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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….

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Supersymmetry at the LHC: Status and a Thought or Two about the Future

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  1. 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

  2. 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

  3. 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!

  4. 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.

  5. 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

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

  7. A Striking Aspect of Nature: mtop >>> mbottom

  8. SUSY Successes III: Top Mass Higgs scalar potential contribution m2Humust 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]

  9. 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…

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

  11. 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…

  12. Strong vs. Electroweak Production However: if colored states are decoupled, EW production will dominate • Dedicated EW prod. analyses • Pure-EW simplified models STRONG COUPLING  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)

  13. 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” ICHEP 2016: SUSY with Photons and Taus

  14. 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

  15. The LHC

  16. ATLAS (and ~CMS) Luminosity Integration No Results yet Some Results Many Results

  17. The ATLAS Detector Non-prompt tracks Photon conversions

  18. CMS Detector

  19. 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”

  20. 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

  21. Here We Go… OK – Let’s Find SUSY!

  22. SUSY Cross Sections Obvious place to start: gluino production…

  23. 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

  24. 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.

  25. 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?

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

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

  28. 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”…

  29. 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

  30. 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…

  31. 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

  32. 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

  33. 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

  34. 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 (mTetc…)

  35. 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

  36. 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”)

  37. 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

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

  39. Highly Degenerate SUSY: the Monojet Analysis • Pure Etmisstrigger; 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

  40. 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!

  41. 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

  42. Diphoton + Etmiss Analysis (3.2 fb-1) • (mg,m) focuspoints 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

  43. 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

  44. 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 L H L H H Optimization reckoned by considering two points in each region (see “L” and “H” above)

  45. 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

  46. 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 GMSBmodel

  47. 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!

  48. Some Pet Projects at SCIPP

  49. Some Pet Projects at SCIPP

  50. Some Pet Projects at SCIPP

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