search for the η6 particle

I k q l U m L ~ k q l g t l m m U

PROCEEDINGS SUPPLEMENTS

Nuclear Physics B (Prec. Suppl.) 25B (1992) 48-51 North-Holland

SEARCH FOR THE q6 PARTICLE *

The CDF Collaboration**

Presented by Nikos GIOKARIS

"i'he Rockefeller University, New York, New York 10021-6399

The 116 particle is a sextet quark pseudoscalar state proposed to explain the high p value measured by the UA4 experiment at

CERN and the Mini-Centauro and Geminion events of cosmic ray experiments. We have searched for the 116 decaying into

two photons in the 1988-89 CDF data. in this report we describe the analysis and present limits on the ~6 production cross

section times branching ratio into two photons.

1. INTRODUCTION

The UA4 experiment at the CERN collider has

measured I the real over imaginary part of the forward elastic

scattering amplitude (the p value) and obtained an

unexpectedly high value. Also, the total pbar-p cross section

does not change very much in going from C£RN to FNAL

collider energies 2. These two facts lead K.Kang and A.

White to propose3 the existence of a sextet quark state, called 116, with a mass of 30+-10GeV. For some time

now, several theorists have strongly advocated an

elect~'oweak symmetry breaking scheme in which the usual

Higgs sector of the standard model is replaced by a flavor

doublet of color sextet quarks4,5,6,7,8, 9.

Kang and White point out that the Mini-Centauro and

Geminion cosmic ray eventsl0,11 could actually be

identified as the hadronic and the two photon decay products

of the 116, respectively. The threshold Center of Mass energy

is estimated to be around 450 GeV, slightly below the SPS collider energy. The 116 is supposed to be produced

diffractively with a very high cross section ( several mb at

1800 GeV) and the branching ratio of its decay mode into

two photons is twice that into hadrons. The mass, the

diffractive production nature and the decay branching ratios

*Work in progress. **The collaborating institutions are listed in the Appendix.

of the 116 ate forced upon the model by the characteristics of

the Mini-Centauro and the Geminion events. The large value

of its production cross section is needed to fit simultaneously

the p value at 540 OeV and the total cross section in the

CERN SIS to FNAL TEVATRON energy range.

Production of ri6 is possible at high energy e + e"

colliders. T. Hatsuda and M. Umezawa have proposed 12

a way to search for the 116 in Z 0 radiative decays at LEP.

They estimate the F(Z 0 ->,'~I6)/F(Z 0 ->~t+lt ") ratio to be of

the order of 10 -5 .

2. DATA ANALYSIS

Because of background considerations, we have

limited our search for the rl6 to the two photon decay

mode. The diffractive production of the 116 results in

"lopsided" events, with two photons at high rapidity on one

side of the detector, and no energy deposition on the other

side. This rapidity topology does not fire the CDF level zero

trigger, and is therefore not included in the standard CDF

data stream. However, the large (theoretical) production

0920-56~2/92/$05.00 © 19~32 - Elsevier Science Publishers B.V. All rights reserved.

N. Giokaris /Search for the ~ particle 49

cross section and branching fraction for TI6--->YY allows

us to search for this process in special runs, called LOQuery,

in which the trigger comes from a clock synchronous with

the beam crossing. Therefore the data collected this way

have no trigger bias at all.

We have looked for the 116 in such a run. The three main

elements in the analysis are: (a) Use the standard CDF

offline calorimeter clustering algorithms and count the

number of events with one or more electromagnetic cluster.~

with E T > 5 GeV. (b) Find the integrated luminosity of the

LOQuery run. (c) Construct a Monte Carlo for a diffractively

produced 116 decaying into two photons. The Monte Carlo

events are then analyzed with the CDF calorimeter

simulation programs to obtain acceptances and detector

efficiencies.

2.1. EM Clusters

The fwst pass through the raw data selected events

with one or more energy clusters. This requirement reduced

the number of events from a total of 16,992 to 2417. The

second pass searched for events with electromagnetic energy

clusters with ET>SGeV and HAD/EM ratio of less than 0.1.

No other cuts were required, so that both electrons and

photons (~0) were accepted. We ended up with 31 events

with one or more electromagnetic clusters. The 31 events

cont~.ined 40 e~ectromagnetic energy clusters and were hand

scanned. Most of these clusters appeared over a very small

period of 't~me during the run and were identified as

electro.-./.c noise i3. Ne genuine electromagnetic clusters,

passing the above cuts, were found in the forward region

where one expects to detect ~'s from 116 decay 3"

2.2. Integrated Luminosity

The CDF luminosity module was used to identify events

with one or more interactions. There are 3277 such events in

the analyzed run which, for an effective Beam-Beam counter

cross section 14 of 46.8+-3.2 mbarns, has an integrated

luminosity of 70+-5 (mbarns) "1. This number is corrected

for multiple interactions - a 10% correction at this

luminosity.

2.3. Monte Carlo - Detection Eff '~mey

In order to estimate the acceptance fo¢ Ti6->yy , MBR (the

existing CDF minimum bias Monte Carlo) has been

modified. We take the simplest pc~ible model where the

beam proton (antiproton) transforms, through the excha~g=

of a pomeron, into an object (X) with a mass equal m the

sum of the proton and 116 masses (we have considered ~16'$

in the mass range 15 to 40GeV). The transverse

momentum distribution of the X behaves like e bt, where

the slope b is taken 15 to be 12 (GeV/c) -2. This o~ect

decays into the 116 and a proton (antiproton). The beam

momentum (900 GeV/c) is divided between the 116 and the

proton (antiproton) proportionally to their masses. In its

center of mass the 116 (a pseudoscalar state) decays

uniformly into 2 photons. The momenta of the two photons

are subsequently transformed into the Lab system. The

whole 116 production and decay into two photons chain is as

follows:

pbar ÷ p .... >pbar + X

I • > yy

The photons have relatively high PT but they are distribute~

close to 1] = 4 (edge of the CDF detector).

After the detector simulation the standard CDF

electron/photon analysis modules are used to analyze these

events exactly the same way as real data. The detection

efficiencies for one or both photons, as a function of the 116

mass, are listed in Table I and plotted in Figure 1. The El"

of the photon(s) was required to be greater than 5 GeV. The

two photon efficiency is zero for eta-six masses below 35

GeV.

50 N, Gio~ar~s /Search /or the ~ particle

Table I

]DETECTION EFFICIENC]ES FOR ETA-SIX PHOTONS

Em - six mass One photon Two Photons

(OeV) (%) (%)

20 0.26+-0.02 <0,006

22 3.0~+-0.17 < 0.03

2 5 1 6 . ' / + - 0 . 4 < 0 . 0 3

30 49.6+-0.2 <0.03

35 77.I+-02 0-02+-0.006

38 823+-0.2 0.$0+-0,03

40 85.2+-0.4 2.31+-0,15

45 88.8+-0,4 13,6+-0.5

50 8g.6+.~.4 2 4 . 0 + - 0 . 6

55 $g.I+-0.4 32.1+-0.7

3. RESULTS-CONCLUSION

This search resulted in zero events within the

plug/forward region, Although there are 3 events in the

central calorimeter, there is no acceptance in this region for a

diffractively produced 116 decaying into two photons.

Therefore we conclude that we observe no events with a

topology consistent with the model of reference 3. Since no

events have been observed, we calculate the 95% CL upper

limit for u . Br (pbar-p . . . . . >~q6 . . . . . >27) as :

(~. Br = ( 3 1 7 0 mb-l . e)

where ~ is the detection efficiency.

This is plotted in Figure 2 along with the prediction of

reference 3. Using the one photon selection curve our data

pretty much exclude "~6's in the mass range and cross

section level predicted 3.

a) (3 c: 3 ID r.J f.)

,<

I00

CDF Work in Progress

80

BO

40

20

0 0

0 - 1"~ setectiot~ ~ > 5 GeV) x - 2y selection (F,v > 5 GeV)

Fidueisl ©ut for ~,'s 0551q1~1.0

t.s ~ ln l~ : ' . z s.4 ~lnlss.8

0

.o

,.x

x

~) X"

." X" . . . . I . . . . z ~ . ~ , , 1 , , ~ . , , , . , , I . . . .

1o ~o ~o ~o 50 6~ M(~e) (Gev/d)

103

,,.--. t02 e,

' ~ " 101

Ce~

I00

b l O - !

1 0 - 2

CDF Work in Progress

0 - IT selection (E v > 5 GeV) x - 2"~ s e l e c t i o n (F_~r > 5 GeV)

O

O

'D

" ~1 . Kang-White Model

x

(M = 3 0 ~ I 0 GeV)

x "~¢. ×

o , " ' ' ' O O o o . o . . . . O O

. . . . I . . . . I . . . . I . . . . I . . . . I . . . . .

Io 20 3o 40 50 t~

M[,;6) (GeV/c ~)

FIGURE 1

TI6-->W acceptance

FIGURE 2

~(~6 "->W) upper limit

N. Giokaris / Search /'or the ~ partide 51

ACKNOWLEDGEMENTS

This work was carried out in cooperation with my

colleagues mark Timko and Teruki Kamon. We would like

to thank Milciades Contreras for checking our luminosity

estimate and Konstanline Goulianos for reading this note and

making many useful suggestions.

APPENDIX

Argonne National Laboratory, Brandeis University,

University of Chicago, Fermi National Accelerator

Laboratory, II'4FN,Frascati-Harvard University-University

of Illinois-National laboratory fo High Energy Physics

(KEK)-Lawrence Berkeley Laboratory-University of

Pennsylvania-INFN, University and Scuola Normale,

Pisa-Purdue University-Rockefeller University-Rutgers

University-Texas A&M University-Univursity of

Tsukuba-University of Wisconsin.

5. E. Braaton et al., J. Mod. Phys. A1 (1986) 693.

6. K. Fukazawa et al., HUPD-8917, May 22, 1990.

7. P. Forgas and G. Zoupanos, Phys. Lett. 148B

(1984) 99.

8. G. Zoupanos, Phys. Leu. 129B (1983) 315.

9. D. Lust, E. Panagiotopoulos, K. Streng and G.

Zoupanos, Nucl. Phys. B268 (1986) 49.

10. S. Hasegawa, Fermilab CDF Seminar ICR-Repon No.

151-87-5, 1987 (unpuplished).

l l .Chacaltaya and Pamir Collaboration, ICRRo

Report-232-91-1.

12.T. Hatsuda and M. Umezawa, Phys. Lett. 254B,

(1991) 493.

REFERENCES

1. Bernard et al., Phys.Lett. B 198 (1987) 583.

2. N.A. Amos et all., Phys. Rev. Lett. 243 (1990) 158.

3. K. Kang and A.White, Phys. Rev. D42 (1990) 835.

4. W.J. Marciano, Phys, Rev. D21 (1980) 2425.

13.N. Giokaris, T. Kamon, M. Timko, "Se~,rch for the ~!6

Particle", CDF Note # 1437.

1 4 .C .G . Pilcher and S. White, "CDF Luminosity

Calibration", CDF Note # 1202.

15. S. Belforte and K. Goulianos, "A Complete Minimum

Bias Event Generator', CDF Note # 2~6,