MissingET performanceand

impact on SUSY physicsSupersymmetry in 2010’s June 21st in Hokkaido Univ.

Naoko Kanaya(Univ. of Tokyo / ICEPP)

PrefaceMissing Transverse Energy (MissingET) is the mostimportant observable for SUSY search (in case of invisible/stable LSP…)

0=MissingET(x,y) - ΣEobj(x,y)Most of energy is measuredby calorimeter and MissingETof SUSY signature is large.

Understanding and control MissingET is crucial!

MissingET:

MissingET (10fb-1)

Outline ATLAS and CMS calorimeter

MissingET commissioning

Summary

MissingET performance• Fake MissingET• Resolution, scale and tail

• MET Calibration• MET Cleaning

ATLAS and CMSCalorimeter

Requirement from MissingET measurement:• Good coverage• Full shower containment (less leakage)• Less insensitive (dead material) region

ATLAS Calorimeter• Liquid-argon and tile sampling calorimetersLiquid-argon and tile sampling calorimeters•• High granularityHigh granularity•• 3+3/3+4 longitudinal segments in barrel/endcap. 3+3/3+4 longitudinal segments in barrel/endcap.•• Nearly full coverage : Nearly full coverage : |η| |η| <4.9 (HC), <4.9 (HC), |η| |η| <3.2 (EC)<3.2 (EC)•• e/h~1.36(HB), 1.7(HE)e/h~1.36(HB), 1.7(HE)•• Absorption length ~(1.2+8.9)Absorption length ~(1.2+8.9)λλ00

H1-style weight: ΣEcell*wcell(E/V)• Energy Calibration

ATLAS : w(Ecell/Vcell)

EM-like

HAD-likeTopological clustering(remove incoherent noise)

• Noise Suppression

C1*exp(-E/V*C2)+C3

CMS Calorimeter•• PbWO PbWO44(EC) and tile sampling(HC) calorimeters(EC) and tile sampling(HC) calorimeters•• Calorimeter inside of magnets.Calorimeter inside of magnets.•• 1+3/1+2 longitudinal segments in 1+3/1+2 longitudinal segments in barrel/endcapbarrel/endcap..•• Nearly full coverage : Nearly full coverage : |η| |η| <5.0 (HC), <5.0 (HC), |η| |η| <3.0 (EC)<3.0 (EC)•• e/h~1.4 (HB)e/h~1.4 (HB)•• Absorption length ~(1.1+5.9+3.9)Absorption length ~(1.1+5.9+3.9)λλ00

EEC(photons), EHC(hadrons)• Energy Calibration

• Noise Suppression

HB HO HE ΣEB ΣEE 0.9 1.1 1.4 0.2 0.45

Cell Thresholds (GeV)

ATLAS vs CMS

4 Tesla : pT swept < 700 MeV2 Tesla : pT swept < 350 MeVB field innerregion

σ(ET) ΣET ≈ 123% √ΣET + 2%σ(ET) ΣET ≈ 53% √ΣETMET resolution

(TDR)

σ(pT)/pT = 0.5% + 15% pT

(pT in TeV)σ(pT)/pT = 1.8% + 60% pT

(pT in TeV)Inner tracker

resolution (TDR)

Ecal+Hcal pionresolution

CMSATLAS

EE

8.1%8.1

%9.41

E!"#

$%&

'+=

(%7

%90

E!=

E

"

e/h calibrated

e/h uncalibratede/h calibrated

Resolution can be better with appropriate e/h correctionin CMS.

MissingET performance• Origin of “fake” MissingET• Resolution and scale• Tail

Fake MissingETEven ATLAS and CMS have full-coverage hadroncalorimeters, there are many sources causing“fake” missingET

Energy loss in crack or dead material Mismeasured muons Detector Failure (hot/dead/noisy cells) Backgrond (beam gas and beam halo)

Dangerous background is QCD + fake MissingETsince the cross-section is huge and difficult tocontrol “tail”.

Understanding “fake” MissingET (tail) is moreimportant than getting the better resolution and

scale for SUSY discovery.

Dead Material/Crack region

ATLAS : 500GeV pi-

Detailed detector simulation is done.Understand possible problem and impacton MissingET.

Warm + coldcryostat wall

ID services+cables

η=1.4

η=3.2

Interfaceregion

Energy CorrectionDue to non-compensating and non-linearity ofcalorimeter and energy loss in dead materials,Need correction to get right MissingET scale andalso better resolution.

jet pT scale(ATLAS)

AftercorrectionBefore

Ejet = Ejetraw * f(Ejet, ηjet)

PT jet = 320~640GeV

ΣEiraw*w(Ei/Vi)+Eloss

Jet reconstruction isstrongly correlated toMissingET performance.

Mis-measured muons

muonCorrection(QCD)

• w/o• with

CMS

Muon correction(considering pT measured by muonsystem and energy deposit in Calorimeter system)gives better resolution, but also could be a source ofMissingET “tail”.

ATLAS

ResolutionMissingET resolution is strongly determined bycalorimeter stochastic term, σ~√ΣET

QCDUncalibratedTowers

CMSTDR

ATLASCSC

QCD

<MissingET>=1.23√ΣET+5.4+0.019ΣET <MissingET>=0.51√ΣET+4.5+0.018ΣET

Preliminary

ScaleJet energy scale calibration helps to get correctMissingET scale, especially imbalanced event orjets in largely different rapidity.

ATLASCSCPreliminary

<+/- 2%

MissingET Shift (relative)MissingET Shift

CMSTDR

w correction

ttbar

QCD is comparable background with other processesin 0-lepton mode analysis. bb (i.e. with real MissingET)would be dominant background with a cut ofMissingET > 100GeV.

Tail (QCD)

MissingET ATLAS(Fast simulation)

Blue: t tRed: WGreen: ZMagenda: QCD

Most of QCD background withMissingET >100GeV comes fromsemi-leptonic b,c decays

This is true only if jet and METdistribution is Gaussian…

SUSY (～1TeV)

MissingET (GeV)

MissingET commissioning

• MissingET calibration• MissingET cleaning

MissingET Calibration (1)Minimum Bias events are good calibration sampleat early run (large statistics, almost no energyimbalance, I.e. no real MissingET ).

Resolution can be validated in low Etsum region.Contribution from out-of-acceptance and sweep-out charged particles are large.

~0.52 √ Etsum

σ(MissingEX)---- Refined---- Truth---- Truth(muons)---- Truth(acceptance)

MissingETATLAS(Preliminary)

<>~80MeV<>~3.1GeV<>~4.4GeV

MissingET Calibration (2)Calibrate MissingET scale byZ mass peak using Z(ττ -> lepton+hadron)

Use the collinear approximationto reconstruct Z mass.

h

l

νν

νν

Z

21 !!!!

xx

MM

jj"

~4% / 1GeV

Ptau = pl/xllh

215/7000(MU15,EM15)

MissingET Calibration (3)Calibration using various physics process is usefulbecause of cross-check and topology dependence.

Z(ee,µµ)+njetsReplace pT(ll) with MissingET

W(lν)+njetsUse shape of Jacobian peak

reso=7GeVreso=7GeVreso=8GeVreso=8GeV

Scale=0.9Scale=0.9Scale=1.0Scale=1.0

MissingET Cleaning (1)Difficult to understand and clean-up MissingET.Learn from Tevatron’s experience.

D0 RunIIMET-30GeV Trigger

V. Shary CALOR04

••after cleaningafter cleaning

•• Fake Fake MissingETMissingET•• Beam lossBeam loss•• Cosmic Cosmic muonsmuons•• Detector failureDetector failure

• ≥1 central jet• ≥4 tracks• ≥1 vertex• Fem > 0.1• Fch > 0.175

Possible sets ofpreselection (CDF)

source

MissingET Cleaning (2)

Events with possible detector failure is simulatedto develop monitoring, event by event detectionand correction (if possible).

Important to detect detector failure by DCS anddata and understand its effect on MissingET.

•• Perfect detectorPerfect detector•• Miscalibrated LArMiscalibrated LAr• Miscalibrated LAr+Tie

MissingET : ATLAS Z(ee) + jets

Introduced problems:0.1% LAr EM HV lines2 LAr Frond-end crate (B,E)2 Tile drawers

SummaryMissingET is the key observable for SUSY discovery.Important issues are: Control/Remove “fake” MissingET events >> QCD Understand what we measure (commissioning)Achievement of the best performance(in terms of resolution andscale) is not important for discovery but precise measurement.

Nobody(should not) believe the result of “EXCESS”w/o result of control sample.

MissingET measurement at LHC is difficult tohandle, but hope to manage it!

>> proof of our understanding detector andbackground (next talk by D.Tovey).