ATLAS by babbian



Searches with Multi-Lepton
  Signatures at the LHC

            Bing Zhou
     The University of Michigan

            Jan. 8, 2007
      At Aspen-07 Conference
         The Large Hadron Collider at CERN
         Energy = 14 TeV, Lumi = 1034 cm-2 s-1
  LHC Missions: Explore new physics in TeV energy scale


First Beams:
Fall 2007
Physics Runs:
from Spring 2008
~ few fb-1 in 1st year
              ATLAS and CMS Detectors                                   ATLAS

       > 10 years of hard work in design and constructions

ATLAS                                      CMS
      Length : ~45 m                          Length : ~22 m
      Diameter : ~24 m                        Diameter : ~14 m
      Weight : ~ 7,000 tons                   Weight : ~ 12,500 tons
      Electronic channels : ~ 108             Solenoid : 4 T
      Solenoid : 2 T                          Fe yoke
      Air-core toroids                        Compact and modular
Excellent Standalone Muon Detector           Excellent EM Calorimeter

Lepton Signals Are the Keys for Discovery !                       ATLAS




   • Lepton identifications: high efficiency, low fake rate
   • Excellent energy and momentum resolution
   • Trigger at low Pt
   • Clean Signature for new physics discoveries!
   • Detector can be well understood from Z l+l- events
                 Detector Technologies                                     ATLAS

                     ATLAS                               CMS
            (A Toroidal LHC Apparatus)       (The Compact Muon Solenoid)

           Si pixels + strips               Si pixels + strips
TRACKER    TRT → particle identification    No particle identification
           σ/pT ~ 5x10-4 pT ⊕ 0.01          σ/pT ~ 1.5x10-4 pT ⊕ 0.005

           Pb-liquid argon                  PbWO4 crystals
EM CALO    σ/E ~ 10%/E uniform             σ/E ~ 2-5%/√E
           longitudinal segmentation        no longitudinal segmentation

           Fe-scint. + Cu-liquid argon (
                                            Brass-scint. ( 5.8+catcher)
HAD CALO   10 λ)
           σ/E ~ 50%/√E ⊕ 0.03              σ/E ~ 100%/√E ⊕ 0.05

           MDT, CSC, RPC, TGC               DT, CSC, RPC
 MUON      σ/pT ~ 7 % at 1 TeV              σ/pT ~ 5% at 1 TeV
           standalone                       combining with tracker

High Precision Tracking for Muon Detections
|h| coverage to 2.7, Dp/p ~ 8% @ 1TeV (stracking ~ 50 m)                    ATLAS


                             Simulation of a H  mm ee event in ATLAS

                                  Pm + DE = Ptrk
                                                       Inner Tracker

                                   Muon Spectrometer
                ~ 40% of
                total cost

      ATLAS Test Beam Results : Muon detector resolution                        ATLAS

    Barrel Sagitta s vs Beam Energy

                                                           Calculated Sagitta
                                                           Measured Sagitta

                                                          Endcap stand

                                                          Beam Energy (GeV)
• Barrel: good agreement between data   • EC sagitta calculated according to the
  and G4 Simulations (solid curves)       nominal material distribution
(important for simulation validation)   • Agreement of the measurements
• Threshold effect on the intrinsic       with G4 is good, correction for the
  resolution                              aluminum support bar applied

CMS: Muon Detection Resolution   ATLAS

           ATLAS: ECAL Energy Resolution                                               ATLAS

Resolution with new reconstruction at h=0.68
                                               Local energy resolution well understood
                                               since Module 0 beam tests and well
                                               reproduced by simulation :

                                               -Sampling term given by lead/argon
                                               sampling fraction and frequency : quality
                                               control measurements during construction

                                               - Noise term under control

                                               - Local constant term (within a cell) given
                                               by impact point correction

                                               Uniformity is at 1% level quasi online
                                               but achieving ATLAS goal (0.7 %) needs
                                               a lot of work, and most of the time was
                                               used to correct for setup problem…
CMS: ECAL Energy Resolution   ATLAS

Oct. 2005

     - The last(8-th) Barrel Toroid coil installed in Aug. 2005
     - Barrel calorimeter (LAr EM + HAD Fe/Scint. Tilecal) in final position at Z=0 (Nov. 2005)
     - Barrel toroid: cool down completed, first tests towards full field started in Sep. 2006
ATLAS                         Endcap Muon Big-Wheel installation
Barrel muon system complete          Started in June 2006          ATLAS

TGC Big-Wheel (C-1)                 MDT Big-Wheel (C)

                 Sept. 2006                           Dec. 2006
 CMS: Magnet Test and Cosmic Challenge              ATLAS


 HCAL                           Tracker

                                    Muon chambers

Detector installation to pit started in Dec. 2006
   Detector Performance & Physics Studies (TDRs)                  ATLAS

May 1999      May 1999

                                CSC (Computing System
                                Commissioning) notes are to
                                be produced in spring 2007,
                                covering software and physics
                                analysis validation for the
                                early physics run with 0.1 fb-1
                                and 1 fb-1.

Feb. 2006     Jun. 2006

                                Instead of 3-rd vol. of TDR,
                                short notes on startup will
                                be submitted to LHCC in
                                summer 2007, along with the
                                very early physics reach with
                                0.1 fb-1 and 1 fb-1.

       Search for New Physics Studies                                                        ATLAS

SM Higgs H0                Look for final states with l, and g :
                           Hgg, Hbb (with tt or W with lepton decays), Htt ( via
                           HZZ*/ZZl+l-l+l-, l+l-nn, l+l-jj, HWW* l+n l-n or ln jj (via
Extended Models            SM-like: h  gg, bb; H  4l,
H0,h0,A0,H+H- & H++, H--   MSSM-specific: A/H  mm, tt; H  hh, A  Zh; H  tn
                                               A/H  c20 c20  4l + missing Energy
Supersummetry              Like-sign leptons, multi-leptons and Jets with Missing ET

Heavy Q Q                  Q W q  l + jets

New bosons Z’, W’          Z’ l+l-, W’ l n

Technicolor                rT  WZ  ln ll, rT  Wp  lnbb

L/Q structure              Pp LQ LQ  lq lq: High-mass di-leptons, Missing ET

Extra-dimension            High-mass di-leptons, narrow lepton resonances, Jets+Missing ET

Composite Models           ppL+L- ZZ+2leptons  6 leptons, pp ee* eeg

Strongly-couples           High mass spectra: WLZL  WLZL  ln ll, ZLZL  ZLZL  ll ll
Vector-bosons              WLWL  ZLZL  ll ll                                         15
      New Physics with Multi-lepton Final States                                  ATLAS

Single lepton SM:                W’ l n
                                 Hbb +W/tt(with W  l n )
              W l n
                                 HWW* l n jj (via BVF)
              W+jets ln +x      rT  Wp  l nbb
              tt/bb  l + x      Q W q  l + jets
                                 HWW* l+n l-n
Di-lepton       SM
                                 A/H  mm, tt
                Z/g* l+l-       Like-sign dileptons from SUSY particle decays
                Z+jets l+l-+x   High mass narrow resonances: Z’ l+l-, G* l+l-,…
                                 pp LQ LQ  lq lq
                tt/ww l+l- +x   pp ee* eeg
Triple-lepton   SM               rT  WZ  ln ll
                                 WLZL  WLZL  ln ll
                WZ ln ll
                                 pp W*  c1+c20 W+c10 + Z*c10  l ll + Missing ET

Four-leptons SM                  H ZZ*/ZZ  l+l-l+l-
                                 A/H  c20 c20  4l + missing Energy
             ZZ l+l-l+l-
                                 ZLZL  ZLZL  ll ll, WLWL  ZLZL  ll ll
Six-leptons                      ppL+L- ZZ+2leptons  6 leptons

  ATLAS : Muon Detection Efficience         ATLAS

Study based ATLAS CSC data sample: Z  mm

    Muon Pt                       Muon h

      Fake m rate as a function of Muon PT                     ATLAS

Full simulation: tt  m + x (1M events), Z mm (1M events)

                               25 GeV

                                                     500 GeV
For pT > 500 GeV,   Standalone Muon System: fake rate ~10-4
                    MuID Combined:          fake rate ~ 10-5
    Benchmark Studies on Muon Final States                  ATLAS

                     ATLAS                         ATLAS

2m Mass resolution
(standalone muon system)

                              2m acceptance ( in |h|<2.7)
                              (standalone muon system)

                     ATLAS                        ATLAS
4m Mass resolution
(standalone muon system)

                                4m acceptance ( in |h|<2.7)
                                (standalone muon system)

       ATLAS: Muon Spectrometer Performance                            ATLAS

   High Pt Muon Charge Identification is Essential for new physics
                                         Unique feature of the ATLAS
X-dim : dilepton from G* exchange        Standalone Muon System



•Charge asymmetry measurement
  would help to pin-down the ‘origin’
   ATLAS: Bench mark: Z’  mm                  ATLAS

3 TeV Z’ mass spectrum   Z’ Charge Asymmetry

CMS: Electron Detection Performance Studies   ATLAS

   CMS: Benchmark Studies: H  4e         ATLAS

   Before the cuts       After the cuts

MC experiment         MC experiment

     Higgs Discovery Channels at LHC                                     ATLAS

                                              Dominant BR for mH<2mZ:
                                               s (H  bb)  20 pb;
                                               s (bb)       500 mb
                                              for m(H) = 120 GeV
                                               no hope to trigger
                                                 or extract fully
                                                 hadronic final states
                                               look for final
                                                  states with l, g
                                                  (l = e,m )

                                               m(H) > 2 mZ :
Low mass region: m(H) < 2 mZ :                 H  ZZ  4l
H  gg : small BR, but best resolution         qqH  ZZ  ll nn *
H  bb : good BR, poor resolution  ttH, WH    qqH  ZZ  ll jj *
H  ZZ*  4l                                   qqH  WW lnjj *
H  WW*  lnln or lnjj : via VBF               * for mH > 300 GeV
H  tt : via VBF                               forward jet tag

t ID: Fraction of Energy in DR<0.1

t-ID efficiencies


        VBF H tt Reconstruction


CMS Studies: H  tt   ATLAS

H  WW dileptons+MET         ATLAS


                   H  gg             ATLAS


                          H (2 jet)
  H (0 jet)

              H (1 jet)

            Discovery Sensitivity                            ATLAS

  CMS PTDR                          ATLAS
  NLO          NLO       TDR (LO)   New, NLO    New, NLO
cut based   optimized*              Cut based   likelihood
 6.0         8.2          3.9         6.3        8.7

 MSSM Higgs Discovery Potential

Plane fully covered with 30 fb-1

 5s discovery contours
     Strongly-Coupled Vector Boson System

No light Higgs boson? Study Longitudinal gauge boson scattering in high
energy regime (the L-component which provides mass to these bosons).

                              l n ll       WL WL -> ZL ZL-> 4 leptons
   WL ZL      WL ZL
                                           ZL ZL -> ZL ZL-> 4 leptons

            S / B = 6.6/2.2                    S / B ~ 10

      Strong Symmetry Breaking: Technicolor                            ATLAS

No fundamental scalar Higgs (it is a new strong force bounded state)
Technicolor predicts existence of technihadron resonance: rT  WZ lll+n


              SUSY: Supersymmetric Extensions of SM       ATLAS

•   Provide candidate particles for Dark Matter (LSP)
•   Higgs mass calculable
•   Unification
•   Path to gravity: local supersymmetry  supergravity

m1/2: universal gaugino mass at GUT scale
m0: universal scalar mass at GUT scale
tan: vev ratio for 2 Higgs doublets
sign(m): sign of Higgs mixing parameter
A0: trilinear coupling
    Need study many benchmark points…
           Mass Spectrum from SUSY Particle Decays                  ATLAS

                                    The distribution of the invariant
                jet      l1   l2       mass of the two leptons can be
                                       shown to have a kinematic edge


               Physics TDR

   Discovery Potential of SUSY (mSUGRA)   ATLAS

               No EWSB

        Looking forward the LHC Collision Beams!
        Staged commissioning plan for protons
                                       Stage I                II         III                         IV

  Hardware        Machine       Beam             43 bunch    75ns                                  25ns
                                                                      25ns ops I    Phase II
commissioning     checkout   commissioning       operation   ops                                   ops II
                                                                                    and MKB

        No beam                                      Beam

           I.     Pilot physics run
                     First collisions
                     43 bunches, no crossing angle, no squeeze, moderate intensities
                     Push performance (156 bunches, partial squeeze in 1 and 5, push intensity)
                     Performance limit 1032 cm-2 s-1 (event pileup)
           II.    75ns operation
                      Establish multi-bunch operation, moderate intensities
                      Relaxed machine parameters (squeeze and crossing angle)
                     Push squeeze and crossing angle
                     Performance limit 1033 cm-2 s-1 (event pileup)
           III.   25ns operation I
                      Nominal crossing angle
                                                                               up to 1-2 fb-1 end 2008,
                     Push squeeze                           2008-2009         up to 10fb-1 end 2009 ?
                     Increase intensity to 50% nominal
                     Performance limit 2 1033 cm-2 s-1
           IV.    25ns operation II
                     Push towards nominal performance              2010      O(100) fb-1

         Note: dates and integrated luminosities are MY interpretation (F. Gianotti)                 38
     List of New Physics Reaches at LHC                                ATLAS

SM Higgs                           100 GeV ~ 1 TeV (30 fb-1)
MSSM Higgs                         covers full (mA, tan)
SUSY (squark, gluino)              ~ 3 TeV (300 fb-1)
New gauge bosons (Z’)              ~ 5 TeV (100 fb-1)
Quark substructure (LC)            ~ 25/40 TeV (30/300 fb-1)
   q*, l*                          ~ 6.5/3 TeV (100 fb-1)
Large ED (MD for n=2,4)            ~ 9/6 TeV (100 fb-1)
Small ED (MC)                      ~ 6 TeV (100 fb-1)
Black holes                        < 6 ~ 10 TeV

   Any one of those would change the understanding of our universe !

Additional slides

CMS: Muon Trigger Studies   ATLAS

Overall Efficiency of Electron ID   ATLAS

  Identify Z in the Z-mass ‘windows’ (Standalone)   ATLAS

Overall Acc
= 44%                        muons

 Barrel -                    endcap
 endcap                      muons

Atlas Studies: H  tt   ATLAS

       Higgs Production Mechanism @ LHC                      ATLAS

4 production mechanism   key to measure H-boson parameters


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