MSSM Higgs Searches at LEP

2001-11-23 [email protected] Fourth Nordic LHC Physics Workshop Stockholm 22-24 Nov 2001 1

MSSM Higgs Searches at LEP

Tord EkelöfUppsala University

Sweden


What is the rational for supersymmetry?

SM has problems with quadratic divergencies (mass hiarchy problem)

Supersymmetry leads to coupling unification at high energy

Supersymmetry needed for superstrings->supergravity->unification of general relativity and quatum field theory


Introduction• SM One Higgs Field Doublet

– One physical Higgs H• Production

– Higgsstrahlung

– Vector boson fusion, small

• Decay H->bb, , W*W*...

• MSSM Two Higgs Field Doublets– Five physical Higgs h0 A0 H0 H+ H-

Z0e+

e-

Z0

H0 e+,

e-,

e+

e-

Z,WZ,W H0


– MSSM free parameters• MSUSY Sfermion mass parameter at EW scale SUSY Higgs mass parameter• M2 SU(2) gaugino mass param at EW scale

• Xt Stop mixing term=At- tan, At trilinHt• tan ratio between vacuum expectation values of

Higgs field doublets

• mA A Higgs boson mass

• mg Gluino mass

– On tree level mh calculable from (mA,tan) and mh< mz. In one and two loop corrections to production cross-sections and branching ratios all free parameters are involved. Can make mh larger.

~

~


• MSSM Higgs production– h0

• Higgsstrahlung, SMsin2(-)

• Vector boson fusion, small• Higgs pair production, SMcos2(-)

– A0 – Higgs pair production, SMcos2(-)

• h0 decay if 2mA<mh

– H0

• Higgsstrahlung if large, SMcos2(-)

– H+H-

• Pairproduction

e+

h0

e-

A0

h0

Z0

h0

Z0

e-

A0

h0

Z0

h0

Z0

e+

h0A0

A0

e+

e-

e+,

e-,

Z,WZ,W

Z0e+

e-

Z0

h0

e+

e-

Z0

H0

Z0

e+

e-

Z0H+

H-


• MSSM Higgs decay– h

• “standard” h0->bb, +-• invisible, LSP/Majoron h0->1

010, JJ

• fermiophobic, 2HDM type I h0->• flavour independent, MSSM large h0->cc, ss, gg

– A • “standard” A0->bb, +-• bosonic A0->Z0h0

– H+-

• “standard”, 2HDM if at LEP2 H+-->cs, • bosonic, 2HDM type I H+-->W*A0

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- -

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• MSSM Bench Mark Scenarios

– Three points in the MSSM parameter space• plus general parameter space scan

Parameter 1. mhmax 2. no mixing 3. large general MSSM scan

unit GeVMSUSY 1000 1000 400 200 to 1000 -200 -200 1000 -500 to +500M2 200 200 400 200 to 1000Xt =At- tan 2MSUSY 0 -300 -2MSUSY to 2MSUSY

mg 0.8MSUSY 0.8MSUSY 200

mA 4-1000 4-1000 4-1000 4 to 1000tan 0.4-50 0.4-50 0.4-50 0.4 to 50


• 1. Mhmax scenario

• Designed to maximize the largest h0 mass value as function of tan with the aim to obtain the most conservative exclusion of tan, or , conversely, to possibly exclude MSSM by excluding h0 up to a maximal limit mh

max< 130 GeV, which depends on the exact value of mtop=174.3+-5.1 GeV.

• 2. No-mixing scenario• Same as mh

max but with no mixing in the stop sector to see the effect of mixing, mh

max<114 GeV

• 3. Large- scenario• In this scenario h0 (or H0) does not decay to b quarks in

certain parameter-space regions. Motivates flavor independent search. mh

max<108 GeV


Searches for h and A with data collected up to 209 GeV• e+e-->Zh same as SM with production cross

section reduced by sin2(-) and different decay BRs

• e+e-->hA has cross section proportional to cos2(-) with final states bbbb (dominates), +-bb and bb+-. Cross-section largest when mAmh.

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LEP combined distribution of CLb in themh

max scenario

Along the mAmh diagonal Distribution of confidence (tan>20, cos2(-) 1) level in the (mA, mh) plane


LEP combined CLs in the mhmax scenario

Along the mAmh diagonal Distribution of exclusion

(tan>20, cos2(-) 1) in the (mA, mh) plane

mA>91.9(95.0) GeV mh>91.0(94.6) GeV observed expected observed expected


LEP combined exclusion plots in the mhmax

scenario in tan vs mh, mA and mH+ planes excluded region 0.4(0.5)<tan <2.4(2.6)


OPAL

Exclusion plots in the mhmax scenario

in tan vs mh planes for A, D and O

ALEPH DELPHI OPALmh> 89.6(91.7) 89.8(89.0) 79.3(85.1)tan> 0.7 0.49(0.54) 0.80(1.1)tan< 2.2 2.36(2.36) 1.7(1.9)


LEP combined exclusion for the no mixing scenario in the mA vs mh and the tan vs mh and mA planes mh>91.5(95.0) mA>92.2(95.3) excluded 0.7(0.8)<tan <10.5(16.0)


OPAL

Exclusion plots in the no mixing scenarioin tan vs mh planes for A, D and O

ALEPH DELPHI OPALmh> 89.8(89.0) 80.9(85.6)tan> 0.5 0.59(0.72) 1.2(1.2)tan< 6.0 9.36(9.36) 3.8(4.6)


Production and decay of charged Higgs bosons

2HDMs predict s-channel pair-production of H+H-

with a tree-level cross-section which is fully determined by (mH+,s) and with H+H- decay into cscs, cs- and +-. No prediction for the BR(H+->+). In tree-level MSSM mH+>mW and mH+>mA.

Search for qqqq, qqp and p final states. Use equal masses constraint, acoplanarity, H+ zero spin, polarization (A,D) and cs identification (D).

/ /

- -- - --


Searches for charged Higgs, exclusion plots from of A, D, L & O

ALEPH DELPHI L3 OPALmH+<78.0(76.9) 73.8(75.4) 65.6(75.1) 72.2(74.5)


1-CLb for charged Higgs, ADO and ALDO and for different BR(H->)


Combimed searches for charged Higgs BR(H->) vs H+ mass, and cross-section limit

mH+>78.6(78.8)

Combined ALDO searches for charged Higgs, mass limit and cross-section limit


The L3 charged Higgs excessat 68 Gev


Comparison with charged Higgs hadronic decay massdistributions in A, D and O


Neutral Higgs flavour-independenthadronic decays

In both the SM and in the MSSM the neutral Higgsdecay predominantly into bb or +-.

In MSSM large- scenario and certain other 2HDMs Higgs decays into cc or gg can become predominant.

Same as SM analysis of e+e-->Z0H0, with H0->qq but without imposing requirement on the qq flavour. SM production cross-section and BR(H->had)=1 assumed.

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-

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Flavour-independent search for a neutral Higgs

ALEPH

ALEPHmHinv>109.4(109.8)

OPALmHinv>101.8(107.3)


Higgs decay into photon pairs - fermiophobic Higgs

In the MSSM h0 can decay into two photons via a quark or W-boson loop, but rates are low ~10-3.

In other models, like 2HDM Type I, h0 only couples to gauge bosons (i.e not to fermions) for certain choices of parameter values.

Analysis made assuming SM Higgs production cross-section and BR(Higgs->qq or l+l-) set to 0.

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ALEPH mH>105.4

OPAL mH>105.5 (106.4)

L3 () mH>104.3 (104.4)L3 (,WW)mH> 104.8 (108.4)

Search for Higgs decaying into photon pairs


LEP combined data for h° -> 2


Higgs decay to invisible particles

e+e+->Z0h0 where Z0 ->qq or l+l- at SM cross-section

h0->101

0 , lightest neutralinos (R parity cons., LSPs) orh0->JJ , Majoronsorh0->other invisible (undetectable) particles, BR=100%.

Mmiss=recoil mass, Mvis=visible massM2

miss=s-2mZEviss/Mvis+mZ2

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Searches for invisibly decaying Higgs

For BR(H->inv.)=100% ALEPH minv>114.1(112.6) DELPHI minv>113.0(110.7) OPAL minv>107.0(107.4)

For BR(H->inv.)=any DELPHI minv=112.7


LEP combined data for h°->invisible


Conclusion NO MSSM/2HDM HIGGS FOUND

Combined results of the four LEP experiemnts MSSM mh

max mh>91.0 (94.6) GeV All limits at 95% CL

mA>91.9 (95.0) GeV 0.5<tan<2.4 (0.5<tan<2.6) excluded Charged Higgs m>78.6 (78.8) GeV Flavour blind Higgs m>112.9 (113.0) GeV Photonic Higgs m>108.2 (109.0) GeV Invisible Higgs m>114.3 (113.6) GeV

All results still preliminary

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MSSM Higgs Searches at LEP

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