The Origin of Mass. Understanding the Higgs Mechanism. of Mass Generation at. Marco Battaglia. TESLA Colloquium DESY, Hamburg, March 2001

Transcription

1 DESY, amburg, 23- Understanding the iggs Mechanism of Mass Generation at Marco Battaglia CERN Geneva on behalf of the Study Page 1

2 and the iggs Mechanism LEP 1 σ hadron SM: s / s >.1 SM: s / s > s [GeV] V(Φ) Φ What gives mass to matter? Is mass an intrinsic property or the effect of particle interactions? ow is mass accounted for in the present picture of particle physics? Which data are available, which crucial experimental tests are planned, how can we get answers at the TESLA collider? Page 2

3 : Setting a Problem Since electron discovery, physics has unveiled a rich variety of particles, determined their quantum numbers, probed their structure and interactions LEP log(l) 5 σ hadron Events/(1 GeV/c 2 ) M top (GeV/c 2 ) SM: s / s >.1 SM: s / s > s [GeV] Reconstructed Mass (GeV/c 2 ) Present picture characterised by apparently disconcerting range of masses for matter (fermion) and force (boson) particles (M t /M e =35): Matter Particles ν e u d µ s τ c b t Force Particles γ g W Z Mass (GeV) Page 3

4 Understand the Origin of Mass: A Modern Scientific Quest Newton established the relationship between Weight and Mass: F w = Mg and Einstein that between Energy and Mass: E = Mc 2...but so far the Origin of Mass question has been left unanswered: Matter Particles Standard Model does not explain the pattern of matter particle masses and their origin; These need to be determined experimentally and count for the majority of SM free parameters; Force Particles Observed difference in strength of weak and electro-magnetic interactions explained by actual pattern of force particle masses: while Gauge symmetry requires mass-less force particles. Page 4

5 The mechanism of Mass generation through Field Coupling: 1957: Fermion masses: Schwinger: a coupling will produce effective mass terms through the action of the vacuum fluctuations : Boson masses: iggs; Englert and Brout: Page 5

6 The iggs Mechanism of Mass Generation Introduce (one doublet of) scalar fields Φ (iggs field) that acquires a non-zero strength = v/ 2 at the ground state: iggs Potential V (Φ Φ) = λ(φ Φ 1 2 v2 ) 2 Vacuum Vacuum V(Φ) Φ = Evolution of iggs potential and field strength at ground state with Temperature points to symmetric configuration in the Early Universe; iggs field Φ to permeate the space and give mass to force and matter particles through its interaction: one iggs boson witness of the inset of the iggs mass generation mechanism. M f = g ff v M V = gv 2 M = 2λv Φ Φ Page 6

7 iggs Mechanism and Superconductivity: An Analogy γ At T<T c Cooper pairs collective effect cancels material resistivity and expels an external magnetic field; Magnetic field penetration depth in superconductor λ c =1 6 m Equivalent to photons mediating the electro-magnetic field to have acquired a mass M γ =1/λ c Z/W iggs condensate permeate the space and cancels W and Z fields within a depth: λ W,Z =1/M W,Z c m and equivalently the W/Z bosons acquire mass M W,Z =1/λ W,Z c. Page 7

8 Supersymmetry and the iggs Sector The appearance of fundamental scalar fields becomes natural in theories with one-to-one correspondence between matter and force particles (SUperSYmmetry) that protect the value of v from corrections from higher scales Λ >> v (= 246 GeV 1 17 M Pl ). SUSY theories require at least two iggs doublets: oneproviding mass to up-type and the other to down-type quarks: Minimal Supersymmetric extension of SM 1 Doublet 2 Doublets 4-3 d.o.f = 1 Boson ( ) 2 4-3d.o.f. =5Bosons(h,, A, ± ) vacuum < Φ >= v/ 2 vacua v 1, v 2, tan β = v 2 v 1 SUSY iggs Phenomenology characterised by 5 iggs bosons and shifted values of iggs-fermion couplings g ff w.r.t. fermion masses M f. Page 8

9 β + - iggs Boson Discovery Tevatron LC TESLA iggs Couplings LC TESLA ATLAS Determine Mass and Quantum Numbers M 2 =2 λ v 2 LC TESLA g ff /g FF =M f /M F J PC = ++ SM iggs Branching Ratio 1 1 bb ττ gg cc 1 2 WW γγ M (GeV) iggs Potential TESLA multi TeV LC + Extended iggs Sector h, A,,, e+e >Z >ff ff 7 g ff Indirect + - (a) LC e e o A o tb tb 4 TESLA LC (b) 6 8 M = M A = 3 GeV M = 3 GeV 3 1 γγ 8 GeV 1 ab >/A >bb 2 5 A 6 tt TESLA 4 1 e+e >+ >tbtb 4 fermions e+e >A >bbbb multi TeV LC LEP mh max 2 Summer M (GeV) A Reconstructed Mass (GeV) Reconstructed mass (GeV) tan g =3 λ v Events/1 GeV V( Φ) Events / 1 GeV λ from M λ from g Φ Page 9

10 χ 2 The Way to Probe the iggs Mechanism LEP+SLD+LEP2 Precise Electroweak Data δρ iggs log M 2 M 2 W theory uncertainty α (5) had =.2761± ±.2 Direct Searches at LEP-2 in e + e Z b bf f at s 29 GeV provided events consistent with iggs decays at M 115 GeV: ALEP DALI_F1 ECM=26.7 Pch=83. Efl=194. Ewi=124. Eha=35.9 BEOLD Run=54698 Evt=4881 Nch=28 EV1= EV2= EV3= ThT= :32 Detb= E3FFFF 5 Gev EC 5 Gev C (φ 138)*SIN(θ) o o xo o o ox o x o x oo ox o x o o x x x x o Excluded 1 2 m [GeV] Preliminary P>.5 Z<1 D<2 F.C. imp. SM MSSM (M+1)SSM SUSY RO TPC.3cm.6cm Y" 1cm 1cm X" o o o o o x x o x o x x o o o 15 GeV x θ=18 θ= Indirect and Direct Indications of light iggs with M 3 GeV µ o o x Page 1

11 The Way to Establish the iggs Mechanism TheTevatronandtheLC gg fusion WW/ZZ fusion LC to provide break-through in understanding the origin of mass by observing iggs boson over its γ γ tt ( bb) allowed mass range, ZZ (*) 4 l WW (*) lνlν 1 if couplings std. 2 ZZ llνν WW lνjj Signal significance Total significance at LC 1 5 σ 1 ATLAS LC 1 L = 3 fb TEVATRON 1 L = 1 fb m (GeV) Page 11

12 The Way to Establish the iggs Mechanism Is it really the iggs? After discovery, verify that iggs mechanism does its job of providing other particles with their masses; LC experiments to obtain first data on iggs couplings to fermion and boson particles g ZZ, g WW, g tt : M (GeV/c 2 ) δ(x)/x LC ATLAS+CMS 2 3 fb 1 M M g ZZ g WW 16.5 g t t g WW g b b g WW g W /g W (SM) MSSM prediction: m = 12 GeV 2 GeV < L m A L < 3 GeV 1 GeV L < m A L < 2 GeV MSSM prediction: 3 GeV L < m A L < 1 GeV LC 1σ g top /g top (SM) Page 12

13 A istorical Digression: The Case of the W /Z Bosons End of 7s: Structure of Standard Model predicts the W and Z vector bosons, at M W =(79±2) GeV and M Z =(89±2) GeV; 1981: Formal approval of the e + e LEP collider with s 91 GeV; 1982: First observation of the W and Z by UA1 and UA2 at the Sp ps; 1989: Start of LEP and SLC; 2: Completion of LEP Program. sin 2 θ W vs. M W EW Test: sin 2 θ W Summer 1989 sin 2 θ lept eff Summer 2 m m t = ± 5.1 GeV m = GeV M W (GeV) α Preliminary m t 68% CL M W [GeV] Page 13

14 The iggs Landscape at the TESLA LC Number of Events / 1.5 GeV 2 1 Data Z µµ X m = 15 GeV Recoil Mass [GeV] Events/1 fb g b /g b (SM) MSSM prediction: 2 GeV < m A < 4 GeV 4 GeV < m A < 6 GeV GeV < m A < 8 GeV 8 GeV < m A < 1 GeV LC 95% CL LC 1σ m = 12 GeV light Quark Tag c Quark Tag b Quark Tag g c /g c (SM) TESLA Linear Collider to provide powerful probe of the iggs mechanism Large statistics to achieve high statistical accuracy and to access low probability configurations Specific kinematics of iggs boson production in e + e collisions to guarantee model independent study of iggs properties ighly granular detector and tolerable backgrounds to provide accurate reconstruction of iggs boson production and decay properties Page 14

15 e Z Λ e e + W Λ W Λ p s = GeV ν e μν e The Way to Establish the iggs Mechanism The TESLA LC iggs Events year 1 e + ab (e + e ;! iggs) [fb] Z Z M M (GeV) Large signal data samples at TESLA and specific iggs production in e + e and γγ collisions guarantee model independent study of iggs profile. Validation of iggs mechanism through test of iggs couplings to matter g ff = M f /v and force particles g V V =2MV 2 /v = M V g Page 15

16 iggs Boson Detection at the TESLA LC X e Z X e + Z l + b b l Nb. of iggs Bosons Observable at TESLA in 1.5 Years in Model-Independent Way Number of Events / 1.5 GeV Z 2 1 µ + µ Data Z µµ X m = 12 GeV M s 35GeV GeV GeV GeV GeV Max M =5 fb Recoil Mass [GeV] Page 16

17 Number of Events / 1.5 GeV M Data Z µµ X 2 m = 12 GeV Recoil Mass [GeV] The iggs Boson Profile SM iggs width (GeV) Γ g VV m (GeV) e + e - Events / 5 fb -1 4 a) Simulated Data WW Fusion Z Background 3 Fit result s = 35 GeV Missing mass (GeV) J PC - Z g ff events/ V( Φ) Events/1 fb cos(θ z ) N event 12 1 light Quark Tag c Quark Tag b Quark Tag NN output Page 17

18 Tools to Establish the iggs Mechanism: The TESLA Vertex Detector igh Resolution Silicon Vertex Detector (based on LEP/SLD experience and LC R&D results), Run 33544, EVENT APR :5 Source: Run Data Pol: R Trigger: Energy CDC adron Beam Crossing Track Properties y z x 4. centimeters 8. Advanced analysis techniques (developed from those adopted at LEP/SLC/LEP2): for TESLA to promote iggs Physics into the domain of precision measurements. Accuracy ( µm) LEP DELPI VD SLD VXD3 TESLA VD particle p t (GeV) Page 18

19 Identify Fermion Flavour Since iggs couplings to fermions g ff M f, flavour identification unique tool to determine couplings and validate iggs mechanism. eavy quarks identified as heavy short-lived hadrons in hadronic jets purity SLD-c c SLD-b c (b bkgr) efficiency b Page 19

20 The iggs Landscape at TESLA The Mass iggs mass M = 2λv not predicted by theory: important to obtain its accurate experimental determination. Once M is fixed, profile of the iggs particle is uniquely determined in SM. Events / GeV 1 5 (a) Data Fit result m = 12 GeV Number of Events / 1.5 GeV Data Z µµ X m = 18 GeV Recoil Mass [GeV] Mass from 5C fit [GeV] δm M =(3 5) 1 4 Page 2

21 The iggs Landscape at TESLA Couplings to Gauge Bosons Number of Events / 1.5 GeV 2 1 Data Z µµ X m = 12 GeV Events / 5 fb a) Simulated Data WW Fusion Z Background Fit result s = 35 GeV δg ZZ g ZZ Recoil Mass [GeV] =(1 3) Missing mass (GeV) δg WW g WW =(1 3) 1 2 Indirect determination of the iggs boson Width Γ : iggs resonance Γ very narrow, if M < 2 M Z Γ = VV BR( VV) δγ Γ =(3.5 6.) 1 2 Page 21

22 The iggs Landscape at TESLA Loop Mediated Couplings iggs boson not coupled directly to mass-less particles: γγ gg processes mediated by loops sensitive to SM couplings to W ± and t but also to new particles. γγ production at the photon collider to determine the strength of the effective iggs-photon coupling: N ev 3 25 M =12 GeV L γγ (.65<z<z max )=43 fb -1 background electron bunch laser 2 iggs signal abs(cosθ) T <.7 e. C γ (e) α IP γ(e) 15 E vis / s ee >.6 1 p z / s ee <.1 n jet =2,3 5 ε b =7%,ε c =3.5% Reconstructed invariant mass (GeV) δσ(γγ ) σ(γγ ) =2 1 2 δbr( gg) BR( gg) = Page 22

23 The iggs Landscape at TESLA Couplings to Fermions Extract couplings to lighter fermions from BR( b b, c c,τ + τ ) fit from jet flavour tagging response: SM iggs Branching Ratio bb ττ gg cc WW Extract coupling to heavy top from iggs radiation off top below t t threshold or BR( t t) for heavy iggs boson: M =4 GeV M =1 GeV (reference) e + e tt, e + e tt, qq, WW 1 3 γγ M (GeV) δg f f g f f =(2 1) δg t t g t t Visible mass (GeV) =(3 6) 1 2 Page 23

24 The iggs Landscape at TESLA iggs Quantum Numbers Identification of the iggs boson through check of its quantum numbers: spin, parity and charge conjugation: J PC. J CP CP (1=)d=dcos p s =5GeV M =12GeV <O> <O> SM σ tot (η)/σ tot cross section (fb) 1 5 J= J=1 J=2.6.4 e + e ;! Z e + e ;! ZA e + e ;! ZZ SM -.15 σ tot (η)/σ 1 tot cos s (GeV) η J 1from γγ and J =from threshold behaviour of σ Z. CP-even iggs ++ () distinguished from CP-odd iggs + (A) or superposition M Φ = M Z + ηm ZA by Z angular distributions in e + e Z process. Page 24

25 The iggs Landscape at TESLA iggs Potential First non-trivial test of the shape of the iggs potential through independent determination of g in double iggs production. In SM g = 3 2 M 2 v e ē Z Z Challenging b bb bq q final state accessible by high TESLA luminosity: Test V (Φ Φ) = λ(φ Φ 1 2 v2 ) 2 V( Φ) λ from M λ from g Φ Page 25

26 Precision Investigation of the iggs Profile at TESLA M (GeV) δ(x)/x TESLA 5b 1 M (3-5) 1 4 Γ tot g WW g ZZ g tt g bb g cc g ττ CP test 12.3 g g b /g b (SM) g W /g W (SM) MSSM prediction: 2 GeV < m A < 4 GeV 4 GeV < m A < 6 GeV 6 GeV < m A < 8 GeV 8 GeV < m A < 1 GeV LC 95% CL LC 1σ m = 12 GeV m = 12 GeV 2 GeV < m A < 3 GeV 1 GeV < m A < 2 GeV g c /g c (SM) MSSM prediction: 3 GeV < m A < 1 GeV LC 1σ LC 95% CL LC 1σ g top /g top (SM) Page 26

27 From the iggs Sector to the New Physics Beyond Events / 1 GeV tb tb M = 3 GeV + - (a) β tan TESLA LC 1 8 GeV 1 ab e+e >Z >ff ff g ff Indirect γγ >/A >bb 4 1 e+e >+ >tbtb 3 5 e+e >A >bbbb 2 1 LEP mh max Summer Reconstructed mass (GeV) M (GeV) A Relative Accuracy M =12 GeV BR( > invisible) LEP LC TESLA Accurate TESLA iggs Data to open a window on New Physics beyond the Standard Model Identify the Nature of the iggs Boson and probe existence of additional Scalar Particles Test alternative scenarios of Mass generation Page 27

28 The Most Elusive Building Block of the Standard Model asawindowonthephysicsbeyondit TheNatureoftheiggsBoson Indirect sensitivity to SUSY iggs through highly accurate determinations of neutral iggs boson couplings; Direct observation of heavy iggs bosons produced in e + e and γγ collisions at TESLA and study of their properties: e + e Z e + e A γγ, A BR MSSM / BR SM Events/1 GeV e e A M = M = 3 GeV A tt o o A 4 fermions (b) σ(γγ bb _ ) [fb] cosθ <.5 tanβ = 7 M A = 3 GeV = ±2 GeV A tot signal A background M A (GeV/c 2 ) Reconstructed Mass (GeV) E ee [GeV] Page 28

29 MSSM iggs Sector at LC and TESLA β tan TESLA LC e + e 8 GeV e+e >+ >tbtb e + e 5 GeV γγ 8 GeV γγ >/A >bb 5 e+e >A >bbbb e+e >Z >ff ff Indirect g ff LEP mh max Summer M (GeV) A Page 29

30 ints on the Scale of New Physics Define scale Λ as limit of validity for SM as effective theory, once the iggs mass, M,isknown: M =12 GeV TESLA LEP LC Page 3

31 Recoil Mass [GeV] Data Z µµ X m = 12 GeV cos(θ z ) m (GeV) NN output a) Simulated Data WW Fusion Z Background Fit result s = 35 GeV Missing mass (GeV) light Quark Tag c Quark Tag b Quark Tag Towards a Conclusion Number of Events / 1.5 GeV M SM iggs width (GeV) Γ g VV e + e - Events / 5 fb -1 PC J - Z g ff events/.1 V( Φ) Events/1 fb -1 N event Origin of Mass is one of the central questions for the understanding of Nature; iggs mechanism is the most plausible solution to mass generation and symmetry breaking embedded in the Standard Model which describes experimental data; Strong iggs indications with M 3 GeV guarantee decisive tests at the LC and at TESLA; After iggs boson discovery, precision measurements at TESLA will reveal the details of the mass generation mechanism. Finis Operis? Page 31

32 iggs Mechanism and the EarlyUniverse Field strength of iggs potential ground state evolved in the early universe: At T>>v, shape of iggs potential dominated by temperature term (Φ =) later evolved to produce non-zero strength at vacuum (=lowest possible energy density) (Φ = v/ 2): v = v(t) (GeV) T (GeV) Dynamics of scalar iggs field evolution basic principle in Inflationary theories of evolution of the Universe; making the experimental verification of existence of scalar fields, capable to acquire distinct vacuum states, a common goal of Particle Physics and Cosmology. Page 32

33 Indirect sensitivity to MSSM iggs through precise determination of neutral iggs couplings; In extended models iggs couplings to up-like and down-like fermions originate from different iggs doublets giving deviations of BR uu /BR dd from SM BR MSSM / BR SM Even if additional iggs bosons heavy and not directly observable TESLA: New Physics indirectly inferred from couplings of light iggs M A (GeV/c 2 ) Page 33

34 =3 tan =1TeV MA M 1 =M 2 Non Standard iggs Decays: invisible l + l Recoil analysis of e + e Z Xl + l provides with flavour blind tag of production; invisible can be measured by comparing N Z l+ l with BR(Z l + l ) i=b,c,τ,... N Z fi fi + j=w,z,γ N Z Bj Bj =14 =22GeV M 2 =25 =25GeV M Relative Accuracy BR(h! ) BR( > invisible) Page 34