MultiW events at the LHC from a Warped Extra Dimension

1
Multi-W events at the LHC from a Warped Extra
Dimension
1
Multi-W events at the LHC

• Chris Dennis, Muge Karagoz Unel, Jeff Tseng
  (Oxford University),
• Geraldine Servant (CEA/SaclayCERN)
• 29 March 2007
• XXV Workshop onRecent Developments inHEP
  Cosmology, Athens, Greece

MKU
2
Introduction
2

• Extra Dimensions Solution to problems in
  Particle physics, favorite since 1990s
• Warped extra dimensions (RS) has been especially
  popular
• Current favourite model building in warped space
• Gauge hierarchy problem
• Unification
• Fermion masses
• Cosmology,

Multi-W events at the LHC
MKU
3
Model Specifics
3

• Basic ingredients of model building
• Randall-Sundrum ED for gauge hierarchy
• Extended EW gauge symmetry
• Original model RS SO(10) (ServantAgashe,hep-ph
  /0411254), a heavy bR (1.5 TeV) along with a
  Dark Matter Candidate
• Revised models embed into SU(2)LxSU(2)RxU(1)
  (Contino, et al.,hep-ph/0612048)
• Additional custodial symmetry in SU(2)LxSU(2)R to
  protect EW precision observables (Z?bb) from new
  contributions
• Light degenerate KK fermions (custodians) with
  no zero modes
• bR,L, Q 2/3, -1/3, 5/3

Multi-W events at the LHC
MKU
4
Strategy
4

• Investigate feasibility of searching for the KK
  quarks and related signatures through multi-W
  events
• Heavy quark searches at LHC is has become in
  general a hot topic (see Gokhan Unels talk)
• Uncommon in SUSY searches for example
• Try to stay as inclusive as possible
• Preprint hep-ph/0701158

Multi-W events at the LHC
Signature 4W 2b-jets
MKU
5
Production
5
Multi-W events at the LHC

• Dominated by pair production (focus in bR
  others basically the same, except enhanced EWK
  coupling)
• Main production mechanism is from strong
  interactions. EWK much smaller.

MKU
6
Details of bR Decay
6

• Decay channels tW, bZ, bH
• bRbR?tWtW? 4W 2b
• If H heavy enough, H?WW can give same signature
  (not simulated here)
• q5/3 are also produced decay entirely via tW
• Simulate only tW decay modes of bR (Q-1/3)
• Scale up by 2(1B2)/B2 to get total
• rate including q5/3
• Studying cases with benchmark
• Higgs masses (300, 115 GeV)

Multi-W events at the LHC
MKU
7
Multi-W Backgrounds
7

• Generic form
• nW mb-jets k X
• Candidate backgrounds any associated t and/or W
  production
• tt
• ttH, esp. if M(q) gt1 TeV with H-gtWW (similarly
  ttnW)
• tttt, negligible by order of 4 below tt
• Here we concentrate on ttbar as the dominating
  background source

Multi-W events at the LHC
MKU
8
Multi-W Signature
8
Multi-W events at the LHC

• At bR mass of 500 GeV in 10fb-1 of data
• 4000 tW
• 700 bH, H?WW (Higgs mass 300 GeV)
• At q5/3 mass of 500 GeV
• 22000 tW

MKU
9
Feasibility Study
9

• Count Ws in leptonic and hadronic decays
• Purely generator-based
• Calchep 2.4.3 Pythia 6.4.01 (CTEQ6L)
• Hadronic jets
• Use chargedneutrals (non-?) within ?lt4.9
• Seed with pTgt1 GeV
• Softer tracks added if within ?Rlt0.4 of jet
  centroid
• b-jets hadronic jet closest to generated b
• Background sample mostly tt (Toprex 4.11 Pythia
  6.4.03), also some ttH (Pythia)

Multi-W events at the LHC
MKU
10
Trigger Requirements
10

• Follow standard W leptonic trigger
• e or µ, pT gt 25 GeV in ?lt2.4
• Missing ET gt 20 GeV

Multi-W events at the LHC
MKU
11
S vs B after trigger
11

• pT distributions of decay products (all
  normalized to unit area)
• Will require W pT gt 150 GeV

signal
Multi-W events at the LHC
MKU
12
S vs B after trigger
12
Multi-W events at the LHC

• Require jet pTgt20 GeV
• 4 hadronic Ws?
• Probably semileptonic quark decays

MKU
13
S vs B after trigger
13

• Require SETgt800 GeV, for bR mass of 500 GeV

Multi-W events at the LHC
MKU
14
Counting hadronic Ws
14

• Reconstruct W?jj
• Loop over dijet pairs (no leptons)
• Add 4-vectors, assuming zero jet mass

Multi-W events at the LHC
MKU
15
Distinguishing Multi-W Signal
15

• One W is already identified by lepton
• Typical SM events have two Ws (or Zs)
• Eliminate one hadronic W
• When looping over dijets, start from the
  highest-energy jet
• If we find another jet which can make a W mass
  (70-90 GeV), start plotting with next pair
• Method has been tested with Wjets sample to make
  sure it doesnt sculpt background distribution
• Remaining Ws are mostly from non-SM sources

Multi-W events at the LHC
MKU
16
Result in 1 leptonic W
16

• Final comparison, normalized to 10 fb-1

Multi-W events at the LHC
MKU
17
Number of Leptonic Decays
17

• 4 leptons 2 bs suggested as a golden
  discovery channel, although the event yield is
  extremely low,
• but can we distinguish it from SUSY?
• However, requiring 2 leptons seems more
  reasonable to do

Multi-W events at the LHC
MKU
18
Dilepton Events
18

• Requiring two leptons mostly eliminates tt
  background without having to eliminate a hadronic
  W
• This work is in progress

Multi-W events at the LHC
Same-sign
Opposite-sign
MKU
19
Further on q5/3
19

• Identifying this would be a telltale indication
  for this model
• Unfortunately only leptons have reliable charge
  information, not jets
• Possible analysis
• Select same-sign dilepton events
• Exclusively reconstruct bR on other side (similar
  to ATALS TDR analysis of 4th gen quarks)
• Looking into this right now

Multi-W events at the LHC
MKU
20
Conclusion Outlook
20

• Present analysis
• Feasibility study promising
• Need more realistic simulation, first steps in
  ATLASs Atlfast
• Relating size of W peak to cross section is
  nontrivial
• Could suppress SM backgrounds further by
  tightening trigger requirements and selecting
  dileptons
• Multi-W/Z events are generically interesting
• Recent work on identification using single-jet
  mass (e.g., SkibaTucker-Smith, hep-ph/0701247)
• Also Butterworth, et al., for WW scattering
  identification
• Further directions
• q5/3 analysis the smoking gun
• Sensitivity vs mass of bR, Higgs
• Exotic, long-lived quarks CHAMP signatures

Multi-W events at the LHC
MKU
21
21
BACKUP
Multi-W events at the LHC
MKU
22
22
L?P Dark Matter Candidates
nature
Multi-W events at the LHC
symmetry
mass
detection
MKU