• No results found

UNIVERSITY OF STOCKHOLM

N/A
N/A
Protected

Academic year: 2021

Share "UNIVERSITY OF STOCKHOLM"

Copied!
7
0
0

Loading.... (view fulltext now)

Full text

(1)

UNIVERSITY OF STOCKHOLM

INSTITUTE OF PHYSICS

LIGHT HIGG8 BOSONS AT L E P

G. EKSPONG

STUDSVIK

Bibliot«k«t

1981 -I?-1 6

(2)

LIGHT HIGGS BOSONS AT LEP

G. Ekspong

Institute of Physics, University of Stockholm Vanadisvägen 9, S-113 46 Stockholm, Sweden

June 18, 1980

(Presented at COLLEPS meeting, CERN, January 19, 1981)

ABSTRACT

Among possible production reactions for neutral Higgs bosons it is known that e e -* Z + H offers advantages of relatively high production cross section and low background from other reactions. With Z decaying to two electrons, which are measured, the existence of a Higgs candidate will be seen as a peak in the missing mass spectrum. It is shown that a sufficiently good mass resolution is obtainable to make a search for Higgs feasible at LEP. In its first phase, the energy of LEP limits the search to Higgs bosons of mass around 10 GeV.

(3)

1. INTRODUCTION

In gauge theories of electroweak interactions one Higgs boson, H , is an important ingredient. Besides the study of the intermediate bosons, 7. , and W , the search for Higgs bosons will be important for LEP experiments. In contrast to the case with the gauge particles whose masses are predicted well

by theory, no prediction exists for the Higgs boson. Some upper and lower 2)

limits have been suggested and also a favoured mass around 10 GeV . With

a LEP-energy of 100 GeV in its first phase and a Z -mass of about 90 GeV

this puts the production of Higgs bosons up to the favoured mass within reach at an early period of LEP-experimentation. However, a pessimistic view of the experimental resolution of recoiling Higgs has been published giving ;i mass resolution of Am = 25 GeV for a 10 GeV Higgs boson and even worse

H

for lower masses. The aim of this paper is to point out that a mass resolution of 1 to 2 GeV is quite feasible and that therefore experiments to search for Higgs bosons can start as soon as LEP reaches energies in the Z mass

region-2. PRODUCTION AND DECAY

Since the coupling of Higgs bosons to other particles is increasing with their masses the production of Higgs might have passed unnoticed even if the mass is low. It is clear that LEP offers new unique possibilities. Two reactions will be of special interest for early LEP experimentation. One reaction is the decay of a new, heavy onium into H + y . Another is the production of

o o + - o o H via a virtual Z i n e e - * Z + H

o

(4)

In the following we will concentrate on this process. Of great importance is that the production cross section reaches a maximum rather soon alter the treshold energy has been reached, namely at Vs m •+ m •< Q where

H

3)

Q = (V2 -1) m ' . This means that a LEP with 100 GeV energy can produce H

with maximum cross section a Higgs boson with 8 GeV mass together with a Z of 88 GeV mass, and that a 10 GeV Higgs boson would require a LEP energy of 102 GeV for the same conditions.

It has been shown that the maximum cross section is given by

g ( e V -»Z°4 H°)

=

47

In the range of energies available at LEP, phase 1, this ratio is then about 5 2

or larger. The point cross section is ff(e e -* n fi ) = —— — nb . os s

3 2 —2 —1

With a LEP-luminosity of 0.4 • 10 cm s the rate of production will

be 140 events per day or more. The decay of a Higgs boson will give a splash of hadrons by a chain of decays through the heaviest quarks available down to K-mesons and pions. Alternatively the Higgs boson decays to the heaviest available leptonpairs which then decay further to electrons, muons and neutrinos. The study of these decay products will be important at a second stage of experimentation once the existence of the Higgs boson has been established.

3. EXPERIMENTAL METHOD

The obvious method to find Higgs bosons is to reconstruct the Z from its decay products and then compute the missing mass in order to search for

(5)

Higgs. To be successful in such a search a relatively high mass resolution 2)

is required. The published values for the mass resolution is very poor for

Higgs masses below 20 GeV. ( A mu = 25 GeV at mu - 10 GeV).

H H

The most suitable decay of Z is Z -*e e rather than Z ~* n n since electrons can be measured more accurately than muons at these high energies. We assume that the error in electron energy is given by

— = - p (E in GeV)

a VE

where a = 0.10 for good sampling shower detectors.

By measuring the energies (E+, E ) and angle 0 of the e e -pair the 7°

is reconstructed and we have

= E+ + E_ 2 2 S m_ = 4 E E sin / 2 Z + and = s ( 1 ) ( 3 )

The errors in the angle 6 contributes negligibly and the same is true for the beam energy spread which is only about 0.1 GeV in Vs . From this we get

(6)

Near the threshold (Vs = m + m + Q , with Q « V s ) we have approximately Z H

E * E = m . Equ. (4) gives * " / 2

= ( mH+ Q ) A E+ + ( m H + Q )

Since the errors of the electron energies are independent we get by squaring and adding

VE

where AE = aVE has been inserted. Again, near the threshold E ^ m and thus

Am = aV2m

H Z

since Q = (= CV2 - 1 )m at the peak of the production cross section.H

A good shower detector will have a = 0.10 and thus 4m = 1 . 3 GeV

H

This mass resolution is independent of the mass of m within the range of n

energies available at the phase 1 of LEP. The experimental requirements call for a good electron detector together with detection capability of H

decay products. As was pointed out in ref. (2) this allows to eliminate

back-ground events and give a sample relatively free of backback-ground. The rate, considering a branching of 3% for Z *• e e is about 4 events per day for

32 -2 -1

(7)

REFERENCES

1. S. Weinberg - Phys. Rev. Lett. Jj), 1264

A. Salam - Proceedings of the 8th Nobel Symposium of Elementary Particle Theory (Almqvist & Wiksell, Stockholm 1968).

2. G. Barbiellini, G. Bonneaud, G. Coignet, J . Ellis, M.K. Guillurd,

J . F . G r i v a z , C . M a t t e u z z i , and B . H . Wiik - DESY 7 9 / 2 7 (1979)

3 . J . E l l i s , M . K . Gaillard, and D . V . N a n o p o u l o s - N u c l . P h y s . B ' 0 6 , 292

( 1 9 7 6 )

References

Related documents

H1a: The legitimacy and historical continuity of Botswana’s political institutions from pre-colonial, through colonial and into the post-colonial era, made Tswana

This study, based on a longitudinal epidemiological cohort, provides evidence that harsh parenting during the early years of development is associated with lower

Cookie management When a user logs in, Acrobat Connect Pro returns a cookie that identifies the user’s session.. You need to pass the cookie back to the server on all calls made

The prototype described here (see Figure 2) was developed as a proof-of-concept tool to demonstrate some example search results using pataphysical algorithms. In this case the

Abstract: It will show that, the second structural phase transition (BCC-FCC) may be took place in the semimetals cause of extra condition as temperature or doping… The

COMPENSATION UNIT IN MICROGRID SYSTEM In conventional methods [13], [14], the series harmonics reduction units are placed at the grid side, as shown in Fig.1 where

observations from the EIRIS database; Lewis and Webley (1994) observed that the majority of investors showed an attitude revealing a positive predisposition to make social and

• The Management Plan identifies the most pressing problems in an estuary and establishes goals, objectives, and actions for resolving them. • Implementation of