Introduction: SUSY with 5 fb-1 at the LHC. Maxim Perelstein, LEPP/Cornell University May 2, 2012, BNL

Transcription

1 Introduction: SUSY with 5 fb-1 at the LHC Maxim Perelstein, LEPP/Cornell University May 2, 2012, BNL

2 Introduction: No SUSY with 5 fb-1 at the LHC Maxim Perelstein, LEPP/Cornell University May 2, 2012, BNL

3 No Evidence For Supersymmetry Has Been Discovered in the 2011 LHC Data

4 Questions for the Workshop Do we still think SUSY is a good candidate for TeVscale physics? (My personal opinion: Yes, I do. In fact my assessment of likelihood of TeV SUSY has not changed that much in 2011)

5 Questions for the Workshop Do we still think SUSY is a good candidate for TeVscale physics? (My personal opinion: Yes, I do. In fact my assessment of likelihood of TeV SUSY has not changed that much in 2011) How did 2011 data affect our ideas about how exactly SUSY might be realized? How should SUSY search strategies at the LHC be affected by these new ideas?

6 Central Question since ~1980 Electroweak Symmetry Breaking: Strong or Weak Coupling? Strong Coupling: fermion condensate breaks EW symmetry Just like in QCD, only higher scale ( technicolor ) Dimensional transmutation - no more surprising than Weak Coupling: a scalar field, the Higgs field, gets vev, breaks EW symmetry Calculable and testable: new spin-0 particle! Needs new physics at TeV to be natural, SUSY is the most elegant candidate

7 1990 s: Precision Electroweak Constraints Measurement Fit O meas!o fit /" meas #$ (5) had (m Z ) ± m Z [GeV] ± % Z [GeV] ± " 0 had [nb] ± R l ± A 0,l fb ± A l (P & ) ± R b ± R c ± A 0,b fb ± A 0,c fb ± A b ± A c ± A l (SLD) ± sin 2 ' lept eff (Q fb ) ± m W [GeV] ± % W [GeV] ± m t [GeV] ± strong hint for weakly-coupled EWSB, but with a caveat: new physics effects in loops might cancel

8 The Final Nail in the TechniCoffin? Zoom in:,-.$%&''$(+*/-)$ pper limits on SM Higgs boson production at the Tevatron Looks like a solid, direct hint for a new particle, consistent with a 125 GeV BFKAH*.

9 The Final Nail in the TechniCoffin? Zoom in:,-.$%&''$(+*/-)$ pper limits on SM Higgs boson production at the Tevatron Looks like a solid, direct hint for a new particle, consistent with a 125 GeV BFKAH*. * Boson Formerly Known As Higgs

10 SUSY and the 125 GeV Higgs Big picture: Light Higgs weaklycoupled EWSB hierarchy problem TeV-scale SUSY is by far the most elegant solution SUSY seems very likely! But, there are some unsettling details

11 Minimal Supersymmetric Standard Model (MSSM) Promote each SM field to a superfield + 1 extra Higgs doublet (needed for holomorphic masses, anomaly cancellation) Write most general superpotential + soft SUSY- breaking terms, imposing R-parity to avoid rapid proton decay (>100 new free parameters) FCNC and CPV constraints same soft masses for 1st and 2nd generations, no new phases pmssm (20 free parameters)

12 MSSM and the Higgs Mass In spite of this huge parameter space, MSSM is more predictive than the SM on the Higgs mass Reason: in the SM free parameter! In the MSSM (D-terms only!) Firm upper bound: However, this prediction has been falsified by LEP-2 more than 10 years ago! ( )

13 Loops to the Rescue! Loop-hole : the upper bound is tree-level, loop corrections can increase the Higgs mass However, there is a price to pay: Fine-Tuning! EWSB in the MSSM: If, need terms on the RHS to cancel precisely: fine-tuning! Problem: same loops that raise also raise

14 Aside: On Fine-Tuning Definition of fine-tuning: FT if Observable A clever model may correlate and in just the right way; Presumption of Guilt is a good start Other definitions (e.g. sensitivity to parameters) agree in most cases, though care is needed Different definitions may give numbers differing by order-one factors, but not order-ten Imperfect, but it is the only meaningful metric to impose on SUSY parameter space Contributions of different physical origin

15 Higgs and Top, Alone Together Higgs physics in the MSSM is to a good degree independent of most of the >100 parameters Higgs couples weakly, or not at all, to most SM fields TOP/STOP HIGGS SU(2)xU(1) Gauge Bosons/inos SU(3) Gluons/gluinos 1st/2nd Gen. (s)quarks, (s)bottom, (s)leptons So, a decent approximation is just consider Higgs +top alone few parameters, can build intuition

16 The Little Hierarchy Problem... Three soft parameters in the top sector: One-loop corrections to both and are proportional to linear combs. of these (*logs) rho parameter LEP-2 Higgs mass bound 1% fine-tuning 3% fine-tuning [Figure: MP, Spethmann, 07] A few % tuning at least is required for >114 GeV ( SUSY little hierarchy problem, a.k.a. the LEP Paradox )

17 ... Just Got a Little Bigger! 3000 Higgs Mass vs. Fine Tuning 3000 Lightest Stop Mass 2500 Suspect FeynHiggs 2500 Suspect FeynHiggs m t GeV m t GeV mh X t m t 200 With a 125 GeV Higgs, minimal fine-tuning in the Minimal stop mass is about 500 GeV 500 [Hall, Pinner, Ruderman, ] X t m t Figure 4: Contours of m h = 126 GeV in the MSSM as a function of a common stop mass m Q3 = m u3 = m t and the stop mixing parameter X t, for tan β = 20. The red/blue lines show the result from Suspect/FeynHiggs. The left panel shows contours of the fine tuning of the Higgs mass, MSSM mh, and we see that is 1% mh > 100 in order to achieve a Higgs mass of 126 GeV. The right panel shows contours of the lightest stop mass, which is always heavier than 500 GeV when the Higgs mass is 126 GeV. boost the Higgs to 126 GeV using the loop correction. The (well-known) problem is that heavy stops lead to large contributions to the quadratic term of the Higgs potential, δm 2 H u, δm 2 H u = 3y2 ( t m 2 8π 2 Q3 + m 2 U 3 + A t 2) ( ) Λ ln, (5) m t 500 m t1 where Λ is the messenger scale for supersymmetry breaking. If δm 2 H u becomes too large the

18 Beyond the Minimal: Next-to-MSSM Need to change the tree-level prediction for the Higgs mass Simple idea: add a singlet field, coupled via Tree-level expression for the (~SM) Higgs mass: Problem: runs, gets stronger at higher scales, hits a Landau pole No L.p. up to ; up to

19 R γγ =1.56 R WW =1.65 R bb =0.49 Table 1: A benchmark point in λ-susy with a large λ of 2 and a 126 GeV Higgs boson mass, The parameters are shown to the left and various masses, mixing angles, and phenomenologically relevant Higgs couplings are shown to the right. The Higgs boson mass is not fine-tuned relative to the fundamental parameters, mh 6. Here, the R i parameters represent the ratio of σ Br, relative to the SM, with σ corresponding to gluon fusion for the γγ and WW final states and associated Z/W + h production for h bb. which results from Higgs-singlet mixing. NMSSM Is Less Tuned Tan Β 2 Suspect FeynHiggs Suspect Tan Β 5 15 FeynHiggs m Χ m h m h mh m t GeV m t GeV X t m t ms GeV m 2 h 0 X t m t mh M s Gev 5 Tuning ~ 10% Figure 9: The Higgs mass in λ-susy Tuning varying the ~ singlet 20% supersymmetric mass, M S, and soft mass, m S. The Higgs mass contours are shown blue, contours of Higgs fine tuning, mh, are shown in red, and the region where the Higgs is tachyonic, due to Higgs-singlet mixing, is shown in purple. The fine tuning is increased when the Higgs mass drops, however, a Higgs mass of 126 GeV is achieved in a region of low fine tuning, mh 5. The orange region is where the lightest neutralino is lighter than half the Higgs mass, and in this region the Higgs would dominantly Figure 7: Contours of Higgs mass fine tuning, mh, in the NMSSM with the maximal value of λ =0!7 for tan β = 2 and 5, moving from left to right, with Q3 = u3 = t. Contours of h = 126 GeV are overlaid, including loop corrections from Suspect and FeynHiggs. When tan β = 2 the tuning can be low, mh 15, while for tan β = 5 heavier stop masses are required because the tree-level Higgs mass [Hall, is lower. decay Pinner, invisibly. Ruderman, ] dominates the tree-level mass. The λ term grows at small tan β, and this means that the largest Higgs mass is achieved with low tan β and as large λ as possible. Plugging in λ =0!7, we find that ( 2 h ) tree is always smaller than 122 GeV. 15 Because the tree-level contribution is insufficient to raise the Higgs mass to 126 GeV, we also

20 What About Superpartners? ) 1 fb -1 summary =<ST!""#$%&'() *'+', -./ +'0**'1%2 ' =<ST Bottom line: gluino/squark mass bounds are above 1 TeV

21 Is Supersymmetry in Trouble? Higgs mass parameter renormalization: Two possibilities: Natural Higgs with New Physics (e.g. SUSY) at Fine-Tuned Higgs with the tree and loop terms and precise cancellation between Superpatrner mass scale plays the role of the scale Is SUSY already being pushed from natural into fine-tuned territory?

22 SCIENCE & ENVIRONMENT 27 August 2011 Last updated at 02:41 ET LHC results put supersymmetry theory 'on the spot' By Pallab Ghosh Science correspondent, BBC News Results from the Large Hadron Collider (LHC) have all but killed the simplest version of an enticing theory of sub-atomic physics. Researchers failed to find evidence of so-called "supersymmetric" particles, which many physicists had hoped would plug holes in the current theory.

23 But Wait a Second... This argument is a bit too fast! = Higgs-X coupling constant, = # of d.o.f. in X Recall: Most SM fields couple only weakly, or not at all, to the Higgs! TOP/STOP HIGGS SU(2)xU(1) Gauge Bosons/inos SU(3) Gluons/gluinos 1st/2nd Gen. (s)quarks, (s)bottom, (s)leptons

24 The real one-loop naturalness upper bound on the mass of SUSY partner of particle X is not 1 TeV, but For 1st, 2nd gen. squarks, sbottom, sleptons, this bound is 10 TeV or more. For stop, it s in fact lower: required for (complete) naturalness is NB: since left-handed top and bottom are in the same SU(2) doublet, their superpartners must be close in mass one light bottom is required. There s no one-loop upper bound on gluino mass: However two-loop naturalness requires (Majorana gluinos) (Dirac gluinos) [Brust, Katz, Lawrence, Sundrum, 11]

25 SUSY In the Era of Austerity NWSNX m H GeV O&:%/.CB%2(4#C#PQRR#'"&:!-",#ELSTESNLEE =+(6(/#P"'(++(#C#>R=Y Left Handed Stop Sbottom ATLAS 2 4 j, 1.04 fb 1 CMS Α T, 1.14 fb 1 CMS H T MET, 1.1 fb 1 D0 b b, 5.2 fb 1 m bl m H m tl GeV Ascetic SUSY spectrum is 200 completely consistent with the fb-1 constraints, and helps with SUSY flavor problem [GeV] 0 1 χ m ATLAS 200 D0 b Preliminary b, 5.2 fb 2-lepton SS, 4 jets m H GeV ~ g - ~ g production, ~ g ttχ m~ q 1,2 Right Handed 0 Stop 1 ATLAS CLs observed 2 4 j, limit 1.04 fb 1 CLs expected limit CMS Expected Α T, CLs 1.14limit fb 1 ±1σ CMS H T MET, 1.1 fb lepton plus b-jets 2.05 fb >> m~ > m~ t g 1 0 ttχ g ~ 1 forbidden m tr m H m~ [GeV] g m tr GeV L dt = 2.05 fb -1, s=7 TeV 1 Maximum cross section [pb] Figure 2: Expected and observed 95% C.L. exclusion limits in the g t t χ 0 1 (via off mass-shell t, m t = 1.2 TeV) simplified model as a function of the gluino and neutralino Figure 3: masses, Expected together and observed 2#/4%7.22'2F%8/?%GH'>%:'9#?.3-:/%BI)%J'KC%% 7.22'2@%AA%B-:%?'>C%.:>%(1D'#%B-:%(39'C%3-7-#2%% with existing 95% C.L. exclusion limits in the phenomenological MSSM as a functionof ofthe the figure. gluino The and upper stop.:>%;$.?=-:/%b*!)%j'kc%7.22'25%%% production masses assuming that m χ limits [26]. The lower part of the ±1σ band lies outside the range ± 1 = 2m χ 0 ;/,'?%;/743'7':#.?E%?'=-/:2%/8%4.?.7'#'?%%. The lower part of the ±1σ band lies 1 cross section limits at 95% C.L. are also shown. outside the range of the figure. ev] 650 ~ ~ ~ g - ~ g production, ~ g t t 1 +t, 1 b+ χ ATLAS Preliminary ± 1 L dt = 2.05 fb -1, CLs observed limit CLs expected limit s=7 TeV [GeV] m χ ~ g - ~ g production, ~ g tt χ 0 1 CLs observed limit CLs expected limit Expected CLs limit ±1σ 1 lepton plus b-jets 2.05 fb ATLAS Preliminary 2-lepton SS, 4 jets m~ q 1,2 >> m~ > m~ g t 1 0 ttχ g ~ 1 forbidden m~ [GeV] L dt = 2.05 fb -1-1, s=7 TeV Figure 2: Expected and observed 95% C.L. exclusion limits in the g t t χ 0 1 (via off mass-shell t, m t = 1.2 TeV) simplified model as a function of the gluino and neutralino masses, together with existing limits [26]. The lower part of the ±1σ band lies outside the range of the figure. The upper production cross section limits at 95% C.L. are also shown. [GeV] t 1 m~ ~ ~ ~ g - ~ g production, ~ g t t 1 +t, 1 b+ χ ATLAS Preliminary 2-lepton SS, 4 jets m 0 = 60 GeV χ 1 m ± 2 m 0 χ χ m~ 1 q 1,2 1 >> m~ g 0 χ g ~ tt 1 ± 1 forbidden [GeV] g L dt = 2.05 fb -1, CLs observed limit CLs expected limit Expected CLs limit ±1σ 1 lepton plus b-jets 2.05 fb %%%%%%%%%%%%%%%%%%%%%%%%%%%%,-.%/012$'33%2#/45%%!g!g! tt! 0 tt! 0!g!g! t!tt!t! tb! ± tb! ± 6-7-#%.2%.%89:;</:%/8%=39-:/%.:>%% 6-7-#2%.2%.%89:;</:%/8%=39-:/%.:>%:'9#?.3-:/% 24.;'5%%% m~ g s=7 TeV regions, limits have been derived in the context of simplified models where top quarks are produced in gluino decays and MSUGRA/CMSSM scenarios. In all these signal models, gluino masses below -1 1 Maximum cross section [pb] [Cohen, Kaplan, Nelson, 95]

26 Ascetic-SUSY Search Example: Boosted Tops from Gluino Decays Most gluinos decay via tops: For typical allowed parameters, most tops are relativistic: e.g. Hadronic top decays top jets! Use recently developed top-jet tagging capabilities, search for events with top-jets+met (in gluino rest frame) m t GeV [Berger, MP, Saelim, Spray, 11] LHC, 5 Σ 95 CL expected exclusion m g m t m t s 14 TeV, L int 10 fb m g GeV FIG. 3: The 95% c.l. expected exclusion and 5-sigma discovery reach of the proposed search at the 14 TeV LHC run with 10 fb 1 integrated luminosity. Errors Stat.-only; S/B>10 everywhere signal events to pass these cuts in a data set of 10 fb 1, and with S/B = 27.5 the expected statistical significance of observation is 6.5. The reach of a search with these parameters is shown in Fig. 3. Discovery is possible up to TeV gluino masses with stops in the GeV mass range. In this case, S/B > 10 throughout the discovery region. Given how effective the top tagging technique is in sup-

27 Impact on Models of SUSY-Breaking So far, all discussion was in the context of the MSSM (>100 par.) or pmssm (20 par.): all soft SUSY-breaking terms treated as free parameters Deeper theory: understand how SUSY is broken, predict soft terms (or at least reduce the number of parameters) Modular structure Hidden Mediator Visible (MSSM) NO UNIQUE BEST MODEL (despite > 20 yrs of trying). Some ideas: Gravity mediation: Gauge mediation:

28 Impact on Models of SUSY-Breaking So far, all discussion was in the context of the MSSM (>100 par.) or pmssm (20 par.): all soft SUSY-breaking terms treated as free parameters Deeper theory: understand how SUSY is broken, predict soft terms (or at least reduce the number of parameters) Modular structure Hidden Mediator Visible (MSSM) NO UNIQUE BEST MODEL (despite > 20 yrs of trying). Some ideas: TOO SIMPLE? Gravity mediation: Gauge mediation:

29 Generating Ascetic SUSY Basic point: 3rd generation of quarks already looks special, why not 3rd generation of squarks? A Warped 5D example: Accidental SUSY [Gherghetta, Pomarol, 03] SUSY broken at UV scale elementary SUSY X ( ẽ e ) A µ, λ ( t t ) composite X H, H ( ψ φ ) e ( 1 2 c)ky bulk mass parameter Fermion mass spectrum determines sparticle spectrum! UV IR Low-energy SUSY spectrum t, H ( f 1,2, λ decouple) KK spectrum m (n) f m (n) f n =1, 2,...

30 Generating Ascetic SUSY Don t like 5D? Use AdS/CFT to construct a 4D dual - composite 3rd generation! [Csaki, Randall, Terning, 11] Or, just plain old deconstruction H u,h d 10 1,5 1 G A G B 10 3, ,5 2 [Craig, Green, Katz, 11] [Craig, Dimopoulos, Gherghetta, 12]

31 Super-Ascetic Supersymmetry? Recall: To lower fine-tuning needed to get a 125 GeV Higgs, extend MSSM to NMSSM with large : say ( -SUSY) The old EWSB formula still works: But now is not an input parameter, but a vev of the singlet field S need to solve for it! When expressed in terms of Lagrangian parameters, Tuning suppressed by, stop bound raised from 400 GeV to 1.2 TeV! So, NO colored superpartners below TeV are required for naturalness!

32 Low-MET ( Stealthy ) SUSY Experiments place significant MET cuts to suppress SM backgrounds ) 1 fb -1 summary In SUSY events with X production, For example: no bound on gluino from MET+jets if No strong degeneracies in the spectrum are required - pretty generic possibility, not a hole! Very important to explore this region: lower MET cuts? ISR tagging?

33 No-MET SUSY: Visible (N)LSP In the MSSM, ANY superpartner can be the LSP: neutral LSP NOT predicted Motivation for neutralino LSP is cosmological: good dark matter candidate, strong bounds on electrically charged and colored relics However: many other good DM candidates (e.g. axion); charged/colored bounds rely on untested assumption of standard cosmology before BBN If LSP is gravitino, NLSP lifetime is basically a free parameter (with cosmological bound <1 sec) NLSP may travel and decay in any part of the detector, or outside SUSY searches for stable/quasi-stable charged/colored LSP are just as important as the standard MET searches, should be pursued with equal vigor! [Example: Graham, Kaplan, Rajendran, Saraswat, 12]

34 No-MET SUSY: R-Parity Violation R-Parity is a discrete symmetry that s not required by SUSY, but imposed in most models to forbid operators leading to super-fast proton decay R-parity is responsible for stability of the LSP much of SUSY phenomenology t s b s There are OTHER WAYS to stop proton from decaying: e.g. impose lepton or baryon number conservation, or confine R-violation to 3rd generation Resulting theories have very long-lived proton but unstable LSP no MET or stable exotics! Example: Approximate, accidental R-parity follows from minimal flavor violation hypothesis for the MSSM (which is needed anyway to avoid FCNCs) bl br t [See the talk by Josh Berger tomorrow] [Csaki, Grossman, Heidenreich 12]

35 CONCLUSIONS 2011: SUSY searches at the LHC have begun in earnest Possible Higgs discovery overall good news for SUSY 125 GeV Higgs requires 1% tuning in Minimal SUSY model non-minimal scalar sector? Lack of superpartner discovery is not yet too worrisome: we re just getting started

36 CONCLUSIONS Several ways to accommodate current bounds, with no fine-tuning required: Ascetic SUSY: minimal sub-tev spectrum Low-MET SUSY: modest spectrum degeneracy (~30% is sufficient) No-MET SUSY: RPV or quasi-stable (N)LSP Not holes : all are generic in MSSM (unless specific SUSY-breaking schemes are assumed)

37 Looking Forward to 2012 Definitive data on the Higgs Dedicated ascetic SUSY search results (this Friday?) RPV/Quasi-stable NLSP searches? New data-driven theory ideas on SUSY breaking?

38 Looking Forward to 2012 Definitive data on the Higgs Dedicated ascetic SUSY search results (this Friday?) RPV/Quasi-stable NLSP searches? New data-driven theory ideas on SUSY breaking? SUSY DISCOVERY?