Baryon-antibaryon production in pp-collisions at 450 GeV/c seen by the CERN-collaboration WA102 is discussed in terms of an intermediate non-resonant "colorball"

Jacobsen, T

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12 March 2002Probable \colorball" production in pp-collisionsat 450 GeV/cT. JacobsenDepartment of Physics, University of Oslo, PB 1048 BlindernN-0316 Oslo, NorwayAbstractBaryon-antibaryon production in pp-collisions at 450 GeV/c seen by theCERN-collaboration WA102 is discussed in terms of an intermediate non-resonant \colorball".EXT-2002-02312/03/20021. IntroductionA motivation for the CERN-project WA102 was that central produc-tion has been proposed to be a good place to produce glueballs via dou-ble pomeron exchange [1]. The WA102 collaboration has reported baryon-antibaryon production in the central region of the reactionpp! pXp (1)at 450 GeV/c, where X is one of the four systems , pp, pp0or pp+ [2]. Since no resonance production was seen for any X , no glueball candidatewas found in these nal states. These four nal states, one with and threewithout starnge particles, have six characteristic features in common:a) Every X is centrally produced according to tests on rapidity [2], ore-sumably by double exchange processes.b) The energy dependence of production cross sections (not measuredfor pp0) excludes double pomeron exchange, but no alternative exchangeand production mechanism was identied [2, 3].c) A slope parameter b  5 GeV 2of the distribution of fourmomentumtransfer t at a proton vertex [2] (which one is not specied in [2]).d) A \at" distribution of the azimuthal angle  between the transversemomentum vectors of the two nal state protons [2, 4].e) A ratio R  1=3 between the number of events observed for dpt< 0:3GeV/c and for dpt> 0:5 GeV/c, respectively, where dptis the numericalvalue of the dierence between the transverse momentum vectors of the twonal state protons [2, 5], in disagreement with double pomeron exchangeand with exchanges with a gluonic component.f) Background-like distributions of eective mass enhanced towards min-imum mass for every X , i.e. no resonance production is seen for any X [2].22. CommentsThat four nal states have six observed characteristic features in commonas described above suggests that one common process produces these fournal states.Also, since every X , e.g. X = pp, is centrally produced, every X isprobably a nal state of a common intermediate system S produced in adouble peripheral pp-reaction by two exchanges y and z, i.e.y + z ! S ! p+ p (2)as shown in Fig. 1.Furthermore, since the assumed S has two main decay modes, with orwithout strangeness, S has probably received only colors and anticolors butno avours and antiavours from the exchanges y and z.3. The Intermediate SystemWe now assume that S is an intermediate \colorball" without quarks andantiquarks, but with e.g. these colors and anticolors,r, b, g, r,b and g,which may form two separate colour singlets, i.e.S(rbgrbg)! B(rbg) +A(rbg); (3)where B(rbg) is a baryonium [6] and A(rbg) an antibaryonium, respectively,both without quarks and antiquarks. These two colour singlets hadronizeto a baryon and an antibaryon, i.e.B(rbg) + A(rbg)! baryon(qrqbqg) + antibaryon(qrqbqg) (4)where a quark q in this context is a u-, d- or s-quark, and where the su-perscripts and subscripts symbolize colour and anticolour, respectively. Ifthese two nal state systems are excited and decay, or if S contains addi-tional colours and anticolours which hadronize, additional mesons may alsobe produced.34. The ExchangesSince double pomeron exchange and exchange of mesons which couldhave a gluonic component are inconsistent with the experimental data [2],and since exchange of quark-antiquark mesons is unlikely because of strange-and non-strange decay modes of the assumed intermediate system, othertypes of exchange are probably responsible for the reactions (1).Exchanges which can supply the assumed intermediate state with thecolors and their anticolors needed for the recombination mechanism dis-cussed above are requested by our model. Since the colliding protons cannot change their colors, exchange of \colorballs" with e.g. two colors andtheir anticolors would full the requirements in this context. If so, theircharacteristic features would be those found experimentally by WA102 [2].5. ConclusionIf, in a double peripheral process with particle production in the centralregion, the exchanges do not carry avour and antiavour while the pro-duced particles do, then an intermediate system and the exchanges behaveas \colorballs".Therefore, if we assume that the exchanges behave as \colorballs" whichcarry those colors and their anticolors which via an intermediate \colorball"recombine to two color singlets which hadronize to a baryon-antibaryon pair,a possible and because of its simplicity likely model for baryon-antibaryonproduction in the central region of high energy pp-reactions appears.If such a \colorball", which is assumed to be a system of colors, shouldbe equivalent to a glueball, which is an assumed system of gluons, then aglueball could not be a resonance.AcknowledgementDiscussions with H.A.Olsen, NTNU, Trondheim, Norway, are gratefullyacknowledged.4References[1] D.Robson et al., Nucl. Phys. B130 (1977) 328;F.E.Close, Rep. Prog. Phys. 51 (1988) 833[2] D.Barberis et al., Phys. Lett. B446 (1999) 342[3] A.Kirk, Yaz. Fiz. 62 (1999) 439[4] T. Jacobsen and K.M.Danielsen, Phys. Lett. B518 (2001) 23[5] F.Close and A.Kirk, Phys. Lett. B397 (1997) 333[6] G.C.Rossi and G.Veneziano, Phys. Rept. 63 (1980) 1495FigureFig. 1The reaction p+ p! p+ (p+ p) + p in terms of a double peripheraldiagram.6

Probable "colorball" production in pp-collisions at 450 GeV/c

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