exotica: overview of the searches for new vector boson high mass states cory fantasia py898 03/30/09
TRANSCRIPT
Exotica: Overview of the Searches for New Vector Boson High Mass States
Cory Fantasia
PY898
03/30/09
The Exotic:
Z′ W′ RS Graviton
3 Particles
Z′ W′ RS Graviton
Z′ Models
Sequential Standard Model (SSM) Same Coupling Strength as SM Z Simplest extension of SM Basis for this talk
Littlest Higgs E6 and SO(10) Grand Unifying Theories Kaluza-Klein Excitation of SM Z
Z′ - Tevatron
Dilepton channel Z′ → ee Z′ → μμ Z′ → ττ Z′ → t tbar
With 450 pb-1 CDF limits SSM Z′ to 825 GeV Dielectron / dimuon channels most powerful Other models are less strict on mass
Search Z′ → μμ
Channel will offer first glimpse of signal
Using first data assumptions Misalignment Larger uncertainties
Decay Modes - Z′
Z′ → ee Z′ → μμ Z′ → WW
Harder to utilize
Background Z′
Photons Require track
QCD Jets Require isolation Require > 90% of energy to be in ECAL Require hits in muon system
Require oppositely charged leptons Drell-Yan (irreducible) – find mass peaks
Discovery
Z′ →WW
Peak resolution more difficult
Clearest channel WW → eν jj Allows for discrimination
between two W’s Aids in background
suppression Background
W + jets
Discovery - Z′ → WW
Using Cuts |η| < 2 for jets ET of W > M(Z′)/3 Reconstructed W’s good
mass values (|diff| < 15) Assumes coupling falls
off like 1/m(Z′)2
300 fb-1
3 Particles
Z′ W′ RS Graviton
W′
Sequential Standard Model Same couplings as W
Makes signal more difficult to extract MET is now a factor
W′ - Tevatron Results
Using W′ → eν or W′ → t bbar Minimum mass set to 788 GeV using 205 inv
pb-1
Set with leptonic decays
W′ → μ ν
Require single muon Isolation >13 hits along track Largest source of
background is SM W Must use reconstructed
mass peak
Discovery
Discovery potential with 1 fb-1 up to 3.5 TeV
W′ → e ν
Largest source of background comes from SM W decays Use similar cuts to
resolve mass peak Isolated, tracked
W′ → WZ → 3l + ν
Resolution (with no cuts) decreases with increasing mass
W′ still visible past 2 TeV with 300 fb-1
W ′ → WZ → 3l + ν Opposite signed leptons
form Z Leaves lepton + MET to
form W
Background
WZ → 3l + ν Mass peak distinction
ZZ → 4l 1 lepton missed (shows up as MET)
tt → Wb Wb b quark yields a lepton plus 2 from W’s b lepton won’t be isolated
W′→ WZ Discovery
300 fb-1
Using worst case model to obtain 5 sigma assuming coupling falls off like 1/m(W′)2
W′ (Higgsless)
W′ Z → WZZ → jj4l Remove
reconstructed Z mass (oppositely charged leptons)
Remaining WZ mass shows peak
Cuts - W′ Z → WZZ → jj4l
Require large (>4) η separation between jets Reduces gluon jet
background
Ej > 300 GeV
pTj > 30 GeV
pTl > 10 GeV
Discovery - Higgless
Larger cross section of WZjj offers chance of quicker discovery as the mass of the W′ increases
3 Particles
Z′ W′ RS Graviton
RS Graviton
Motivation? Explain Weakness of Gravity
Difference between Planck mass and TeV Scale Unify Gravity with other forces
Theory
Lisa Randall and Raman Sundrum 15 Orders of Magnitude between Mplanck and
TeV scale Expand Universe to 5th Dimension
Scales ~ e-kπR
kR ~ 11 k ≡ curvature of new dimension R ≡ is the size of the dimension
Theory
TeV Brane → Planck Brane SM interactions exist on TeV Brane
Can propagate in 5-D SM particles fixed between these branes Since Higgs is on TeV Brane, the closer a SM
particle lies to TeV Brane the larger its mass “Naturally” form mass hierarchy
Production
c ≡ k/Mplanck
Dominate factor is graviton interactions
Discrimination – RS
Spin 2 particle Different angular distribution Use θ*
Angle between quark and lepton
G → ee High energy electron jets
End Caps are Critical for Discrimination
Signal over Background
E > 100 GeV Isolated 2 Hit Track > 90% of energy in
ECAL
Discovery CMS
c = 0.01 (green) c = 0.02 (blue) c = 0.05 (pink) c = 0.1 (red) With similar cuts
Isolated High Energy
Discovery CMS
Depending on the coupling parameter discovery could come with 1 fb-1
Conclusions
Z′ muonic decay offers best hope seeing signal early Subsequent use of electron decay for
confirmation and refinement of signal W′ searches will require more work
MET in the final state RS Graviton offers exciting answers but will
need a more careful analysis