The Quest for the Origin of Mass

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The Quest for the Origin of Mass The concept of Mass in Physics Classical: Newton, Einstein Quantum: matter waves, fields Standard Model: iggs mechanism Standard Model iggs Searches LEP: status

1 The Quest for the Origin of Mass The concept of Mass in Physics Classical: Newton, Einstein Quantum: matter waves, fields Standard Model: iggs mechanism Standard Model iggs Searches LEP: status Tevatron: status and prospects LC: prospects ATLAS and Canada Beyond the SM: Supersymmetry Conclusions University of British Columbia Vancouver, B.C., Canada 14 March Michel Lefebvre Physics and Astronomy University of Victoria Michel Lefebvre UBC, 14 March 1

2 The Quest for the Origin of Mass Abstract The concept of mass is at the very heart of physics. In Newtonian mechanics, mass appears as a primary characteristic of any physical object. But the concept of mass becomes more elusive, less fundamental, in modern formulations of the laws of nature. The Standard Model (SM) of particle physics offers a very successful description of the interactions of the fundamental constituents of matter at the smallest scales and highest energies accessible to current experiments. A key ingredient, yet unverified, of the SM is the iggs mechanism, responsible for the generation of the W and Z mass, themselves responsible for the apparent weakness of the weak force. Within the SM, it is their interaction with the iggs field that gives rise to the mass of quarks and charged leptons. An experimentally important by-product of the iggs mechanism is the predicted existence of the iggs particle. Its search is central to many particle physics efforts, and crucial to our understanding of the origin of mass. After a review of the concept of mass, the SM and the iggs mechanism, the status of searches for the SM iggs particle (LEP and Tevatron) are briefly summarized, and prospects for future discoveries (Tevatron and LC) are discussed. Canadian activities on the ATLAS detector at the LC are also described. Michel Lefebvre UBC, 14 March

Mass and Newton The concept of mass lies

appears as a primary characteristic of any

3 Mass and Newton The concept of mass lies at the heart of Newtonian physics F F = ma= = GMm r dp dt nd Law Law of Universal Gravitation Sir Isaac Newton Mass appears as a primary characteristic of any physical object Michel Lefebvre UBC, 14 March 3

4 Lagrangian Formulation of Mechanics Consider a (non relativistic) particle. All the information about its motion is given by its Lagrangian Lagrangian = v L( x ) i, xi, t i = 1,, 3 xi i S = dt L action δ S= amilton s principle: Euler-Lagrange equation: For a free particle, experiment shows that i i i i equations of motion d L L = dt x x symmetry of L conservation law x x = x + a p= constant t t = t+ t E = xi x i = Aijxj T A A= I L= constant j Michel Lefebvre UBC, 14 March 4 i i constant L = 1 mv defines m!

5 E p = γmc = γmv Mass and Einstein E = pc = E ( ) ( ) pc + mc v c γ 1 ( v ) c 1/ m = E = pc and v = c massless particles carry momentum!! E E = mc m = c equivalence of mass and energy!! L Albert Einstein E x momentum conservation M box v v = E c Isolated system: CM fixed! M L x = M x x= v t = L v v + c pulse ( ) M c = pulse Mass now appears less basic, not so irreducible E box Michel Lefebvre UBC, 14 March 5

6 Equivalence Principle: Newton Einstein Mass and Einstein The response of a body to gravitation is independent of its mass GM a = independent of m! r ν ν π ν R 1 g R = 8 G 4 T c palace of gold curvature of space-time hovel of wood energy-momentum of matter and radiation This is where masses of particles occur raw Can mass be replaced by something finer? Michel Lefebvre UBC, 14 March 6

7 Mass and Quantum Mechanics Radiation and Matter really are particulate Their dynamics is given by a quantum theory where waves associated with the particles give us a measure of the probability of the state of the particles de Broglie - Einstein The waves follow wave equations, e.g. Schrödinger equation Dirac equation Maxwell equations E = hν = ω p = h = k λ non relativistic particle ± e γ What is waving?? One can learn about the structure of a crystal by studying e - diffraction λ = h p = 1.3A for K = 1 ev even if the electrons are sent one at at time!! Where is the mass of the electron? Michel Lefebvre UBC, 14 March 7

8 Wave Equation (non relativistic) Free particle plane wave: ( ω ) ψ exp i t kx Identify the following operators: ˆψ = Eψ ˆ = i t pˆψ = pψ pˆ = i x E = hν = ω p = h = k λ Boldly go from particular to general: Schrödinger equation 1 p E = mv + V = + V i ψ = + V m t m x ψ Michel Lefebvre UBC, 14 March 8

9 Free particle plane wave: p = k We use the relativistic energy-momentum relation Wave Equation (relativistic) ( ψ exp ik x exp i k x k x) = pˆ ψ = p ψ pˆ = i = i x E = pc + mc p p = mc ( ) ( ) ( ) Klein-Gordon equation p p ( ) ˆ ˆ mc = p p ( mc) ϕ ( x) = Dirac equation p γ mc= c ( m ) ϕ ( x) + = ν ν ν ν γ, γ γ γ + γ γ = η ( ) γ ψ ( ) p p mc = i mc x = From now on we use the natural units = c = 1 Michel Lefebvre UBC, 14 March 9 + ν η 1 = 1 1 1

10 Wave Equation (relativistic) Maxwell equation F = F A A ν ν ν ν ( A ) ν ν or A = Maxwell equation is invariant under the gauge (local) transformation A x A F ν ( ) ( φ, ) ( x) ν 1 3 E E E E B B = E B3 B1 E B B ( ) A A = A + f f x 3 1 Lorentz gauge: A = A ν p = p = Each component of the free field A follows a massless Klein-Gordon equation! Proca equation G + m Z = G Z Z ν ν ν ν ( m ) ν or + Z = Z = always. No gauge invariance Each component of the free field Z follows a Klein-Gordon equation! Michel Lefebvre UBC, 14 March 1

11 Mass and Quantum Field Theory The primary elements of reality are fields Particles are quanta of excitations of fundamental fields Particles acquire the properties of the field charge (global phase invariance) spin (field behavior under Lorentz transformation) mass ALL electrons and positrons are quanta of excitations of ONE Dirac field electrical charge ±e, spin 1/, same mass What does the mass of a field mean? Michel Lefebvre UBC, 14 March 11

12 Lagrangian Formulation We now consider the Lagrangian density of a field L S ( ψ, ψ, x ) Lagrangian density =,1,, 3 = 4 d x L amilton s principle: δ S= Euler-Lagrange equation: action equations of motion L L = ( ψ ) ψ ( ) ( ) m Free Klein-Gordon: LKG = ϕ ϕ ϕ ϕ spin global symmetry of L conservation law x x = x + a p = =Λ Λ ηλ= η = ν T ν x x x M Michel Lefebvre UBC, 14 March 1 constant ν constant spin iε ϕ ϕ ϕ constant = e Q= the number of particles is not constant! of the field!!

13 Free Dirac: Lagrangian Formulation D i m L = ψ γ ψ ψ ψ γ spin 1/ global symmetry of L conservation law ψ ψ = ψ i e ε Q = constant 1 ν Free Maxwell: M = F F gauge (local) symmetry of L L spin 1 4 ν ( ) A A = A + f f x Free Proca: 1 1 P = 4G ν G m Z ν + Z L spin 1 no local symmetry of L : the mass term violates gauge invariance! Michel Lefebvre UBC, 14 March 13

14 Gauge Invariance and the EM Interaction Consider the interaction between the Dirac field and Maxwell field Free Dirac field LD = ψ iγ m ψ ψ ψ γ ε i ψ ψ = e ε ψ invariant under global phase transformation Free Maxwell field L 1 ν M = 4 F F F ν ( x) A ν ν A ν A A = A + f f x invariant under gauge transformation ( ) Impose Dirac field local phase, U(1) Q gauge, invariance to the theory!!! Obtain 1 ν with = + L = ψ iγ D m ψ 4 F F D iqa ν invariant under the gauge transformations The interaction is obtain from D M int ( x) iε ( x) ε ψ ψ = e ψ A A A L = L + L + L L int = qψγ A ( x) 1 ε = + q The requirement of U(1) Q gauge invariance couples both fields and prescribes the form of the interaction!! QED Michel Lefebvre UBC, 14 March 14 ψ ε

Most of the Mass Quarks come in three colours We require the strong colour interaction to be invariant under an SU(3) C gauge QCD mediated by gluons Gluons carry colour!

15 Most of the Mass Quarks come in three colours We require the strong colour interaction to be invariant under an SU(3) C gauge QCD mediated by gluons Gluons carry colour! confinement only colour singlets can exist freely QCD with massless u and d quarks predicts the mass of the proton to about 1%! m = E again! energy of gluons and quarks in baryons Protons and neutrons make up over 99% of the mass of ordinary matter... We are getting closer to mass without mass! Michel Lefebvre UBC, 14 March 15

16 Weak Interaction We want to obtain the weak interaction from a gauge principle But the weak interaction is mediated by massive particles, and boson mass terms violate gauge invariance... Furthermore, the weak interaction violates parity! Charged weak interaction is only felt by chiral-left particles chiral-right antiparticles Experiment maximal chirality violation Massless particles Massive particles mass term mixes chirality Michel Lefebvre UBC, 14 March 16 d d u W ν e e - u d u ν e W e - - ν chirality = helicity is Lorentz invariant chirality helicity spin flip! ψψ = ψ ψ + ψ ψ negative chirality (eigenvalue of γ 5 ) L R R L handedness e - disfavoured e - spin e - spin e - favoured Chirality and mass are not friendly neighbours Chiral gauge invariance SU() L violated by ALL mass terms! - spin

17 We want: gauge invariance to generate interactions We need: gauge invariant mechanism to generate mass hidden symmetry (spontaneous symmetry breaking ) Consider a model where the equilibrium state is not unique nature makes a choice, hiding the invariance of the theory equilibrium state: all fields null, except one ϕ(x) Lorentz invariance ϕ(x) is a scalar Goldstone model: consider L V ( ) ( = ϕ ϕ) V ( ϕ) ( ) ( ) Goldstone Model ϕ = ϕ ϕ + λ ϕ ϕ λ > Michel Lefebvre UBC, 14 March 17 ( ) < Self-interacting Klein-Gordon field where m = > V ( ) v ϕ = ϕ = ϕ = > min The equilibrium is characterized by v 4 λ Nature spontaneously chooses, say, always possible because of global U(1) phase invariance ϕ = v eiθ V ϕ < v θ= ϕ = > ϕ(x) is a complex scalar λ > ϕ

18 Goldstone Model (continued) [ ] σ x and η We write ( ) 1 ϕ x = + σ( x) + iη( x) v where ( ) ( x ) deviation of ϕ(x) from equilibrium. We get L L We can interpret: and n.d.f do add up ( )( ) ( )( ) σ σ σ η η = + + L 1 1 ( ) ( ) 1 = λvσ σ + η λ σ + η int 4 1 real Klein-Gordon field m = real Klein-Gordon field = σ η Initially: complex ϕ After : real massive real massless σ η m η n.d.f 1 1 measure the int Goldstone boson field No truly massless Goldstone bosons are observed in nature We need a hidden symmetry mechanism that does not generate physical massless Goldstone bosons π, π +, π - come pretty close... Michel Lefebvre UBC, 14 March 18

iggs Model Generalize the Goldstone model to be invariant under U(1) gauge transformation D = + iqa Obtain < L Invariant under ( ) ( ) 1 ν = D ϕ D ϕ 4 F Fν V ( ϕ) ( ) ( = + ) > V ϕ ϕ ϕ λ ϕ ϕ λ ( x)

19 iggs Model Generalize the Goldstone model to be invariant under U(1) gauge transformation D = + iqa Obtain < L Invariant under ( ) ( ) 1 ν = D ϕ D ϕ 4 F Fν V ( ϕ) ( ) ( = + ) > V ϕ ϕ ϕ λ ϕ ϕ λ ( x) iε ( x) ε ϕ ϕ = e ϕ A A A ( x) 1 ε = + q Scalar electrodynamics with self-interacting Klein-Gordon field where m v min > λ > V( ϕ) = ϕ = ϕ = 4 The equilibrium is characterized by ϕ = v eiθ Nature spontaneously chooses, say, always possible because of global U(1) phase invariance again, use [ ] ( ) 1 ϕ x = + σ( x) + iη( x) v v ε v θ= ϕ = > = iggs 199- Michel Lefebvre UBC, 14 March 19

20 iggs Model (continued) Obtain L = σ σ σ + η η 4 F ν F + qv A A + qv η A + L ( )( ) ( )( ) ν ( ) ( ) can interpret but cannot interpret σ real Klein - Gordon field m = and n.d.f would NOT add up L contains an unphysical field which can be eliminated through a gauge transformation yielding the form 1 η(x) η real Klein-Gordon field m = A real Proca field M = qv [ ] ϕ( x) = + σ( x) Initially: After : v unitary gauge would-be Goldstone boson field Aaarg! Michel Lefebvre UBC, 14 March 1 η complex ϕ real massless A real massive σ 1 real massless η 1 A n.d.f real massive A 3 4 5! int

21 iggs Model (end) In this gauge, we obtain 1 1 ν 1 L = σ σ σ F F + qv A A + can interpret and n.d.f do add up ( )( ) ( ) 4 ν int 4 1 m σ real Klein-Gordon field = A real Proca field M = qv The massless Goldstone boson field η(x) has disappeared from the theory and has allowed the A (x) field to acquire mass!! L Initially: After : Michel Lefebvre UBC, 14 March 1 A ( v ) = λvσ λσ + qaa σ + σ complex ϕ real massless A real massive σ 1 n.d.f real massive A 3 σ(x) is a iggs boson field vector boson acquires mass without spoiling gauge invariance iggs mechanism...and we get a prescription for the interactions between σ and A! L int 4 4

iggs Mechanism A room full of physicists chattering quietly is

.. a well-known scientist walks in, creating a disturbance as he

acquires mass, just like a particle moving through the iggs

.. it creates the same kind of clustering, but this time among

22 iggs Mechanism A room full of physicists chattering quietly is like space filled with the iggs field... a well-known scientist walks in, creating a disturbance as he moves across the room and attracting a cluster of admirers with each step... this increases his resistance to movement, in other words, he acquires mass, just like a particle moving through the iggs field... if a rumor crosses the room... it creates the same kind of clustering, but this time among the scientists themselves. In this analogy, these clusters are the iggs particles Michel Lefebvre UBC, 14 March ATLAS educational web page, adapted from an idea from Dr D. J. Miller

in the electroweak sector iggs mechanism: U(1) Y SU() L U(1) Q Residual (non-hidden)

23 The Standard Model of Electroweak and Strong Interactions Gauge invariance U(1) Y SU() L SU(3) C Glashow 193- Salam Weinberg Spontaneous symmetry hiding in the electroweak sector iggs mechanism: U(1) Y SU() L U(1) Q Residual (non-hidden) symmetry: U(1) Q SU(3) C massless photons massless gluons Michel Lefebvre UBC, 14 March 3

24 fermions bosons The Standard Model particle content leptons quarks U(1) Y SU() L SU(3) C iggs doublet ν e e u d B W 1 W W 3 g 1-8 ϕ 1 +iϕ ϕ 3 +iϕ 4 ν c s EW ν t τ t b γ W + W - Z g /3-1/3 electroweak strong matter radiation Michel Lefebvre UBC, 14 March 4

25 SM iggs Interactions SM iggs mechanism with U(1) Y SU() L gauge ϕ(x) is a complex doublet W +, W -, Z acquire mass left with one massive iggs boson ( ) 1/ = 46 GeV ϕ(x) coupling with massless fermion fields fermion masses f γ charged f v = G F iggs couplings proportional to mass igmf ν M W coloured igm W g W + W - γ g g W + W - g = 4 G M igm Zg cosθ F Z W ν W Z Z Z Michel Lefebvre UBC, 14 March 5

26 SM iggs Decays Fat! 1 bb _ WW ZZ opens up BR() ZZ 1-1 τ + τ cc _ tt - gg 1 - γγ Zγ WW opens up M [GeV] due to c reduced running mass Michel Lefebvre UBC, 14 March 6

27 Theoretical Constraints on M M is a free parameter of SM but it must lie in a limited region for electroweak symmetry hiding to work m M is too large: the higgs selfcoupling blows up at some scale Λ = λ( m ) v λ New physics perturbativity vacuum stability 13 GeV < M < 18 GeV then, in principle consistent with Λ=M PL V(φ) Λ M is too small: the higgs potential develops a second (global!) minimum values of the scalar field of the order of Λ ν Λ E φ New physics Michel Lefebvre UBC, 14 March 7

28 Winter Experimental Constraints on M enters into loops Global fits to precision EW data where M is the only unconstrained parameter.7 M < 196 GeV (95% CL) Michel Lefebvre UBC, 14 March 8

29 Large Electron Positron Collider DELPI L3 OPAL ALEP Michel Lefebvre UBC, 14 March 9

30 LEP Data Sets and SM iggs Production e - iggstrahlung e + Z Z Fusion e - e + W - W + n e n e for example at -9 GeV we get, for a 115 GeV mass iggs, 1.5 pb pb = 11 events produced! Michel Lefebvre UBC, 14 March 3

31 SM iggs Topologies Michel Lefebvre UBC, 14 March 31

32 iggs Reconstructed Mass Distribution stronger cuts LEP iggs Working Group M > 114 CL Signal hypothesis yields a mass of 116 GeV, but only about σ above background LEP is now dismantled, to install the LC When will we know if LEP really detected a iggs? Michel Lefebvre UBC, 14 March 3

The Tevatron at Fermilab pp collider Run I s = 1.8 TeV 6+6 bunches, 3.5 s 1.6 1 31 cm - s -1 pb -1 week -1 per exp. Run IIa s =.

33 The Tevatron at Fermilab pp collider Run I s = 1.8 TeV 6+6 bunches, 3.5 s cm - s -1 pb -1 week -1 per exp. Run IIa s =. TeV bunches, 396 ns start March 1st 1 goal, by end 1 3 cm - s -1 > fb -1 per exp. Run IIb s =. TeV more bunches, 13 ns goal, by end cm - s -1 >15 fb -1 per exp. Michel Lefebvre UBC, 14 March 33

34 SM iggs Production at the Tevatron M.Spira E. Barberis typical cross-sections ( s = TeV) gg W Z σ[pb] (m =1 GeV) WZ 3. Wbb 11 tt 7.5 tb+tq+tbq 3.4 QCD O(1 6 ) W/Z production are preferred Michel Lefebvre UBC, 14 March 34

35 SM iggs Searches at the Tevatron CDF PRELIMINARY Run I CDF: SVX b-tagging W ννbb 1 and b-tag W lνbb 1 and b-tag Z ννbb 1 and b-tag Z llbb 1 b-tag σ(pp - V) BR( bb) - (pb) % C.L. upper limits - - ll bb lν - - bb qq - - bb νν - - bb V combined 1-1 Standard Model iggs Mass (GeV/c ) one order of magnitude away from prediction Michel Lefebvre UBC, 14 March 35

36 SM iggs Discovery at the Tevatron per experiment E. Barberis and hep-ph/ fb -1 by end 7? fb -1 by end? LEP searches EW fits fb -1 95% CL barely extend the LEP result 1 fb -1 95% CL exclusion to M 18 GeV in the absence of signal 15 fb -1 discovery potential for up to M 115 GeV Michel Lefebvre UBC, 14 March 36

37 Aerial View of CERN Michel Lefebvre UBC, 14 March 37

38 Large adron Collider at CERN pp collider s = 14 TeV Michel Lefebvre UBC, 14 March 38

Large adron Collider at CERN pp collider s = 14 TeV 835+835 bunches, 5 ns octan test in 4 ring cooled by end 5 beam for physics 6 1 33 cm - s -1 after 7 months latest: 1 fb -1 by March 7 expect 1 fb

8K to Reach Ultimate Field of 9 Tesla Quench Number MBPO1.T1 MBPO1.T MBPO1.T3 MBPO1.T4 B nominal = 8.36 Tesla B ultimate = 9T First Th. Cycle Second Th. Cycle Third (Fast) Th.

39 Large adron Collider at CERN pp collider s = 14 TeV bunches, 5 ns octan test in 4 ring cooled by end 5 beam for physics cm - s -1 after 7 months latest: 1 fb -1 by March 7 expect 1 fb -1 /y for first 3 years design: cm - s -1, 1 fb -1 /y ATLAS pit July 1 Magnetic Field at Quench B [Tesla] Extract of Natural Training Quenches at 1.8K to Reach Ultimate Field of 9 Tesla Quench Number MBPO1.T1 MBPO1.T MBPO1.T3 MBPO1.T4 B nominal = 8.36 Tesla B ultimate = 9T First Th. Cycle Second Th. Cycle Third (Fast) Th. Cycle 5 superconducting magnets (196 dipoles) Cu-clad Nb-Ti cables to operate at 1.9K with up to 15kA Dipole field of 8.36T (Tevatron 4.5T, ERA, 5.5T) Contracts for all main components of dipoles are now placed and series production has started. L.R. Evans, Scientific Policy Comitte, CERN, 11/1/ LC: 5 E and 1k L of SPS for same power Michel Lefebvre UBC, 14 March 39

40 Space, Time and the Energy Frontier Michel Lefebvre UBC, 14 March 4

41 The ATLAS Detector Alberta Carleton CRPP Montréal SFU Toronto TRIUMF UBC Victoria York UVic graduates J. White (M.Sc. 93) S. Robertson (M.Sc. 94) S. Bishop (M.Sc. 95) D. O Neil (Ph.D. 99) D. Fortin (M.Sc. ) M. Dobbs (Ph.D.) T. Ince (M.Sc.) V. Singh (M.Sc.) Michel Lefebvre UBC, 14 March 41

42 Canada and ATLAS Activities focused on Liquid Argon Calorimetry 4 Major Projects Funded by Major Installation Grants Endcap adronic Calorimeter Forward adronic Calorimeter Frontend-Board Electronics Endcap Signal Cryogenics Feedthroughs New Initiatives ATLAS Computing ATLAS OO Software Alberta Carleton CRPP Montréal SFU Toronto TRIUMF UBC Victoria York Other Activities Radiation ardness Studies Pixel Detector Contribution Physics Studies Michel Lefebvre UBC, 14 March 4

Toronto TRIUMF UBC Victoria York One of many

43 Canada and ATLAS in pictures Endcap calorimeter rotator at CERN Alberta Carleton CRPP Montréal SFU Toronto TRIUMF UBC Victoria York One of many endcap calorimeter modules Michel Lefebvre UBC, 14 March 43

Toronto TRIUMF UBC Victoria York Forward calorimeter

44 Canada and ATLAS in pictures Forward calorimeter module 1 under construction Alberta Carleton CRPP Montréal SFU Toronto TRIUMF UBC Victoria York Forward calorimeter module under construction Michel Lefebvre UBC, 14 March 44

45 igh density endcap signal feedthroughs Canada and ATLAS in pictures Alberta Carleton CRPP Montréal SFU Toronto TRIUMF UBC Victoria York ATLAS LAr electronic frontend board Michel Lefebvre UBC, 14 March 45

SFU Toronto TRIUMF UBC Victoria York view of the endcap

46 Canada and ATLAS in pictures testing the insertion of the FCAL in the endcap cryostat Alberta Carleton CRPP Montréal SFU Toronto TRIUMF UBC Victoria York view of the endcap cryostat and feedthrough ports Michel Lefebvre UBC, 14 March 46

47 ATLAS Multi-purpose pp detector designed to exploit the full discovery potential of the LC Designed to operate at high luminosity and at initial lower luminosities Designed to be sensitive to many signatures e, γ,, 1 34 jet, cm miss E T and to more complex signatures, like top and heavy flavour from secondary vertices LC PP Cross Section s 1, b - tagging,... σ pp (14TeV) 1mb 1b 1nb 1pb 15 1 inelastic Events for 1 fb -1 (one year at 1 33 cm - s -1 ) bb QCD jets (P T > GeV) W eν Z ee t t = 175 GeV) (m t iggs SUSY m = 1 GeV m = GeV m = 8 GeV m(g) m(q) 1 TeV Michel Lefebvre UBC, 14 March 47

48 SM iggs Production at the LC (one year at 1 34 cm - s -1 ) g g t t t q q,q W,Z W,Z q q,q g g t t t t q q W,Z Michel Lefebvre UBC, 14 March 48 W,Z

49 Main SM iggs Search Channels Large QCD backgrounds: σ σ ( bb) ( bb) 5 b pb M =1 GeV, direct production No hope to trigger on or extract fully hadronic final states Look for final states with photons and leptons Detector performance is crucial: b-tag, γ/l E-resolution, γ/j separation, missing energy resolution, forward jet tag,... Michel Lefebvre UBC, 14 March bb _ BR() τ + τ cc _ gg γγ Zγ WW M [GeV] M < tt l γγ M Z ZZ WW bb + X 4l l ZZ ν l M > M Z ZZ 4l ZZ l l ν ν ZZ l l j j WW l ν j j ν tt - large backgrounds low branching ratio Gold-plated channel! M > 3 GeV forward jet tag

50 Events / GeV Signal γγ background (irreducible) QCD jet background m γγ (GeV) Signal-background, events / GeV γγ at ATLAS σ BR = 43 fb (m = 1 GeV) dσ 1 fb/gev (mγγ = 1 GeV) dmγγ σγ,j σ (reducible) σ γγ m (GeV) signal events γγ background γ - jet, jet - jet background Statistical significance j,j, σγγ m γγ (GeV) σ σ σ Analysis: Two isolated γ s: p T1 >4 GeV, p T >5 GeV, η <.5 Good γ/jet separation: QCD jet background at the level of 1 to % of the irreducible γγ background Good mass resolution: σ m =1.3 GeV for m =1 GeV Michel Lefebvre UBC, 14 March 5

51 ATLAS SM iggs Discovery Potential LEP LEP SM iggs can be discovered over full mass range with 3 fb -1 In most cases, more than one channel is available. Signal significance is S/B 1/ or using Poisson statistics Michel Lefebvre UBC, 14 March 51

52 LC SM iggs Discovery Potential need 1 fb -1 for 5σ 115 GeV iggs discovery (during 7?) larger masses is much easier! Michel Lefebvre UBC, 14 March 5

53 SM iggs Mass and Width Michel Lefebvre UBC, 14 March 53

54 Beyond the Standard Model In principle, if 13 GeV < M < 18 GeV then the SM is viable to M PL But, SM one loop corrections M = ( M ) + bg Λ b O( 1) ( M ) is parameter of fundamental theory The natural value for M is gλ, which leads to the expectation M Λ O g ( 1TeV) If Λ >> 1 TeV, need unnatural tuning ( M ) M Λ g If Λ=M PL, need adjustment to the 38 th decimal place!!! = Violation of naturalness = hierachy problem Low-energy supersymmetry is a way out... Λ Beware what seems unnatural today... Not the only way out extra dimensions! Michel Lefebvre UBC, 14 March 54

55 Supersymmetry } Maximal extension of the Poincaré group SUSY actions are invariant under superpoincaré Lorentz pure 3D rotations boosts Poincare superpoincare 4D translations SUSY translations they are composed of an equal number of bosonic and fermionic degrees of freedom SUSY mixes fermions and bosons exact SUSY there should exist fermions and bosons of the same mass clearly NOT the case SUSY IS BROKEN WY BOTER WIT SUSY?? A solution to the hierarchy problem If the iggs is to be light without unnatural fine tuning, then (softly broken) SUSY particles should have M SUSY < 1 TeV. SUSY can be viable up to M PL AND be natural! GUT acceptable coupling constant evolution The precision data at the Z mass (LEP and SLC) are inconsistent with GUT s using SM evolution, but are consistent with GUT s using SUSY evolution, if M SUSY 1 TeV A natural way to break EW symmetry The large top Yukawa coupling can naturally drive the iggs quadratic coupling negative in SUSY Lightest SUSY particle is a cold dark matter candidate Local SUSY is SUperGRAvity Michel Lefebvre UBC, 14 March 55

56 UBC, 14 March Michel Lefebvre 56 Minimal SUSY iggs Sector MSSM: SM + an extra iggs doublet + SUSY partners SUSY breaking g W W W B l l ν q q q q g W W W B l l ν q q q q L R L u L u R d L d R u u d d L R L u L u R d L d R u u d d g W W γ Z l l ν q q q q g χ χ χ χ χ χ χ χ l l ν q q q q h A L R l u L u R d L d R l u 1 u d 1 d EW symmetry breaking CP odd CP even 5 massive iggs particles, with M h < 13 GeV At tree level, all iggs boson masses and couplings can be expressed in terms of two parameters only (in constrained MSSM ) vev vev tanβ and m d u A =,q q,q q l, l l, l χ,, W, B χ, W γ,z W, B 1 R L 1 R L 1,,3,4 d u 1, ± ± ± Note that we also have the following mixings with off-diagonal elements proportional to fermion masses

ATLAS MSSM iggs Search Full parameter space covered, SM and MSSM can be distinguished for almost all cases Most part of the parameter space covered by at

57 ATLAS MSSM iggs Search Full parameter space covered, SM and MSSM can be distinguished for almost all cases Most part of the parameter space covered by at least two channels, except low m A region (covered by LEP) Discovery of heavy iggses (m A > 5 GeV) seem to be difficult (top modes) Michel Lefebvre UBC, 14 March 57

58 Fundamental Mass Values Experimental values or limits The SM does not say anything about the origin of the VALUES of the masses They have to be obtained from EXPERIMENT exception: photons and gluons are predicted to be massless Why such a large range of fundamental masses? Indirect searches yield very small neutrino masses why are neutral fermions so light? mγ < 1 5 GeV Michel Lefebvre UBC, 14 March 58

59 Mass without mass? Conclusions The SM iggs sector still requires direct experimental verification Origin of electroweak symmetry hiding Origin of mass LEP results tantalizing M 116 GeV M > 114 CL if signal hypothesis valid σ Must now wait for the Tevatron and the LC If M 115 GeV both Tevatron and LC may discover it in 7 If M larger then LC rules Strong Canadian participation in ATLAS New physics at O(1 TeV) very likely, supersymmetry is a big favorite This is going to be a very exciting decade! Michel Lefebvre UBC, 14 March 59

The Quest for the Origin of Mass: Status of Higgs Particle Searches

The Quest for the Origin of Mass: Status of iggs Particle Searches Mass and the Standard Model of Particle Physics iggs mechanism University of Victoria Victoria, B.C., Canada 8 March Standard Model iggs