muon detection at cms: from detector and software commissioning to sm physics and higgs discovery

Muon Detection at CMS: from Muon Detection at CMS: from Detector and Software Detector and Software

Commissioning to SM Physics Commissioning to SM Physics and Higgs discoveryand Higgs discovery

2° year Ph.D. Seminar, February 2008

Sara Bolognesi - Torino University and INFN

Drift Tubes: Hardware and Drift Tubes: Hardware and Software CommissioningSoftware Commissioning

Outline

Introduction on Muon Detector System in CMS:

Drift Tubes detector at work!

single cell operation principle (calibration procedure)

chamber structure and track segment reconstruction

barrel: Drift Tubes (DT) and Resistive Plate Chambers (RPC)

endcap: Cathode Strip Chambers (CSC) and RPC

DT Commissioning with Cosmic Muons:

…continuous integration/commissioning effort ever since …

Magnet Test and Cosmic Challenge in 2006

Sara Bolognesi half PhD seminar (2008 Febr. 22 Torino) 3

Barrel:5 wheel (+/-2, +/-1,0) in

4 DT stations (from inner MB1 to outer MB4)

12 sectors in

Magnetic field map

B≈4T

B≈1.8T

6 RPC stations

Endcaps: 4 disks in z

2-3 rings18-36 trapezoidal CSCin outer rings (<1.6) 18-36 trapezoidal RPC

Muon detectors

half PhD seminar (2008 Febr. 22 Torino) Sara Bolognesi 4

Drift Tubes

ionization (E<1TeV, ArCO2 gas) → electron drift→avalanche at wire→signal:

drift velocity calibration: time synchronization:

tmeas = telectr + t.o.f. + tprop + tdrift

e- drift time measured and converted into distance (with L/R ambiguity)

TDC spectrum

time pedestal (ttrig)

vdrift = L / (2 × <Tmax>)

resolution = vdrift × <Tmax>

Tmax distributions


time pedestal (ttrig)

DT chambers

2D segments reconstructed in each SLpattern recognition and linear fit → L/R ambiguity solved

1D hit from drift time measurement:constant vdrift or vdrift = f(tdrift, ,Bwire,Bnorm).

3D segments reconstr. in each camber

conflicts solved and ghosts suppressed (, nhits)

r- and r-z segments matched (all combinations)

Resolutions:

r- 90m (7mrad on angle)

r-z 120m (60mrad on angle)only 4 hits

bending coordinate → 8 hits

(non-Gaussian tails from -rays)

simulation simulation

r- residuals r-z residuals


DT Commissioning with Cosmics

Timing:

Angular distribution:

cosmics have random arrival time while CMS trigger designed for bunched muons (40 MHz) with fixed t.o.f. → additional smearing of (25/√12) ns ≈ 400 m

CMS (software and hardware) designed for from IPe.g.: DT trigger < 45°, track reconstruction with vertex constraint

CMS is not designed for cosmics!

correct segment (33°)

wrong reconstructed segment (65°)

real cosmic in CMS visualization:

total rate ≈ 30000 Hz (600 Hz in cavern)

2.7dNE

dE

Distributions on CMS surface (510m on sea level):cos sin

dN

d

1.3N

N


wheel 2wheel 1

Magnet Test and Cosmic Challenge

B ramping up and down (0-4T) various times

Detector run in stable mode for more then 2 months → 230 M recorded events

14 DT chambers 21 RPC chambers

3 Barrel sectors + 60° slice of adjacent Endcap:

(some tracker modules, ECAL crystals and HCAL sectors also in the DAQ)

DAQ & trigger

subset of final readout and trigger electronics, global trigger and DAQ

36 CSC chambers


TDC spectra

trigger source:

DT Commissioning & Global Runs

noise

Test pulse signals for a single wire

good test pulse signals

electronic noise due to enabling/disabling masks

Test of calibration procedures in real life:e.g. integration of different sub-detectors

• robust software implementation• reliable strategy of databases production and storage

The full detector monitored/calibrated run by run:• high automation

Monitor of the detector performances: noise, dead wire, interchannel synchronization


My work on DT I was strongly involved in

software development:calibration, local reconstruction, Data Quality Monitoring

data taking

real and simulated data analysiscalibration, residuals, noise/dead channels

(DQM responsible at MTCC)

(calibration responsible in 2007):

Publications:

Measurement of Drift Velocity in the CMS Barrel Muon Chambers at the CMS Magnet Test Cosmic Challenge

Results of the first integration test of the CMS drift tubes muon trigger

Offline Calibration Procedure of the Drift Tube Detectors

Local Muon Reconstruction in the Drift Tube Detectors Test of the DT Simulation and Local Reconstruction Algorithms on the 2004 Test-Beam data

Nucl.Instrum.Meth.A579:951-960,2007.

CMS NOTE-2007/034.

CMS NOTE-2008/003.

CMS NOTE in publication

CMS NOTE in preparation

The CMS Precision Muon Chamber in the Magnet Test Cosmic Challenge (MTCC).

CMS NOTE in preparation


Muon momentum scale Muon momentum scale calibrationcalibration

Outline

Muon reconstruction strategy in CMS

Calibration of muon momentum scale exploiting the Z peak:

likelihood method based on real data and Z mass precise knowledge

effects due to realistic detector behavior (misalignment, B field distortion)

a use-case: evaluation of Z cross section systematics

Z resonance as a tool for “physics commissioning”


future plans: resolution, low mass resonances, backgrounds

Muon Reconstruction Tracker Muons: good resolution at low pT,

high background StandAlone Muons (DT, CSC, RPC):high purity, good resolution at high pT

Global Muons (matching):

pT resolution (barrel)

a compromise betweenmultiple scatteringand lever arm

Resolution results from

Sara Bolognesi 13

STA purity and Tracker resolution

||<2.5, M()>20 GeVMC cut:

xsec(Z→) ≈ 1.8 nbxsec × kin. accept. ≈ 0.8 nbefficiency trigger 98.1% ≈ 8000 Z with 10 pb-1

lumi ≈ 14 pb-1 ;

Physics Commissioning: Z→ “Standard candle” to measure detector performance from data and to control uncertainties and systematics:

• tag&probe method → trigger and reconstruction efficiency

• mass peak → momentum scale calibration and resolution measurement• well known xsec → constraint on PDF and luminosity

Z @ LHC


Calibration strategy The muon pT is modified to force the Z peak in the right position

pTcorr = k × pT

NOT a simple pT shift BUT a correction as a function of muon kinematic:

k = a1 + a2pT + a3|| + a42 +

8 correction parameters (ai) computed maximizing a likelihood:

(i=1,2) different for + and -

+ q×a5,i sin(+a6,i)fit Lorentzian + decr. expo.

2 2

1ln ln

2 4

Nevt

corri

i ref

LM M

Micorr computed event by event using the muon momentum correction

With a likelihood you can take into account the full kinematic for each event without averaging!!

Mref MonteCarlo or PDG value


Generated Z mass Lorentzian + decr. expo fit:

• generated Z mass 91.13 GeV

≈ 50 MeV PDF effect

• generated mass 90.89 GeV

≈ 250 MeV Final State Radiation

Results from the fit used as reference and MZref value in the likelihood

fit Lorentzian + decr. expo.

FSR


Reconstr. Z mass

Tracks

Tracks

STA scale bias > 10%

GLB and Tracks scale bias 0.5%

bias linear in pT and parabolic in (no dependence)

Mean 90.89 ± 0.02

Gamma 2.95 ± 0.05

Mean 88.2 ± 0.2

Gamma 17.7 ± 0.4

Mean 89.7 ± 0.1

Gamma 16.4 ± 0.3

Mean 90.89 ± 0.02

Gamma 2.95 ± 0.05

Mean 88.2 ± 0.2

Gamma 17.7 ± 0.4

Mean 89.7 ± 0.1

Gamma 16.4 ± 0.3

STA


Realistic detector Scenarios with worsening of the detector behaviour:

Tracker and Muon System misaligned in 10pb-

1 scenario:

B field distortion:

Tracks: additional dependence

B'=B*1.002

B'=B*1.02

B'=B*1.05

Tracks:• new little dependence on

STA• big dependence on

• new dependence

• additional correction as a function of pT

(only 2‰ distortion)

(barrel yoke: 2% distortion)

(endcap: 5% distortion)

(B increased => pT underestimated)

GLB: not sizeable effects


Systematics on Z cross section

Muon momentum scale systematics:

GLB+Track+STA 2.7%

;orig corr orig

orig

syst

GLB+Track 0.03%

Z reconstructed with GLB+GLB, GLB+Tracks, GLB+STA to maximize efficiency,standard selection cuts applied on pure signal sample

Other systematics:

Tracker misalignment:• 3.5% without corrections • 0.9% after corrections

B field misknowledge: • 1.8% without corrections • 0.5% after corrections

mod ; ;

;

i corr orig corr

orig corr

syst


Muon System misalignment:• 3.2% without corrections • 0.3% after corrections

consider background in the likelihood (from sidebands)

Future plans Improve the likelihood convolving resolution function

resolution = Gaussian resolution = Crystal Ball

Extract also the muon resolution as a function of muon kinematic

Study low mass resonances (J/, ) to calibrate low pT muons

( ') ( ) exp( ) ( ')F M lorentzian M M resol M M dM (Gaussian with asymmetric queue)

FSR

FSR effect well fitted

= 1.2

= 1.15±0.05 GeV

= 3.4

= 1.08±0.05 GeV


Plans for H→ZZ→Plans for H→ZZ→

H→ZZ→4, MH = 150 GeV

H→, MH = 100 GeV

H→ZZ→4e, MH = 150 GeV

exc

lud

ed

by

LE

PHiggs @ LHCPRODUCTION

DECAY


New channel : H→ZZ→ Leptonic final states favored inside the big hadronic background at LHC

quite high BR ≈ 10 × BR(4)

Difficult to work with MET: good detector control needed; high DY background

H→ZZ→4l “golden channel”

H→WW→lnln most promising @ 160GeV

Not yet considered:

H→ for low Higgs mass

g

g

HZ

Z

HZ

Z

V

V

≈ 50 fb ≈ 9 fb

150 GeV

MH

200 GeV

500 GeV

Nev(1 fb ≈ start-up year)

59

15

30


H→ZZ→analysis strategy

Ask for

Main backgrounds: ttbar → bb ≈ 9.4 pb

ZZ → ≈ 0.10 pbWW → ≈ 1.3 pb

Drell-Yan (+jets) → jets) ≈ 65 pbWZ → ≈ 0.25 pb

→ irreducible

→ big (QCD process)

→ high efficiency needed→ MET resolution is crucial!!

exactly 2 with high pT (>20 GeV) in barrel region with opposite charge and M() ≈ MZ

high MET = pTZ (big for high MH)

central jet veto

• b-tagging against ttbar

Analysis cuts as a function of MH → maximum significance for right MH

• single Z has lower pT,• ZZ more soft and less central (same for from ttbar),• WW are back-to-back → lower MET,

kinematical cuts:

ATLAS significance (3years low lumi)


Publications on Z and H

CMS technical design report, volume II: Physics performance. J.Phys.G34:995-1579,2007.

Boson-boson scattering and Higgs production at the LHC from a six fermion point of view: Four jets + l nu processes at O( alpha(em)**6 ). JHEP 0603:093,2006, e-Print: hep-ph/0512219

W and Z bosons physics at LHC at low luminosity. IFAE proceedings: Pavia 2006, High energy physics

Workshop on CP Studies and Non-Standard Higgs Physics e-Print: hep-ph/0608079

Les Houches physics at TeV colliders 2005, standard model and Higgs working group: Summary report.e-Print: hep-ph/0604120

HERA and the LHC: A Workshop on the implications of HERA for LHC physics. Proceedings, Part A.HERA and the LHC: A Workshop on the implications of HERA for LHC physics: Proceedings Part B.CERN-2005-014, DESY-PROC-2005-01, e-Print: hep-ph/0601013 + e-Print: hep-ph/0601012

Higgs at CMS with 1, 10, 30 fb-1. 2007 International Linear Collider Workshop proceedings to be published

Workshop sui MonteCarlo la Fisica e la Simulazione a LHC. Proceedings in preparation

Study of VV-scattering processes as a probe of electroweak symmetry breaking.CMS Analysis Note, CMS-AN 2007/005

Towards a measurement of the inclusive W→ and Z→ cross sections in pp collisions at √s = 14 TeV. CMS Analysis Note, CMS-AN 2007/031


The end. Thanks!The end. Thanks!

Back-up slides Back-up slides

Drift Tube non-linearities

test beam (0°) test beam (30°)

A parameterization of the cell response can be used:

vdrift = f(tdrift, ,Bwire,Bnorm).

Angular effects:

Magnetic field effects:

simulation (wh+/-2)

reconstr. with constants vdrift

Residuals

TDC spectrum TDC spectrum

e-

half cell



half cell

half cell

Drift Tubes in real life! rays: high energy e- knocked out from atoms by the e-

after-pulses: primary e- produce that can extract secondary e- from cell wall

shorter drift time

secondary signals after Tmax

Other effects:

(a),(f) random electronic noise

(b),(e) pile-up hits from muons in other bunches of the beam(d) after-pulses

(c) signal region

test beam

MTCC

simulationResiduals

TDC spectrum

tsecondary - tprimary

e-

e-

e-

W1

10 10 11 10 10 11 10 10 11

W2 W1 W2 W1 W2

MB1 MB2 MB3 MB4

W1 W2 W1 W2

10 11 14 14

TOF effect (10 ns)

10

B = 3.8 T (global run)B off (local run)

ttrig for two trigger configuration:

Shift ~ 28 BX

Tm

ean

[n

se

c]

MB1

MB2

MB3

MB4

ttrig for two MTCC runs:

Station & Sector1-> 12 1-> 12 1-> 12 1-> 12

Technical Trigger

Default Cosmic

ttrig calibration


Meantimer computation

Different formulas for different track patterns

Tmax distributions (“meantimer”)

(most simple case)

123 1 3max 22

t tT t

234 2 4max 32

t tT t

It’s the average Tmax mediated on the whole semicell:



~2%

W1 W2 W1 W2 W1 W2

MB1 MB2 MB3 MB4

W1 W2 W1 W2

vdrift for each SL

W1 W2 W1 W2 W1 W2

MB1 MB2 MB3 MB4

W1 W2 W1 W2

SL thetaSL phi

vdrift(Boff) - vdrift(Bon)

vdrift(Boff)for each SL

10 10 11 10 10 11 10 10 11 10 11 14 14

10 10 11 10 10 11 10 10 11 10 11 14 14

10

10

vdrift calibration

Sara Bolognesi 31

hit resolution = vdrift × meantimer

hit resolution distribution for each SL

deviation from linearity

mean 560m

mean 600m


With B on the resolution become worse because of deviations from linearity

W1 W2 W1 W2 W1 W2

MB1 MB2 MB3 MB4

W1 W2 W1 W2

CM

S N

OT

E 2

005/018

10 10 11 10 10 11 10 10 11 10 11 14 1410

Resolution calibration


muon detection at cms: from detector and software commissioning to sm physics and higgs discovery

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