Search for Anomalous Couplings in the Higgs Sector at LEP

a r X i v :h e p -e x /0403037v 1 24 M a r 2004

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

CERN-PH-EP/2004-002January 30,2004

The L3Collaboration

Abstract

Anomalous couplings of the Higgs boson are searched for through the processes e +e ?→H γ,e +e ?→e +e ?H and e +e ?→HZ.The mass range 70GeV

√

1Introduction

The mechanism of spontaneous symmetry breaking is a cornerstone of the Standard Model of the electroweak interactions [1].It explains the observed masses of the elementary particles and postulates an additional particle,the Higgs boson.Despite its relevance,experimental information on the Higgs boson is scarce and indirect.It leaves room for deviations from the Standard Model expectations such as anomalous couplings of the Higgs boson.

The Standard Model can be extended,via a linear representation of the SU (2)L ×U (1)Y symmetry breaking mechanism [2],to higher orders where new interactions between the Higgs boson and gauge bosons become possible.These modify the production mechanisms and decay properties of the Higgs boson.The relevant CP-invariant Lagrangian terms are [3]:

L e?=g H γγHA μνA μν+g (1)

HZ γA μνZ μ?νH +g (2)

HZ γHA μνZ μν

+g (1)

HZZ Z μνZ μ?νH +g (2)

HZZ HZ μνZ μν+g (3)

HZZ HZ μZ μ

+g (1)

HWW (W +μνW μ??νH +h.c.)+g (2)

HWW HW +

μνW μν?,

(1)

where A μ,Z μ,W μand H are the photon,Z,W and Higgs ?elds,respectively,and X μν=

?μX ν??νX μ.The couplings in this Lagrangian are parametrized as [4–6]:

g H γγ=

g m W

?g Z 1sin2θW ??κγtan θW

(3)

g (2)

HZ γ=

m W

?g Z 1cos2θW

+?κγtan 2

θW

(5)

g (2)

HZZ =

2cos 2θW

δZ (7)

g (1)

HWW =

g m W

m W

HZ γcouplings.These processes probe Higgs masses,m H ,up to the centre-of-mass energy of the collision,√s ?m Z ,this analysis is complemented by the results from the L3searches for the e +e ?→HZ process [8,9],which are sensitive to anomalous HZZ and HZ γcouplings,as shown in Figure 1c.

The existence of H γγand HZ γcouplings would lead to large H →γγand H →Z γbranching fractions,which at tree level are zero in the Standard Model.These decay modes have comple-mentary sensitivities and allow to probe a large part of the parameter space.In addition,the decay H →WW (?)would also be enhanced in the presence of anomalous HWW couplings.The data used in this analysis were collected with the L3detector [10]at LEP at

√s =189GeV [11].This decay is dominant for m H m Z ,where H →γγis strongly suppressed and H →Z γis kinematically forbidden.At the centre-of-mass energies considered in this Letter,this region is e?ciently covered by an interpretation of the results of the search

for the e +e ?→HZ process [8]and the H →b ˉb

decay is not considered here.No dedicated selection is devised for the e +e ?→HZ process and the limits obtained by L3in the searches for the Standard Model Higgs boson and for a fermiophobic Higgs boson are interpreted in terms of anomalous Higgs couplings.

The analysis is performed as a function of m H in steps of 1GeV.The H →γγ,H →Z γand H →WW (?)decays probe the ranges 70GeV

After the event selections described below,variables which depend on m H are built to discriminate signal and background.Finally,the number of events in a mass window around the m H value under study is compared with the Standard Model expectation and interpreted in terms of cross sections and anomalous couplings.

3Data and Monte Carlo samples

Table 2lists the centre-of-mass energies and the corresponding integrated luminosities used in this analysis.The data at

√s =189?209GeV are

reported here.All other analyses discussed in this Letter refer to the

√s =189GeV [11].

To describe the e+e?→Hγprocess we wrote a Monte Carlo generator which assumes a 1+cos2θH dependence of the di?erential cross section as a function of the cosine of the Higgs production angle,θH.It includes e?ects of initial-state[14]and?nal-state[15]radiation as well as spin correlations and o?-shell contributions in cascade decays such as H→Zγ→fˉfγ. The e+e?→e+e?H process is interpreted as the production of a narrow-width spin-zero resonance in two-photon collisions,and modelled with the PC Monte Carlo generator[16]. The di?erential cross section of the process e+e?→HZ in the presence of anomalous couplings is taken from Reference17.References18and19are used for the branching fractions and partial widths of a Higgs boson with anomalous couplings.The interference between the e+e?→HZ process in the Standard Model and in presence of anomalous couplings[17]is taken into account in the simulation.It is negligible for the e+e?→Hγand e+e?→e+e?H cases.

Signal events are generated for70GeV

Standard Model processes are modelled with the following Monte Carlo generators:GGG[20] for e+e?→γγ(γ),KK2f[21]for e+e?→qˉq(γ),PYTHIA[22]for e+e?→ZZ and e+e?→Ze+e?,KORALW[23]for e+e?→W+W?(γ)and EXCALIBUR[24]for e+e?→Weνand other four-fermion?nal states.

The L3detector response is simulated using the GEANT program[25]which takes into ac-count e?ects of energy loss,multiple scattering and showering in the detector.Time-dependent detector ine?ciencies,as monitored during the data-taking period,are included in the simula-tions.

4Event selection

All analyses presented in this Letter rely on photon identi?cation.Photon candidates are de?ned as clusters in the electromagnetic calorimeter with a shower pro?le consistent with that of a photon and no associated track in the tracking chamber.To reduce contributions from initial-state and?nal-state radiation,photon candidates must satisfy Eγ>5GeV and |cosθγ|<0.97,where Eγis the photon energy andθγits polar angle.

Events with hadronic decays of the Z and W bosons in the H→Zγand H→WW(?)

channels are pre-selected requiring high particle multiplicity and a visible energy,E vis,satisfying √

0.8

s/2.Out of the three possible two-photon combinations,the one with a mass,mγγ,closest to the m H hypothesis under investigation is retained.As an example,Figure2a presents the distribution of mγγfor m H=110GeV.The event is accepted as a Higgs candidate if

|mγγ?m H|<0.05m H.

√The numbers of events observed and expected in the full data sample at

4.2The e+e?→e+e?H→e+e?γγanalysis

In the process e+e?→e+e?H,the?nal state e?and e+tend to escape detection at low polar angles,originating events with missing longitudinal momentum and missing mass.The selection

requires two photon candidates from the H→γγdecay in the central region of the detector.

A kinematic?t is performed assuming the missing momentum to point in the beam pipe and the visible mass of the event to be consistent,within the experimental resolution,with the m H hypothesis under investigation.The distribution of theχ2of the?t is shown in Figure2b for m H=130GeV.Events are accepted as Higgs candidates ifχ2<50?0.2GeV?1×m H.The dependence of the cut on m H re?ects the decrease of the background contribution for increasing

values of m H.

√The numbers of events observed and expected in the full data sample at

4.3The e+e?→Hγ→Zγγanalysis

Pre-selected hadronic events with two isolated high energy photons are considered for the e+e?→Hγ→Zγγanalysis.Events are retained which have a recoiling mass,m rec,calculated from the four-momenta of the two photons,compatible with m Z:80GeV

as a Higgs candidate if|m qqγ?m H|<15GeV.

√The numbers of events observed and expected in the data sample at

s.Pre-selected hadronic events are retained if they have a photon with energy compatible with the m H hypothesis under investigation,E recγ(m H+20GeV)

A kinematic?t,in which the jet angles are?xed and the jet energies can vary,is performed to improve the resolution on the reconstructed W-boson mass.For m H>2m W both W bosons are on-shell and the constraint that both invariant jet-jet masses be compatible with m W is included in the?t.For m H<2m W one of the W bosons is o?-shell and only one of the invariant jet-jet masses is required to be compatible with m W.The?t is repeated for all possible jet pairings and the pairing is chosen for which theχ2of the?t is minimal.An event is considered as a Higgs candidate ifχ2<6.0for the hypothesis m H<2m W orχ2<15.0for m H>2m W.

The invariant mass of the four-jet system,m qqqq,estimates m H.Its distribution is presented in Figure2d for m H=170GeV.

√The numbers of events observed and expected in the data sample at

s is observed.The background is dominated by the processes e+e?→qˉq(γ) and e+e?→W+W?(γ),which is above65%for m H>150GeV.

5Cross sections limits

The results of all the analyses agree with the Standard Model predictions and show no evidence for a Higgs boson with anomalous couplings in the m H mass range under study.Upper limits on the product of the production cross sections and the corresponding decay branching fractions are derived[27]at the95%con?dence level(CL).The cross section of the e+e?→e+e?H process is proportional to the partial Higgs width into photons,Γ(H→γγ),and limits are

quoted onΓ(H→γγ)×Br(H→γγ).

√s)= In order to combine data sets at di?erent

√

ζσSM(

√

s whileζis a parameter which does not depend on

s>= 197.8GeV.

The cross section limits for the investigated processes are given in Figure3together with the expectations for non-zero values of the anomalous couplings.

6Limits on anomalous couplings

6.1Results from e+e?→HZ with H→fˉf or H→γγ

The process e+e?→HZ,with H→fˉf,studied in Reference8,is sensitive to anomalous HZZ and HZγcouplings in the Higgs production vertex.In addition,the process e+e?→HZ with H→γγ,object of the search for a fermiophobic Higgs[9],is sensitive to the Hγγcoupling in the decay vertex.

Limits on the couplingξ2are derived from the results of our search for the Standard Model Higgs boson[8].They are obtained by interpretingξ2as a scale factor of the Higgs production cross section and are shown in Figure4.They include the systematic uncertainties on the search for the Standard Model Higgs boson[8].

The limits on the couplings d,d B,?g Z1and?κγare extracted from the numbers of observed events,expected background and signal events reported in References8and9.These limits are driven by the size of the deviations of the productσAC×Br AC with respect toσSM×Br SM, where Br AC and Br SM denote the Higgs branching ratios in the presence of anomalous couplings and in the Standard Model respectively.The ratios R=(σAC×Br AC)/(σSM×Br SM)are shown in Figure5for H→fˉf and H→γγ,for m H=100GeV.

The H→fˉf and H→γγchannels have di?erent behaviours with respect to the parameters d and d B,as these describe the Hγγcoupling.The parameters?g Z1and?κγdescribe the

HZγand HZZ couplings and hence a?ect only the Higgs production vertex in the e+e?→HZ process.They give similar deviations for both the H→fˉf and H→γγchannels.

6.2One-dimensional limits

Figure6presents the limits on d,d B,?g Z1and?κγas a function of m H.A coupling at the time is considered,?xing the others to zero.Limits from the most sensitive channels are shown

in addition to the combined results.

√

The region m H

where the dependence of g Hγγand g(2)

HZγon the d and d B couplings is given by Equations2

and4.This Lagrangian is used to compute the maximal partial widths and branching fractions of the decays H→Zγand H→γγ,allowed by the limits on d and d B.The results are presented in Figure7for two di?erent Higgs masses,in the region of interest for Higgs searches at future colliders.The results are consistent with the tree level Standard Model expectations Γ(H→Zγ)≈Γ(H→γγ)≈0.

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Letters.

The L3Collaboration:

P.Achard,20O.Adriani,17M.Aguilar-Benitez,25J.Alcaraz,25G.Alemanni,23J.Allaby,18A.Aloisio,29M.G.Alviggi,29 H.Anderhub,49V.P.Andreev,6,34F.Anselmo,8A.Are?ev,28T.Azemoon,3T.Aziz,9P.Bagnaia,39A.Bajo,25G.Baksay,26 L.Baksay,26S.V.Baldew,2S.Banerjee,9Sw.Banerjee,4A.Barczyk,49,47R.Barill`e re,18P.Bartalini,23M.Basile,8

N.Batalova,46R.Battiston,33A.Bay,23F.Becattini,17U.Becker,13F.Behner,49L.Bellucci,17R.Berbeco,3J.Berdugo,25 P.Berges,13B.Bertucci,33B.L.Betev,49M.Biasini,33M.Biglietti,29A.Biland,49J.J.Blaising,4S.C.Blyth,35G.J.Bobbink,2 A.B¨o hm,1L.Boldizsar,12B.Borgia,39S.Bottai,17D.Bourilkov,49M.Bourquin,20S.Braccini,20J.G.Branson,41

F.Brochu,4J.D.Burger,13W.J.Burger,33X.D.Cai,13M.Capell,13

G.Cara Romeo,8G.Carlino,29A.Cartacci,17

J.Casaus,25F.Cavallari,39N.Cavallo,36C.Cecchi,33M.Cerrada,25M.Chamizo,20Y.H.Chang,44M.Chemarin,24

A.Chen,44G.Chen,7G.M.Chen,7H.F.Chen,22H.S.Chen,7G.Chiefari,29L.Cifarelli,40F.Cindolo,8I.Clare,13R.Clare,38 G.Coignet,4N.Colino,25S.Costantini,39

B.de la Cruz,25S.Cucciarelli,33J.A.van Dalen,31R.de Asmundis,29

P.D′e glon,20J.Debreczeni,12A.Degr′e,4K.Dehmelt,26K.Deiters,47D.della Volpe,29E.Delmeire,20P.Denes,37

F.DeNotaristefani,39A.De Salvo,49M.Diemoz,39M.Dierckxsens,2C.Dionisi,39M.Dittmar,49A.Doria,29M.T.Dova,10,?D.Duchesneau,4M.Duda,1B.Echenard,20A.Eline,18A.El Hage,1H.El Mamouni,24A.Engler,35F.J.Eppling,13

P.Extermann,20M.A.Falagan,25S.Falciano,39A.Favara,32J.Fay,24O.Fedin,34M.Felcini,49T.Ferguson,35H.Fesefeldt,1 E.Fiandrini,33J.H.Field,20F.Filthaut,31P.H.Fisher,13W.Fisher,37I.Fisk,41G.Forconi,13K.Freudenreich,49

C.Furetta,27Yu.Galaktionov,28,13S.N.Ganguli,9P.Garcia-Abia,25M.Gataullin,32S.Gentile,39S.Giagu,39Z.F.Gong,22 G.Grenier,24O.Grimm,49M.W.Gruenewald,16M.Guida,40R.van Gulik,2V.K.Gupta,37A.Gurtu,9L.J.Gutay,46

D.Haas,5D.Hatzifotiadou,8T.Hebbeker,1A.Herv′e,18J.Hirschfelder,35H.Hofer,49M.Hohlmann,26G.Holzner,49

S.R.Hou,44Y.Hu,31B.N.Jin,7L.W.Jones,3P.de Jong,2I.Josa-Mutuberr′?a,25M.Kaur,14M.N.Kienzle-Focacci,20

J.K.Kim,43J.Kirkby,18W.Kittel,31A.Klimentov,13,28A.C.K¨o nig,31M.Kopal,46V.Koutsenko,13,28M.Kr¨a ber,49

R.W.Kraemer,35A.Kr¨u ger,48A.Kunin,https://www.360docs.net/doc/e15955852.html,dron de Guevara,https://www.360docs.net/doc/e15955852.html,ktineh,https://www.360docs.net/doc/e15955852.html,ndi,17M.Lebeau,18A.Lebedev,13 P.Lebrun,24P.Lecomte,49P.Lecoq,18P.Le Coultre,49J.M.Le Go?,18R.Leiste,48M.Levtchenko,27P.Levtchenko,34

C.Li,22S.Likhoded,48C.H.Lin,44W.T.Lin,44F.L.Linde,2L.Lista,29Z.A.Liu,7W.Lohmann,48E.Longo,39Y.S.Lu,7

C.Luci,39L.Luminari,39W.Lustermann,49W.G.Ma,22L.Malgeri,20A.Malinin,28C.Ma?n a,25J.Mans,37J.P.Martin,24 F.Marzano,39K.Mazumdar,9R.R.McNeil,6S.Mele,18,29L.Merola,29M.Meschini,17W.J.Metzger,31A.Mihul,11

https://www.360docs.net/doc/e15955852.html,cent,18G.Mirabelli,39J.Mnich,1G.B.Mohanty,9G.S.Muanza,24A.J.M.Muijs,2B.Musicar,41M.Musy,39S.Nagy,15 S.Natale,20M.Napolitano,29F.Nessi-Tedaldi,49H.Newman,32A.Nisati,39T.Novak,31H.Nowak,48R.O?erzynski,49

https://www.360docs.net/doc/e15955852.html,antini,39I.Pal,46C.Palomares,25P.Paolucci,29R.Paramatti,39G.Passaleva,17S.Patricelli,29T.Paul,10

M.Pauluzzi,33C.Paus,13F.Pauss,49M.Pedace,39S.Pensotti,27D.Perret-Gallix,4B.Petersen,31D.Piccolo,29F.Pierella,8 M.Pioppi,33P.A.Pirou′e,37E.Pistolesi,27V.Plyaskin,28M.Pohl,20V.Pojidaev,17J.Pothier,18D.Proko?ev,34

J.Quartieri,40G.Rahal-Callot,49M.A.Rahaman,9P.Raics,15N.Raja,9R.Ramelli,49P.G.Rancoita,27R.Ranieri,17

A.Raspereza,48P.Razis,30D.Ren,49M.Rescigno,39S.Reucroft,10S.Riemann,48K.Riles,3

B.P.Roe,3L.Romero,25

A.Rosca,48C.Rosemann,1C.Rosenbleck,1S.Rosier-Lees,4S.Roth,1J.A.Rubio,18G.Ruggiero,17H.Rykaczewski,49

A.Sakharov,49S.Saremi,6S.Sarkar,39J.Salicio,18E.Sanchez,25C.Sch¨a fer,18V.Schegelsky,34H.Schopper,21

D.J.Schotanus,31C.Sciacca,29L.Servoli,33S.Shevchenko,32N.Shivarov,42V.Shoutko,13

E.Shumilov,28A.Shvorob,32 D.Son,43C.Souga,24P.Spillantini,17M.Steuer,13D.P.Stickland,37B.Stoyanov,42A.Straessner,20K.Sudhakar,9

G.Sultanov,42L.Z.Sun,22S.Sushkov,1H.Suter,49J.D.Swain,10Z.Szillasi,26,?X.W.Tang,7P.Tarjan,15L.Tauscher,5

L.Taylor,10B.Tellili,24D.Teyssier,24C.Timmermans,31Samuel C.C.Ting,13S.M.Ting,13S.C.Tonwar,9J.T′o th,12

C.Tully,37K.L.Tung,7J.Ulbricht,49E.Valente,39R.T.Van de Walle,31R.Vasquez,46V.Veszpremi,26G.Vesztergombi,12 I.Vetlitsky,28

D.Vicinanza,40G.Viertel,49S.Villa,38M.Vivargent,4S.Vlachos,5I.Vodopianov,26H.Vogel,35H.Vogt,48

I.Vorobiev,35,28A.A.Vorobyov,34M.Wadhwa,5Q.Wang31X.L.Wang,22Z.M.Wang,22M.Weber,18H.Wilkens,31

S.Wynho?,37L.Xia,32Z.Z.Xu,22J.Yamamoto,3B.Z.Yang,22C.G.Yang,7H.J.Yang,3M.Yang,7S.C.Yeh,45An.Zalite,34 Yu.Zalite,34Z.P.Zhang,22J.Zhao,22G.Y.Zhu,7R.Y.Zhu,32H.L.Zhuang,7A.Zichichi,8,18,19B.Zimmermann,49M.Z¨o ller.1

1III.Physikalisches Institut,RWTH,D-52056Aachen,Germany§

2National Institute for High Energy Physics,NIKHEF,and University of Amsterdam,NL-1009DB Amsterdam, The Netherlands

3University of Michigan,Ann Arbor,MI48109,USA

4Laboratoire d’Annecy-le-Vieux de Physique des Particules,LAPP,IN2P3-CNRS,BP110,F-74941 Annecy-le-Vieux CEDEX,France

5Institute of Physics,University of Basel,CH-4056Basel,Switzerland

6Louisiana State University,Baton Rouge,LA70803,USA

7Institute of High Energy Physics,IHEP,100039Beijing,China△

8University of Bologna and INFN-Sezione di Bologna,I-40126Bologna,Italy

9Tata Institute of Fundamental Research,Mumbai(Bombay)400005,India

10Northeastern University,Boston,MA02115,USA

11Institute of Atomic Physics and University of Bucharest,R-76900Bucharest,Romania

12Central Research Institute for Physics of the Hungarian Academy of Sciences,H-1525Budapest114,Hungary?13Massachusetts Institute of Technology,Cambridge,MA02139,USA

14Panjab University,Chandigarh160014,India

15KLTE-ATOMKI,H-4010Debrecen,Hungary?

16Department of Experimental Physics,University College Dublin,Bel?eld,Dublin4,Ireland

17INFN Sezione di Firenze and University of Florence,I-50125Florence,Italy

18European Laboratory for Particle Physics,CERN,CH-1211Geneva23,Switzerland

19World Laboratory,FBLJA Project,CH-1211Geneva23,Switzerland

20University of Geneva,CH-1211Geneva4,Switzerland

21University of Hamburg,D-22761Hamburg,Germany

22Chinese University of Science and Technology,USTC,Hefei,Anhui230029,China△

23University of Lausanne,CH-1015Lausanne,Switzerland

24Institut de Physique Nucl′e aire de Lyon,IN2P3-CNRS,Universit′e Claude Bernard,F-69622Villeurbanne,France 25Centro de Investigaciones Energ′e ticas,Medioambientales y Tecnol′o gicas,CIEMAT,E-28040Madrid,Spain?

26Florida Institute of Technology,Melbourne,FL32901,USA

27INFN-Sezione di Milano,I-20133Milan,Italy

28Institute of Theoretical and Experimental Physics,ITEP,Moscow,Russia

29INFN-Sezione di Napoli and University of Naples,I-80125Naples,Italy

30Department of Physics,University of Cyprus,Nicosia,Cyprus

31University of Nijmegen and NIKHEF,NL-6525ED Nijmegen,The Netherlands

32California Institute of Technology,Pasadena,CA91125,USA

33INFN-Sezione di Perugia and Universit`a Degli Studi di Perugia,I-06100Perugia,Italy

34Nuclear Physics Institute,St.Petersburg,Russia

35Carnegie Mellon University,Pittsburgh,PA15213,USA

36INFN-Sezione di Napoli and University of Potenza,I-85100Potenza,Italy

37Princeton University,Princeton,NJ08544,USA

38University of Californa,Riverside,CA92521,USA

39INFN-Sezione di Roma and University of Rome,“La Sapienza”,I-00185Rome,Italy

40University and INFN,Salerno,I-84100Salerno,Italy

41University of California,San Diego,CA92093,USA

42Bulgarian Academy of Sciences,Central Lab.of Mechatronics and Instrumentation,BU-1113So?a,Bulgaria

43The Center for High Energy Physics,Kyungpook National University,702-701Taegu,Republic of Korea

44National Central University,Chung-Li,Taiwan,China

45Department of Physics,National Tsing Hua University,Taiwan,China

46Purdue University,West Lafayette,IN47907,USA

47Paul Scherrer Institut,PSI,CH-5232Villigen,Switzerland

48DESY,D-15738Zeuthen,Germany

49Eidgen¨o ssische Technische Hochschule,ETH Z¨u rich,CH-8093Z¨u rich,Switzerland

§Supported by the German Bundesministerium f¨u r Bildung,Wissenschaft,Forschung und Technologie.

?Supported by the Hungarian OTKA fund under contract numbers T019181,F023259and T037350.

?Also supported by the Hungarian OTKA fund under contract number T026178.

?Supported also by the Comisi′o n Interministerial de Ciencia y Tecnolog′?a.

?Also supported by CONICET and Universidad Nacional de La Plata,CC67,1900La Plata,Argentina.

△Supported by the National Natural Science Foundation of China.

Production Decay mode

H→γγH→WW(?)

e+e?→Hγ2γ+2jets1γ+bˉb[11]

e+e?→He+e?–bˉb+p/[11]

e+e?→HZ–fˉff′ˉf′[8]

Table1:Experimental signatures for the search for anomalous couplings in the Higgs sector. The symbol p/denotes missing energy and momentum.Searches in the e+e?→Hγ→bˉbγand e+e?→e+e?H→e+e?bˉb channels are only performed at√

s(GeV)

176.828.882.467.636.174.7135.6

Table2:Average centre-of-mass energy and integrated luminosity of the data samples used for the search for anomalous couplings in the Higgs sector.

Hγ→γγγe+e?H→e+e?γγHγ→ZγγHγ→WW(?)γN D N B?(%)N D N B?(%)

7000.019.5–––

906 1.724.2–––

1109 4.928.5–––

1301110.930.41011.518.0

1501919.931.92222.825.5

1703849.732.47274.726.8

1902429.530.1113107.319.5

Table3:Numbers of observed,N D,and expected,N B,events and signal selection e?ciencies,

?,for di?erent analysis channels and values of the Higgs mass.Centre-of-mass energies in √

the range189GeV<

s<209GeV range.

e ?H

γe ?

e +e

Figure 1:Relevant production processes in the search for anomalous couplings in the Higgs sector at LEP:a)e +e ?→H γ,b)e +e ?→e +e ?H and c)e +e ?→HZ.

m γγ [GeV ]

E v e n t s /2 G e V

E v e n t s /5

m qq γ [GeV ]

E v e n t s /8 G

e V

m qqqq [GeV ]

E v e n t s /4 G e V

Figure 2:Distributions of the ?nal discriminant variables for a)the e +e ?→γγγchannel:the mass,m γγ,of the two-photon system;b)the e +e ?→e +e ?γγchannel:the χ2of the constrained ?t;c)the e +e ?→Z γγchannel:the mass,m qq γ,of the system of the two-jets and a photon and d)the e +e ?→WW (?)γchannel:the mass,m qqqq ,of the hadronic system.The points represent the data,the open histograms the background and the hatched histograms the Higgs signal with an arbitrary cross section of 0.1pb.The Higgs mass hypotheses indicated in the ?gures are considered.The arrows indicate the values of the cuts.

H [GeV]m

[GeV]

Figure3:Upper limits at95%CL as a function of the Higgs mass on:a)σ(e+e?→Hγ)×Br(H→γγ);b)Γ(H→γγ)×Br(H→γγ);c)σ(e+e?→Hγ)×Br(H→Zγ);d)σ(e+e?→Hγ)×Br(H→WW(?)).The dashed line indicates the expected limit in the absence of a signal. Predictions for non-zero values of the anomalous couplings are also shown.

m H [GeV ]

95% C L l i m i t o n ξ

Figure 4:The 95%CL upper bound on the anomalous coupling ξ2as a function of the Higgs mass,as obtained from the results of the search for the Standard Model Higgs boson [8].The dashed line indicates the expected limit in the absence of a signal.The dark and light shaded bands around the expected line correspond to the 68.3%and 95.4%probability bands,denoted by 1σand 2σrespectively.

1101010d

-1

102

103

-0.2-0.100.10.2

d B

-1

10102

103-1

?g 1

Z R

-1

102

103

-101

?κγ

Figure 5:The theoretical predictions for the ratios R =(σAC ×Br AC )/(σSM ×Br SM )for the

e +e ?→HZ channel for the couplings a)d ,b)d B ,c)?g Z

1and d)?κγ.The solid line corresponds to the decay H →f ˉf and the dashed line to H →γγ.The predictions refer to m H =100GeV.

The ratios for the two decay modes coincide for ?g Z

1and ?κγ.

Exclusion (95% CL):

Combined Expected limit

ee →γγγ, ee

γγee →Z

γγ

ee →

ee →WW (*)

m H [GeV ]

?g 1

Z m H [GeV ]

?κγ

Figure 6:Regions excluded at 95%CL as a function of the Higgs mass for the anomalous

couplings:a)d ,b)d B ,c)?g Z

1and d)?κγ.The limits on each coupling are obtained under the assumption that the other three couplings are equal to zero.The dashed line indicates the expected limit in the absence of a signal.The di?erent hatched regions show the limits obtained by the most sensitive analyses:e +e ?→H γ→γγγ,e +e ?→e +e ?H →e +e ?γγ,e +e ?→H γ→Z γγ,e +e ?→HZ and e +e ?→H γ→WW (?)γ.

10110

Γ(H→γγ) [MeV]

Figure7:Regions excluded at95%CL for:a)the partial widthsΓ(H→Zγ)vs.Γ(H→γγ) and b)the branching fractions Br(H→Zγ)vs.Br(H→γγ)in presence of the d and d B anomalous couplings.Two values of the Higgs boson mass are considered.The results are consistent with the tree level Standard Model expectationsΓ(H→Zγ)≈Γ(H→γγ)≈0.