1. Exotica at the LHC
UK HEP Forum, Abingdon
Ian Tomalin (RAL)
17/11/2017

2. Introduction
LHC exotica searches offer real possibilities of exciting discoveries this year !
I will:
Summarize UK interests
Review all the public CMS/ATLAS exotica results. (probably the last time it will be possible to do this in one talk ...)
Look at what we can expect in the near future.
Ian Tomalin (RAL)
17/11/2017

3. UK Exotica Interests
The UK has provided both ATLAS & CMS exotica conveners:
ATLAS: Cigdem Issever (Oxford)
CMS: Chris Hill (formally Bristol)
and is pursuing many analyses:
CMS: Stopped Gluinos (Bristol), Z’  e+e- (Bristol/RAL) , Displaced Fermions (RAL), Boosted Z from q*... (RAL)
ATLAS: Black holes & Extra Dimensions (Cambridge/Oxford), Z’  e+e- (RHUL), q*  dijets (Oxford/Glasgow) , Ggg (Liverpool), Boosted Top from Z’ (Oxford/UCL) those I missed !
Ian Tomalin (RAL)
17/11/2017

4. First Exotica Results with LHC Data !
A pleasure to see results with real data !
LHC is already competitive for some strongly produced exotica.
Areas with UK involvement in pink.
ATLAS
CMS
Heavy Stable Charged Particles 
Stopped Gluinos
q*  dijets
Dijet contact interactions
Black holes
LQ  e + jet
W’  e n
Ian Tomalin (RAL)
17/11/2017

5. Search for Heavy Stable Charged Particles (CMS)
Theoretical Models
Gluino in Split-SUSY. (Squarks very heavy, so gluino can only decay via virtual squarks).
Stop is NLSP (so can only decay radiatively to charm + neutralino).
Both hadronize to R-hadrons. These are highly ionizing in the Tracker
and look like muons in the calorimeters. They can flip charge whilst
Traversing CMS !
Trigger & Selection
Muon trigger, supplemented by MET and Jet triggers in case of charge flip.
Select high Pt track with large dE/dx in Tracker, optionally also requiring muon ID. (Later analyses will also use time-of-flight info).
Ian Tomalin (RAL)
17/11/2017

6. Search for Heavy Stable Charged Particles (CMS)
dE/dx was calibrated module to module using relativistic particles.
dE/dx & Pt agree well in data and MC. As uncorrelated, can use to estimate background from data alone.
Both variables offer clear separation for gluino signal.
Gluino
Gluino
S.M. MC
S.M. MC
Data
Data
Ian Tomalin (RAL)
17/11/2017

7. Search for Heavy Stable Charged Particles (CMS)
Bethe-Bloch ionization curves for K, p, D clearly visible
Ionization from gluino allows its mass to be determined.
Ian Tomalin (RAL)
17/11/2017

8. Search for Heavy Stable Charged Particles (CMS)
No events pass cuts !
M(gluino) > 284 GeV/c2 (Slightly better than
Tevatron limit).
Ian Tomalin (RAL)
17/11/2017

9. Stopped Gluinos (CMS)
If the `Split SUSY’ gluino is very non-relativistic, it will lose so much energy by ionization that it will stop before leaving CMS.
Decay to gluon/quarks + neutralino can take micro-seconds  days. Observe it during beam-gaps or shutdowns !
Trigger using jet-trigger + beam veto (using orbit monitors).
Select requiring calorimeter energy cluster > 50 GeV. N.B. So only sensitive if M(gluino) – M(neutralino) >> 50 GeV.
Many cuts to suppress calorimeter noise. Optimised before LHC switched on !
Ian Tomalin (RAL)
17/11/2017

10. Stopped Gluinos (CMS)
19 events pass cuts. This compares their time distribution with that expected for gluino with t = 1 ms.
Ian Tomalin (RAL)
17/11/2017

11. Stopped Gluinos (CMS)
For gluino mass of 200 GeV/c2 exclude gluino lifetimes of ms, not previously covered by Tevatron.
N.B. More stringent limits currently set by HSCP search.
Ian Tomalin (RAL)
17/11/2017

12. Dijet Mass Resonances (ATLAS & CMS)
Theoretical Models
Excited quarks: q*  qg
Z’  q qbar
RS Gravitons  q qbar
etc. etc.
Selection
Use anti-Kt jet algorithm
Calorimeter & jet cleaning
Plot dijet mass of 2 leading jets.
Ian Tomalin (RAL)
17/11/2017

13. Dijet Mass Resonances (ATLAS & CMS)
Dijet spectrum fitted with (binned) smooth function to describe background (a different function for ATLAS & CMS ...)
Ian Tomalin (RAL)
17/11/2017

14. Dijet Mass Resonances (ATLAS & CMS)
Signal shape taken from MC.
Its position depends on ~10% uncertainty in jet energy scale.
CMS noted that spectrum broader for gluon states, so quotes separate limits for these.
Ian Tomalin (RAL)
17/11/2017

15. Dijet Mass Resonances (ATLAS & CMS)
ATLAS excludes excited quarks with < M < 1290 GeV.
CMS excludes those with M < 1140 GeV using a higher luminosity of 836/nb ATLAS may be profiting from its ~40% better calorimeter-jet energy resolution ...
Both surpass Tevatron limit of 870 GeV.
Ian Tomalin (RAL)
17/11/2017

16. Dijet Angular Distribution (ATLAS & CMS)
Motivation
Z’ etc. whose mass exceeds the √s of the partons will not be seen as a resonance, but will modify the dijet spectra.
The effect can be parametrized as `contact interaction’.
Changes to the dijet mass spectrum hard to distinguish from systematics.
Better to plot `dijet centrality ratio’ vs. dijet mass so systematics cancel: N_dijets(|| < 0.7) / N_dijets(0.7 < || < 1.3) Flat for QCD, whereas exotica produced mainly in central  region.
Ian Tomalin (RAL)
17/11/2017

17. Dijet Angular Distribution (ATLAS & CMS)
Dijet centrality ratio compared with predictions in low mass region, where no signal expected.
Very good agreement.
Main systematic is effect of ~10% jet energy scale uncertainty on signal.
Ian Tomalin (RAL)
17/11/2017

18. Dijet Angular Distribution (ATLAS & CMS)
At higher mass, measured ratio compared to contact interaction predictions (L = 0.5, 1.0, 1.5 TeV).
Also compared with other models:
q* (CMS)
black holes (ATLAS)
Ian Tomalin (RAL)
17/11/2017

19. Dijet Angular Distribution (ATLAS & CMS)
CMS limit determined from log-likelihood ratio (S+B/B) L = 1.9 TeV from 120/nb
ATLAS limit from less lumi:
L = 0.9 TeV from 60/nb
c.f. Current Tevatron limit L = 2.8 TeV
Ian Tomalin (RAL)
17/11/2017

20. Black Holes & High Mass, Many Body Events (ATLAS)
Theory
In ADD models, gravity propagates in additional spatial dimensions, which can have a size of up to millimetres..
Below these distance scales, gravity rapidly becomes stronger, leading to an effective Planck mass MD far below normal.
Tevatron says MD > 800 GeV
As gravity couples to energy (not mass !), black holes evaporate democratically to all fermion/boson species. Many body final state.
Other exotica will also give many body final state ...
Ian Tomalin (RAL)
17/11/2017

21. Black Holes & High Mass, Many Body Events (ATLAS)
Jets, photons, electrons, muons & MET counted.
Tricky analysis, since must understand all of these ...
S.M. multiplicity dominated by jets. (Could reduce by requiring leptons ...)
Ian Tomalin (RAL)
17/11/2017

22. Black Holes & High Mass, Many Body Events (ATLAS)
Count events in signal region defined as:
N  3
Minv > 800 GeV/c2
 |Pt| > 700 GeV/c
For black-holes produced with MD = 800 GeV ( 6 extra dimensions) get interesting limit of /nb
Ian Tomalin (RAL)
17/11/2017

23. Black Holes & High Mass, Many Body Events (ATLAS)
Systematics reduced by normalising background in control region. (Low Minv or  |Pt|).
Nonetheless remain large:
Simulation of N jet QCD final states (ALPGEN vs. Pythia) (26%)
PDF choice (12%)
Ian Tomalin (RAL)
17/11/2017

24. Leptoquarks (CMS) Theory gluon  LQ pair has high cross-section.
Each (1st generation) LQ decays to electron + jet.
Selection
Require at least 2 electrons & 2 jets.
Cut on their Sum |Pt|.
Require M(e+e-) > 100 GeV/c2 to suppress main background (Z + jets) (& measure background by reversing this cut ...)
Ian Tomalin (RAL)
17/11/2017

25. Leptoquarks (CMS) No events found in signal region with 1.1/pb.
Limit M(LQ) > 200 GeV for BR(LQ  e j) = 1
Inferior to Tevatron, but not for long ...
Main systematics:
Electron efficiency (soon from Z events ...)
ISR/FSR simulation.
Ian Tomalin (RAL)
17/11/2017

26. W’  e n (ATLAS) From electron + MET, reconstruct transverse mass.
Background taken from MC. Uncertainty of ~7% from PDF, scale ...
Signal uncertain by ~8% because of electron ID.
Ian Tomalin (RAL)
17/11/2017

27. W’  e n (ATLAS)
Get limit at M(W’) by counting events with MT > 0.7 M(W’).
No events pass cuts in signal region.
Limit = 0.47 TeV (c.f. Tevatron limit of 1 TeV)
Ian Tomalin (RAL)
17/11/2017

28. Future Prospects (CMS, but ATLAS similar)
This table shows the luminosity needed to surpass Tevatron limits in some key channels. We expect 100/pb this year !
b’  tW
100/pb
Leptoquark  m j or e j
10/pb
ADD KK Graviton + jet = MET + jet
ADD KK Gravitons  g g spectrum change
50/pb
RS KK Graviton  g g resonance
Z’ or RS Gravition  e+e- or m+m-
Heavy stable charged exotics
Stopped (long-lived) gluinos
1032/cm2 /s
Excited quark  dijet
5/pb
4 quark contact interactions (dijets)
2/pb
Ian Tomalin (RAL)
17/11/2017

29. Expected Z’  l+l- Reach (CMS)
For SSM Z’, expect limits in both e+e- and m+m- channels of ~1.1 TeV/c2 by end 2010 and ~1.7 TeV/c2 by end 2011 !
Both CMS and ATLAS UK working on e+e- channel.
e+e-
m+m-
Ian Tomalin (RAL)
17/11/2017

30. Expected Z’  e+e- Reach (CMS)
Expected signal + background by end of this year in case of 1 TeV/c2 SSM Z’  e+e-.
Electron efficiency measured in data using Z0  e+e-.
Backgrounds extremely small in signal region.
Ian Tomalin (RAL)
17/11/2017

31. Conclusions
LHC already sets the World’s best limits for heavy stable charged exotica and (in some regions of phase space) stopped gluinos. M(gluino) > 284 GeV/c2 for long-lived gluinos
LHC also sets the best limits for excited quarks decaying to dijets. M(q*) > 1290 GeV/c2.
As the LHC luminosity increases, new results are now flooding in. At Winter Conferences, expected to see limits (discoveries !??) of Z’, lepto-quarks, extra dimensions ...
Ian Tomalin (RAL)
17/11/2017

32. Backup
Ian Tomalin (RAL)
17/11/2017

33. B’  tW
Ian Tomalin (RAL)
17/11/2017

34. RS Gravition  gamma gamma
Ian Tomalin (RAL)
17/11/2017

35. Leptoquarks  muon + jet
Ian Tomalin (RAL)
17/11/2017

36. HSCP
Ian Tomalin (RAL)
17/11/2017

37. q*  dijet
Ian Tomalin (RAL)
17/11/2017