

 10 May 1995

H

\Gamma \Gamma events in the ZEUS Detector

E. Accomando(1

;2),M. Iori (2), M. Mattioli(2)

(1) Dipartimento di Fisica,

Universita' di Torino, Italy

(2) Dipartimento di Fisica,

Universita' di Roma "La Sapienza", Italy

and I.N.F.N., sez. di Roma, Italy

April 10, 1995

Abstract The supersymmetric left-right models suggest a production of doubly charged Higgs particles. Still there is no evidence for the existence and only some lower limits for their mass are present from the Z decay. Here we investigate the possibility of observing the doubly electronic Higgs decay assuming a MH\Gamma \Gamma = 50 Gev and MH\Gamma \Gamma = 100 Gev.

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1 Higgs boson at HERA The doubly charged Higgs boson, H

\Gamma \Gamma are the basic particles of a class of model of

elettro-weak interaction beyond the Standard Model with spontaneous parity violation [1,2]. In the recent paper [3] the authors pointed out the possible production of a single double Higgs boson at Hera, in e \Gamma p collider at Desy with ps = 313 GeV . Their calculated the following processes:

e

\Gamma p ! e+p H\Gamma \Gamma (1)

where

H

\Gamma \Gamma ! e\Gamma e\Gamma (_\Gamma _\Gamma ; o/ \Gamma o/ \Gamma )

and

e

\Gamma p ! _+p H\Gamma \Gamma (2)

where

H

\Gamma \Gamma ! e\Gamma _\Gamma (e\Gamma o/ \Gamma ; _\Gamma o/ \Gamma )

whose diagrams are shown in Fig. 1

2 Study of the topology of the generated events In order to investigate the possibility of observing the processes (1,2) in the Zeus detector was written a generator based upon the cross section and the decay rate [2]. In this generator the mass of Higgs may be varied also. The decay mode as well the coupling constant gee,ge_. Fig. 2 shows a plot of the calculated cross section as function of Higgs mass. The dashed line refers to the process (1) and the full line to the process (2). The first step in the analysis was to investigate the topology of the generated events in order to estimate the fraction for which the lepton would visible in the detector. As shown before the Higgs boson can decay in two identical lepton (e

\Gamma e\Gamma ; _\Gamma _\Gamma ) or in

electron- muon (e

\Gamma _\Gamma ). In the first case according to the leptonic number and charge

conservation in the final state is present a positron in the second case a positive muon. In both situations they follow the electron beam direction (backward respect to the proton beam direction). The processes (1,2) have the caratterisctics to be diffractive ( high Q2) then the proton goes in the beam pipe (forward direction) and no information in the hadronic calorimeter are left.

2.1 Study of reaction e

\Gamma p ! p e+ H \Gamma \Gamma ! p e+ e\Gamma e\Gamma

The Zeus Monte Carlo provides a detailed simulation of the detector geometry and resolution based upon the Geant package. The output is read in Zephyr and recontruction of events is carried out.

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Using this software in the offline enviroment we have investigated the global properties of the event. For the reason the calorimeter is hermetic we devoted our study to the e

\Gamma \Gamma e\Gamma

Higgs decays in particular to the following reaction

e

\Gamma p ! p e+ H\Gamma \Gamma

where

H

\Gamma \Gamma ! e\Gamma e\Gamma

As shown in Ref [3] those results exclude an Higgs-boson mass 6:5 ! MH\Gamma \Gamma ! 36:5 GeV as function of the coupling strength of the Higgs boson to lepton pairs,gll. We have chosen a Higgs mass value of 50 GeV and of 100 GeV with gee = 0:5 10

\Gamma 4 and gee = 0:1 respectively.

An electromagnetic cluster finding algorithm for Uranium calorimeter [6]and CTD finding software [7] was used to identified a global track.

Figs 3a-b show the energy deposited as electromagnetic cluster in the calorimeter and the distribution of the polar angle, \Theta l, of one of the negative leptons in the final state for MH\Gamma \Gamma = 50 GeV respectively.

We find the most of the energy relased by the electron in the calorimeter is greater than 20 GeV and the energy distribution of the electromagnetic cluster (Fig. 3a) is peacked at 25 GeV. In Fig 3b we find a deleption of events at small \Theta l angle due to calorimeter acceptance in forward region.

Figs 4a-b show the same distribution as Fig 3a-b using MH = 100 GeV . We find again an excess of events with very low energy deposited in em-calorimeter and the \Theta l distribution is shifted to low values as expected. Each time the decay track loses the energy deposited in the calorimeter the track can be identified by the cone algorithm as pion or muon.

After a generation of 1000 events ,using the setup of 1994 data taking, with MH\Gamma \Gamma = 100 GeV ,by the cluster identification, we find the 88% \Sigma 3% are identified electron , 8% \Sigma 1 pion and the rest are muons and jets. The misindentification of the cluster as pion increases to 9:5% \Sigma 1 when we assume MH\Gamma \Gamma = 50 GeV .

Fig 5a-b show the \Delta OEee angle distribution respectively obtained using only the two highest electromagnetic clusters found in the calorimeter with Ecal ? 20 GeV at least and the Higgs mass reconstructed imposing 150 ! \Delta OEee ! 200, \Theta l ? 30 degrees for the decay leptons. A clear peack at MH = 50 GeV is found. Fig 6a-b show the some distribution of Fig 5a-b assuming MH\Gamma \Gamma = 100 GeV .

The topology of this sample of events is characterized by a two isolated tracks in the Central Tracking Detector (CTD), back-to-back in the transverse plane leaving large amount of energy in the electromagnetic calorimeter.

The general conclusion to be drawn from these investigations is that the detector acceptance is able to detect two leptons decaying from Higgs boson and is approximately constant if we assume an Higgs mass of 50 GeV and 100 GeV but we lose electron identified track by the calorimeter at small \Theta l values (15 ! \Theta l ! 40)

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3 Background The nature of the Higgs boson signal chosen with two high energy electron seen in the detector makes the physics background rare. The transverse energy, Et and longitudinal energy Ez for the decay electrons is plotted in Fig 7-8 rispectively for MH\Gamma \Gamma = 50 GeV and MH\Gamma \Gamma = 100 GeV and Ee ? 20 GeV . We find the Et distribution is peacked at 20 GeV and 45 GeV for MH\Gamma \Gamma = 50 GeV and MH\Gamma \Gamma = 100 GeV respectively. Appling a cut in tranverse energy , Et ? 15 GeV we remove possible contribution from elastic J=\Psi where a charge misidentification is present.

4 Conclusions We have investigated one of the production processes of Higgs boson at Hera energies in the framework left-right symmetric model proposed by Senjanovic and Mohapatra. The presence of MH\Gamma \Gamma ? 40 GeV is allowed both theoretically and experimentally assuming gee ? 10

\Gamma 3. A remarkable signature enables us to search for the Higgs mass. According

with this analysis after 100 pb

\Gamma 1 we extimate have 18 \Sigma 1 events from Higgs with MH

\Gamma \Gamma =

50 GeV characterized by a two isolated tracks in the Central Tracking Detector (CTD), back-to-back in the transverse plane leaving ECal ? 20 GeV

5 Acknowledgments We thank to Prof. S. Petrarca for valuable discussions.

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6 References

[1] R.H. Mohapatra and G. Senjanovic, Phys .Rev. Lett. 44 1980 912 [2] G.B. Gelmini and M. Roncadelli, Phys. Lett. B 99 1981 411 [3] E. Accomando and S. Petrarca Phys. Lett. B 323 1994 212 [4] The generator is supported on UNIX stations,the source code of the program can

be found in e3rs01.roma.infn.it; The generate input to the Zeus detector simulation programme (Mozart) was obtained by the interface program to ZDIS (ZN-94-031)

[5] M. Swartz et al. P.R.L. 64 24 1990 2877 [6] P. DeJong et al Status of the Calorimeter Reconstruction Programme ZEUS-91-36 [7] K. Long at al CTD Reconstruction Programme User's Guide ZEUS-90-122

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7 Figures

6 Figure 1: Feynman graphs for single H

\Gamma \Gamma production at Hera

1 Figure 2: Plot of the total cross sction at ps = 313 GeV versus MH\Gamma \Gamma from Ref [3]

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Figure 3: Energy in the EmCAL a) Electron energy in the electromagnetic cluster b) \Theta of electromagnetic cluster of one electron in the final state both distributions are obtained with MH\Gamma \Gamma = 50 GeV

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Figure 4: Energy in the EmCAL a) Electron energy in the electromagnetic cluster b) \Theta of electromagnetic cluster of one electron in the final state both distributions are obtained with MH\Gamma \Gamma = 100 GeV

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Figure 5: MH\Gamma \Gamma = 50 GeV : a) \Delta OEee distribution of the electromagnetic cluster for the two highest electron b) Higgs mass evaluated using the electromagnetic clusters; the cuts are discussed in the text

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Figure 6: MH\Gamma \Gamma = 100 GeV : a) \Delta OEee distribution of the electromagnetic cluster for the two highest electron b) Higgs mass evaluated using the electromagnetic clusters; the cuts are discussed in the text

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Figure 7: MH\Gamma \Gamma = 50 GeV : Transverse energy, Et and longitudinal energy, Ez for the decay electron with Ee ? 20 GeV

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Figure 8: MH\Gamma \Gamma = 100 GeV : Transverse energy, Et and longitudinal energy, Ez for the decay electron with Ee ? 20 GeV

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