The CMS Muon System Towards LHC Run2 and Beyond Luigi Guiducci

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The CMS Muon System

Towards LHC Run2 and Beyond Luigi Guiducci

INFN & Bologna University

on behalf of the CMS collaboration

37th International Conference on High Energy Physics

2-9 July 2014

Valencia, Spain

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ICHEP2014 - Valencia CMS Muon System L. Guiducci - Università di Bologna & INFN

Outline

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‣ The CMS detector and its muon system

‣ Run 1 operations and performance

‣ Activity during LS1: muon system towards Run 2

‣ CMS muon upgrade plans and LHC schedule

‣ CMS Phase1 upgrades: L~2x10

³⁴

cm

^-2

s

^-1

, 300 fb

^-1

‣ CMS Phase2 upgrades: L~5x10

³⁴

, 3000 fb

^-1

(3)

The CMS detector

(4)

The CMS muon system

‣ Robust, efficient and redundant muon system

‣ Muon Identification

‣ Measurement of the transverse momentum

‣ Bunch crossing (BX) assignment

4

‣ Planar endcap region

‣ 4 planar stations interleaved with the iron return yoke plates

‣ Cathode Strips Chambers (CSC) and Resistive Plate Chambers (RPC)

‣ Cylindrical barrel region

‣ 4 coaxial stations interleaved with the iron return yoke plates.

‣ Drift TUbes (DT) and

Resistive Plate Chambers (RPC)

‣ Excellent

performance at LHC Run 1

‣ >98% working channels for all

muon subsystems at the

end of Run 1 (~30 /fb)

‣ >95% single muon trigger efficiency, including BX-ID and PT cut

‣ very good HLT isolation and high quality for offline analysis

(5)

CMS muon detectors

250 Drift Tube Chambers

•

Barrel, |η|<1.2

•

4 stations, 5 wheels, 12 sectors

•

(4+4) layers in ɸ, 4 layers in z

•

Local segment reconstruction

•

Hit resolution ~250 um

540 Cathode Strip Chambers

•

Endcap, 0.9<|η|<2.4

•

2x4 stations, 1-3 rings, 18-36 sectors

•

6 layers of strips in ɸ, 6 layers of wires in r

•

Local segment reconstruction

•

Hit resolution ~150 um

480+432 Resistive Plate Chambers

•

Barrel+Endcap, |η|<1.6

•

Barrel:4 stations, 1-2 layers, 5 wheels, 12 sec Endcap: 2x3 stations, 2 rings, 36 sectors

•

Local hit per chamber

•

Time resolution < 3 ns

(6)

Performance of the muon detectors

‣ Very high trigger segment efficiency (≳95%) from DT&CSC L1 electronics

‣ High efficiency and low noise of RPC hits

‣ Expected resolution of ~200um in tracking detectors (<100 um for reconstructed segments)

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DT L1 trigger segment efficiency

RPC efficiency RPC noise

CSC L1 trigger segment efficiency DT resolution

CSC resolution

(7)

Muon Trigger

‣ Very good BX ID, efficiency and Pt measurement at Level 1

‣ Very clean HLT: ~85% of events used offline after all cuts

‣ Full use of muon and tracking information at HLT for isolation, vertexing and momentum

measurement

(8)

Background: measured rates

8

RPC backgroound rates vs luminosity

DT background rates

‣ Main sources of background in the muon system

‣ Photon-like background (neutron capture): neutrons populating the cavern

‣ Highest rates in outer chambers and in top sectors (no shielding, far from the concrete floor)

‣ Prompt background: mostly punchthrough/flythrough

‣ Inner chambers, forward region

‣ Rate measurements in 2011 and 2012 show linear behavior

‣ Extrapolation + safety factor + cross-check with simulations to prepare for higher luminosity runs

(9)

DT interventions during Long Shutdown 1

‣ Sector Collector relocation: move DT trigger & readout concentrator from UXC to USC

‣ 20 new electronic crates, ~400 boards installed

‣ New fibers from UXC to USC, full trigger information available in USC

‣ In preparation for the Level-1 trigger upgrade in 2016 (TwinMux, new DT/RPC/HO concentrator)

‣ Install FPGA version of theta-trigger-board in external wheels

‣ Refurbish stock of Bunch-and-Track-Identifier ASIC spares

‣ Reparations on electronics/HV: 3.5k channels recovered (173k channels total)

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CSC interventions during Long Shutdown 1

‣ Replacement of ME11 FE electronics

‣ Improve trigger and pattern recognition in 2.1<|η|<2.4 (fine strip granularity of ME11a)

‣ ME42 construction and installation

‣ Improve trigger performance of endcap muon system at L>10³⁴ cm^-2s^-1(better Pt resolution, fewer fakes)

‣ CSC reparations

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ME11

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RPC interventions during Long Shutdown 1

‣ Reparation campain (HV, LV, electronics): 99.5% working channels today

‣ Installation of RE4 chambers

‣ 686 gaps produced in 22 months

‣ Installation completed, commissioning almost finished

(12)

ME4/RE4 completion - performance

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‣ Muon ID efficiency vs PT before and after Long Shutdown 1

‣ Fist estimaton of the improvement in the muon ID efficiency with and without ME4 and RE4 for 1.2<|η|<1.8; around 2% efficiency improvement

Target 5 kHz

‣ Completing the 4^thendcap station allows tightened trigger criteria

‣ L1 trigger rates a 2E34; tolerable single muon rate ~5 kHz

‣ Threshold can be reduced from 48 to 18 GeV

(13)

Phase 1 Muon trigger upgrade

‣ CMS 2012 architecture: separate regional trigger

(tracking across multiple stations) for each of DT/RPC/CSC

‣ Phase 1 architecture (2016): Track Finder processors for barrel (|η|<0.8) overlap (0.8-1.2) endcap (1.2-2.4),

using all detector hits available in each region

‣ Early combination of trigger segments and RPC hits:

better timing and efficiency of TF inputs

‣ Pt assignment improvements: rate reduction at little cost in efficiency

Combined DT/RPC trigger primitives

Upgrade

Rate vs threshold Plateau eff. vs threshold

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ICHEP2014 - Valencia CMS Muon System L. Guiducci - Universita’ di Bologna & INFN

LHC program and CMS upgrades

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Reparations and LS1 projects: in production

‣

Completion of muon coverage (ME4)

‣

Improve muon operations: ME1, DT electronics

‣

Replace HF (PMTs) and HO (SiPM) photodetectors

Phase 1: production

‣

Pixel detector replacement

‣

HCAL electronics upgrade

‣

L1-Trigger upgrade

Phase 2: Tecnical Proposal 2014

‣

Tracker replacement, Track Trigger

‣

Forward region: Calorimetry, Muons, Pixels

‣

GEMs in first two endcap stations

‣

New RPCs in 3^rd and 4^thstation

‣

^|

η

|>2.4: “ME0” GEM, up to

η

=4?

‣

New CSC and DT electronics

‣

Further Trigger and DAQ upgrade: 10us, 1MHz

LS1 LS2 LS3

2013-2014

<PU>~40

2018

<PU>~60

2022-2023

<PU>~140

Nominal lumi

~ 14 TeV

2x nominal lumi

300 fb

^-1

5x10

³⁴

cm

^-2

s

^-1

3000 fb

^-1

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Phase 2 physics

‣ Conservative scenario: focus on precision Higgs measurements

‣ Muon system critical for both bosonic and fermionic couplings

‣ H→WW and H→ZZ key to precision on HVV couplings

‣ H→ττ is key for measuring fermion coupling (muon+hadronic tau)

‣ H→µµ can be measured with 3000 fb^-1

‣ In general, thresholds ≲ 20 GeV (!) yield high efficiency for EW bosons and top quark decays to leptons

‣ H^→ZZ^→4µ channel: >30% increase in signal yeld extending muon coverage to |η|<4

‣ SUSY and Exotica scenarios

‣ High mass objects → very high PT leptons

‣ Heavy stable charged particles

‣ Non-pointing muons

‣ Collimated “muon jet”

‣ Need good muon standalone trigger capability and enhanced ability to resolve multiple tracks

(16)

Phase 2 muon upgrade

‣ There are three types of upgrades proposed for the Phase 2 CMS muon system:

‣ actions that ensure the longevity of the present muon detectors

‣ additional muon detectors to increase redundancy and enhance the trigger capabilities in the forward region 1.6 < |η| < 2.4

‣ extension of muon coverage to |η| > 2.4 in the rebuilt endcap calorimeter, to take advantage of the pixel tracking coverage extension

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‣ Will detectors and electronics be ok after approximately 30 years and 3000 /fb ?

‣ Detectors should stand the radiation;

repeat measurements with higher rates/doses at GIF++

‣ Electronics: too much aging and radiation for some components

‣ Phase 2 DAQ with 10 us latency and 1 MHz L1Accept rate: is the readout of exisiting detectors electronics safe?

‣ Need replacement of CSC electronics

‣ New on-detector DT electronics and improved trigger algorithm

‣ New detector for post-LS3 need high rate capability

‣ From present maximum ~1 kHz/cm² up to 10-100 kHz/cm²

‣ In addition we want exceptional performances:

‣ Time resolution to O(100 ps)

‣ Spatial resolution O(1-0.1 mm)

‣ Rejection of neutron hits

‣ Use of eco-friendly gases

‣ Given the rate capability, the choice is driven by

physics performance, robustness, cost, simplicity, etc.

Requirements for Phase 2 muon systems

CSC FE buffer losses

phase2 trigger

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New muon detectors for Phase 2

‣ Installation of GEMs in endcap stations 1 and 2, covering 1.5<|η|<2.2-2.4

‣ Improve redundancy in the muon system for robust tracking and triggering

‣ Improve L1 and HLT muon momentum resolution to reduce or mantain the trigger rate

‣ Ensure efficient operation through high pileup HL-LHC running

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‣ Installation of iRPCs in stations 3 and 4, reaching |η|<2.4

‣ Improve redundancy in the muon system

‣ Excellent time

resolution for reducing neutron background, pileup mitigation, HSCP searches

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New muon detectors for Phase 2

‣ Installation of GEMs in endcap stations 1 and 2, covering 1.5<|η|<2.2-2.4

‣ Improve redundancy in the muon system for robust tracking and triggering

‣ Improve L1 and HLT muon momentum resolution to reduce or mantain the trigger rate

‣ Ensure efficient operation through high pileup HL-LHC running

‣ Installation of iRPCs in stations 3 and 4, reaching |η|<2.4

‣ Improve redundancy in the muon system

‣ Excellent time

resolution for reducing neutron background, pileup mitigation, HSCP searches

10-100 kHz/cm 2

~1 kHz/cm 2

~1-10 kHz/cm 2

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iRPC/gRPC for Phase 2 upgrades

‣ RPC rate capability: limited by V drop in the resistive electrode

‣ Possible improvements

‣ Reducing the electrode resistivity (< 10¹⁰Ωcm): faster recovery

‣ Reducing the charge per particle: requires improved

amplification electronics and better rejection of detector noise

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‣ New detector configuration to improve (signal)/(charge in the gap):

‣ multigap, low resistivity bakelite, glass-RPC (smooth electrode, low noise; but smaller size)

‣ Requires R&D and further tests: 3000 fb^-1 corresponds to integrated charge ~ 1-1.5 C/cm²+ safety factor

‣ GIF++ in 2015 to study rate, radiation and aging effects on prototypes

Glass RPC prototype

multigap HPL prototype

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The GEM technology

‣ Perforated 50um thick capton foil with copper (5um) on both sides

‣ Multiplication in traversing holes

‣ More foils in cascade to achieve O(10⁴) multiplication factor

‣ Rate capability up to 10⁵ Hz/cm²

‣ Non flammable gas (Ar/CO2/CF4)

‣ Industrial process

‣ Experience in Compass, Totem, LHCb

Developed by

F. Sauli in 1997

(22)

CMS performance with GEMs

‣ Improvement to L1 trigger pt measurement

‣ CSC are thin (~11 cm): not enough resolution on track angle (bending)

‣ GE1/1: increase lever arm by combining

the high resolution GEM point with the CSC segment

‣ Simulation studies show up to one order

of magnitude rate reduction (wrt CSC alone) for a Pt cut around 20 GeV

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(23)

Muon pseudorapidity extension

‣ Opportunity for offline muon tag with pixel tracking extension

‣ ME0: space left in the back the new compact endcap calorimeter

‣ Beneficial for yields and/or S/N for final states with muons

‣ Especially multiple-muon final states; better identification of top and W events;

improvement of missing transverse energy determination

‣ Six layers to suppress neutron background O(10-100kHz/cm²)

‣ And incorporate borated polyethylene and lead shielding

‣ Match ME0 hits and tracks from forward pixel extension

(24)

Conclusions

‣ Excellent performance of the CMS muon detectors during Run 1

‣ Huge effort of subdetector teams to mantain ~100% efficient detectors and electronics

‣ Electronics upgrade and completion of the 4th endcap station will provide

new handles into higher luminosities in Run2 for muon trigger and reconstruction

‣ High Luminosity LHC will set goals and constraints beyond the original CMS specifications: “CMS Phase 2 Upgrade”

‣ New frontend and backend electronics

‣ New detectors in the muon endcap

‣ New detectors for extended muon acceptance in pseudorapity

‣ Outlook

‣ Techical Proposal in 2014

‣ Technical Design Report in 2016

‣ GE1/1 slice installed in Year-End-Shutdown 2016

‣ Full GE1/1 installed as early as LS2

‣ DT and CSC electronics upgrade and GE2/1, RE3/1, RE4/1 and ME0 installed in LS3

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LHC and CMS data taking performance

‣ CMS recorded about 22 fb^-1 in 2012 (8 TeV) and ~6 fb^-1 in 2011 (7 TeV)

‣ Excellent performance of the LHC (~30 fb^-1 delivered in 2011+2012)

‣ Excellent data taking efficiency by CMS muon systems

~750 Higgs bosons per hour

‣ Excellent subdetector status (live channels %) at the end of 2012 data taking

‣ Even improving through LS1 reparations

(26)

Muon system stability

‣ Efforts to achieve stability of RPC wrt atmospheric pressure

‣ Stable efficiency and stable cluster size

‣ important in trigger Pt measurement -> stable trigger rates

‣ DT trigger BX identification stable with different LHC bunch spacing

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DT electronics for Phase 2

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GEM performance

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Very good time resolution

(depending critically on the gas mixture) Excellent spatial resolution

Fully efficient at 10

⁴

overall gain

(29)

Trigger and DAQ in Phase II

‣ The L1-trigger will build on the Phase I architecture, with:

‣ track information (from outer tracker) available to all trigger objects

‣ increased granularity (EB at crystal level) &

ability to operate up to 1 MHz

‣ improved isolaEon of e, γ, µ, τ candidates

‣ vertex association to reduce effect of pileup in multiple object triggers

‣ Replacement of detector FEs

‣ Allow 10 µs latency at L1 and 1MHz L1A rate

‣ Need new FE electronics in DTs, CSCs

‣ HLT and DAQ will be upgraded to handle up to 1 MHz into HLT and 10 kHz out, maintaining present HLT rejection factor

‣ “Moore’s Law” (CPUs, networks, and storage) suggests that market technology will handle this on the timescale of LS3

(30)

HLT upgrade

‣ Now: ~13000 CPU cores

‣ Faster computers -> more calculation time -> more complex algorithms

‣ from ~160 ms/event to 500 (1000) ms per event for pileup 100 (200)

‣ Improvement in moving from shared memory use to message queues

‣ Decouple HLT algorithms from DAQ software

‣ File based processing

‣ Can run offline code directly in HLT

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Expected background rates

From measurements in existing detectors

From FLUKA simulation

(32)

L1 Trigger upgrade: technology

‣ Use of largest possible FPGAs and build more compact systems

‣ Use of standardized electronics as much as possible

‣ Still custom built, but the same for more systems

‣ New form factor replacing VME: uTCA

‣ Extensive use of optical links

‣ High data rates (high precision, more objects)

‣ Small form factor for high data density interconnections

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Upgrade:

uTCA crate,

optical connections

NOW:

VME crates with many custom

galvanic connections (pic: DTTF,

muon trigger)

(33)

Phase II tracker design

‣ High granularity tracker to provide excellent performance beyond PU 140

‣ “Pt-modules” (stack of two strip modules) provide trigger information (pT > 2 GeV)

‣ Inner stacked strip-pixel modules (improved z/r segmentation)

‣ Improved material budget

‣ Pixel with 4 barrels and 10 disks, |𝜂|<4

‣ Thin sensors, 100 um; smaller pixels 30x100 um

‣ R&D activities in progress

‣ Prototyping of 2S modules

‣ Track trigger with associative memories

W+jets, Delphes

H. Behnamian - The CMS Tracker Upgrade for HL-LHC: Sensors R&D A. Tricomi - Upgrade of the CMS tracker

(34)

Phase II tracker performance

‣ Improved pT resolution

‣ Very good resolution at L1 trigger can be achieved (picture: full tracking with L1 tracker stubs)

‣ Impressive rate reduction e.g. wrt current L1 Muon

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single 𝝻 , p

T

10 GeV

L1 stubs only

(35)

Phase II muons: H→ZZ→4 𝝻 in Delphes

‣ Using Delphes (parametrized detector description) to evaluate several CMS analyses in Phase II scenarios

‣ Validation: Delphes Phase I

configuration vs CMS Phase I FullSim

‣ Assumptions for forward muon

+tracking efficiency and resolution

‣ H→ZZ→4µ yeld increase by 35-40%

| 𝜂 |<2.4

| 𝜂 |<4.0

(36)

R&D for Phase II

‣ R&D is essential:

‣ Develop cost effective solutions

‣ Meet the challenge of high radiation and bandwidth

‣ Ongoing developments for Tracker, Track Processor, Calorimeters and Muon chambers

‣ Radiation tolerant silicon sensors for the pixel and strip detectors

‣ Radiation tolerant ASIC development (including 65 µm process), especially for trackers

‣ High bandwidth and radiation tolerant optical data transmission

‣ Radiation tolerant powering scheme

‣ Light mechanical structures, detector assemblies and high density interconnections

‣ Fast processors for track-triggers

‣ Radiation tolerant crystals, tiles and fibres for calorimeters, and radiation hard photo-detectors

‣ High rate gas chambers with improved spatial and timing resolution

‣ New “eco” gases (no impact on global warming)

‣ Demonstration of high precision timing in calorimeter pre-sampling

‣ Software development for new processing technologies (multicore processing, GPU, etc...)

‣ Many of these areas are are common with other experiments!

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Plans from LHC to HL-LHC

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LHC physics priorities in next 20 years

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‣ With LHC 13/14 TeV data until 2022 (~300 fb^-1)

‣ Measure the SM scalar boson properties

‣ Mass, J^PC

‣ Individual couplings with 5-15% precision

‣ Search for new physics at higher mass scale (new energy region)

‣ SUSY

‣ Exotics

‣ With HL-LHC 14 TeV data until ~2032 (~3000 fb^-1)

‣ High Precision SM scalar boson measurements

‣ Couplings < 5%, study rare decays and self-coupling

‣ Study VV scattering

‣ Study new physics discovered during Phase I?

‣ Search for new physics in very rare processes

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Higgs couplings with 3000 fb -1

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Higgs couplings with 3000 fb -1

39

• Extrapolation by two orders of magnitude to higher luminosity

– is subject to large uncertainties

– scenarios 1 and 2 provide likely upper and lower bounds

23

(41)

• Extrapolation by two orders of magnitude to higher luminosity

• Experience at LEP and Tevatron indicates that scaling with 1/√L is not unrealistic

(42)

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• Extrapolation by two orders of magnitude to higher luminosity

23

Scenario 1: systematics as in 2012

Scenario 2: theory syst. scaled by a factor ½, other systematics scaled by 1/√L

CMS

(43)

• Extrapolation by two orders of magnitude to higher luminosity

•With 3000 fb

^-1

the Higgs couplings can be determined with high

precision (1-4%)

Scenario 1: systematics as in 2012

Scenario 2: theory syst. scaled by a factor ½, other systematics scaled by 1/√L

CMS

(44)

Run 1 muon reconstruction performance

‣ Stable efficiency vs pileup

‣ Very good undestanding of pi/p misidentification probability and match with the simulation

40

(45)

TeV muon Pt resolution (from cosmics)

(46)

CMS Run 1 L1 Trigger architecture

42

final decision

“Level-1 Accept”

(47)

L1 Trigger in 2012

‣ Typical L1 trigger table for running in 2012

‣ Main single and multi- object triggers shown

‣ Rates reported for lumi

~6.6E33

also (0,0) “high quality” for B-physics

7.5E33 ^cha 6.7E33

nge of prescale column

95kHz

‣ Record lumi fill with peak lumi ~ 7.5E33

‣ Start near to 100kHz

‣ ~5% initial deadtime, rapidly goes <3%

(48)

L1 Muon performance

‣ Rate improvements in 2012

‣ CSCTF tighter Pt assignment

‣ Improvement in Global Muon Trigger pt merging

‣ About 50% rate reduction, for few % efficiency cost

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2012: 50% rate reduction

‣ RPC trigger for HSCP searches

‣ Implemented in 2011

‣ Possible due to 50ns bunch spacing

‣ RPC hits extended to 2 BX duration

‣ Slow particle at BX+1 produce trigger at collision BX

(49)

RPC trigger for slow particles

(50)

DT details

46

(51)

RPC details