Searches at LEP. Ivo van Vulpen CERN. On behalf of the LEP collaborations. Moriond Electroweak 2004

Transcription

1 Searches at LEP Moriond Electroweak 2004 Ivo van Vulpen CERN On behalf of the LEP collaborations

2 LEP and the LEP data LEP: e + e - collider at s m Z (LEP1) and s = GeV (LEP2) Most results (95% CL limits) based on LEP2: Int. Lum. 2.6 fb -1 4 experiments: Aleph, Delphi, Opal and L3 Outline of the talk iggs searches USY searches e otica Moriond EW 2004 Ivo van Vulpen 2

3 Higgs Searches Higgs Searches Moriond EW 2004 Ivo van Vulpen 3

4 Higgs Searches Higgs Searches covered in this talk SM Higgs boson General 2HDM MSSM (CP-conserving) 3 benchmarks Flavour independent Charged Higgs boson MSSM (CP non-conserving) Fermiophobic Invisible Higgs boson Not covered: MSSM Gluophobic (LHC), Double charged Higgs bosons, Anomalous Higgs couplings, Yukawa Higgs production, Extended Models, many many more Moriond EW 2004 Ivo van Vulpen 4

5 Higgs strahlung h SM Higgs boson Higgs Searches Weak boson fusion In the SM we know everything about the Higgs boson (except its mass) m h > GeV (expected) h bb m h > GeV (observed) Excess at 115 GeV: -2ln(Q) at m h = 115 GeV 100,000 signal+background experiments (MC) 100,000 background-only experiments (MC) Exclusion on HZZ coupling LEP data Moriond EW 2004 Ivo van Vulpen 5

6 Higgs Searches Two Higgs Doublet Models (2HDM) Simplest extension of the SM: Add 2 complex Higgs Doublets (H 1, H 2 ) Parameters: tan(β) (=v1/v2), α (=mixing h 0,H 0 ) + Higgs boson masses Higgses: 2 CP-even: h 0, H 0 1 CP-odd: A 0 2 charged: H +,H - Models: 2HDM(I): One doublet for all fermions 2HDM(II): One up-type doublet One down-type doublet MSSM Neutral Higgs boson production: h h Higgs boson decay: Depends on model parameters couples to mass, so mainly: σ Higgs strahlung = sin 2 ( β α) SM hz σ hz σ A Associated production = cos 2 ( β α) λ ha SM σ ν ν h( A) bb Moriond EW 2004 Ivo van Vulpen 6

7 Higgs Searches MSSM 7 parameters Tree-level parameters tan(β) Higgs vev ratio m A Mass of CP-odd Higgs Three benchmark scenarios: Loop-level parameters 1) m h -max (max m h for each tan(β) ) A Trilinear Higgs-sfermion coupling 2) no-mixing (in the stop sector) m g µ m susy M 2 Mass of the gluino Higgs mass parameter Sfermion mass at EW scale Gaugino mass at EW scale 3) large-µ (H in reach, but regions with reduced bb couplings) Moriond EW Xt = 2004 stop mixing = A Ivo van Vulpen 7 t - µ cot(β)

8 Higgs Searches MSSM benchmark (large µ) Lightest Higgs: m h < 108 GeV Flavour independent Higgs bosons "Higgs decays only to quarks or gluons" Reduced couplings to bb Higgs decays to cc or gluons LEP combined: GeV 100% 10% m S2 DELPHI ha -> hadrons (preliminary) Model independent hz ha m S1 unexcluded Adding flavour independent excludes large-µ scenario Mass exclusion using σ SM (hz): m h > GeV (expected) m h > GeV (observed) 2.3 GeV worse than SM Higgs OPAL also made a decay mode independent search Moriond EW 2004 Ivo van Vulpen 8

9 Higgs Searches M h -max MSSM benchmarks No-mixing σ hz small σ ha kinem. out of reach ha hz M h >2m A: h->aa dominant Extend searches for h->aa (m A <m b ) and H + conservative tan(β) exclusion depends strongly on the top mass Scenario m h m A Excluded tan(β) M h -max >91.0 > < tan(β) < 2.4 No mixing >91.5 > < tan(β) < 10.5 Moriond EW 2004 Ivo van Vulpen 9

10 Influence of the top mass on tan(β) exclusion region: In MSSM benchmarks: m top = 175 GeV Maximum m h : in the MSSM < 135 GeV ~ Computation of m h -max: Loop corrections m 4 top FeynHiggs: higher order corr. -> m 3 GeV h m h -max benchmark scenario m top 5 GeV -> m h 5 GeV m h If m top is larger than 175 GeV, the LEP-excluded tan(β) region shrinks Depends on results from CDF & D0 --> K. Bloom & Y.Kulik (this session) Moriond EW 2004 Ivo van Vulpen 10

11 MSSM CP non-conserving scenarios Higgs Searches Break CP symmetry by radiative corrections CP conserved: (H 1, H 2 ) -> mass eigenstates are CP-eigenstates h,h (CP-even), A (CP-odd) e + e - -> hz and e + e - -> ha Low mass regions open up tan(β) versus m H1 CP: H 1, H 2 H 3 are mass-, but not CP-eigenstates A h,h t,b H 1 A Note: only h,h (CPeven) couple to Z. Different CP-phase tan(β) M 2 m 4 top Im (µ,a t ) / v 2 m 2 susy CP benchmark: CPX Scan parameters: tan(β) and m H+ (M susy = 500 GeV, µ=4 M susy, A t,b = m g =2 M susy ) OPAL m H1 Moriond EW 2004 Ivo van Vulpen 11

12 Fermiophobic Higgs bosons Higgs Searches In 2HDM (I) models Higgs couplings to fermions can be close to 0 Decays to photons (W-loop) is dominant γ h m h > GeV (observed) Z Roughly 100 times SM prediction γγ WW 100 GeV ZZ* Moriond EW 2004 Ivo van Vulpen 12

13 Higgs Searches Invisible Higgs bosons MSSM: Higgs boson might decay into ~ χ ~ χ h 0 ~χ 1 stable LEP combined Expected Cross section 0 ~χ 1 Excluded Cross section Mh > GeV (exp.) Mh > GeV (obs.) Moriond EW 2004 Ivo van Vulpen 13

14 Higgs boson summary: Higgs scenario Observed Lower limit on m h (GeV) SM Higgs GeV MSSM (h) 91.0 GeV MSSM (A) 91.9 GeV Flavour independent GeV Charged Higgs bosons 78.6 GeV Fermiophobic GeV Invisible GeV Moriond EW 2004 Ivo van Vulpen 14

15 SuperSymmetry Moriond EW 2004 Ivo van Vulpen 15

16 SUSY model covered in this talk SUSY Searches R-parity conservation there is a stable Lightest Supersymmetric Particle (LSP) SUSY particles are produced in pairs Mass universality at the GUT scale sfermions (m 0 ) gauginos (m 1/2 ) cmssm 8 parameters: m 1/2, m 0, tan(β), µ, m A and A f (A t, A b,a τ ) SUSY broken by gravitation (SUGRA): The LSP is either the neutralino ( ~ 0 χ ) [or the sneutrino ( ~ 1 ν )] Signature: Missing energy (escaping neutralino) and dependence on M (m sparticle -m LSP ) This talk: Last slide: Results on sleptons, squarks, charginos --> lower limit on the mass of the LSP Results on R-parity violation, GMSB. Moriond EW 2004 Ivo van Vulpen 16

17 SUSY Searches sleptons production e + Z/γ e - ~ l ~ l + e e e e ~ t channel 0 ~χ 1 e~ e~ production M small cross sections for l R smaller than l L decay ~ l + M 0 ~χ 1 + l if M is small very soft leptons µ = -200 GeV and tan(β) = 1.5 Mass limits: Lower limits in GeV m 0 χ1 m 0 χ1 m~ e m~ µ m~ τ m~ τ = 0 GeV = 40 GeV ~τ decoupled from the Z Moriond EW 2004 Ivo van Vulpen 17

18 SUSY Searches squarks production: e + Z/γ q~ e - q ~ (main) decays ~ t + stop 0 ~χ 1 c ~ t + stop χ ~ + ~l ν b b ~ 0 ~χ 1 b sbottom sbottom Mixing in 3 rd family: ~ t = ~ t cos( θ ) ~ ~ + t sin( θ~ ) 1 L t R t ~ ~ t ( b or ~ τ ): NLSP for medium(high) tan( β ) can decouple from the Z Signature: acoplanar jets + E and P M< m c : squark is a quasi-stable particle Mass limits (in GeV): M = 20 GeV & for (non)-decoupled from Z channel ~ t c~ χ Mass limit 100 (98) 99 (96) 99 (95) Moriond EW 2004 Ivo van Vulpen ~ t bl ~ ν ~ b b~ χ 0 1

19 new A light sbottom SUSY Searches Excess in bb cross section at the Tevatron: How about a GeV gluino and GeV sbottom?? Moriond 2003: (ALEPH) Stable sbottoms: M sbottom > 92 GeV Hadronic cross section data from: LEP1, LEP2 and PEP, PETRA, TRISTAN, The older generations in the LEP family help out (use s = GeV) 95% CL lower limit on m sbottom (GeV) P.Janot Small coupling sbottom to Z hep-ph/ Hadronically decaying sbottom: M sbottom > 6.0 GeV cos θ mix Moriond EW 2004 Ivo van Vulpen 19

20 production e + e - Z/γ χ ~+ ~ χ e + e - Charginos: large m 0 Large cross section in large part of parameter space χ ~+ ~ χ Negative interference if chargino is gaugino ν ~ decay + ~χ 1 Small m 0 : light sfermions σ ~ + ~ ( χ χ ) decreases ~ + ~ χ l ν l~ χ 0 ν opens 0 ~χ 1 W + W-> qq (68%) / lv (32%) + ~χ 1 ν ~ l + 0 ~χ 1 ν Different M ( m ~ + m ~ 0 χ 1 χ 1 ) regions 1) M > 3 GeV: ~ > m ν 300 GeV m~ + >103.5 GeV χ LEP combined 2) 200 MeV < M < 3 GeV: low momentum particles (use ISR -> high P T -γ) 3) M < 200 MeV: kinky tracks and displaced vertices Long lived charged particles (de/dx information) Moriond EW 2004 Ivo van Vulpen 20

21 SUSY Searches The LSP cmssm Interpret the combined results in the cmssm framework (mass of the LSP : Combining results from Higgs searches with slepton, chargino and neutralino searches ~ 0 χ 1 ) Use cmssm mass relations m 0 large Lower limit on the LSP ( ~ m~ χ > χ 1 45 GeV ) mass (in GeV) m 0 small Assuming m 0 < 1 TeV and m top = 175 GeV and no stau mixing Moriond EW 2004 Ivo van Vulpen 21

22 SUSY Searches The LSP msugra Interpret the combined results in the msugra framework (mass of the LSP : ~ 0 χ 1 ) MSUGRA = cmssm + 1) common scalar mass (m A via m 0 ) + 2) common trilinear coupling at GUT (A t, A b,a τ = A) + 3) fix µ (EW symmetry breaking) (µ -> sign(µ)) 5 parameters: m 1/2, m 0, tan(β), sign(µ), A A=0, m top = 175 GeV A=0, m top = 180 GeV Any A m top = 175 GeV Lower limit on the LSP ( ~ Assuming m 0 < 1TeV 0 χ 1 ) mass (in GeV) A 0 0 any sign(µ) m top positive negative Moriond EW 2004 Ivo van Vulpen 22

23 SUSY summary: ± χ ~ 0 ~χ 1 Not shown: AMSB & scenarios where the sneutrino or the gluino is the LSP Moriond EW 2004 Ivo van Vulpen 23

24 Exotica Searches Low scale gravity in Extra dimensions Gravity strong near the EW scale 2 2+ n M pl ~ Meff n extra (space) dimensions of radius r Virtual graviton exchange affects: r n Data/MC d dcos(θ ) σ e + e e + e Put limits on M H (gravitational mass scale): M H > 1.20 TeV (λ= +1) M H > 1.09 TeV (λ= -1) cos(θ e ) Not shown: technicolour, single top, leptoquarks, excited fermions, Z, cont. interactions, 4 th generation quarks Moriond EW 2004 Ivo van Vulpen 24

25 Conclusions: SM Higgs combined and published Searches for SUSY Higgs bosons -> exclude large part of MSSM parameter space Final benchmark scans this summer (also gluophobic interesting for LHC) LEP combined searches for sparticles Interpretations in a wide variety of SUSY models Rest of the cheese is for the Tevatron & LHC Moriond EW 2004 Ivo van Vulpen 25

26 Backup slides Moriond EW 2004 Ivo van Vulpen 26

27 Higgs Searches Hypotheses testing: Likelihood ratio method Construct 2-dim distr. for background(m h ) and signal(m h )+background --> (M h rec, ξ) For each event i -> you know w i = P(s+b)/P(b) ~ si Q ω ωi = ln(1 + ~ ) b Define test-statistic as 2ln(Q), with Q = L s+b / L b (=Π i w i ) 2ln( ) 2( N = s =1 ) i i with weights Number of expected signal events Number of selected candidates 100,000 signal+background experiments (MC) 100,000 background-only experiments (MC) LEP 1-Cl b : incompatibility with the background-only hypothesis 1-Cl b < > 3 sigma 1-Cl b < > Nobel Prize! separating variable Ratio of the expected number of signal events over the expected number of signal events in a locql bin of (Mh rec, ξ) The rules: Higgs mass estimator CL s+b : compatibility with the signal+background hypothesis i 1-Cl b Cl s+b CL s : compatibility with a signal hypothesis. CL s CL s+b /CL b Cl s < > Signal hypoth. excluded at 95% CL Moriond EW 2004 Ivo van Vulpen 27

28 Charged Higgs bosons Higgs Searches H H + cs cs ( τ + ν ) ( τ ν ) Assumption of fermion decay is not valid in unexcluded 2HDM(II) no-mixing point Br(H + -> AW +* ) can be 60% Assumption : Br(H cs) + BR(H τν ) = 1 Analysis: only for m A >12 GeV (bb) m A < 12 GeV --> special effort BR(H--> τν τ ) Extended h->aa reach (A->cc/τ + τ - /gluons) Excluded WW background OPAL M h > 78.8 GeV (exp.) M h > 78.6 GeV (obs.) Excluded LEP1 Excluded But unfortunately Included in next (final?) benchmark scan Moriond EW 2004 Ivo van Vulpen 28

29 Neutralinos SUSY Searches neutralino production neutralino decay e + Z ~χ 0 e + e ~ e - ~χ 0 e - ~χ 0 ~χ 0 0 ~χ 2 0 ~χ 1 Z 0 ~χ 2 ν ~ ν 0 ~χ 1 ν Positive interference if neutralino is gaugino Z-> qq (70%) / v v (20%) / ll(10%) Phenomenology depends on M, but also on m 0 (common sfermion mass at GUT scale) Moriond EW 2004 Ivo van Vulpen 29

30 Exotica Excited leptons: Fermion sub-structure: (compositness scale in TeV region) Decay: l* -> lγ / lz / Wν τ* Excluded µ* More sensitive due to t-channel γ- exchange e* Not covered: technicolor, single top, leptoquarks, extra dimensions, etc Moriond EW 2004 Ivo van Vulpen 30