tracking/vertexing/beamspot/b-tag results from first...

Tracking/Vertexing/BeamSpot/b-tagResults from First Collisions

(TRK-10-001)

Yanyan Gao, Fermilab

on behalf of Tracking-Btagging POGs

03 March 2010 / CERN

CMS General Weekly Meeting: GWM8

Contributors and Acknowledgement• TRK-10-001 summarizes ∼ 10 analyses performed with Dec09 data by

many people in Tracking/B-tagging POGs and Tracker DPG.

• List of the ContributorsW. Adam, J. Bendavid, J. Bernardini, P. Bortignon, G. Bruno, K. Burkett,

G. Cerati, S. Chauhan, T. Dorigo, B. Drell, F. Fiori, M. Galanti, Y. Gao,

A. Giammanco, M. Gouzevitch, G. Hanson, G.-Y. Jeng, H. Liu, B. Mangano,

M. Margoni, N. Marinelli, F. Palla, L. Perrozzi, G. Petrucciani, F. Ptohos,

L. Quertenmont, A. Raspereza, A. Rizzi, F. Simonetto, G. Sguazzoni, C. Saout,

L. Spiegel, K. Stenson, K. Ulmer, L. Uplegger, A. Venturi, J.-R. Vlimant, F. Yumiceva

• We would like to thank the ARC memembers

James Alexander, Vyacheslav Krutelyov, Michele Pioppi

for their help and support

Yanyan Gao, Fermilab Tracking/Vertexing/BeamSpot/b-tag Results from the First Collisions March 03, 2010

Introduction and Documentation• TRK-10-001 demonstrates tracking works in collision based on

– basic tracking/vertexing variables

– primary vertex resolution and beam spot reconstruction

– K0S, Λ, φ, Ξ±, and K⋆(892) reconstruction

– K0S and Λ lifetime measurements

– photon conversion and nuclear interaction reconstructions

– initial study of b-tagging observables

• Supporting Analysis Notes

– Tracking and Vertexing Results from First Collsisons: AN 2010/055

– dE/dx measurement: AN 2010/020

– φ → KK analysis: AN 2010/035

– Photon conversions: AN 2010/039

– Photon conversions (CTVMFT-based):AN 2010/049

– Material Budget estimate from photon conversions: AN 2010/040

• Dedicated Twiki: https://twiki.cern.ch/twiki/bin/view/CMS/TRK10001


Approval Talks

1. Tracking/Vertexing/BeamSpot/b-tag Results from First Collisions

2. K0S, Λ0,K⋆±, Ξ±, φ resonances + dE/dx applications

3. Conversions and Nuclear Interactions


Outline

• Data/MC Samples and Event Selections

• Tracking Reconstruction

• Primary Vertex Reconstruction and Resolution

• BeamSpot Reconstruction

• b-tag Related Variables

• Conclusion


Data/MC Samples and Event Selections• Data/MC samples

– Data: /MinimumBias/BeamCommissioning09-BSCNOBEAMHALO-Dec19thSkim 336p3 v1/

– 900Gev MC: /MinBias/Summer09-STARTUP3X V8K 900GeV-v1/

– 2360GeV MC: /MinBias/Summer09-STARTUP3X V8L 2360GeV-v1/

• Common Baseline Event Selections (Not strict)

1. Trigger: BPTX/BSC/No BeamHalo {0 & (40|41) & !(36-39)}2. Run/Lumi: Select Tracker on and PhysicsDeclared Bit

3. Primary Vertex:– At least 1 real primary vertex

– Primary vertex ndof>= 3 (equivalent to nTracks>= 4)

– Primary vertex |z|< 15 cm

– Primary vertex√

(xpvtx − xbs)2 + (ypvtx − ybs)2 < 2 cm

4. Fraction of highPurity tracks > 0.2 if nTracks>= 10

• Selection efficiency on BSCNOBEAMHALO skim ∼ 85%, ∼260K events left


Basic Tracking Distributions

Basic Tracking Distributions (1/3)• Study fundamental kinematic quantities of reconstructed track

nTracks, Track η, Normalized χ2, nHits, pT , φ, dxy and dz

• Addtional track selection to reject low pT fake tracks

– Select HighPurity Tracks

– dz significance: |dz/σ| < 10 (σ =√

σd2z + σz2

pvtx)

– σpT /pT < 10%

• Selection variable distributions (NOT IN PAS)

dz significance w.r.t. pvtx-20 -15 -10 -5 0 5 10 15 20

Num

ber

of T

rack

s

310

410

510

610

ηTrack -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

Num

ber

of T

rack

s

0

20

40

60

80

100

310×

dz|>10σ|dz/

dz|<10σ|dz/

Track pT (GeV)0 0.5 1 1.5 2 2.5 3

Num

ber

of T

rack

s

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

610×

pT/pT<0.1σ

pT/pT>0.1σ

⋆ The peak at |η| ∼ 0 is mainly due to the loopers in the tracker


Basic Tracking Distributions (2/3)• nTrack and η disagreement is due to imperfect D6T MC tuning

This is also seen from underlying event studies (see PAS QCD-10-001 and backup slides)

Number of Tracks0 10 20 30 40 50 60

Num

ber

of E

vent

s

0

2

4

6

8

10

12

14

16

310×CMS Preliminary

=900GeVs

DataMonte Carlo

Track Pseudorapidity-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

Num

ber

of T

rack

s / 0

.1

0

0.02

0.04

0.06

0.08

0.1

0.12610×

CMS Preliminary

=900GeVs

DataMonte Carlo

• Data and the MC in general agree in the shape of all other variables.

2χNormalized 0 1 2 3 4 5 6 7 8 9 10

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ber

of T

rack

s / 0

.1

0.05

0.1

0.15

0.2

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0.3

0.35

0.4

0.45


=900GeVs

DataMonte Carlo

Number of Valid Hits Per Track0 5 10 15 20 25 30 35 40

Num

ber

of T

rack

s

0

0.05

0.1

0.15

0.2

0.25


=900GeVs

DataMonte Carlo


Basic Tracking Distributions (3/3)• Track pT and φ

The dip at φ ∼ −1.2 is due to inactive modules affecting mainly low-pT tracks with few layers

(GeV/c)T

p0 1 2 3 4 5 6 7 8 9 10

Num

ber

of T

rack

s / 0

.2 G

eV/c

1

10

210

310

410

510

610 CMS Preliminary

=900GeVs

DataMonte Carlo

Track Azimuthal Angle-3 -2 -1 0 1 2 3

Num

ber

of T

rack

s / 0

.1

0

10

20

30

40

50

60

70

80


=900GeVs

DataMonte Carlo

• Track impact parameters dxy and dz w.r.t. primary vertex

Track dxy corrected by pvtx (cm)-0.15 -0.1 -0.05 0 0.05 0.1 0.15

Num

ber

of T

rack

s / 0

.005

cm

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4


=900GeVs

DataMonte Carlo

Track dz corrected by pvtx (cm)-0.3 -0.2 -0.1 0 0.1 0.2 0.3

Num

ber

of T

rack

s / 0

.01

cm

0.1

0.2

0.3

0.4

0.5


=900GeVs

DataMonte Carlo


Primary Vertex Reconstruction and Resolution

Primary Vertex Reconstruction• Primary vertex efficiency ǫ ∼ 95% on BSCNOBEAMHALO skim

• Primary vertex 2D distributions


Primary Vertex Resolution (1/3)

• Primary vertex resolutions depend on nTracks used and their < pT >

• Data-driven“two-vertex” method to measure primary vertex resolution

1. Split tracks into two independent sets

2. Run PrimaryVertexProducer (offlinePrimaryVertices) on each trackset

3. Compare the two fitted vertex positions and calculate

- Resolution: σ of the gaussian fit to x1−x2√2

- Pull: σ of the gaussian fit to x1−x2√σx2

1+σx2

2

• Twiki:https://twiki.cern.ch/twiki/bin/view/CMS/PrimaryVertexResolution

https://twiki.cern.ch/twiki/bin/view/CMS/PisaVertexing


Primary Vertex Resolution (2/3)• Primary vertex resolution vs nTracks used in the pvtx

Number of Tracks0 5 10 15 20 25

m)

µP

rimar

y V

erte

x R

esol

utio

n X

(

0

50

100

150

200

250

300

350

400

450

Data

Simulation

=900GeVsCMS Preliminary,


m)

µP

rimar

y V

erte

x R

esol

utio

n Y

(

0

50

100

150

200

250

300

350

400

450

Data

Simulation



m)

µP

rimar

y V

erte

x R

esol

utio

n Z

(

0

50

100

150

200

250

300

350

400

450

Data

Simulation


• Fitted pulls vs nTracks from the primary vertex distributions


Prim

ary

Ver

tex

Pul

l X

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Data

Simulation



Prim

ary

Ver

tex

Pul

l Y

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Data

Simulation



Prim

ary

Ver

tex

Pul

l Z0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Data

Simulation



Primary Vertex Resolution (3/3)• Primary vertex resolution vs nTracks for different average pT


m)

µP

rimar

y V

erte

x R

esol

utio

n X

(

0

100

200

300

400

500

600 = 900 GeVsCMS Preliminary,

< 0.4 GeVTPData 0.0 GeV <

Simulation


Simulation


Simulation


m)

µP

rimar

y V

erte

x R

esol

utio

n Y

(

0

100

200

300

400

500



Simulation


Simulation


Simulation


m)

µP

rimar

y V

erte

x R

esol

utio

n Z

(

0

100

200

300

400

500



Simulation


Simulation


Simulation

• Fitted pulls vs nTracks for different average pT


Prim

ary

Ver

tex

Pul

l X

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8



Simulation


Simulation


Simulation


Prim

ary

Ver

tex

Pul

l Y

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8



Simulation


Simulation


Simulation


Prim

ary

Ver

tex

Pul

l Z0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8



Simulation


Simulation


Simulation


BeamSpot Reconstruction

BeamSpot Reconstruction• Exploit d0-φ0 correlation to fit BeamSpot (CMS Note 2007/021)

d0(φ0, z) = x0 · sin φ0 + dxdz

· sin φ0 · z − y0 · cos φ0 −dy

dz· cos φ0 · z

d0-φ0 for a displaced beamSpot when (0,0) (left) and fitted BS are used (right) for a single run

• Beamwidth measured in 900(2360)GeV

σx ∼ 200(120)µm, σy ∼ 250(120)µm and σz ∼ 4(2.8)cm

• Compare with results from the primary vertex distributions

Run

904 907 907 911 911 911 912 912

916 (2.36 TeV)919

923 (2.36 TeV)

x (c

m)

0.105

0.11

0.115

0.12

0.125 CMS Preliminary 2009

PrimaryVertex

Beam Spot

Run

904 907 907 911 911 911 912 912

916 (2.36 TeV)919

923 (2.36 TeV)

y (c

m)

0.02

0.03

0.04

0.05

0.06 CMS Preliminary 2009

PrimaryVertex

Beam Spot

Run

904 907 907 911 911 911 912 912

916 (2.36 TeV)919

923 (2.36 TeV)

z (c

m)

-1.5

-1

-0.5

0

0.5

1

1.5CMS Preliminary 2009

PrimaryVertex

Beam Spot


b-tag Related Variables

b-tag Related Variables Crucial at Higher√

s

• Data has few well-defined jets or tracks with P used in b-tag

• We validate the variables that are crucial for b-tag

− 3D impact parameter significance

− Data/MC match well, indicate data is udsg dominated

• Add more comments..


SV Reconstruction Using All Tracks• Secondary vertex reco. tested on all tracks and we reconstruct K0

S

• Inclusive secondary vertex finder works well on two-track vertices


SV Reconstruction Using Tracks in Jets• nTracks (Left) and normalized χ2 for vertices in jets

– Secondary vertex reconstruction has been performed with a slightly modified version of algorithm

– K0

S veto is applied Lxy < 2.5cm and |MKs− Mvtx| > 0.015GeV

• Secondary vertex 3D decay length (left) and vertex mass (right)


Conclusion• We have studied the reconstructed tracks in the first data and observe

agreement with simulation

1. Shape of fundamental track kinematics matches well

2. Primary vertex resolution measured with data-driven method

σx,y ∼ 50µm and σz ∼ 70µm with nTracks(pvtx) > 10

3. BeamSpot reconstructed with d0-φ0 fitter and with primary vertices

900(2360) GeV Data: σx ∼ 200(120)µm, σy ∼ 250(120)µm and σz ∼ 4(2.8)cm

4. b-tag related variables match well between data/MC

– Tracking impact parameter significance indicate 2009 data is udsg-dominated

– Inclusive secondary vertex reconstructed tested in all tracks and K0

S is reconstructed

– Secondary vertex reconstruction using tracks in jets are tested with good data/mc agreement

• V0, γ conversion and nuclear interaction results follow next


Supporting Material

Run/Lumi SelectionsRun LS ranges Triggered Events Selected Events

123592 Physics Declared Bit never set

123596 2-end 4657 3821

123615 Not available in December 19th processing

123732 62-109 2546 2096

123815 8-end 515 431

123818 2-42 1267 1051

123906 19-28 228 183

123908 2-12 152 124

124006 7-end 78 62

124008 1-end 57 49

124009 1-68 13183 11121

124020 12-94 22131 18876

124022 67-179 49293 42414

124023 38-96 44005 37756

124024 2-83 37664 32415

124025 5-13 3051 2624

124027 24-end 15351 13205

124030 2-end 21360 18279

124120 1-end 11866 10542

124230 26-end 74380 63711

124275 3-30 1833 1635


• Compare Data with D6T/ProQ20 MC

h1Entries 3824228Mean 0.00998RMS 1.397


Num

ber

of T

rack

s

15

20

25

30

35

40

45

310×






h1 900GeVFeb9ReRecoDT6V16DProQ20V16D

• Similar disagreement seen in UE analysis (PAS QCD-10-001)

• No perfect tune to account for both disagreement yet

Basic Tracking Distributions In Pre-Approval (12/02)• This version does not have the dz signifance and σpT/pT cut

• η peak ∼ 0 is removed by dz signficance cut


Basic Tracking Distributions Normalized by nEvents• The excess in the tracks are not localized in any specific region


Num

ber

of T

rack

s P

er E

vent

/ 0.

1

0

0.05

0.1

0.15

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0.5CMS Preliminary

=900GeVs

DataMonte Carlo

2χNormalized 0 1 2 3 4 5 6 7 8 9 10

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ber

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/ 0.

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1.8 CMS Preliminary

=900GeVs

DataMonte Carlo

Number of Valid Hits Per Track0 5 10 15 20 25 30 35 40

Num

ber

of T

rack

s P

er E

vent

0

0.2

0.4

0.6

0.8

1

1.2CMS Preliminary

=900GeVs

DataMonte Carlo

Track Azimuthal Angle-3 -2 -1 0 1 2 3

Num

ber

of T

rack

s P

er E

vent

/ 0.

1

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35CMS Preliminary

=900GeVs

DataMonte Carlo

Track dxy corrected by pvtx (cm)-0.15 -0.1 -0.05 0 0.05 0.1 0.15

Num

ber

of T

rack

s P

er E

vent

/ 0.

005

cm

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1.6 CMS Preliminary

=900GeVs

DataMonte Carlo

Track dz corrected by pvtx (cm)-0.3 -0.2 -0.1 0 0.1 0.2 0.3

Num

ber

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/ 0.

01 c

m

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2CMS Preliminary

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DataMonte Carlo


BeamSpot Positions Fit Results• Fitted beamspot x0 and y0 (left) and z0 (right) by run

• Fitted beamspot x0 and y0 (left) and z0 (right) by fill


tracking/vertexing/beamspot/b-tag results from first...

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