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Kaon Reactions (Exp) Kaon Reactions (exp) Rapporteur's talk: Chairman: Filthuth H. (Heidelberg) Rapporteur: Morrison D. R. 0. (CERN) Secretary: Yamdagni N. (Stockholm) Parallel sessions: SA. Total cross-sections, elastic scattering. Discussion leader: Lundby A. (CERN) Secretary: Blomqvist G. (Stockholm) SB. Inelastic two-body reactions. Discussion leader: Sens J. C. (FOM/CERN) Secretary: Jonsson L. (Lund) SC. Many-body reactions. Discussion leader: Goldschmidt-Clermont Y. (CERN) Secretary: Holmgren S. 0. (Stockholm) ' Review of Strong Interactions of Kaons D. R. 0. MORRISON CERN Introduction cross section is greater than the K+p cross section at all ener­ gies, including infinity. Naively it may be noted that in K-p This review of the strong interactions of K-mesons will be interactions the summed cross section for the channels divided into the following subjects K-+p-+ hyperon+pions (1) 1. Total cross sections 2. Elastic scattering is "'5 mb whereas such reactions do not exist in K+p interac­ 3. Inelastic two-body reactions tions presumably due to the absence of a positive strangeness 4. Many-body reactions 5. Production of "Rare" particles, p, 8, Q- 6. Summary and future. 26 o. Galbraith el al bl • IHEP-CERN (Preliminary) The outstanding results are: 25 1. The first data on total cross sections from Serpukhov 24 have given an unexpected result. 'j)' 23 2. A large amount of new data on elastic scattering has ..§., 22 become available, in particular polarisation experiments. The 0 '6 21 second peak is discussed. + t 3. In a two-body reaction a strong disagreement with Regge 20 + pole predictions has been ob. erved. 4. The subject of many-body reactions has suddenly become 19 "fashionable" because of the development of calculable theo­ 180 10 20 30 40 50 60 70 ries and of new ways of presenting the data. P [GeV/c] As agreed with other rapporteurs, phase shift analysis of low energy K-Nand K+Nwill be presented by Dr. Levi Setti, while Fig. 1. Plot of total K-p cross section against the incident lab. certain aspects of many-body reactions of pions will be treated momentum. in this review paper. 6 Galbrailh •l al bl o Foley et al <l • lHEP·CERN (Pr~iminary) 1. Total Cross Sections - R•ggepoletitloprevious data 50· Bug er et al dl a. K- with hydrogen Tho · ·RN-lH P ollaboration [I] has presented preliminary data on the first tot'tll ross section measurements of K- , 1r­ and p made at lhc 70 eV Seri ukhov accelerator. The results Asympto~c -+ 0 limll for K-p interactions are shown in F ig. 1. The outstanding b 3 result is that the cro s section is approximately constant over the momentum range from 20 to 60 GeV/c. The importance of these results may be appreciated from Fig. 2 where the data 20 for K-p, n-p and pp reactions are shown with a Regge pole fit to the data at lower energies made by Barger, Ollson and Reeder [2]. This fit has been extrapolated to higher ehergies making use of the assumption that particle and antiparticle 0 10 20 30 ,0 50 60 'IO cross sections are equal at infinite energy. Thus for K-p and P [ GeV/c] K+p interactions the two total cross sections should both approach a value of 17.2 mb at infinite energy. It can be seen ig. 2. Total cross section for pp, rep and K- p reactions plotted against t11c incldent lab. momentum. The pp total cross section curve from Fig. 2 that the new experimental data, especially the K-p is shown fot• comparison. The other curves arc Regge Pole fits to low results, deviate significantly from the Regge pole predictions. energy data, which are extrapolated to higb energy but which do not One is tempted to wonder whether it is possible that the K-p agree witl1 the new experimental data [1]. 238 D. R. 0. Morrison AND K p TOTAL CROSS SECTIONS 60 50 .0 40 E 30 z 0 u~ w 20 (/') (/') (/') 0 a::: u 3 5 6 7 B 9 10 1 2 3 'l 5 6 7 B 9 10 CMS ENERGY SQUARED GEV• •2 Fig. 3. Compilation of K+p and K-p total cross sections plotted against lab. momentum. Data from ref. 4 and 1. baryon. It is interesting to note that at 10 GeV/c the K-p total The relative absence of structure in the K+p total cross section cross section exceeds that of K+p by about 5 mb, and that the suggests that there is little or no direct formation. The maxi­ cross section for reaction (l) is also about 5 mb [3]. On the mum near 1.2 GeV /c may be due to threshold effects. other hand the assumption of equality of particle and antipar­ It has been shown [5] that for two-body reactions at high ticle total cross sections at infinite energy is based on crossing energies the cross section a varies with the incident laboratory symmetry which is not a principle that one abandons lightly. momentum, PLab according to the relation However, when the unthinkable, becomes thinkable, progress a=K Pr,ab-n (3) is sometimes made. The new Serpukhov data is presented in Fig. 3 where a where Kand n are constants. Fitting the K +p total cross section compilation [4] of K-p and K+p total cross section data above data above 5 GeV /c with such a formula, one finds n= + 0.01, 1 GeV/c are shown. It may be seen that the K +p curve rises that is effectively constant cross section. Fitting the 22 data sharply to about 1.2 GeV/c, falls slowly to near 3 GeV/c and points* for K-p above 10 GeV/c, one finds n= 0.04± 0.01, then is about constant. It shows little evidence of structure that is a small decrease. Some of this decrease may come whereas the K-p total cross section at low energies has consid­ from the 10 to 20 GeV/c, region but not all. Thus further erable structure, but such structure dies out (or becomes too experimental work would be welcome. It is interesting to small to be detectable) at about 4 GeV/c. The K-p cross section note from Fig. 3 and from similar distributions, that systematic then decreases slowly with increasing energy. This structure in errors between one experiment and another exist and that the K-p total cross section is due to the direct formation of these systematic errors may sometimes exceed the quoted errors. resonant states, that is It has been suggested by Cabibbo et al. [6] that total cross sections are zero at infinite energy (this naturally satisfies the x-+ p--+ Y*--+ x-+ p. (2) Porneranchuk theorem). They propose that the ar should 0 07 "' Note that the numerical values above 20 GeV/c were read off decrease as PLab - • • It may be seen that the exponents observ­ from Fig. 1. ed are significantly less than this value of 0.07. Kaon Reactions 239 1- I 1 -~.--- , r-rn n --·r--1 ,--, 1-, ·, t A general comment, for which further illustration is given 10,000 1-,--rrn K2 , >4 GeV/c MEAN ~7 GeV/c SLAC/ HEPL later, may be made about the failure of the Regge pole model .D , n , 10 GeV /c to fit the data from Serpukhov. This comment is experimental E in the sense that it is based on the history of the Regge pole z Q model since 1962. uw 1/l Applied to known experimental results -successful 1/l 1,000 1/l Interpolation between known experimental 0 0:: results -successful u Extrapolation or new processes -often unsuccessful. _J f:! 0 I- The Serpukhov results are an example of extrapolation. However, past history shows that because of the large number 100 t J I 1 1 1 1 [ I Ll~-~ 1 -L...L.Lu,J 10 100 of parameters available in the Regge pole model, data which ATOMIC NUMBER initially gave disagreement have, with further efforts, been successfully fitted. Fig. 5. Total cross section plotted against Atomic number for "'7 GeV/c K3°-meson [7] and 10 GcV/c neutrons [8]. b. Total and absm·ption cross sections on nuclei The CERN-IHEP Collaboration reported on absorption cross On ly Ku 0-mesons of energy greater than 4 GeV were taken by section measurements with x-, n- and antiprotons of 40 GeV/c using (ime of flight criteria. The average energy was about on eight different nuclei. The extrapolation range used was 7 GeV. Tlie results are shown in Fig. 5 together with those for 0.09:0:: it l:O:: 0.23 GeV 2 where tis the square of the four momen­ 10 GeV/c neutrons [8). It may be seen that in first approxima­ tum transfer. Since the t-region near t= 0 was not investigated, tion the data can be fitted with two parallel lines corresponding these results are for absorption and not for total cross sections. to equation (4). From a fitting of the data l'rom A= 12 to The results are shown 'on a log-log plot in Fig. 4 as a function A= 206, we find o good fit (x2 = 1.1 for 2 degrees of freodom) of the Atomic Number A. It may be seen that the data are well for K ~ 11 with the c poncnt c= 0.86± 0.02, while for the 10 GcV /c fitted by the expression neutrons c= 0.
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