String Theory in the LHC Era

Transcription

1 String Theory in the LHC Era J Marsano (marsano@uchicago.edu) 1

2 String Theory in the LHC Era 1. Electromagnetism and Special Relativity 2. The Quantum World 3. Why do we need the Higgs? 4. The Standard Model 5. Physics Beyond the Standard Model and Supersymmetry 6. Einstein s Gravity 7. Why is Quantum Gravity so Hard? 8. String Theory and Unification 9. String Theory and Particle Physics 2

3 The Standard Model of Particle Physics Electromagnetism Quarks Strong nuclear force Leptons (electrons and neutrinos) Weak nuclear force 3

4 2012/04/25/what-particle-are-you/ 4 Hat tip R Lipscomb

5 Quantum Electrodynamics Weak Nuclear Force Photon e e Massless force carrier Long range force e e Weak bosons W ±,Z 0 Short range force Range set by Massive force carriers 1 Mass of W ±,Z 0 p + n W Quantum Chromodynamics e Gluons g Many massless force carriers Strongly coupled at long distances q g q q e q 5

6 The Standard Model of Particle Physics Electromagnetism Quarks Strong nuclear force Leptons (electrons and neutrinos) Weak nuclear force + Higgs Boson All particle masses from coupling to Higgs 6

7 The Standard Model of Particle Physics Quarks Electromagnetism Strong nuclear force Photon massless long range force Gluons massless but many of them confinement Leptons (electrons and neutrinos) Weak nuclear force W and Z bosons massive short range force Quark and lepton masses from Higgs + Higgs Boson All particle masses from coupling to Higgs 6

8 Beyond the Standard Model Why? 7

9 Standard Model doesn t incorporate gravity More on this in the remaining lectures... 8

10 Grand Unification Inverse electromagnetic coupling Inverse weak interaction coupling Inverse QCD coupling F. Wilczek, Nature 433, 239 Grand Unified Theory (GUT) that gives common origin to the three forces of the Standard Model? 9

11 Beyond the Standard Model Why? We will focus on two additional reasons: 1. Dark Matter 2. Hierarchy Problem 10

12 1. Dark Matter 11

13 Dark Matter Fritz Zwicky Stars near the edge of galaxies are rotating faster than they should New dark matter contributes to the gravitational field that accelerates the stars 12

14 Gravitational Lensing Can see dark matter more directly

15 Gravitational Lensing Can see dark matter more directly

16 Dark Matter also affects the Cosmic Microwave Background Key component of standard cosmology What does this mean for particle physics?

17 Standard cosmology: Dark Matter is a WIMP Weakly Interacting Massive Particle Couples to the weak interactions not to electromagnetism or the strong interaction

18 Standard cosmology: Dark Matter is a WIMP Weakly Interacting Massive Particle Couples to the weak interactions not to electromagnetism or the strong interaction Must be stable or have lifetime longer than the age of the universe (~ 10 billion years)

19 Standard cosmology: Dark Matter is a WIMP Weakly Interacting Massive Particle Couples to the weak interactions not to electromagnetism or the strong interaction Must be stable or have lifetime longer than the age of the universe (~ 10 billion years) There is no particle like this in the Standard Model

20 There is no particle like this in the Standard Model...but good reason to see it soon Early universe Dark matter in thermal equilibrium Standard Model Particles Dark Matter Particles Dark Matter Particles Standard Model Particles Standard Model particles collide to make dark matter Dark matter particles annihilate back to Standard Model

21 There is no particle like this in the Standard Model...but good reason to see it soon Standard Model Particles Dark Matter Particles Dark Matter Particles Standard Model Particles

22 There is no particle like this in the Standard Model...but good reason to see it soon Standard Model Particles Dark Matter Particles Dark Matter Particles Standard Model Particles As the universe expands, these reactions stop Roughly, particles too far apart for them to continue annihilating

23 There is no particle like this in the Standard Model...but good reason to see it soon Rate at which dark matter annihilates into Standard Model particles Dark 1 h vi m2 Dark g 4 Dark matter density

24 There is no particle like this in the Standard Model...but good reason to see it soon Rate at which dark matter annihilates into Standard Model particles Dark 1 h vi m2 Dark g 4 Dark matter density 0.1 for WIMP with m Dark 100 GeV

25 There is no particle like this in the Standard Model...but good reason to see it soon Rate at which dark matter annihilates into Standard Model particles Observed value Dark 1 Dark matter density h vi m2 Dark g for WIMP with m Dark 100 GeV

26 There is no particle like this in the Standard Model...but good reason to see it soon Rate at which dark matter annihilates into Standard Model particles Observed value Dark 1 Dark matter density h vi m2 Dark g for WIMP with m Dark 100 GeV Mass scales probed at the LHC

27 There is no particle like this in the Standard Model...but good reason to see it soon Rate at which dark matter annihilates into Standard Model particles Observed value Dark 1 Dark matter density h vi m2 Dark g for WIMP with m Dark 100 GeV Mass scales probed at the LHC The WIMP Miracle

28 Get the right (observed) amount of dark matter if we assume it is A WIMP with mass ~ GeV ~ Electroweak scale!

29 The WIMP Miracle Get the right (observed) amount of dark matter if we assume it is A WIMP with mass ~ GeV ~ Electroweak scale!

30 Dark Matter Searches Direct Detection Indirect Detection Look for dark matter colliding with heavy nuclei (Ge, I, Xe,...) Look for signs of dark matter annihilation in the sky

31 Direct Detection DAMA and CoGent see something but nobody else does

32 Indirect Detection Fermi Satellite Evidence for 130 GeV dark matter annihilation in galactic center? waiting for official analysis from Fermi/LAT collaboration C Weniger arxiv:

33 2. Hierarchy Problem 23

34 Hierarchy Problem Energy Scales GeV 10 2 GeV 1 GeV 10 3 GeV Quantum gravity 16 orders of magnitude Weak scale Proton mass Electron mass Where did this large scale separation come from? Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons 24

35 Hierarchy Problem Energy Scales GeV 10 2 GeV 1 GeV 10 3 GeV Quantum gravity 16 orders of magnitude Weak scale Proton mass Electron mass Where did this large scale separation come from? Why do we care? Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons 24

36 16 orders of magnitude Energy GeV Quantum gravity Electroweak Hierarchy 10 2 GeV 1 GeV 10 3 GeV Weak scale Proton mass Electron mass Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons Scale of electroweak symmetry breaking determined by Higgs physics Potential for Higgs field sets the scale of the Higgs bath Determined by quantum effects 25

37 16 orders of magnitude Energy GeV Quantum gravity Electroweak Hierarchy 10 2 GeV 1 GeV 10 3 GeV Weak scale Proton mass Electron mass Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons h t h Many important contributions, including top loop t 26

38 16 orders of magnitude Energy GeV Quantum gravity Electroweak Hierarchy 10 2 GeV 1 GeV 10 3 GeV Weak scale Proton mass Electron mass Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons h t h Many important contributions, including top loop t = 1 (Infinity)! 26

39 t h h = 1 (Infinity)! t Quantum Field Theory generates many infinities General Rule: 27

40 t h h = 1 (Infinity)! t Quantum Field Theory generates many infinities General Rule: Quantum Field Theory is smarter than we are If we get an infinite answer then we must have done something wrong 27

41 t Quantum Field Theory is smarter than we are h h If we get an infinite answer then we must have done something wrong t Ok so what are we doing wrong? 28

42 We always sum over histories t Richard Feynman h t h...so we allow virtual top quarks to carry arbitrarily high momenta/energies If we cap this energy at then the result is 2 The infinity comes precisely from the top quarks with very high energies 29

43 We always sum over histories t Richard Feynman h t h...so we allow virtual top quarks to carry arbitrarily high momenta/energies Do we really know what physics If we cap this energy at then the result is 2 looks like at such high energies? The infinity comes precisely from the top quarks with very high energies 29

44 We always sum over histories t Richard Feynman h t h...so we allow virtual top quarks to carry arbitrarily high momenta/energies Do we really know what physics If we cap this energy at then the result is 2 looks like at such high energies? The NO! infinity comes precisely from the top quarks with very high energies 29

45 t h h = 1 t We got a nonsense answer because we made an incorrect assumption Our formalism is not a good description of short distance (high energy) physics 30

46 What can we do? Parametrize our ignorance of short distance physics t h h + h h t New, unknown short distance physics Our old computation Controlled by new parameter Must be fixed by measurement 31

47 Infinities everywhere! Standard Model depends on many details of short distance physics Miracle of the Standard Model: Depends on short distance physics only through 19 parameters (particle masses and couplings) 32

48 If we could describe physics at all distance scales, we could compute all particle masses and interactions...but we do not know what is going on at very short distances The parameters of the Standard Model (masses and couplings) parametrize what we don t know about this short distance physics 33

49 Measured Parameter Values Standard Model Predictions 34

50 16 orders of magnitude Energy GeV Quantum gravity Measured Parameter Values 10 2 GeV 1 GeV 10 3 GeV Weak scale Proton mass Electron mass Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons Standard Model Predictions How sensitive are these large mass hierarchies to our parameter values? Question about robustness of the Standard Model 35

51 Hierarchy Problem Energy Scales GeV 10 2 GeV 1 GeV 10 3 GeV Quantum gravity 16 orders of magnitude Weak scale Proton mass Electron mass This hierarchy is not too sensitive to Standard Model parameters 36 Happens because the Standard Model effectively captures the physics that sets the proton mass

52 Energy GeV Quantum gravity The QCD Hierarchy is dynamically generated g g 1 GeV Proton mass q q + q q + QCD is strong at long distances u d u Strength determines size of proton (and its mass) p + 37

53 16 orders of magnitude Energy GeV Quantum gravity Measured Parameter Values 10 2 GeV 1 GeV 10 3 GeV Weak scale Proton mass Electron mass Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons Standard Model Predictions Hierarchy problem: The electroweak hierarchy is extremely sensitive to the input parameter values Our model for physics is not robust Suggests that essential features are missed 38 No explanation for Higgs bath in Standard Model

54 16 orders of magnitude Energy GeV Quantum gravity Measured Parameter Values Standard Model 10 2 GeV Weak scale Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons Predictions Hierarchy problem a matter of taste Maybe our world is just finely tuned...most physicists don t like this idea 39

55 Beyond the Standard Model Why? Gravity Neutrino mass Cosmology Dark matter Dark energy (related to gravity?) Matter/antimatter asymmetry Hints of Grand Unification Hierarchy problem 40

56 Many ideas for physics beyond the Standard Model We will focus on one: Supersymmetry 41

57 Coleman-Mandula Theorem Space-time and internal symmetries cannot be combined in any but a trivial way As with most No-Go theorems, this one has a loophole Supersymmetry 42

58 Supersymmetry is an extension of spacetime symmetry (rotations etc) that mixes particles of different spin Electron e Selectron ẽ Spin 1 2 fermion Spin 0 boson e e ẽ ẽ Supersymmetry same interaction strength 43

59 Supersymmetry Each Standard Model particle has a superpartner Top quark Gluon Stop squark Gluino Electron 44 Selectron

60 Minimal Supersymmetric Standard Model (MSSM) Howard Georgi Savas Dimopoulos Don t see superpartner particles (yet) Supersymmetry not an exact symmetry of nature 45

61 Minimal Supersymmetric Standard Model (MSSM) Supersymmetry is broken at some energy scale m SUSY Superpartner particle masses are around m SUSY No fundamental reason to expect m SUSY low enough to be accessible in near future If m SUSY 100 GeV can address many problems of Standard Model... 46

62 16 orders of magnitude Energy GeV Quantum gravity Hierarchy Problem t h h 10 2 GeV Weak scale Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons t Top loop Superpartner contributes with opposite sign Stop loop t~ Contribution of high energy tops canceled by high energy stops h h 47

63 t General Rule: h h t Supersymmetry causes infinities to cancel Top loop Reduces sensitivity to ultrashort distance physics Stop loop t~ h h 48

64 16 orders of magnitude Energy GeV Quantum gravity Hierarchy Problem 10 2 GeV Weak scale Higgs boson breaks electroweak symmetry Generates mass for W and Z bosons Supersymmetry also gives natural mechanism for generating Higgs potential at the scale m SUSY can explain electroweak hierarchy if m SUSY GeV 49

65 Dark Matter Natural symmetry that distinguishes particles and their superpartners R-parity + - conserved in all interactions and decays 50

66 Dark Matter If we make a superpartner particle in a collision......it may decay

67 Dark Matter If we make a superpartner particle in a collision......it may decay t Standard Model Particles Superpartner particle but there must be at least one superpartner particle in the final state 51

68 Dark Matter t Standard Model Particles Superpartner particle the Lightest Superpartner Particle (LSP) is stable! Dark Matter Candidate! 52

69 Supersymmetry and Grand Unification Inverse electromagnetic coupling F. Wilczek, Nature 433, 239 Inverse weak interaction coupling Inverse QCD coupling Grand Unification? + e e e e

70 Supersymmetry and Grand Unification Inverse electromagnetic coupling F. Wilczek, Nature 433, 239 Inverse weak interaction coupling Inverse QCD coupling Grand Unification? + e e e + e ẽ e e ẽ with supersymmetry

71 Supersymmetry and Grand Unification Inverse electromagnetic coupling Inverse weak interaction coupling Inverse QCD coupling Grand Unification? With supersymmetry at ~100 GeV, unification looks much better 54 F. Wilczek, Nature 433, 239

72 Supersymmetry is hypothetical but if present at ~100 GeV it can: Solve the hierarchy problem by generating mass for the W and Z bosons Provide a natural dark matter candidate of the right mass Improve the picture of Grand Unification 55

73 Searching for Supersymmetry Minimal Supersymmetric Standard Model (MSSM) has ~125 parameters Very complicated to do a systematic search of entire parameter space 56

74 What we see depends mostly on this Hidden Sector Supersymmetry Broken Here Messenger Sector Top quark Gluon Stop squark Gluino Gravity, Charged Messengers, etc Electron Selectron Minimal Supersymmetric Standard Model (MSSM) 57

75 What we see depends mostly on this Hidden Sector Supersymmetry Broken Here Messenger Sector Top quark Gluon Stop squark Gluino Gravity, Charged Messengers, etc Electron Selectron Messengers Supersymmetry breaking fields Minimal Supersymmetric Standard Model (MSSM) 57 Standard Model Particles

76 Simplest framework: msugra Replace125 parameters with 5 Spin Gaugino mass 2. Scalar mass 3. Trilinear A coupling 4. Tan β 5. Sign(µ) partners of force carriers Scalar partners of quarks, electrons, etc Interaction between squarks/sleptons and ganginos Higgs sector parameters 58

77 Experiments must think about many possibilities Signatures vary widely Supersymmetry not found yet but too soon to rule out RPV Long-lived particles DG Third generation Inclusive searches MSUGRA/CMSSM : 0-lep + j's + E T,miss MSUGRA/CMSSM : 1-lep + j's + E T,miss MSUGRA/CMSSM : multijets + E T,miss Pheno model : 0-lep + j's + E T,miss Pheno model : 0-lep + j's + E T,miss ± ± Gluino med. χ ( ~ g qqχ ) : 1-lep + j's + E T,miss GMSB : 2-lep OS + E SF T,miss GMSB : 1-τ + j's + E GMSB : 2-τ + j's + E T,miss T,miss GGM : γγ + E T,miss ~ 0 Gluino med. b ( ~ g bbχ ) : 0-lep + b-j's + E 1 T,miss ~ 0 Gluino med. t ( ~ g ttχ ) : 1-lep + b-j's + E 1 T,miss ~ 0 Gluino med. t ( ~ g ttχ ) : 2-lep (SS) + j's + E 1 T,miss ~ 0 Gluino med. t ( ~ g ttχ ) : multi-j's + E 1 T,miss ~ ~ ~ 0 Direct bb ( b χ ) : 2 b-jets + E T,miss ~ 1 b 1 Direct tt (GMSB) : Z( ll) + b-jet + E T,miss ± 0 0 Direct gaugino ( χ χ 3l χ ) : 2-lep SS + E T,miss ± 0 0 Direct gaugino ( χ χ 3l χ ) : 3-lep + E T,miss ± AMSB : long-lived χ Stable massive particles (SMP) : R-hadrons SMP : R-hadrons SMP : R-hadrons SMP : R-hadrons (Pixel det. only) GMSB : stable τ RPV : high-mass eµ Bilinear RPV : 1-lep + j's + E T,miss MSUGRA/CMSSM - BC1 RPV : 4-lepton + E T,miss m kl Hypercolour scalar gluons : 4 jets, m ij 1-1 L=4.7 fb -1 L=4.7 fb -1 L=4.7 fb -1 L=4.7 fb -1 L=4.7 fb -1 L=4.7 fb -1 L=1.0 fb -1 L=2.1 fb -1 L=2.1 fb -1 L=1.1 fb -1 L=2.1 fb -1 L=2.1 fb -1 L=2.1 fb -1 L=4.7 fb -1 L=2.1 fb -1 L=2.1 fb -1 L=1.0 fb -1 L=2.1 fb 118 GeV -1 L=4.7 fb (2011) [CF ] -1 L=34 pb -1 L=34 pb -1 L=34 pb -1 L=2.1 fb -1 L=37 pb -1 L=1.1 fb -1 L=1.0 fb -1 L=2.1 fb -1 L=34 pb ATLAS SUSY Searches* - 95% CL Lower Limits (Status: March 2012) (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ATLAS-CONF ] (2011) [ ] (2011) [ATLAS-CONF ] (2011) [ ] (2011) [ATLAS-CONF ] (2010) [ ] (2010) [ ] (2010) [ ] (2011) [ATLAS-CONF ] (2010) [ ] (2011) [ ] (2011) [ ] (2011) [ATLAS-CONF ] (2010) [ ] 170 GeV 136 GeV ~ ~ 1.40 TeV q = g mass -1 ~ ~ 1.20 TeV q = g mass Ldt = ( ) fb ~ s = 7 TeV 850 GeV g mass (large m 0 ) ~ ~ TeV q mass (m( g) < 2 TeV, light χ ) 1 ATLAS ~ ~ 0 g mass (m( q) < 2 TeV, light χ ) Preliminary 940 GeV 1 ~ 0 ± 1 0 ~ 900 GeV g mass (m( χ ) < 200 GeV, m( χ ) = (m( χ )+m( g)) 1 2 ~ 810 GeV g mass (tanβ < 35) ~ 920 GeV g mass (tanβ > 20) ~ 990 GeV g mass (tanβ > 20) ~ GeV g mass (m( χ ) > 50 GeV) 1 ~ GeV g mass (m( χ ) < 300 GeV) 1 ~ GeV g mass (m( χ ) < 150 GeV) 1 ~ GeV g mass (m( χ ) < 210 GeV) 1 ~ GeV g mass (m( χ ) < 200 GeV) 1 ~ GeV b mass (m( χ ) < 60 GeV) 1 ~ GeV t mass (115 < m( χ ) < 230 GeV) 1 ± 0 0 ± 0 ~ χ mass ((m( χ ) < 40 GeV, χ, m( χ ) = m( χ ), m( l, ν) = (m( χ ) + m( χ ))) ± GeV χ mass (m( χ ) < 170 GeV, and as above) 1 1 ± ± χ mass (1 < τ( χ ) < 2 ns, 90 GeV limit in [0.2,90] ns) 1 1 ~ 562 GeV g mass ~ 294 GeV b mass ~ 309 GeV t mass ~ 810 GeV g mass 185 GeV τ mass 760 GeV, ν τ mass (λ 311 =0.10, λ 312 =0.05) ~ q = ~ g mass (cτ LSP < 15 mm) ~ 1.77 TeV g mass 1.32 TeV < 100 GeV, m sg sgluon mass (excl: m sg 140 ± 3 GeV) *Only a selection of the available mass limits on new states or phenomena shown Mass scale [TeV] 59

78 SUMMARY The Standard Model is very successful but not complete No viable dark matter candidate No explanation of electroweak hierarchy Hierarchy problem is a question about robustness Calculations in Standard Model get infinities from short distance physics We don t know about physics at short distances...introduce model parameters (particle masses and interactions) to parametrize this ignorance Hierarchy problem: physics we see very sensitive to parameter choices Model not robust -- missing essential physics Supersymmetry solves many problems of Standard Model Lightest SuperPartner (LSP) is a dark matter candidate Cancellation of infinities removes strong dependence on short distance physics Dynamically generates Higgs bath that gives mass to all particles Improves Unifcation picture -- very suggestive Very challenging to look for supersymmetry at the LHC 60