GE2/1 Case Considerations - PowerPoint Presentation

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GE2/1 Case Considerations

Alexei

Safonov

CMS Muon Upgrades

CMS Technical Proposal in its part related to

muon

systems lists following:MEX/1 electronics upgrade (needed to keep up with L1 rate and latencyGE1/1 detector (“early Phase-2” to aid forward muon trigger) & a matching GE2/1 (regular Phase-2)GE0/1 detector (extends offline coverage beyond h=2.4, a.k.a. ME0)

RPC stations 3/1 and 4/1 (based on improved technology)DT mini-crates

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GE2/1: Local Reconstruction

Helps improve local stub-reconstruction efficiency in station 2

Without it, local stub reconstruction inefficiency due to CSC HV spacers

Overall increase in efficiency due to requiring 3 hits instead of 4 if GEM hits are presentCant drop it in near stations as without an extra confirmation as neutron backgrounds can increase

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GE2/1: L1 Muon Track Reconstruction

Better

local reconstruction propagates into higher efficiency for Track Finding

Here, we use 3+ stub configuration, which is the tighter option leading to low trigger rate (assume we are considering up to 200 PU)Caveat: below plots also include RE3/1-4/1, but with CSC 3 hit requirement in far stations we only lose 1% in plateau if RE3/1 and RE4/1 are disabledEffect on trigger rate is limited: even without GE1/1, on itself GE2/1 rate reduction is less than x1.5-2 (limited by ME2/1 resolution at L1)

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Muon Triggering at HL-LHC

Tracking trigger will help tremendously for the entire physics program

Matching

muons with tracks allows dramatic improvement in resolution and trigger rateBut… many physics models (new and old ones) predict long lived particlesHiggs portal, dark sector, new bosons, SUSY extensions, W-primes etc.CMS won’t see any of that new physics if it’s there

Tracking trigger inefficient for dxy above ~2 mm

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Is Standalone Muon Trigger at HL-LHC Possible?

Absolutely! Even with no improvements, a

dimuon

trigger will workTake thresholds from Phase-1 L1 Upgrade Trigger TDR for 2.2x1034: pt=15 and 10 GeV yielding 10 kHz of rateGE1/1 will make it more like 7.5 kHzAt 5x10

^34 that trigger will yield a rate of ~15 kHz as all muon triggers evolve linearly

Efficient

to modestly displaced

muons

:

Studied in

the

barrel:

current

muon

trigger is efficient to

muons

with

dxy

up to ~10

cm

Beyond that the problem is in

p

T

assignmentStill beats 2mm by a large margin!So it is absolutely doable, but requires maintaining standalone muon trigger capabilities (dimuon = 2 x standalone muon)

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Muon Trigger at HL-LHC

Current barrel

muon

trigger pT assignment is inefficient for highly displaced muonsIt finds them, but pT is measured lowImpact

parameter of ~10cm still beats 2mm by a large margin, but we may be able to do better

Study shows the problem is a consequence of the momentum measurement algorithm focusing on

absolute values of bending angles in station 1

Great for prompt

muons

, really non-optimal for displaced

muons

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Stub Alignment Algorithm

Checks if the stubs are aligned with each other

If aligned, it’s high

pT, whether prompt or displacedFigure of merit: difference of inverse bend angles 1/

fImplies we can measure bending angles in at least some stationsNew p

T assignment works well with even a very simplistic algorithmTrigger rate (PU only) is the same as for the current algorithm

Should

decrease with adding more features to the algorithm

Gearing up for a more complete simulation

Working

on implementing

it in HLT (Sven)

Started expanding

into forward

region (Jose)

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Bending Angles

Important for triggering on highly displaced

muons

Work well in the barrel:Thick detectors make a large lever arm, large magnetic fieldCSC

bending patterns in ME-X/2 may be sufficient as magnetic field is much larger in ME2/1 compared to ME1/1The only problem is we won’t have these studies done by the end of this Summer

Works in the very forward region

Weakened

magnetic field, but

GE1

/1 example

says

that an increased lever arm

helps

Need more than a single angle measurement (GE2/1!)

Region of eta below 1.6:

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Further Considerations

If ME1/1 performance at HL-LHC is significantly degraded, having high efficiency in station 2 will help

GE2/1 helps increase that efficiency from 80-85% to 95%

Can be important for matching with tracking trigger tracks as GE1/1 aloneHLT uses standalone muon reconstruction in its selectionsIf ME3/1 and ME4/1 do not receive new electronics, expect decrease in reconstruction efficiencyAdditional points from GE2/1 and GE2/1-ME2/1 bending angle will help strengthening standalone muon

reconstruction in that regionAt the very least descoping both GE2/1 and ME3/1+ME4/1 in the same scenario seems worrisome

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