1. Searching for New Exotic Physics at the LHC
a.k.a. Searches Beyond Supersymmetry
Dave Charlton
University of Birmingham
Before, Behind and Beyond the Discovery of the Higgs Boson
Royal Society, January 2014

2. Menu
Why search for exotic physics?
Simple event types – “bump hunting”
Top as a probe
Long-lived particles
Dark matter
Conclusions

3. Simple Event Types
“Bump Hunting”

4. m(ee)=1.54 TeV

5. m(μ+μ−)=1.82 TeV

6. Dilepton resonances
Model Mass limit (95% CL)
Z'SSM 2.96 TeV
Z'(ψ) 2.60 TeV
Z'SSM 2.86 TeV
Z'(E6 models) TeV
G*(k/MPl=0.1) 2.47 TeV
CMS
ATLAS
excluded
Convert to lower mass limits for specific models
In these models, mass of a new resonance must be more than 2-3 TeV
Upper limits placed on rate of events (cross-section times branching ratio σ∙B(X→ℓℓ) at 95%CL)
ATLAS-CONF
Next step:
13 TeV LHC operation – mass reach will ~double

7. High-mass eeγ event

8. W' decaying to leptons Simplest case: W' → ℓν
Single high-pT lepton and Etmiss
Again, no excess above backgrounds observed
Combining e,μ channels, SM-like W' excluded by CMS for
m(W') > 3.35 TeV (95% CL)
CMS PAS EXO

9. Event selected in the W'→ℓν analysis, with mT=2.3 TeV

10. Searches in dijets
CMS PAS EXO
Inclusive dijet mass spectrum – extends up to 5 TeV!
Fit with smooth function, look for resonances
Limits on many models: string resonances, excited quarks, axigluons, colorons, s8 resonances, E6 diquarks, W' and Z' bosons, and Randall-Sundrum gravitons, up to 5 TeV
5 TeV
Further searches in: dijet final states, look at angular distributions in the detector, look at b-tagged jets; multijet topologies searching for 3-jet resonances … …

11. Top as a Probe

12. High transverse momentum top quarksb W− q q′
jet t b W− q q′
jet
High transverse momentum top quarks
Low pT
Common experimental challenge for searches for heavy particles decaying to top quarks – identification of high-pT tops
At high-pT, the top decay products can merge into a single “fat” jet t
merged jet
High pT
Sophisticated “jet substructure” techniques to identify these

13. Search for X → tt Search for a heavy particle decaying to tt
Both semileptonic (tt → bℓvbqq') and hadronic (tt → bqq'bq''q''') decays
Search both for resolved and merged jets → extend to very high momentum top quarks
ATLAS-CONF
Phys Rev Lett 111 (2013)

14. Candidate tt event with m(tt)=2.6 TeV

15. New heavy quarks (“vector-like”)
New heavy quarks (T, B): decay modes
T → bW, T → tZ, T → tH
B → bZ, B → tW, (B → bH)
arXiv:
Several event signatures:
Single lepton plus jets/ETmiss
Same- and opposite-sign dileptons plus jets/ETmiss
Trileptons plus jets/ETmiss
Use b-tagging to improve signal/background
Specially constructed discriminant

16. Put all the information together – complex multidimensional exclusion
Vector-like quarks
Put all the information together – complex multidimensional exclusion

17. Combining all channels analysed, CMS obtain lower mass limits of
Vector-like quarks
Combining all channels analysed, CMS obtain lower mass limits of
m(T) > GeV (95% CL)
m(B) > GeV (95% CL)
CMS PAS B2G
arXiv:

18. Long-lived Particles

19. Dark Matter

20. TeV
TeV