In this work, we describe some recent results concerning the application of Resistive Plate Chambers operated in avalanche mode at atmospheric pressure for high-resolution time-of-flight measurements. A combination of multiple, mechanically accurate, thin gas gaps and state-of-the-art electronics yielded an overall (detector plus electronics) timing accuracy better than 50 ps [sigma] with a detection efficiency up to 99% for MIPs. Single gap chambers were also tested in order to clarify experimentally several aspects of the mode of operation of these detectors. These results open perspectives of affordable and reliable high granularity large area TOF detectors, with an efficiency and time resolution comparable to the existing scintillator-based TOF technology but with a significantly, up to an order of magnitude, lower price per channel.http://www.sciencedirect.com/science/article/B6TJM-45F4WHB-7/1/95e90d633532cd93d712a5bfad6b902

Fonte, P.

Peskov, V.

Staff Senate

The Keep

September 9, 1993

Estudo Geral

Nuclear Instruments and Methods in Physics Research A 477 (2002) 17–22
High-resolution TOF with RPCs
P. Fontea,b,*,1, V. Peskovc
aCERN-EP, Geneva, Switzerland
bLIP-Coimbra, Dep. de Fisica, Universidade de Coimbra, P-3004-516 Coimbra, Portugal
cRoyal Institute of Technology, Stockholm, Sweden
Abstract
In this work, we describe some recent results concerning the application of Resistive Plate Chambers operated in
avalanche mode at atmospheric pressure for high-resolution time-of-ﬂight measurements. A combination of multiple,
mechanically accurate, thin gas gaps and state-of-the-art electronics yielded an overall (detector plus electronics) timing
accuracy better than 50 ps s with a detection eﬃciency up to 99% for MIPs. Single gap chambers were also tested in
order to clarify experimentally several aspects of the mode of operation of these detectors. These results open
perspectives of aﬀordable and reliable high granularity large area TOF detectors, with an eﬃciency and time resolution
comparable to the existing scintillator-based TOF technology but with a signiﬁcantly, up to an order of magnitude,
lower price per channel. r 2002 Elsevier Science B.V. All rights reserved.
PACS: 29.40.Cs
Keywords: Gaseous detectors; Time resolution; TOF; RPC
1. Introduction
Heavy-ion Collision physics at very high en-
ergies is emerging in many accelerator centers
around the world (RHIC at BNL, SIS at GSI, and
LHC-HI at CERN), emphasizing the need for
large area particle identiﬁcation systems able to
cope with high particle multiplicities. Time-of-
ﬂight (TOF) sub-detectors, in particular, are fore-
seen for many such experiments (STAR, FOPI,
ALICE), stimulating R&D on new, more cost
eﬀective, approaches to the timing of MIPs.
In this paper, we describe some recent work
done in the framework of the ALICE experiment
on the development of Resistive Plate Chambers
(RPCs) for TOF measurements (timing RPCs).
The work included beam tests of single chambers
and of a multichannel TOF prototype equipped
with such chambers.
Some studies aimed to clarify experimentally the
origin of the very good detection eﬃciency (99%)
observed for MIPs in our timing RPCs will be also
described.
2. Experimental setup
Details on the mechanical construction, electro-
nics, experimental setup and data analysis for the
*Corresponding author. LIP-Coimbra, Dep. de Fisica,
Universidade de Coimbra, P-3004-516 Coimbra, Portugal.
Tel.: +351-239-833-465; fax: +351-239-829-158.
E-mail address: fonte@lipc.ﬁs.uc.pt (P. Fonte).
1On leave of absence from ISEC, Coimbra, Portugal.
0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 8 - 9 0 0 2 ( 0 1 ) 0 1 9 1 4 - 3
timing RPCs were already given elsewhere [1,2]
and we will describe here only the few modiﬁca-
tions introduced for the single cell tests.
Timing RPCs were made with glass [1] and
aluminium electrodes forming a pair of double-gap
chambers. The four gas gaps of 0.3mm were
accurately deﬁned by glass optical ﬁber spacers.
The single gap RPCs were built essentially along
the same lines, being a schematic drawing shown
in Fig. 1.
The signals were sensed by a custom made pre–
ampliﬁer [2], whose output was split in three
identical channels via analogue buﬀers. One of the
outputs was directly fed to a LeCroy 2249W ADC
that measured a charge proportional to the total
signal charge. Another output had the ion signal
component (1 to 3 ms long) cancelled by forming
the diﬀerence between the signal and it’s image
delayed by 16 ns. A LeCroy 2249A ADC inte-
grated the resulting short pulse, measuring a
charge proportional only to the electron (fast)
component of the signal. The third output was
further ampliﬁed by a factor 10 and fed to a
custom-made ﬁxed threshold discriminator (typi-
cally set at a level equivalent to a total signal
charge of 0.2 pC), followed by a LeCroy 2229
TDC with a 50 ps bin width.
The total charge was calibrated by injecting to
the test input of the pre-ampliﬁer a current pulse of
an intensity and width similar to the ion current
pulse from the chambers.
3. Results
3.1. Timing RPCs
Timing RPCs in a single channel conﬁguration
have shown timing resolutions below 50 ps s with
an eﬃciency of 99% for MIPs [2]. A typical signal
charge distribution is shown in Fig. 2.
A 32-channel prototype equipped with similar
chambers and suitable multichannel electronics
has shown an average time resolution of 88 ps s
with a spread of 9 ps and an average eﬃciency
of 98% with a spread of 0.5%. The crosstalk
between neighboring channels generally did not
exceed 1% [3].
3.2. Single gap chambers
In Fig. 3, we show the signal charge distribu-
tions measured at diﬀerent applied voltages in
single gas gaps of 0.1 and 0.3mm ﬁlled with
methane, isobutane or a ‘‘standard RPC mixture’’
containing C2H2F4+10%SF6+5%isobutane, also
used for the timing RPCs.
In pure isobutane and in the ‘‘standard mix-
ture’’, for both gap sizes, the distributions show an
extended ﬂat region for the larger applied voltages.
This is quite surprising because it can be shown
theoretically2 that the event by event variations in
the position of the leading cluster (closer to the
cathode) causes strong ﬂuctuations in the ﬁnal
Fig. 1. Structure of a single-gap detector cell.
Fig. 2. Comparison between the signal charge distribution
observed in a timing RPC (histogram) with four gas gaps and
the 4-fold self-convolution of the charge distribution from a
single-gap chamber (solid line) measured in similar operating
conditions. The overall good agreement between both distribu-
tions suggests that the charge distribution observed in the four-
gaps chamber can be interpreted as the analog sum of four
independent single gaps.
2See for instance the Appendix in Ref. [5].
P. Fonte, V. Peskov / Nuclear Instruments and Methods in Physics Research A 477 (2002) 17–2218
avalanche size, resulting in a charge distribution
almost proportional to 1/Q (being Q the signal
charge). The observed distribution is much more
favorable for an eﬃcient particle detection than
the expected ‘‘1/Q’’ distribution, allowing for the
excellent detection eﬃciency measured in cham-
bers with four gaps (see also Fig. 2).
In methane only a modest gas gain could be
reached due to the onset of discharges, presumably
caused by photon feedback. Indeed, while for the
other gases all results were essentially independent
of the cathode material (aluminum or glass), in
methane larger gains could be reached with the
glass cathode, presumably due to the smaller
quantum eﬃciency of glass.
Even for a single 0.1mm gas gap the
detection eﬃciency was still around 45% (isobu-
tane). From the corresponding ineﬃciency
ﬁgure and the gap length it can be calculated
that the mean number of primary clusters per
unit length must be at least 6mm1 (at least
one cluster must be produced for a particle to be
detected). However, due to the exponential
dependence of the ﬁnal avalanche size on the
cluster position, only a small region of the gas gap
(closer to the cathode) will be sensitive to the
ionizing particles. Therefore, to explain the ob-
served eﬃciency, the ionization density must be a
few times larger than the ﬁgure calculated above,
being quite doubtful whether this is physically
possible [6]. In fact, there is some indication that a
process other than gas ionization may be also
contributing to the observed detection eﬃciency
(Fig. 4).
Fig. 3. Distribution of the signal charge in single gap chambers for several applied voltages, ﬁlling gases and gap widths. The
innermost distributions correspond to the ADC pedestal and the peak close to 0 pC corresponds to the detector ineﬃciency. The
eﬃciency ﬁgures were measured by the method described in Ref. [2].
P. Fonte, V. Peskov / Nuclear Instruments and Methods in Physics Research A 477 (2002) 17–22 19
Some further information can be obtained by
plotting the average signal charge as a function of
the applied ﬁeld (Fig. 5). There is a strongly
sub-exponential growth of the average charge with
the applied ﬁeld, indicating the presence of a gas
gain saturation eﬀect.
Although similar eﬀects have been observed
in parallel geometry counters at low pressures [4]
and wire counters, being generally attributed to
space-charge eﬀects, such strong saturation has
never been, to the author’s knowledge, observed at
atmospheric pressure in proportional-mode parallel
geometry counters. This may be related to the fact
that our detectors work in an E/p range (around
100V/cm Torr) similar to those typically found in
low-pressure parallel-plate counters or at the sur-
face of wires in cylindrical counters and MWPCs.
Further evidence of a strong space charge eﬀect
is presented in Fig. 6, were correlation plots
between the fast (electron) signal charge and the
total signal charge were drawn for the same
experimental conditions studied above. Standard
detector theory [4] shows that the ratio between
these quantities should be independent of the
avalanche size and equal to ðavÞ1; where a is the
First Townsend Coeﬃcient and v is the electron
drift velocity. This situation is observed for the
case of a 0.1mm gap ﬁlled with methane. For all
other cases the upward curving correlation is
compatible with a space charge eﬀect that would
reduce the eﬀective value of a for the larger
avalanches [4].
4. Conclusions
Timing RPCs made with glass and metal
electrodes, forming four accurately spaced gas
gaps of 0.3mm, have reached time resolutions
below 50 ps s with a detection eﬃciency of 99%
for MIPs [2]
A 32-channel prototype equipped with such
chambers has shown an average resolution of
88ps s with a spread of 9 ps and an average
eﬃciency of 98% with a spread of 0.5%. The
crosstalk between neighboring channels generally
did not exceed 1% [3].
It was found that in single gas gaps the signal
charge distribution departs strongly from the theo-
retically expected shape and that the gas ampliﬁca-
tion process seems to be strongly inﬂuenced by a
space charge eﬀect. This eﬀect may be related to the
unexpected charge distribution observed.
The relatively large detection eﬃciencies ob-
served in single gas gaps (up to 45% for 0.1mm
gaps and up to 75% for 0.3mm gaps) seem to be
incompatible with a primary detection process
based uniquely in the ionization of the gas by the
incoming particles.
These conclusions seem to be quite indepen-
dent on the nature of the ﬁlling gas, applying both
Fig. 4. The extrapolation of the observed detection eﬃciency to
a vanishing gas gap width suggests that some additional
process, other than gas ionization, may be contributing to the
detection eﬃciency. Fig. 5. Average signal charge as a function of the applied
electrical ﬁeld, calculated from the data presented in Fig. 3. The
solid lines correspond to exponential functions ﬁtted to the
lower three points of each experimental series and extrapolated
to the larger ﬁelds, evidencing the sub-exponential character of
experimental data (gain saturation). The onset of gain
saturation for the 0.1mm gaps occurs at a charge level that is
an order of magnitude smaller than for the 0.3mm gaps.
P. Fonte, V. Peskov / Nuclear Instruments and Methods in Physics Research A 477 (2002) 17–2220
to the operation in pure isobutane and in a
strongly electronegative mixture containing freon
and SF6.
Acknowledgements
The use of the instrumented beam line
installed by the ALICE experiment for the tests
in the T10 PS beam under the supervision of W.
Klempt is acknowledged, as well as the kind
support of the CERN EP/AIT group. The data
acquisition infrastructure and the tracking system
were implemented and managed by Paolo Marti-
nengo.
We are also very grateful to P.G. Innocenti, W.
Klempt, C. Louren-co, G. Paic, F. Piuz, R. Ribeiro
and J. Schukraft for their comments and sugges-
tions and for their interest on our work.
We beneﬁted also from many discussions and
from the accumulated experience of the members
of the ALICE-TOF project and from the technical
expertise of Dave Williams.
This work was partially supported by the
Portuguese research contract CERN/FAE/1197/
98. One of us (V. Peskov) acknowledges the
ﬁnancial support of LIP-Coimbra.
References
[1] SCHOTT ATHERMALs.
[2] P. Fonte, R. Ferreira Marques, J. Pinh*ao, N. Carolino, A.
Policarpo, Nucl. Instr. and Meth. A 449 (2000) 295.
Fig. 6. Correlation plots between the fast (electron) signal charge and the total signal charge. Standard detector theory shows that the
ratio between these quantities should be a constant, being the observed upward curving correlation compatible with a space charge eﬀect.
P. Fonte, V. Peskov / Nuclear Instruments and Methods in Physics Research A 477 (2002) 17–22 21
[3] A. Akindinov, et al., A four-gap glass RPC time-of-ﬂight
array with 90 ps time resolution, preprint CERN-EP-99-
166.
[4] H. Raether, Electron Avalanches and Breakdown in Gases,
London, Butterworths, 1964.
[5] M. Abbrescia, et al., Nucl. Instr. and Meth. A 431 (1999)
413.
[6] F. Sauli, Principles of operation of multiwire pro-
portional and drift chambers, CERN Yellow Report 77-09,
1977.
P. Fonte, V. Peskov / Nuclear Instruments and Methods in Physics Research A 477 (2002) 17–2222


High-resolution TOF with RPCs

Eastern Illinois University

Eastern Illinois UniversityThe KeepMinutes Staff Senate1993September 9, 1993Staff SenateFollow this and additional works at: http://thekeep.eiu.edu/staffsen_minThis Article is brought to you for free and open access by the Staff Senate at The Keep. It has been accepted for inclusion in Minutes by an authorizedadministrator of The Keep. For more information, please contact tabruns@eiu.edu.Recommended CitationStaff Senate, "September 9, 1993" (1993). Minutes. 4.http://thekeep.eiu.edu/staffsen_min/4Staff Senate Minutes of September 9,1993 (Vol. 1, No.4) Called to order by Staff Senate President, Shirtey Stewart at 1:00 p.m., Casey Room, Union. Present: Tami Babbs, Sandy Bingham-Porter, Mickey Carrell, Kathy Cartwright, Danny Cross, John Aynn, Vickie Gilbert, Dennis Jones, Lynn Kimbrough, Roger Miller, Teresa Sims, Shirtey Stewart, Anita Thomas Absent: Wayne Bosler, Maggie Dell, Adam Due Visitors: President Joms Minutes A motion (Cross/Carrell) to approve the minutes of August 9, 1993 passed. I, Old Business A. 	 Response to Strategic Plan Pres. Jorns spoke to the Staff Senate regarding the Strategic Plan. He realizes that the deacline of 9/15 is difficult, and stated the main concern at the present time is to receive approval regarding the Vision Statement of the Strategic Plan. He read a press release and stated that an Ad Hoc committee will be formed to review the ethical hiring practices stated in the Articulated Plan for the President's Council. He reviewed the President's Council's Articulated Plan. There will be several reassignments and the Ad Hoc committee will review them to make sure they follow Affirmative Action guidelines and are both legal and ethical. This committee will be made up of members of the Facuhy Senate, the Staff Senate and the Affirmative Action Advisory Council. Senator Cross questioned Pres. Joms regarding the purpose of a consuhant to review the BSW management structure and whether this meant that one vice president would now be over Housing and the Physical Plant. Pres. Joms said that this was not the case; the consuhant is to determine if the department is as efficient and effective as it could be. Senator Cartwright asked if there would be anyone that the Ad Hoc committee could go to if they had questions on the legal and ethical issues. Pres. Joms said the committee could call any witnesses that are necessary. Senator Bingham-Porter had a statement regarding IV.a. of the Strategic Plan. She indicated as a commitment to our facuby and staff we should promote them as resources to the students and not worry just about competitive salaries. Pres. Joms stated that the statement "our nation in all its diversity" is a very ambitious statement. We are saying that we want EIU to renect the nation proportionately. We are setting our standards very high. Senate Pres. Stewart asked the definition of staff. Pres. Joms said that staff includes all that are not facuby. Senator Carrell asked for the definition of administrator in Objective #2 of the Articulated Plan. Pres. Joms said that it would effect Larry Williams and perhaps Winiam Hine. No demotions would occur, perhaps one promotion would take place. Senator Jones asked if there would be a search before the promotion. Pres. Joms said no, that there would be no new job, an existing job would be given increasing responsibilities. Senator Sims asked which one would be selected. Pres. Joms said that Affirmative Action guidelines would be followed and, thus far, no provision has been made for an internal search, but if that is what the guidelines say to do, it will be done. Senate Pres. Stewart asked when the committee would be formed. The presidents of the Staff Senate and the Faculty Senate, and the director of Affirmative Action will meet with Pres. Joms soon to form the committee. Senator Sims asked about the entrepreneurial "bank" on page 7 of the Articulated Plan; was this an appropriated account and was the bank centraliZed. Pres. Joms said that the account receiving the loan must be able to make money to repay the loan plus interest. Marlyn Finley and Jeff Cooley said it would be a local account. A provision would be made for those that failed to repay their loan. Senator Jones asked if areas outside of the university could use this. Pres. Joms said it was for on-campus accounts only. Senate Pres. Stewart said that she had heard sev«al positive comments regarding the Vision Statement. Pres. Joms stated that the second semester would involve hands-on work among the departments. Senator Flynn asked about the inconsistencies regarding the NACUBO report. Pres. Joms said each department plan must be written in consuhation with all in the department and all within the department must agree that the data is acceptable. Senator ,Aynn commented on how broad the goals of the S1rategic Plan were. Pres. Joms said that some think the goals are too restrictive, but they are made to be broad so that the departments have the latitude to work with them. Senator Bingham-Porter asked if the academic college restructuring caused any elimination of positions. Pres. Joms said, yes, and Senator Thomas commented that they were through reassignments due to attrition. Senator Bingham-Porter asked if the $125,000 on the volunteer goal would create an administrative poSition. Pres. Joms said that they may have to add one position, but pointed out the funding is through grants, gifts and reallocation. Senator Flynn said that some of the problems with funding is that those outside of the university give us mandates without the funding to follow through. Senate Pres. Stewart asked if there were any other questions or recommendations. Pres. Joms told the Senate to take their time. He welcomed comments on the entire plan, but asked for a response on the Strategic Plan. Senator Cross felt that the plan is a positive move and Senator Sims stated that most have questions on the President's Council's Articulated Plan. Senate Pres. Stewart suggested' that we make our recommendation in two parts. Senator Carrell suggested adding "staff" to the third sentence of the Vision Statement. A motion was made to this effect (Cross/Cartwright). Motion carried. Senator Flynn asked if units can live within these limitations. Senator Carrell gave the background on 'how the plan was developed and that this is an umbrella under which each department does their own planning. Senators Babbs and Jones had a concern about the wording in IIl.c. Senator Babbs suggested they add "diverse" to the statement"...non-traditional student" (traditional being age 18-22). A motion was made to this effect (Cross/Cartwright). Motion carried. Senator Jones felt that La. and I.d. opposed each other. Senator Sims asked about funding for the research. Senator Jones replied that research is usually funded by grants. Senator Bingham-Porter questioned IV.b. regarding support budgets. Senator Cross said that the budgets are left up to the departments. Senator Carrell commented 1hat tenure-track people had more of a commitment to the University. The decentralized budgets leave the decisions up to the departments. Senator Jones asked that if the professors are expected to do research, how are they to teach at the same time. Senator Flynn feh that the research was in addition to, rather than instead of, teaching. Senator Jones also questioned where athletics fit in the Vision Statement. He feh that a statement should say "competitive intercollegiate athletics." Senate President Stewart feh that it fell under the umbrella of "enhance the quality of student life." Senate Pres. Stewart asked and received a motion to send the recommendations on the one-page Strategic Plan only to Pres. Joms (Carrell/Bingham-Porter). Motion carried. Recorrmendations regarding the President's Council's Articulated Plan wil be forwarded following the findings of the Ad Hoc Committee reviewing the ethical hiring practices of the position changes indicated in the document. B, 	 Repon .rom Stall Senate Re"NI Plennlng Commln .. Senator Bingham-Porter distributed an agenda and informed the committees that they will each have time to meet at the retreat. Pres. Jorns and all of the Vice Presidents were invited to anend the luncheon. VP Falk and VP Hencken are able to attend. The others will be out-of-town anending the BGU meeting. The Senate will also discuss how to distribute information and questionnaires to our constituents. C, 	 R..ponse to BGU Enrollment Management Repon and Recommendations Senator Cross questioned page 2, number 4 regarding whether intemships are decided by EIU. Senator Flynn said they were decided by the BGU. No other comments. Motion made to accept (Bingham-PorterlSims). Motion carried. Senate Pres. Stewart will send a memo to VP Hencken and Jill Nilsen. D, 	 Response to 1993-1994 Ac:Idemlc Calendar Senator Cross said people in food service would lose 4 to 5 days with the changes made in the calendar, mainly due to Thanksgiving break. The Senate feh they would gain days at the beginning of each semester. The moving of spring break was at the request of the Faculty Senate. Senator Bingham-Porter feh that the committee should ask the offices involved, if the calendar was functional for them. Senator Flynn said it would be a time crunch for Financial Aid. Since there will be no Saturday exams in spring and fall, this was a financial saving for Testing Services. It was questioned as to why there was a Saturday exam in August as well as why August 8 was not being used. Senate Pres. Stewart felt that as far as the job search was concemed for May graduates, they would have an advantage over other colleges. The Senate agreed with the removal of the fall break. Motion was made (Jones/Cross) and passed to accept the calendar. Senate Pres. Stewart will send a memo to VP Hencken. E. 	 Leamer's Program Agenda lor September 13 Meeting A copy of the memo sent to Linda Moore was distributed which included the agenda for the leamer's Program meeting. The goal of the meeting is not to put someone on the spot, but to make the Leamer's Program bener. Senate Pres. Stewart will state the ground rules at the begiMing of the meeting_ No one requested in advance to speak at the meeting. If visitors show up with questions, they can be put on the agenda for the next meeting of the Staff Senate. Senator Cross will read all leners that have been received. II. New Busln... A. 	 Appointment to CUPB Senate Pres. Stewart reported receiving leners from individuals governed by the Staff Senate who stated an interest in volunteering for the Staff Senate appointment to the CUPB. Senator Bingham-Porter stated she thought the representative should be from the Staff Senate. The rest of the Senators agreed. Senator Carrell is interested in serving on CUPB since the Civil Service Council has no representation on it, and she could represent both the Civil Service Council and Staff Senate groups. Senator Sims nominated Senator Carrell for appointment and Senator Bingham­Porter recommended Senator Flynn to represent Administrative and Professional. Nominations closed (KimbroughlThomas) and passed. Senator CarreH will serve a one-year term and Senator ,Flynn will serve a two-year term. Senator Flynn feels that the structure for CU PB is bener than it has been in the past. B. 	 Appointment to Women's Study CouncH Sharon Bartling sent a request to Senate Pres. Stewart for representation from the Staff Senate to serve on their council. They rneet the first and third Thursday of each month. The first meeting will be 9/16. Senator Thomas nominated Senator Sims. A motion was made to close nominations (Bingham-PorterlThomas). Motion carried. C. 	 Other Senator John Flynn is unable to aHend the Staff Senate Retreat due to check disbursement. III. Agenda The meeting on September 13, 1993 has only one agenda item - the leamer's Program. As such, all other agenda items will be postponed until the October 11 meeting. The Staff Senate Retreat will be held September 23, 1993 in the lord Dining Room of Pemberton Hall from 10:00 a.m.-2:00 p.m. A motion was made to a~oum the meeting (Thomas/Bingham-Porter). Motion carried. The meeting adjourned at 2:47 p.m. Respectfully submitted, Tami Babbs, Secretary 

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High-resolution TOF with RPCs

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