P. Sphicas/SSI2001. Standard Model Higgs

Transcription

1 Standard Model Higgs

2 SM Higgs (I) Production mechanisms & cross section Studying EWSB at the LHC 2

3 Decays & discovery channels Higgs couples to m f 2 SM Higgs (II) Heaviest available fermion (b quark) always dominates Until WW, ZZ thresholds open Low mass: b quarks jets; resolution ~ 15% Only chance is EM energy (use γγ decay mode) Once M H >2M Z, use this W decays to jets or lepton+neutrino (E T miss ) Studying EWSB at the LHC 3

4 Low mass Higgs (M H <140 GeV/c 2 ) H γγ: decay is rare (B~10-3 ) But with good resolution, one gets a mass peak Motivation for LAr/PbWO 4 calorimeters CMS: at 100 GeV, σ 1GeV S/B 1:20 Studying EWSB at the LHC 4

5 Intermediate mass Higgs H ZZ λ + λ λ + λ (λ =e,µ) Very clean Resolution: better than 1 GeV (around 100 GeV mass) Valid for the mass range 130<M H <500 GeV/c 2 Studying EWSB at the LHC 5

6 H ZZ λ + λ jet jet Need higher Branching fraction (also νν for the highest masses ~ 800 GeV/c 2 ) At the limit of statistics High mass Higgs Studying EWSB at the LHC 6

7 Higgs discovery LHC The LHC can probe the entire set of allowed Higgs mass values; in most cases a few months at low luminosity are adequate for a 5σ observation CMS Studying EWSB at the LHC 7

8 Status of HfiH bb (I) Low mass Higgs; useful for coupling measurement H bb in t t H production σ.br=300 fb Backgrounds: Wjjjj, Wjjbb t t jj Signal (combinatorics) Tagging the t quarks helps a lot Trigger: t b(e/µ)ν Reconstruct both t quarks In mass region 90GeV<M(bb )<130GeV, S/B =0.3 Studying EWSB at the LHC 8

9 Status of HfiH bb (II) H bb in WH production Big background subtraction Mainly: Wjj, t t (smaller: tx,wz) Example (below) at 105: in mass region 88GeV<M(bb )<121GeV, S/B =0.03 After bkg subtraction Studying EWSB at the LHC 9

10 SM Higgs properties (I): mass Mass measurement Limited by absolute energy scale leptons & photons: 0.1% (with Z calibration) Jets: 1% Resolutions: For γγ & 4l 1.5 GeV/c 2 For bb 15 GeV/c 2 At large masses: decreasing precision due to large Γ H CMS ATLAS Studying EWSB at the LHC 10

11 SM Higgs properties (II): width Width; limitation: Possible for M H >200 Using golden mode (4λ) CMS Studying EWSB at the LHC 11

12 SM Higgs; width for M H <2M Z Basic idea: use qq qqh production (two forward jets+veto on central jets) Can measure the following: X j = Γ W Γ j /Γ from qq qqh qqjj Here: j = γ, τ, W(W*); precision~10-30% One can also measure Y j = Γ g Γ j /Γ from gg H jj Here: j = γ, W(W*), Z(Z*); precision~10-30% Clearly, ratios of X j and Y j (~10-20%) couplings But also interesting, if Γ W is known: Γ = (Γ W ) 2 /X W Need to measure H WW* ε=1-(b b +B τ +B W +B Z +B g +B γ )<<1 (1-ε)Γ W = X τ (1+y)+X W (1+z)+X γ +X g z= Γ W /Γ Z ; y= Γ b /Γ τ =3η QCD (m b /m τ ) 2 Studying EWSB at the LHC 12

13 SM Higgs properties (III) Biggest uncertainty(5-10%): Luminosity Relative couplings statistically limited Small overlap regions Measure Error M H range ( γγ ) ( ) ( γγ ) ( ) σ( ) σ( ) ( ( ) ) ( ) ( ) 30% % % % Studying EWSB at the LHC 13

14 Strong boson-boson scattering Example: W L Z L scattering W, Z polarization vector ε µ satisfies: ε µ p µ =0; for p µ =(E,0,0,p), ε µ =1/M V (p,0,0,e) P µ /M V +O(M V /E) Scattering amplitude ~ (p 1 /M W ) (p 2 /M Z ) (p 3 /M W ) (p 4 /M Z ), i.e. σ~s 2 /M W2 M Z 2 Taking M H the H diagram goes to zero (~ 1/M H2 ) Technicalities: diagrams are gauge invariant, can take out one factor of s but the second always remains (non-abelian group) Conclusion: to preserve unitarity, one must switch on the H at some mass Currently: M H 700 GeV Studying EWSB at the LHC 14

15 The no Higgs case: V L V L scattering Biggest background is Standard Model VV scattering Analyses are difficult and limited by statistics Resonant WZ scattering at 1.2 & 1.5 TeV Non-resonant W + W + scattering M H =1 TeV L=300 fb -1 W T W T Studying EWSB at the LHC 15

16 Other resonances/signatures Technicolor; many possibilities Example: ρ T± W ± Z 0 λ ± νλ + λ (cleanest channel ) Many other signals (bb, t t resonances, etc ) Wide range of observability ATLAS; 30 fb 1 Studying EWSB at the LHC 16

17 Supersymmetry SUSY Higgses

18 Problems with the Higgs Quadratic divergence of its mass ( ) = ( Λ ) + Λ Λ is a cutoff momentum Put simply: why is the Higgs mass low? Studying EWSB at the LHC 18

19 Supersymmetry (SUSY) One possible solution: for every particle there exists a partner particle with ½ spin difference With SUSY, infinities disappear: As long as M p =M sp Studying EWSB at the LHC 19

20 SUSY doubles the particle spectrum It must also be broken To explain why unseen till now If broken at E SUSY: ( ) = ( Λ ) + Supersymmetry World Studying EWSB at the LHC 20

21 Supersymmetry and Unification Couplings run with Q 2 : Loop diagrams (quantum corrections) make the coupling between the force and matter particles dependent on the energy at which the interaction occurs Extrapolating the couplings for the EM, WK and strong interactions: Without SUSY With SUSY Studying EWSB at the LHC 21

22 MSSM Higgses: : phenomenology Complex analysis; 5 Higgses (H ± ;H 0,h 0,A 0 ) At tree level, all masses & couplings depend on only two parameters; tradition says take M A & tanβ Modifications to tree-level mainly from top loops Important ones; e.g. at tree-level, M h <M Z cosβ; radiative corrections push this to 150 GeV. Important branch 1: SUSY particle masses (a) M>1 TeV (i.e. no decays of the Higgses to them); wellstudied (b) M<1 TeV (i.e. allows decays of the Higgses to them); new Important branch 2: stop mixing; value of tanβ (a) Maximal No mixing (b) Low (1.5) and high ( 30) values of tanβ Studying EWSB at the LHC 22

23 MSSM Higgses: : masses Mass spectra for M SUSY >1TeV Studying EWSB at the LHC 23

24 Biggest branch is tanβ MSSM: h/h production Studying EWSB at the LHC 24

25 h is light MSSM: h/a decay Decays to bb (90%) & ττ (8%) Decays to cc, gg suppressed H/A heavy Decays to top open (low tanβ) Otherwise still to bb & ττ Negative: WW/ZZ channels suppressed; lose golden modes for H No mixing Studying EWSB at the LHC 25

26 Higgs channels considered Channels currently being investigated: H, h γγ, bb (H bb in WH, t t H) h γγ in WH, t t h l γ γ h, H ZZ*, ZZ 4 l h, H, A τ + τ (e/µ) + + h + E T miss e + + µ + E T miss h + + h + E T miss H + τ + ν from t t (very) important and hopeful inclusively and in bb HSUSY H + τ + ν and H + t b for MH >M top A Zh with h bb ; A γγ H, A χ~ 0 2 χ ~ ~ 0 2, χ~ 0 i χ~0 j, χ~+ i χ~ j H + χ~ + 2 χ~0 2 qq qqh with H τ + τ H ττ, in WH, t t H new and promising using OO code (tough ) work started; tough Studying EWSB at the LHC 26

27 MSSM Higgses: : last (published) results Little room for h left; A is still open Maximal mixing: M h >84 GeV/c 2 exclude 0.8<tanβ<1.9 M A >84 GeV/c 2 No mixing: M h >84 GeV/c 2 (95%CL) exclude 0.5<tanβ<3.2 M A >85 GeV/c 2 Studying EWSB at the LHC 27

28 MSSM Higgses: : expected LEP reach Taking 208 GeV and actual luminosity recorded tanβ No mixing Max mixing M(h) M(h) tanβ M(A) Studying EWSB at the LHC 28

29 H,Afitt Most promising modes for H,A τ s identified either in hadronic or leptonic decays Mass reconstruction: take lepton/jet direction to be the τ direction Studying EWSB at the LHC 29

30 H, A reach via t decays Contours are 5σ; M SUSY =1 TeV Studying EWSB at the LHC 30

31 H + detection Associated top-h + production: Use all-hadronic decays of the top (leave one neutrino ) H decay looks like W decay Jacobian peak for τ-missing E T In the process of creating full trigger path + ORCA analysis E T (jet)>40 η <2.4 Veto on extra jet, and on second top Bkg: t t H Studying EWSB at the LHC 31

32 SUSY reach on tanb-m A plane Adding bb on the τ modes can close the plane Wh (e/µ)ν bb No stop mixing maximal stop mixing with 30 fb -1 maximal stop mixing with 300 fb -1 Studying EWSB at the LHC 32

33 MSSM Higgs reach; M SUSY ~1TeV Summary: γγ ( ) l ττ (l/ ) + miss,, µµ; same for bb H SUSY from t Hb H ± τ ± ν from H tb A γγ A Zh H hh A / H tt Studying EWSB at the LHC 33

34 Observability of MSSM Higgses MSSM Higgs bosons h,a,h h,a,h,h ± h,h ± 4 Higgs observable 3 Higgs observable 2 Higgs observable 1 Higgs observable 5σ contours H,H ± h h,h Assuming decays to SM particles only h,,h,h ± h,a,h,h ± h,h ± Studying EWSB at the LHC 34

35 If SUSY charg(neutral) (neutral)inos < 1 TeV (I) Decays H 0 χ~ 0 2χ~ 0 2, χ~ + iχ~ - j become important Recall that χ~ 0 2 χ~ 0 1l + l _ has spectacular edge on the dilepton mass distribution Example: χ~ 0 2χ~ 0 2. Four (!) leptons (isolated); plus two edges 100 fb 1 Four-lepton mass Studying EWSB at the LHC 35

36 If SUSY charg(neutral) (neutral)inos < 1 TeV (II) Adding bb on the τ modes can close the plane Wh (e/µ)ν bb No stop mixing Area covered by H 0 χ~ 0 2χ~ 0 2, 4l eptons 100 fb -1 maximal stop mixing with 30 fb -1 maximal stop mixing with 300 fb -1 Studying EWSB at the LHC 36

37 MSSM: Higgs summary At least one φ will be found in the entire M A -tanβ plane latter (almost) entirely covered by the various signatures, however: Full exploration requires 100 fb 1 Difficult region: 3<tanβ<10 and 120<M A <220; will need: > 100 fb 1 or h bb decays Further improvements on t identification? Intermediate tanβ region: difficult to disentangle SM and MSSM Higgses (only h is detectable) Studying EWSB at the LHC 37

38 Sumersymmetry Sparticles

39 Simplest SUSY LHC Ample cross section for direct squark and gluino production M sp (GeV) σ (pb) Evts/yr ~ ~ M=500 GeV Gauginos produced in their decay; example: q L χ 20 q L Studying EWSB at the LHC 39

40 SUSY mass scale Events with 4jets + E T miss Clean: S/B~10 at high M eff Establish SUSY scale (σ 20%) M eff = 4 P T, j j=1 + E T miss SM LHC Point 1 SUSY Effective mass tracks SUSY scale well LHC Point 5 Studying EWSB at the LHC 40

41 SUSY decays Squarks & gluinos produced together with high σ Gauginos produced in their decays; examples: q ~ L χ ~ 20 q L (SUGRA P5) q ~ g ~ q χ ~ _ 20 qq (GMSB G1a) Two generic options with χ 0 : (1) χ 20 χ 10 h (~ dominates if allowed) (2) χ 20 χ 10 λ + λ or χ 20 λ + λ Charginos more difficult Decay has ν or light q jet Options: Look for higgs (to bb) Isolated (multi)-leptons Studying EWSB at the LHC 41

42 SUSY Huge number of theoretical models Very complex analysis; MSSM-124 Very hard work to study particular scenario assuming it is available in an event generator To reduce complexity we have to choose some reasonable, typical models; use a theory of dynamical SYSY breaking msugra GMSB AMSB (in less detail) Model determines full phenomenology (masses, decays, signals) Studying EWSB at the LHC 42

43 SUGRA Five parameters All scalar masses same (m 0 ) at GUT scale All gaugino masses same (m 1/2 ) at GUT scale tanβ and sign(µ) All tri-linear Higgs-sfermion-sfermion couplings common value A 0 (at GUT scale) Full particle table predictable 26 RGE s solved iteratively Branches: R parity (non)conservation Extensions: relax GUT assumptions (add parameters) Studying EWSB at the LHC 43

44 Simplest SUSY Ample cross section for squark and gluino production Gauginos produced in their ~ ~ decay; example: q L χ 20 q L msugra Studying EWSB at the LHC 44

45 SUGRA spectroscopy Basic assumption: mass universality Scalar masses: m 0 ; gaugino masses: m 1/2 ; Higgs masses: (m 02 +µ 2 ) 1/2 RGE: run masses down to EWK scale M(squark): large Increase (due to α 3 ) M(slepton): small increase (due to α 1, α 2 ) Gauginos: gluino is fast-rising; B-ino, W-ino mass decreases Mixing leads to charginos (2) and neutralinos (4) Higgs: strong top coupling drives µ 2 <0; Symmetry Breaking mechanism arises naturally in msugra(!) Studying EWSB at the LHC 45

46 Sparticles in SUGRA ~ ~ ~ ~ Contours of fixed g/q and χ/λ mass m( g ~ ) m( q ~ ) 3m m 1/ m 2 1/ 2 m( χ~ ~ m( λ 0 1 ) m ~ 1/ 2 / 2; m( χ~ ± ± 2 L, λr ) m , χ~ ± ) m (0.5,0.15) m 1/ 2 2 1/ 2 ; Studying EWSB at the LHC 46

47 SUGRA: the five LHC points Defined by LHCC in 1996 Points 1,3,5: light Higgses LEP-excluded (3; less for 1,5) Restore with larger tanβ Points 1&2: Squark/gluinos 1TeV Point 4: at limit of SB Small µ 2, large χ,φ mixing Heavy squarks Point 5: cosmology-motivated Small m 0 light sleptons P M 0 M 1/2 A 0 tanβ s(µ) increase annihilation of χ 1 0 reduce CDM Studying EWSB at the LHC 47

48 Sparticles (e.g. SUGRA) Formidable number of options Five parameters All scalar masses same (m 0 ) at GUT scale All gaugino masses same (m 1/2 ) at GUT scale tanβ and sign(µ) All tri-linear Higgs-sfermion-sfermion couplings common value A 0 (at GUT scale) Full particle table predictable 26 RGE s solved iteratively Branches: R parity (non)conservation Extensions: relax GUT assumptions (add parameters) Studying EWSB at the LHC 48

49 Experimentally: spectacular signatures Prototype : χ ~ 0 2 χ ~ 10 λ + λ Straightforward: dileptons + E miss T Example from P3 SM even smaller with b s Also works at other points But additional SM (e.g. Z 0 ) M measurement easy Position of edge; accurate Studying EWSB at the LHC 49

50 Multi-observations other points Main peak from χ ~ 20 χ ~ 10 λ + λ Measure m as before Also peak from Z 0 through χ ~ 20 χ~ 10 Z 0 Due to heavier gauginos P4 at edge of SB small µ 2 (a) χ ± and χ ~ 0 are light (b) strong mixing between gauginos and Higgsinos LHC Point 4 At P4 large Branching fractions to Z decays: e.g. B(χ ~ 3 χ ~ 1.2 Z 0 ) 1/3; size of peak/p T (Z) info on masses and mixing of heavier gauginos (model-dependent) Studying EWSB at the LHC 50

51 Determining SUSY parameters From the edges of the spectra P5: q L qχ ~ ~ 20 qλλ qλ + λ ATLAS example: 2 isol, OS leptons+=4jets+e T miss Combine leptons with 2 harder jets M max λλq = ( )( ) M ~ M 0 M 0 M 0 q L χ / M χ χ χ 550 Similarly, minimum at 270 GeV/c 2 Both min & max visible Example shown: eµ subtracted Studying EWSB at the LHC 51

52 Distinguishing 2 & 3-body 3 decays Two scenarios can be disentangled directly From asymmetry of two leptons: P A = P max T max T + P P min T min T In analogy with τ decays Studying EWSB at the LHC 52

53 Example from Point 1 SUGRA reach tanβ=2;a 0 =0;sign(µ)= But look at entire m 0 -m 1/2 plane Example signature: N (isolated) leptons + = 2 jets + E T miss 5σ (σ=significance) contours Essentially reach is ~2 (1) TeV/c 2 for the m 0 (m 1/2 ) plane CMS 100 fb 1 Studying EWSB at the LHC 53

54 The other scenario: c 0 2 fi c 0 1 h Followed by h bb: h discovery at LHC E.g. at Point 1, 20% of SUSY events have h bb But squarks/gluinos heavy (low cross sections) b-jets are hard and central Expect large peak in (btagged) di-jet mass distribution Resolution driven by jet energy measurement Largest background is other SUSY events! Studying EWSB at the LHC 54

55 Building on the h In analogy with adding jets to χ 20 χ 10 λ + λ Select mass window (e.g. 50 GeV) around h Combine with two highest E T jets; plot shows min. mass Again, use kinematic limits Case shown: max 550 GeV/c 2 Beyond this: Model dependence ATLAS 30fb 1 Studying EWSB at the LHC 55

56 Observability of decays into h Examples from CMS (tanβ=2&10) Studying EWSB at the LHC 56

57 Varying tanb τ modes eventually become important At tanβ>>1 only 2-body χ ~ 20 decays (may be): χ ~ 20 τ ~ ~ 1 τ ττχ 0 1 Visible eµ excess over SM; for dilepton edge: need ττ mass Studying EWSB at the LHC 57

58 SUSY parameters; SUGRA Point/Lumi m 0 (GeV) m 1/2 (TeV) tanβ s(µ) ± ±8 2.00±0.08 ok ± ±8 10±2 ok ±50 200±2 10±2 ok ±4 300±3 ±0.1 ok Essentially no information on A 0 (A heavy evolve to fixed point independent A 0 ) Studying EWSB at the LHC 58