Barbaro-Galtieri, A.

Chadwick, G.B.

Guiragossian, Z.G.T.

Matison, M.J.

Pickup, E.

Rittenberg, A.

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleSEARCH FOR I = 2 HYPERONS AND STUDY OF RESONANCES IN K-d INTERACTIONSPermalinkhttps://escholarship.org/uc/item/7f54x7vjAuthorsBarbaro-Galtieri, A.Matison, M.J.Rittenberg, A.et al.Publication Date1968-05-01eScholarship.org Powered by the California Digital LibraryUniversity of California',I ,"I'· , . \ .. \ TWO-WEEK LOAN COpy This is a library Circulating Copy which may be borrowed for two weeks. , For a personal retention copy. call . Tech. Info. Division. Ext. 5545 DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. ,'.; .. .: .:' ' . ; . . Submitted to Phys~. Rey~ Letters . UCRL-18237 . Preprint .,-1' ';\. i:. ~ . . ..' .. . '.. . UNIVER$iTY0F- CALlFORNIA .' La wrepce.Radiatioh Laboratory . '. Berkel~y, California . '1,.'" ! 'AEC Contf~ct No . . W ~7405-eng-48 . ·SEA.RCHFORi~"2 HYPERONS AND STUDY OF RESONANCES ' ,!' ,. . 'IN k";dlNTERACTIONS: . A. Barbaro'" Galtie ri,M,J. Matis on,A~ Rittenberg, 'G. 'E. Chadwick,Z. G; T. Guiragossian,and E. Pickup . ~I{ May 1968 . . . ~ ,. '. " ": "L ." ,',},': . '. . '~"':', . :'>" ' . . ) .. :1,' • -1- UCRL-18237 SEARCH FOR 1= 2 HYPERONS AND STUDY OF RESONANCES . IN K-d INTERACTIONS* .. A. Barbaro-Galtieri, M. J .. Matison" and A.Rittenherg Lawrence Radiation Laboratory ,Berkeley, California and G. B. Chadwick, Z. G. T. Guiragossian, and E. Pickup Stanford Linear Accelerator Stanford, California May 1968 We have. searched for isospin-2 hyperon resonances pro-~ucedin K-ninteractions at 2.11 and 2.65 GeV/c and decaying into ~- 'IT- or ~- 'IT - 'ITo. We find no evidence for any such state with M ~ 2300 MeV, and obtain a cross section upper limit of 30 }lb, with 99% confidence level. . , . . . Recent experiments on K+ p total cross sections (hypercharge state Y = 2) have shown the presence of four enhancements, three in the isospin I = 1 state and one in the I = 0 state, which might be attributed to resonances. 1 An alternative explanation can be found for at least the first I = 1 enhance-2 ment; . however, at this time, the large (= 6 mb) bump in the I = 0 isospin state (at M = 1865 MeV) does not seem to have any other plausible explana-tion. All the other established baryon resonances can be classified in singlets, . octets, and decuplets of the SU(3) symmetry scheme, but Y = 2 states would belong to higher representations (10 for I = 0, 27 for I = 1). -2- UCRL-1.8237 Investigation of the existence of other resonances that would belong to such higher representations is relevant ~or the quark model because ,as it stands now it cannot accommodate high Y or I states, since a five-quark structure (qqqqq) would be ,needed to describe such states. , 3 Horn et al. , using the five-quark model, obtained some selection rules which forbid the decay mode B+P (spin-1/2 baryon + pseudoscalarmeson) for some spin-parity 'assignments of high Y, I states, and they suggest that B+P+P decays should also be' investigated.' Only the Z IT I = 2 state has been investigated so far, , " ' - 4 and it failed to show any structure at masses below M = 1800 MeV. We re-port here the results ofa search for I = 2, ,Y = 0, resonances decaying into the E:"lT- and Z- IT - nO channels, with M ~ 2300 Me V. In this experiment the 72-inchbubble chamber, filled with deuterium, was ~xposedto a'K~ beam at momenta 2.11 and 2.65 GeV/c.' The reactions studied were , - - + -K d - (p ) E n IT , S (1 ) and (2) where (p s) indicates the spectator proton, which was measuraBle in 300/0 of the events. A total of 5000 events was measured on Franckenstein measuring , ' machines andprocessed with the LRL standard program~ (P'KG, DST-EXAM, SUMX). For the events in which the spectator proton was not visible or was too short to be measured, it was assigned a momentum equal to zero, with appropriate errors in the x, y, z components, and then fitted as if it were rnea-• / sured. This method turns out to be very good for four-constraint' (4-c) fits, ". ..... though it results in a slightly worse resol~tion for the (1-c) fits. 5 Almost all events were cl1.ecked on the scanning table, either to confirm the choice of the programs or to resolve the ambiguity of the fit whenever necessary. Only -3- UCRL-i8237 about 3% of the events remained ambiguous after this check. For the following analysis, only events having a proton momentum P < 280 MeV/c were used., sp Figure iashows the invariant-mass-squared distribution for the 2; 'IT '. . . - - - - 0 I = 2 final state in reaction (i); Figs. i band i c show the 2; 'IT and 2; Tr 1T Z I = 2 final states in reaction (2). The plots show no obvious enhancement at z any mass. In order to determine the expected shape of the mass distributions for the case in which lio I = 2 resonance is present, we have investigated the effects qnthes~'distrib~tions of known resonances that might be produced in the reactions under study •. This investigation has been made with the aid of a maximum-likelihood program, MURTLEBER T, 6 which fits the events to a frequency function obtained by incoherently adding phase space to Breit- Wigner {or Gaussian) shaped resonances and can use as parameters the mass. width (M.I'), and percentage of each resonance. As a result of this method. the re-flections of ~e~onanc'es on the different mass combinations are properly treated •. The events at the two momenta have been fitted independently and. with a fe'w exceptions to be discus'sed late.r, no difference was found in the positions and widths of the resonances at the two momenta. Table I lists the resonance processes which, added to phase space, give the best fit for reactions (i) and (2) at the two momenta, and the cross sections for the two reactions. 7 Reaction (i) is dominated by production of the p n:ieson in the Tr + 'IT - final state and of the A (1520) in the 2::- 'IT + final state. Reaction (2) is dominated by the production of the w meson and the 2:: (1385). In Fig. 2 we show some of the mass plots, with curves corresponding to the fits of Tabler. We turn now to a discussion of these fits. The baryon states, A (1405), A (15i8), and 2:: (1385), have the expected masses and widths within the accuracy of this experiment. However. we list -4- UCRL-18237 three different values of M and r for states in the mass interval 1670 to 1705 MeV. 8 . There are four known. resonances in this energy region, therefore we pos sibly see the production of several of these states 'decaying into· 2:-1T + or + ':c 2:-1T 1To. The Y~ ° (1840) has a nar.row width and might be identified with the . . p + 9· A(1860), r = 34 MeV and J. ='7/2 • reported by Armenteros et al. . The distribution of the invariant mass squared of the three-pion final state is sh~wn :in Figs. lc and 2d.The 'l1 and .ware clearly produced at both . . . momenta. The 2.11-GeV/c data show an Emhancementat a mass of~1.0 GeV (2.8 ±13events)"which als·o 'appe'ars in the low-.6.2 ·events in both plots. ,Since ; we cannot distinguish between' a 1T O ~nd a 'I. a possible explanation 6fthis en-hancement is the '1T1TY decay mode of the "1 1 • Although the mass of the ,,' is 960 MeV. two systematic e'ffects p'resent in our data would cause· an 11' signal . . . ..' 10 to appear at a higher mas s. In order to determine the number of 1)'- 1T1Ty . events we would expect to see. we have looked at the reacti~n K-d - (p) ~- '11' • s· with ,,'- "N 1T + 1T- (including o~~y the neutral T\ 4ecays). We found, again at a slightly high mass, 28 ±7 ev~nts (20 ±5 at low ~2) for the 2.11-GeV/c· data and . .. . 2· . 18±8 events (9±4at low.6. ) for the 2.65-GeV/c data. The,,' branching ratios11 predict these same numbers of ~vents for ,,' .... 1T+1T-y. What we see agrees numerically with the,,' interpretation,. leaving no evidence for the H . h d 12 meson ln t es.e ata. As for the I =2 hyperon states. the curves shown in Fig. 1 . represent <./ the expected mass distributions corres'ponding to the fits reported in Table I. ~ * These fits assume that no Y 2 resonance is present. and include all known ~ ... . resonances that appear at a level ~ 2 standard deviations. The curves seem to fit the data very well except for a small fluctuation in the ~- 1T -1T O mass distribution. The result of the fit for this small enhancement was (3 ± 2) % of "I -5- _ UCRL.:18237 the 2.65-GeV Ic data, therefore of no statistical significance. This error, as well as the errors quoted in Table I, includes all the uncertainties of the multi-parameter fit, and therefore it is larger than that obtained by taking the statisti-cal error on the projected mass plot. For the purpose of calculating cross-section upper limits we have fitted the data at the two momenta together. This reduces the errors quoted in Table I by about 30%;- from these errors it fol-lows that a three-standard-deviation effect corresponds to ~% of the com-bined data. For mass above -2150 MeV only the 2.65-GeV Ic data contribute, and -a different upper -limit is evaluated. As for the possibility that a narrow ~ n or ~- n - nO resonance might be spread out and thus not observed, Table I shows that our resolution is very goodfor the analogous ~-n+ and ~-n+nomass com-binations (note, for example, the A(1705) - ~-n+no with a 35-MeV width). We - * quote the following upper limits for a Y 2: For M < 2150 MeV r < 60 MeV CJ< 20 fJ.b, r <120 MeV CJ< 30 fJ.b, for M < 2300 MeV r< 60 MeV CJ< 30 fJ.b, r<120 MeV CJ< 40 fJ.b, with a 99% confidence level. 13 ·-6- UCRL-18237 REFERENCES *Work done under auspices of the U. s~ Atomic Energy Commission. 1. R. L. Cool, G. Giacomelli, T. F. Kycia, B. A. Leontic, K. K. Li, A. Lundby, and J. Teiger, Phys. Rev. Letters~, 1228 (1966); R. J. Abrams, R. L. Cool, G. ·Giacomelli, T. F. Kycia, B. A. Leontic,· k. K. Li, and D. N. Michael. Phys. Rev. Letters .!1,. 678 (1967)~ 2.· R. W. Bland,· M. G. Bo·wler,· J. L. Brown, G. Goldhaber, S. Goldhaber,· v. H. Seega~, ·and G. H. Trilling, Phys. Rev. Letters~, 1077 (1967). 3. D. Horn, J.' H~ Lipkin, and S. Meshkov, Phys. Rev. Letters.!2. 1200 (1966). 4. G. R. Kalbfleisch, G. Alexander, O. 1. Dahl, D. H. Miller, A. Rittenberg, andG. A. Snl;ith, Phys. Letters ~ 225· (1963); M. H. Als.ton, A. ~arbaro-Galtieri, A. H. Rosenfeld, and S. G. Wojcicki, Phys. Rev. 134,B1289 (1964); R. B.Bell, R. P. Ely, and Yu-Li Pan, Phys. Rev. L~tters 18, 921 (1967). 5. The 'r"esolutiori for the invariant mass of pairs or triplets of particles other than the 3tr mas s is quite good, as can be checked by comparing the widths used to fit the data (Table I) with those quoted in the world com-pilation by A •. H. Rosenfeld, N. Baras·ch-Schmidt, A. Barbaro-Galtieri, L. R~ Price, P. SlSding, C. G. Wohl,M. Roos, and W. J.Willis, Rev. Mod·. Phys. 40, 77 (1968). For the three-pion system the resolu-ti~n is worse; this results from the spreading of thetr° momentum pro-. . .. . ( duced by the uncertainty in the momentum of the unmeasured spectator pro- (yr ton. In the 2.11-·GeV Ic events, which have a larger beam momentum spread than do the 2.65-GeV Ic events, this effect is increased. ~ .. -7- UCRL-18237 6. J. 'Friedman, MURTLEBERT, Alvarez Programming Group Note P-156, 1966. 7. The effective path lengths were calculated with scanning and measuring \, efficiency t ak e n into account, as well as the detection efficiencies for ~- (a length cutoff of 3 mm was used), the cutoff on the spectator protonmomenturri, and the Glauber correction for the screening of the neutron in the deuterium nucleus. The path lengths were )..~ 1.61 ±0.21 events/iJ.b and L62 ±O.21 eventsjJ.1b at 2.11 and 2.65 GeV jc, respectively. 8. See the particle data compilation of Ref. 5. Note that the A(1 705), which we find in the neutral but not in the charged ~ 1T1T state, has previously been detected only in fo~mation experiments. 9. R. Armenteros, M. Ferro-Luzzi, D. W. G. Leith, R. Levi-Setti, A. Minten, R. D. Tripp, H. Filthuth, V. Hepp, E. Kluge, H. Schneider~ R. Barloutaud, P~ Gianet, "J. Meyer, and J~ P. Porte, Nucl. Phys. B3, 592 (1967). 10. The upward displacement (about 40 MeV at 2.11 GeV/c and = 25 MeV at 2.65 'Gevjc)of the mass of the TJ'arises from two different sources: (a) The use of the 1Tom~ss instead of the y mass produces an effect that amounts to = 15 MeV, as we found by refitting the events with the 'I instead of the 1T 0 mass. (b) The uncertainty in the 1To momentum in the 70% of the events in which the spectator is not visible produces an , additional shift not present in those events with a measured spectator. This was confirmed by the fact that when the latter events were refitted, ignoring the measurement of the spectator proton, there Vl!:as an upward shift (larger at 2.11 than at 2.65 GeV/c)in the three-pion mass spectrum in the 1.0-GeV region. This refitting produc~d no such shift in the w ,region, consistent with the fact that the wappears at its correct mas s in our events. 11 •. The ratio R = -8-+ -TJI - 1T 1T Y UCRL-18237 is R= 0.96±0.12, where (1T 01Tol1C)B indicates the background of this decay mode under the + - . 1T 'IT "N (A. Rittenberg, Lawrence Radiation Laboratory, private communication). 12. At the Heidelberg Conference we had reported a 2.5-standard-deviation effect at a mass of about 990 MeV which was attributed to the H meson. See I~ Butterworth, in Proceedings of the Heidelberg International Conference on Elementary Particles (North-:Holland Publishing Company, Amsterdam, 1968), p. 11. However, an increase of about 35% in the amount of data and a better understanding of the systematic mass shift and resolution in our data led us to the present conclusions. ,.The evidence for the existence of the H meson is currently less than t\vo stanc1.ard deviations in only one experiment~ See A. Barbaro-Galtieri and P. S~ding in ".Is There Evidence for the H Meson ?"(UCRL-18271,. June 1968) to be published in Proceedings of the Philadelphia Conference on Meson Spectroscopy (W. A. Benjamin, Inc., New York, 1968) • 13. To check the error calculations such resonances were artificially added to the data. The resulting fits correspond to 3.5 standard deviations fr·om "no resonance. II I I I I I i I • I I ~.~ I I i '! , -9- UCRL-18237 FIGURE LEGENDS Fig. 1. Plots of all the possible I =2 mass combinations in reactions (1) and z ' Fig. 2. (2). The two momenta have been combined in these plots in order to increase statistics. , 2 - - ' ' (a) M (~ 1T ) for reaction (1); (b) 2, - -M (L: ,1T ) for reaction' (2). " 2 - - 0 (c) M (~ 1T 1T,) for reaction (2). The curves correspond to the best fits of Table I, which do not need any resonance in the I = 2 system. - + (a-b) The mass squared distributions of the ~ 1T system for reaction (1). (c-d) The mass squared distribution of the three pions in reaction (2); dashed histograms refer to events with low momentum transfer to the - 2' 2/ 2 ~ , 6. <.6 GeV c" 'The curves correspond to the best fit reported in Table 10 -10·- UCRL-18237 Table, I. Best fit to the data of reactions (1) and (2). Description of model Reaction (1) Process - - +-Kn-~TITI . M, r (MeV) 1405,35 , 1518,18 1675,55 1840,35 K-n~~-po 760,120 . (j tot for reaction (1) (tJ.b) Process M, r· (MeV) - *0 - 0 Kn-Y TITI .;. . ' >',c- + .... Kn:+Y TITI a - -Kn-~T\ a K - n _ ~- w a - -K Ii -~ ,,1 1~10,30 ·1520,20 1675,35 1390,45 1705,35 ·2190,60 548,40 783,40 960,60 for reaction (2) (~b) 2.1 GeV/c 876 events 6.7±1.3 21.3 ±109 10.4±2.0 2.5 ± 1.3 35.9 ±3.4 545 ± 70 775 events 7.1 ;1:2.0 10.6 ± 2.4 .2.6 ±0.7· 27.i±2.3 3.q±1.7 480 ±62 2.7 GeV/c· 605 events 0/0 10.8±1.7 18.9 ± 2.2 8.8± 200 7.0±1.8 21.8±304 370 ± 50 892 events % 6.3±1.6 5.6 ± 1.5 3.9±t".6 5.0±1.8 2.1 ± 1.·0 3.2±1.8 2.2:f0.6 14.5±1.5 3.1 ±1.6 550 ± 72 a. See footnotes 4 and to for a discussion of the resolution and mass shifts for the three meson states. For the wat 2.11 Gev/c we have used M == 789 MeV ,. and r == 80 MeV. For the ,,' we have used (1000,50) and (985,70) at 2.11 GeV Ic and 2.65 GeV Ic respectively (at 2.11 GeV Ic the ,,' is at the edge of phase space and thus requires a smaller width). ~ . . .. ~ . :', -1" , \ " • N > Q) (!) 00 o -11-60 (0) UC~L-18237 K-n - 2-17"+"" -1481 events O~~~~==~==~~==~==~==~~ 100 K-n --.- 2-17"+.".-.".0 1667 events d 50 (b) " en +-c Q) > w 0 L----.lL......J_ ___ --L-_ __...._--1.._---I._...=3~_.L.....__.L._______A 2.03.0 4.0 5.0 M2 (2- 1T-) [(Gev)2] 80 (c) 1667 events 40 0~--.....J-~~~--I....---1..-~-~~--~--~~ 2.0 3.0 4.0 5.0 M2 (2- 1T- .".0) [(G e V)2] Fig.! XBL686":3027 -12- UCItL-18237 '-i 120 i' .(0) (c) K-n- ~-7T+7T- K-n ...:...- ~-vt7T-17'0 PK = 2.11 GeV/c PK = 2.IIGeV/c 80 876 events 775 events I!lI 317 events /).2<0.6 N 40 N .> > . Q) Q). (!) (!) <X) ~ a a d 0 d "- "- (d) !?80 (b) CJ) K-n -~- vt7T-7TO -c: c: PK= 2.65 GeV/c . Q) K-n-~- 7T'+1r"- Q) > > 892 events· W PK = 2.65 GeV/c W ml308 events 605 events /).2< 0.6 3.0 4.05.0 M2(I-1T+) [(GeV)2] . Fig. 2 X8l686~ 3028 • This report was prepared a~ an account of Gov~rnment sponsored work. Neither the United States, nor the Com-mISSIon, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, wiih respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, appa-ratus, method, or process disclosed in this report may not infringe privately owned rights; or 8. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any infor-mation, apparatus, method, or process disclos~d in this report. As used in the abov,e, "person acting on behal f of the Commission" includes any employee or contractor of the Com-mission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. 

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SEARCH FOR I = 2 HYPERONS AND STUDY OF RESONANCES IN K-d INTERACTIONS

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SEARCH FOR I = 2 HYPERONS AND STUDY OF RESONANCES IN K-d INTERACTIONS

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