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75th Compton Lectures: String Theory in the LHC Era J. Marsano Lecture 5: Physics Beyond the Standard Model and Supersymmetry Beyond the Standard Model? • Why do we need physics beyond the Standard Model? • The Standard Model does not describe gravity • Hints of Grand Unification • Two more issues that we discuss in detail • Dark Matter • ’Hierarchy problem’ Dark Matter • Stars at the edges of galaxies are moving too fast • Cannot be explained from gravitational pull of visible matter alone • Zwicky proposed additional ’dark matter’ that contributes its own gravitational field • Doesn’t couple to electromagnetism so we don’t readily see it • Dark matter can be observed through ’lensing’ effects where its gravitational field bends the light from distant objects • The standard model of cosmology requires about 23% of the energy in the universe to be comprised of dark matter Cartoon of Dark Matter Halo of a spiral galaxy • Precision tests in Cosmic Microwave Background observations 75th Compton Lectures: String Theory in the LHC Era J. Marsano Detecting Dark Matter • The abundance of dark matter that we see today is naturally explained by a simple model where • Dark matter particle is a WIMP, meaning – Wearly Interacting Massize Particle – Couples to W and Z bosons of Weak Interactions – Neutral under electromagnetism and strong interactions Fermi Satellite • The dark matter mass ∼ 100-1000 GeV – mZ ∼ 91 GeV and mW ∼ 80 GeV → Dark matter mass ∼ Weak scale • WIMP Must be stable or have lifetime longer than the age of the universe (10 billion years) • No such particle in the Standard Model • Many ways to see WIMPs • Production at LHC – WIMPs may be directly produced in proton-proton collisions at the LHC • Indirect Detection • Direct Detection • Balloon and satellite experiments look for dark matter produced by cosmic rays and signs of dark matter annihilation in space – Look for dark matter collisions with heavy nuclei (Ge, I, Xe, etc) – Some experiments (DAMA, CoGeNT) reporting a positive signal – Others (CDMS, Xenon, etc) don’t see it–no consistent picture yet – The Fermi satellite may have seen evidence of dark matter annihilation in the galactic center! The Hierarchy Problem • What sets scale of W and Z boson masses? • Connected to physics of Higgs field and, more specifically, the dynamics that generates the ’Higgs bath’ that gives masses to particles • Where does the scale 100 GeV come from? Why so different from the fundamental scale of quantum gravity? • Why do we even care about this? 75th Compton Lectures: String Theory in the LHC Era J. Marsano Infinities in the Standard Model • Importance of Hierarchy Problem related to infinities–look closer at those • The ’Higgs bath’, along with the scale of W and Z masses, is determined by a dynamically generated potential for the Higgs field • This potential is determined by quantum effects involving interactions of the Higgs field with Standard Model particles • When we compute quantum corrections to Higgs potential, we get infinite answers • Quantum field theory is smarter than us • If we get a nonsense answer, we must have done something wrong • When we ’sum over histories’, we include all possible top quark energies/momenta • Implicitly assumes that we understand physics at very short distance scales (very high energies) • Infinity comes from very high energy top quarks so it is a sign that this assumption is wrong! • We do not know the physics at short distance scales so all we can do is parametrize our ignorance • Introduce new local interaction to model unknown short distance physics • Comes with a parameter that must be fixed by measurement 75th Compton Lectures: String Theory in the LHC Era J. Marsano The Hierarchy Problem Revisited • The Standard Model is miraculous • It only depends on unknown short distance physics through a finite number of parameters (19) • These parameters are the particle masses, interaction strengths, etc • A fundamental description of physics at all energy scales would determine the masses and interaction strengths from first principles. In the Standard Model these are parameters that reflect our ignorance of physics at short distance scales • Once we make a finite number of measurements (19), the Standard Model can make predictions • We can now state the Hierarchy problem more cleanly: • The W and Z masses depend very sensitively on the parameters that we use to characterize short distance physics → The model is not robust – As with any model, ultrasensitivity to input parameters is a sign that essential features are not properly understood Why New Physics at the LHC? • Need something like Higgs below a few TeV (i.e. few 1000’s of GeV) • Suggestion of dark matter at 100-1000 GeV • Evidence already in Fermi data? • ’Natural’ solution to hierarchy problem requires new physics around 100-1000 GeV • Many signs point to TeV scale physics! 75th Compton Lectures: String Theory in the LHC Era J. Marsano Supersymmetry • Supersymmetry (SUSY) is a nontrivial extension of space-time symmetries (rotations, etc) that relates particles of different spin • If a spin 12 electron e− couples to electromagnetism, there must be a spin 0 particle, the selectron ẽ− , with exactly the same coupling to electromagnetism • The Minimal Supersymmetric Standard Model (MSSM) adds a superpartner like the selectron for each ordinary particle • Superpartners not seen (yet) so SUSY not an exact symmetry of nature • Can address issues of Standard Model if SUSY is broken around 100-1000 GeV Supersymmetry and the Hierarchy Problem • For each Standard Model contribution to a computation, one gets additional superpartner contributions • Superpartners contribute with an opposite sign relative to Standard Model particles so bad behavior like infinities cancel between diagrams • Removes ultra-sensitivity of Higgs potential on short distance physics • Not a complete solution because we must understand why supersymmetry is broken at 100-1000 GeV • Nevertheless supersymmetry provides a possible physical origin of electroweak symmetry breaking and the electroweak scale 75th Compton Lectures: String Theory in the LHC Era J. Marsano Supersymmetry and Dark Matter • Supersymmetric models often come with a new symmetry, R-parity, that distinguishes Standard Model particles from their superpartners • A superpartner cannot decay to only Standard Model particles. Another superpartner must always be among the decay products • The Lightest SuperPartner (LSP) has nothing to decay into – it is stable! • Natural dark matter candidate! Supersymmetry and Grand Unification • Superpartners contribute quantum corrections that determine the strengths of electromagnetism, weak interactions, and strong interactions • Adding superpartners at 100-1000 GeV substantially improves the unification picture – very suggestive! Looking for Supersymmetry • Organize searches based on simplified scenarios for how supersymmetry-breaking is communicated to the MSSM MSUGRA/CMSSM : 1-lep + j’s + E T ,miss L =4.7 fb (2011) [ATLAS-CONF-2012-041] L =4.7 fb (2011) [ATLAS-CONF-2012-037] L =4.7 fb (2011) [ATLAS-CONF-2012-033] GMSB : 1-τ + j’s + E 1 Third generation -1 940 GeV L =4.7 fb (2011) [ATLAS-CONF-2012-033] 900 GeV -1 810 GeV L =1.0 fb (2011) [ATLAS-CONF-2011-156] -1 L =2.1 fb (2011) [ATLAS-CONF-2012-002] -1 -1 T ,miss T ,miss ∼± χ ∼0 → 3l χ ∼0) : 3-lep + E Direct gaugino (χ T ,miss 1 2 1 ∼± AMSB : long-lived χ 1 -1 1 ~ ∼ ) < 300 GeV) g mass (m(χ 1 ~ ∼0 g mass (m(χ1 ) < 150 GeV) ~ ∼0 ) < 210 GeV) g mass (m(χ 900 GeV -1 L =2.1 fb (2011) [ATLAS-CONF-2012-003] 710 GeV -1 650 GeV L =2.1 fb (2011) [ATLAS-CONF-2012-004] 0 1 ~ ∼0 830 GeV g mass (m ( χ ) < 200 GeV) 1 ~ ∼0 ) < 60 GeV) b mass (m(χ 1 ~ 0 ∼ -1 L =2.1 fb (2011) [ATLAS-CONF-2012-036] 310 GeV t mass (115 < m ( χ ) < 230 GeV) 1 ~∼ 1 ∼± ∼0 ∼0 ∼± ∼0 ∼0 ∼0 -1 L =1.0 fb (2011) [1110.6189] 170 GeV χ mass (( m ( χ ) < 40 GeV,χ , m ( χ ) = m ( χ ), m ( l,ν ) = ( m ( χ ) + m ( χ ))) 1 1 1 1 2 1 2 2 ∼± ∼0 -1 L =2.1 fb (2011) [ATLAS-CONF-2012-023] 250 GeV χ mass (m ( χ ) < 170 GeV, and as above) 1 1 118 GeV ∼± ± ∼ -1 χ mass (1 < τ(χ ) < 2 ns, 90 GeV limit in [0.2,90] ns) L =4.7 fb (2011) [CF-2012-034] -1 L =4.7 fb (2011) [ATLAS-CONF-2012-037] -1 L =2.1 fb (2011) [1112.3832] 390 GeV 1 L =34 pb (2010) [1103.1984] SMP : R-hadrons L =34 pb (2010) [1103.1984] 1 -1 562 GeV -1 294 GeV -1 309 GeV L =34 pb (2010) [1103.1984] -1 -1 L =37 pb (2010) [1106.4495] L =1.1 fb (2011) [1109.3089] Bilinear RPV : 1-lep + j’s + E T ,miss L =1.0 fb (2011) [1109.6606] 136 GeV ~ g mass ~ b mass ~ t mass 810 GeV L =2.1 fb (2011) [ATLAS-CONF-2012-022] RPV : high-mass eµ Hypercolour scalar gluons : 4 jets, m ij ≈ m kl ~ ∼0 ) > 50 GeV) g mass (m(χ 805 GeV L =1.1 fb (2011) [1111.4116] L =2.1 fb (2011) [ATLAS-CONF-2012-003] Stable massive particles (SMP) : R-hadrons SMP : R-hadrons SMP : R-hadrons (Pixel det. only) GMSB : stable ∼τ 1 ~ ∼0 ∼± ∼0 ~ g mass (m(χ1 ) < 200 GeV,m(χ ) = 1(m(χ )+m(g)) 2 ~ g mass (tanβ < 35) ~ 920 GeV g mass (tanβ > 20) ~ 990 GeV g mass (tanβ > 20) -1 L =4.7 fb (2011) [ATLAS-CONF-2012-041] L =2.1 fb (2011) [ATLAS-CONF-2012-005] MSUGRA/CMSSM - BC1 RPV : 4-lepton + E T ,miss • Too early to ’rule out’ TeV scale SUSY -1 T ,miss ~ ∼0) : 0-lep + b-j’s + E Gluino med. b (~ g→bbχ T ,miss 1 ~ ∼0) : 1-lep + b-j’s + E Gluino med. t (~ g→t t χ T ,miss 1 ~ ∼0) : 2-lep (SS) + j’s + E Gluino med. t (~ g→t t χ T ,miss ~1 ∼0) : multi-j’s + E Gluino med. t (~ g→t t χ T ,miss 1 ~~ ~ ∼0) : 2 b-jets + E Direct bb (b1→ bχ T ,miss 1 ~~ Direct t t (GMSB) : Z(→ll) + b-jet + E T ,miss ∼± χ ∼0 → 3l χ ∼0) : 2-lep SS + E Direct gaugino (χ 1 2 1.20 TeV -1 T ,miss ∫ 1.40 TeV -1 Pheno model : 0-lep + j’s + E T ,miss Pheno model : 0-lep + j’s + E T ,miss ∼± (~ ∼± ) : 1-lep + j’s + E Gluino med. χ g→ qqχ T ,miss GMSB : 2-lep OSSF + E T ,miss ~ ~ q = g mass Ldt = (0.03 - 4.7) fb-1 ~ ~ q = g mass ~ s = 7 TeV 850 GeV g mass (large m 0 ) ~ ~ ∼0 1.38 TeV q mass (m ( g) < 2 TeV, light χ ) ATLAS 1 0 ~ ~ ∼ Preliminary g mass (m(q) < 2 TeV, light χ ) -1 MSUGRA/CMSSM : multijets + E T ,miss GGM : γ γ + E DG • Collider signatures vary significantly across the parameter space – systematic searches difficult L =4.7 fb (2011) [ATLAS-CONF-2012-033] GMSB : 2-τ + j’s + E Long-lived particles • Many fixed by current observation but complicated parameter space remains RPV • The MSSM has ∼ 125 new parameters Inclusive searches ATLAS SUSY Searches* - 95% CL Lower Limits (Status: March 2012) MSUGRA/CMSSM : 0-lep + j’s + E T ,miss ∼τ mass -1 760 GeV -1 -1 ∼ mass (λ =0.10, λ =0.05) ν τ 311 312 ~ ~ q = g mass (cτLSP < 15 mm) ~ 1.77 TeV g mass 1.32 TeV L =2.1 fb (2011) [ATLAS-CONF-2012-035] L =34 pb (2010) [1110.2693] ~ g mass , -1 185 GeV 10-1 sgluon mass (excl: msg < 100 GeV, msg ≈ 140 ± 3 GeV) 1 10 *Only a selection of the available mass limits on new states or phenomena shown Summary of ATLAS SUSY searches Mass scale [TeV]