“search for multi-lepton events with the zeus detector at ...parenti/dtesi/dtalk.pdf · luca...

Università degli Studi di PadovaDottorato di Ricerca in Fisica – XVI Ciclo

“Search for multi-lepton events with the

ZEUS detector at HERA”

and“VCMVD: an algorithm for MVD tracking

at TLT”Dottorando: Andrea Parenti Tutore: Dott. Luca Stanco

Coordinatore: Prof. Attilio Stella

Padova, 18 Dicembre 2003Multi-leptons at HERA – MVD tracking at ZEUS TLT – p.1/92

Outline – Part I

• The experimental setup• Introduction and motivations• Multi-electron events search• Di-muon events search

Multi-leptons at HERA – MVD tracking at ZEUS TLT – p.2/92

The HERA ColliderHERA is a particle accelerator

located in Hamburg...

ZEUS

...and collides e±p at√s =

300/318 GeV:E =820 (920) GeVpE =27.5 GeVe

In 1992-2000 HERA sup-

plied the following inte-

grated luminosity:Years Lumi [pb−1] Type

1992-94 2.19 e−p

1994-97 70.92 e+p

1998-99 25.20 e−p

1999-00 94.95 e+p

• In 1998√s was raised from 300 GeV to 318 GeV.


The HERA ColliderHERA kinematics:

• Centre-of-mass energy:s = (P + k)2.

• Transferred 4-momentum, squared:Q2 = −(k − k′)2.

• Bjorken-x: x = Q2/(2P · q).• Inelasticity: y = (P · q)/(P · k).

• Proton-photon mass, squared:W 2 = (P + q)2.

Electron-Proton scattering•• Neutral Current: ep→ eX

• Charged Current: ep→ νX


The ZEUS Detector

ZEUS is a general purpose detector:

The components used in the anal-yses are:

• Central Tracking Detector(CTD),

• Uranium Calorimeter (CAL),

• Muon Chambers (B/RMUON+ FMUON),

• Luminosity Monitor.


Di-lepton production at HERALepton pair production is a pure QED process, well predictable in

the Standard Model (SM) context.

• Main contribution: Bethe-Heitler (BH) process.

• Other contributions: Cabibbo-Parisi (CP) and Drell-Yan (DY).

Feynmann diagrams:l

l

l

Drell−Yan

ee

ee

l

l

pX

p

l

l

X

X

Cabibbo−Parisi

X

l

l

l

e

e

p

e

pe

Xp

Bethe−Heitler

ee


Backgrounds

• Vector meson decays: Υ → l+l− (BR ∼ 1-2%).

• Single lepton production:• Heavy quark decays: q → q′W ⋆ → q′lν;

• W-production;

• τ decays.

• Backgrounds to multi-electron search:processes where hadrons or photons aremisidentified as electrons:• Neutral Current DIS;

• QED-Compton.


Motivations

• Test QED & photon spectrum of the proton.

• Cross-check H1 excesses:High Mass multi-electrons at H1:

10−3

10−2

10−1

1

10

102

0 50 100 150

2e

H1 Data 115 pb −1

Pair Production(GRAPE)

DIS+Compton

M12

(GeV)

Even

ts

1

10

0 50 100 150

M12

(GeV)

Even

ts

10−3

10−2

10−1

3e

Selection Data MC

2e, M12 > 100 GeV 3 evts 0.30±0.04

3e, M12 > 100 GeV 3 evts 0.23±0.04(see hep-ex/0307015)

Isolated leptons with P/T :H1 Data

All SM processes

SM error

Signal (W+Z prod)

−

10−2

10−1

1

10

102

0 50 100 150 200

MT

/ GeV

Even

ts

Ndata

= 18

NSM

= 12.4 1.7

Combined Electron and Muon

+

Type Data MC

e+p 10e 9.9 ± 1.3

8µ 2.56 ± 0.44

e−p 1e 1.69 ± 0.22

0µ 0.37 ± 0.06

(see Phys. Lett. B561, 241)


Multi-electron search


Event Selection

XY View ZR View

Zeus Run 33753 Event 4607 date: 24-09-1999 time: 23:52:03ZeV

is

E=200.12 GeV =106.49 GeVt

E = 49.86 GeVzE-p =144.54 GeVfE = 55.58 GeVbE= 0.00 GeVrE = 3.35 GeV

tp = -0.69 GeVxp = 3.27 GeVyp =150.26 GeVzp

phi= 1.78 = 0.43 nsft = 0.27 nsbt =-100.00 nsrt = 0.39 nsgt= 55.05 GeVeE = 1.22eθ = 0.15eφ = 0.17

e,DAx = 0.27

e,DAy

2=4531.09 GeVe,DA2Q

PreselectionFast selection and reduction of

data. Selection criteria:

• Trigger selection: di-electron ORNC-DIS OR High-ET ;

• No. of CTD tracks: 1 ≤ NTrkVtx ≤ 9;

• Transverse momentum in CTD:Pi PT,i > 3 GeV.

Electron selection• EM electron finder (CTD+CAL info);

• Isolation cuts:• Econe < 0.3 GeV in R=0.3 (ηφ),• NTrk = 0 in R=0.4 (ηφ);

• Ee > 10 GeV (θ ≤ 164) OREe > 5 GeV (θ > 164).

Event Selection• Vertex: |z| < 50 cm;

• two electrons in 17 < θ < 164;

• Ee1T > 10 GeV;

• Ee2T > 5 GeV.

Two classes: “2e” (2 electrons)

and “3e” (3 electrons) events.Multi-leptons at HERA – MVD tracking at ZEUS TLT – p.10/92

Data to MC comparison1996-2000 data taking L=120.49 pb−1

Selection Data All SM di-ele MC NC-DIS MC QED-C MC

All 2e+3e 209 235.82 207.00 18.72 10.10

M12 > 50 GeV 23 35.01 30.14 3.40 1.47

M12 > 100 GeV 1 1.12 0.91 0.08 0.13

10-2

10-1

1

10

102

0 20 40 60 80 10010

-3

10-2

10-1

1

10

102

0 50 100 150

10-2

10-1

1

10

0 1 2 3

ZEUS 2e+3e

ETe1 (GeV)

ZEUS 1996-00GRAPE+NC+QEDCNC+QEDCQEDC

Ee1 (GeV)

θe1 (rad) φe1 (rad)

1

10

-2 0 2

10-2

10-1

1

10

102

0 20 40 60 80 100

10-2

10-1

1

10

102

0 50 100 150

1

10

0 1 2 3

ZEUS 2e+3e

ETe2 (GeV)


Ee2 (GeV)

θe2 (rad) φe2 (rad)

1

10

-2 0 2

10-2

10-1

1

10

102

0 50 100 150

10-1

1

10

-2 0 2

10-1

1

10

102

0 1 2 3

ZEUS 2e+3e

M12 (GeV) abs(θe1-θe2) (rad)

φe1-φe2 (rad)


(E-Pz)ee (GeV)

10-2

10-1

1

10

102

0 20 40 60

E − Pz permits to separate Bkg from signal.

Monte Carlo describes data reasonably well.Multi-leptons at HERA – MVD tracking at ZEUS TLT – p.11/92

Cross section: sample selectionA clean ep → eeX sample is needed for

cross section measurement.

“γγ” selection• 2 electrons in 17 < θ < 164;

• Ee1T > 10 GeV and Ee2

T > 5 GeV;

• M12 > 5 GeV;

• E−Pz < 45 GeV (cuts NC-DIS and QED-C).

ResultsSelection Data All SM di-ele MC

All γγ 51 52.86 52.71

M12 > 50 GeV 3 2.88 2.80

M12 > 100 GeV 0 0.09 0.08

10-3

10-2

10-1

1

10

0 20 40 60 80 100

10-2

10-1

1

10

0 1 2 3

10-3

10-2

10-1

1

10

0 20 40 60 80 100

ZEUS γγ

ETe1 (GeV)


θe1 (rad)

ETe2 (GeV) θe2 (rad)

10-2

10-1

1

10

0 1 2 3

10-3

10-2

10-1

1

10

0 50 100 150

10-2

10-1

1

-2 0 2

10-1

1

10

0 1 2 3

ZEUS γγ


φe1-φe2 (rad)

ZEUS 1996-00

GRAPE+NC+QEDC

NC+QEDC

QEDC

(E-Pz)ee (GeV)

10-3

10-2

10-1

1

10

0 20 40 60

Nic

eag

reem

ento

fdat

aan

dM

C.


Total cross section

Period Purity Acceptance σDATA (pb) σMC

1996-97 0.825 0.234 1.66 ± 0.43+0.18−0.14 1.55

1998-99 0.773 0.292 0.82 ± 0.41+0.13−0.12 1.66

1999-00 0.790 0.283 1.73 ± 0.31+0.22−0.17 1.66

1996-00 1.62 ± 0.23+0.21−0.16

1996-97: cross-section is measured at√s = 300 GeV.

1996-00: cross-section is referred to√s = 318 GeV.

First uncertainty is statistical, second is systematic.

Main systematics: CAL energy scale simulation (+9.4−4.1%), isolation cut (+7.3%).


Differential cross section

0

0.1

0.2

0.3

20 30 40 50 60

10-2

10-1

20 30 40 50 60

0

0.1

0.2

10 15 20 2510

-2

10-1

10 15 20 25

0

0.1

0.2

0.3

0.4

0.5 1 1.5 2 2.5

M12 (GeV)

Acc.

M12 (GeV)

dσ/

dM12 (pb/GeV)

PTe (GeV)

Acc.

PTe (GeV)

dσ/

dPTe (pb/GeV) ZEUS 1996-00

GRAPE MC

θe (rad)

Acc.

θe (rad)dσ/

dθ e (pb/rad)

1

0.5 1 1.5 2 2.5


Discussion• Multi-electron events sought in ZEUS 1996-2000 data.

• Data distributions compared to SM: good description.

• The excess found by H1 is not confirmed.

• Total and differential cross sections were measured:

agreement with SM in shape and normalisation.

• Outlook: reduce systematic uncertainties, analyse 1994-95.

Phase space

• 2 electrons in 17 < θ < 164

• Ee1T > 10 GeV and Ee2

T > 5 GeV

• M12 > 5 GeV

• E − Pz < 45 GeV

Total cross section

σ(ep→ eeeX) = 1.62 ± 0.23+0.21−0.16 pb

σMC = 1.66 pb


Di-muon search


Event Selection

PreselectionFast selection and reduction of

data. Selection criteria:

• Trigger selection: B/RMUON activityOR FMUON activity;

• No. of CTD tracks: 2 ≤ NTrkVtx ≤ 7;

• Transverse momentum in CTD:Pi PT,i > 1.5 GeV.

Muon selection• Muon finding:

• GLOMU: CTD + CAL + B/RMUI,• MPMATCH2: CTD + FMUON,• CTD + CAL (MIPs);

• Isolation cut: DµTrk > 1 in ηφ;

• PT > 5 GeV.

Event Selection• Vertex: |z| < 50 cm ANDp

x2 + y2 < 0.5 cm;

• 2 muons (1 matched to chambers);

• cosmic muons rejection:• acollinearity: cos Ω > −0.995,• timing cut.


Backgrounds [pb/GeV]

µ t/dP

σd

10−3

10−2

10−1

1

10

10−3

10−2

10−1

1

10

)/

DATA

EW(GRAPE)

(LPAIR)γ

SM

γµµττγγ

cc + cbb

µµΥµµ0

Z

[GeV]µt

P

10 20 30 40 50 60 70 80

σSM

σ −

σ(

−1

0

←←

←←

1

2

3

H1 Muon Pair Analysis

Backgrounds (Υ, heavy quarks

and τ decays) were analysed by H1:

found to be negligible.

In my analysis they were ne-

glected.


Comparison of data to MC1996-2000 data taking L=101.47pb−1

Selection Data di-mu MC

All 218 241.14

Mµµ > 50 GeV 6 3.91

Mµµ > 100 GeV 0 0.23

10-1

1

10

102

0 10 20 30 40

1

10

102

0 1 2 3 4 5

10-1

1

10

0 1 2 3

PTµ1 (GeV)

ZEUS 1996-00

GRAPE MC

Dµ1Trk

θµ1 (rad) φµ1 (rad)

10-1

1

10

0 2 4 6

10-1

1

10

102

0 10 20 30 40

1

10

102

0 1 2 3 4 5

10-1

1

10

0 1 2 3

PTµ2 (GeV)

ZEUS 1996-00GRAPE MC

Dµ2Trk

θµ2 (rad) φµ2 (rad)

10-1

1

10

0 2 4 6

10-1

1

10

-2 0 210

-1

1

10

102

0 1 2 3

10-1

1

10

-1 -0.5 0 0.5 1

∆θ (rad) abs(∆φ) (rad)

ZEUS 1996-00

GRAPE MC

cos(Ω) Mµµ (GeV)

10-1

1

10

102

0 25 50 75 100 125

Three di-muons crowd at Mµµ ≃ 50 GeV: genuine events.

Monte Carlo describes data reasonably well.Multi-leptons at HERA – MVD tracking at ZEUS TLT – p.19/92

Total cross section

Period Purity Acceptance σDATA (pb) σMC

1996-97 0.953 0.436 4.65 ± 0.56+0.35−0.31 5.31

1998-99 0.956 0.438 4.97 ± 0.98+0.29−0.27 5.21

1999-00 0.968 0.427 4.81 ± 0.45+0.35−0.33 5.32

1996-00 4.79 ± 0.33+0.35−0.32

1996-97: cross-section is measured at√s = 300 GeV.

1996-00: cross-section is referred to√s = 318 GeV.

First uncertainty is statistical, second is systematic.

Main systematics: muon chamber eff. (+5.4−4.8%), isolation cut (+4.0%).


Differential cross section

00.10.20.30.4

20 40 60 80 10010

-3

10-2

10-1

20 40 60 80 100

0

0.2

0.4

10 20 30 40 50

10-2

10-1

1

10 20 30 40 50

0

0.2

0.4

1 2

Mµµ (GeV)

Acc.

Mµµ (GeV)

dσ/

dM

µµ (pb/GeV)

PTµ (GeV)

Acc.

PTµ (GeV)

dσ/

dPTµ (pb/GeV) ZEUS 1996-00

GRAPE MC

θµ (rad)

Acc.

θµ (rad)dσ/

dθ µ

(pb/rad)

1

1 2


Discussion• Di-muon events sought in ZEUS 1996-2000 data.

• Data distributions compared to SM: good description.

• 3 events found at Mµµ ∼ 50 GeV: genuine di-muons.

• Total and differential cross section were measured:

agreement with SM in shape and normalisation.

• Outlook: reduce systematic uncertainties, analyse

background (bb, cc, Υ, τ decays).

Phase space

• 2 muons in 15 < θ < 164

• P µT > 5 GeV

• Mµµ > 5 GeV

Total cross section

σ(ep→ eµµX) = 4.79±0.33+0.35−0.32 pb

σMC = 5.32 pb


VCMVD: MVD tracking at ZEUSThird Level Trigger


Outline – Part II

• Introduction and motivations• The ZEUS Micro-Vertex Detector (MVD)• Description of the method• Results• Discussion


Introduction: track parameterisation

Internal detectors are plunged in a magnetic field :charged particles follows helix-like trajectories.

Helices are characterised by 5 parameters ai and areference point (x0, y0):

DH

φ1

Hφ

(x ,y )0 0

(0,0) x

y

R

s=0

(Q=+1)

(α,β)• a1 = φH : azimuthal angle at s = 0;

• a2 = Q/R: helix curvature;

• a3 = Q DH : closest approach to(x0, y0);

• a4 = ZH : z coordinate at s = 0;

• a5 = cot θ; θ is the polar angle at s = 0.


MVD: motivationsF charm

2 measurement

MVD will allow better charmtagging (higher efficiencyand larger kinematicalrange).

Measurement ofF charm

2 and gluon density.

Photoproduction of jets

Resolved PHPDirect PHP

MVD will allow better tag-ging of resolved and directcharm/beauty photoproduc-tion and thus better eventselection and cross-sectionmeasurement.

Exotic processes

Heavy states are boostedforward.

daughters’ decaylenghts may be detectedeven if particles are short-lived.


VCMVD: motivations

• After Micro-Vertex Detector (MVD) installation in 2001the ZEUS tracking package (VCTRAK) needed to beupdated to benefit from the new detector

• A “fast” algorithm was needed for the use in the ThirdLevel Trigger (TLT)

• VCMVD (VCtrak+MVD) has been developed to refineVCTRAK tracks by means of MVD hits

• Effects: great improvement in a4, a3 precision.


The ZEUS MVD

Barrel Section

• 3 layers of silicon detectors;

each layer measures 2 views: rφ and z;

• intrinsic resolution: ∼ 20 µm;

• angular coverage (3 layers):22 < θ < 159.

Forward wheels

• 4 wheels of silicon detectors;

• extend coverage to θ = 7.

Only BMVD is used in the package.


VCMVD: the method

• Tracks are found in CTD by

VCTRAK;

• MVD hits are reconstructed;

• VCTRAK tracks are propagated

from CTD to MVD;

• MVD hits are collected on the

outer layer;

• track parameters are updated;

• the same procedure is repeated for

middle and internal layers.

Cluster 1

Cluster 2

Cluster 3

Lad

der

Beam−Pipe


Results: efficiency

Geometrical coverage

• 2 layers: 72 in φ;

• 3 layers: 288 in φ;

Expected intersections:

〈n〉 ≃ 2.8/track/view.

Assigned clusters

• Single muon MC: 〈n〉 = 2.9;

• bb MC: 〈n〉 = 2.4 ÷ 2.5;

• Data (offline): 〈n〉 = 2.0.

0

200

400

600

800

1000

1200

0 2 40

200

400

600

800

1000

1200

0 2 4

IDEntriesMeanRMS

3000 2000

2.895 0.6675

2003/12/10 15.13

n(Rφ)

IDEntriesMeanRMS

3100 2000

2.918 0.6934

n(z)

IDEntriesMeanRMS

3050 2000

5.814 1.292

n(Rφ)+n(z)

0

200

400

600

800

1000

1200

0 5 100

500

1000

1500

2000

2500

3000

3500

4000

4500

0 2 40

500

1000

1500

2000

2500

3000

3500

4000

4500

0 2 4

IDEntriesMeanRMS

3000 9810

2.457 1.018

2003/12/10 15.16

n(Rφ)

IDEntriesMeanRMS

3100 9810

2.412 1.016

n(z)

IDEntriesMeanRMS

3050 9810

4.869 1.883

n(Rφ)+n(z)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 5 100

200

400

600

800

1000

0 2 40

200

400

600

800

1000

0 2 4

IDEntriesMeanRMS

3000 2738

2.016 1.110

2003/12/10 15.18

n(Rφ)

IDEntriesMeanRMS

3100 2738

1.993 1.062

n(z)

IDEntriesMeanRMS

3050 2738

4.009 2.016

n(Rφ)+n(z)

0

200

400

600

800

1000

0 5 10

b−b Monte Carlo_

Single mu MC Real Data

4

3

8

2

4

2

6

2

3

4

2

3

4

6

4

8

2

3

2

4

6

4

23 3

4

4


Results:DH and ZH

SAMPLE: Single muon Monte Carlo, pT = 0.5 ÷ 1.5 GeV

Results

• σ(DH): 650 µm (VCTRAK) → 300 µm (VCMVD);

• σ(ZH): 3.2 mm (VCTRAK) → 0.26 mm (VCMVD).

IDEntriesMeanRMS

1900 2000 0.3010E-01 0.1065E-01

2003/12/09 15.26

σ(a3) (cm)

Evt

s

Before MVD Fit

After MVD Fit

0

100

200

300

400

500

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

IDEntriesMeanRMS

1950 2000 0.2627E-01 0.1469E-01

2003/10/04 18.50

σ(a4) (cm)

Evt

s

Before MVD Fit

After MVD Fit

0

200

400

600

800

1000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

(a3)σ (a4)σ

2003/12/12 18.07

PT (GeV)

σ(a3

) (c

m)

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 1 2 3 4 5 6 7 8

b−b Monte Carlo_

• σ(DH) → 100 µm at high-PT .


Results: Execution TimeThe execution time is evaluated as fraction of VCTRAK

(CTD tracking package) time.

• Monte Carlo: 40% (single muon) → 11% (bb).

• Data (offline): 20 ÷ 25%.

IDEntriesMeanRMS

110 2000

0.3800 0.2919E-01

2002/12/24 17.45

T(VCMVD)/T(VCTRAK)

Evt

s

0

200

400

600

800

1000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

IDEntriesMeanRMS

110 374

0.2023 0.1881

2002/12/24 17.52

T(VCMVD)/T(VCTRAK)

Evt

s

0

10

20

30

40

50

60

70

80

0 0.2 0.4 0.6 0.8 1 1.2 1.4

IDEntriesMeanRMS

110 999

0.1143 0.4663E-01

2002/12/24 17.50

T(VCMVD)/T(VCTRAK)

Evt

s

0

100

200

300

400

500

0 0.2 0.4 0.6 0.8 1 1.2 1.4

_b−b Monte CarloSingle muon MC Real data

Absolute execution time increases steeply for VCTRAKMulti-leptons at HERA – MVD tracking at ZEUS TLT – p.32/92

Results:PT and probabilitiesSAMPLE: Single muon Monte Carlo, pT = 0.5 ÷ 1.5 GeV

PT measurement

IDEntriesMeanRMS

1700 2000 0.8236E-02 0.1336E-02

2003/10/29 14.58

σ(PT) (GeV)

Evt

s

Before MVD Fit

After MVD Fit

0

50

100

150

200

250

300

350

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

• σ(PT , VCTRAK) = 11 MeV.

• σ(PT , VCMVD) = 8 MeV.

Probability of ai:

0

50

100

150

0 0.2 0.4 0.6 0.8 10

50

100

150

0 0.2 0.4 0.6 0.8 1

0255075

100

0 0.2 0.4 0.6 0.8 10

200

400

0 0.2 0.4 0.6 0.8 1

VCMVD2002/12/24 17.47

Prob(χ2)

Evt

s

Prob(χ2)

Evt

s

Prob(χ2)

Evt

s

Prob(χ2)

Evt

s

Prob(χ2)

Evt

s

0

100

200

300

0 0.2 0.4 0.6 0.8 1

a1 a2

a3 a4

a5

Definition of proba-bility:

P

(

(afitν − atrue

ν )2

σ2fit

, 1

)

Flat probabilities: fitting procedure is

correct.

Peaks at 0: hint of non gaussian tails.


Discussion• A new vertex detector has been installed in 2001 at ZEUS

• The VCMVD tracking package has been developed to

update VCTRAK parameters

• VCMVD package has been tested offline: very good results

in execution time and tracking improvement

• VCMVD has been implemented in the online software: data

are coming for further testing


Conclusions


ConclusionsPart I

• HERA collisions have been analysed in the search for

multi-electron and di-muon events

• The data are nicely described by the SM simulation

• The excess observed by H1 in high-mass di/trielectrons is

not confirmed

Part II

• A tracking package, VCMVD, has been developed for use of

MVD in TLT

• VCMVD behaves well on (offline) data and MC

• Online data are coming for testingMulti-leptons at HERA – MVD tracking at ZEUS TLT – p.36/92

ADDITIONAL SLIDES


The ZEUS detector


The Central Tracking Detector (CTD)• Cylindrical wire drift chamber, 72 layers of

sense wires divided into 9 super-layers.

• -100 cm < z < 104 cm, 15 < θ < 164.

• Filled with Ar, CO2 and C2H6 (ethane) inthe proportion 85:5:1.

• Wires are tilted by 45 to compensate theLorentz angle.

The resolution on pT for tracks with pT > 150 MeV, constrained to theinteraction vertex and passing three CTD super-layers is

σ(pT )

pT

= 0.0058 · (pT /GeV) ⊕ 0.0065 ⊕ 0.0014

(pT /GeV).

The CTD also supplies information on the energy loss dE/dx.Multi-leptons at HERA – MVD tracking at ZEUS TLT – p.39/92

The Uranium Calorimeter (CAL)• Longitudinally divided into three

parts (RCAL/BCAL/FCAL).

• Surrounds the tracking devicesand the solenoid.

• Consists of 3.3 mm thick depleteduranium plates alternated with2.6 mm thick organic scintillator.

• Compesation: same response forelectrons and hadrons.

Electromagnetic energy resolution

σ(E)

E=

18%√

E/GeV⊕ 2%

Hadronic energy resolution

σ(E)

E=

35%√

E/GeV⊕ 1%


The Barrel/Rear Muon Chambers

• Large area to be covered ⇒ modular structurebased on the chamber.

• Two layers of LST tubes placed on both sides ofa honeycomb support structure.

• x and y coordinates read by each LST plane(signal induced on conductive strips orthogonalto the wires, glued outside the plane).

• Cells filled with Ar, CO2 and C4H10 (isobutane).

• Chambers have different shape and dimension,depending on their position.

⋆ BMUI-RMUI: chambers between the CAL and the yoke.

⋆ BMUO-RMUO: chambers outside the yoke.


The Forward Muon Chambers

The FMUON detector consists of:

• 4 LST trigger planes, with digital ρ and φ

read-out (LST1–4);

• Two coverage planes of LSTs, in the large polarangle region (LW1–2);

• 4 planes of drift chambers (DC1–4);

• Two large toroidal magntes, providing a 1.7 T fieldfor momentum separation and measurement inthe small polar angle region.

FMUO

LST4 LST3 LST2

LW1 LW2

DC4 DC3 DC2

FMUI

DC1

LST1

⋆ FMUI: LST1–DC1, inside the yoke.

⋆ FMUO: other chambers, outside the yoke.


The Lumi Monitor

• Photon calorimeter atz = −(104 ÷ 107) m.

• Resolution:

σ(E)

E=

23%√

E/GeV.

• Photons from ep→ epγ are counted.

• Luminosity is extracted usingBethe-Heitler formula for σ(ep→ epγ).

• Precision: σ(L)/L = 1 ÷ 2%.


Past results


Multi-electrons at H1Data taking: 1994-00 Lumi used: 115.2 pb−1

Event Selection• Two “central” (20 < θ < 150), “isolated”, electrons

• PT cut: P e1T > 10 GeV, P e2

T > 5 GeV

Event Classification• “2e”: Only 2 central electrons

• “3e/4e”: Additional “isolated” electrons (also Forward and Rear)

“γγ” subsample• Just 2 opposite charge electrons: ep → e+e−X

• E − Pz < 45 GeV (ie y < 0.82, Q2 < 1 GeV2)

“Cleaner” sample; scattered electron is lost in beam–pipe; both detected electronscome from interaction


Multi-electrons at H1

Different topology for “2e” and “3e” events:A “2e” event:

preliminary

PT=63 GeV

PT=62 GeV

Multi-electron Event M(12)=130 GeV

P e1T = 63 GeV, P e2

T = 62 GeV

M12 = 130 GeVHarder PT in “2e”

A “3e” event:

preliminary

PT=25 GeV

PT=16 GeV

PT=20 GeV

Multi-electron Event M(12)=118 GeV

P e1T = 25 GeV, P e2

T = 20 GeV

M12 = 118 GeVMore forward es in “3e”


Multi- e at H1: global variablesH1 Preliminary Multi-electron Analysis

0

20

40

60

0 50

2eH1 Data 115 pb-1

GRAPE

NC-DIS+Compton

E-Pz (GeV)

Eve

nts

10-2

10-1

1

10

10 2

0 20

2e

PT

miss (GeV)

Eve

nts

10-1

1

10

10 2

0 20 40

2e

PT

hadrons (GeV)

Eve

nts

0

10

20

0 50

3e

E-Pz (GeV)

Eve

nts

10-2

10-1

1

10

0 20

3e

PT

miss (GeV)

Eve

nts

10-1

1

10

0 20 40

3e

PT

hadrons (GeV)

Eve

nts

•G

RA

PE

:γγ

inte

ract

ion

+γ

&Z

0co

nver

sion

•N

C-D

IS+

Com

pton

:fa

ke“2

e”-”

3e”

even

ts


Multi- e at H1: electron variablesH1 Preliminary Multi-electron Analysis

10-2

10-1

1

10

10 2

0 50

2e

PTe1 (GeV)

Eve

nts

10-2

10-1

1

10

10 2

0 50

2e

PTe2 (GeV)

Eve

nts

10-1

1

10

0 20 40

3e

PTe1 (GeV)

Eve

nts

10-1

1

10

0 20 40

3e

PTe2 (GeV)

Eve

nts

10-1

1

10

0 20

3e

H1 Data 115 pb-1

GRAPENC-DIS+Compton

PTe3 (GeV)

Eve

nts

Three “2e” events with P e1T > 50 GeV (but low SM expectation)


Multi- e at H1: Mass distributionsH1 Preliminary Multi-electron Analysis

10-2

10-1

1

10

10 2

0 50 100 150

2e

H1 Data 115 pb-1

GRAPENC-DIS

+Compton

M12 (GeV)

Eve

nts

0

50

100

150

0 50 100 150 M12 (GeV)

PT

e1+

PT

e2 (

GeV

)

2eLMC(GRAPE)≅500×LDATA

10-2

10-1

1

10

0 50 100 150

3e

M12 (GeV)

Eve

nts

0

50

100

150

0 50 100 150 M12 (GeV)

PT

e1+

PT

e2 (

GeV

)

3e LMC(GRAPE)≅500×LDATA

M12 = Mass of two

highest PT electrons

Harder PT for “2e”

At M12 > 100 GeV

“2e” events:

3 found

0.25±0.05 expected

“3e” events:

3 found

0.23±0.04 expected


Multi- e at H1: γγ Cross Section

10−3

1

10−2

10−1

PT

e 1

1

21

2

(GeV)

dσ/

dP

Te

10

(p

b/G

eV)

15 20 25

M12

(GeV)

dσ/

dM

12 (

pb

/GeV

)10

−3

10−2

20 40 60

e p e e+e

− X

PT

e ≥ 10 GeV, PT

e ≥ 5 GeV

20o ≤ θe ,e ≤ 150

o

y ≤ 0.82, Q2 ≤ 1 GeV

2

10−3

H1 Data

PT

hadrons (GeV)

dσ/

dP

Thad

ron

s

10

(p

b/G

eV)

−2

SM (GRAPE)

10−1

0 10 20

• Extracted from “γγ”sample

• Good Agreement withSM


Multi-electrons at H1: Overview

Selection DATA SM GRAPE NC-DIS + Compton

Visible 2e 105 118.2±12.8 * 93.3±11.5 25.0±5.5

Visible 3e 16 21.6±3.0 21.5±3.0 0.1±0.1

Visible 4e or more 0 0.1±0.0 0.1±0.0 0.0±0.0

γγ → e+e− subsample 41 48.3±6.1 46.4±6.1 1.9±0.9

Visible 2e M(12) >100 3 0.25±0.05 0.21±0.04 0.04±0.03

Visible 3e M(12) >100 3 0.23±0.04 0.23±0.04 0.00±0.00

* Statistical ⊕ Systematic Uncertainty

DATA agree with SM at low M12

Excess in DATA at high M12


Multi-electrons at ZEUSData taking: 1994-00 Lumi used: 130.5 pb−1

Event Selection• “Good Vertex”: |Zvtx| < 50 cm

• Two “central” (17 < θ < 164) electrons: Ee1T > 10 GeV, Ee2 > 10 GeV

A “2e” event


Multi- e at ZEUS: electron variables

ZEUS

10-2

10-1

1

10

10 2

0 20 40 60 80 100ET,1 (GeV)

even

ts ZEUS (prel.) 94-00GRAPE+NC+QEDCNC+QEDCQEDC

a)

10-1

1

10

10 2

0 1 2 3θe,1 (rad)

even

tsb)

10-2

10-1

1

10

10 2

0 20 40 60 80 100ET,2 (GeV)

even

ts c)

10-1

1

10

10 2

0 1 2 3θe,2 (rad)

even

ts

d)

Good Agreement


Multi- e at ZEUS: Mass distributionZEUS

10-2

10-1

1

10

10 2

0 20 40 60 80 100 120 140M12 (GeV)

even

ts

ZEUS (prel.) 94-00

GRAPE+NC+QEDC

NC+QEDC

QEDC

Two events with M12 > 100 GeV; expected 1.2±0.1Multi-leptons at HERA – MVD tracking at ZEUS TLT – p.54/92

Multi- e at ZEUS: Overview

Type Data SM GRAPE NC-DIS Compton

2e sample

2e 191 213.9±3.9 * 182.2±1.2 23.9±3.7 7.8±0.5

Ee1T > 30 GeV 6 5.7±0.3 4.4±0.2 0.9±0.2 0.4±0.1

M12 > 100 GeV 2 0.77±0.08 0.47±0.05 0.12±0.06 0.18±0.03

3e sample

3e 26 34.7±0.5 34.7±0.5 - -

Ee1T > 30 GeV 2 1.43±0.08 1.43±0.08 - -

M12 > 100 GeV 0 0.37±0.04 0.37±0.04 - -

* Only Statistical Error


Di-Muons at H1

Data taking: 1999-00Lumi used: 70.9 pb−1

Muon Selection• Reconstructed track in both CTD

and Muon Detectors

• Angular region: 20 < θ < 160

• For low momentum muons:CTD Track + Calorimeter MIP

Run 276837 Event 89128 Class: 8 10 16 20 22 23 24 27 29 Date 6/02/2002

Z

R

X

Y

-180.

-90.

0.

90.

180. -4.-2.

0.2.

4.

7

3.5

0

E[G

eV]

(DC

LU)

ϕ[degree]

η

Event Selection• Two muons: P µ1

T > 2.00 GeV, P µ2T > 1.75 GeV

• Invariant mass cut: Mµµ > 5 GeV

• Muon Isolation: DµTrk,jet > 1.0 in ηφ (or Dµ

Trk,jet > 0.5 if P µT > 10 GeV)


Di-Muons at H1: Cross section [

pb

/GeV

]µ,µ

/dM

σd

10-4

10-3

10-2

10-1

1

10

[p

b/G

eV]

µ,µ/d

Mσ

d

10-4

10-3

10-2

10-1

1

10H1 DATA (Prelim.) SM (GRAPE)

(LPAIR)γ γµµ → ττ → γ γ

c + cbbµµ → Υµµ → 0Z

[GeV]µ,µM

S

Mσ

) /

SM

σ -

σ( -1

0

1

2

3

10 10020 506


[p

b/G

eV]

µ t/d

Pσ

d

10-3

10-2

10-1

1

10

[p

b/G

eV]

µ t/d

Pσ

d

10-3

10-2

10-1

1

10

H1 DATA (Prelim.) SM (GRAPE)

(LPAIR)γ γµµ → ττ → γ γ

c + cbbµµ → Υµµ → 0Z

[GeV]µtP

10 20 30 40 50 60 70 80

S

Mσ

) /

SM

σ -

σ( -1

0

1

2

3


•M

ain

cont

ribut

ion:γγ

inte

ract

ion

•S

mal

lcon

trib

utio

ntoµ

+µ−

from

:Υ

,qq

andττ

deca

ys

Total Cross–Section: σ = 46.5±1.3±4.7 pb

Good Agreement with SM: σ(GRAPE) = 46.2 pbMulti-leptons at HERA – MVD tracking at ZEUS TLT – p.57/92

Di-Muons at H1: Cross section [

pb

/GeV

]µ,µ

/dM

ela

σd

10-4

10-3

10-2

10-1

1

10H1 DATA (Prelim.)

SM (GRAPE)

[GeV]µ,µM20 40 60 80 100 120

S

Mσ

) /

SM

σ -

σ( -1

0

1

2

3

) µµ ep→H1 Muon Pair Analysis (ep

Elastic

[p

b/G

eV]

µ,µ /d

Min

elσ

d

10-4

10-3

10-2

10-1

1

10H1 DATA (Prelim.)

SM (GRAPE)

[GeV]µ,µM20 40 60 80 100 120

S

Mσ

) /

SM

σ -

σ( -1

0

1

2

3

X)µµ e→H1 Muon Pair Analysis (ep

Inelastic

•E

last

ican

dIn

elas

ticse

para

ted

byta

ggin

gpr

oton

rem

nant

Inelastic Cross–Section: σinel = 20.8±0.9±3.3 pb

Good Agreement with SM: σinel(GRAPE) = 21.5 pbMulti-leptons at HERA – MVD tracking at ZEUS TLT – p.58/92

Di-Muons at ZEUS

Data taking: 1997-00Lumi used: 105.2 pb−1

Muon Selection• Track in CTD (PT > 5 GeV)+ MIP in CAL

• Angular region: 20 < θ < 160

ZEUS

10-2

10-1

1

10

10 2

20 40 60 80 100 120 140 160 180Mµµ (GeV)

even

ts

ZEUS (prel.) 97-00

GRAPE

Event Selection• Two muons: 1µ matched to muon chambers

• Muon Isolation: Ntrks(Rηφ < 1) = 0

• Good Vertex: |Zvtx| < 40 cm,q

X2vtx + Y 2

vtx < 0.5 cm

• Acollinearity: cos(Ω) > −0.995


Multi-electron search


The electron taggingThe EM electron finder analyses energy deposits in the CAL to

distinguish electromagnetic from hadronic clusters.Sketch of the algorithm:

• Calorimeter cells are grouped in clusters;

• 4 quantities are evaluated for each cluster:• fraction of hadronic energy,• fraction of electromagnetic energy outside two highest-energy modules,• fraction of energy outside two highest-energy modules,• non-electron energy in a R=0.8 cone in ηφ;

• when a CTD track matches the cluster, are evaluated:• θTrk − θCal,• φTrk − φCal,• 1/PTrk − 1/ECal;

• a probability is computed using the above defined quantities.


Variable reconstruction

Very nice correlation of true and reconstructed variables:

0

0.5

1

1.5

2

2.5

3

0 1 2 30

0.5

1

1.5

2

2.5

3

0 1 2 3

0

0.5

1

1.5

2

2.5

3

0 1 2 3

GRAPE MC

θe1 (rad) - true

θ e1 - reco

θe2 (rad) - true

θ e2 - reco

φe1 (rad) - true

φ e1 - reco

φe2 (rad) - true

φ e2 - reco

0

0.5

1

1.5

2

2.5

3

0 1 2 3

0

5

10

15

20

25

30

35

40

0 10 20 30 400

5

10

15

20

25

30

35

40

0 10 20 30 40

-1-0.8-0.6-0.4-0.2

00.20.40.60.8

1

-1 -0.5 0 0.5 1

GRAPE MC

PTe1 (GeV) - true

PTe1 - reco

PTe2 (GeV) - true

PTe2 - reco

cosΩ - true

cos

Ω -reco

M12 (GeV) - true

M12 - reco

0102030405060708090100

0 20 40 60 80 100



Resolutions:

• σ(θ)/θ = 0.5%;

• σ(PT )/PT = 10%;

• σ(cos Ω)/ cos Ω = 2%;

• σ(M12)/M12 = 10%.

Excellent resolution for angles.

Good resolution for energies.

0

5

10

15

20

-0.02 0 0.02 0.04 0.060

5

10

15

20

-0.02 0 0.02 0.04 0.06

0

5

10

15

20

-0.5 0 0.5 10

5

10

15

20

-0.5 0 0.5 1

0

5

10

15

20

-0.05 0 0.05 0.1

GRAPE MCIDEntriesMeanRMS

622 45309

0.1249E-02 0.5522E-02

(θe1,reco-θe1e,true)/θe1,true

IDEntriesMeanRMS

623 45309

0.6508E-03 0.5317E-02

(θe2,reco-θe2,true)/θe2,trueIDEntriesMeanRMS

620 45309

0.4555E-01 0.9085E-01

(Pe1

T,reco-Pe1

T,true)/Pe1

T,true

IDEntriesMeanRMS

621 45309

-0.8825E-02 0.1027

(Pe2

T,reco-Pe2

T,true)/Pe2

T,true

IDEntriesMeanRMS

650 45309

0.1214E-02 0.1733E-01

(cosΩreco-cosΩtrue)/cosΩtrue

IDEntriesMeanRMS

617 45309

0.1739E-01 0.7944E-01

(M12,reco-M12,true)/M12,true

0

10

20

-0.5 0 0.5 1


Trigger chainDi-electron chain

• Elastic di-e: good vertex + few CTD tracks + 2 electrons.

• Inelastic di-e: good vertex + 2 electrons + high mass.

Neutral Current DIS chain

• good vertex + 1 electron + large ET + large Q2 + large

E − Pz.

High-ET chain

• high ET in the CAL.


Data to MC comparison: 2e

1996-2000 data taking L=120.49 pb−1


All 2e 183 197.78 169.11 18.57 10.10

M12 > 50 GeV 17 27.47 22.68 3.32 1.47

M12 > 100 GeV 1 0.67 0.46 0.08 0.13

10-2

10-1

1

10

102

0 20 40 60 80 100

10-2

10-1

1

10

0 1 2 3

10-3

10-2

10-1

1

10

102

0 20 40 60 80 100

ZEUS 2e

ETe1 (GeV)


θe1 (rad)


1

10

0 1 2 3

10-2

10-1

1

10

102

0 50 100 150

10-1

1

10

-2 0 2

10-1

1

10

102

0 1 2 3

ZEUS 2e


φe1-φe2 (rad)


(E-Pz)ee (GeV)

10-2

10-1

1

10

0 20 40 60



1996-97 period

10-2

10-1

1

10

0 20 40 60 80 100

10-2

10-1

1

10

0 1 2 3

10-3

10-2

10-1

1

10

0 20 40 60 80 100

ZEUS 2e

ETe1 (GeV)


θe1 (rad)


10-1

1

10

0 1 2 3

1998-99 period

10-3

10-2

10-1

1

10

0 20 40 60 80 100

10-3

10-2

10-1

1

10

0 1 2 3

10-3

10-2

10-1

1

10

0 20 40 60 80 100

ZEUS 2e

ETe1 (GeV)

ZEUS 1998-99 (e-)GRAPE+NC+QEDCNC+QEDCQEDC

θe1 (rad)


10-3

10-2

10-1

1

10

0 1 2 3

1999-2000 period

10-2

10-1

1

10

0 20 40 60 80 100

10-2

10-1

1

10

0 1 2 3

10-1

1

10

0 20 40 60 80 100

ZEUS 2e

ETe1 (GeV)

ZEUS 1999-00 (e+)GRAPE+NC+QEDCNC+QEDCQEDC

θe1 (rad)


1

10

0 1 2 3



1996-2000 data taking L=120.49 pb−1


All 3e 26 38.03 37.88 0.15 0.00

M12 > 50 GeV 6 7.54 7.46 0.08 0.00

M12 > 100 GeV 0 0.44 0.44 0.00 0.00

10-1

1

10

0 20 40 60 80 100

10-1

1

0 1 2 3

10-1

1

10

0 20 40 60 80 100

ZEUS 3e

ETe1 (GeV)

ZEUS 1996-00

GRAPE+NC+QEDC

NC+QEDC

QEDC

θe1 (rad)


10-1

1

0 1 2 3

10-1

1

10

0 50 100 150

10-1

1

-2 0 2

10-1

1

10

0 1 2 3

ZEUS 3e


φe1-φe2 (rad)

ZEUS 1996-00

GRAPE+NC+QEDC

NC+QEDC

QEDC

(E-Pz)ee (GeV)

10-1

1

10

0 20 40 60



1996-97 period

10-1

1

0 20 40 60 80 100

10-1

1

0 1 2 3

10-1

1

0 20 40 60 80 100

ZEUS 3e

ETe1 (GeV)

ZEUS 1996-97

GRAPE+NC+QEDC

NC+QEDC

QEDC

θe1 (rad)


10-1

1

0 1 2 3

1998-99 period

10-2

10-1

1

0 20 40 60 80 100

10-2

10-1

1

0 1 2 3

10-2

10-1

1

0 20 40 60 80 100

ZEUS 3e

ETe1 (GeV)

ZEUS 1998-99 (e-)GRAPE+NC+QEDCNC+QEDCQEDC

θe1 (rad)


10-2

10-1

1

0 1 2 3

1999-2000 period

10-1

1

10

0 20 40 60 80 100

10-1

1

0 1 2 3

10-1

1

10

0 20 40 60 80 100

ZEUS 3e

ETe1 (GeV)

ZEUS 1999-00 (e+)

GRAPE+NC+QEDC

NC+QEDC

QEDC

θe1 (rad)


10-1

1

0 1 2 3


Cross section: Method

• Ng : MC events generated;

• Nr : MC events reconstructed;

• Nrg : MC events generated AND

recontsructed;

• Nd: events selected in data.

Definitions• efficiency: e = Nr

g /Ng ;

• purity: p = Nrg /Nr ;

• acceptance: a = Nr/Ng .

Cross sectionTotal:

σMC =Ng

L

σDATA =Nd

L a

Differential:

dσMC

dx=

Ng

L ∆x

dσDATA

dx=

Nd

L a ∆xMulti-leptons at HERA – MVD tracking at ZEUS TLT – p.69/92

Cross section: combination of periods

Correction for√

s

To refer cross-section to√s = 318 GeV:

σ318x =

σMC99−00

σMCx

σDATAx

x = 1996-97 or 1998-99

Combination of periods

σ96−00 =

∑

x σ318x Lx

∑

x Lx

x = 1996-97, 1998-99 or1999-2000


Systematic uncertainties

Type Variation Effect

Lumi measurement 2% 2%

CAL energy scale 5% +9.4−4.1%

Prob. cut in EMPgrand>0.01→0.1

Pcal>0.1→0.2 −4.8%

Isolation cut Econe < 0.3 → 0.2 GeV +7.3%

Mass cut 8% 0%

Total +13−10%

Statistical uncertainty: ±14%.

-1

-0.5

0

0.5

1

10 20 30 40 50 60 70 80 90

-1

-0.5

0

0.5

1

10 20 30 40 50 60 70 80 90

Variation

Variation

M12 (GeV)

Variation

-1

-0.5

0

0.5

1

10 20 30 40 50 60 70 80 90

UCAL Energy Scale

Probability cut in EM

Isolation cut

Systematic UncertaintyStatistical Uncertainty


Cross section: Tables

Bin definition Pur. Acc. dσDATAdx

(pb/[x]) dσMCdx

(pb/[x])

15 < M12 < 25 GeV 0.723 0.309 (4.2 ± 1.1 ± 1.0)E−02 5.7E−02

25 < M12 < 40 GeV 0.840 0.330 (5.2 ± 1.0 ± 0.6)E−02 4.5E−02

40 < M12 < 60 GeV 0.803 0.206 (1.50 ± 0.57+0.34−0.32)E−02 1.38E−02

10 < P eT < 15 GeV 1.154 0.223 (2.20 ± 0.42+0.28

−0.20)E−01 1.94E−01

15 < P eT < 20 GeV 1.073 0.236 (5.6 ± 2.1+1.1

−1.0)E−02 4.9E−02

20 < P eT < 25 GeV 0.924 0.239 (1.13 ± 0.93+0.45

−0.43)E−02 1.69E−02

0.349 < θe < 1.105 rad 0.831 0.381 (6.6 ± 1.4+1.0−0.9)E−01 7.2E−01

1.105 < θe < 1.862 rad 0.828 0.334 (5.1 ± 1.4 ± 0.6)E−01 5.6E−01

1.862 < θe < 2.618 rad 0.681 0.198 (8.1 ± 2.2+1.2−1.0)E−01 6.8E−01


Di-muon search


Muon tagging: GLOMUThe GLOMU package tags muons in the barrel/rear region.

It combines info from inner B/RMUON, CTD, CAL.

Sketch of the algorithm:

• CTD tracks with high momentum and close to vertex are collected;

• B/RMUI tracks are collected;

• MIP-like deposits are searched in the CAL;

• a match is attempted in θ-φ for these objects;

• a cut χ2 < 20 is set to accept a match.


Muon tagging: MPMATCH2 and MIPsThe MPMATCH2 package tags muons in the forward region.

It combines info from inner FMUON and CTD.Sketch of the algorithm:

• tracks are reconstructed in the FMU detector;

• these tracks are backwards propagated to the CAL surface;

• CTD tracks are extrapolated to the same surface;

• a match is attempted of the two sets of tracks;

• track parameters are refitted.

To raise efficiency in muon finding, a matching of CTD tracks and

MIP-like deposits in the CAL is attempted.

• CTD tracks are extrapolated to the CAL and matched to MIP-likedeposits.



Very nice correlation of true and reconstructed variables:

0

0.5

1

1.5

2

2.5

3

0 1 2 30

0.5

1

1.5

2

2.5

3

0 1 2 3

0

0.5

1

1.5

2

2.5

3

0 1 2 3

GRAPE MC

θµ1 (rad) - true

θ µ1 - reco

θµ2 (rad) - true

θ µ2 - reco

φµ1 (rad) - true

φ µ1 - reco

φµ2 (rad) - true

φ µ2 - reco

0

0.5

1

1.5

2

2.5

3

0 1 2 3

02.5

57.510

12.515

17.520

22.525

0 5 10 15 20 250

2.55

7.510

12.515

17.520

22.525

0 5 10 15 20 25

-1-0.8-0.6-0.4-0.2

00.20.40.60.8

1

-1 -0.5 0 0.5 1

GRAPE MC

PTµ1 (GeV) - true

PTµ1 - reco

PTµ2 (GeV) - true

PTµ2 - reco

cosΩ - true

cos

Ω -reco

Mµµ (GeV) - true

Mµµ - reco

05101520253035404550

0 10 20 30 40 50



Resolutions:

• σ(θ)/θ = 0.3%;

• σ(PT )/PT = 10÷ 15%;

• σ(cos Ω)/ cos Ω = 1%;

• σ(Mµµ)/Mµµ = 10%.

Excellent resolution for angles.

Good resolution for energies.

0

20

40

60

-0.02 0 0.020.040.060

20

40

60

-0.02 0 0.020.040.06

010203040

-0.5 0 0.5 10

20

40

-0.5 0 0.5 1

0

20

40

60

-0.05 0 0.05 0.1

GRAPE MCIDEntriesMeanRMS

622 59166

0.8319E-04 0.3287E-02

(θµ1,reco-θµ1,true)/θµ1,true

IDEntriesMeanRMS

623 59166

0.6389E-04 0.2935E-02

(θµ2,reco-θµ2,true)/θµ2,true

IDEntriesMeanRMS

620 59166

0.5338E-01 0.1417

(Pµ1T,reco-P

µ1T,true)/P

µ1T,true

IDEntriesMeanRMS

621 59166

-0.2024E-01 0.9417E-01

(Pµ2T,reco-P

µ2T,true)/P

µ2T,true

IDEntriesMeanRMS

650 59166

0.9365E-03 0.1277E-01

(cosΩreco-cosΩtrue)/cosΩtrue

IDEntriesMeanRMS

617 59166

0.2000E-01 0.1123

(Mµµ,reco-Mµµ,true)/Mµµ,true

0

20

40

-0.5 0 0.5 1


Trigger chainB/RMUON chain

• Inner chambers trigger: (few CTD tracks + B/RMUI signal)

OR (B/RMUI signal matched to CTD tracks and MIP-like

deposits).

• Outer chambers trigger: Signal in B/RMUI and B/RMUO +

CAL activity and CTD tracks

• Both chains: a GLOMU matching

FMUON chain

• few CTD tracks + matching (FMU and MIP-like deposits) +

two CTD tracks with high invariant mass


B/RMUI Efficiencies

B/RMU inefficiencies are not simulated in MC

Efficiencies were measured (M. Turcato, A. Bertolin, M. Corradi)

MethodDi-muon events are selected (J/ψ,Bethe-Heitler, ...) by

• A hit in muon chambers

• 2 CTD tracks withM > 2.5 GeV

• Acollinearity: cosΩ > −0.95

The efficiency is

e = No. of GLOMU tracks

No. of CTD tracks

ResultsThe ratio R =

e(DAT A)e(MC)

is used to weight

Monte Carlo samples

Region Data/MC ratio

Years 1996-97 Years 1998-2000

BMUI 0.854 ± 0.061 0.709 ± 0.042

RMUI 0.819 ± 0.068 0.853 ± 0.050

BMUI cut: 4.25 < P µT < 10 GeV

RMUI cut: 5 < P µT < 10 GeV


Di-muon events

Three events found

around Mµµ = 50 GeV

All of them look like gen-

uine di-muons


Systematic uncertainties

Type Variation Effect

Lumi measurement 2% 2%

B/RMUI Efficiency 7.5% in 1996−976.0% in 1998−00

+5.4−4.8%

cos Ω cut cosΩ > −0.995 → −0.985 +2.8%

Isolation cut DµTrk > 1 → 2 +4.0%

Prob. cut χ2<20→10 (GLOMU)P >0.01→0.05 (MPMATCH2)

−0.4%

Total +7.2−6.6%

Statistical uncertainty: ±6.9%.

-1-0.8-0.6-0.4-0.2

00.20.40.60.81

20 40 60 80-1

-0.8-0.6-0.4-0.2

00.20.40.60.81

20 40 60 80

-1-0.8-0.6-0.4-0.2

00.20.40.60.81

20 40 60 80

Variation

Variation

Mµµ (GeV)

Variation

Mµµ (GeV)

Variation

-1-0.8-0.6-0.4-0.2

00.20.40.60.81

20 40 60 80

Ωcos( ) Cut

Prob. Cut

B/RMUI Efficiency

Isolation Cut

Systematic uncertainty

Statistical uncertainty


Cross section: Tables

Bin definition Pur. Acc. dσDATAdx

(pb/[x]) dσMCdx

(pb/[x])

10 < Mµµ < 20 GeV 0.968 0.437 (3.44 ± 0.28+0.24−0.22)E−01 3.70E−01

20 < Mµµ < 30 GeV 0.977 0.412 (8.0 ± 1.4+0.8−0.7)E−02 10.7E−02

30 < Mµµ < 45 GeV 0.928 0.388 (2.02 ± 0.58+0.32−0.31)E−02 2.40E−02

45 < Mµµ < 100 GeV 0.787 0.437 (2.04 ± 0.91 ± 0.65)E−03 1.90E−03

5 < P µT < 6.5 GeV 0.949 0.401 1.53 ± 0.16+0.11

−0.10 1.55

6.5 < P µT < 8 GeV 1.009 0.437 (7.6 ± 1.1+0.6

−0.5)E−01 8.3E−01

8 < P µT < 13 GeV 0.994 0.447 (2.17 ± 0.31+0.23

−0.22)E−01 2.72E−01

13 < P µT < 50 GeV 0.885 0.473 (7.9 ± 2.1+1.3

−1.2)E−03 10.3E−03

0.262 < θµ < 0.912 rad 0.963 0.339 2.36 ± 0.42+0.18−0.17 2.81

0.912 < θµ < 1.562 rad 0.977 0.523 1.65 ± 0.22+0.13−0.12 1.83

1.562 < θµ < 2.212 rad 0.970 0.516 1.83 ± 0.23+0.14−0.13 1.69

2.212 < θµ < 2.862 rad 0.963 0.385 1.41 ± 0.24+0.14−0.13 1.84


MVD tracking at ZEUS TLT


Track parameterisation

DH

φ1

Hφ

(x ,y )0 0

(0,0) x

y

R

s=0

(Q=+1)

(α,β)

Coordinates

x(φ) = x0 +

(

a3 +1

a2

)

sin a1 −sinφ

a2

y(φ) = y0 −(

a3 +1

a2

)

cos a1 +cosφ

a2

z(φ) = a4 −a5

a2

(φ− a1)

Pathlegth

s = −φ− a1

a2


The ZEUS MVD: design

Sensor design

300

1

14 12

20

120

12

1

1,5

n-substrate

p+ inter-strip

p+ readout-strip

backplane(aluminum)

n+

aluminum-readout-

strip

SiO2

Si3N4

• 64x64 mm n-type siliconsensors

• p+ strips every 20 µm

• a strip over 6 is read-out

BMVD designr- ϕ readoutr- ϕ readout

electronicselectronics

to front-end

60 mm

60 m

m

r-z readoutr-z readout

to front-end

512 channels 512 channels

• Two sensors form a“half-module”

• Two half-modules form a“module”, 2.2% X0 thick

• A module measures rφ and z

coordinates


The ZEUS MVD: performancesTest beam

Cluster resolution on a single detec-

tor (6 GeV beam), with different re-

constuction algorithms.

Example: c-quark selection

Using D∗ tagging:

eff ≃ 1% @ pur ≃ 30%

Using MVD (simulation):

eff ≃ 10–20% @ pur ≃ 30%


The clustering procedureProcedure

• Pedestal and common mode

are subtracted;

• Consecutive strips above

threshold are clustered;

• Centre and width: accordingly

to centre of gravity:

〈ξ〉 =1

Q

∑

i

Qiξi

σ2(ξ) =1

Q

∑

i

Qi(ξi − 〈ξ〉)2

Results

IDEntriesMeanRMS

1000000 2000

1.061 0.1247

2003/10/25 16.31

BMVD clusters / MC hits

Evt

s

0

200

400

600

800

1000

1200

1400

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

IDEntriesMeanRMS

3201 12781 0.8390E-02 0.1683E-02

2003/10/25 16.31

Clusters Width (cm)

Evt

s

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 0.005 0.01 0.015 0.02 0.025 0.03

Left: Eff =

(No. of meas. hits)/(No. of GEANT hits)

Right: Cluster widths

Results obtained on a single µ MC


Multiple scattering

Dead materials:

• Ladders (rectangular boxes);

• Support tube (cylinder);

• Beam pipe (ellipsoidal cylinder).

D is the traversed material (g/cm2)

Scattering angle

δ2D =0.0136

p/GeV

√D (1 + 0.0038 lnD)

δRMS =δ2D

| sin θ|Effect on covariance matrix

cov(a1, a1) → cov(a1, a1) + δ2RMS

cov(a1, a3) → cov(a1, a3)+Q s δ2RMS

cov(a3, a3) → cov(a1, a3)+(s δRMS)2

Minor effect on the other covariances


Energy lossBethe-Bloch Formula:

−dE

dx= Kz2Z

A

1

β2

[

1

2ln

2mec2β2γ2Tmax

I2− β2 − δ

2

]

βγ

−d

E/d

x (

Ge

V g

−1 c

m2)

W/O Density Corrections

With Density Corrections

10−3

10−2

10−1

1 10 102

103

104

where:

• K = 3.07075 · 10−4 GeV cm2 mol−1

• Incident particle:• z is the charge number• M is the mass• βc is the particle speed• γ = 1/

√1 − β

• Tmax = 2mec2β2γ2

1+2γme/M

• Medium:• Z/A: atomic / mass number• I is the mean excitation energy• δ is the density effect correction


Pattern Recognition

Cluster 1

Cluster 2

Cluster 3

Lad

der

Beam−Pipe

• Each helix is propagated inwards;

• intersections with ladders are found;

• the closest BMVD hit is collected;

• track parameters are updated;

• the procedure is iterated for the

remaining layers;

• external layer only: hits are preferrd

which leads to hits in the internal lay-

ers.


Multiple assignmentT

rack

1

Tra

ck 2

Cluster 1

Cluster 2

Ladder

The same hit may be assigned to

more tracks.

If one hit is present:

• hit is assigned to the closest track

If two or more hits are present:

• assignment is done to minimise

(Trk1 − Clun)2/σ2 + (Trk2 − Clum)2/σ2


Parameter FitMeasurement

• Fm ±σm: measurement No. m

• f(m;~a): expected position

Before fit

χ20 of old fit (minimised wrt ~a).

A measurement Fm is added.

• χ2(~a) = χ20 + [Fm−f(m;~a)]2

σ2m

• Bµ(~a) = −12

∂χ2(~a)∂aµ

• Uµν(~a) = −Bµ(~a)∂aµ

χ2(~a) is no more minimised.

χ2 Minimisation

Parameter ~a is updated by minimis-

ing χ2: ∂χ2(~a+δ~a)∂aµ

= 0

δaµ = U−1µν (~a) Bν(~a)

After fit

• ~anew = ~a+ δ~a;

• Bµ(~anew) = 0;

• Uµν(~anew) = Uµν(~a);

• χ2(~anew) = χ2(~a) −Bµ(~a)δaµ.


“search for multi-lepton events with the zeus detector at ...parenti/dtesi/dtalk.pdf · luca...

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