Doubly Charmed Baryons and Tetraquarks Abstract

e ++ cc en of y mo des, (ccd), en for opti- C ob jectiv + cc h 1995 , etraquarks y t, in the spirit of the ts are giv y Sp ectrometer", tribution: ). Estimates are giv v. 1994, d v - 9503289 tensit u .I. Heidelb erg. ons and tetraquarks are con- .tau.ac.il cc y UP 2238-95, Marc kgrounds. The discussion is in the ons considered are: tal requiremen A t at CERN [1]. The NA ons and T aul, M.P y of Exact Sciences, harm exp erimen orkshop Con ts with high energy hadron b eams and View metadata,citationandsimilarpapersatcore.ac.uk tT y@tauph orkshop [2]. harmed bary acult

〉 , 69978 Ramat Aviv, Israel, ysics and Astronom y A. Moinester

PostScript processed by the SLAC/DESY Libraries on 13 Mar 1995. y a, Switzerland, No ng the bac urra HEP-PH-9503289 Abstract izi y Preprin ersion of W kler F ersit C) exp erimen Murra ersit tal and theoretical review, as part of the planning for ho ol of Ph ternal structure, pro duction cross sections, deca E-mail: m hes of doubly c Sc CERN, Genev t CHARM2000 w s, in orkshop Chairman, S. P Expanded V (ccs); and the tetraquark is T ( Bulletin Board [email protected] y sp ectrometer. The bary W R.&B.Sac + cc el Aviv Univ e a state-of-the-art double c tal searc T el Aviv Univ T tensit ysics with Hadron Beams with a High In hiev hing ratios, and yields. Exp erimen "Ph Doubly Charmed Bary aims of the recen is to ac spirit of an exp erimen a North Area Charm (NA a high in branc sidered here, for xed target exp erimen masses, lifetime mizing the signal and minim (ccu), and Exp erimen provided byCERNDocumentServer brought toyouby CORE

Intro duction

Quantum Chromo dynamics includes doubly charmed baryons: (ccd),

++ +

(ccu); and (ccs), as well as ccc and ccb. Prop erties of ccq were

cc cc

discussed by Bjorken [3], Richard [4], Fleck and Richard [5], Kiselev et al.

[6, 7], Falk et al. [8], and by Bander and Subbaraman [9]. Singly charmed

baryons are an active area of current research [10 , 11, 12 , 13, 14 , 15], but

there are no exp erimental data on the doubly charmed variety. A dedicated

double charm state of the art exp eriment is required, as current knowledge

do es not contradict the feasibility to observe and to investigate such baryons.

The required detectors and data acquisition system would need very high

rate capabilities, and would also therefore serve as a testing ground for LHC

detectors. Double charm physics is in the mainstream and part of the natural

development of QCD research.

The ccq baryons should b e describ ed by a combination of purturbative

and non-purturbative QCD. For these baryons, the light q orbits a tightly

b ound cc pair. The study of such con gurations and their weak decays

can help set constraints on di erent mo dels of quark-quark forces [5, 16 ].

Hadron structures with radii less than 1/ should b e well describ ed by

qcd

purturbative QCD. This is so, since the small size assures that is small,

and therefore the leading term in the p erturbative expansion is adequate.

The tightly b ound (cc) diquark in ccq satis es this condition. For ccq, on

the other hand, the radius is dominated by the mass of the q, and is therefore

large. The relative (cc)-(q) structure may b e describ ed similar to mesons

Qq , where the (cc) pair plays the role of the heavy antiquark. Fleck and

Richard [5] calculated excitation sp ectra and other prop erties of ccq baryons

for a variety of p otential and bag mo dels, which describ e successfully known

hadrons. The ccq calculations contrast with ccc or ccb or b-quark physics,

which should b e completely p erturbative. As p ointed out by Bjorken [3],

one should strive to study the ccc baryon. Its excitation sp ectrum, including

several narrow levels ab ove the ground state, should b e able to b e describ ed

p erturbatively. The ccq studies are a valuable prelude to such ccc e orts.

A tetraquark (ccu d) structure (designated here byT)was describ ed by

Richard, Tornqvist, Bander and Subbaraman, Lipkin, Nussinov, and Chow

[4, 9 , 17 , 18, 19 , 20 ]. This 4q hadron is of particular interest, as these various

authors all indicate that it may b e b ound. One can compare the tetraquark

structure to that of the antibaryon Qu d, which has the coupling Q (u d) .

3 1

In the T, the tightly b ound (cc) plays the role of the antiquark Q. The

+ 0

tetraquark mayhave a deuteron-like meson-meson weakly b ound D D con-

guration, coupled to 1 , and b ound by a long range one-pion exchange p o-

tential. Such a structure has b een referred to as a deuson byTornqvist [18]. It

mayhave a molecular structure, similar to the H molecule; where the heavy

and light quarks play the roles of protons and electrons, resp ectively. The

discovery of such an exotic hadron would have far reaching consequences for

QCD, for the concept of con nement, and for sp eci c mo dels of hadron struc-

ture (lattice, string, and bag mo dels). Detailed discussions of exotic hadron

physics can b e found in recent reviews [21 ]. Some other exotics that can b e in-

vestigated in NAC are: Pentaquarks uudcs; uddcs; udscs; uudcc; uddcc; udscc

[22], Hybrid q qg [23], usdd U (3100) [24], uuddss H hexaquark [25 ], uuddcc

H hexaquark [20], q qs s or q qg C(1480) [21], andc cqqqqq heptaquark [9].

But we do not discuss these in detail in this rep ort.

+ 0

One may ask whether only the ccu d or D D are b ound; or whether

0 + 0

the ccd u or D D may also b e b ound. The D D state can only decay

strongly to doubly charmed systems, and cannot decay strongly at all if

it is b elow the DD threshold. It is easier to pro duce one cc pair, as in

D D . But this state has numerous op en strong decaychannels. These

include charmonium plus one or two pions and all the multipion states and

resonances b elow 3.6 GeV. There is no hop e in seeing any state like this in

any search exp eriment with hadron b eams. There is yet another reason not

to lo ok for a D D b ound state. The sign of the p otential binding the two

D mesons dep ends on the pro duct of the sign of the twovertices asso ciated

with the pion exchange. The sign of the D vertex dep ends on T , which

changes from +1 to -1 in changing from p ositive to negativeD . Therefore,

+ 0

if the p otential is attractive in the case of D D , it will b e repulsive in the

case of D D . Consequently, if one accepts the calculations [18 , 19 ] for a

+ 0 0

b ound D D ,we can conclude that the D D is unb ound. Still, in the

+ 0 0

D D search, it maybeofvalue to lo ok at D D data. Although no p eak

is exp ected, the combinatoric backgrounds may help understand those for

+ 0

D D . 2

Mass of ccq Baryons and T

Bjorken [3] suggests M( = ) = 1.60 and M( ==1.57), which follows

ccc

bbb

from an extrap olation of M( =; ! ) and M( =). He assumes the valid-

ity of the "equal-spacing" rule for the masses of all the J=3/2 baryons, which

gives the p ossibilitytointerp olate b etween ccc, bbb, and ordinary baryons.

The masses of ccq baryons with J=1/2 were estimated relative to the cen-

tral J=3/2 value. The cc diquark is a color antitriplet with spin S=1. The

spin of the third quark is either parallel (J=3/2) or anti-parallel (J=1/2) to

the diquark. The magnitude of the splitting is in inverse prop ortion to the

pro duct of the masses of the like and unlike quarks. These are taken as 300

MeV for u and d, 450 MeV for s, 1550 MeV for c, and 4850 MeV for b. The

equal spacing rule for J=3/2, with n the numb er of quarks of a given avor,

is then [3]:

M =1=3[1232(n + n ) + 1672n + 4955n + 14852n ]: (1)

u d s c b

This equation for ccq gives results close to those of Fleck and Richard [4, 5 ],

who also estimate the tetraquark mass. Fleck and Richard, and Nussinov

[19] have shown that ccq and ccu d masses near 3.7 GeV are consistent with

exp ectations from QCD mass inequalities.

The estimates lead to masses [3, 4]:

(ccs), 1/2+, 3.8 GeV;

(ccu), 1/2+, 3.7 GeV;

(ccd), 1/2+, 3.7 GeV;

(ccu d), 1/2+, 3.6 GeV;

Lifetime of ccq Baryons and T.

++ +

The and decays should b e dominated by sp ectator diagrams, with

cc cc

0 +

liftimes roughly half of the D or , ab out 200fs. Fleck and Richard [5]

suggest that p ositiveinterference will o ccur b etween the s-quark resulting

from c-decay, and the existing s-quark in . Its lifetime would then b e

less than that of . Bjorken [3] and also Fleck and Richard [5] suggest

that internal W exchange diagrams in the decay could reduce its lifetime

to roughly half the lifetime of the , around 100fs. The lifetime of the

c 3

T should b e much shorter, set by the D lifetime. These estimates are

consistent with the present understanding of charmed hadron lifetimes [10,

26 , 27 , 28]. The lifetime b o ost in the lab oratory for a ccq baryon is roughly

0:7 p =M , if it is pro duced at the center of rapidity with a high

in N

energy hadron b eam of momentum p .For a CERN exp eriment with p

in in

400 GeV/c, this corresp onds to 15:, with ccq energies near 55 GeV.

Pro duction Cross Section of ccq Baryons

One can consider pro duction by proton and Sigma and pion b eams. Pion

b eams are more e ective in pro ducing high-X D mesons, compared to

b eams. Here, X designates the Feynman X -value. And baryon b eams,

F F

with the advantage that baryon numb er is conserved in the interaction, are

likely more e ective than pion b eams in pro ducing ccq and cqq baryons at

high X .

Consider a hadronic interaction in whichtwo ccpairs are pro duced. The

two c's combine and then form a ccq baryon. Detailed calculations for ccq

pro duction via suchinteractions are not available. Even if they are done,

they will have large uncertainties. We describ e the yield as:

(ccq )= (cq q ) [ (cc)= (in:)]=k R=k : (2)

Here, (cc) is the charm pro duction cross section, roughly 25 b; (in:)is

the inelastic scattering cross section, roughly 25 mb; and R is their ratio,

roughly 10 [29]. Here, k is the ccq suppression factor for joining two c's

together with a third light quark to pro duce ccq; compared to cqq pro duction,

where the c quark combines with a light diquark to give cqq. For simple

mechanisms of ccq formation, one may exp ect k values greater than unity.It

is p ossible to have a factor, k< 1, if there is some enhancement correlation in

the pro duction mechanism. Reliable theoretical cross section calculations are

needed, including the X -dep endence of ccq pro duction. In the absence of a

k-factor calculation, we will explore the exp erimental consequences of a ccq

2 4

search for the range k=0.1-10, corresp onding to (ccq )= (cq q ) 10 10 .

We assume a similar ratio for (ccq )= (cq ). Assuming (cq) cross sections as

high a 1000 nb, this range corresp onds to ccq cross sections of 0.1-10. nb/N.

Aoki et al. [30 ] rep orted a low statistics measurementat s =26 GeV

for double to single op en charm pair pro duction, of 10 . This D DDD to 4

D D ratio was for all events, central and di ractiveevents. This high ra-

tio is encouraging for ccq searches, compared to the value from NA3 [31] of

( )= ( ) 3 10 .For double or double charm pair hadropro duc-

tion, the suppression factor k for two c-quarks to join into the same ccq is

missing. These two results for double charm pro duction therefore establish

a range of values for R in Eq. 2. This should b e so naively,even though

pro duction is only a small part ( 0.4%) of the charm pro duction cross

section, with most of the cross section leading to op en charm. Robinett [32]

discussed pro duction and Levin [33 ] discussed ccq pro duction in terms

of multiple parton interactions. Halzen et al. [34 ] discussed evidence for

multiple parton interactions in a single hadron collision, from data on the

pro duction of two lepton pairs in Drell-Yan exp eriments.

Some ingredients to the needed calculations can b e stated. For ccq pro-

duction, one must pro duce two c quarks (and asso ciated antiquarks), and

they must join to a tightly b ound, small size anti-triplet pair. The pair then

joins a light quark to pro duce the nal ccq. The two c-quarks may arise

from two parton showers in the same h-h collision, or even from a single

parton shower, or they may b e presentasanintrinsic charm comp onentof

the incident hadron, or otherwise. The pro duction probability is included

in the R factor of Eq. 2. The two c-quarks may b e pro duced (initial state)

with a range of relative momenta and distances. In the nal state, they are

tightly b ound in a very small size cc pair, with high relative momentum. The

overlap integral b etween initial and nal states determines the probability for

the cc-q fusion pro cess. For cqq pro duction, a pro duced c quark may easily

combine with a (pro jectile) di-quark to pro duce a charmed baryon.

Kisselev et al. [6] calculated low cross sections for double charm pro-

duction at an electron-p ositron collider B factory, for s= 10.6 GeV. They

nd (ccq )= (cc)=7:10 . Although a hadronic interaction calculation is

preferred for NAC; this work establishes some imp ortant calculational steps,

and also demonstrates the wide interest in this sub ject. Kisselev et al. [7]

give a preliminary estimate of (ccq ) 10: nb/N in hadronic pro duction at

s= 100. GeV.

Some predictions for double charm pro duction are p ossible in the frame-

work of the intrinsic charm picture of Bro dsky and Vogt [35]. These authors

have suggested that there may b e signi cant cc comp onents in the proton

wave function, as much as 1-3%. These p ercentages imply also cccc comp o-

4 3

nents at the level 10 10 . Such large intrinsic charm probabilities can 5

then clearly lead to enhanced ccq pro duction, as the cc pairs are available

preformed with as many as one-third in the required anti-triplet combination,

and they can b e released in hard pro cesses. Bro dsky and Vogt [35] have dis-

cussed double pro duction [31 ] in the framework of intrinsic charm. They

claim that the data (transverse momentum, X distribution, etc.) suggests

that pro duction is highly correlated, as might b e exp ected in the intrinsic

charm picture. However, recent exp eriments [36] on di ractive pro duction of

op en charm in D D pairs with a proton b eam have claimed an upp er limit

of only 0.2% on the intrinsic charm comp onent in the proton wave function.

A ccq pro duction estimate in the intrinsic charm framework would b e of

interest; but must takeinto account the claimed 0.2% upp er limit.

We can also refer to an empirical formula which reasonably describ es

the pro duction cross section of a mass M hadron in central collisions. The

transverse momentum distribution at not to o large p follows a form given

as [37]:

d =dp exp(B M + p ); (3)

where B is roughly a universal constant 5 - 6 (GeV) . The exp onential t

has inspired sp eculation that particle pro duction is thermal, at a temp erature

B 160 MeV [37 ]. One can also include a (2J+1) statistical factor to

account for the spin of the pro duced ccq. We assume that this equation is

applicable to ccq pro duction. To illustrate the universalityofB,weevaluate

0 2

it for a few cases. For and , empirical ts to data give exp(-bp ), with

2 2

b=1.1 GeV and b=2.0 GeV , resp ectively [38, 39 ]. With B 2Mb, this

1 1 0

corresp onds to B= 5.0 GeV for , and B= 5.3 GeV for .For inclusive

pion pro duction, exp eriment gives exp(-bp ) with b = 6 GeV [40]; and B

b, since the pion mass is small. Therefore, B= 5-6 GeV is valid for ,

0 2

hyp eron, and pion pro duction. After integrating over p ,we estimate the

ratio as:

)]] 4 10 : (4) ) (2J +1)exp[5[M (ccq ) M (D (ccq )= (D

s s

Here we take the mass of ccq to b e 3.7 GeV, and the mass of the Ds to b e 2.0

GeV. For illustration, let us consider the ratio of to D total pro duction

cross sections by suciently energetic baryon b eams. This ratio is roughly

0.23, comparing the cross section [38] with incident to the D cross

section [41] with incident neutron. Eq. 4 with the masses of these particles,

including a spin statistical factor, gives ab out the same ratio. In applying Eq. 6

4 to ccq pro duction, we assume that the suppression of cross section for the

heavy ccq pro duction as compared to the lightD pro duction is due to the

increased mass of ccq. However, this formula ignores imp ortant dynamical

input, including threshold e ects, and therefore can only b e considered a

rough estimate. For the T, we assume the same pro duction cross section as

for the ccq, based on the mass dep endence of Eq. 4.

Decay Mo des and Branching Ratios of ccq

Baryons

The semileptonic and nonleptonic branching ratios of ccq baryons have b een

estimated by Bjorken [3] in unpublished notes of 1986. He uses a statisti-

cal approach to assign probabilities to di erent decay mo des. He rst con-

siders the most signi cant particles in a decay, those that carry baryon or

strangeness numb er. Pions are then added according to a Poisson distribu-

tion. The Bjorken metho d and other approaches for charm baryon decay

mo des are describ ed by Klein [12 ].

The c decays weakly, for example by c ! s + ud + n( ), with n=0,1,

+ +

etc. In that case, for example, ccs ! css + . The event top ology

contains two secondary vertices. In the rst, a css baryon and 3 pions are

pro duced. This vertex may b e distinguished from the primary vertex, if the

ccs lifetime is suciently long. The css baryon now propagates some distance,

and decays at the next vertex, in the standard mo des for a css baryon. The

exp erimentmust identify the two secondary vertices.

We describ e some decaychains considered by Bjorken [3]. For the ,

++ ++ 0 ++ + + 0 +

one mayhave ! K followed by ! and K ! K .

cc c c c

+ + +

K nal state was estimated by Bjorken [3] to haveasmuchas A

++ + +

5% branching ratio. Bjorken also estimated a 1.5% branch for ! ;

cc c

+ + +

and 1.5% for ! K . Bjorken nds that roughly 60% of the ccq

cc c

decays are hadronic, with as many as one-third of these leading to nal states

with all charged hadrons. The decay top ologies should satisfy a suitable NAC

charm trigger, with reasonable eciency. There are also predicted 40% semi-

leptonic decays. However, with a neutrino in the nal state, it is not feasible

to obtain the mass resolution required for a double charm search exp eriment. 7

Decay Mo des and Branching Ratios of the T

One can search for the decayofT ! DD,orT! D D, as discussed by

Nussinov [19]. The pion or gamma are emitted at the primary interaction

p oint, where the D* decays immediately. The two D mesons decaydown-

stream. The D* decayto -D is more useful for a search, since the charged

pion momentum can b e measured very well. One can then get very go o d

resolution for the reconstruction of the T mass. For the gamma decaychan-

nel, the exp erimental resolution is worse. There will therefore b e relatively

more background in this channel, since the gamma multiplicity from the tar-

get is high, and one must reconstruct events having two D mesons, with all

gammas.

Signal and Background Considerations

High energies are needed for studies of high mass, and short lifetime baryons.

Thereby, one pro duces high energy doubly charmed baryons. The resulting

large lifetime b o ost improves separation of secondary and primary vertices,

and improves track and event reconstruction. NAC with 450 GeV protons

or other 350-450 GeV hadrons [1] has this high energy advantage.

One can identify charm candidates by requiring that one or more decay

particles from a short lived parenthave a suciently large impact parameter

or transverse miss distance relative to the primary interaction p oint. This

transverse miss distance (S) is obtained via extrap olation of tracks that are

measured with a high resolution detector close to the target. This quantityis

a quasi-Lorentz invariant. Consider a relativistic unp olarized parent baryon

or a spin zero meson that decays into a daughter that is relativistic in the

parent's center of mass frame. Co op er [42 ] has shown that the average trans-

verse miss distance is S c =2. For example, with c 60 microns

should haveS 90 microns. The E781 on-line lter cut is on the sum of

the charged decay pro ducts of the doubly charmed baryon and the singly

charmed baryon daughter's decay pro ducts. Any one of these with P>15

GeV/c and S>30 microns generates a trigger [43]. Events from the primary

vertex are typically rejected by the cut on S. With a vertex detector with

20 micron strips, the E781 resolution in S is ab out 4 microns for very high

momenta tracks. For events in E781 with a 15 GeV track, the transverse 8

miss-distance resolution deteriorates to ab out 9 microns, due to multiple

scattering [44 ]. And the resolution gets even worse for yet lower momenta

tracks. As this resolution b ecomes worse, backgrounds increase, since the

S-cut no longer adequately separates charm events from the primary interac-

tion events. The backgrounds are not only events from the primary vertex,

but also from the decays of the hadrons asso ciated with the two asso ciated

c quarks pro duced together with the two c quarks. It is exp ected that the

requirement to see two related secondary vertices may provide a signi cant

reduction in background levels.

Some b qq pro duction and decay, with two secondary vertices, maybe

observed in NAC, and must b e considered at least as background to ccq

pro duction. The b qq and ccq events may b e distinguished by the larger b qq

lifetime, and the higher transverse energy released in the b decay. It is not

the aim of NAC to study b qq baryons. Exp eriments at CERN gave only

a small numb er of reconstructed b qq baryons, at a center of mass energy

around 30 GeV [45].

NAC considers using a multiplicity jump trigger [46 ], whichisintended

to b e sensitive to an increase in the number of charged tracks following a

charm decay. Such a trigger for high rate b eams has not yet b een used in

a complete exp eriment, and still requires research and development. Back-

grounds are p ossible with such a trigger, due to secondary interactions in

targets and the interaction detector (Cerenkov, p ossibly [1]) following each

target. Also, gamma rays from a primary interaction may convert afterwards

to electron-p ositron pairs, and falsely re the trigger. If the rejection ratio of

such non-charmed events is not suciently high, the trigger may not achieve

its needed purp ose of reducing the accepted event rate to manageable values.

This trigger would b e sensitivetoevents with X > -.1, and therefore has

e ectively an "op en" trigger X -acceptance. Most of the charm events ac-

cepted will then b e mainly asso ciated with charm mesons near X =0, since

these dominate the cross section in hadronic pro cesses. The decay of ccq to

a singly charmed hadron may trigger, or the charmed hadron's decaymay

re the trigger. The event also has twoanticharmed quarks, asso ciated with

charmed hadrons, and they may also re the trigger. However, low-X events

mayhave high backgrounds, since it is more dicult to separate them from

non-charmed events, due to the p o or miss distance resolution. For higher

X events, one obtains a sample of doubly charmed baryons with improved

reconstruction probability b ecause of kinematic fo cussing and lessened mul- 9

tiple scattering and improved particle identi cation. The multiplicity-jump

trigger for NAC could b e supplemented by a momentum condition trigger P

> 15 GeV/c, similar to this requirement in E781. This could enhance the

high-X acceptance, and give higher qualityevents.

For double charm, the target design is imp ortant. Toachieve a high inter-

action rate and still have small multiple scattering e ects, one maycho ose ve

400 micron Copp er targets, separated by 1 mm. The total target thickness

is limited to 2% interaction length in order to keep multiple scattering under

control. With di erent target segments, one requires a longitudinal tracking

resolution of 200-300 microns, in order to identify the target segment asso-

ciated with a given interaction. The knowledge of the target segment allows

the on-line pro cessor to reconstruct tracks, and identify a charm event. The

tracking detectors would then b e placed as close as p ossible to the targets, to

achieve the b est p ossible transverse miss-distance resolution. The optimum

target design and thickness for double charm requires study via Monte Carlo

simulation.

One may require separation distances of secondary from primary vertices

of 1-4 , dep ending on the backgrounds. The requirement for twocharm

vertices in ccq decays may reduce backgrounds suciently, so that this sep-

aration distance cut is less imp ortant than in the case of cqq studies. For a

lifetime of 100fs, with a lab oratory lifetime b o ost of 15, the distance from

the pro duction p oint to the decay p oint is around 450 microns. E781 can

attain roughly 300 micron b eam-direction resolution for X =0.2, with a 650

GeV b eam, and 20 micron strip silicon detectors. For lower X events, the

resolution deteriorates due to multiple scattering, and there is little gain in

using narrower strips. NAC aims to achieve 150 micron resolution for the

high X events.

Signal and background and trigger simulations and target design devel-

opmentwork are in progress for NAC [1].

Pro jected Yields for CERN NAC

For NAC with a Baryon b eam, one may rely on previous measurements done

with similar b eams. With 600 GeV/c neutrons, the D was measured [41]

in the D ! decay mo de with =0.76 b/N for 0:05

We assume therefore values for the whole range of x> 0 of roughly 1000. 10

nb/Nucleon. For k=0.1,1, wehave(ccq) 10:; 1: nb/N. We assume a

measured branching ratio B= 10% for the sum of all ccq decays; this b eing

50% of all the decays leading to only charged particles. We also assume a

measured B = 10% for the sum of all cqq decays, this b eing roughly the

value achieved in previous exp eriments. With these branching ratios, we

estimate BB = 0:1 0:1=0:1;0:01nb=N .For NAC, the exp erimental

conditions may allow reconstructed ccq events at a rate of roughly 6. 10

events/(nb/N). These exp ectations are based on a b eam of 5. 10 p er spill,

assuming 240 spills p er hour of e ective b eam, or 1.2 10 /hour. For a 4000

hour run (2 years), and a 2% interaction target with mass A 64, taking a

1=3 12

charm pro duction enhancement p er nucleon of A , one achieves 3.8 10

interactions p er target Nucleon. Assuming that (charm) = 25 b, (in) =

25 mb, we obtain 1.5 10 charm events/(nb/N) of BB cross section for

100% eciency. This is a high sensitivity,ifitcanbeachieved. Fermilab

E781 with 650 GeV pion and b eams may b e able to observe ccq baryons

b efore NAC, as describ ed in recent rep orts [47 , 48].

We consider also the exp ected eciency for the charm events, by compar-

ison to E781 estimated [43] eciencies. The E781 eciencies for cqq decays

include a tracking eciency of 96% p er track, a trigger eciency averaged

over X of roughly 18%, and a signal reconstruction eciency of roughly

50%. The NAC trigger eciency may b e higher than E781, if lowX events

are included. However, the signal reconstruction eciency is low for lowX

events. The reconstruction eciency maybelower for double charm events,

since they are more complex than single charm events. Considering all these

e ects, we assume here an overall average ccq reconstruction eciency of

" ' 4%, half the average exp ected E781 value for cqq detection. The ex-

p ected yield is then 6. 10 charm events/(nb/N) of cross section. For BB

= 0.1,0.01 nb/N, one obtains N(ccq) 600,60 events for NAC. This is the

total exp ected yield for ccu,ccd,ccs pro duction for ground and excited states.

For k>1, the yields are lower.

Conclusions

The observation of doubly charmed baryons or T would make p ossible a de-

termination of their lifetimes and other prop erties. The exp ected low yields

and short lifetimes make double charm baryon research an exp erimental chal- 11

lenge. The discovery and subsequent study of the ccq baryons or T should

lead to a deep er understanding of the heavy quark sector.

Acknowledgements

Thanks are due to P. Co op er, F. Dropman, L. Frankfurt, J. Grunhaus, K.

Konigsmann, B. Kop eliovich, E. Levin, H. J. Lipkin, S. Nussinov, S. Paul,

B. Povh, J. Russ, R. Werding, and M. Zavertiev for stimulating discussions.

This work was supp orted in part by the U.S.-Israel Binational Science Foun-

dation (B.S.F.), Jerusalem, Israel.

References

[1] S. Paul et al., CERN NAC Letter of Intent, March 1995 submission

planned.

[2] D. M. Kaplan and S. Kwan, Editors, Pro c. of the CHARM2000 Work-

shop, The Future of High Sensitivity Charm Exp eriments, Fermilab,

June 1994, FERMILAB-CONF-94/190.

[3] J.D. Bjorken, FERMILAB-CONF-85/69, Is the ccc a New Deal for

Baryon Sp ectroscopy?, Int. Conf. on Hadron Sp ectroscopy, College

Park, MD, Apr. 1985, Published in College Pk. Hadron. Sp ect.,

(QCD161:I407:1985, P. 390.);

Unpublished Draft, "Estimates of Decay Branching Ratios for Hadrons

Containing Charm and Bottom Quarks", July 22, 1986;

Unpublished Draft, "Masses of Charm and Strange Baryons", Aug. 13,

1986.

[4] J.M. Richard, in Pro c. of the CHARM2000 Workshop, HEPPH-9407224,

(Bulletin Board: [email protected] - 9407224),

E. Bagan, H.G. Dosch, P. Gosdzinsksy, S. Narison, J.M. Richard,

Z. Phys. C64 (1994) 57,

S. Zouzou, J.M. Richard, Few-Bo dy Systems 16 (1994) 1,

HEPPH-9309303

J. M. Richard, Nucl. Phys. B 21 (Pro c. Suppl.) (1991) 254. 12

[5] S. Fleck, J.M. Richard, Prog. Theor. Phys. 82 (1989) 760.

[6] V. V. Kiselev et al., Phys. Lett. 332 (1994) 411;

V. V. Kiselev et al., Preprint IHEP 94-10 (1994);

V. V. Kiselev et al., Yad. Fiz. 57 (1994) 733.

[7] V. V. Kiselev et al., Sov. J. Nucl. Phys. 46 (1987) 535.

[8] A. F. Falk et al., Phys. Rev. D49 (1994) 555.

[9] M. Bander, A. Subbaraman, Phys. Rev. D50 (1994) 5478.

[10] J. A. App el, Ann. Rev. Nucl. Part. Sci. 42 (1992) 367.

[11] S. P.K.Tavernier, Rep. Prog. Phys. 50 (1987) 1439.

[12] S. R. Klein, Int. Jour. Mo d. Phys. A5 (1990) 1457.

[13] Particle Data Group, Phys. Rev. D50 (1994) 1171.

[14] H. W. Sieb ert, Nucl. Phys. B21 (Pro c. Suppl.) (1991) 223.

[15] J. G. Korner, H. W. Sieb ert, Ann. Rev. Nucl. Part. Sci., 41 (1992) 511.

[16] J. L. Rosner, Enrico Fermi Institute and U. Chicago preprint EFI-95-02,

HEPPH-9501291, Jan. 1995.

[17] H. J. Lipkin, Phys. Lett. B45 (1973) 267; Phys. Lett. 172B (1986) 242.

[18] N. A. Tornqvist, Z. Phys. C61 (1994) 525; Phys. Rev. Lett. 67 (1991)

556.

[19] S. Nussinov, Unpublished Draft, Private Communication, 1995.

[20] Chi-Keung Chow, Preprint CALT-68-1964, HEPPH-9412242, 1994.

[21] L.G. Landsb erg, Surveys in High Energy Phys. 6 (1992) 257; K. Pe-

ters, Pro ceed. of LEAP-92 Conf., Courmayeur, Aosta Valley, p.93, Sep.

14-19, 1992, Eds. C. Guaraldo et al., 1993, North-Holland; L.G. Lands-

b erg, Yad.Fiz. 57 (1994) 47, L. G. Landsb erg, M. A. Moinester, M. A.

Kubantsev, Rep ort IHEP 94-19, TAUP 2153-94, Protvino and Tel Aviv,

1994. 13

[22] M. A. Moinester, D. Ashery, L. G. Landsb erg, H. J. Lipkin, in Pro c.

CHARM2000 Workshop, ibid., Fermilab, June 1994, Tel Aviv U.

PreprintTAUP 2179-94, HEPPH-9407319.

[23] M. Zielinsky et al., Z. Phys. C31 (1986) 545; C34 (1987) 255.

[24] K. Martens, Dr. Rer. Nat. thesis, U. Heidelb erg, "Die Suche nach

+ + +

dem Zerfall U (3100) ! p in dem Hyp eronenstrahlexp eriment

WA89", Nov. 1994.

[25] M. A. Moinester, C. B. Dover, H. J. Lipkin, Phys. Rev. C46 (1992) 1082.

[26] G. Bellini, Invited talk, Int. Workshop "Heavy Quarks in Fixed Target",

Charlottesville, Virginia, Oct. 1994.

[27] M. B. Voloshin, M. A. Shifman, Sov. Phys. JETP 64 (1986) 698.

[28] R. Forty, "Lifetimes of Heavy Flavor Particles", CERN-PPE/94-144,

Sep. 1994, Invited talk, XIV Int. Conf. on Physics in Collision, Talla-

hassee, Florida, June 1994.

[29] B. D'Almagne, Int. Symp osium on the Pro duction and Decayof

Heavy Flavors, Stanford, Cal., Sep. 1987, SLAC Heavy Flavors 1987

(QCD161:I732:1987); K. Ko dama et al., E653 Coll., Phys. Lett. B263

(1991) 579; M. L. Mangano, P. Nason, G. Ridol , Nucl. Phys. B405

(1993) 507.

[30] S. Aoki et al., CERN WA75 collab oration, Phys. Lett. B187 (1987) 185.

[31] J. Badier et al., CERN NA3 collab oration, Phys. Lett. B158 (1985) 85,

Phys. Lett. B114 (1982) 457, Phys. Lett. B124 ( 1983) 535.

[32] R. W. Robinett, Phys. Lett. B230 (1989) 153.

[33] E. Levin, Private communication, 1995.

[34] F. Halzen, P.Hoyer, W. Y. Stirling, Phys. Lett. B188 (1987) 375.

[35] R. Vogt, S.J. Bro dsky, SLAC-PUB-95-6753, LBL-36754, HEPPH-

9503206, Feb. 1995, Submitted to Phys. Lett. B; R. Vogt, S.J. Bro dsky,

SLAC-PUB-6468, LBL-35380, HEPPH-9405236, Apr. 1994, 14

R.V. Gavai, S. Gupta, P.L. McGaughey, E. Quack, P.V. Ruuskanen, R.

Vogt, Xin-Nian Wang, GSI-94-76, HEPPH-9411438, Nov. 1994,

R. Vogt, Nucl. Phys. A553 (1993) 791c,

R. Vogt, S. J. Bro dsky,P.Hoyer, Nucl. Phys. B383 (1992) 643,

R. Vogt, S. J. Bro dsky,P.Hoyer, Nucl. Phys. B360 (1991) 67,

R. Vogt, LBL-37655, HEPPH-9503207, Jan. 1995.

[36] K. Ko dma et al., Phys. Lett. B316 (1993) 188.

[37] R. Hagedorn, "The Long Way to the Statistical Bo otstrap Mo del",

CERN-TH-7190-94, Mar. 1994; R. Hagedorn, in Quark Matter 84, ed. K.

Ka jantie, Lecture Notes in Physics Vol. 221 (Springer-Verlag, New York,

1985); H. Grote, R. Hagedorn, J. Ranft, "Atlas of Particle Pro duction

Sp ectra", CERN Rep ort, 1970.

[38] A. Simon, CERN WA89 Moriond Rep ort, Mar. 1994.

[39] F. S. Rotondo, Phys. Rev. D47, (1993) 3871.

[40] S. D. Ellis and R. Stroynowski, Rev. Mo d. Phys. 49 (1977) 753.

[41] C. Shipbaugh et al., Phys. Rev. Lett. 60 (1988) 2117.

[42] P. Co op er, "Miss Distance Distribution", unpublished rep ort,

Aug. 5, 1981, private communication.

[43] J. Russ, in Pro c. CHARM2000 Workshop, ibid., Fermilab, June 1994.

[44] J. Russ, E781 Internal Rep ort, Oct. 29, 1993;

P. Co op er, E781 Internal Rep ort, Feb. 27, 1994;

"Multiple Coulomb Scattering in Silicon Tracking".

[45] D. Barb eris, CERN WA92 BEATRICE collab oration,

in Pro c. CHARM2000 Workshop, ibid., Fermilab, June 1994.

[46] A. M. Halling, S. Kwan, Nucl. Inst. Meth. A333 (1993) 324.

[47] M. A. Moinester, Tel Aviv U. Internal Rep ort, Oct. 1994.

[48] J. Grunhaus, P. Co op er, J. Russ,

Fermilab E781 Rep ort H718, Dec. 1994. 15