Heidelberg 2009 Non-minimal models and their challenges for the LHC

1. Heidelberg 2009Non-minimal models and their challenges for the LHC Matthew Strassler Rutgers University

2. The bias of minimalism • One of the greatest threats to progress in science is bias. • Therefore important to search for and eliminate sources of bias. • Minimal models that solve a theoretical problem are elegant. • The love of elegance is a bias. • Nature has not been elegant so far • Should we expect elegance at the LHC? • As a result of this bias, we have largely ignored non-minimal models. • This is extremely dangerous. Effects on LHC pheno can be drastic! • But there is still time.

3. Theory vs. Experiment • A large change to a theory may be a small change to an experiment • Minimal SUSY vs UED • A small change to a theory may be a large change to an experiment • Add one real scalar field to the Higgs sector of SM: • 2 Higgs bosons h, H • h  bb, tau tau, H  WW,ZZ • Or 2 Higgs bosons h, H • h  bb, tau tau, H  hh • Or one invisible Higgs boson • SUSY + one new (s)particle not at all like MSUGRA! Lose 50% of MET? Soft jets? What if I add two, or three, or… • Very easily end up with largely or completely new signatures

4. This Talk – Pure Chaos • 04/06 Zurek and I have gone hiking and gotten lost in hidden valleys • 06/08 Kang and Luty have become very quirky lately • 07 Georgi, Terning and others have stopped doing particle physics We are all looking at interesting dynamics in new hidden gauge sectors • A lot of weird signatures have been uncovered which • are completely reasonable, but • have not been considered enough, or at all, by hadron collider experiments Note “effective” Lagrangians, mass reconstruction methods can fail here • Motivation • Experimental: must not miss any signals of new physics! • Theoretical: not the point… but string theory, SUSY breaking and dark matter motivate existence of hidden sectors • Dark matter motivation, CDF multimuons  recent upsurge in hidden valley models

5. Hidden Sectors at the LHC • A scenario: • Not a Model, or even a Class of Models • A Very Large Meta-Class of Models • Basic minimal structure Communicator Hidden Sector Gv with v-matter Standard Model SU(3)xSU(2)xU(1)

6. Hidden Sectors • a collection of SM-neutral fields (1, 10, 100,…) • very weak interactions with (light) SM fields, • arbitrary self-interactions (maybe strong) • Common in string theory, extra dimensions, supersymmetry breaking • Reasonable to expect, given that there is dark matter Of course, they are often inaccessible at LHC: too weakly coupled or too heavy But if accessible, a hidden sector can drastically alter LHC pheno, so we must prepare! Very few constraints on hidden sectors • Cosmological constraints are easily evaded without altering LHC signals • LEP, Tevatron constraints are relatively weak (it’s hidden!) Thus hidden sectors are easily added to SM, MSSM, ExDim, higgs, • Without fouling anything up theoretically • Without violating any existing experimental constraints • But totally changing the LHC experimental signatures

7. Hidden Sectors • Various non-hidden extensions of SM have been considered • More elaborate Higgs sector • New vectorlike matter • New abelian gauge groups • Coupling them to new hidden-sector dynamics can give entirely new signatures • Matter with new dynamics (e.g “quirks”, “colored unparticles”) • Badly distorted Higgs (e.g. “unHiggs”) • Badly distorted Z’, etc. • Very exotic decay modes of Higgs, Z’, etc.

8. A Conceptual Diagram Energy Entry into Valley via Narrow “Portal” Multiparticle Production in Valley Some Particles Unable to Decay Within Valley Slow Decay Back to SM Sector via Narrow Portal Inaccessibility

9. A Conceptual Diagram Energy Quirk pairs are permanently bound! Quirks Inaccessibility

10. A Conceptual Diagram Energy Quirk pairs are permanently bound! Quirks Relax toward ground state emitting soft particles Inaccessibility

11. A Conceptual Diagram Energy Quirk pairs are permanently bound! Quirks Relax toward ground state emitting soft particles Annihilate into hard SM particles Inaccessibility

12. A Conceptual Diagram Energy Quirk pairs are permanently bound! Quirks Relax toward ground state emitting soft particles Annihilate into Hidden Sector Inaccessibility

13. Hidden Valleys, Unparticles, Etc. MJS-Zurek 2006

14. Hidden Valleys, Unparticles, Etc. Lower mass gap  invisible (almost) to LHC

15. Hidden Valleys, Unparticles, Etc. Lower mass gap  invisible (almost) to LHC Conformal Dynamics well above mass gap  “unparticles” (unusual kinematic distributions in inclusive distributions) Georgi 2007 Scale Invariant

16. Hidden Valleys, Unparticles, Etc. Lower mass gap  invisible (almost) to LHC Conformal Dynamics well above mass gap  “unparticles” (unusual kinematic distributions in inclusive distributions) Conformal Dynamics above Mass Gap below unparticle AND hidden valley Scale Invariant Mass Gap

17. Hidden Valleys, Unparticles, Etc. Both Hidden Valley and Unparticle phenomenology may be simultaneously present. But HV phenomenology appears in exclusive measurements: 2010 Testing for scale invariance requires inclusive ones – hard!! 2015 Lower mass gap  invisible (almost) to LHC Conformal Dynamics well above mass gap  “unparticles” (unusual kinematic distributions in inclusive distributions) Conformal Dynamics above Mass Gap below unparticle AND hidden valley Scale Invariant Mass Gap

18. Need to divide and conquer • New invisible signatures • MET + X; how do we study a invisible sector? • Novel visible signals found in standard places • Careful tests of SM distributions • High-precision measurements of deviations • New visible signatures found in weird places • Long-lived particles • New resonances or endpoints requiring unusual event selection • High-multiplicity events • Unusual clustering of objects • Strange event shapes • Unusual tracks • Physics hiding in underlying event

19. Need to divide and conquer • New invisible signatures • MET + X; how do we study a invisible sector? • Novel visible signals found in standard places • Careful tests of SM distributions • High-precision measurements of deviations • New visible signatures found in weird places • Long-lived particles • New resonances or endpoints requiring unusual event selection • High-multiplicity events • Unusual clustering of objects • Strange event shapes • Unusual tracks • Physics hiding in underlying event Very important But not so urgent Very important But not so urgent Potentially Urgent

20. New Invisible Signatures from Any Source How do we study and diagnose a invisible hidden sector? • First, find MET + X signal ! (2010) • This is a standard search. • Second, measure it to death: (2012) • Find MET+ X’, MET + X’’ • Measure lots of kinematic distributions • Third, figure out what’s going on: (2015) • Rule out simple ideas using transverse-mass methods (MT2 etc.?) • Combine measurements to determine production mechanism • Remove its kinematic dependence, then constrain the source of the MET • This process will typically take a long time! Not urgent. • Rarely will a single, early analysis figure out what is behind a MET signature

21. Invisible Hidden Sectors t  c + invisible What’s the invisible stuff? • Three free invisible particles? • A variety of invisible bound states? • Unparticles? (scale-invariant dynamics not describable as particles) • Challenge: to test for “unparticles”, observables inclusive Georgi 07 • must measure all events (or correct for those you don’t) c b t t e Find the MET signal first! A Standard Search

22. Urgent Exception: Invisible “UnHiggs” If the Higgs mixes with and/or decays to an invisible hidden sector, problematic! • Gunion et al. 97 • Consider a very large number of doublet and/or singlet Higgs bosons, some with vevs • Effect: Higgs signals are all spread out into a continuum or near-continuum • Quiros et al. (“singlet” unHiggs) • Terning et al. (“doublet” unHiggs) • The first is obviously consistent, the second non-obviously consistent, with LEP bounds • Higgs may be completely invisible in these cases • Similar experimental issues as very wide Higgs with huge invisible width. • In this case it may have been accessible, but missed, at LEP • Signatures? • Broad invisible Higgs very tough; needs study in VBF. Are there other signatures? • If hidden sector is visible, it may be much better. • UnHiggs may have hidden-valley-type high-multiplicity decays; • Difficulty varies: 4 b’s, tough; 4 leptons, easy; many other options.

23. Novel Signals in Standard Searches Classic model-independent searches for deviations from SM predictions may well turn up visible effects due to a hidden sector. • Certain hidden valleys and other models can give • Diphoton resonances in di-photons+jets • Higgs  Z’ Z’  4 leptons (Z’ very light) • Quirk annihilation can give • Excess and kinematic structure in W+photon events • Certain hidden valley and unparticle(Feng et al.) models can give • Excess of 3 or 4 photon events, multilepton events, … • Many other examples… This takes a long time – 2012? 2015? – and is not urgent Model-dependent, targeted searches can be done, in principle, but suffer from • Too many models • In many models, lack of theoretical methods for accurately calculating signals

24. Novel Signals in Quasi-Standard Searches • Stau-like particles or R-hadron like particles may have hidden interactions • With MET disappearing into invisible hidden sector • Possibly unparticle sector [Terning et al. 07, colored unparticles] • Or accompanied by visible effects from hidden valley [MJS + Zurek 06] • Long-lived particles • Multiparticle production • Experimentally this is not urgent: • Find the stau-like or R-hadron like objects (2011) • Measure the MET or accompanying particles (2013)

25. Signals in new places: • Hidden Valleys • Lots and lots and lots of new signals (I’ll show just a few) • Quirks • Weird tracks • Hiding physics where you least expect it

26. General Predictions of HV Scenario hep-ph/0604261 • New neutral resonances • Maybe 1, maybe 10 new resonances to find • Many possible decay modes • Pairs of SM particles (quarks, leptons, gluons all possible; b quarks common) • Triplets, quartets of SM particles… • Often boosted in production; jet substructure key observable • Long-lived resonances • Often large missing energy • Displaced vertices common (possibly 1 or 2, possibly >10 per event) • … in any part of the detector • Great opportunity for LHCb if rates high • Problem for ATLAS/CMS trigger if event energy is low • Multiparticle production with unusual clustering • Exceptionally busy final states possible • 6-20 quarks/leptons typical in certain processes • up to 60 quarks/leptons/gluons in some cases • Breakdown of correspondence of measured jets to partons • Very large fluctuations in appearance of events

27. Effects on Narrow-Width Particles: hep-ph/0604261 hep-ph/0605193 • Possible big effect on Higgs • Long lived particles: H  XX, X decays displaced  new discovery mode • not unique to HV!!! Chang Fox Weiner 05 / Carpenter Kaplan Rhee 06 • High multiplicity decays: H  XXX, XXXX, etc • not unique to HV!!! Chang Fox Weiner 05 • Big effect on SUSY, UED, Little Higgs– any theory w/ new global charge • LSP (or LKP or LTP) of our sector can decay to the valley LSP/LKP/LTP • Plus SM particles or • Plus hidden particles which decay back to SM particles or • Plus both • Either the hidden particles or the LSP/LKP/LTP may be long-lived; • LSP may have high-multiplicity decays; • SUSY events have significantly reduced MET Generalizes well known work from 90s [GMSB, Anomaly, Hidden Sector] hep-ph/0607160

28. Long-lived particles

29. hep-ph/0604261 hep-ph/0605193 Very difficult to trigger at ATLAS/CMS… Reconstruction challenges… LHCb opportunity!! Displaced vertex b g b h hv b Similar Observations: hep-ph/0607204 : Carpenter, Kaplan and Rhee Precursor (LEP focus): Chang, Fox and Weiner, limit of model mentioned in hep-ph/0511250 g b mixing v-particles Displaced vertex

30. Charged hadron High pT Low pT Electron Muon Photon Neutral Hadron Tracker All tracks are “truth tracks” No magnetic field Tracks with pT < 3 GeV not shown Tracker radius 3 m Calorimeter. Energy per 0.1 bin in azimuth Length of Orange Box = Radius of Tracker for total transverse energy = 1 TeV

31. Long-Lived Neutral Weakly-Interacting X • Partial List of Experimental Challenges for H  X X , X long-lived • Trigger • Muons lack pointing tracks • Jets are low pT, don’t trigger • Vertex may be rejected (too far out to be a B meson) • Weird-looking event may fail quality control • Reconstruction • Event may be badly mis-reconstructed • Tracks may be missed • Calorimeter effects may be misconstrued as cavern background etc. • Event may not be flagged as interesting • May be thrown into bin with huge number of unrelated, uninteresting events • Event Selection • The events may be scattered in different trigger streams, reconstruction bins • If an event was not flagged as interesting in reconstruction, how is it to be found? • Analysis • What precisely to look for if the decays are outside the early layers of the tracker? • What can be done if decays are in calorimeter or muon system?

32. Production #1: Higgs boson decay What can a new valley sector do? • Higgs  X X (new [pseudo]scalars) • X  heavy flavor • H  4 b’s or tau’s • Higgs  F F (new fermions) • F  jets + MET, etc. • Higgs  Y Y (new vectors) • Y  jets, mu pairs, e pairs, neutrinos • Other final states possible • H YY XXXX  8 b’s or tau’s (or mu’s) • H FF  4 b’s, tau’s plus MET • H  XX  YYYY  8 soft quarks/leptons • …

33. Example #2: Decays to QCD-like Sector A case illustrating high multiplicity events without a corresponding Feynman diagram…

34. q q  Q Q : v-quark production v-quarks Q q Z’ q Q Analogous to e+e-  hadrons

35. q q  Q Q v-gluons Q q Z’ q Q Analogous to e+e-  hadrons

36. q q  Q Q Larger mass gap from Higgsing, Confinement, etc.? Hidden Valley: Possibly Visible No (or very low) mass gap? Invisible; Maybe Unparticle-like Q q Z’ q Q Analogous to e+e-  hadrons

37. q q  Q Q v-hadrons q Q Z’ q Q Analogous to e+e-  hadrons

38. q q  Q Q Some v-hadrons may be (meta)stable and therefore invisible v-hadrons But some v-hadrons may decay in the detector to visible particles, such as bb pairs, qq pairs, leptons etc. q Q Z’ q Q Analogous to e+e-  hadrons

39. Z’  many v-particles  many b-pairs, some taus, some MET • Must be detected with very high efficiency • Online trigger to avoid discarding • Offline reconstruction to identify or at least flag • Note: • Decays at many locations • Clustering and jet substructure • Unusual event shape (can vary widely!)

40. Z’  v-hadrons Average: 8 b’s Max: 22 b’s Prompt decays: MJS 08 Z’ mass = 3.2 TeV v-pi mass = 50 GeV Flavor-off-diagonal v-pions stable

41. Prompt Decays: Various Lessons Low-mass dilepton (e, mu) or diphoton resonances – easy, BUT • Low-mass resonances may be produced only in high-energy events • Typically produced with high boost, small angles: • May violate lepton/photon isolation requirements; need to loosen these criteria • (Analysis? Reconstruction? Trigger???) • Low-mass resonances sometimes produced with multiplicity>1 • Look especially in events with >2 leptons and/or photons • Rare resonances/edges/endpoints swamped by SM background unless one imposes unusual event selection criteria • Look for rare di-lepton resonances in events • With large MET, or • With 6 or more jets, or • With unusually high hemisphere mass, or … An Example: Han, Si, Zurek & Strassler 2007 See also unpublished Haas, Wacker And Arkani-Hamed and Weiner 2008

42. Non-Isolated? With MET? With >1 Hard Jets? Z’  v-hadrons Including ~ 10 GeV dilepton resonances HVMC1.0 Mrenna,Skands,MJS

43. More lessons: • Easiest way to find di-jet resonances is if boosted • boost is common in decays of heavy particles to hidden sector (Z’, H, etc.) • cf. technical advances: Butterworth, Davison, Rubin & Salam 2008 • The problem is to find them; without correct event selection, drowned in QCD • So we have a three-step problem: • Select events that have a chance of containing a resonance • Study high-pT jets, look for substructure consistent with a boosted particle • Look for invariant mass peak built from the substructure of the jets • Start with the substructure, then turn to event selection methods

44. Z’  v-hadrons Average: 3 b’s Max: 12 b’s MJS 2008 Z’ mass = 3.2 TeV v-pi mass = 200 GeV Flavor-off-diagonal v-pions stable As the mass goes down, this becomes harder

45. Event Selection Criteria • Standard-Object-Based – • Exceptional numbers or combinations of jets/leptons/photons -- isolation?! • HT / MET – • Exceptional energetics – process and cross-section dependent; typically not enough • Tracks/Displaced Tracks/Vertices – • High (but possibly soft?) jet multiplicity; many b jets; particles with few ps lifetimes • New Objects – • Hadronic jets with substructure • Pairs or clusters of non-isolated leptons • Narrow di-tau candidates • R-hadron candidates (loose criteria) • Jets with very low ECAL/HCAL and few tracks • Overall Event Shapes – needs development • High-thrust events vs. Spherical events • Spiky events vs. Mushy events • Asymmetric events vs. Symmetric events How do we calibrate these techniques and measure backgrounds?!!!?

46. Event Selection Criteria Object-Based Selection • High multiplicity of standard objects • Caution: at very high quark/lepton/gluon/photon multiplicity, jets merge, leptons/photons fail isolation • Multiple leptons or photons? • Relax or remove isolation criteria? • Look at clustering?

47. Z’  v-hadrons Average: 8 b’s Max: 22 b’s Prompt decays: MJS 08 Z’ mass = 3.2 TeV v-pi mass = 50 GeV Flavor-off-diagonal v-pions stable

48. Quarks vs Jets Counting objects can be inefficient

49. Event Selection Criteria Tracks/Vertices • Signal with many soft particles: • count tracks rather than jets/leptons • Signal with many v-particles  b quark pairs • Many B-mesons – often many more B-mesons than jets • Don’t just tag the jets – count tracks, vertices, displaced tracks study clustering of tracks and vertices • Signal with v-particles  jets with lifetime 1 ps • One vertex for each jet pair • Look for jets that share a displaced vertex with many tracks

50. Event Simulated Using Hidden Valley Monte Carlo 0.4 (written by M. Strassler using elements of Pythia) Simplified event display developed by Rome/Seattle ATLAS working group Pixels All tracks are Monte-Carlo-truth tracks; no detector simulation 5 cm Dotted blue lines are B mesons Track pT > 2.5 GeV Multiple vertices may cluster in a single jet