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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
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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
Martina Schäfer 2
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 3
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.
Exotics meeting @ CERN 23 June 2004Martina Schäfer 4
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 5
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 6
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 7
KinematicsKinematicsfor the SSM at 1.5TeV (generation level)
pT of e- e+
|| of e- and e+=(e-,e+)
(lab) pz of Z’
fullsim
fullsimfullsim
Exotics meeting @ CERN 23 June 2004Martina Schäfer 8
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 9
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%
Exotics meeting @ CERN 23 June 2004Martina Schäfer 10
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 11
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 12
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|
Exotics meeting @ CERN 23 June 2004Martina Schäfer 13
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 14
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 15
Discriminating variablesDiscriminating variables
Total decay widthTotal decay widthLeptonic cross Leptonic cross
sectionsectionAsymmetriesAsymmetries
Exotics meeting @ CERN 23 June 2004Martina Schäfer 16
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 17
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 18
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 19
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 20
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 21
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 22
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 23
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 24
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 25
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 !
Exotics meeting @ CERN 23 June 2004Martina Schäfer 26
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 27
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 28
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)
Exotics meeting @ CERN 23 June 2004Martina Schäfer 29
A_FBA_FB (5) (5) as a function of Mas a function of M
A(true), 4TeV generation
Exotics meeting @ CERN 23 June 2004Martina Schäfer 30
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)
Exotics meeting @ CERN 23 June 2004Martina Schäfer 31
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 32
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 33
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 34
FINFIN
BACK-UP
Exotics meeting @ CERN 23 June 2004Martina Schäfer 35
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%
Exotics meeting @ CERN 23 June 2004Martina Schäfer 36
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 37
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
Exotics meeting @ CERN 23 June 2004Martina Schäfer 38
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)
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