Py/ \J:rrr4iO
INSTITUTE FOR HIGH ENERGY PHYSICS
IHEP 94-19
L.G.Laadsberg Institute for High Energy Physics, 142284, Protvino, Russia M.A.Moinester School of Physics and Astronomy Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, 69978 Ramat Aviv, Israel M.A.Kubantsev Institute of Theoretical and Experimental Physics 117259, Moscow, Russia
ON THE SEARCH FOR EXOTIC HADRONS IN THE EXPERIMENTS WITH HIGH ENERGY HYPERON BEAM
Protvino 1994 UDK G81.3.06.069 M24
Abstract Landsberg L.G., Moinester M.A., Kubantsev M.A. On the Search for Exotic Hadrons ihe Experiments with High Energy Hyperon Beam: IHEP Preprint 9419. Prctvino, 1994. , 43, figs. 14, tables 9, refs.: 39. The possibilities to search for exotic mesons, baryons and dibaryons in the framework of E7S1 Fermilab .xperiment with high energy hyperon and m°son beams with momenta of ~600 GeV are analyzed, [t is shown that there are good possibilities for the observation f different types of exotic hadrons in E781 experiment. Аннотация Лапдсберг Л.Г., Мойнестер М.А., Кубанцев М.А. О поисках экзотически:: алронов в экс периыентах на гнперониых пучках высоких энергий: Препринт ИФВЭ 9419. Протвино. 1994. 43 с, 14 рис., 9 табл., библногр.: 39. Рассмотрены возможности поисков экзотических мезонов, барпонов и дибарнопов в рамках эксперимента E7S1 Фермнлаб в пучках гиперонов и мезонов с импульсом ~»600 ГэВ. Показано, что имеются очень благоприятные услоеггя для наблюдения экзотических адро нов в этом опыте.
© Institute for High Energy Physics, 1994. INTRODUCTION
This work was done in the course of preparation for the experiment E7S1 Fermilab with the SELEX facility. It should begin in the middle of 1995 in the 600650 GeV hyperon beam of the Tevatron accelerator. Tins experiment would be carried out by a large international collaboration (see Ref.[I]). The main research progiam of E781 includes a high statistics study of the spectroscopy of charmed and strangecharmed baryons and weak decays of these states. It is expected to obtain several tens of thousands of events in each :jf
the main decay channels of Лс, Нс and fic baryons. The high energy hyperon beam of Fennilab with big intensity opens also some, new possibilities for the search and study of exotic hadrons with charmed and strange quarks in different processes. Besides, it is planned to study coherent production of exotic hadrons in the reactions in the Coulomb field of heavy nuclei and in some diffractivc pro liiction processes. Here the program of exotic hadron studies on the SELEX facility is de veloped. Although the corresponding analysis and cross section and statistics estimations are performed for the particular experiment on the SELEX setup. it seems that the largest part of this analysis goes far beyond the scope of tliis experiment and may be of general interest.
1. EXOTIC HADRONS AND POSSIBLE MECHANISMS FOR THEIR HIGH ENERGY PRODUCTION
The rapid development of the hadron spectroscopy in recent years has led to a significant advance in the systematics of "ordinary" hadrons witli the sim plest valence quark structure: qq for mesons and qqq for baryons. At the same time several unusual hadrons with some anomalous features have been found.
1 The v do no' fit into this quark systematics and nrr irtrrpretrd as new li.ni:^ of hadronic mailer exotii hadrons. The?" stairs can include multiqcark fHiua •ioii {•j'jYi meson and qqqqq baryons). hybrid systems with inlenre quark and gluons (i/'/.v mesons and qqa'j baryons), or glucballs. i.e. mesons consisting solely of \,ili4ire gluons [gg. ggg). The discovery of the exotic hadroiis has farreaching 'onsrquenrrs for quantum chromodynamics. for com ept of confinmont and for specific models of hadron structure (lattice, string and bag models). Detailed discussions of exotic hadron ]>hysics can be found in recent reviews [25]. All exotic hadrons can be subdivided into three groups.
1.1. Exotic states of the first kind These are the states with manifestly exotic values of nasi quantum numbers such as the electric charge, strangeness, isotonic spin (mesons with \Q\ ":> - or ;>'| > 2 or 1 > 1; baryons with \Q\ > 2 or 1 > 3/2 or S > (I). Su.h particles
merely cannot have the usual quark .structure such ;, 77 or ./77. and must necessarily be exotic multiquark states.
1.2. Exotic states of the second kind These arc particles with an exotic combination of quantum numbers such ;.s spin 7. parity P. and charge parity C. which hadrons with ordinary quark structure cannot have. For neutrai (qq) mesons with total quark spin 5 ami orbital angular momentum I, the parity and charge parity are known to be cjvru by P = (1)л, С — (1)''+5, so that such mesons can only have the following conibinations of quantum numbers' С = f = ( 1)"' or ( 1) '+1. and also С' = (!)•', P = (1)'/+'. There cannot be (*/,/) states with С = /П'+>
!;!,l p - (-i)J „r .7 = 0 and С = -\ (if ./ = 0 then S - I. - I): 1 and ('' — +1). The exotic sets of meson quantum numbers are therefore as follows: ./''' =• 0+~. (Г~. 1" + . 2f",3'+). etc. All forms of exotic mesons such ,ts muhiquavk states, hybrids and glueballs can have such values of J1'' • Kxotic h.idrons of the hist and second kinds are often referred to as open ••Xotie states.
1.3. Exotic states of the third kind These are hadronic states with hidden exotic properties (the socalled crvp to'V'tic hadrons). They do not have open exotic features, and their couipli . 11• •• * Miner structure can be established only indirectly from specific features
9 in their properties (anomalously small widths, anomalous decay channels, spe• cial production modes and so on). Exotic hadrons of all types can belong to this class.
1.4. Models for the exotic hadrons There is a great diversity of available theoretical models of exotic hadrons. Thus it Las been suggested that exotic particles are resonance states of quasireal "white" hadrons and they decay into colorless components without creation of additional qq pairs from vacuum [6]. We call these hadronic resonance states as "hadronic molecules" (for example, there are some attempts to identify
5*//„(975) and 6/ao(980) mesons with KK molecules). If there is no kine• matic suppression, "hadronic molecules" can have a very large decay width (these axe the so-called supcrallowed transitions) and are therefore practicall> unobservable. However, it has also been suggested that there are relatively narrow exotic states caused by the complex inner color structure of these objects and by the peculiarities of color dynamics. Thus, if an exotic hadron consists of two colored parts that are separated in space (e.g., because of the presenece of a centrifugal barrier), then its decay into color singlets will be suppressed. Such exotic particles can be characterized by normal or anomalously narrow decay widths, depending on the degree of suppression that in turn depends on the mechanism of decoloration of the decay states [7].
1.5. Production and decay of exotic states The analysis of possible systematics for exotic mesons has shown that in the mass interval between 1 and 2 GeV one may expect more than 100 of such objects to exist. Since the typical decay width of these states exceeds 100- 200 MeV, one meets with considerable difficulties in the identification of certain resonances. Only some states in particular production and decay processes with a clearly defined signature have a chance to be identified Therefore we should not be surprised that we see only a small fraction of all exotic particles, it is more surprising that wc observe some of them at all. Searches for exotic states play a particular role in the recent experiments on nanobarn hadron spectroscopy. One of the most complicated problems is the identification of cryptoexotic hadrons, since only indirect dynamic features can give us ideas about the complicated valence structure of the particles. The experimental facilities assigned for the study of exotic hadrons should have large
3 acceptance and high sensitivity, since the cross sections for their production are. as
1.5.1. Reactions in the fragmentation or in the deep fragmentation regions It is well known that the combinatorial background in inclusive processes is significantly reduced in the fragmentation region (xf > 0.5 - 0.6) and thus one may expect here more favourable conditions for the identification of resonance states (for illustration see Fig.l). It seems that especially propitious are the processes in deep fragmentation region (if > 0.8 -f 0.9), for example, quasicx- clusive reactions, i.e. the reactions of an inclusive type in the bottom vertex (Fig.2). In these processes all admissible states in the bottom vertex
4 1 1 1— 1 T 1
7 b) • Г rrrr * 6 -
XF>0.6
S • ' ,
4 •
• A 3 «t
2 / f vv$T* & 1 - • 0 , i. .*. i , 0.8 1.2 1.6 2.0 0Л 0.8 1.2 1.6 2.0 M(a*a_),Gev Figure 1. Effective maas spectra A/(ir+jr_) in the inclusive reaction т~ +p > (I+JT~) + A' at
P,- = P*- = 360 GeV/c: a) for rF ~ 0; b) for xF > 0.6. The effective reduction of combinatorial backgrounds in this reaction for the p'meson and /2(1270)meson in the fragmentation region (if > 0.6) is clearly seen.
N •-
Figure 2. The diagram for the quasiexlusive reaction in the deep fragmentation region (inclu sive on the bottcm vertex).
5 arc summed up, the total cross sections may very weakly
1.5.2. Diffractive production mechanism (Pomeron exchange) As it is stated in a number of papers (see, for example, Refs.[l3;7;<3]). the diffractive production reactions with Pomeron exchange offer some new possi bilities to search for exotic hadrons especially in the high energy region, since the cross sections of these exclusive processes do not decrease with energy. Ac cording to the modern notions, Pomeron is a multigluon system, which leads to the possibility of exotic hadron production in diffractional processes (see the diagrams on Fig.3). Indeed, as it is apparent from the Pomeron exchange mech anism for the diffractive reactions, only the staces with the same charges and flavors as for the primary hadron can be produced in these processes. Besides, there is an additional limitation for the quantum numbers of the hadrous to be produced, which is stipulated by the GribovMorrison selection rule for chang ing the parity (ДР) and spin (&J) in the transitions from primary hadron to a diffractively produced hadronic system: AP — (—l)^J. For example, in the proton diffraction only baryonic states with natural sets of quantum numbers Jp - l/2+; 3/2;5/2+;7/2~ etc. can be excited due to this rule. Uut the GribovMorrison selection rule is not a rigorous law and has an approximate character. In spite of all these limitations and serious problems with the separation be tween the diffractive production of resonance states and some nomesonance hadron clusters it should be noted that the diffractive production mecha nism seems to be quite perspective in searching and observation of new exotic hadrons. The Pomcron exchange mechanism in diffractive production react ions opens the possibility to study coherent processes on the target nuclei. It has been suggested that coherent production on nuclei is a good tool for the separation of resonances against multiparticle background because of the difference in their absorption in the target nuclei (see Ref.[10]). It is possible also to search for the states with new flavors in the processes of diffractive pair production [llj (see the diagrams on Fig.4). We will discuss these processes later, in connection with the possible production processes for pentaquark anticharmed baryon P and double strange dihyperon H.
6 Г
Figure 3. Diagrams for the exotic baryon production in Hit dilfractir.nal processeb with Pomeron exchange.
o)
_».A h-— —A
—-В
-»-N N —
Figure 4. Diagrams for the diffracttve production jf hadron pairs;a) h i N —* [ЛМ •+• JV, b) h + iV — [.4Й] + A'*»..
7 1.5.3. Reactions with multiple Pomeron exchange (rescattering processes) The use of coherent reactions on nuclei, i.e. processes with very small P|•. is not the only way for better separation of rcsonmre production against back ground. In some cases the best conditions for the exotic hadron searches can lie obtained in the region of big enough or intermediate transverse momen tum (Я£ JS 0.2 — 0.3 GeV2) where the background from peripheral processes is strongly reduced. It should be noted, that exotic hadron producton in the intermediate P% region could take place through multiple Pomeron exchangc inechanism (i.e. again through multigluon process). For example, in the study of the chargeexchange reactions 7t~p —> щ + n and тг~» —» ijjj' + n after the selection of events with Pj- ^ 0.2 — 0.3 (GeV)2 unusually narrow meson states Л'(1740) » Щ [12,13] and Л'(ШО) — щ' [14,15] were observed. These anomalous states arc good candidates for cryptoexotic mesons. The mechanism of multiple rescattering with Pomeron exchange may explain the .Y(1740) and A'(1910) production see Fig.5 [16]. For the case of very high energy instead of charge exchange reactions of Fig.5a type, the diffractive production with rescattering (Fig.5b) can be used for the nonperipheral exotic hadron searches. The cross sections for these pro cesses must be energy independent. The'use of P$ > 0.2 H 0.3 GeV2 cut in the diffractive production gives one the possibility to separate these gluonrich reseat tering processes with multipomeron exchange and to search for new exotic hadrons in this region.
1.5.4. Coherent Coulomb production mechanism for hadrons (Primakoff production) The study of coherent production reactions in the Coulomb field of target nuclei (see the diagram on Fig.6) is a very promissing method for the search for now hadrons with strong enough coupling to the hV channel [17]. This coupling is necessary for the effective Coulomb production of such particles (here h is primary hadron and V is vector meson see Fig.6). In general the process of coherent production of "a" state by "ft" particle on a nucleus with charge Z and atomic number A is fairly complex, since it originates from both electromagnetic and strong interactions (see the diagrams of Fig.7a). The differential cross section of coherent production of particle "a"
8 on a nucleus has the form
,f 7 da/d\t\ = \Tc + e Ts\ ., (1|
where 7"c is the amplitude of the Coulomb production, Ts is the amplitude oi coherent strong interaction (e.g. through the и pole exchange), and p is rhc relative phase of these amplitudes. In the approximation of the smallwidth resonance state "a' the electromagnetic cross section takes the form i
г 2 l 2 = |гс| а 8™г ^^ I> - AT) •-~^\FAt)\ . (2) '/If! (2Л + 1)
Here Z is the charge of nucleus, a is the fine structure constant, Г(<г » It')) is the radiative width of the corresponding decay "a", .7/, and ./„ are the spins of
paj titles "A" and "а", яц anci ma are their masses, F.(t) is the electromagnetic f 2 formfacfo' of !:!i nucleus, |/,„,n | = (?n„ m\) jiPj{ is the minimum value for the squared momentum transfer, P/, is the particle "A" momentum. If the primary partible is a photon, then an additional factor of 2 enters the expression for the differential cross section. As it follows from (2), the cross section for the Coulomb production of a particle is proportional to the radiative decay width T(a •-* A/!. Therefore the measurement of the Coulomb process cross section makes it possible to find directly the absolute value for the radiative width. The difficulty lies in singling out the Coulomb process and suppressing strong interaction background. Fig.Tb shows the general structure of the cross section of the Coulomb pro duction of particles. The Coulomb cross section rises steeply with the decreasing momentum transfer. As is easily seen from (2) the cross section reaches its max _1 imum at \t0\ = 2|rmj„| and in this point [rfcr/rfr]c mal а |Л,.г„j' 9 a) pc b) Z, , h^^K.» >N Kigim ."j. Diagram* foi Un. uxotic production with the mechanism of multiple Pomc.on ex change: a) in chargeexchange reactions; b) in ditfractive production reactions. I'iguie ("•. Diagram of liaJron production in tht: nucleus Coulomb field. Coherent Cuutomb production cross section is proportional to Г(Л —* a>). V is a vector meson. 10 <г,я> [of/au] mb/GeV1 ''""'СтЛЫ; »« A/Getf' Figure 7. (a) Diagrams of the amplitudes for coherent nuclear production processes: Coulomb production [Tcmdomb) and coherent strong production (Г,(гопя); (b) General be haviour of the differential cross sections for the coherent nuclear production re actions n + (Z, A) > a + (Z, A). Here |im,,| = (Ml т$ЦЕ\ is tl « minimal valu. of the squared momentum transfer in this reaction; \t0\ = 2\tmm\ is a position of the maximum in the Coulomb production cross section [da'd^Wc^tomh- 11 2. EXOTIC HADRONS WITH LIGHT QUARKS (u, d, s) 2.1. Hyperon states with open exotics There are many hadron dynamical models that predict the cxistance of exotic baryons with open exotic quantum numbers: nonstrange baryons with / > 5/2: strange hyperons with 5 = 1 and / ^ 2, S = 2 and / Js 3/2, ,S = —3 and / ^ 1. Among these models are those with bootstrap mechanism, the bags and chromodynamical strings with junctions, soliton models, the su perconvergont sum rules for the amplitudes of reggeon scattering on baryous (SSR) and some others. The short review of these possibilities can be found in Ref.[18] together with a detailed discussion of the predictions of SSR for the exotic strange hyperons and their production in the hyperon beams at high energy. These estimations may be of some interest in the framework of E7S1 experiment and are partly reproduced here. The decay properties of exotic an< ш hyperon states Sfi2.3/2' ^5/23/21/2 ^ ^s/aa/si/s SSR model are presented in Table 1 (see designations in the note for this table). Their production cross sections in the fragmentation region, where the combinatorial background is significantly reduced, can be found in Table 2. The widths of these exotic hy perons are large, because of the large value of the coupling constants gseyr in the SSR model. The widths of exotic baryons are limited only by kinemati cal factors. This means that it is practically possible to search for such states only in the limited range of their masses near the decay thresholds, where their widths do not exceed the values Г <150200 MeV. As it is seen from Table 2, the expected statistics of these events in £781 (or in CERN hyperon experi ment WA89) is very large and, if such particles do exist, they can be found in these experiments. But it is also possible that exotic hyperons have a more complicated inner color structure and their decays to the color singlet final states would be strongly suppressed by decolorization mechanisms. In such case exotic hadrons cart Ъе characterized by normal or even anomalously narrow decay widths in a wide mass range. It may be expected, however, that the cross sections for the production of these exotic objects with small decay widths will bo also significantly suppressed in comparison with the characteristic cross sections for the production of hadrons with ordinary quark composition. But it is clear from Table 2. that if the cross sections for SE production lay on microbain level or even smaller the sensitivity of E781 is still enough for the observation of EE , E~ and, maybe, even of fie states in the analysis of effective mass 12 spectra of Лтг Л", Е'~тг~, ^.*~7г and П 7г , systems. Certainly, it L Air" I— 5тг° L ЛЛ' would be possible only if background conditions are not too poor, which would strongly dependent on Xp region, on cross section level, on masses, decay widths and quantum numbers of these exotic hyperon states. Table 1. The decay properties of exotic hyperons in the SSR mode! [IS] 1. Decay widths (in MeV) predicted by the SSR method for 5 = — i, / = 2 exotic hyperons at different masses of exotics Decay Mass of exotics (GeV) 1.40 1.45 1.50 1.55 1.60 1.65 170 1.75 1.80 4 24 59 108 172 250 Щг *> 17 43 79 127 1S5 253 332 — £•* 2 5 9 2. Decay widths (in MeV) piedicted by the SSR method for 5 = 2, / = 3/2 exotic hyperons at different masses of exotics Decay Mass of exotic (GeV) 1.5 1.6 1.7 1.8 1.9 2.0 3 31 90 180 -з/г 21 53 101 167 24S 10 30 60 1/J * * 32 86 155 249 363 5 16 35 3. Decay widths (in MeV) predicted by the SSR method fcr S = -3, 1 •• exotic hyperons at different masses of exotics Decay Mass of exotics (GeV) 1M 1.9 2.0 2.1 2.2 2.3 fi£2 — Sb 4 15 61 139 249 391 ftfL —» fix Practically the same as for fif/2 —• П nf/2 > fiir 4 20 " 87 218 431 Note: here and below we use the foHov.ing notations: 1) Sf \J is the spin), or more precisely Sf(5 = 1), Hf(5 = 2) and fiffS = 3) for exotic hyperons; 2) E" for S(1385) hyperon; 3) H" for H"(1530) hypcron. 13 ilab[£_=i Kstim«:tioii4 of cross section4; and exjicrtcd statistics tor exotic yt:- ri',. , «yft'" hyptTons (in ,ic<:urdame with (I8|) Exotic baryons and с: / Effective BR £ Cruss section est.imai.ions Expected decay channels range o[Y- -* N -* SF— + X\ statistics for M (jF>0.6) (GeV) •1 2 < 1.75 0.56 0.2 (1.5 40.5) x 10s ev./day ~ (75 r 25) /*b £3/2 ""* ^ * —* я" л1 » t 1 2 < 1.6 1 0.05 cr(SN £*y + X) ~ 800 /,b ЛГ ~ 7 X 105 ev./Ллу L» 7Г П 2 3/2 <2.0 0.2 0.1 A'~(103H4 102)ev./week ~ 25 H10 f.b Hf/V Hir . Лтir L. Л1Г _2 3/2 < 1.9 0.64 0.2 ff|SA'.H^ + AP!~250^b N ~ 7.5 • 10' ev./woek t—* pjr~ 3 I <2.15 0.4 0.2 П3'Д" —» П~7Г" —• ЛЛ'"?Г~ • p.T"/\ 7Г~ 1 < 2.15 0.4 0.2 oinN ^ n^y + A'] ~ 350 /il. /V ~ 650 ev./week 1 < 2.05 0.4 0.2 £" hyperons (Щ6 S/sec) 6 • Ю10 inter, for 16 weeks (full the run) 3.75 • W'inl./week 5.35 • 10» int./day 5~ hyperons (2 • 10' H/sec) 1.2 10'J inter, for 16 weeks 7.5 Kl'int./week 1.1 • 10T int./day » hyperons (2 • 10' П/sec) 1.2 I07 inter, for 16 weeks 7.5 105iut./wcck 1 1 • 10s int./day 2) The cross section estimations nie in accordance with inclusive process Y~ + N -* SF— + .V .villi pione.vchange mode) (sec |18j). The coupling of S|y3 and Hfy2 wil h ) ' ;r is reduced (we use tin: suppression factor for the corresponding cross section К ~ If) r 25). .'!) UK is the produc' of Inaie hillg ratios of nil secondaiv decays (lor example for !)'' —> !!~JT~ processes ЦП = |ВЙ(Я" —> ЛЛ'~) = O.fiS] • |/ЩЛ — pit) = 0 fit] ~ U.4. •I) Infective range f"i Л/ the iiiaas range near I he decay threshohl when the total widlh of SE is esliinated III tile SSR model to be < 15fi2U0 MeV (see Table 1) 2.2. Strange cryptoexotic baryons In this Section we use no theoretical models and are based on the results i>i the experiments with the SPHINX facility in a proton beam of the ШЕР .«•cclerator with £,,=70 GcV. The study of the diftractive production reaction /. + Л* р(1385)°Л'+] + Л\ (3) 1— Ля0 w.is performed in the SPHINX experiment and these data are used here as a guidebook for planning the search for cryptoexotic strange hyperons in E781 experiment. The detailed description of the measurements with reaction (3) and the analysis of the mass spectra M[E(13S5)°A'+j in this process are presented in Refs.p 921]. Here we have summarized the main results of this study. As a first step of the SPHINX measurement, the reaction p + N ->(tU°K*-) + N (4) was singled out and for this reaction the invariant mass speclum M(I\TI°) was obtained (see Fig.8). As it is clear from Fig.8, the peak of £(1385)° —> Ля" is dominating here and the background level under the peak is very small. Thus reaction (3) can be studied without background subtraction procedure. As is shown from the study of dN/dPj- distribution for (3) (Fig.9), a strong forward peak with the slope b > 30 GeV2 is observed, which corresponds to a coherent production process on carbon nuclei. On fig.lOa the effective mass spectrum of £(1385)°Л'+ in reaction (3) is presented for the coherent events with Pj- < U.075 (GeV)2. But the form of the observed spectra does not change too much in going from the region P£ <0.07o (GeV)2 to the region of Я2 >0.075 (GeV}2. There is a structure with mass M ~ 2060 MeV and width Г ^ 120 MeV in all spectra. The nature of this "X(2060)" structure is quite unclear. There is a feasibility of its resonance interpretation, but it. is also plausible to explain the form of the observed spectra by the diffrai.tivo nonrcsonance production mechanism with account of the Deckeffect.. This drastically calls for the determination of quantum lumbers of ''A'(2060)" as well as thorough study of the dynamics of reaction (3). As the first. s'ep in this direction let one analyze the role of the P\ cut in singling out the coherent diffractive production process on carbon nuclei. Baaing on the study of dN/rtPj- distributions we have used up to now the cut Pj <0.075 (GeV)" for the selection of coherent production reaction and the rejection of noncoherent events. 16 :200 [Mev] Figure 8. The invaziant mass spectrum of Air° system in reaction (4). The parameners of the Ц1385)" peak are M - 1377 ±3 MeV and Г = 39 ±3 MeV. They are in agreement with the tabulated values of these parameters (with the account of the apparatus mass resolution a = ±9 MeV and systematic errors). The arrows indicate the region of £(1385) band. 0 0.2 0.4 OS 0.8 I 2 2 PT [GeV ] Figure 9. The dN/d/%. distribution for the events (3) with E(J3S5)"A'+ in the final stale. This distribution was fitted in the form dN/dPj = ci£.rp( —щР?) *• ciexp(~b2Py). The large values of the slope &i 2; 30±8 GeV-2 shows that, there is a strong contribution of coherent reaction on сагЬэп nuclei. 17 I* i л soli ..ir v.liHi allows for more than 30% of the noncoherent back ;;.'•••:!.:••! iii '!!• n.is> spr<iruin(Kig.lfla'. Besides, the measured value of the slope ••i .h' diffi'iK liv' <ни'' for carbon mielci />i rz 30 (GeY)' seems to be somo •.\!i;.: reduced due to fhr it.smimeni a) uncertainties. If the real value of «i is in .i",rei4ii''iit witii the expected value for rarbon nuelei (£ 50 GeV~') then one vui;:.l anticipate an additional increase of noncoherent, background in this mass j>' clpilIJ. 1ч ii'ilff fi reduce this noncoherent background and to obtain the ':"', l.'„'i)"Л'" mass spectrum for "pure'' coherent production reaction a strin siem le^inrcineiit FT < (J 02 (GeV)2 has been used isei Fig.10b). As is seen front rlic comparison of t.Jie nas spectra in Fig.IOa and h, under the stringent /';; cut «he narrow peak with mass M = 2050±6 MeV and Г=а0±19 McV i. cic;ir!y observed. This narrow .structure can not be explained by diffavCtive iiouresunant process of Deck type and seems to be caused Ьу the production of iiiw laryoii with hidden strangeness. This conclusion must be considered as preliminary and should be confirmed in further measurements with increased statistics. The main results for A'(2060) state are presented in Table 3. Let us suppose that narrow nonstrange cryptoexotic baryon resonance .\'(21Г>!1) with hidden strangeness does exist and is observed through its de cav .V(205f))+ = \uudss >— Е(1385)°Л'+. (5) Then, the sUange analog of this state Sf22()0) = \ddsss >— H*;i550)~K" (6) том also exist ami can be produced in a coherent diffractive reaction in 5~ iiyp.'iou beam with the sune cross section, as A'(2050) baryon in proton beam Г)';.Me 3). Thus, as it follows from Table, it is possible to observe in the ETS1 run several thousand events of ГЛ2200Г —> E*(1550)~A"° type in the coherent pro duct iuu react ton ^" + С — Е'(22ПП) Л С . L Е*(Ш0Г /i'° LEV UTT+Л (7) L.u '—• ;IIT "" 18 <5 <0 al I» S 30 * га 23 "5 10 - /••"'"•• % - m I "гНьйш kL ft ! i : ft— l , , _ l • • TirTlrJftAP* 1800 2000 ?200 2*00 2600 2800 М[£(13в5)"к^] [MeV] 28 •i 2 2* I ' £ M 16 1 12 e 1 < 0 • .M . i . . . . i J. ]ИПтяы1й. 1800 2000 2200 2400 2600 2800 M[Z(13B5)°K*][MeV] Figure 10. a) The invariant mass spectrum of the Ц1385)"К * system in the SPHINX ex periment for coherent production process (3) on carbon nuclei (i.e. .it Py < 0.075 (GeV)2). The spectrum is fitted by the sum of polynomial background and the BreitWigner peak with M = 2065 ± 11 MeV and Г = 118 ± 19 MeV. The soft Pj. cut which 19 Table 3. Comparison of .V(2050) Mid £(2200) production />beam; £p=70 GeV (SPHINX) E'beam; £^=600 CcV (E781) a) Reaction a) Reaction Е + С ЕЧ2200)" + С p + C-> Jf(2050) + C L»E'(1530)A'' U E'(13B5yJf+ U 3х» U T+r L.Ai° UAIT" 1—* ртт~ (coherent production; P} <0.02 GeV). b) Cryptoexotic state: b) Main assumptions: + + X(2050) = |uu .[Х(2050)+1и..8Я= H^cleon l ( 20 For the selection of reaction (7) it is possible to use the 'rigger with only inn charged particle just after the target and with 5 charged particles ai the nil of the SELEX setup (the first and second level of trigger will be used for this purpose). To separate the interactions in the setup targets one must шеами;' in the first level trigger the vertical angle of the secondary track after the target (for fly > 10~4 rad). Certainly, in the same run it would be possible ю siv.rch for other cryptoexotic E* states and other decay channels: £*(22C0) _ = A'" . U ля- U (b) I—» ртг~ Л A'" A", L L + (91 >—> m '— тег. — S°A A'". u Л7 LiV (и» i—* pr~ As is stated above (cection 1.5.3), another perspective way of the search for exotic baryons is the study of nonperipheral processes in the intermediate transverse momentum region (Pp >0.10.3 GeV2). Here the multiple Pomeron exchange mechanism of rescattering (sec the diagram on Fig. 5b) may take place. Again here we can use as a guide the SPHINX results, where there arc some indications on visible enhancements in this Pp region. Thus, the study of pro cesses of (7)(10) types in the intermediate Pj- region would be carried our in the E781 run with £~ beam. 2.3. Coulomb production experiments and C(14S0) meson nature 2.3.1. Reaction тг~р ~> rpn" and observation of vector meson CY1480) + фтг" In the experiment with the "LeptonF" apparatus in the analysis of the mass spectrum of the фп" system m the reaction 7Г +p —- (фтт") + n (Hi a new meson C(1480) with the following characteristics was observed ^?2.:J.'j: (a) the mass and width of the С meson are Mc = 1480 ± 40 MeV , 1% = 130 ± GO MeV ; (12) 21 (b) the cross section tor exclusive production of the C(1480) meson is a[x~p > C(1480)n] • BR[C(U80y > фк°\ = 40 ± 15 nb ; (13) (c) from the data on the OPE character of the reaction n~p —> Cn and irom angular distributions for the cascade decays (7(1480)" —> фтт°, ф —» Л'+Л'~ the i[ii.intum numbers of C(1480) meson JFC — 1 have been determined. Jn the study of possible decay channels C(1480) —> фя° and C(1480) —• uit0 tbo following restriction has been obtained: tlt = BR{C(\AS.O) -> фтг°}/ВВ{С(И80) * штт°\ > 0.5 (95% C.L.). (14) Hence the ratio Rc turns out to be anomalously large for the mescnic states uf ordinary qq type, whose decay along the фл° channel is suppressed by the OZ[ selection rule. The expected value for Rc for such hadrons is й (1/200) r (1 /400). For instance, for the wellknown 6](1235) meson ('Pi q,jstatc) this ratio is limited by the value of Дь < 5 • 10~3. Anomalous violation of the OZI rule in the C(1480) decays cannot be explained, if this state is a meson of a usual ijij type. It is a rather strong argument in favour of interpreting C(1480) as an exotic hadron with the structure jC(1480) >= \(ий dd)ss/y/2 > (multiquark meson) or |C(1480) = \(ий - dd)gj\/2 > (hybrid meson). But to be sure in exotic interpretation of C(1480), it is very important to measure the absolute value of the branching ВЯ|С(1480) > фк°]. 2.3,2. How can we measure BR\C( 1480) » тг]? Л straightforward determination of the absolute value for ВЯ[С(1480) —» ci.TJ is of extreme importance for the interpretation of the C(1480) nature. If its value is higher than 5 f 7%, the exotic nature of C(M80) meson becomes completely evident, and the model [24] with |C'(1480) >= |p',(i45C) >= \{uv. - 22 stressed that this precise mechanism allowed one to carry out. the partialwave analysis and to single out new mesons more reliably, as compared with the t;us< of usual hadronic processes. The cross section for reaction (15) turns out to be proportional to (.he radia tive width Г[С(1480) » jr?], which in the VDM model has the form [2a.8,26j: г Г[С(1480) » jr7j = 1а/(£/х)]1К,/Кф) Г[С(.иЩ- Ф*-} = 3 = [а/(д1/п)}(К,/Кф) ВЩС(1тГ ^ Ф^]ГГ = 7.4 • 10' KeV • BR[C{U8Qy > фк]. (16) Here Ky, Кф are photon and ф meson momenta for the corresponding decay channels of (7(1480), Гс = 130 ± 60 MeV is its total decay width, g\jr. ~ 9 is the constant of the ф-у transition in VDM. For the Coulomb production of C(1480)~ —* фя~ one has the cross section с (С- -•> фк-)См1отЬ = x BR[C(l№)- » фп~\ • Г[С(1480)" > •*--,] x 2 2 x / [\t - tmin\/t ]\FAt) \d\t\. (17) 'm.n s 4 Here |imin| = [Ml mj] /4£j, Д ~ 1 • 10 GeV (for Pb nuclei), f\{l) is the electromagnetic formfactor of the nucleus (Z. A). Prom (16) and (17) for the lead target one may obtain [8,23,26]: [ 2.4in3 fib (E, = 210;i GeV) 2 3 1 a(C~ -> ф^-)Ст,1шЛ = [BR(C- ф*-)] х< 1.5 • Ю / 23 As it follows from simple estimates, in the experiments with the Coulomb production of particles with the 600 GeV pion beam (see Table -i) one can observe the C(1480) meson production (15), if ВЛ[(С(1480) — фт~) > (4 ~ •j) • 1()J. И this branching ratio turns out to be large (> G%), then, as was noted before, this would be a decivise argument in favour of the identification of C{ 14S0) as exotic meson. The analysis carried out above is correct, if Г(С —• ,V.T) < Г(С — 6~), and the C~ —> ъ:я~ —» 7?r~ vertex contribution to reaction (15) is small Namely, such situation should take place if C(1480)niesou : a 1rjuark state. In general we must take into account С —+ фп and С —» лг. contribution to С —* >7r vertex and for complete analysis we need a detailed study of the processes к' + Pb -> C(1480) + Pb\ C(1480)" (Атг (19) All 'hese data can be obtained in E781l simultaneously with the main mea surements in the hyperou ueam, or, in some part, in the spear. Оишиш.. pro duction run, which is foreseen now. Table 4. Sensitivity cf the experiment or. the Coulomb production of C( USD) The pion Аич in the run Л'. ~ 1.5 • lO12; The PririaUIT target 1.4 g/crr.2 . n(Pb)=4 • 1021 Pb/cra2; The efficiency £(C~ » фх' * A''A'T) ~ 0.5; The result: The sensitivity n{C • ф-Г~}\со,1етЬ = of the experi , ment up td = \,-ЩРЬ)-е- ВЯ{Ф-^ Л' Л')т(С^!г)СоЫ„„6 = = 1.5 1П'2 1 !021 0.25 1.5 • 103 IQ-™ • [BR[C- — лт-)\"- I3IT(C~ — ф.т-) ^•i- о'[ая(с- -и»г-)р ' > (4 4 5) • 11)'. 24 3. EXOTIC STATES WITH HEAVY QUARKS 3.1. General consideration Let us now consider possible exotic hadronic states with heavy quaiks (<•, /))• As is shown in Refs.[2730], such states may possess rather specific proper ties. In particular, one can expect, that among lightest multiquark statos with strangeness and charm, or with strangeness and beauty, or with beauty and charm, hadrons with exotic values of the flavors (strangeness, isospin, charm, etc.) may be excited. As has already been noted, such states are exotic hadrons of the first kind (open exotic states). Moreover, with high probability these heavy exotic hadrons may be quasistable and may decay only due to electro magnetic and weak (or only weak) interactions. These new properties of hadrons, which contain quarks with four different flavors (e.g. u, d, s, c), follow from the general principle of "flavor antisymme try" [27]. In agreement with this principle (or rather a hypothesis), under all other conditions being equal, the quark systems, characterized by the maximum possible antisymmetry of quark flavors (both quarks and antiquarks) turn out to be most strongly bounded. For instance, this means that the uuds system will be more bounded, than uuds one, etc. This also means that for dibaryons with six light quark configurations the most bounded will be the H = uuddss system, for which not more than 2 quarks are in the states with identical flavors. We shall consider 4quark mesons qqqq as an example. If there are only u, d, s quarks in these mesons, then for the most bounded system one quark antiquark pair (e.g. ий for the uuds systems, considered earlier) will be charac terized by opposite values of one and the same flavor, i.e. it will correspond to the zero total value of this flavor. Then the quantum numbers of hadrons arc determined by the remaining qq pair (in our case, it is as), i.e. this hadron has cyptoexotic quantum numbers. Hence from the flavor antisymmetry it follows that the lightest qqqq hadrons consisting of u, d and s quarks are cryptoexotic. However the situation changes if qqqq mesons contain quarks with four differ ent flavors. From now the "flavor antisymmetry" principle admits the existence of the state with obvious exotic values for the quantum numbers among lightest. mesons of this type, e.g. Fs = [csud] mesons with "wrong" (i.e. exotic) values of strangeness or Fj = [cs(g7)/=i] with a "wrong" isospin. The properties of such mesons are enumerated in Table 5. The existence of 5quark obviouslyexotic "anticharmed" baryons (pentaquarks) of the P" = (csuud) type or analogous "antibeauty" baryons (see Table 5) is also possible. Refs.[2750] give argu ments in favour of a quasistable character of Fs, F/, P" (due to the properties of chromomagnetic interactions). 25 ЪЫЕ Some types of exotic hadrons with licavy quarks Type of exotic particles Nota Quark Main Decay channels tions composition characteristics •I ()p''ii rxotic strangecharmed mc F* r.siul {I; S; C) = 0;l; +1 /•?. D+K- -> K-h-**n+. Utlie sons (with ни exotic set of qu mads of nicsoit is below the DK antum numbers /; 5; С (27, 28]) threshold then a weak decay F," • K~K~x+ir* takes place F' (/; 5; C) = 1; 1; 1 F,++ fl+K+;B+i! + , 0 «(«)(=• (/; S; C) = 1, 1, 1 / ,°.D A'J°,D> (/; S; C) = 1; Cryptoexolic melons of this type F+ "(w)/=o ('; S; C) -0; Eleciromag. decays: F/ —> 0* + 27, D}x';D+*'7 (if iM(F,+ ) < M(Dli)) Open exotic .nesons with two Q'f) B: The lightest states 01 the (idfirf), licuvy quarks: Q = b\ c, [29] (Гкш2) tyne should be stable w.r.t. to strong and electromagnetic inter ts = i actions (from QOD analysis) C = l etc. •\. Slvaugeanltcnarmcd baryous with P° {tiiuds) ('; S, C) 1" •> рфи~;М<*.;- (wei\!i de rxotir quantum numbers [30] /J" (r.udds) = i/2; I; I cays). Willi a large pniliahilily these states ale stable w.r.l. to strong and electromagnetic interactions ГК [iwlss) (/; S; C) = 0;2;I /"" .£0;F./W (weak de cays). These stales may Instable iv.r.I., strong am) tlerlHimag'iitie inletaetions 1 i=i [n»l.«) (/; 5; C) = I;2; I Table 5 (continued) 1 2 3 4 5 6 4. Similar states with bquarks (bqqqs) (bqqss) 5. Cryptoexotic mesons with hidden <> I«(«)r=l] I = l;S = C = 0 М^' . фж;фр charm (4quark mesons and hy I = 0; S = С = 0 Л^0) » фу\фт1';фи <> M Г* 7. Cryptoexotic baryons with hidden n* (qqqcc) / = 3/2 and / = 1/2 ^.0ЛГ;Л+5 charm Ефа {qqscc) / = 1 and / = 0 Яу, * 0К; Л+ZJ; 8. Similar baryons with hidden beauty Rx etc. (qqqb'b) Дт*ТЛГ Notes: D;fFerent decay channels for strangecharmed mesons, some of which are given in the table, are determined by the mass values of these particles: (a) M{F) > M{DK)\ (b) M(DK) > M{F) > M{D3n); (c)_ M{D3TT) > M(F). For^ instance, for Ft mesons with M{Fj) < M{DS-K) one may have only electromagnetic and weak decays, and for FJ mesons with mass M(FM) < M(DI\) only weak ones. Notations for mesons with exotins: Fa particles with "anomalous" strangeness; Fj - particles with "anomalous" •sospin. The table does not claim to be complete. Other exotic states with beauty and charmed quarks were also considered (see e.g.,[32]). The pentaquarks P" are being looked for now in K~N interactions at high energies [31]. But it seems, that for the searches of the strangecharmed exotic hadrons the hyperon beam experiments may be extremely promising. 3.2. Search for P°, F~ peotaquark baryons and F°, Ft exotic mesons with charm and strangeness The E~ beam of E781 is a good tool for the searches of these new types of strangecharmed openexotic hadrons, some of them might be quasistable particles that can decay only through weak interaction mechanism. In this case they can be identified in the vertex detector of Б781. The inclusive reactions of their production in £~ЛГ interactions would be as follows E + JV— \csuud>° +X (20) i (for P° baryons), YT+N-* \csndd>- +X (21) (for P~ baryons), £~ + ЛГ > \csud >" +X (22) (for Fmesons). Цк'/г»**» Let us do some estimations for the pentaquark baryon production in the hyperon beam of E781 (which are clost enough to those in Ref.[3lJ). These es timations are grounded on the data for the strangecharmed baryon production in the experiment with CERN hyperon beam with momentum 135 GeV [32]. These data are presented in Table 6. The results of the cross section estimations may be summarized as follows: 3.2.1. For the inclusive production of exotic pentaquark baryons P" and P~ in the £~beam the conservative lower limits for the cross sections can be obtained [31] {Pt) a(P-)" »] > 10*ff(H+). (23) 28 Table 6. Comparison of the P° = \csuud > and : \csu > production in the hyperon beam P° = \auud>-* фрт-,М< + к- 1 ,w H* = \сзи >—» PD =\addu>~>i JJ _ фркj тт ;ЛЛ« r4+т г J1 v eak decavs. —> AK-*+x* (weak decay) E + /V. 5J + X (6.1) S+JV» P° + X (6.3) U ЛЛТ+Т+ *—» ф*~ Р 1 . ЛЯ+г" РЕ=135 GeV . P + X (6.4) U ЛА'+irir *—» фрх~х~ For reaction(6.1) <*lr,>o.6 • ВЯ 0.5 /jb/nucleon. For the whole range of XF an Instead of 3 quarks in Hc, there are 5 quarks extrapolation must be done: in Р°л Р~, i.e. an additional {ud) pair must for dr/dxF =s (1 if)3 be fused. The estimation of reduction factors ffUooB/J^(10r20)^b R in the cross sections of (6.3), (6.4) in com For Bfl[EJ — ЛЯ*+!г+! ~ 0.1 parison with (6.1) gave the value R > 1С2. sections (6.2) by factor ~ 5 o(P°), ff(P")|,y>o.e > 50 nb/nucleon (from the data on charm pro o{P°), Note: To estimate the reduction factor ft ^lO2 ior exotic baryon production (the fuse of the additional ud pair), one can use the data for antideuteron production d/p ~ 10~3 (the fuse .'! ) the reduction factor R ~ 10"2 or, more correctly, R > 10"', because: a) d is a loosely bound system and correspondingly cross section additionally decreases; b) in reaction (6.3) theie is a transfer of quark рг'т sd from primary S" hyperon to P' (or even 3 quarks from E~ to P~ in (6.4)). It is well known, chat such "quark sharing" increases the cross section of the corresponding reactions. 29 3.2.2. Thus, from the data on opc] (see Ref.[33] and Table 6) one can estimate a(P°), *{/"), Table 7. Cross section and statistics for quasistable Ppentaquark baryon pcoJucUon a(.P°)UF>o •*• 1 Jib/nucleon; °{P%1I = ZBR{F° -> фрг~; \К+*-) ~ 0.05 0.01; N(P') = Ns-{inter.) • W{P°).„l < c(xF > 0) >:= 0.2; s 4000 •*• 20000 events; Л'г(interactions) = 6 • 10'°/гы1. The same number is aiso expected for P~ baryons. 3.2.3.2. If M(P) > M(p) + M(D~). then pentaquark baryons would decay strongly in the channel P'-'P + D; (27) and one must study the effective mass spectrum of pD~ system to detect this new exotic baryon resonance. Certainly, the separation from combinatorial background would be much more difficult in this case. To reduce this back ground significantly one must use the fragmentation region with Xf > 0.6. 30 Again it is possible to obtain some estimations for the cross sections and tin expected statistics for the P° baryon resonance production (see Table 8). Table 8 Cross section and statistics for strongly decaying P baryons <т(Р°)|,г>о.б > 50 nb; l<7(/»)l«//.rt.« ° Bli < ~ ВЯ[Р°»р+ £>.]0.5; ~ 50 nb (0.05 = 0.25) 0.4 ~l n!> 4 0.3 nb ^DR[D- . фх-, фх-х+т-; К+К'х- \.->IC*K- LA'+rf The number of the reconstructed events and other reconstructed channels)* G.l f 0.05; per run: t(if > 0.6) ~ 0.4 = 0.5 N(P') s 6 • Ю10 • '•'""•5'",b ^s (interactions) =61010/run v ' 32ltf ПЬ (lr2)H)3ev. Thus it seems, that if exotic pentaquark baryons 'do exist as qim.sistablc particles or as resonances with not very large decay width (Г < 150i200 MoV) it is a good chance to see them in E781 experiment (with a large enough safety factor against possible uncertainties in the crosssection estimations). 3.2.4. Cross sections of the diffractive production of pentaquark baryons P Let us consider the diagrams of Fig.4 type for the diffraction associative production of PD complex in the reactions (Fig.12): Е + Л' — (P°D~) + N (28) r,- +N -+(Р"й-) + Х>. (20) The cross section for "inclusive on bottom vertex" reaction (33) is only by ~~ 10% larger than "elastic part" of this cross section (reaction (32)) because the ratio of these cross sections is equal to \oo + аоо}/со — 1i (see Fig.ll). Here op and ODD ale single and double diffractive dissociation cross sections for high energy protons { p + N .(ЛА'Т) + Л' '30l 31 Ь) 2- — р" Figure 11, The diagrams of diffractive associative production of P°Z)~paiis in ^~A' interactions, a) "Elastic*1 process in the bottom vertex; bj Inclusive in the bottom vertex; c) The "inclusive bottom vertex" cress section is only en >-< 10% larger than "elastic" part of this cross section. Hereto and trpo - total cross sections for single and double diffrative dissociation; UDD/^D ^ 0> 1 for high energy proton interactions (see [34]). (ГГ " 19 P 9 P Figure >2. The diagrams for tile different diffra ctive pair production re • _м actions with d'barvons. 32 at £,,=70 GeV. The rough estimation of the cross section for (30) after the subtraction of isobar contributions gives the value a\p + N t (\K+) + N]diffr. ~ 2.5 4 5 ^b/nuclson. (31) The connection between the diffractive type cross sections for the associate pair production of particles with different flavors (charm or strangeness) can be obtained as follows a[£~ +N-* {E°D-} + NUffr,6oo Gev = /(2ms)/(,/I=11.5GeV 1^1 .[р + Лг^(Л/П + ^д//г,70. f(2mc)/(yS = 33.6 GeV ) ~ (0.0J. г 0.05) The kinematical function f(2m,l/y/s) does not change the cross section estima tion in our case, because /(2m,/11.5 GeV ) ~ /(0.08) й f(2mc/>/s) sc /(0.09). From (23) and (25) we obtain for pentaquark baryon diffractive production cross section <7[£ + N > (P°D~) + N\diffr,m GeV > > 10~V[E + N > (Z°D-) + N]Mffr,m Ccv > (1 H 5) nb. (33) It seems that this value is not in a very serious contradiction with o P + X)lIF>0.e50nb. 4. SEARCH FOR STRANGE DIBARYONS IN HYPERON BEAMS In this section, we consider diffractive reactions initiated with the 650 GeV hyperon beam in E781 at FNAL. The goal is to produce and identify strange dibaryons. We consider S = — 1 Sigmons [35] (E~proton resonances, denoted by S), S = —2 ffdibaryons [36], and S = — 3 Omegons [37] (fi~pvoton res onances, denoted by O). Here we widely use the results and ideas of Ref.[ll], where it is possible to find also detailed references. 4.1. General considerations There is a considerable theoretical and experimental interset in searches foT dibaryon resonances or bound states (other than the deuteron) A doubly 33 ,rranp' hound slate candidate is the H dibaryon proposed by Jalfc ;30l Thi^ has a quark structure vuddss, coupled to spinparity ./'' = 0+ and isuspin / — 0, and is a SU{3) singlet. The predicted masses mj and lifetimes Ti: vary significantly. A short summary of the main theoretical models and experimental searches icr the H is given in Ref.[ll]. The decay mode of a hound Я or an unbound Я* resonance depends on its mass. For the bound Я with тг,ц ^ '2тл. i lie dominant decay mode is H —> S p. For тц- .^ 2mA, H —> Л Л is favored, followed by Л —• p7r~. For тц ~£ m= + mp, Я —> H*p is favored, followed by H' —* TT~ A. The ЛЛ dibaryons are here designated as L (Lambdoib). We follow the lines of Ref.(ll] in describing possible experimental searches tor the H using energetic hyperon beams. We discuss cross sections for quasistable strange dibaryons (5, H, O) having decay widths less than 50 MeV. Estimates of cross sections for strange dibaryon production suffer from the uncertainty in the probability of fusion of two baryons. We base our esti mates on comparison with the analogous processes of deuteron production m leartions that produce two nucleons followed by nuclecnnuclenii fusion, with the caveat that the fusion processes in deuteron and dibaryon production may be completely different. It is beyond the scope of the present work to give a complete estimate of backgrounds. Deuteron production from 300 GeV proton micleas collisions was discussed recently in terms of nucleonnucleon fusion via pp —* TT+d final state interactions [38]. The use of hyperon beams for Я production has certain advantages. For instance, the 5" brings in the required two units of strangeness, so one does not suffer the penalty factor associated with the creation of additional ss pairs (of lourse. this penalty is already reflected in the moderate intensity of E" beams, but the nonstrange background is already removed in the beam production). We require detection of the Я decay products. At high energies, the produced particles and the decay fragments from the Я are all focused in the forward .мне in the laboratory system, so one has a reasonable efficiency for detecting all particles in the final state. The experimental feasibility for detecting Я decay products depends on the decay length Lo — /ЗТ/СТ of the H itself or of its decay product 1С", on the selectivity of the trigger, the acceptance of the detector, the quality of the par ticle identification for beam and detected particles, the expected counting rate of the signal, and the expected signaltobackground ratio. If Lo is too larg?. i; will pass through the apparatus without decaying and without detection. Aside from the Я. Greenberg and Loman calculated masses and widths and the hadronic content of exotic S = 1 Sigmon dibaryons [35]. Tliey describe how these can be observed via the decay of EJV, AN, 2Д, ЛД, S'A. Goldman 34 cf al. calculate the properties of two S = —3 Omegon states, decaying into Q.Y and ЛН [37]. The pair production of such states diffractively using E. S., U beams is possible, as shown in Fig.12. One expects a measurable cross section for the cases when a simple baryon exchange is possible, as in T.~p — S, E~p —• H, S'p —~ H, "E~p —* O, and Q~p —» O. For cases requiring more than a single baryon exchange, as in E~p —• O, the cross section should be lower. 4.2. Dibaryon production mechanisms and cross section estimates At higher energies, binary reaction cross sections зш.h as pp — ~+ E~ + N » (ЯЁ) + N, (34) E + N > (Hp) + N. (35) The exchanged object in the diagrams of Fig.13 is the Pomeron [11 j, which provides the energyindependent part of the cross section at large yG; othc mechanisms lead to cross sections which drop off as .*"" (?i=3 for Fig.13, for instance).1 In Fig.l3ac, the Pomeron dissolves into a protonantiproton pair with vacuum quantum numbers (Jpc = 0++, / = 0). Equivalontly. these diagrams describe the fragmentation of the incident E~ into a Hp combination, after which the p elastically scatters from the Pomeron, and is detected. The antiparticle is produced at lower Xp along with the }' at higher xp, and could provide an important experimental tag of H production. One would then look for the final state E~ + p+antiparticle, after the decay H —» S" + p. The // dibaryon can be observed as a peak in the invariant mass of E~p system. Another theoretical approach involves the reggezicd onemeson exchange model, with the meson coupled to a Pomeron as in Fig. 14. The cross section for binary reactions at energies 320 GeV of the form E~p —» HK° were estimated in Ref.[ll]. One, therefore, knows also the binary reaction E~K" > Hp. 'The cross section in Ref.[ll] were estimated for the leactions Z~ + Л' — [///>) + .V and У.' + Л' — [Ht\ + X (with inclusive on the bottom vertex). But, as was see» from Kig12 the truss хтопля foi these "inclusive" reactions were only by ~ 10% larger than for their "elastic" narts {'.U) and (35). Then we will consider beiow only these "elastic" processes. 35 =>н — П°;?.р d) — П";?г/ ^>H *-к"-к «•) ^»н -КМ<'° р —- -К*:К' р •*. Q ли 9) .gv.ta 13. The diagrams for different twobody reactions with baryon exchange mechanisms for H dibaryon production in hyperon Interactions (af) and deuteron production in proton interactions (g). I~« £• — K° N -m- • igurc 14 Tlie diagram for reggezised one meson exchange model for i^ + N —> (HpK") f Л reaction. 36 For this process via reggezied exchange, one could measure the // deray prod ucts S~p in coincidence with pK", or only with p. The calculations of this process at 650 GeV are in progress [39]. It is very difficult to calculate the absolute value of the cross section for a process like S~ + p —* H from first principles. Hence we use the e\perimental data on the production of the only known dibaryon, namely the deuteron, to estimate the Hjd ratio. We neglect effects due to the differing r.ni.s. radii of the d aud H. If H is deeply bound, it will be a smaller object than the d with a size approaching that of a prcton. The volume in momentum space for Я formation depends on fcff, while for d formation it is k\, where fcj and кц are the characteristic relative momenta (inverse range) at which p and n join d or at which E~ ana p join H. This size effect could give Hjd production cross section ratios higher than those given above by a factor of ~ 10 or m)re [11]. In what follows, we will not take into account this size enhancement facto.. In our estimates, we assume also that the d and H production reactions have the same kinematical form factors [11]. First, we summarize the salient features of the existing data on dcuteron production. The twobody reaction p + p —» n+ + d has been studied up to lab momenta pL of 24 GeV. At 21 GeV, for small angles [11]. da[pp > Ti+d)/dtt и 0.3 /Л/sr. (36) The total cross section at 21 GeV is 0ш(р + P -* *"+ + d) PS 15 nb. (37) Vsing an s~3 dependence to extrapolate to 650 GeV, one obtains a very low cross section estimate: + dot(p + P-> ?- + d)\m GeV «0.5pb. (3S) Since the H cross sections may be of the same order of nagnkude as for (/ formation, as we shortly discussed, it does not appear feasible to measure H production via twobody reactions (Я+meson) at the Feiuiilah energies. How ever, the twobody final state 7r+ + d represents only a small fraction of the inclusive p + p —» d + X cross section. The integrated inclusive cross section for p + p —» d + X at small angles is of the order of 1 mb/sr [11]. The ratio of the cross sections at small angles is: ~[j> + p 7T+ + d)/~(p + p d + X) и 0.3 ,/b/lmh я З х КГ4. (39) 37 Assuming thai the same ratio roughly holds for the total cross sections, at 21 GeV one estimates it to be [II]: °м(р+Р — d + X) as 15 ub/3 • 10 "' s= 50 pb. (40) Hence 5tE+£zl^Q ж ю. (4i) This ratio is of the order of a typical coalescence probability. The cross section for inclusive p + p — d + X should not drop off rapidly with \/s. Hence we expect that 5" . )1>Я + Х and E~ + p —» К + X would have measurable rates for the Fermilab energies. Another possibility is to use diffractive paii production reactions (34) and (35), where the background conditions would be iii..^h better than in inclusive reactions. 4.3. Estimates of cross sections Now we estimate the H/d ratio for 3~ and n beams. For the fusion of a np pair to form the denteron, as in Fig.13, the appropriate spinflavor weight factor a(n + p —» d) for the np —• d vertex is given by [Л]: a(n+pd) = . (42) The spinflavor factors for the fusion probabilities of the baryonbaryon channels of Fig.2 are given by: e(H + p > H) == a(S+ + S > H) ~ 1. (43) These factors are described in detail in Ref.[ll]. From Eqs. (42), (43) we have: Wo obtain a rough estimate for the cross section of reaction (35). stalling with the ratio [11] a[=." + p » H + X)/a{p + p — d + X) ~ cp"" + p — (Яр) + p]/ff[p + p • (f/n) + p] ~<Г(±-рИ)/3!)\пр4) = 1/П. (45) There are no measurements of the deutercn production ;n coincidence with an antinucleon. To get an order of magnitude estimate, we assume that eq. 38 (40) holds at high energy. Also, the (d + n +p)/(d + X) ratio is assumed to be around 0.1 [11]. Then, it is possible to obtain: a[S~ +p -r M + X) s= [E~ + N » Я 4 X] ~ ^ • 50 /Л й 4 , ff[£ 4 p _ (Яр) + p] и <7[H" + TV (Hp) + N] « —a[p + p (Ai) + pj .i&!J2lM.{ »)а1М/1Ьй0.4,Ь. (47) 0[p + p>(dra)fp] *0 12° The corresponding cross section for E~ + TV + (Я£) + Лт (£~ is the an tiparticle of £+) is suppressed by a factor A = P(ss)/P(uu). This represents a penalty factor for producing an additional strange quarks (ss) pair in the final state. From a number of measurements the ratio of probabilities P for ss vs. ий production was estimated as A w 1/5. Before the £~ decays, it can be detected in the spectrometer. After its decay, the £~ —» гт°р can be reconstructed, with good resolution. 4.4. Hyperon beams at very high momentum Let us consider the diffractive production reactions on nucleons (or on nu clei) in the hyperon beam at Fermilab with momentum бООнбоО GoV. £ + N + (Hp) + N, (48) S~ + N (ЯЕ) + ЛГ. (49) Complementing the detection of the Я decay products, the detection of an antiproton should be a valuable signature. For the £~ + p —» Я + £~ + reaction, the anti£+ has a chance to be detected in the magnetic spectrometer before it decays into an antiproton and 7r°. In that case, it is easily distinguished from a E". If it decays before the spectrometer, then only the antiproton may be detected, which is a weaker signature for Я production. With £" and Я detection, such inclusive reaction may provide interesting data at 650 GeV. The high incident energy allows the E~ from the Я decay to be detected in a magnetic spectrometer before decaying. The cross section estimate of reactions (48) and (49) are ff[£~ + TV — (Hp) + N] ~ 0.1 r 0.05 /Л, (50) 39 Table 9. Я dibaryon production in E781 Reaction Cross BR(efficiency) Hyperon Number of section flux events per run (sec-') 3-+.V- (Hp) + N 0.4 (1) • (0.25 -s- 0.1) 2-10' 4.103-H.5-103 L-p+£- E" + ;V - (Ht~) + N 8 0.1+0.05 (1/2) (0.15 ч-0.075) to 1.4- I04 -5-3.5- 103 Up + E- E- + JV-. (HpK°) + N 0.1-r 0.05 е 3 Up+E- (1/3)-(0.2-=-0.1) 10 1.2-10" -=-3 • 10 E- + N-. ;/ + x e 5 Up + E- 0.5-0.25 (1). (0.2-0.1) i0 2 10 T-5.10* (IF > 0.5 -i- 0.6) The total fluxes of different type of hyperons per run (see note to Table 2): /V(E") 2: 6 • 10"'interactions ЛГ(Е~) ~ 1.2 • 10s'interactions CONCLUSION In spite of the big uncertainties in all estimations of the statistics, given above, which are inevitable for all the searching experiments, it seems that there are very good possibilities for the observation of different types of exotic hadrons in E781 experiment. It is quite important to use these possibilities. Acknowledgments This work was done in the summer and autumn of 1993 when the authors were in Fermilab and had a possibility to participate in E781 Collaboration workshops and meetings, where many aspects of E781 experiment were dis cussed. It is a pleasure for us to express our gratitude to Peter Cooper. Tom Ferbel, Joe Lach, Jim Russ and other members of E781 Colloboration for stim ulating discussions. We are aiso indebted to the Fermilab Directorate for hospi tality. This work was supported in part by the U.S. Israel Binationa! Science Foundation, Jerusalem, Israel. References [1] Edelstein R. et al. Fermilab Proposal E781 (1987) (revised July 1993). [2] Landsberg L.G. Usp. Fi'z. Nauk 160, 1 (1990) [Sov. Phys. Usp. 33 (3), 169 (1990)]; L.G.Landsberg. Preprint IHEP 91180, part I and II. Protvino. 1991; Surveys in High Energy Phys., 6, 257 (1992). [3] Landsberg L.G. Preprint IHEP 9301. Protvino IHEP 9301, Protvino, 1993. Yad. Fiz. (to be published). [ч] Peters K. LEAP92, Proc.of the Second Biennial Conference on Low Energy Antiproton Physics, Courmayeur, Aosta Valley, Italy, September 1419, 1992 (ed. C.Guaraldo et al., NorthHolland, AmsterdamLondon New YorkTokeo, 1993), p. 93. [5j Chung S.U.. Preprint BNL 40599, Upton, 1987; Chund S.U. Nucl. Phys. 473A, 511 (1988); Chung S.U...Z.Phys. 46C, 111 (1990). [6] Jaffe R.L. Phys. Rev. 15D, 15D, 267, 281 (1977); 17D, 1444 (1979). 41 [7] Chan HongMo. Hoggasen H. Phys. Lett. 72B, 121 (1977); Hogaascn H„ Sorba P. Nucl. Phys. 145B, 119 (1978); Invited Talk at the Conf. on Hadron Interactions at High Energy, Marseiler, June, 1978. [8] Landsberg L.G.. Yad. Fiz. 52, 192 (1990) [Sov. J. Nucl. Phys. 52, 121 (1990)]; Landsberg L.G. Proc. of the Rheinfels Workshop on Hadron Mass Spectrum, St.Goar, Germany, Sepn mber 36, 1990, Nucl. Phys. B. (Proc. Suppl.) 21L 179 (1991). [91 Aleev A.N. et al. Z. Phys. 25C, 2C5 (1984). [10] Bellini G. et al. Nuovo Cim., 79A, 282 (1984). [11] Moinester M.A., Dover C.B., Lipkii H.J. Phys. Rev. C46, 1082 (1992). [12] Aide D. et al. Yad. Fiz. 47,1273 (19Ь8) [Sov. J. Nucl. Phys. 47, 810 (1988)]. [13] Aide D. et ai. Pistna v JETF 44, 44 (1986); Phys. Lett. 182B, 105 (1986). [14] Aide D. et al. Yad. Fiz. 54, 745 (1GJ1). [15] Aide D. et al. Yad. Fiz. 48, 1724 (1988); Phys. Lett. 216B, 447 (1989) [16] Gershtein S.S. Hadron89, Proc. of the Third Intern. Conf. on Hadron Spectroscopy, Ajaccio, Corsica, September 2327, 1989, Ed. F.Binon et al., Paris, 1989, p. 175. [17] Primakoff H. Phys. Rev. 8_i, 89 (1951). [18] Ferrer A., Perepelitsa V.F., Grigoryan A.A., Z. Phys. 56Л 215 (1992). [19] Balatz M.Ya. et al. Preprint IHEF 9306. Protvino, 1993. D.V.Vavibv D.V. et al. Yad. Fiz. (to be publisi ed). [20] Balatz M.Ya. et al. Preprint IHEP 9397. Protvino, 1993. [21] Landsberg L.G. Preprint IHEP 93100. Protvino, 1993. Proc. of Hadron 93, Como, Italy, 20 (to be publish(d). [22] Bityukov S.I. et al. Yad. Fiz. 38, 1205 (1983) [Sov. J. Nucl. Phys. 38, 727 (1983)]; Yad. Fiz. 46, 506 (1987) [Sov. J. Nucl. Phys. 46, 273 (1987)]; Phys. Lett. 188B, 383 (1987); Pis'ma Zh. Eksp. Teor. Fiz. 42, 310 (1985) [JETP Lett. 42, (1985)]; Landsberg L.G. 'reprint IHEP 8787. Serpukhov, 1987 (see also Proc. of the Intern. Euophysics Conf. on High Energy Phys., Uppsala, Sweeden, June, 1987, L, ~>25). 42 [23] Landsbcrg L.G. Fiz. Elem. Chastits At. Yadia. 21. Ю54 il'j'in) |S»v. J. Part. Nucl. 21, 446, 1990). [24] Achasov N.N., Kozhevnikov A.A. Phys. Lett. 207B. 199 (1988.: 2I)9JL 373 ' (1988): Z. Phys. 48C 121 (1990). [23] Zielinsky M. et al. Z. Phys. 31C, 545 (1986); 34C 255 il9S7). [26] Landsberg L.G. Yad. Fiz. 55, 1896 (1992). [27] Lipkin N.I. Phys. Lett. ZQB, 113 (1977). [28] Isgur N.. Lipkin H.J. 99IL 151. (1981). [29] Cignox С et al. Phys. Lett. 193B. 323 (1987). [30] Lipkin H.J. Phys. Lett. 195Д, 484 (1987). [31] Lichtenstadt J. Proc. of the Rheinfels Workshop on the Hadroii Mass Sper trum, St. Goar. Germany, September 36, 1990. Ed. Klcmpf E. and Peters K. Nucl. Phys. В (Proc. Suppl.), 211, 1991, p.264. Ashery D. Invited Talk. Lake Louise Winter Institute (1991). [32] Visotsky M.I. et al. Proc. of Workshop on Exp. Program at UNK IHEP. Protvino, December 1417, p.94, Serpukhov. [33] Biagi S.F. et al. Phys. Lett., 122B, 455 (1983); 1ЩВ. 230 (1985). [34] Baksay L. et al. Phys. Lett., 5j>B 491 (1993). [35] Greenderg W.R., Loman E.L. Phys. Rev. D_47, 2703 (1993). [36] Jaffe R.L. Phys. Rev. Lett. 3_£, 195 (1977); 38, I617E (1977). [37] Goldmar, N. et al. Phys. Rev. Lett. 52, 627 (1987). [38] Gugelot P.C., Paul S.M. Z. Fhys. A344 (1993) 325. [39] Volkovitsky P. et al. (Private communication). RKCHVIA D'.a.mli,;r 7, Г.Л'-Ч. 43 Л.Г.Ландсберг и др. О поисках экзотических адронов в экспериментах на гиьеронных пучках высоких энергий. Оригинал-макет подготовлен с помощью системы I^T^X. Редактор Л.А.Антипова. Технический редактор Н.В.Орлова. "чоррекгор Е.Н.Горина. Подписано х печати 14. 04. 1994 г. Формат 60 х 90/16. Офсетнаи печать. Печл. 2,68. Уч.-изд.л. 3,20. Тираж 260. Заказ 1068. Индекс 3649. Цена 400 руб. ЛР №020498 06.04.1992. Институт физики высоких энергий, 142284, Протвино Московской обл. 400 руб. Индекс 3G49 ПРЕПРИНТ 94-19. И Ф В 3, 1994 30%, see the text); b) The same spectrum, but with more stringent cut (Л2. < 0.02 (GeV)2) to exceed the selection of coherent events. The spectrum is fitted by the sum of smooth polynomial background and ihc nrcilWigner peak with M = 2050 ± 5 MeV and Г = 50 ± 20 MeV.