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1. Multi-W events at the LHC from a Warped Extra Dimension. Multi-W events at the LHC. Chris Dennis, Muge Karagoz Unel, Jeff Tseng (Oxford University), Geraldine Servant (CEA/Saclay&CERN) 29 March 2007 XXV Workshop on Recent Developments in HEP & Cosmology, Athens, Greece. MKU. 2.

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multi w events at the lhc from a warped extra dimension

1

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

Multi-W events at the LHC

Chris Dennis, Muge Karagoz Unel, Jeff Tseng (Oxford University),

Geraldine Servant (CEA/Saclay&CERN)

29 March 2007

XXV Workshop onRecent Developments inHEP & Cosmology, Athens, Greece

MKU

introduction

2

Introduction
  • 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

model specifics

3

Model Specifics
  • Basic ingredients of model building:
    • Randall-Sundrum ED for gauge hierarchy
    • Extended EW gauge symmetry
    • Original model: RS + SO(10) (Servant&Agashe,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

strategy

4

Strategy
  • 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 Unel’s 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

production

5

Production
  • 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.

Multi-W events at the LHC

MKU

details of b r decay

6

Details of bR Decay
  • 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(1+B2)/B2 to get total

rate including q5/3

  • Studying cases with benchmark

Higgs masses (300, 115 GeV)

Multi-W events at the LHC

MKU

multi w backgrounds

7

Multi-W Backgrounds
  • Generic form:
    • n×W + m×[b-jets] + k× [X]
  • Candidate backgrounds: any associated t and/or W production
    • tt
    • ttH, esp. if M(q)>1 TeV with H->WW (similarly tt+n×W)
    • 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

multi w signature

8

Multi-W Signature

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

feasibility study

9

Feasibility Study
  • Count Ws in leptonic and hadronic decays
  • Purely generator-based
    • Calchep 2.4.3 + Pythia 6.4.01 (CTEQ6L)
  • Hadronic jets:
    • Use charged+neutrals (non-ν) within |η|<4.9
    • Seed with pT>1 GeV
    • Softer tracks added if within ΔR<0.4 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

trigger requirements

10

“Trigger” Requirements
  • Follow standard W leptonic trigger:
    • e or μ, pT > 25 GeV in |η|<2.4
    • Missing ET > 20 GeV

Multi-W events at the LHC

MKU

s vs b after trigger

11

S vs B after trigger
  • pT distributions of decay products (all normalized to unit area)
  • Will require W pT > 150 GeV

signal

Multi-W events at the LHC

MKU

s vs b after trigger1

12

S vs B after trigger
  • Require jet pT>20 GeV
  • 4 hadronic W’s?
  • Probably semileptonic quark decays

Multi-W events at the LHC

MKU

s vs b after trigger2

13

S vs B after trigger
  • Require ΣET>800 GeV, for bR mass of 500 GeV

Multi-W events at the LHC

MKU

counting hadronic ws

14

Counting hadronic Ws
  • Reconstruct W→jj:
    • Loop over dijet pairs (no leptons)
    • Add 4-vectors, assuming zero jet mass

Multi-W events at the LHC

MKU

distinguishing multi w signal

15

Distinguishing Multi-W Signal
  • One W is already identified by lepton
  • Typical SM events have two W’s (or Z’s)
  • 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 W+jets sample to make sure it doesn’t sculpt background distribution
  • Remaining W’s are mostly from non-SM sources

Multi-W events at the LHC

MKU

result in 1 leptonic w

16

Result in 1 leptonic W
  • Final comparison, normalized to 10 fb-1

Multi-W events at the LHC

MKU

number of leptonic decays

17

Number of Leptonic Decays
  • 4 leptons + 2 b’s: 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

dilepton events

18

Dilepton Events
  • 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

further on q 5 3

19

Further on q5/3
  • 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

conclusion outlook

20

Conclusion & Outlook
  • Present analysis:
    • Feasibility study promising
    • Need more realistic simulation, first steps in ATLAS’s 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., Skiba&Tucker-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

slide21

21

BACKUP

Multi-W events at the LHC

MKU

slide22

LKP

LZP

LSP

Dirac fermion

gauge boson

Majorana fermion

Z3

KK parity

R parity

~ 600GeV – 1000GeV

~ 20GeV – Few TeV

~ 50GeV – 1TeV

  • LHC
  • Indirect(Astro)
  • LHC
  • Direct(Astro)
  • Indirect(Astro)
  • LHC
  • Indirect(Astro)

22

L?P Dark Matter Candidates

nature

Multi-W events at the LHC

symmetry

mass

detection

MKU

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