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

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Heidelberg 2009Non-minimal models and their challenges for the

LHCMatthew Strassler

Rutgers University

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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.

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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

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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

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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

Standard ModelSU(3)xSU(2)xU(1)

Communicator

Hidden SectorGv with v-matter

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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

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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.

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A Conceptual DiagramEnergy

Inaccessibility

Entry into Valleyvia

Narrow “Portal”Multiparticle Production

in Valley

Some ParticlesUnable to Decay

Within Valley

Slow Decay Back to SM Sector

via Narrow Portal

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Inaccessibility

Quirk pairs are permanently bound!

Quirks

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Inaccessibility


Quirks

Relax toward ground state emitting soft particles

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Inaccessibility


Quirks

Annihilate into hardSM particles


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Inaccessibility


Quirks

Annihilate intoHidden Sector


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Hidden Valleys, Unparticles, Etc.

MJS-Zurek 2006

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Lower mass gap invisible (almost) to LHC

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Conformal Dynamics

well above mass gap

“unparticles”(unusual kinematic distributions in inclusive distributions)

Georgi 2007

Scale Invariant

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Conformal Dynamics

well above mass gap


Conformal Dynamics above

Mass Gap below

unparticle AND hidden valley

Scale Invariant

Mass Gap

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Conformal Dynamics

well above mass gap


Conformal Dynamics above

Mass Gap below

unparticle AND hidden valley

Scale Invariant

Mass Gap

Both Hidden Valley and Unparticle phenomenology may be simultaneously present.

But HV phenomenology appears in exclusive measurements: 2010Testing for scale invariance requires inclusive ones – hard!! 2015

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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

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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 importantBut not so urgent

Very importantBut not so urgent

PotentiallyUrgent

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New Invisible Signatures from Any SourceHow 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

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Invisible Hidden Sectorst 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)

t

b

et

c

Find the METsignal first!A Standard Search

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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.

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Novel Signals in Standard SearchesClassic 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

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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)

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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

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General Predictions of HV Scenario 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

hep-ph/0604261

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Effects on Narrow-Width Particles: 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 METGeneralizes well known work from 90s [GMSB, Anomaly, Hidden Sector]

hep-ph/0607160

hep-ph/0604261hep-ph/0605193

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Long-lived particles

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g

g

hh hhvv

mixing

bb

bb

bb

bb

Displaced vertex

Displaced vertex

Very difficult to trigger at ATLAS/CMS…Reconstruction challenges…

LHCb opportunity!!

Similar Observations: hep-ph/0607204 : Carpenter, Kaplan and Rhee

Precursor (LEP focus): Chang, Fox and Weiner, limit of model mentioned in hep-ph/0511250

hep-ph/0604261hep-ph/0605193

v-particles

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Charged hadronHigh pT Low pT Electron

Muon

Photon

Neutral Hadron

Tracker All tracks are “truth tracks” No magnetic fieldTracks with pT < 3 GeV not shownTracker radius 3 m

Calorimeter.Energy per 0.1 bin in azimuthLength of Orange Box = Radius of Tracker for total transverse energy = 1 TeV

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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?

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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 …

X decay Comment

Prompt Difficult if all b’s, tau’s; easy if many muon or electron pairs

Displaced New Discovery Channel?!

Highly Displaced

New Discovery Channel?!

Outside Detector

Invisible Higgs

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Example #2: Decays to QCD-like Sector

A case illustrating high multiplicity events without a corresponding Feynman diagram…

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q q Q Q : v-quark production

qq

qq

QQ

QQ

Z’Z’

v-quarks

Analogous to e+e- hadrons

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q q Q Q

qqQQ

qq QQ

Z’Z’

v-gluons


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q q Q Q

qqQQ

qq QQ

Z’Z’


No (or very low) mass gap? Invisible; Maybe Unparticle-like

Larger mass gap fromHiggsing, Confinement, etc.? Hidden Valley: Possibly Visible

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q q Q Q

qq

qq

QQ

QQ

v-hadrons

Z’Z’


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q q Q Q

qq

qq

QQ

QQ

v-hadrons

But some v-hadrons may decay in the detector to visible particles, such as bb pairs, qq pairs, leptons etc.

Z’Z’

Some v-hadrons may be (meta)stable and therefore invisible


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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!)

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Z’ mass = 3.2 TeVv-pi mass = 50 GeVFlavor-off-diagonal v-pions stable

Prompt decays: MJS 08

Z’ v-hadronsAverage: 8 b’sMax: 22 b’s

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Prompt Decays: Various LessonsLow-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, WackerAnd Arkani-Hamed and Weiner 2008

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With MET?

With >1 Hard Jets?

Non-Isolated?

Z’ v-hadronsIncluding ~ 10 GeV dilepton resonances

HVMC1.0 Mrenna,Skands,MJS

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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

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MJS 2008


As the mass goes down, this becomes harder

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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?!!!?

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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?

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Quarks vs Jets

Counting objects can be inefficient

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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 tracksstudy 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

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5 cm

Pixels

Dotted blue lines are B mesons

Track pT > 2.5 GeV

Multiple vertices may cluster in a single jet

Event Simulated UsingHidden Valley Monte Carlo 0.4(written by M. Strassler using elements of Pythia)

Simplified event display developed byRome/Seattle ATLAS working group

All tracks are Monte-Carlo-truth tracks; no detector simulation

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1 cmDotted blue lines are B mesons

Jet

Jet

VTX

VTX

Track pT > 2.5 GeV

Event Simulated UsingHidden Valley Monte Carlo 0.4(written by M. Strassler using elements of Pythia)

Simplified event display developed byRome/Seattle ATLAS working group

All tracks are Monte-Carlo-truth tracks; no detector simulation

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Dotted blue lines are B mesons

Dotted green lines are v-pions

1 cm

Jet

Jet

VTX

VTXVTX

The third vertex does not “belong” to either jet

Track pT > 2.5 GeV

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HT / MET

For a process with high parton-parton invt. mass

Few if any v-particles decay invisibly

large HT, low MET, high multiplicity

Moderate QCD, tt backgrounds

Large fraction of v-particles decay invisibly

medium HT, medium MET, medium multiplicity

Large Z + jets etc. backgrounds

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Z’ mass = 3.2 TeVv-pi mass = 50 GeVFlavor-off-diagonal v-pions unstable

MJS 2008


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MET vs HT

Models with all v-particles decaying visibly

Models with ~2/3 of v-particles stable and invisible

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Overall Event Shapes … relatively unexplored territory

Events with few invisible particles: Tend to be oblong to spherical, not like dijets Tend to be different from tri-jets (acoplanarity in some frame) May be “spiky” or “mushy”

Events with many invisible particles Tend to be asymmetric (but so is Z + jets) Highly variable!!!! Hard to get large sample with any one criterion

E.g. multiplicity of visible particles varies widely May be “spiky” or “mushy” but not always so distinctive

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Z’ mass = 3.2 TeVv-pi mass = 50 GeVFlavor-off-diagonal v-pions unstable

MJS 2008


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UV Weak-Coupling(small anom dims)

~ 10 v-hadronsSome hard, some soft

~ of order 20 quarks/leptonsof widely varying pT

Z’Z’

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UV Strong-Coupling Fixed Point(large anom dims)

~ 30 v-hadronsSofter v-hadrons

~ 50-60 soft SM quarks/leptons

Event from educated guesswork!

Crude and uncontrolled simulation

•Fix in HV Monte Carlo 0.5 at large value•This increases collinear splitting

•Check that nothing awful happens•Check answer is physically consistent with my expectation

Z’Z’

This hidden valley is also an “unparticle theory with a mass gap”

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Quirks Two heavy SM-charged particles bound by a hidden flux tube

If charged, color-neutral quirk is like stau If colored, forms new hadron (like R-hadron)

Dynamics depends on tension of flux tube (i.e. hidden confinement scale)

Very low tension – two charged particles following weird tracks Interesting trigger and tracking issues -- timing

Higher tension – Relaxes toward (not always to) ground state in microscopic time Annihilates to hard SM or hidden-sector particles (visible or invisible)

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Quirk Annihilation Products are Hard Quirks W gamma

300 GeV 500 GeV

800 GeV

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Quirk Relaxation Products are Soft Quirks W gamma + relaxation effects –

400 soft photons + 400 soft charged pions?

300 GeV 500 GeV

800 GeV

Correlation of hard W+gamma with oddly shaped active UE allows diagnosis!

Kang Luty 08 see also Chacko et al 07

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Summary of the Chaos Theorists have uncovered a plethora of fascinating signatures that new

physics might display – but do not yet fully understand how to find them

Some of these can be studied after discovery of a deviation from the SM is made using standard methods [Badly distorted Higgs?!]

But many (esp. hidden valleys and quirks) require new types of searches Standard searches with non-standard event selection New types of criteria for event selection New methods to deal with high multiplicity, poor isolation, soft physics New jet methods to deal with substructure, clustering New shape variables needed Specialized searches for long lifetimes, weird tracks

Many of these require specialized trigger, reconstruction, and/or analysis

Some Event Generators Exist!

Documents

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