Transcript prova poster

Production and Test of 150 Barrel RPC Chambers of the CMS
experiment at LHC collider
Pierluigi Paolucci – I.N.F.N. of Naples (Italy)
Dip. di Fisica & INFN di Bari (Italy), Dip. di Fisica & INFN di Pavia (Italy), IRNE & Univ. of Sofia (Bulgaria), Peking Univ. (China)
105 Hz
Trigger efficiency .vs. Pt
The Compact Muon Solenoid is a general purpose
p-p detector at the Large Hadron Collider
103 Hz
Trigger efficiency .vs. 
Trigger Rate
fig.1
Muon detector is designed to trigger and identify muons and measure their
momentum. It consists of four sub-detectors: Drift Tubes (DT) in the barrel
region, Cathod Strip Chambers (CSC) in the endcap region and Resistive Plate
Chambers (RPC) as dedicated trigger detectors in the barrel/endcap.
HV
Gas Gap
backelite
Gas Gap
GND
strip planes
Gas Gap
Gas Gap
The chamber is a self-supporting
mechanical structure producing a
gentle pressure (about 15 Kg/m2) in
order to keep the strip planes in place
and in contact with the two gaps.
Barrel RPC Chamber consists of 2
double-gaps, each equipped with a
common plane of 96 strips read-out by
6 front-end boards. The two doublegaps have different lengths and are
staggered to reduce the dead zone.
Double-gap are made by 2
superimposed gaps with the spacers
overlapped in order to do not produce
gap deformation. The gap is made by
two 2 mm thick bakelite plates
(resistivity 1-3·1010 ·cm) kept at a
fixed distance of 2 mm by insulating
spacer (diameter of about 10 mm). The
chambers will at 9.2-9.5 KV with a
Freon based gas mixture (96.2 C2H2F4,
3.5% i-C4H10, 0.3% i-SF6).
About 150 RPC chambers have been produced (General Tecnica, Bari
and High Tech) and tested (Bari and Pavia) in Italy, corresponding to
1450 gaps and 400 double-gaps. A very accurate Quality Control
check is made on the single gaps, double gaps and chambers.
fig.2
fig.3
The LHC bunch crossing frequency is 40 MHz and with a Luminosity of 1034 cm-2s-1 the average
number of inelastic interaction in a crossing is 17.3. A rate reduction of a factor 4·105 is needed to
reach the recording capability of 100 Hz. The barrel has 3 independent L1 muon trigger systems
(DT-RPC-CSC), each generating 4 muon candidates with an associated Pt and track quality. The
Global Muon Trigger receives this data and properly combines them to generate 4 final muon tracks.
The combined trigger efficiency (see fig.2) is always greater than 90%. The estimated Muon Trigger
Rate in the barrel region (||<1.04) goes from 102 Hz up to 105 Hz as function of the Pt (at L = 1034
cm-2s-1) and the RPC trigger system is able to trigger muon with a Pt > 6-8 GeV/c with an efficiency
greater than 90% (see fig.3).
RB4
RB3
RB2
DT
RPC
RB1
The Barrel Muon System is made by 5 wheels,
divided in 12 sectors with 4 stations or magnet iron
gaps (called for the RPC system RB1, RB2, RB3 and
RB4) each. The iron gaps will be filled with a
sandwich made by RPC-DT-RPC in the station RB1RB2 and RPC-DT in the station RB3-RB4.
RPC system numbers
• area covered
2.400 m2
• number RPC chambers
480
• number of strips
75.000
• number of front-end cards 4.700
Two Cosmic rays telescopes have been built in Bari (10 chambers) and Pavia
(5 chambers) in order to study in details the performances of the RPC chambers.
One more “short” test will be done at the ISR (CERN) before installing them.
The trigger is made by two planes
of scintillators, placed on the
opposite ends of the structure.
The DAQ is based on a custom
VME TDC running at 40 MHz in
common stop mode and with a bin
size of 25 nsec
The gas mixture is:
96.2% C2H2F4, 3.5% i-C4H10, 0.3% i-SF6
Chamber production trend
Chamber efficiency, cluster size, noise rate and dark current are measured for
every chamber and the results are stored in the RPC database (http://www.ba.infn.it/rpc)
The dark current and efficiency curves as
function of the HV working point are very
similar showing a very good reproducibility of
the RPC chambers.
fig. 1
fig. 2
fig. 3
<Dark Current> = 5mA
Noise Rate < 6 Hz/cm2
<Cluster Noise Rate> = 2.4 Hz
<Cluster Size> = 3 strips
Hz/cm2
<efficiency> = 98.7 %
reconstruction
counting
Mean Global Efficiency is measured using two
different methods (fig.5):
The Counting method calculates the efficiency as
the ratio between the number of chamber signals
in a fixed time window and the number of
triggers.
The Reconstruction method uses reconstructed
cosmic tracks in order to reduce the number of
“fake” events generated by cosmic showers, fake
triggers and multi-particle events.
The Cluster size (fig.6) is defined as the number
of contiguous strips of the same chambers.
The Noise Cluster Rate (fig.6) and the Noise rate
(fig.4) are measured using the number of hits and
clusters found outside the trigger window (3 TDC
bins = 75 ns).
eff = 98.7%
fig. 5
fig. 4
fig. 6