Comparing Vertex from Z μμ to the Remaining Tracks

SEDWG April 22, 2023 R. Kelley

Comparing Vertex from Z μμ to the Remaining

Tracks

April 22, 2023

Ryan Kelley

SEDWG April 22, 2023 R. Kelley2

Introduction

• Compare vertex of the Z μμ • Idea is to take the μ’s from the Z

μ from primary interaction point used two μ tracks to form a vertex

using KalmanVertexFitter

used remaining tracks with pT > (1.0, 0.5, 0) or |p| > (0.5,1.0, 2.0) to form another vertex

using KalmanVertexFitter using TrimmedVertexFitter using AdaptiveVertexFitter

compare the difference in X,Y,Z positions

Selection• Used SEDWG PAT configuration 2_2_10• Datasets:

– /Zmumu/Summer08_IDEAL_V11_redigi_v2/GEN-SIM-RECO

• 20K Events• Selection

– μ's• pT > 10.0 GeV• GlobalMuonPromptTight (recommended by μ I.D. note)

– χ2/dof < 10

– |d0| < 2 mm (designed to reject decays in flight and punch through)

– nHits from track ≥ 11

– Z Candidates• Created Z’s from μ+μ- (from above mu’s)

• mZ – 4ΓZ < mμ+μ- < mZ + 4ΓZ

Several Fitting Option oob

• The fitters now available are – The KalmanVertexFitter: the simple least-squares algorithm (uses all the tracks

with a weight of 1)– The AdaptiveVertexFitter: iterative re-weighted KalmanFitter? which down-

weights tracks according to their distance to the vertex– The TrimmedVertexFitter: conventional robust version of the Kalman fitter, which

removes tracks incompatible with the vertex– The GaussianSumFitter: fitter using the non-Gaussian distributions of

measurement errors– The AdaptiveGsfVertexFitter: a combination of the adaptive fitter and the

Gaussian-sum fitter

• The GSF fitters are designed for objects that use GSF error calculations (e.g. Electrons)

– wouldn’t work for tracker Tracks (from the μ’s and general tracks)

• https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideVertexFitting

Vertex formed from Tracks

• Used all tracks not from the Z candidates’ μ’s with– pT > 1.0 GeV

– pT > 500 MeV

– |p| > 500 MeV– |p| > 1.0 GeV– |p| > 2.0 MeV

– no pT cut

Convergence of the Fits

• Only looked at the first three types– GSF fitting primarily for electrons

– KVF and AVF w.r.t BeamSpot (TVF not implemented in CMSSW)

• Log scale• The TVF rejects tracks when

they’re killing the fit more invalid.

Validity of the Fits

χ2/dof of the Fits

χ2/dof of the Fits (zoom)

# d.o.f of Fits

χ2 prob of Fits

# Tracks Used

Track Weights Used

# Tracks Used vs # d.o.f

Vertex formed from Z’s

• Used the two tracks not from the Z candidates’ μ’s with– Used KalmanVertexFitter since only two

tracks and we want the weight always =1

Validity and # d.o.f of vertex from Z candidates

χ2/dof and χ2 prob. of vertex from Z candidates

Delta = Track - Z

• Used attribute (vx, vy, vz) to calculate

– Δvx = vxtracks – vx

– Δvy = vytracks – vy

– Δvz = vztracks – vz

• Showing AVF results

• Δvx = vxtracks – vx

• no pT on Tracks

• pT > 500 MeV on Tracks

• pT > 1.0 GeV on Tracks

• Δvy = vytracks – vy

• no pT on Tracks

• Δvz = vztracks - vz

• no pT on Tracks

• Δvz = vztracks – vz

• no pT on Tracks

Resolution = Track - Gen

– Res vx = vxtracks – vx

– Res vy = vytracks – vy

– Res vz = vztracks – vz

Resolution vxTracks

• Res vx = vxtracks - vx

• no pT on Tracks

Resolution vxTracks

• pT > 1 GeV on Tracks

Resolution vxTracks

• Res vx = vxtracks – vx

Resolution vxTracks

Resolution vytracks

• Res vy = vytracks - vy

• no pT on Tracks

Resolution vytracks

• Res vy = vytracks – vy

Resolution vytracks

Resolution vztracks

• Res vz = vztracks - vz

• no pT on Tracks

Resolution vztracks

• Res vz = vztracks – vz

Resolution vztracks

Resolution = Z - Gen

– Res vx = vxZ – vx

– Res vy = vyZ – vy

– Res vz = vzZ – vz

Resolution vxZ

• Res vx = vxZ – vx

Resolution vyZ

• Res vy = vyZ - vy

• μ = 0.06 μm, σ = 12 μm

Resolution vzZ

• Res vz = vzZ – vz

Back Up

Definitions

• PCA– Point of Closest

approach (x0,y0,z0)

vxz and vy

Calculation of Weights

• Used sum of two Gaussians (core + wide)

• Mean

• Standard Deviation• √variance

μ Variables: pT

μ Variables: η

What causes this bump?

μ Variables: Φ

μ Variables: x0 and y0

μ Variables: z0

μ Variables: d0

μ Variables: # hits and χ2

Number of Z’s per Event

Comparing Vertex from Z μμ to the Remaining Tracks

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