Muon Detectors: Challenges at High Luminosity

Pascal Dupieux (ALICE) Alexei Safonov (CMS)Peter Kluit (ATLAS)

Giacomo Graziani (LHCb)

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Muon Detection at the LHC• The “Big Four” at the LHC: – So different in physics programs,

detector designs and technologies – Yet so similar in their reliance on

robust muon triggering and detection in delivering on their physics goals

𝐵𝑠→𝜇𝜇

𝐻→𝑍→ 4 𝑙

J /ψ→𝜇𝜇 𝐻→𝑊𝑊→2𝑙2𝜈

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CMS & ATLAS at HL-LHC• Robust muon triggering and identification are

major discovery drivers at the LHC:– Critical for precision Higgs measurements of both

bosonic and fermionic couplings:• HWW and ZZ drive HVV couplings• Httmth+X: key for Hff couplings

– Requires triggering on a soft muon

– SUSY: need access to low pT muons

• Relative impact increases at high luminosity– Muons are least affected by collective effects of

occupancy, e.g. trigger rates grow only linearly with luminosity

• Focus on maximizing the potential of large datasets to be collected at HL-LHC– Maintain current performance

• Pseudorapidity coverage and momentum range– Seek acceptance gains where possible

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CMS and ATLAS: Common Challenges• High luminosity can adversely affect

muon system performance– Forward region |h|2.0 especially

challenging• Rate in 10’s of kHz/cm2 and higher towards

higher h– Reduced resolution and longevity issues

• Accumulated charge in C/cm2

– New requirements often exceed capabilities of the existing electronics• Trigger and readout

• Trigger rate increases– Even if scales linearly with instantaneous

luminosity, the rates get too highLevel-1 Trigger Muon Candidate h

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CMS: Forward Region Challenges• CMS Muon system: offline and

trigger coverage to |h|=2.4– Drift tubes (DT) in the barrel– Cathode Strip Chambers (CSC in the

endcap)– RPC provide additional redundancy to

|h|=1.6• Key element is the region of 1.6 <|

h|>2.4:– Highest background rates yet least

redundancy, most vulnerable at high luminosity

– Challenging B-field topology• Awkwardly, if there is one place to

make large physics acceptance gains, it is in the forward region

HZZ4m : ~50% acceptance increase if hmax=2.44.0

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CMS: Forward Trigger Challenges• Not loosing trigger coverage is key

– pT mismeasurements drive trigger rate– Level-1 track trigger helps, but in the high eta

“corner” track trigger has reduced performance • Large rate reduction using bending angle

– Need good spatial resolution and rate capability– Larger lever arms using new detectors and existing

CSC chambers in the same station– Must measure bending angle close to the

interaction point

• Else radial B-field and multiple scattering quickly diminish discrimination

• Two regions:– Lower eta 1.6<|h|<2.1: a new

GEM station GE-1/1• “Early” Phase-II, install in LS-2

– Higher eta 2.1<|h|<2.4: even larger challenge • Upper part of ME0 in trigger

(paired w/ CSC ME-1/1)• GEM station GE-2/1 • iRPC stations RE-3/1 and 4/1

• Expect x5-10 rate reduction with new detectors

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CMS: Forward Muon Extension• Extend offline muon

coverage to |h|=4– ME0: small area, but nearly

doubles CMS muon coverage– Can be optionally integrated

into the new forward calorimeter

• Match muon “stubs” and forward pixel extension tracks– ME0 is a multi-layer detector to suppress

neutron backgrounds• High efficiency and low fake rate

– Resolution is good enough and multiple scattering is low enough in ME0

– Muon system can improve momentum measurement

2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023LS1 LS2 Phase 1 Phase 2Nominal lumi

~14 TeV

2 x lumi~14 TeV 3000 fb-1

LS1: Detector consolidation

Install originally planned ME4/2 + RE4/2

Move part of DT electronics from detector to cavern and redesign in higher performance uTCA technology.

Upgrade ME1/1 electronics.

LS2: Anticipated phase-2 upgrades

Muon trigger: Additional detectors in forward region of all 4 stationsRapidity extension of tracker, calo, muon to |h|~4

Installation of GE1/1Combined CSC+GEM trigger

Other CMS upgrades, e.g. L1 trigger

LS3: HL upgrades

Redesign of DT on-chamber electronics

Elec

tron

ics

Dete

ctor

s

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ATLAS: Endcap Detector Challenges The high luminosity will lead to higher rates and occupancies.This becomes critical after LS2 in the endcap region at low radii.The New Small Wheel NSW detectors are designed to have lower occupancies and more capabilities to reduce the backgrounds.

NSW containing MMs and sTGCs detectors

Micromegas (MM)

small-strip Thin Gap Chamber (sTGC)

Current detector and location of the NSW

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ATLAS: Endcap Trigger Challenges Triggering efficiently on muons becomes more difficult at high luminosities:• In the endcap fake trigger rates should be reduced to keep a manageable LVL1 trigger;• The unmatched low momentum particles shown below left should be reduced significantly ; • The current endcap trigger only uses the direction and position in the Big Wheel. A significant reduction is possible with the NSW by using in addition the direction and position in the NSW.

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ATLAS: High Luminosity Challenges • At the HL-LHC a new triggering scheme will be implemented implying a level 0 trigger and more sophisticated level 1 trigger algorithms. The trigger electronics for the RPCs and TGCs will be upgraded to cope with larger latencies.

• In the Endcaps the full capabilities of the NSW detectors will be exploited to sharpen the trigger threshold.• Offline combined muon reconstruction will be extended down to|η| = 2.7 using the upgraded ATLAS Inner Tracker.

2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023

LS1 LS2Nominal lumi~14 TeV

2 x lumi~14 TeV 3000 fb-1

LS1: Detector consolidation

Installed originally planned EE chambersin barrel-endcap region

LS2: Installation of NSW and other upgrades

LS3: HL upgrades

Redesign of trigger architecture and electronics, for RPC, TGC and MDT

ATLAS muon upgrades

Installation of New Small Wheel and smaller upgrades

Installation Small Wheel in 2008

LS3

ALICE Muon Spectrometer• Forward Muon Spectrometer– 2.5 < h < 4.0– 17 m long

• Tracking = 10 planes of Cathode Pad/Strip Chambers – High spatial resolution ~70 mm

• Trigger = 4 planes of Single gap RPCs– Typical threshold on single muons of pT~1 GeV/c

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ALICE Muon Spectro: Upgrade Focus• Detailed investigation of the Quark Gluon Plasma properties at

high temperature by means of rare probes produced in HI collisions– Total integrated luminosity in Pb-Pb (goal) ~10 nb-1– High-precision measurements of quarkonium states and open heavy

flavor production and flow• Medium temperature/density, production mechanisms• Equation of state, thermalization• Color charge and mass dependence of parton in-medium energy loss

– High-precision measurement of low mass vector mesons• chiral nature of the phase transition

• Addition of a detector based on pixel CMOS sensors (the Muon Forward Tracker, MFT) in the Muon Spectro acceptance for improving the muon physics capabilities – Secondary vertices – Background reduction – Better mass resolution

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ALICE : Challenges at High Luminosity• Pb-Pb 100 kHz (MAX collision rate)

– One order of magnitude above the MS present design Readout rate up to 100 kHz => no more specific

muon trigger

• Constraints in pp are expected to be less if beam induced background is limited

• Foreseen Upgrades– Replacement of front-end and readout electronics of all existing sub-detectors– No existing detector upgrade foreseen– Addition of the MFT– All upgrades scheduled to be fully installed during the LS2

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First Station M1(only used for L0 muon trigger)

LHCb: Muon System• Muon detector covering very high

rapidity 1.8< η <4.9• Operated up to 4x1032 cm-2s-1

during Run1• Average rates in most irradiated

region (detector):– 120 (260) kHz/cm2 (M1)– 60 (90) kHz/cm2 (M2-M5)

• Requirements:– station efficiency > 99%– time resolution < 5 ns

• Technology:– MWPC in most regions,– triple GEM detectors in inner region

of M1

• Upgrade conditions:– (scheduled from 2019, after LS2)– L=1 to 2 x 1033 cm-2s-1

– (independent of LHC upgrade!)• Aim is to collect 70 fb-1

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Average rates per region @1033100 kHz/cm2

10 kHz/cm2

M1

LHCb: Challenges• Detector performances at

higher luminosity must be maintained

• Rate increase critical for M1– but station not needed anymore

(trigger redesigned)• For the inner region of M2,

both rate (>1 MHz/channel at highest lumi) and integrated charge beyond safety limits in the long term– New detectors after LS3

• Readout saturation– New FE chip for new detectors– Increased number of off-

detector digital channels

• Present trigger, with L0 level based on standalone calorimeter and muon response, not suited for higher luminosity– New trigger capable of full event

reconstruction up to 40 MHz– Implies redesign and replacement of all off

detector readout boards

4 x 1032

~14 TeV 70 fb-1

LS1: Detector maintainance

LS2: Upgrade phase-1

LS3: Upgradephase-2

2 x 10331 -> 2 x1033

Replace few damaged detectors and FE boards (< 1%)

Install new 40 MHz compliant DAQ and control boards,with increased number of channels.

M1 station removed.

Install new GEM detectors in inner part of station M2

2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023LS1 LS2 Phase 1 Phase 2

LHCb muon upgrades

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Summary• Muon detection plays a key role in physics programs of all four

experiments– Clean physics signatures and relatively low backgrounds

• The impact at high luminosity can become even larger– Muon systems suffer the least from non-linear effects of high

luminosity• Overlaps still rare, trigger rates scale better with luminosity that for most

other systems

• All four experiment have a reasonably clear understanding of what needs to be done

• But challenges are significant and continued good performance of muon systems should not be taken for granted