Leslie Groer

1
Jet and Electron Identification in the Run 2 DØ
Detector

• Tevatron Run 2
• DØ Detector upgrade
• SMT
• CFT
• Preshower ICD
• Calorimeter

• Jet ID
• Algorithms
• NADA
• Trigger
• Selection
• Energy Scale
• QCD Results

• EM ID
• Reconstruction
• Trigger
• Profile
• Scale

• Leslie Groer
• Columbia University, New York
• DPF 2002, Colonial Williamsburg, VA
  May 25,
  2002

2
Tevatron Run 2

• New Main Injector and Recycler rings
• Increased luminosity and energy
• 48 pb-1 delivered
• 15.2 pb-1 recorded physics events
• ?L dt expected for 2002 300 pb-1
  Run 2a 2 fb-1

?p source
Run 2b
140x103
1.96
5.2x1032
8.6x1031
1.6x1030
typ L (cm-2s-1)
105
17.3
3.2
? Ldt (pb-1/week)
132
396
3500
bunch xing (ns)
4.8
2.3
2.5
interactions/xing
3
Overview of Run 2a DØ Upgrade

• Upgrade Calorimeter electronics readout and
  trigger
• Add scintillator in muon for fast trigger and
  extended coverage for drift chambers
• Replace inner tracking volume with Silicon and
  Fiber trackers with 2T solenoid magnetic field
  for central tracking and momentum measurement
• Add preshower detectors and replace intercryostat
  detectors
• Pipelined 3 Level trigger
• Increase DAQ capability for 132 ns bunch
  crossings

azimuthal angle ? pseudorapidity ? -ln tan(?/2)

• Muon, Calorimeter, Silicon fully commissioned and
  operational
• Fiber tracker and preshowers fully instrumented.
  Central electronics complete, forward in a few
  weekscommissioning this summer

4
Silicon Microstrip Tracker
4 H-Disks
12 F-Disks
6 Barrels

• Tracking up to ? 3
• Provide good position resolution for vertexing
• Innermost layer at r 2.6 cm
• Central region
• 6 barrels, 4 layers, axial 2o/90o stereo12 cm
  long each, SSDS
• 12 F-disks (SS)
• Forward region
• 4 H-disks (SS)
• 793k channels
• Radiation hard up to 1 Mrad
• gt90 channels operational
• SN gt 101

SS single sided DS double sided
More in Harald Foxs talk
5
Central Fiber Tracker

• Tracking out to ? 1.7
• Good momentum resolution
• 20 cm lt r lt 51 cm, 1.8 / 2.6 m fibers
• 8 double layers (axial, stereo 3o)
• 77,000 830?m fibers readout with VLPC
• Operate at 9 K, 85 Q.E., good S/N
• 10 photons/m.i.p. get to the VLPC
• Impact parameter resolution 42 ?m for SMTCFT
  tracks with pt gt 3 GeV
• No individual ladder or layer alignments yet
• Beam spot size is about 28 ?m
• Trackers shifted in z by 2.9 cm w.r.t calorimeter
  ? shifts zo

pT gt 3 GeV
d42 ?m
Beam spot 28 ?m
CFT axial stereo SMT
d
6
Preshowers and Intercryostat Detector

• Central and Forward Preshowers
• Central mounted on solenoid (h lt 1.2)
• Forward on calorimeter endcaps
• (1.4 lt h lt 2.5)
• CPS 7,680 FPS 14,000 channels
• Extruded triangular scintillator strips with
  embedded WLS fibers and Pb absorber
• Improve energy resolution measurements
• Trigger on low-pT EM showers
• Reduce overall electron trigger rate by x3-5
• Same readout electronics as CFT
• Intercryostat Detector (ICD)
• 384 scintillator tiles with WLS fiber to
  phototubes in low-B field region for readout
• Improve coverage for the region 1.1 lt ? lt 1.4
• Improves jet ET and missing-ET
• Readout through Calorimeter electronics
• LED pulsers used for PMT calibration
• Relative yields measured gt 20 p.e./m.i.p.

CPS
FPS
ICD
7
Calorimeter Overview
Central Cal.
South End Cap
North End Cap
L. Ar in gap 2.3 mm
Cu pad readout on 0.5 mm G10 with resistive
coat epoxy
Drift time 430 ns

• 50k readout cells (lt0.1 bad)
• Fine segmentation,
• 5000 semi-projective towers (0.1x0.1)
• 4 EM layers, shower-max (EM3) 0.05 x 0.05
• 4/5 Hadronic (FH CH)
• L1/L2 fast Trigger readout 0.2x0.2 towers

Ur absorber
MG

• Liquid argon sampling
• Stable, uniform response, rad. hard, fine spatial
  seg.
• LAr purity important
• Uranium absorber (Cu (CC) or Steel (EC) for
  coarse hadronic)
• Compensating e/? ? 1, dense ? compact
• Uniform, hermetic with full coverage
• h lt 4.2 (? ? 2o), l int gt 7.2 (total)
• Single particle energy resolution
• e sE / E 15 /ÖE 0.3 p sE / E 45 /ÖE
  4

OH
CH
ICD
FH
MH
EM
FPS
IH
EM
8
Calorimeter Electronics Calibration
ADC vs DAC

• Electronic readout ? live sampled energy
  in L.Ar. ? calibrated energy scale
• Determine electronic calibration coefficients for
  absolute and channel-to-channel variations from
  pulser charge injection (DAC?ADC)
• Dual gain readout with analog storage in switched
  capacitor arrays (SCA)
• Non-linear behavior of SCA chip observed for low
  energies
• ADC to GeV about 300 MeV underestimation per cell
  
• Nonlinearity lt 0.5 for cells gt 1 GeV
• Has significant effect in low energy region (jet
  widths and resolutions etc)
• Can apply universal parametrized correction for
  all channels
• Residuals after correction are better than ?5
  ADC counts on the whole range for both gains
• Correct energy in cells before clustering

dual gain
Parameterized correction based on residuals
compared to linear fit
1 ADC 4 MeV

• In calibration, correct for signal shape
  difference with simulation
• Also correct for cell-to-cell gain (ADC/DAC)
  dispersion (5 to 10)
• Apply ? intercalibration comparing slices in ? --
  flat within 2 after correction
• Improves both Zmass mean and resolution

9
Jet Finding

• Calorimeter jet
• Jet is collection of towers with a given cone R
• Cone direction maximizes the total ET of the jet
• Various clustering algorithms
• Particle jet
• After hadronization
• A spread of particles running roughly in the same
  direction as the parton
• Correct for finite energy resolution
• Subtract underlying event (modeled by minimum
  bias data)

• Parton jet
• Parton hard scattering and parton showers well
  described by pQCD
• Higher cross-section expected in Run 2 for
  higher c.m.s ?s1.96TeV
• x2 ? for pT gt 400 GeV

Jet inclusive pT spectrum
10
Run 2 Jet Algorithms

• Cell Nearest Neighbor
• Floor-by-floor clustering starting with EM3
• Each local maximum starts a floor cluster then
  add in neighbors
• Energy sharing according to transverse shape
  parameterization
• Angular matching of floor clusters
• Search for minima in longitudinal energy
  distribution to separate EM and hadronic showers
• Energy Flow algorithm
• use tracking information to better characterize
  the contributions from charged particles
• In development

• Run 1 Legacy Cone
• Draw a cone of fixed size around a seed
• Compute jet axis from ET-weighted mean and jet ET
  from ?ETs
• Draw a new cone around the new jet axis and
  recalculate axis and new ET
• Iterate until stable
• Algorithm is sensitive to soft radiation
• Improved Run 2 cone
• Use 4-vectors instead of ET
• Add additional midpoint seeds between pairs of
  close jets
• Split/merge after stable protojets found
• Algorithm is infrared safe
• kT-algorithm
• Recombination algorithm based on relative
  momentum between particles
• Theoretically favored, no split-merge
• To reduce computation time, start with 0.2 x 0.2
  preclusters

Most results using simple cone for now
11
NADA

• NADA New Anomalous Deposit Algorithm
• Identify anomalous isolated energy deposits in
  the calorimeter Hot Cells
• Source electronics, U noise, beam splash,
  cosmics etc
• Improve object resolution and MET
• Run 1 AIDA
• Only examine neighbors in the same tower for
  Ecell gt 10 GeV
• 99 efficient, BUT 5-10 misidentification rate
• Not used for cells on boundaries of layers
• FH1 and CH1 have more material

• Examine all cells with gt 1 GeV
• Remove cells lt -1 GeV gt 500 GeV
• ET lt 5 GeV removed if no neighbor with E gt 100
  MeV
• ET lt 500 GeV removed if no neighbor with E gt 2
  Ecell
• High efficiency (90) and low misidentification
• ET gt 1 GeV 0.5
• ET gt 10 GeV 0
• On average about 0.8 cells / event

12
Jet Selection

• Central jets (Run 2 cone, R0.7)
• Event Quality Cuts
• Number of jets ? 1
• Etotal in the calorimeter ? 2 TeV
• Missing ET ? 70 of the leading jet pT
• Zvtx lt 50 cm
• Leading Jet Cuts
• Jet pT gt 8 GeV (offline cut)
• 0.05 ? EMF ? 0.95
• CHF ? 0.4 (0.25 tight)
• HotF ? 10 (5 tight) (HotF ET1st
  cell / ET2nd cell )
• n90 gt 1 (number of towers that
  contain 90 of jet ET)
• Efficiencies from MC
• Loose 100 Tight 98
• Flat in eta

DØ Run 2 Preliminary

• Non-linearity of SCA included in MC

13
Jet Energy Scale

• Correct Jet Energy back to the particle level

• Eoffset energy offset from underlying event,
  pile-up, Uranium noise
• determined from Min. Bias Events
• Rcalo calorimeter response
• Calibrate EM response on Z?ee mass peak
• Measure from ET balance in ?jet events
• Rcone energy contained in jet cone
• Correct for losses due to out-of-cone showering
• Use MC-energy in cones around the jet axis

Photon-jet Events
Preliminary correction being applied with 10
systematic uncertainty
14
Central Jet Triggers
All L1 trigger towers at ? lt0.8 are
instrumented, complete coverage coming soon

• L2 jet
• Cluster 3x3 or 5x5 trigger towers around L1 seed
  towers
• L3 jet
• Simple cone or tower NN algos 0.1x0.1 towers
• 3 single jet triggers (single tower)
• JT_LO L1 5 GeV, L310 GeV
• JT_HI L110 GeV, L315 GeV
• CJT40 L140 GeV
• Efficiency
• Standard jet selection, offline pT gt 8 GeV
• Very sharp turn on

Efficiency vs jet pT CJT(1,3) CJT(1,5) CJT(1,7) CJ
T(1,10)
L1 Trigger efficiency CJT(1,x)
L1 Trigger efficiency CJT(2,x)

• L1 single jet efficiencies
• Ask for one or two hadronic trigger towers
  (0.2x0.2) above threshold
• Use muon trigger as unbiased reference for
  statistics to measure turn-ons
• Ask for one and only one reconstructed jet in
  ?lt0.7
• L1 hadronic response about 40 low for current
  data set

15
First Run 2 QCD Physics
Dijet mass spectrum at 1.96 TeV
Inclusive jet pT spectrum at 1.96 TeV
?Ldt 1.9 0.2 pb-1
?Ldt 1.9 0.2 pb-1
Highest 3-jet event ETjet1 310 GeV Etjet2
240 GeV ETjet3 110 GeV Etmiss 8 GeV
Only statistical errors
Only statistical errors

• Central jets
• Not fully corrected distributions
• Preliminary correction for jet energy scale(but
  no unsmearing or resolution effects)
• 30-50 systematic error in cross-section
• No trigger selection efficiency corrections

16
EM ID and Reconstruction

• Concentrate on high PT objects
• Look for narrow isolated clusters with high EM
  fraction, track match for electrons, none for ?
• Electron object reconstruction
• PTmingt1.5 GeV
• EM fraction gt 0.9
• Isolation
• CC ?3x3 EM towers
• EC All cells in cone of 20 cm radius at EM3
  around hottest channel
• Track match pT gt 1.5, ?Rlt0.5
• Preliminary fake rate calculated from 2nd
  unbiased jet passing standard EM selection in jet
  triggers ? 0.6?0.1

• Hmatrix
• Measure compatibility of EM cluster with an
  electron shower ? ?2
• Discriminate against hadronic (?) decays that
  pass EM fraction and isolation cuts
• Use longitudinal and transverse shower shapes to
  take into account correlations between energy in
  cells

• Tuned on MC in ? ? bins of 0.1, ? lt 3.2 for
  different energies
• HMx8 / HMx9 / Hmx41
• Energy fractions in eachfloor (PS), EM1, EM2,
  EM3, EM4
• ??, ?? in EM3 ? grid (6,6)
• log(Etot)
• Z/?z vertex

17
Triggering on electrons

• L1 EM Trigger
• Look for single EM trigger tower (0.2 x 0.2)
  over threshold
• Scale calibrated 10
• No hadronic veto
• Use bootstrap method to calculate efficiencies
  
• L2 EM Trigger
• Use 3x3 NN algorithm with 1 GeV seed
• L3 EM Trigger
• To measure the trigger efficiency, select good EM
  objects
• EM frac gt 0.9, isolation lt 0.2,HM41 lt 200, h lt
  0.8
• L3EM(1,15,emfr) rejection 5.1
• Add shower shape? can drop energy
  thresholdL3EM(1,12,emfr,shape) rejection 4.2

L1 Trigger effic. CEM(1,x)

• L3 Trigger effic.
• L3EM(1,15)
• L3EM(1,12,shape)
• L3EM(2,10)

18
Reconstructed EM profiles
DØ Run 2 Preliminary

• Energy Fractions
• pTgt20 GeV from EM_HI trigger
• QCD MC

• Energy Fractions
• good EM candidates that reconstruct to Z
  mass
• Zee MC

Efficiency from 2nd e in Zee sample (pTgt20GeV,
with track match) HMx9 lt 100 94
HMx9 lt 25 82
19
Energy Scale from Z? ee

• Compare data and Zee MC Mass distributions to get
  absolute energy scale
• Use standard EM selection with geometrical
  corrections (phi cracks, eta dependence etc)
• ? 2 EM objects, ET gt 20 GeV
• isolation lt 0.1
• 0.95 lt EM fraction
• HMx8 lt 100
• Paramaterize Etrue E(1 ?)
• Fit for Z mass with Breit-Wigner and find ? which
  maximizes a likelihood

CCEC

• Not applied phi-intercalibration, pulser
  corrections etc. so calculate energy correction
  for each cryostat region to restore Z-peak to its
  expected value
• Gives correction lt few
• Work underway to add tracking information,
  calibration for individual cryostat quadrants

20
Check Energy Scale with W? e?

• em objects
• with track match
• el-id criteria

EM cluster with SMT track
Search for cluster-global track match in EM
sample (scale corrected)

• EM Object
• ETgt25 GeV in ? lt 0.8
• -0.05 lt isolation lt 0.1
• 0.95 lt emf lt 1.05
• HM8lt50, HM41lt200
• MET gt 25 GeV

• Global tracks
• 10 lt Nhits lt 16
• pT gt 5 GeV
• Track to EM cluster match
• ?? lt 0.05, ?? lt 0.2

W selection
Fit the electron p spectrum
E/p 1
21
Summary

• Tevatron Run 2 well underway
• DØ detector performing extremely well but many
  new systems coming online
• Complete readout and integration of tracking and
  preshowers
• L1 extend coverage in eta track triggers
• L2 calorimeter and track triggers
• New EM/jet algorithms (e.g. did not discuss
  identification of softer electrons in jets,
  especially useful for semileptonic b-decays use
  road method)
• Expect rich physics program from large statistics
  for high pT events
• Improve knowledge of QCD, proton structure
  functions
• Measurements of heavy flavor and Electroweak
  physics
• Searches for new phenomena, quark compositeness,
  extra dimensions, W, Z
• The elusive Higgs boson
• D0 detector poised to take full advantage of the
  higher instantaneous and integrated luminosities

22
EM geometric corrections and resolution

• EM Geometric Correction
• Energy corrections for geometric effects (e.g.
  phi cracks, eta dependence due to dead material
  in front of calorimeters)
• Single electron MC
• EM Resolution
• Single electron MC
• Calorimeter info only (no preshower)
• Correcting for phi cracks and eta correction
  Calculate ? from cluster position in EM3

Eta correction factor
E (GeV)