Transcript ANALYSIS OF THE TILE-CAL (ATLAS) PROTOTYPES AND …

ANALYSIS OF THE TILE-CAL (ATLAS)
PROTOTYPES AND STUDY OF HIGGS
PRODUCTION AT LHC
SANTIAGO GONZÁLEZ DE LA HOZ
19 - DECEMBER - 2000
SUMMARY

Introduction
Theoretical motivations to the Minimal Supersymmetric
Standard Model (MSSM).
 The experimental setup (LHC and ATLAS).


Test beam performance of the TileCal prototypes

The 1997 test beam


The 1998 test beam



Analysis of the data for the Extended Barrel Modules 0.
Analysis of the data for the Barrel Module 0.
Higgs decay to top quarks at hadron colliders.

Search for MSSM Higgs in the top quark decay mode using a
fast simulation package for ATLAS (ATLFAST)

Comparison between full and fast simulation of ATLAS detector

Discovery potential of the ATLAS detector for the SM and
MSSM Higgs boson
Conclusions
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19-December-2000
INTRODUCTION
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
THEORETICAL MOTIVATIONS

The Standard Model (SM) is the most succesful yet
developed model to explain the physics of the
fundamental particles and their interactions.

The SM gauge group is the product SU(3) x SU(2)
x U(1), associated with the colour,weak and
hypercharge symmetries.

The fermion content of the model is divided into
two categories: QUARKS AND LEPTONS.

There are six types of quarks. Also, there are six
types of leptons.
The gauge bosons are: the massless gluons of
QCD, the massives W and Z of the weak
interaction, and the massless photons of
electromagnetism.

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19-December-2000
THEORETICAL MOTIVATIONS

The most important question of the model is the
origin of the masses.

The question can be answered by the Higgs
mechanism, which requires the Spontaneous
Symmetry Breaking.

The best experimental verification of the mechanism
would be the discovery of the Higgs boson.
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19-December-2000
THEORETICAL MOTIVATIONS
The SM answers the questions of the
structure and stability of matter with six types
of quarks, six leptons, and the four forces.
 But the SM leaves many other questions
unanswered:

•Why are there three types of quarks and leptons of each charge?
•Is there some pattern to their masses?
•Are there more types of particles and forces to be discovered at
yet higher-energy accelerators?
•Are the quarks and leptons really fundamental?
•What particles form the dark matter in the universe?
•How can the gravitational interactions be included in the SM?
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
THEORETICAL MOTIVATIONS

The standard way beyond
the SM:
The same fundamental Fields
with NEW interactions
Supersymmetry (SUSY)
Grand Unification
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19-December-2000
THEORETICAL MOTIVATIONS

What is SUSY?
The general idea
 The strategy

Unification of all forces
of Nature
Increasing unification towards
smaller distances including
Gravity
Photon, Gluon, W, Z
S= 1

Graviton
S=2
Unification of spin 2 & spin 1 forces within unique
algebra is ONLY possible for SUSY
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19-December-2000
THEORETICAL MOTIVATIONS

Q is the new generator of SUSY algebra:
Q | Boson > = | fermion >
Q | Fermion > = | boson >

The SUSY theories postulate that every particle we
observe has a massive particle partner. For example,
for every quark there may be a so-called "squark".

Spin 0
Spin 2

Spin 1/2
Spin 1
Spin 3/2
The Higgs supersymmetry sector requires two Higgs
doublets. After electroweak symmetry breaking, the
physical states of the Higgs boson are two charged
(H±) and three neutral (h, A, H).
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THEORETICAL MOTIVATIONS
 The Minimal Supersymmetric Standard Model (MSSM)
(The supersymmetric extension of the SM)
 MSSM spectrum of particles
Chiral
Supermultiplets
Gauge
Supermultiplets
squarks
quarks
(3 families)
Higgs
Sleptons
Higgsinos
leptons
(3 families)
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bino
B boson
gluino
gluon
Winos
W bosons
19-December-2000
THEORETICAL MOTIVATIONS
 R-parity:

New symmetry which has the effect of eliminating the possibility
of baryon (B) and lepton (L) violating terms in the renormalizable
potential.
PR  (1)
3( B L ) 2 S
For the SM particles and the Higgs bosons the R-parity is +1,
while for all the squarks, sleptons, gauginos and higgsinos is -1.
 If it is exactly conserved, this has three extremely important
phenomenological consequences:

The
lightest supersymmetric particles (LSP) must be absolutely stable.
Each sparticle decays into a state which contains an odd number of LSPs.
In collider experiments sparticles can be only produced in pairs.
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THEORETICAL MOTIVATIONS
 This model contains supersymmetry breaking
Slectron with the same mass as the
electron has not been
discovered yet
 In the MSSM the electroweak symmetry breaking
requires two Higgs doublets and five (H±, A, H, h)
physical states of the Higgs boson (just one in the
SM).
 The Higgs masses and coupling can be expressed
in terms of only two parameters (mA, tan):


The pseudoscalar mass
The ratio of the vacuum expectation values of the Higgs doublets
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19-December-2000
THE EXPERIMENTAL SETUP
 To look for new physics
(Higgs boson), the next
research instrument in
Europe’s particle physics is
the Large Hadron Collider
(LHC).
 The LHC is:
 a proton-proton collider
 working at high-energy
(14 TeV)
 with a high luminosity
(1034cm-2s-1).
 The LHC collider will be
built in the existing LEP
tunnel.
 The LEP/LHC injector
system (Linac, PS and
SPS)
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THE EXPERIMENTAL SETUP
 ATLAS (A Toroidal LHC
Apparatus).
 ATLAS collaboration
involves 34 countries.
 The design considerations
for ATLAS detector are:
 good EM-calorimetry for e, 
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identification and
measurement.
 Hermetic jet and Emiss
calorimetry.
 Efficient tracking at high
luminosity for lepton
measurements, b-quark
tagging and e,  identification.
  and heavy flavour vertexing
and reconstruction capability
of some B decays.
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THE EXPERIMETAL SETUP
 ATLAS calorimetry:
 The EM calorimeter system is
contained in a cylinder of
outer radius 2.25 m and a total
length of 6.65 m.
 The Hadronic calorimeter
barrel system has an outer
radius of 4.23 m and a total
length of 12 m.
 The Electromagnetic end-cap,
Hadronic and Forward
calorimeters are housed in the
same cryostat
 Crucial role at the LHC:
 Detectors are required to
measure the energy and
direction of:
photons and electrons
 isolated hadrons and jets,
 the
missing
transverse
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DE LA
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energy.

19-December-2000
THE EXPERIMENTAL SETUP
 The Hadronic Calorimeter (TILECAL):
 It is based on a sampling technique with plastic scintillator plates
(tiles) embedded in an iron absorber matrix.
 The tiles are placed in the perpendicular plane to the beam axis and
the read out is performed by optical fibres and routing them to the
photomultipliers.
 The calorimeter is segmented in three layers. The barrel and
extended barrels are divided into 64 modules.
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TEST BEAM
PERFORMANCES
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TEST BEAM PERFORMANCES
 In order to reach the physics goals some hadronic
calorimetry requirements are necessary.
Features of the hadronic
calorimetry
Rapidity
Hadronic calorimeter
performaces
|| < 5
Granularity
Total thickness
 x  = 0.1 x 0.1 ||  3
 x  = 0.2 x 0.2 || > 3
50%/E  3% for ||  3
100%/E  10% for 3<|| < 5
2% up to a transverse energy of
4TeV
Less than 5 GeV
(low energy jet)
10 interaction lengths ()
Jet identification
1% accuracy
Jet-jet mass reconstruction
1% error on the top mass
Energy resolution
Energy linearity
Noise
 Test beam results related to the hadron responses for
prototypes and modules zero of the Barrel and Extended
Barrel will be presented.
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19-December-2000
TEST BEAM PERFORMANCES
 The non-compensation concept.
 If a hadron interacts strongly develops
a shower of particles that can be
grouped as:


High-energy (+, -, o, p, n)
Low-energy (, p, n ~1-10 MeV) don’t
contribute to a measurable (visible)
energy
 In a hadronic shower we distinguish an
electromagnetic and purely hadronic
component,
 e/
ratio between the visible energy
released by electrons and pions of
equal incident energy.

e/  1
non-compensation
To achieve
 e/ > 1 compensation:
in our case
 designing an intrinsically compensated
calorimeter (U, Pb, etc..)
 in off-line analysis using different weights for
the electromagnetic and hadronic
components of the shower.

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ANALYSIS OF THE 1997 TEST BEAM
 Two Extended Barrel modules 0 were tested at CERN in
October 1997, one from Barcelona (BCN) and the other
from Argonne (ANL), together with the five 1 meter old
modules.
 The Calorimeter modules were installed on a table that can
be rotated, accessing the towers of different  values.
 Test beam energies from 20 to 400 GeV along the different
values of , from -0.8 up to -1.4 have been used in19-December-2000
this
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analysis.
ANALYSIS OF THE 1997 TEST BEAM
CUTS
On the beam chambers
to eliminate the beam halo
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On the scintillator chambers
to eliminate the events with
simultaneous particles
Applied with the agreement
of the collaboration
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ANALYSIS OF THE 1997 TEST BEAM
 The evolution of the linearity and resolution in the data
reconstruction have been studied in three steps:
Raw data
Benchmark method
H1 weighting method

 RAW DATA
corr
corr
ERAW  EANL
 EBCN
 EOLD
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ANALYSIS OF THE 1997 TEST BEAM
Energy
(GeV)
BCN module for =-1.1
BCN module for =-1.2



/
(%)

/
(%)
20
16.550.04 2.030.03 12.20.2 16.110.05 2.230.02
13.90.2
40
34.170.10 3.300.08
9.80.2
50
42.250.11 3.370.09 7.970.21 44.740.13 4.090.08 9.150.21
80
69.010.12 5.320.09 7.710.13 72.200.13 5.900.09 8.170.15
100
86.240.30 5.940.10 6.890.12 90.080.15 6.980.11 7.670.12
180
160.60.3
9.160.23 5.710.14 168.60.3
11.70.2
6.940.11
300
275.50.3
16.80.3 6.090.10 282.30.4
19.60.3
6.950.10
400
373.80.4
23.50.4 5.780.11 380.00.5
24.90.3
6.550.10
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9.60.2
33.720.08 3.300.08
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ANALYSIS OF THE 1997 TEST BEAM
BENCHMARK METHOD
 This method tries to correct the effect of the
lateral and longitudinal leakage.
ETOT  X E
ANL
TOT
E
BCN
TOT
 ( A  1)(E
ANL
S3
E
BCN
S3
)  BEOLD
 X = 1.26 GeV/pC (The conversion factor from
pC to GeV for the Extended Barrel)
 A-1= 0.17
 B = 0.31
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ANALYSIS OF THE 1997 TEST BEAM
H1 WEIGHTING METHOD
 The energy in each cell is corrected by a parameter
which depends on the energy of the cell:
corr
Ecell
 ai  Ecell
 The ai are obtained from the data at each energy:
k
Ecorr
 a1E1k .......an Enk  BEold
 where
Eik 
E
is the energy sum of all the cells
within “i” energy interval.
 Eold is the energy released in the old modules.
 The set of correction parameters ai is determined
minimising the expression:
N 2 
cell
cells i
k
2
k
(
E

E
)


(
E
 corr beam
 corr  Ebeam )
k 1, N
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k 1, N
19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
 Parametrizing the ai :
(13+1) x 8 beam energies =
112 param.
p2
ai  p1 
Ecell
 The parameters p1, p2 and
B (old modules) are
expressed as a function of
the beam energy.
 We have expressed the
entire set of corrections by
two sets of simple
functions, containing only a
total of 7 parameters.
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19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
 The aim is to reconstruct the pion energy assuming no
knowledge of the beam energy:

Realistic energy reconstruction can be done using the raw data
as the initial estimate of the particle energy; the procedure may
be iterated until it converges.
 RESULTS
 Linearity of the RAW DATA
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MODULE

RMS
BCN
-1.1
4%
BCN
-1.2
5%
ANL
-1.1
4.2%
ANL
-1.2
4%
19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
 Linearity plots obtained with the Benchmark
MODULE

RMS
BCN
-1.1
4.5%
BCN
-1.2
3.8%
ANL
-1.1
4.8%
ANL
-1.2
5%
method
 Linearity minimizing the functional with the Lagrange
multiplier (112 parameters)
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MODULE

RMS
BCN
-1.1
0.4%
BCN
-1.2
0.4%
ANL
-1.1
0.34%
ANL
-1.2
0.12%
19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
 Linearity with the beam energy after the
pararametrization
MODULE
(7 parameters)

RMS
BCN
-1.1
1.2%
BCN
-1.2
3%
ANL
-1.1
1.8%
ANL
-1.2
2.9%
 Linearity plot comparing the method which does not use
the beam energy with the one which does
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MODULE

RMS
BCN
-1.1
2%
BCN
-1.2
3.5%
ANL
-1.1
2.2%
ANL
-1.2
3.2%
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ANALYSIS OF THE 1997 TEST BEAM
 Resolution plots applying all the described methods

A fit of the data is performed in the way:

a%
c

 b% 
E
E
E



a is the statistical fluctuations in the shower development
b is the constant term dominant at high energies
c is the noise term (0.06 GeV).
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ANALYSIS OF THE 1997 TEST BEAM
Method
Module

a%
b%
Raw
Data
BCN
BCN
ANL
ANL
-1.1
-1.2
-1.1
-1.2
BCN
BCN
ANL
ANL
-1.1
-1.2
-1.1
-1.2
H1 with
112 param.
BCN
BCN
ANL
ANL
-1.1
-1.2
-1.1
-1.2
H1 with
7 param.
BCN
BCN
ANL
ANL
-1.1
-1.2
-1.1
-1.2
H1
not
using the
beam Energy
BCN
BCN
ANL
ANL
-1.1
-1.2
-1.1
-1.2
46.70.9
43.71.2
51.70.8
49.91.4
50.11.4
52.21.5
51.51.5
59.11.9
40.00.8
40.50.5
40.50.8
36.31.0
45.10.7
45.20.6
45.40.7
48.61.0
45.60.7
47.80.6
45.20.7
43.71.0
5.340.08
4.800.08
5.090.08
6.040.08
3.100.10
4.210.12
4.870.12
3.710.16
3.860.06
3.160.09
3.870.06
4.890.06
2.660.07
2.550.14
2.990.06
3.760.25
2.710.07
2.250.06
3.100.07
3.910.07
Benchmark
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19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
REMARKS:
 After applying a benchmark technique an improvement in the b




parameter of the resolution was obtained but the linearity and the a
parameter are still quite poor.
The linearity and the resolution of the Tile Calorimeter prototypes
improve using H1 method.
The results are compatible for the two modules and for the two
different values of .
The resolution degrades somewhat when no knowledge of the
particle energy is assumed, being better than the obtained with the
other methods.
The average resolution for the Extended Barrel is:
The statistical term is less than 50%
 45.6%
006
(inside of requirements)
E

E
 2.9% 
E
The constant term is around 3%
(inside of requirements)
The average RMS for the Extended Barrel modules is 2.2%
(requirement
2% up to 4 TeV).

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19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
e/ response
 The response obtained for electrons and pions gives the
possibility to extract the e/h values.
 e/h is the ratio of the calorimeter responses to the
electromagnetic and non-electromagnetic (purely
hadronic) components of hadron showers.
 The e/h ratio was extracted from the data by fitting the
expression:
e


e/h
1  (e / h  1)  0.11  ln( E )
The value e/h = 1.38 corresponding to  = -1.1 is in
good
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agreement with the 1.36 obtained from
previous studies.
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 One Barrel Module 0 was tested at CERN in July 1998, together with
the five 1 meter old modules. The same scanning table as for the test
beam in 1997 was used.
 Test beam energies from 20 to 400 GeV along different values of ,
from -0.25 to -0.55 have been analysed.
 Cuts were applied in the beam chambers to eliminate the beam halo
and events with simultaneous particle in the scintillator chambers (the
same idea that in 1997 test beam).
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19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 The data obtained in the test beam has been compared with
Monte Carlo simulation: GCALOR package (GEANT3.21
and DICE)
 many features of the module 0 are not yet implemented in the
simulation source code:


Fluctuations on the response of the fibres and tiles, including tile-to-tile
and fibre-to fibre fluctuations;
The electronic noise effect in the response of the module 0 to the
particle beams.
 The evolution of the linearity and resolution in the data
reconstruction have been studied in two steps:
Raw data
H1 weighting method

 RAW DATA
SANTIAGO GONZÁLEZ DE LA HOZ
ERAW  EMcorr
0  EOLD
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 Resolution for pions at =-0.35 for test beam data and
Monte Carlo simulation.
Test beam data
Energy
(GeV)


/
(%)
Monte Carlo


/
(%)
20
15.580.03 2.300.02 14.770.15 15.960.04 1.990.03 12.470.22
50
41.050.07 4.090.06
9.960.14 40.750.08 3.680.06
9.030.16
80
65.740.10 6.350.09
9.650.14 65.410.12 5.210.10
7.970.16
100
81.490.14 7.120.10
8.740.12 82.180.13 5.680.11
6.910.14
150
123.30.3
7.760.17
123.80.2
8.290.17
6.670.14
180
148.20.2 11.640.15 7.850.10
149.10.2
9.110.21
6.100.14
300
251.50.3 19.290.25 7.670.09
248.70.3 14.580.39 5.860.16
400
326.90.4 25.360.31 7.750.08
332.10.5 19.300.48 5.810.15
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9.570.21
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 H1 WEIGHTING METHOD
 The same idea that in 1997. The energy in each cell,
Ecell, is corrected multiplying its value by a parameter ai,
which depends on the energy of the cell.
 RESULTS
 Linearity of the Raw Data

RMS
Test beam data
-0.35
2%
Monte Carlo
-0.35
1.3%
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 Linearity plots obtained with the Lagrange multiplier
(112 parameters)

RMS
Test beam data
-0.35
0.46%
Monte Carlo
-0.35
0.48%
 Linearity after the parametrisation with the beam energy
(7 parameters)

RMS
Test beam data
-0.35
1.1%
Monte Carlo
-0.35
0.9%
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 Linearity plot comparing the method which does not use
the beam energy with the one which does

RMS
Test beam data
-0.35
1.3%
Monte Carlo
-0.35
0.9%
 Resolution plots applying all the described methods
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM

a%
0.06

 b% 
E
E
E
Method Module
Raw
Data
H1

M0
M0
M0
M0
-0.25
-0.35
-0.45
-0.55
M0
M0
M0
M0
-0.25
-0.35
-0.45
-0.55
a%
59.11.9
56.31.5
56.51.5
45.21.4
41.11.3
40.71.2
45.91.0
43.21.0
48.31.5
56.31.4
56.61.2
55.21.9
42.81.0
45.71.0
42.61.1
41.01.2
Test beam
SANTIAGO GONZÁLEZ DE LA HOZ
b%
5.600.08
6.880.10
5.350.08
5.100.11
5.440.08
5.330.08
4.220.08
4.870.10
6.010.08
6.900.11
5.750.06
5.200.09
5.220.08
3.700.10
5.000.11
5.100.10
Monte Carlo
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
REMARKS:
 The linearity and the resolution of the Tile Calorimeter prototypes




improve using H1 method. The linearity for the Monte Carlo
simulation is better than for test beam data but at high energies the
hadronic shower simulation is insufficient.
The statistical and constant term in the resolution are very similar for
the Monte Carlo simulation and the test beam data.
The results are compatible for the different values of .
The resolution degrades somewhat when no knowledge of the
particle energies is assumed, being better than the obtained with the
raw data.
The average resolution for the Barrel is:
The statistical term is less than 50%
 42.7%
006
(inside of requirements)
E

E
 4.8% 
E
The constant term is around 5%
(requirement less than 3%)
The average RMS for the Extended Barrel modules is 1.5%
(requirement
2% up to 4 TeV).

SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
e/ response
e


e/h
1  (e / h  1)  0.11  ln( E )
The e/h is greater for =-0.35 than for other ´s because
the shower is better contained for =-0.55 (e/h =1.41) than
for =-0.35
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 Comparison between Extended Barrel and Barrel module 0

MODULE
RMS
BCN
-1.1
The RMS
for
the
Barrel
is better
BCN
-1.2
than for the
Extended Barrels
due to
ANL
-1.1
ANL
-1.2
the M0
quality of the -0.25
data
M0
-0.35
M0 from 1997 -0.45
M0
MODULE
-0.55
1.2%
E.B.
3.0%
1.8%
2.9%
1.4%
1.8%
0.8%
2.0%
B.
a%
b%
45.60.7
2.710.07
47.80.6
2.250.06
ANL
-1.1
45.20.7
The constant
term
is
less
in
ANL
-1.2
43.71.0
M0
-0.25
41.11.3
the Ext. Barrels.
The
Barrel
M0
-0.35
40.71.2
M0
-0.45
45.91.0
has more leakages
than
the
E.B.
M0
-0.55
43.21.0
3.100.07

Statistical
BCN term is similar
-1.1
BCN
SANTIAGO GONZÁLEZ DE LA HOZ
-1.2
3.910.07
5.680.08
5.330.08
4.220.08
4.870.10
E.B.
B.
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 The e/h ratio is very similar for both calorimeter prototypes
(1.4) and there is a good agreement with previous precise
studies and Monte Carlo.
MODULE

(e/h)
BCN
-1.1
1.380.01
BCN
-1.2
1.480.01
ANL
-1.1
1.520.02
ANL
M0
M0
M0
-1.2
-0.35
-0.45
-0.55
1.600.02
1.610.02
1.390.01
1.410.01
 The H1 method seems to be flexible and powerful enough
to represent a starting point for the effective jets
reconstruction algorithm in the ATLAS experiment.
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
HIGGS DECAY TO
TOP QUARKS
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
SEARCH FOR MSSM HIGGS
 The Higgs particle is
produced at hadron
colliders through gluongluon, via virtual top quark
loop.
 There is a large irreducible
background from the QCD
production of top quarks.
 The H  t t branching ratio is too small (10%) to
H /the
A  tt
be observable in SM case. In the MSSM case,
branching ratios are close to 100% for mH,mA > 2mt and
for tan1.
 The H / A  t t decays cannot be distinguished
experimentally one from each other, since the H- and Aboson are almost degenerate in mass.
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
SEARCH FOR MSSM HIGGS
 The strategy used to identify tt events from H/A decays
consists in searching for WWbb final states. One top decay
(tWb) has to be followed by the semileptonic decay of the
W (Wl). The second W-boson is required to decay
hadronically (Wjj).
 The background processes can be classified
into
two
tt  bl
bjj
categories:
 The reducible background from W+jets containing multi-jet
 events.
The irreducible background, consisting of
 The study has been performed using the data sample of
the Monte Carlo simulation for ATLAS detector at LHC
collider:
 ATLFAST, a fast simulation of the ATLAS detector.
 SLUG-DICE-ATRECON, for a sophisticated full detector
simulation.
 PYTHIA 5.7 has been used to generate the signal and
backgrounds in both cases.
 The invariant mass of the tt pair have been studied for
signal events with mH/A=370, 400 and 450 GeV for an
4 pb-1 and 105 pb-1 and for
integrated
luminosity
of
310
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
tan1.5
SEARCH FOR MSSM HIGGS
 The initial selection requires at last 4 reconstructed jets with
pT>40 GeV and ||<2.5, two of them being labelled as b-jets
and at least one reconstructed isolated lepton with pT>20
(20) GeV for muons and pT>20 (30) GeV for electrons and
||<2.5 at low (high) luminosity.
 After the selection cuts are applied, the background from tt
continuum dominates. After requiring top-pair reconstruction
the background from non-tt sources (QCD jets, W+jets, etc.)
can be neglected.
 There is an interference between the signal and the
background amplitudes which causes a suppression of the
observability of the signal. This suppression has been
estimated to be 30% for mH=370 GeV, 50% for mH=400 GeV
and 70% for mH=450 GeV.
 Two algorithms for reconstructing the invariant mass of the tt
pair have been studied:
 All possible combinations of b-jets with reconstructed decay Wl
2
and W jj contribute to the mtt massdistribution.
 (mbl  mt )2  (mjjb  mt )2
 OnlyDEthe
combination with the best 2 is taken into account.
SANTIAGO GONZÁLEZ
LA HOZ
19-December-2000
SEARCH FOR MSSM HIGGS
First algorithm
All possible combinations
of b-jets with jj
The level of
combinatorial
background
Second algorithm
jjb combination
2=(mjjb-mt)2
SANTIAGO GONZÁLEZ DE LA HOZ
Single top-quark
reconstruction in the
hadronic channel
19-December-2000
SEARCH FOR MSSM HIGGS
First algorithm
All possible combinations
of b-jets with l
The reconstruction of
Wl is limited.
The longitudinal
component of the 
can be extracted
solving the W mass
equation
Second algorithm
lb combination
2=(mlb-mt)2
SANTIAGO GONZÁLEZ DE LA HOZ
jl
background
Single top-quark
reconstruction in the
semileptonic channel
19-December-2000
SEARCH FOR MSSM HIGGS
First algorithm
All possible combinations
of b-jets with l and jj
First
Nom.
Val.
370
Algor. Second Algor.
mH
mH


(GeV) (GeV) (GeV) (GeV)
390
36
372.8
13.9
The second algorithm
400
415
39
401.7
16.4
improves substantially
respect the first one:
The450
first algorithm
in more unbiased
440 reproduces
59
446.8
21.6
1) the signal resolutionway the shape and magnitude of the combinatorial
2) the signal-tobackground to the hadronic and semileptonic
First Algori.
Second Algori
background ratio
channels.
3) the statistical
Nom. Signal Bgd. Sig. Signal Bgd.
Sig.
significance
Val.
S/B
S/B
Second algorithm
only combination
2=(mjjb-mt)2+(mlb-mt)2
SANTIAGO GONZÁLEZ DE LA HOZ
370
4400
68700
16.8
400
4050
85700
13.8
450
3250 107200
9.9
4500
34200
24.3
Reconstruction
39500 21.1
of top-quark pairs
4200
3200
52900
14.2
15-December-2000
SEARCH FOR MSSM HIGGS
 After to reconstruct the invariant mass a study in order to
subtract the signal peak from the background has been
performed. The statistical error, the systematic error from
curves
overall normalisation and from the shapeThe
of discovery
the background
cover at best limited
have been taken into account.
region
parameter
 The signal+background for mH/A = 370 GeV
andin 450
GeV
space,
namely that
using a polynomial to fit the background and
a gaussian
corresponding to
distribution on top of it.
2mt<mA<470 GeV
for tan 1
1) The extraction of the signal would only be possible for Higgs masses above the
kinematics peak of the background distribution which is around 400 GeV.
2) For masses close to 400 GeV only an excess of events above the continuum
background would be observed.
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
COMPARISON FULL AND FAST
 In order to be able to cross-check the results obtained with
||<2.5 events
||<2.5were simulated with the
ATLFAST, a||<2.5
total of 20000
pT>20
pT>40 detector
pT>40 (m = 400 GeV and
full simulation
of the ATLAS
A
tan1).
 The acceptances and the quantities involved in kinematics
havemuons
beenleptons
compared.
. electrons
jets bjets
Acccuts
Fast
0.90
0.77
0.88
0.41
0.62
Full
0.89
0.74
0.85
0.49
0.59
Due to the implementation of
the jet energy threshold in both
simulations
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
COMPARISON FULL AND FAST
||
Quantities
involved
in
kinematics
cuts
pT

—

pT
—
pT
SANTIAGO GONZÁLEZ DE LA HOZ
The pT mean value is greater in the full than in
the fast simulation because:
1) In full the pT is slightly overestimated due
to the calibration problems.
2)The electronic noise is taken into account
19-December-2000
Fast
Full
COMPARISON
FULL AND
FAST
simulation
simulation
(GeV)
 (GeV)
jjbtbjj
13.93
21.11
tbl
11.92
12.67
Top and
mtt
17.25
17.5
Higgs
1) The two simulations packages are in good agreement for the
mass
kinematicslb
acceptances and the quantities involved in the analysis.
resolution
2) The top and Higgs mass resolutions are in reasonable agreement,
with the full simulation predicting resolutions which are 10-20%
worse than those from the fast simulation.
3)The two simulations can be used in a complementary way to
study physics channels:
3.1) Full simulation can be used to check in detail the detector
tt
performances.
3.2) Fast simulation can be used for the production of large statistics
samples of events for the physics analysis.
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
<2M :
DISCOVERY1)M
POTENTIAL
H ZZ*  4l
H
Z
H 
H  WW*  ll
2)MH>2MZ:
dominant discovery channel is the four-lepton channe
3)(600-1000) GeV:
H  WW  ljj
H  ZZ  lljj
H  ZZ  ll
1)Large tan (as SM):
H 
H  bb
H  ZZ  4l
H/A 
H/A 
2) Low tan:
H/A tt
A
Zb
H  hh
H  tb
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
CONCLUSION
 The results obtained in the test beam of the Tile - Cal
prototypes are the following:
 The linearity and resolution of the Tile Calorimeter prototypes




improve using the H1 method. Also these results are compatible for
the two prototypes used in the 1997 and 1998 test beam at different
values of . In the ATLAS environment, the aim will be to develop an
effective jet reconstruction algorithm. This method described here
may be flexible and powerful enough to suit this purpose.
The linearity obtained with Monte Carlo simulation is better than for
the test beam data but at high energies the hadronic shower
simulation is insufficient and the shower descriptions became quite
far away from reality.
The statistical and constant terms in the resolution are very similar
for Monte Carlo simulation and test beam data.
The e/h ratio of a sampling calorimeter with an iron-scintillator
structure is expected to be >1 as has been shown in this analysis
and the value is in good agreement with the results obtained from
previous precise studies.
A comparison between the barrel and extended barrel prototypes
has been made. The resolution, linearity and e/h ratio for both
prototypes are inside of the Hadronic Calorimeter requirements.
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
CONCLUSION
 The results obtained in the search for a Higgs boson via its
decay to top quarks in the MSSM are the following:
 The expected mass resolution mtt increases from 14 to 20 GeV as
mH increases from 370 to 450 GeV. This implies that a typical
window to observe most of the signal would be between 28 and 80
GeV.
 The signal-to-background ratio varies between 9% and 1% over the
mass range from 370 to 450 GeV. For an integrated luminosity of 30
fb-1 (3 years at low luminosity) and tan=1.5 about 2120 signal
events and 40000 background events are expected inside a mass
window of 2m around mA= 400 GeV.
 The extraction of the signal would only be possible for Higgs masses
above the kinematics peak of the background distribution which is
around
mtt = 400 GeV.
 For masses close to 400 GeV only an excess of events above the
continuum background would be observed.
 A limited region in parameter space has been found. This limit
corresponds to 2mt< mA <470 GeV for tan1.
 The results obtained for the mass resolution with mA=400 GeV using
ATLFAST have been compared with a full detector simulation. The
two simulation packages are in good agreement for the kinematics
cuts acceptance, the quantities involved in the analysis and the top
andDE
Higgs
mass resolutions.
SANTIAGO GONZÁLEZ
LA HOZ
19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
 Linearity plots obtained with the Benchmark
MODULE

RMS
BCN
-1.1
4.5%
BCN
-1.2
3.8%
ANL
-1.1
4.8%
ANL
-1.2
5%
method
 Linearity minimizing the functional with the Lagrange
multiplier (112 parameters)
SANTIAGO GONZÁLEZ DE LA HOZ
MODULE

RMS
BCN
-1.1
0.4%
BCN
-1.2
0.4%
ANL
-1.1
0.34%
ANL
-1.2
0.12%
19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
 Linearity with the beam energy after the
pararametrization
MODULE
(7 parameters)

RMS
BCN
-1.1
1.2%
BCN
-1.2
3%
ANL
-1.1
1.8%
ANL
-1.2
2.9%
 Linearity plot comparing the method which does not use
the beam energy with the one which does
SANTIAGO GONZÁLEZ DE LA HOZ
MODULE

RMS
BCN
-1.1
2%
BCN
-1.2
3.5%
ANL
-1.1
2.2%
ANL
-1.2
3.2%
15-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 Linearity plots obtained with the Lagrange multiplier (112
parameters)

RMS
Test beam data
-0.35
0.46%
Monte Carlo
-0.35
0.48%
 Linearity after the parametrisation with the beam energy
(7 parameters)

RMS
Test beam data
-0.35
1.1%
Monte Carlo
-0.35
0.9%
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
ANALYSIS OF THE 1998 TEST BEAM
 Linearity plot comparing the method which does not use
the beam energy with the one which does

RMS
Test beam data
-0.35
1.3%
Monte Carlo
-0.35
0.9%
 Resolution plots applying all the described methods
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000
TEST BEAM PERFORMANCES
 A calorimeter consists of a matter block which serves to
intercept primary particles and where all the energy is
deposited in its interior.
The different response to electrons, muons
 General characteristics
and hadrons can be exploited for particle
identification
The average number of secondary particles
is proportional to the energy of the incident
particles
They are sensitive to
charged and neutral
particles
SANTIAGO GONZÁLEZ DE LA HOZ
Calorimeter:  and e- interact
electromagnetically with the absorber material
Hadronic Calorimeter: The hadrons interact
strongly with the absorber material
Electromagenetic
19-December-2000
ANALYSIS OF THE 1997 TEST BEAM
BENCHMARK METHOD
 This method tries to correct the effect of the
lateral and longitudinal leakage.
ETOT  X E
ANL
TOT
E
BCN
TOT
 ( A  1)(E
ANL
S3
E
BCN
S3
)  BEOLD
 X = 1.26 GeV/pC (The conversion factor from
pC to GeV for the Extended Barrel)
 A-1= 0.17
 B = 0.31
SANTIAGO GONZÁLEZ DE LA HOZ
19-December-2000