fine. During the time of setting up and fixing of the production trigger (ProductionMinBias), the MinBiasVtx trigger was run .

The CENTRAL Trigger is not set up yet. The first test of the UPC Topology Trigger was successful. A second test, with modified parameters, yielded zero triggers.

SUBSYSTEM STATUS

Magnet - Starting August 30, the Space Trim East power supply kept tripping. We were not able to run with the full field (despite the presence of good beam!). We took a few shifts with 1/2 field. The problem was fixed by bypassing the breaker. A new breaker was ordered and it will be installed as soon as it arrives.

FTPC - there was a temporary situation in which the FTPC started to show serious problems, i.e. no tracks seen. This was cured by changing the gas bottle.

SVT - was taken out of the run a number of times due to DAQ 100% busy. A noticeable increase of the SVT occupancy was reported a number of times, and SVT experts were informed.

EMC - timing tests in progress. Tests show some problems with data handling.

TOF, Pi_zero - detectors are in the process of commissioning.

RUN SUMMARY

As of today we took slightly over 2.5 M MinBiasVtx events. The RunLog Browser provides information run-by-run.

Organizational items:

hourly check list was instituted (similar to last year)

role of on-line and off-line QA were revisited (see my note from Period Coordinator hypernews August 27)

QA weekly feedback to PC/ShiftLeaders was included into routine

New meeting (between "software" and "hardware" parts of crew running STAR) was instituted: Monday, 2-3 PM, with phone bridge. First meeting next Monday (September 17).

It was agreed that at least one person from software /analysis crew will be present at one of run meetings (10 am or 5 PM) every day.

Things to be followed:

Due to RunLog problems (it stalled practically every day. Later, the problem was found and fixed) there is a significant lack of comments for runs taken last week. Those comments can be entered either at the site or via the RunLog web interface. Shift leaders have been asked to enter comments related to their shifts. Particularly important is to state which runs should not be considered for the analysis.

From QA off-line report:

There are characteristic dips in the z-dependent TPC hit distribution at low multiplicity events - this needs investigation.

The excessive number of tracks with a very low value of dE/dx divided by Bethe-Bloch for pions. It was suggested that this is just the tracks for which dE/dx failed, which then receive a value of 0 and that go into the first bin. The horizontal axis is logarithmic and therefore, this first bin looks big. Yuri is supposed to check this out for sure.

Physics Working Groups - (See the protected area)

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

	Coming Milestones

Announcements

None this month

Employment Opportunities

Max-Planck-Institut fuer Physik, Muenchen: Postdoctoral Position

Max-Planck-Institut fuer Physik, Muenchen, offers the postdoc-position of an Experimental Physicist (Ph.D.) with experience in particle physics and in particular in data processing. The applicant is expected to participate in running and evaluating the STAR heavy-ion experiment at RHIC, where our group contributes the two Forward Time Projection Chambers (FTPCs) with radial drift field. The contract will be initially for two years with the possibility of an extension. The place of work will be the Munich institute while longer stays at BNL are also expected. Applications, together with a curriculum vitae, a list of publications and the names of three references, should be sent to Prof. N. Schmitz, Max-Planck-Institut fuer Physik, Foehringer Ring 6, 80805 Muenchen, Germany. For more details you may also contact: V. Eckardt at BNL, phone: 631-344-3121 or E-mail: voe@mppmu.mpg.de.

Creighton University: Faculty and/or Staff

Creighton University anticipates an opening for a faculty and/or staff position. We seek candidates who enjoy working with students in an academic and research setting and communicate effectively in English. For more information, please contact Janet Seger by email (jseger@creighton.edu) or phone (402-280-4709).

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