STAR Newsletter #85

TOFp - (Bill Llope)

When we joined the data stream in August (run >= 2237001), we saw the pVPD working great but immediately noticed a problem with the FEE in the TOFp tray. The ADC spectra were perfect - 39 of the 41 TOFp channels showed clear peaks corresponding to MIP hits at the expected values. The timing side however indicated the problem, which had two features: large (few hundred mV) DC offsets on the ADC path in each TOFp channel, and large effective thresholds on the TDC path. The ADC offsets were addressed with the usual trick of AC-coupling at the ADC inputs, leading to the good ADC data mentioned above. The large effective threshold feature was however not something that could be addressed from the platform (although we tried). At that time, there were ~10 channels that appeared to still work reasonably well despite this effect, so we stayed under STAR Run Control and took data...

After extensive discussion and a new series of tests of the TOFp FEE boards at Rice, we believe we have determined the cause of the problem: damage to the AD96687BR comparators due to occasional but catastrophically large particle fluxes. In the last week, we have investigated this problem with spare TOFp FEE boards on the bench. The FEE boards were shown not to fail if the inputs are pulses as large as 18 V (note single MIP hits have pulse heights that average 0.5V). However, if one tries even harder to damage a board, i.e. by removing a 50 Ohm terminator at the very front then connecting a 30V DC *level* from a power supply directly (!), it is possible to damage the comparator and produce exactly the symptoms seen at BNL. This implies that, on several occasions, the TOFp tray saw *huge* catastrophic fluxes of particles for brief periods, and over time these catastrophic particle fluxes were enough to slowly kill the comparators.

As of September 12, the pVPD was still working just fine. However the efficiency of the tray FEE for providing stops for hits had decreased to such a low level that it then made more sense to just shut the system down and wait for the first opportunity to physically repair the damaged components. This work requires the removal of the East Pole tip, and we have requested that STAR Operations schedule this to occur, at the latest, during the pre-proton-running shutdown. When this access occurs we'll get inside the tray, fix this problem, improve the input protection, and then rejoin the party. As the problem has been reproduced on the bench, the work required to restore the system to good health is known to involve

the replacement of 41 comparators in the tray, and

the addition of one Schottky diode per channel and a common Zener diode per board,

which will limit any input to the comparators to a maximum of about 4V. This will insure the tray FEE do not suffer from such catastrophic accelerator behavior in the future. This work just involves some soldering and is estimated to take 16 hours, including testing, once we have gained access to the tray interior.

While we were live and officially under STAR run control, STAR took the following numbers of events:

Trigger	# of events
MinBiasVertex	1924573
MinBiasVertexCTB100SVT	118884
MinBiasVertexSVTTest2	9661
MinBiasVtxCTB75noSVT	20499
MinBiasVtxMip15noSVT	9985
Topology	49072
15PerCTB	7027
15PerCTBVertex	18460

That is, there are approximately 2M minimum bias events (~100k in top 5%) plus ~25k events in CTB-based central triggers, which include TOFp information. We expect that these data will support some reasonable analyses, so while we wait for tray access we are now concentrating on that, i.e. software.

The TOF maker needed to insert the TOFp raw data onto the DSTs was released last week. Changes to StEvent were required which were done by Thomas Ullrich early this week. This will allow us to (more quickly and conveniently) perform all of our "higher-level" offline analyses (slat calibration, track extrapolation, track <-> slat matching, and PID) using the DST data sets. The production pass through the 2001 data which will begin in a week or so will thus include this TOF maker. Other makers under development in the group are already investigating the "higher-level" analyses. Root routines for the slew corrections, as well as early versions of the track extrapolation and track <-> slat matching algorithms are already in place in local versions and are being improved using small sets of raw data. Once the DST data is in hand in a few weeks, these routines will be moved down from the raw level to the DST level and the code development towards producing spectra will continue.

	production events	hadronic min-bias (Z vertex cut)
Aug. 15 - 21	302.3	202.0
Aug. 22 - 28	677.0	451.3
Aug. 29 - Sept. 4	506.9	338.0
Sept. 4 - 11	923.7	809.4
Sept. 12 - 18	1633.5	615.8
Sept. 19 - 25	716.7	363.0
Sept. 26 - Oct. 2	1827.8	1046.3
	6587.9	3835.8

About 1M hadronic min-bias events were taken with the normal polarity, the rest with the reversed field.

In conclusion, a large part of the envisaged 5M min-bias events are on tape. The central collision program is starting now. There is hope to achieve the goal of 5M events thanks to the increased DAQ recording rate.

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

	Transitions Gaspare Lo Curto : Accepting a position at ESO in Chile Andreas Schuettauf : Joining the FOPI experiment at GSI Helen Caines has left Ohio State to take a Research Scientist position in the Relativistic Heavy Ion Group at Yale University. Helen will continue in her role as SVT Software Leader and Strangeness Physics Working Group Co-Convenor. Milestones Manuel Calderon has completed his Ph.D. at Yale on "Charged Hadron Spectra in Au + Au Collisions at sqrt{s_NN} = 130 GeV" from STAR data.

Announcements

I have been asked to duplicate John Harris' announcement . "It is a pleasure to announce that the Council has voted unanimously to admit into STAR the Chinese groups from the University of Science and Technology (Hefei), Tsinghua University, Shanghai Institute of Nuclear Research, and the Institute of Modern Physics (Lanzhou). These groups have stated a commitment to the Barrel TOF upgrade project in STAR and to the current STAR scientific program. I wish to welcome them into STAR and look forward to their active participation in all aspects of the program."

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: Tenure-Track Faculty Position

Creighton, a Jesuit university committed to excellence in the liberal arts tradition, has been rated the #1 comprehensive Midwest university for 5 of the past 6 years. It is located in downtown Omaha, a vibrant community of 600,000. The Physics Department offers both BS and MS degrees. For a tenure-track Assistant Professorship, beginning August, 2002, we seek candidates with effective communication skills who will share our commitment to outstanding teaching and to involving undergraduates in research programs. Preference will be given to experimental condensed matter or quantum electronics physicists. A Ph.D. is required. More information about our department and this position is at http://physicsweb.creighton.edu. Submit a current C.V., transcripts of all college-level work, a statement of teaching philosophy, evidence of successful teaching (if available), and a research plan, and arrange to have 3 reference letters sent to Dr. Janet E. Seger, Search Committee Chair, Physics Department, Creighton University, Omaha, NE 68178, jseger@creighton.edu. Review of applications will begin Dec. 1. Creighton is an EO/AA employer and seeks a wide range of applicants in support of our core values--gender, ethnic and cultural diversity.

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