Supersymmetry at the LHC: Status and a Thought or Two about the Future RPM Seminar LBNL October 27, 2016 Supersymmetry at the LHC: Status and a Thought or Two about the Future Bruce A. Schumm Santa Cruz Institute for Particle Physics University of California, Santa Cruz

References… I’ve been too lazy to note each result, reference-by-reference. They are all available from the following two public WEB pages, CMS and ATLAS, respectively (the CMS URL isn’t accidentally truncated, even though it seems it must be!): https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults Bruce Schumm

Stabilize the Higgs Mass SUSY Motivations I Stabilize the Higgs Mass If we try to situate SU(3)SU(2)U(1) in a grand-unified theory, the Higgs self-energy term wants to be at the unification (e.g. Planck) scale. Elegant solution: posit a mapping Fermion  Boson between SM particles and an as-of-yet undiscovered set of “superpartners” with identical couplings but opposite spin-statistics. Provides a cancellation of the dangerous vacuum contributions to the Higgs self-energy term. In fact, SUSY naturally prefers a light Higgs, which is what we observe! Bruce Schumm

Natural Dark Matter Candidate SUSY Motivations II Natural Dark Matter Candidate To avoid lepton/baryon number violation can require that “SUSYness” is conserved, i.e., preserves an additive “parity” quantum number R such that RSM = +1; RSUSY = -1 If you can’t get rid of SUSYness, then the lightest super-symmetric particle (LSP) must be stable  dark matter, missing energy LSP is typically a “neutralino” (dark matter must be neutral); admixture of , known as “10, whose identity is not that relevant to phenomenology Note: This review will be restricted to searches to RP-conserving process. Missing energy (ETmiss) is assumed to always be in use as a discriminating variable. Bruce Schumm

Gauge Coupling Unification SUSY Successes I: Unification Gauge Coupling Unification SM + desert MSSM MSSM = Minimal Supersymmetric Model = minimal set of states and couplings needed to preserve known phenomenology when SM is embedded in SUSY framework Bruce Schumm

SUSY Successes II: Higgs Mass Xt is a combination of fundamental GUT-scale SUSY parameters (masses, trilinear coupling strength); m~t2 an effective squared stop mass Bruce Schumm Baer, Barger, Savoy, arXiv:1502.04127 [hep-ph]

A Striking Aspect of Nature: mtop >>> mbottom Bruce Schumm

Baer, Barger, Savoy, arXiv:1502.04127 [hep-ph] SUSY Successes III: Top Mass Higgs scalar potential contribution m2Hu must be negative to generate EWSB (“Mexican Hat” potential) GUT-scale unification sets m2Hu > 0; but radiative corrections arise in its evolution to the EW scale: mH t = ln(Q2) (RGE scale) ft = top-mass Yukawa coupling S expected to be small SUSY+EWSB “predicts” 100 < mt < 200 GeV Baer, Barger, Savoy, arXiv:1502.04127 [hep-ph] Bruce Schumm

Formal Motivation for SUSY The set of spacetime symmetries of 3+1 dimensional field theory form the Poincare Group. Fermions fit within the fundamental representations of the Poincare group; bosonic representations are formed from tensor products of the spinor representations  fermions and bosons have different formal statures Extensions of the Poincare group that attempt to establish a reciprocity between fermionic & bosonic representations (e.g. the “cover” group SL(2,C) ) generally introduce a symmetry transformation between bosons and fermions  SUSY I think one can certainly say it's pretty, and unifies the representations in an intriguing way.  It's certainly in the category of things "it would be a shame if nature didn't take advantage of". - Michael Dine In addition, SUSY may be a necessary condition for quantizing gravity*. We do put stock in our formal structures SU(3) flavor states (“8-fold way”) Black holes “A typical stationary point of some string effective action is unstable unless it is at least approximately supersymmetric” M. Dine again…

But where are these states?  SUSY must be broken! SUSY States SUSY posits a complete set of mirror states with SSUSY = |SSM – ½| But where are these states?  SUSY must be broken! Bruce Schumm

SUGRA: Local supersymmetry broken by supergravity interactions SUSY Breaking SUGRA: Local supersymmetry broken by supergravity interactions Phenomenology: LSP (usually 10) carries missing energy. GMSB: Explicit couplings to intermediate-scale (MEW <  < MGUT) “messenger” gauge interactions mediate SUSY breaking. Phenomenology: Gravitino ( ) LSP; NLSP is 10 or . Content of 10 germane. AMSB: Higher-dimensional SUSY breaking communicated to 3+1 dimensions via “Weyl anomaly”. Phenomenology: LSP tends to be , with 1+, 10 nearly degenerate. But still, we would naturally expect these states to be within spitting distance of the EW scale… Bruce Schumm

mGMSB Strong vs. Electroweak Production STRONG COUPLING However: if colored states are decoupled, EW production will dominate Dedicated EW prod. analyses Pure-EW simplified models  probe high mass scale steep mass dependence (~M-10) beam energy vs. luminosity lower backgrounds mGMSB ELECTROWEAK COUPLING s = 7 TeV 5 fb-1 reach EW Strong  probe intermediate mass scales higher backgrounds benefit from high L.dt SUSY Breaking Scale  (TeV) Bruce Schumm

e.g. General Gauge Mediation (GGM): Classes of Models Minimal Models Simplified Models GUT unification  few parameters mSUGRA/CMSSM, GMSB e.g. GMSB: Λ: SUSY breaking scale Mmes: Messenger scale N5: Number of messenger fields tan: Ratio of vev for the two Higgs doublets Cgrav: Gravitino mass parameter sgn(): Sign of higgsino mass term e.g. the “SPS 8” model is just a specific set of choices for the GMSB parameters. e.g. General Gauge Mediation (GGM): Start with GMSB and decouple all but a few states; properties of these state become “free” Bruce Schumm ICHEP 2016: SUSY with Photons and Taus

SUSY States: A Closer Look Neutralinos (n0) formed from linear combina-tions of neutral Wino, Bino, Higgsino states Charginos (n) formed from linear combina-tions of charged Wino Higgsino states SUSY Higgs sector has two complex doublets  five physical degrees of freedom Bruce Schumm

The LHC Bruce Schumm

ATLAS (and ~CMS) Luminosity Integration No Results yet Some Results Many Results Bruce Schumm

The ATLAS Detector Non-prompt tracks Photon conversions Bruce Schumm

CMS Detector Bruce Schumm

Photons, leptons, (tagged) jets, composites (boosted objects) SUSY Tools I From the tracks and clusters in the detector, we assemble a collection of objects to be used as tools in our search for SUSY above pesky SM backgrounds. Photons, leptons, (tagged) jets, composites (boosted objects) The more specific you can be, the easier it is to reject backgrounds, but the more model dependent your analysis ETmiss: Transverse momentum imbalance LSP escapes detection (RP conserving SUSY) Meff, HT, etc: Transverse energy scale Strong production can reach high mass scales “Scale chasing” Bruce Schumm

Favorite Discriminating Variables x : Minimum  separation between ETmiss vector and any object of type X. LSP produced in intermediate-to-high mass decay Separation between LSP and decay sibling Jet backgrounds tend to have small separation (combinatoric) Generic Kinematics: Transverse mass (and its descendants), Razor variables, T… Tend to exploit generic kinematic features of high-mass production with invisible decay products Empirically-oriented approach Bruce Schumm

Here We Go… OK – Let’s Find SUSY! Bruce Schumm

Obvious place to start: gluino production… SUSY Cross Sections Obvious place to start: gluino production… Bruce Schumm

SUSY 101: Gluino Production Searches High cross-section gluino production is natural place to start Most simple of all models is gluino  10 + X through virtual gluon or squark channel. If a squark channel, then can be dominated by particular flavor of jets (ttbar, bbar, qqbar) Free parameters of the model are gluino, LSP (10) masses Bruce Schumm

Basic Gluino Searches CMS: Very basic search, requiring 3 jets and various amounts of HT and Etmiss (targeting different regions in the (mg,m) space) At each point in the space, set limit with HT,Etmiss requirement giving the best expected limit.     Bruce Schumm

Basic Gluino Searches (cont’d) Limits on gluino mass (in this context) in 1.6-1.8 TeV range Limits generally less constraining than expected  consistent excess of observed events relative to expectations. What might ATLAS have seen?   Bruce Schumm

No excess observed… ATLAS Gluino Searches via t,b Include requirement of multiple b jets More sensitive More model-dependent   No excess observed…   Bruce Schumm

0 leptons, 2-6 jets (and of course Etmiss) ATLAS Gluino Searches, Flavor-Blind 0 leptons, 2-6 jets (and of course Etmiss) Similar sensitivity to CMS (slight excess in one region) Bruce Schumm

So, lightest stop can’t decouple; must be at EW scales Light Stop: the Celebrity Squark Why so? Argument: The stabilization of the Higgs mass (centerpiece of SUSY motivation) must be dominated by stop, since couplings are largest So, lightest stop can’t decouple; must be at EW scales However… Howie Baer, ICHEP 2016: “The idea that a light stop is a necessary requirement of naturalness has been debunked” (ask him for details…).  Stop searches demoted from “critical” to “highly motivated”… Bruce Schumm

Stop Search Landscape (ATLAS Approach) Depending on stop-10 mass splitting m, top may or may not appear in decay chain 0-lepton, 1-lepton analysis for large m Multi-lepton analysis for lower m Bruce Schumm

Putting it all together… Stop masses towards 900 GeV can be excluded, but only for light 10. Analysis more challenging when top-decay channel is closed Small region for m0 addressed by monojet (“MJ”) analysis; more on this soon. Observed limits below expected… Bruce Schumm

CMS and Light Stop Somewhat different approach from CMS… But results largely the same Again, observed limits a bit below expectation…   These low-mass production scale studies benefit well from increased statistics Bruce Schumm

Event Variable Example: T and Compressed Stop Also require HT = jetsET > 200-300 GeV T = ETj2/MT j2 = subleading jet MT = dijet transverse mass Force two jets for this calculation (excess again…) Particularly sensitive to mstop  m in ~ 300 GeV range Randall & Tucker, arXiv:0806.1049 Bruce Schumm

EW SUSY is intrinsically more difficult to find Small cross section Electroweak SUSY Possible scenario: only accessible states are not strongly coupled (gauginos, higgsinos, sleptons) EW SUSY is intrinsically more difficult to find Small cross section Worse signal-to-SM-background ratio In fact, there are some suggestions that accessible states will be weakly interacting: Dark matter is weakly interacting If it is borne out, (g-2) points to weakly-coupled virtual state Bruce Schumm

SUGRA-inspired EW Searches Key to EW searches has been leptons (plus photons when we get to Gauge Mediation) CMS and ATLAS: Two opposite sign leptons, or three leptons not all of same charge; not necessarily of same flavor. Kinematic cuts to remove W,Z backgrounds (mT etc…) Bruce Schumm

Multi-lepton searches for EW SUSY CMS update with 13 fb-1 of 13 TeV data “Compressed” region Slepton ½ way between production and LSP mass Slepton just above LSP mass Sensitive to masses approaching 1 TeV, but significant model dependence “Compressed region” challenging Bruce Schumm

Compressed SUSY Spectra Compressed spectra in SUSY quite plausible (some would even say preferred): Naturalness again: Mass parameter associated with set of Higgsino states should be at EW scale. i.e., nearly-degenerate set of lightest gauginos Cosmology: Having multiple degrees of freedom at WIMP scale more readily produces observed dark-matter abundance (“co-annihilation”) Bruce Schumm

Nearly-Degenerate EW Scenarios Common (production) scale for 1, 20 Explore reach in m(20,10)  0 New dedicated trigger (last 10 fb-1): ETmiss > 50 GeV 2 muons > 3 GeV Offline Etmiss > 125 GeV Also require at least 100 GeV of jet activity to suppress high cross-section backgrounds Relies somewhat on ISR to boost system & enhance observables Over all SRs, expect 36 events, see 19 Bruce Schumm

Signature: Single lepton + Higgs Other Gaugino Decay Channels: Higgsinos Signature: Single lepton + Higgs Limits are still very forgiving Bruce Schumm

Highly Degenerate SUSY: the Monojet Analysis Pure Etmiss trigger; offline requirements include Etmiss > 250 GeV Jet with pT > 250 GeV Can search for stop in the region m  mc Low-mass production  will benefit greatly from increasing luminosity Bruce Schumm

LSP-Only Scenarios What if the only accessible SUSY partner is a single, lightest neutralino (0)? SM gauge structure (U(1) is abelian; explicit algebra of SU(2)) forbids leading-order pair production of any admixture of Bino or neutral Wino states. One possibility is a multiplet of effectively-degenerate charged and neutral higgsino states (also motivated by AMSB SUSY breaking; sensitivity would be provided by the monojet analysis (has this ever been explored?). Otherwise, LSP-only scenarios seem to be the unique purview of direct-detection experiments! Bruce Schumm

Gauge Mediation Scenarios Generally speaking, gauge mediation has several predominant characteristics: LSP is the nearly-massless gravitino NLSP is either Stau Neutralino, typically all or mostly bino-like  Photonic and tau-onic final states particularly common for gauge-mediation-inspired searched Bruce Schumm

Diphoton + Etmiss Analysis (3.2 fb-1) (mg,m) focus points for optimization: (1500, 100) for low-mass 10 (1500,1300) for high-mass 10 No significant difference found for optimal selection for 3 fb-1 at 13 TeV  single diphoton+Etmiss SR 1 2 1 2 Run I Results Significant requirements only on Etmiss and transverse mass scale Meff  fully efficient even for mbino  mgluino and mbino  0 Bruce Schumm

No Events Observed in SR Diphoton + Etmiss Results (3.2 fb-1) Optimization calls for demanding requirements on Etmiss and Meff leaving little background Gluino mass limits (for case of purely bino-like NLSP) in range of 1600-1750 GeV No Events Observed in SR https://arxiv.org/pdf/1606.09150.pdf Bruce Schumm

Photon + Jets Analysis (13.3 fb-1) Separate optimization for: low-mass bino (“L”; many jets in cascade) high-mass bino (“H”; large Etmiss) Run I Results L H Optimization reckoned by considering two points in each region (see “L” and “H” above) Bruce Schumm

Photon + Jets Results (13.3 fb-1) PRELIMINARY FIRST PUBLIC PRESENTATION At these high mass scales (Meff > 2000 TeV) there is little SM background. Observation of 3 events (SRL) when 0.78  0.18 are expected is 2% likely. Combined-SR gluino mass limits (for case of higgsino/bino NLSP with 50/50 /Z branching) as high as 2 TeV  ATLAS-CONF-2016-066 Bruce Schumm

Multi-Tau Analysis (3.2 fb-1) 2 low-background multi- SRs geared towards mSUGRA model with high gluino mass and large mass gap 1 multi- SR geared towards GMSB model Bruce Schumm

mGMSB Limits for Tau Analyses (3.2 fb-1) Nominal gluino mass limits as high as 2.3 TeV, but note that *L=0.7 events for gluino pair production at this mass  Limit coming from lower-mass EW production, plus GMSB constraints! Bruce Schumm

Some Pet Projects at SCIPP Bruce Schumm

Some Pet Projects at SCIPP Bruce Schumm

Some Pet Projects at SCIPP Bruce Schumm

So Where Do We Stand? Bruce Schumm

So Where Do We Stand? How “ruled out” is SUSY? One approach: “Radiatively Driven Natural SUSY” in the SUGRA framework. Note that this framework admits gauge-coupling unification predicts a light Higgs strongly prefers a heavy top Within this framework Measure of fine tuning provided by (H. Baer& Associates, Phys. Rev. D87 (115028), 2013).     Bruce Schumm

“Natural” SUSY Spectrum Stolen from H. Baer Bruce Schumm

So Where Do We Stand? Bruce Schumm

What are the luminaries saying? Stepping (Way) Back… What are the luminaries saying? Rumors of my death have been greatly exaggerated… I never… no… I never said that. NO. SUSY is dead? Bruce Schumm

And so the Search Goes On… Bruce Schumm

BackUp BackUp… Bruce Schumm

Post-LEP SUGRA mH Prediction SUSY partners below 20 TeV SUSY partners below 5 TeV Bruce Schumm

ISO: The Stop Squark Bruce Schumm

Mono-X experiments for LSP-only scenarios EW production Back-Up Some things to cover Gluinos Squarks – light stop Mono-X experiments for LSP-only scenarios EW production Razor/Edge analyses Maybe CMS CMS-SUS-14-006?… GMSB Small-splitting case R-parity violation Non-pointing, tracklets, low-pt leptons Bruce Schumm

e.g. General Gauge Mediation (GGM) Classes of Models Minimal Models General Models GUT unification: few parameters mSUGRA/CMSSM mGMSB e.g. mSUGRA: m0: GUT scale common scalar mass m½: GUT scale common gaugino mass tan: Ratio of Higgs doublet VEVs A0: Common trilinear coupling Sgn(): Higgs mass term e.g. General Gauge Mediation (GGM) Bruce Schumm