Martina Schäfer

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Martina Schäfer 1 Z’ studies at LHC Z’ studies at LHC Z Z e e + e e - Martina Schäfer Martina Schäfer Exotics meeting @ CERN Exotics meeting @ CERN 23 J 23 J une 2004 une 2004 F.Ledroit F.Ledroit (UJF-CNRS) : (UJF-CNRS) : DEIR DEIR Th.Müller Th.Müller (Universität Karlsruhe) : (Universität Karlsruhe) : Diplomarbeit Diplomarbeit IEKP

description

Z’ studies at LHC Z e + e - Martina Schäfer. Exotics meeting @ CERN. 23 J une 2004. F.Ledroit (UJF-CNRS) : DEIR Th.Müller (Universität Karlsruhe) : Diplomarbeit. IEKP. Martina Schäfer. 1. Z’ models and di scovery limits Data used Kinematics DY and Interference - PowerPoint PPT Presentation

Transcript of Martina Schäfer

Page 1: Martina Schäfer

Martina Schäfer 1

Z’ studies at LHCZ’ studies at LHCZZee++ee--

Martina SchäferMartina Schäfer

Exotics meeting @ CERNExotics meeting @ CERN

23 J23 June 2004une 2004

F.LedroitF.Ledroit (UJF-CNRS) : (UJF-CNRS) : DEIRDEIR Th.MüllerTh.Müller (Universität Karlsruhe) : (Universität Karlsruhe) : DiplomarbeitDiplomarbeit

IEKP

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Z’ models and discovery limits Data used Kinematics

DY and Interference Electron identification

Calibration Z’ reconstruction in full sim

Background Total decay width

Leptonic cross section A_FB

Summary and outlookdis

crim

inati

ng

vari

able

s

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Z’ models (1)Z’ models (1)

SSM Z’ with same couplings as the usual Z boson

E6 models Effectif rang 5 models Based on GUTS, popular extensions: SO(10) and E6 E6SO(10) x U(1)SU(5)xU(1)x U(1)MSxU(1)ß

Z’=sinß Z + cosß Z studied: Z, Z et Z

The research for Z’ bosons is motivated by the high number of models beyond the standard model that propose extra gauge bosons. As it is a channel easy to observe, this channel is an excellent method to distinguish the models.

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tower of Kaluza-Klein resonances for all gauge bosons with M²n=(nMc)²+M0², (Mc compactification scale, M0 mass of the ordinary gauge boson)

Z’ models (2)Z’ models (2) LR symmetric models

SU(2)LxU(1)Y (SM) enlarged to SU(2)LxSU(2)RxU(1)

=gL/gR: ration of the couplings of the left and the right gauge bosons

studied: =1

Z’(KK): extra dimensions fermions confined on a

3-brane, gauge bosons propagate with the gravitation in the extra dimensions (small, orthogonal to the branes)

here: one extra dimension compactified on S1/Z², all fermions are on the same « orbifold point »

n=1 n=2

n=3n=4

MC=1TeV

goal: study of discriminating variables

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Discovery limitsDiscovery limitsDirect and indirect discovery limits

SSM >1.5TeV indirect, >690GeV direct

E6 models >350..680GeV indirect, >590..620GeV

direct

LR symmetric models >860GeV indirect, >630GeV direct

Z’(KK) 4TeV

Mixing between Z’ and Z negligible

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Data usedData used channel Z’ e+e-

low lumi, without pile-up,…

generation with Pythia (within Athena) Z’ at 1.5TeV and 4TeV with complete interference

structure(DY) DY only without ISR/FSR cut CKIN(1) = 1000GeV / 2500GeV

fullsim (DC1) Z’ at 1.5TeV with DY (4TeV not yet done) DY only with ISR/FSR cut CKIN(1) = 500GeV

single electrons, photons and dijet for electron identification and calibration from DC1

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KinematicsKinematicsfor the SSM at 1.5TeV (generation level)

pT of e- e+

|| of e- and e+=(e-,e+)

(lab) pz of Z’

fullsim

fullsimfullsim

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DY and interferenceDY and interference

Mll(GeV) with int.

Interference : SSM (generation level)

Mll(GeV) DY

peak

destructive

narrower

broader

/GeV

Interference : Z’(KK)

destructive !

Mll(GeV) DY+Z’

Mll(GeV) with int.

/GeV

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Electron identificationElectron identification

only clusters with ET>50GeV

selection variable “ISEM” (standard electron identification ) number of tracks (1 or 2) number of hits in the tracker (at least 6)

results (efficiency) electrons (single electrons, DC1, 200GeV): 91% electrons (single electrons, DC1, 1000GeV): 87% photons (single photons, DC1, 200GeV ): 4% jets (dijets, DC1, 560GeV): 0.13%

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CalibrationCalibration “standard” calibration : photons de-calibration and re-calibration only barrel tested with single electrons (200GeV and 1TeV)

Stathes Paganis (University of Wisconsin)H4e

/E0.7%

resolution of electrons (Z’ at 1.5TeV)

Results:Z’ (SSM 1.5TeV)electrons at

750GeV(E)/E (E=750GeV)

=9.5%sqrt(E)-1 0.45% 0.6% ok

(M)/M (M=1.5TeV)= sqrt(2) (E)/E 0.8% ok

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Z’ reconstruction (1)Z’ reconstruction (1)only events with

2 identified electrons e+ and e-

2 electrons in the barrel

resolution on the mass (1.5TeV)

= 11 GeV

+ tails

/E 0.7%

Losts by bremsstrahlung and FSR outside the cluster neglected.

truth

recalibrated

not recalibrated

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Z’ reconstruction (2)Z’ reconstruction (2)acceptance(55%, only barrel 45% )

in |Y|(Y of Z’)

in |cos|

in |cos| for different bins in |Y|

high |Y|

low |Y|

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Background (1)Background (1)

bb

at 1.5 TeV generation

photons and jet rejection: see electron

identification efficiency

90% for electrons

0.1% for jets 4% for photonspT() <<

50GeVat 1.5TeV, with B=DY,

B=S=0.4, 1 year low lumi (20fb-1)

S B

SSM 1540 13

Z’() 450 5

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Background (2)Background (2)

at 4 TeV, generation

Mll/GeV

very clean signal

at 4TeV, with B=DY, B=S=0.4, 1 year high lumi (100fb-1)

S B

SSM 25 0.3

Z’() 10 0.1

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Discriminating variablesDiscriminating variables

Total decay widthTotal decay widthLeptonic cross Leptonic cross

sectionsectionAsymmetriesAsymmetries

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Total decay width (1)Total decay width (1)fit for total decay width -- generation level

exp (DY)

BW

BW*exp+exp

±4peak

DY

parton luminosity + interference

DY only:

Approximated by exp

/GeV

/GeV

exemple:Z’(eta) à 1.5 TeV

KK: NO DY

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Total decay width (2)Total decay width (2)

detector resolution

natural decay width

fit for total decay width -- full sim

[Res][BW*exp+exp]

Resolution function:

Gauss+Gauss (central peak + tails)

Gauss+Gauss+Gauss

(preliminary to take into account the

asymmetry in the resolution/preliminar

y calibration)

G+G+G

G+G

Mass resolution

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Total decay width (3)Total decay width (3)1.5TeV

/GeV

all models (generation)

full sim, SSM 1.5TeV

Mll/GeV

DY

M recalibrated

fit

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Total decay width (4)Total decay width (4)Results at 1.5TeV – generation and full sim

Fit (GeV)

(gen)

Theo.

(GeV)

Fit (GeV)

G+G

Fit (GeV)

G+G+G

SSM 45.9 0.3

44.7 54.7

0.7

46.7

1.5

8.0

0.1

8.0 12.3

0.2

9.3

0.6

10.1

0.1

9.5 13.5

0.2

10.2

0.5

18.9

0.1

17.6 21.8

0.3

19.1

0.8

LR 32.5

0.3

30.6 35.2

0.6

28.4

1.1

syst 1…6%

already atgeneration level,bigger for small

always over-estimated!

stat. error

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Total decay width (5)Total decay width (5)Fit (GeV)

Theo.

(GeV)

SSM 121.90.8

119.2

24.7

0.3

21.2

30.0

0.3

25.2

51.1

0.2

46.8

LR 88.0

0.6

81.6

KK 180.0

1.2

Results at 4TeV – generation level

/GeV

stat. error

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Leptonic cross section (1)Leptonic cross section (1) Calculated with

luminosity (cross section of Pythia)

number of events in the peak without DY

in 4 acceptance 1 (at generation) *

( exotic Z’ decays)

n

(n )/(15 )

LR

resu

lts at 4

TeV

, g

en

era

tion

(fb)

*(GeV fb)

SSM 0.25

0.001

30.7

0.2

0.10

0.0004

1.9

0.3

0.10

0.0004

2.7

0.3

0.14

0.001

7.0

0.1

LR 0.16

0.001

13.9

0.1

KK 2.3

0.01

415

3.21.5TeV, generation stat. error

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Leptonic cross section (2)Leptonic cross section (2)(fb)

*(GeV fb)

Pythia

(fb)

Fullsim(fb)

Fullsim

*(GeV fb)

SSM 76.9

0.3

3531.4

27.0

78.8 84.2

1.4

3934.0

140.5

22.8

0.1

180.9

2.2

23.5 23.8

0.5

221.6

13.9

25.9

0.1

260.5

2.7

26.3 26.7

0.5

271.8

14.8

46.7

0.2

865.0

7.0

47.9 50.0

1.1

957.5

45.1

LR 50.2

0.2

1603.2

12.6

50.0 54.0

1.0

1537

68.5

resu

lts at 1

.5TeV

stat. error

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Forward/Backward (1)Forward/Backward (1)

in pp collisions there is no natural forward/backward definition q direction “forward” q direction approximated

by Z’ direction (in general the quark is a valence quark and so faster than the antiquark from the sea)

wrong in 25% of the events better at high rapidity Y of

the Z’

% of evts with wrong quark direction

|Y| > 0.8: 10% wrong

1.5TeV, generation

parametrised by pol2

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Forward/Backward (2)Forward/Backward (2)

* = (e-,q) * = (e-,Z’) * = (e-,z-axis)

cos * distribution

exemple: Z’(chi) model at 1.5 TeV

(generation)

in the Z’ system

cos* is asymmetric A(true)

cos* : less asymmetric A(obs)

cos* is symmetric

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A_FBA_FB (1) (1) as a function of Mas a function of M

fit to the cos distribution in each bin of M

3/8(1+ cos2) + A_FB cos

real direction of the q

fit

counting

or

conclusion:Agreement

between fitting and

counting.

exemple:Z’(SSM) at 1.5TeV,generation

A_FB(M)=(N+-N-)/N

N+: cos>0, in each  bin of M

! need acceptance correction !

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A_FBA_FB (2) (2) as a function of Mas a function of M

fitting

q direction

Z’ direction

conclusion:Z’ washes theasymmetry out.

exemple:Z’(psi) at 4TeV,

generation

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A_FBA_FB (3) (3) as a function of Mas a function of M

counting, with(out) cut |Y|>0.8

q, without cut

q, with cut

Z’, without cut

Z’, with cut

conclusion:A cut in |Y| reducesthe loss in

asymmetry.But: acceptancedecreases with |Y|.

exemple:Z’(eta) at 1.5TeV,

generation

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A_FBA_FB (4) (4) as a function of Mas a function of M

conclusion:Fit in 2D works fine,eps(y) is

independentof the model, butdependent of themass.Advantage: accessA(true) and not onlyA(obs)

Factor of dilution: A(obs)=D

A(true), D-1=1-2eps(y)Fit 2D, simple

divisiondoesn’t work as Ddepends on the

model.

exemple:Z’(SSM) at 1.5TeV,full sim

Dilution

fit q

fit Z’

fit 2D (dilution)

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A_FBA_FB (5) (5) as a function of Mas a function of M

A(true), 4TeV generation

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A_FBA_FB (6) (6) as a function of Mas a function of M

Results (on peak)

gen. 1.5TeV

gen. 1.5TeV

fullsim

1.5TeV

gen.

4 TeV

gen.

4 TeV

SSM 0.08

0.01

0.08

0.03

0.06

0.06

0.09

0.01

0.07

0.03

0.01

0.01

0.02

0.03

-0.01

0.06

0.01

0.01

-0.01

0.03

-0.35

0.01

-0.26

0.03

-0.31

0.06

-0.31

0.01

-0.26

0.03

-0.07

0.01

-0.05

0.03

-0.08

0.06

0.05

0.01

0.04

0.03

LR 0.19

0.01

0.17

0.03

0.20

0.06

0.19

0.01

0.16

0.03

KK 0.52

0.01

0.47

0.03

DY 0.63

0.01

0.61

0.04

0.41

0.28

0.59

0.03

0.54

0.07

A(true)

fit2D

stat. error

stat. error+ syst. error on eps(y)

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A_FBA_FB (7) (7) as a function of Yas a function of Y

A_FB(Y)=(N+-N-)/NN+: cos>0, in each  bin of Y

! need acceptance correction !A_FB(-Y)= - A_FB(Y)

exemple:Z’(eta) at 4TeVgeneration

Y

exemple:Z’(chi) at

1.5TeVgeneration

exemple:Z’(LR) at

1.5TeVfull sim

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A_FBA_FB (8) (8) as a function of Yas a function of Y

Choice:slope of a straightline to characterizemodels

gen. 1.5TeV

fullsim 1.5TeV

gen.

4 TeV

SSM 0.07 0.01 0.08 0.03 0.12 0.02

0.01 0.01 0.01 0.03 -0.02 0.02

-0.22 0.03

-0.25 0.04

-0.39 0.03

-0.04 0.01

-0.07 0.03

-0.05 0.01

LR 0.16 0.03 0.14 0.04 0.26 0.02

KK 0.67 0.04

DY 0.52 0.07 -0.25 0.04

0.71 0.09stat. error +

syst. error on acceptance

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Summary and OutlookSummary and Outlook

Analysis at generation level at 1.5 and at 4TeV for different models interference background

Study in full simulation Electron identification Calibration Resolution

Discriminating variables decay width cross section A_FB (dilution factor)

To do : 4TeV (fullsim) Selection cuts (fullsim) Background/noise (fullsim) Discriminating

Outlook: « Diplomarbeit » finished in

September ATLAS note

Towards discrimination between models by global fits

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FINFIN

BACK-UP

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Back-up (1)Back-up (1) Theoretical decay width = gx² /48 (cv²+ca²) Mx (for mf=0) gx=g/cosw, g=e/sin w

Extra dimensions S1: y=0..2R, 0=2R Z²: y=-y=2R-y Fix points: 0 et

Dilution A_FB(obs)= (1-2eps) A_FB(true),

eps: % of wrong q direction

Charge miss-identification: 3.5%

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Calibration (1)Calibration (1) “standard” calibration

:photons

de-calibration re-calibration only barrel

beforerecalib.

afterrecalib.

energy

Stathes Paganis (University of Wisconsin)

200GeV

/E=0.9%

(E)/E (E=200GeV) =9.5%sqrt(E)-1

0.45% 0.8% ok

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Calibration (2)Calibration (2)

/E=0.8%

energy

1TeV afterrecalib.

beforerecalib.

(E)/E (E=1000GeV) =9.5%sqrt(E)-1

0.45% 0.5% ok

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Calibration (3)Calibration (3)Results on the Z’ (SSM 1.5TeV), electrons at about 750GeV(E)/E (E=750GeV)

=9.5%sqrt(E)-1 0.45% 0.6% ok(M)/M (M=1.5TeV)

= sqrt(2) (E)/E 0.8% ok

/E0.7%

resolution of electrons (Z’ at

1.5TeV)