Some experimental possibilities for free quarks search at hadron colliders

Nuclear Physics B (Proc. Suppl .) 23A (1991) 21-23 North-Holland

21

SOME EXPERIMENTAL POSSIBILITIES FOR FREE QUARKS SEARCH AT HADRON COLLIDERS P .F . Ermolov Institute of Nuclear Physics, Moscow State University, Moscow 119899, USSR On the base of a multichannel multilayer silicon detector it is proposed to search the production of free quarks on the hadronic colliders . The estimation at the yield of quarks and background conditions in the installation DO at %&-1 .8 TeV is presented .

1 . Theoretical basis . There papers,

in

exist

a

which

lese

number

of

idea

of

the

theoretical incomplete

confinement is being developed .

This

idea

based

the

complete

on

the

absence

of

is

_tomparsmively

to

the

total the . Due to f

interaction cry-sect" the b-quarks p

a to

(10-12 s) it is difficult evidence for the fact of

get

their

the s-quark with wss 0 .5 GeV and

confinement hypothesis . It is turned out 112 10712 cm), at the large distances (

that

1/3, which can

the

The lepton pairs, p

growing potential changes

onto

p +p---®b+'S+X

coulomb decreasing and confinement

area

its

behaviour

quarks

and

can

leave

This

L-----® c + I1

possibility can be realized at high energies of

with

tally .

in

k decay

+ 711

L--10S

+ all

in

which

is

can be used to

produced

is

quarks production . In this case it is

necessary for a free quark to

be

+V0/N 2

, equal to Eth 2M+VO term in the right

side

where

the the

describes

losses onto gluon radiation

of

third

the

energy

quark

point

mass M, moving in a force field from the of its

creation

up

to

maximum

the

potential . It is obviously from this high

that threshold energy is very

of

of

the

equation, for

light

quarks and their real production is practically impossible even for the new Note, that

even

for

the

colliders .

hadron c-quarks

threshold

The threshold energy for heavy b-quarks with mass M = 5 GeV should be in the range 50 -

200

GeV in the rest frame of the colliding partons . The cross-section for free quark production the center of mass energy about order of 1032 cm2 ,

i .e ., of

the

2

to

measure

TeV factor

is

at of 1077

select

the

events

ionization

the

s-quarks in the matter of

bible

produced

the

by

detector .

the

This

indication

onto production of free quarks . The

ionization

produced

by

produced by

s-quark the

a

free

with

direct

measurement can serve as is

smut

minimal

Thus, it is necessary to sensitive detector

with

1/10

have low

one

particles .

ionizing a

of

sufficiently level

noise

to

measure such small ionization . scheme

Note here that the confinement

energy is greater than Eth >500 GeV .

But

charge

red

the colliding particles . It has been schown paper [1], that the threshold energy

direct

t-®c+ 12+ + vL

the

free .

become

the

creation .

experimental and theoretical approv~ertt of the

be

lif

short

predicts

very

with large

incomplete value

for colour

of a free te matter ( 10 bn ) . This value quark with usual of cross-section needs the minimal amount of interaction

matter

cross-section

before

the

detector

measuring

the

ionization produced by s-quark . Additionally if one uses the multilayer detector it is possible

0920-5632/91/$03 .50 0 1991- Elsevier Science Publishers B .V . (North-Holland)

PS. Ermolov/Some experimental possibilities for free quarks search at hadron colliders to

e a direct measurement of the interaction

1

of s-quark in the matter, i .e . the value

of the inelastic cross-section of the

5 . Due to the fact that this process is very rare

coloured

theoretical

including

data,

oolll

is

does

not

the

(eceM

sold be

t'

CEFM

0 .6

i .e ., the

SPFS

se the threshold energies needed at this oollider and s-quark

of +

for

the

with

As follow from the above n

to

carry

an

oisly

consideration out

a

it

special

to search for free quarks experiment production . An should satisfy to the following main conditions : than

1 .5

TeV

and

luminosity of the cm-2s-1 or greater ;

about 1031

charge

of

equal to 1f3, i .e ., it is necessary to experimental

setup

measure

the

Accelerator

Laboratory (FNAL, USA) is the ohly

accelerator

should

length

have

a

the

end

of

energy up to

carried out at INP MSU during 1989 - 1990 years b--quark,

moving

throw

potential barrier, radiates a large

present

time

the

number

of

gluons . This means, that free s-quark should be

1997

-1M .

The

em

magnitude

is

being

discussed

now . at

the Tevatron : the CDF, is acting at the present and Ill, which should start to run in 1991 . The DO setup has a number of advantages s-quark

search

select moons

and

experiment .

calorimetry,

for

electrons

within

range of angles, opportunity the setup additional

to

detector

a

special

detector,

which

detector is placed at the distance = 20 cm from interaction vertex ;

wide into

search

will

for

effectively

register s-quarks . This detector consist of the cylindrical

layers

detectors,

situated

of

silicon around

semiconductor the

interaction point . The multilayer necessary

to

reach

reliable

a

a

the

It is suggested to produce for DO experiment

those reasons a detector

high

to

free s-quarks .

detector .

if

main

include to

Due

to

The

opportunity

s-quark identification more difficult . have

of

There are two largescale experimental setup

measurements of s-quark charge and

should

the

luminosity

accompanied by a hadron bet with an anomalously high multiplicity . This effect makes the

space resolution less or equal to 1 cm2 ,

with

teams at the present time is about 0 .2*1031 l 2s and the increasing of luminosity by

free

4 . The detailed calculation, which have been that

the

advantages are the following : good hadronic and

s-quarks ;

showed,

at

proton-antiproton collision energy equal to 1 .8 and TeV it will be the only accelerator of this

free

a

have a possibility

absorbtion

detectors

electromagnetic

production point and the detector and to

formed together with other

have

minimal amount of matter between the free quark part of the detector should

background,

s-quark

high precision ionization detector ; 3 . The

a

National

2 . It is necessary, to have a possibility for precise measurement of the

surprese

setup .

order of

1 . The energy, of colliding hadrons should be colliding

hadronie

selection

in the world

investigation

more

usual

trigger for useful events

The Tevatron of Fermi

tint in the matter of detector .

is

of

2 . Possible experimental setup .

cross-sectioe could not be registered due

to

10-7

TeV)[2],

Production of free quark have not been reached 1

order

a good opportunity to tmoothesis

contradict to any existing at the present tal

(

processes ), the experimental setup should have

dark with usual nuclei . This

one

pp-beam

detector

is

ionization to

have

a

high supprssion of noise in the electronics and Two approaches to

solve

the

problem

have

been considered . The first one is a setup, set of

silicon

pad

consisting

detectors .

This

of

set

a of

P.F. Ermolov/Som e experimental possibilities for free quarks search at hadron colliders detectors,

situated

consist of

6

around

cylindrical

the

bean

axis

layers

with

inner

radius R=20 cm and length L=88 cm, according to pseudorapidity range -1 .5< % < 1 .5 . Each layer

Nm)

has about 430 wafers (with thickness t=500 and with size 5*5 cm2 and (the width of pad about 50000 There are

2 .5

20

mm) .

registration

a

light

pads

per

Thus,

absorbers

in

with

Our institute has now a F&D program for this type of detector and some results . The detector of this type can be

are

total .

thickness

The second approach, connect of

the

DO

setup

stage of experiment they may be signal from each pad

is

removed) .

measured,

5000/16 ^-z 3000 . main

background

hop . m

registration is noise of detector If it is

used

(AMEX

[3],

special developed

low by

the

amplifiers )

the

equivalente noise charge is equal to

1500

electrons (5 .5 ReV) can be obtained .

The

probable energy

RMS most

Nn)

deposited in Si (t=500

by

free s-qurk is equal to 15 .8 ReV . The triggering of

events

useful

is

being

carried out with the help of other detectors of the

DO setup by observation two

the

decay

b(b)-P,

(e ± ,~+I eP ) 17111

leptons

+

c(c)

+

1t

from v(

within the pseudorapidity range

< 3 and lepton transverse momentum

5-10 GeV/c . The number of year run (107 s ) at

p1

>

after one cm-2s-1 1031

triggers

luminosity

(taking into account the background like c- and b-semileptonic

decays,

Drell-Yon

pairs

other procosses) is estimated as 104 The off-line analysis

-

105

find s-quarks in the events selected . quarks at threshold

energy

Eth-

equal to 50-100 . The level of noise effect

(after

leptonic

100

free

s-

GeV

is

background Z O-boson

from decay

contribution is rejected) is estimated as about 1 event .

lti

requirements

to

this

d

should be the following : - (25-50) - ( 2 .5-5

- inner radius

)

- number of silicon layers- 6 In this case all the estimates for the first approach are also valid

except

conditions . If after 1 will be increased up to 10 radiation dose will be

:n:

the

raâiati m

uprade the 32 1 c 2s 0 .2

"ty than

the

Mrad/year .

It

seems in this case there will be

problems

with electronics situated at the detector . CONCLUSION . There exist a

possibility

real

to

free quarks at the threshold energy GeV

on

the

FNAL

collider

multilayer silicon detector .

with

detect

Eth

100

using

of

accelerators

New

LHC and SSC allow to search for free quarks to Eth >200 GeV . The Eth grows = In {'s but the hadronic accompaniment, as expected, should

be

greater than for the Tevatron energy .

and

should be carried out to

The estimated mumber of registered

the

b-

- psondorapidity interval - ( I % I < I .5 )

to

electronics . GERN

of

the

- the strip width

s-quark

noise

includes

the

equal

free

for

opportunity

got

ADC

i .e .,

number of chips with multiplexing is The

first

to

to c-

detector . The

the

f

registration of rare processes and constructing

free s--quarks registration . (During

IM-W .

quarks tagging,

which can be used as additional

fo

during

DO setup will be

about 1 cm between layers (5 and 6 or 4 and 5), identifier

produced

This approach is possible ig a part of

wafer

there

channels

23

REFERENCES . 1 . Anbuzov B .A . et Serpykhov, 1989 2 . Banner M . et 1985

al .,

al .,

3 . Beurille E . et al ., 1989

Preprint

Preprint Preprint

IHEP

89-8,

CERN-EP/85-42, CERN -EP/89-9,