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ANALYSIS OF THE TILE-CAL (ATLAS) PROTOTYPES AND STUDY OF HIGGS PRODUCTION AT LHC

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).

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ANALYSIS OF THE TILE-CAL (ATLAS) PROTOTYPES AND STUDY OF HIGGS PRODUCTION AT LHC

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  1. ANALYSIS OF THE TILE-CAL (ATLAS) PROTOTYPES AND STUDY OF HIGGS PRODUCTION AT LHC SANTIAGO GONZÁLEZ DE LA HOZ 19 - DECEMBER - 2000

  2. 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 • Analysis of the data for the Extended Barrel Modules 0. • The 1998 test beam • 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 SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  3. INTRODUCTION SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  4. 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. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  5. 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. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  6. 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

  7. THEORETICAL MOTIVATIONS • The standard way beyond the SM: The same fundamental Fields with NEW interactions Supersymmetry(SUSY) Grand Unification SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  8. THEORETICAL MOTIVATIONS Unification of all forces of Nature • What is SUSY? • The general idea • The strategy • Unification of spin 2 & spin 1 forces within unique algebra is ONLY possible for SUSY Increasing unification towards smaller distances including Gravity Photon, Gluon, W, Z S= 1 Graviton S = 2 19-December-2000 SANTIAGO GONZÁLEZ DE LA HOZ

  9. THEORETICAL MOTIVATIONS • Q is thenew 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 1/2 Spin 1 Spin 3/2 Spin 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). SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  10. 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) bino B boson Sleptons leptons (3 families) Higgs Higgsinos gluino gluon Winos W bosons SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  11. 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. • 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. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  12. THEORETICAL MOTIVATIONS • This model contains supersymmetry breaking • 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 Slectron with the same mass as the electron has not been discovered yet SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  13. 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) SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  14. THE EXPERIMENTAL SETUP • ATLAS (AToroidal LHC Apparatus). • ATLAS collaboration involves 34 countries. • The design considerations for ATLAS detector are: • good EM-calorimetry for e,  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. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  15. 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 energy. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  16. 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. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  17. TEST BEAM PERFORMANCES SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  18. TEST BEAM PERFORMANCES • In order to reach the physics goals some hadronic calorimetry requirements are necessary. • Test beam results related to the hadron responses for prototypes and modules zero of the Barrel and Extended Barrel will be presented. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  19. 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 • e/ > 1 in our case • To achieve compensation: • designing an intrinsically compensated calorimeter (U, Pb, etc..) • in off-line analysis using different weights for the electromagnetic and hadronic components of the shower. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  20. 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 in this analysis. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  21. ANALYSIS OF THE 1997 TEST BEAM 19-December-2000 SANTIAGO GONZÁLEZ DE LA HOZ

  22. 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 SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  23. ANALYSIS OF THE 1997 TEST BEAM BCN module for =-1.1 BCN module for =-1.2 SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  24. ANALYSIS OF THE 1997 TEST BEAM • BENCHMARK METHOD • This method tries to correct the effect of the lateral and longitudinal leakage. • 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

  25. 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: • The ai are obtained from the data at each energy: • where 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: SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  26. ANALYSIS OF THE 1997 TEST BEAM • Parametrizing the ai : (13+1) x 8 beam energies = 112 param. • 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. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  27. 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 SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  28. ANALYSIS OF THE 1997 TEST BEAM • Linearity plots obtained with the Benchmark method • Linearity minimizing the functional with the Lagrange multiplier (112 parameters) SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  29. ANALYSIS OF THE 1997 TEST BEAM • Linearity with the beam energy after the pararametrization (7 parameters) • Linearity plot comparing the method which does not use the beam energy with the one which does 19-December-2000 SANTIAGO GONZÁLEZ DE LA HOZ

  30. ANALYSIS OF THE 1997 TEST BEAM • Resolution plots applying all the described methods • A fit of the data is performed in the way: • 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). SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  31. ANALYSIS OF THE 1997 TEST BEAM 19-December-2000 SANTIAGO GONZÁLEZ DE LA HOZ

  32. ANALYSIS OF THE 1997 TEST BEAM • REMARKS: • After applying a benchmarktechnique 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% (inside of requirements) 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). SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  33. 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: • The value e/h = 1.38 corresponding to  = -1.1 is in good agreement with the 1.36 obtained from previous studies. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  34. 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). SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  35. 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 • Raw data • H1 weighting method SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  36. ANALYSIS OF THE 1998 TEST BEAM • Resolution for pions at =-0.35 for test beam data and Monte Carlo simulation. Test beam dataMonte Carlo SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  37. 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 SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  38. ANALYSIS OF THE 1998 TEST BEAM • Linearity plots obtained with the Lagrange multiplier (112 parameters) • Linearity after the parametrisation with the beam energy (7 parameters) SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  39. ANALYSIS OF THE 1998 TEST BEAM • Linearity plot comparing the method which does not use the beam energy with the one which does • Resolution plots applying all the described methods 19-December-2000 SANTIAGO GONZÁLEZ DE LA HOZ

  40. ANALYSIS OF THE 1998 TEST BEAM Test beam Monte Carlo SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  41. 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% (inside of requirements) 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

  42. ANALYSIS OF THE 1998 TEST BEAM • e/ response • 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

  43. ANALYSIS OF THE 1998 TEST BEAM • Comparison between Extended Barrel and Barrel module 0 E.B. The RMS for the Barrel is better than for the Extended Barrels due to the quality of the data from 1997 B. Statistical term is similar E.B. The constant term is less in the Ext. Barrels. The Barrel has more leakages than the E.B. B. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  44. 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. • The H1method 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

  45. HIGGS DECAY TO TOP QUARKS SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  46. SEARCH FOR MSSM HIGGS • The Higgs particle is produced at hadron colliders through gluon-gluon, via virtual top quark loop. • There is a large irreducible background from the QCD production of top quarks. • The branching ratio is too small (10%) to be observable in SM case. In the MSSM case, the branching ratios are close to 100% for mH,mA > 2mt and for tan1. • The decays cannot be distinguished experimentally one from each other, since the H- and A-boson are almost degenerate in mass. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  47. 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 categories: • The irreducible background, consisting of • The reducible background from W+jets containing multi-jet events. • 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 integrated luminosity of 3104 pb-1 and 105 pb-1 and for tan1.5 SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  48. 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 and W jj contribute to the mtt mass distribution. • Only the combination with the best 2 is taken into account. SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  49. 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 Single top-quark reconstruction in the hadronic channel SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

  50. 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 jl background Second algorithm lb combination 2=(mlb-mt)2 Single top-quark reconstruction in the semileptonic channel SANTIAGO GONZÁLEZ DE LA HOZ 19-December-2000

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