1. Imad Laktineh IPN-Lyon On behalf of the CMS muon group
New generation of high-rate fast timing RPC for the high eta CMS muon detector
Imad Laktineh
IPN-Lyon
On behalf of
the CMS muon group
IPRD2016-Siena

2. Outline CMS RPC upgrade project High-rate RPC Fast timing RPC
Conclusions
IPRD2016-Siena

3. RE3/1-RE4/1: 72 chambers in all
CMS RPC upgrade project
To equip the RE3/1 and RE4/1 CMS muon stations with improved RPC chambers
covering 1.8<|η|<2.4; each chamber spans 20° in φ; 1 layer per station
RE3/1
RE4/1
RE3/1-RE4/1: 72 chambers in all
Two scenarios are under investigation :
-Double-gap RPC
-Multi-gap RPC
Using either doped glass or HPL/Bakelite
as electrodes with strips-based readout
Surface of each chamber ≈ 1.4 m2
Present RPC system:
1056 chambers (double-gap HPL/Bakelite RPC)
covering 0 < |η| < 1.6
IPRD2016-Siena

4. Improve muon reconstruction efficiency in offline data
CMS RPC upgrade is a part of the CMS muon upgrade project that proposes to equip the high η muon stations ahead of the HL-LHC with a new generation of detectors (iRPC, GEM, FTM,..) in addition to the present CSC detectors in order to :
Increase muon system redundancy for |η|>1.6, where background rates are the largest
Improve muon reconstruction efficiency in offline data
Recover CSC inefficiencies in local reconstruction (stubs) in muon trigger
CERN-LHCC
phase2
CERN-LHCC
CERN-LHCC
IPRD2016-Siena

5. Requirements
We expect 700 Hz/cm2 in hottest points of RE3/1 and RE4/1(based on Fluka simulation) 
iRPC should stand a particle rate up to
≈ 2 kHz/cm2 (including a safety factor)
with an accumulated charge of ≈ 1 C
RMS pT = 200 GeV gives
~2-3 mm for RE3/1 & RE4/1 
Readout granularity of few mm with digital mode
IPRD2016-Siena

6. iRPC high rate detection capability
Present CMS RPC chambers were certified to be efficient up to 300Hz/cm2
irradiated with photons up to an integrated charge of 0.05 C/cm2, and a neutron fluence of
1012 n/cm2 and equivalent dose of about 45 Gy was reached.
Rate capability of the RPC is related to the voltage drop in the resistive plate: ΔV = I R = q ρ d Φ
To have RPC with increased rate capability one should reduce:
electrode resistivity ρ: as low as the RPC principle still stands (> 109 Ωcm)
 low-resistivity HPL or doped glass (Tsinghua glass)
electrode thickness d: depends on electrode material
easy for glass, possible for HPL
produced charge q : depends on gas mixture and number of gaps
The less the charge produced, faster the eviction : beneficial also for chamber aging but this necessitates to increase FE electronics sensitivity
IPRD2016-Siena

7. Electrode Resistivity and thickness
HPL/bakelite:
Supplier :Puricelli
Present system 1-5x1010Ωcm,
but ~0.5-1x1010Ωcm may be achievable; thickness down to 1 mm,
typical CMS sizes are no problem
Low-resistivity glass:
Developer: Tsinghua. Supplier: Chinese company
tunable resistivity (1010Ωcm or lower) achieved; no oiling procedure needed; no humidification of gas mixture; limited sizes only
Pressing Puricelli
Glass Specifications:
Present max. dimension: 32cm×30cm
Bulk resistivity: ≈1010.cm
Standard thickness: 0.5mm--2mm
Thickness uniformity: 0.02mm
Dielectric constant: ≈
Surface roughness: < 10 nm
DC measurement: Ohmic behavior,
stable up to 1 C/cm2
1kV applied on a glass plate 32days; integrated charge: 1 C/cm2
IPRD2016-Siena

8. HPL-based RPC max. γ rate ~1.4 kHz/cm2
Double-gap: gas gap = 1.6mm, HPL thickness = 2mm
performance studied with cosmic rays in presence of Cs source
performance studied with muon beam in presence of Cs source at GIF++
Plastic
Cs-137
source
RPC
max. γ rate ~1.4 kHz/cm2
ε=0.95 in HV due to γ backgr. ~ 70V
Th = 110 fC
IPRD2016-Siena

9. Glass-based RPC Small chamber : 30x30cm2; 1x1cm2 readout pads
single-gap RPC: gas gap = 1.2mm, glass thickness = 1mm
Small chamber : 30x30cm2; 1x1cm2 readout pads
150 GeV π,μ SPS, H2 (Jun. 2015)
μ GIF++ H2 (Jul. 2015)
70% single-gap efficiency for low resist. > 2kHz/cm2
(i.e. >90% double-gap efficiency)
Beam seen by one detector
IPRD2016-Siena

10. Towards Full-Size GRPC
Gluing method:
Half size of RE4/1
Gluing small pieces of glass
Gluing zone <100μm
Mechanical fixation method:
Half size of RE4/1
Mechanical fixation small pieces of glass
Separation distance of few mm; top and
bottom gaps staggered
Gas tightness ensured by cassette
Mechanical fixation method is more robust; issues regarding glue radiation hardness are absent ; less leakage current is observed
IPRD2016-Siena

11. Towards Full-Size GRPC
Gluing method:
Half size of RE4/1
Gluing small pieces of glass
Gluing zone <100μm
Mechanical fixation method:
Half size of RE4/1
Mechanical fixation small pieces of glass
Separation distance of few mm; top and bottom gaps staggered
Gas tightness ensured by cassette
Large detector built with low-resitivity glass was built and successfully tested at H2 and will be soon exposed to GIF++
IPRD2016-Siena

12. FE Electronics HARDROC ASIC is proposed to read the 2-gap iRPC
64-ch, SiGe technology, gain correction, 10fC-15pC
3 thresh. levels, i.e. semi-analogue readout, will improve spatial resol. beyond digital readout !
~ ASICs were already tested with a dedicated test bench for the CALICE SDHCAL project
Successfully tested on both HPL and glass RPC; two kinds of PCB used:
Pickup pads of 1cmx1cm
4.7 mm
4.3mm
HARDROC2 and 2B:160pins
Strips of 2.5mm pitch .
IPRD2016-Siena

13. Spatial resolution of ~1-2 mm achievable
GRPC telescope consisting of several low resist. Chamber (gas mixture 93% TFE, 5% CO2, 2% SF6), was used to test a 2-gap GRPC with pickup PS, CERN, August 2014
HV = 7200V
Spatial resolution of ~1-2 mm achievable
IPRD2016-Siena

14. Fast timing
Multi-gap RPC is an excellent fast timing detector (ALICE, STAR). For CMS it should help in several
Fields among which:
Background mitigation
Long lived neutrons are captured by nuclei
 γs : Photoelectric effect and Compton scattering
few MeV electrons leaving hits in RPC.
These hits could corrupt the muon track reconstruction
and increase trigger rate.
Looking for correlated hits in time in the different MRPC
stations one could get rid of many noisy hits.
HSCP searches
will get benefit of precise time information by looking for particles reaching the
muon chambers at delayed times with respect to BX.
IPRD2016-Siena

15. Multi-gap HPL/Bakelite RPC
Dual bi-gap RPC (eq. 4- gap RPC)
Using HPL electrodes thickness of (1.5 mm) compared to the present CMS RPC (2 mm)
and gap thicknesses (0.5, 0.8 mm) compared to the CMS RPC (2 mm)
Operating HV = 6.5 ~ 7.0 kV for 0.5 mm and ~ 9.8 kV for 0.8 mm dual bi-gap respectively
Using lower threshold thanks to higher sensitive front end electronics
(min. threshold ~ 70 fC)
For 0.8 mm Dual bi-gap RPC <qe> ~ 0.6 HVε=0.95 = 9.1 kV
Th = 0.60 mV
72 Hz cm-2
1055 Hz cm-2
Dual bi-gap RPC
GIF++:
ε=0.95 in HV due to ~ 1.0 kHz cm-2 γ background ~ 100 V
IPRD2016-Siena
R&D is ongoing to achieve detection capabilities higher than 2kHz/cm2

16. Multi-gap GRPC 5-gap GRPC Prototype Mosaic GRPC
MRPC Component
Size (mm)
PCB
320×540×0.7
Mylar
260×480×0.18
Mosaic Glass
250×330×0.7 & 250×200×0.7
Spacer
0.5
Gap
0.25×5
Total thickness ≈ 5.5 mm
HZDR (September 2015)
30 MeV e-beam
Gas: 90% TFE + 5% i-butane + 5% SF6
Few electronic channels
Glue, brand?
Performance to be validated soon in GIF++
IPRD2016-Siena

17. Electronic readout for Multi-gap CMS-RPC
FE electronics
PETIROC
- 32-ch, SiGe, 0, pC
-32 trigger output
-NOR32_charge
-NOR32_time
-global&individual threshold adjustment
20 ps resolution for Qinj >.3 pC
TDC on FPGA
TDC
-TDC on FPGA (25 ps time resolution)
-TDC on ASIC (based on Vernier principle) is being developed, aiming at better resolution, lower power consumption and more robustness 1 2 3 4 5 --
Ns-1 Ns
Nf-1 Nf
Fast
Slow
Start
Stop T
Same phase
IPRD2016-Siena

18. PCB
pick-up strips read from both sides is being designed with the with the aim to achieve
Absolute time measurement
Y-position determination (η position)
Y= L/2-v*(t2-t1)/2.
No need of η segmentation.
On-detector Strip
Off-detector Strip Y
Strip
jitter rms (charges injected = 5pC) 16
0.0347 18 20 22 24 26 28 30
32 strips of 3 mm width
(4 mm pitch)
Time difference of the two signals detected in channels 16 and 17 associated to two ends of the same strip.
IPRD2016-Siena
Time resolution/channel ≈ 25 ps

19. Conclusions and prospects
New double-gap RPC detectors (glass and HPL) are able to stand the expected high rate fluences of the HL-LHC in the high η region of CMS muon stations (RE3/1, RE4/1).
New low-noise Front End electronics to achieve such performance is available and is being adapted to CMS running conditions.
Fast timing could be an asset. Multi-gap RPC are the best detectors to achieve this. Low-jitters Front-End electronics equipped with TDC providing excellent time resolution is being developed and preliminary results are very encouraging. Simulation studies on trigger and trigger performance will allow to assess the interest of fast timing MRPC.
Additional tests at CERN and elsewhere are planned to confirm the performance of the new detectors and to study their robustness within the CMS conditions.
IPRD2016-Siena