Alston, M.H.

Alvarez, L.W.

Eberhard, P.

Good, M.L.

Graziano, W.

Ticho, H.K.

Wojcicki, S.G.

eScholarship - University of California

Lawrence Berkeley National LaboratoryLawrence Berkeley National LaboratoryTitleA STUDY OF RESONANCES OF THE Z-7r SYSTEMPermalinkhttps://escholarship.org/uc/item/4d90m8pnAuthorsAlston, M.H.Alvarez, L.W.Eberhard, P.et al.Publication Date2008-05-20eScholarship.org Powered by the California Digital LibraryUniversity of California, IJIUCRL 9717UNIVERSITY OFCALIFORNIATWO·WEEK LOAN COPYThis is a Ubrar~J Circu/atinq COP~Iwhich may be borrowed for two weeks.For a personal retent ion copy. callTech. Info. Diuision. Ext. 5545BERKELEY. CALIFORNIA. .UCRL-97l7Limited distributionUNIVERSITY OF CALIFORNIALawrence Radiation LaboratoryBerkeley. CaliforniaContract No. W-7405-eng-48A STUDY OF RESONANCES OF THE 1:-11' SYSTEMMargaret H. Alston. Luis W. Alvarez. Philippe: Eberhard. Myron L. GoodWilliam Graziano. Harold K. Ticho. and Stanley G. WojcickiMay Z3. 1961.~.";I.;~-2- UCRL-9717A STUDY OF RESONANCES OF THE 1T-1l' SYSTEM*Margaret H. Alston, Luis W. Alvarez, Philippe Eberhard, t Myron L. Good, ~**William Graziano, Harold K. Ticho, and Stanley G. WojcickiLawrence Radiation Laboratory and Department of Physic.University of California, Berkeley, CaliforniaMay 23, 1961*Recently aT=. 1 resonance in the A-1l' system called Y1 has been ob-1-6served with a mas. of 1385 Mev. Two types of resonances have been pre-dicted that might relate this observation to other elementary-particle inter-actions: (1) P 3/2 re.onances in the A-Tr and :E -w systema predicted byglobal symmetry, 7,8 corresponding to the (3!2, 3/2) resonance of the w-Nsystem, (2) a spin-l/2 Y -'IT relonance resulting from a bound atate in the 'R-N.ystem. 9,10 The position and the width of the observed Y~ resonance agreewith both theories, but s nce the spin and parity have not yet been determined,we cannot distingUish between the two theoretical interpretationa.Global symmetryl1(including a phase-space factor) predicts a branching*:1: 0 :I: *:t O:*: *:1::1: 0 *:t: 0 :I:ratioF':(Y l -I: +11' )!(Y 1 -A +1f )=(Yl -1:: +1T)!(Yl -A +1T)= (1/4)(O.22Sj So/n. The K .. N bound-state model luggests valueli of R conaid-erably larger than 5 %. However, when nonzero effective ranges are taken into12account, R can become quite small, especially if the "r.-A parity should be odd.To investigate these pos.ibilities, we have continued our study of K--pinteractions at 1.15 Bev!c in the Lawrence Radiation Laboratory IS-in. Hydrogenbubble chamber by studying events in which a ::z; is observed. The total crosssections for these interactions are shown in Table I; only statistical errors areindicated. The 8eparation of ,;% + 1f+ +wO and 1f + 1f'+ + Zw O events was difficultbecause many of the latter events will 'also fit the: first hypothesis. Thenumbers given 1n Table t and in the h!laiSs plots below were corrected-3- UCRL-9717•. .to account for this ambiguity. The correction factor was estimated by using our:4: +" t -I: +1r +1r +11' event•.To obtain an upper limit for the branching ratio. R, we combined the I:-ZlI'eventl into different charge atates of the I:-w Iystem. All charged I: ·hYFercmsowere observed; however, in the I: cales only two-third. of the eventI wereoobservable because of the neutral decays of the A . Furthermore. we had esU-o + - + -mated that about one-third of the I: 1r W events aleo litted a A 11' W inter-pretation and had been included in already published data. 1 Con.equently eacho + -I: 1r 11' event was given a weight of l.l5. The relu1tant ma.s spectra are shown+ -in Fig. 1. In the cases of (I:-1I') and (I:-w) there appears to be no excess ofevents in the region of M I: 1385 Mev. Using the number of (A-,..+) and (.1\-"'-)events with 1355 Mev < M A < 1415 Mev from relerence 1. and as.uming that,,~ -11'•all charged 1;-,.. systemB in the same ma•• regions of Fig. 1 are Yl' we obtainR ~ 81J/o. This treatment yields an unrealistic upper limit, lince there ismax -no evidence of any peaking above background. The Z;* + 11' ++ l"O events possiblymisidentified a8 I::1+,,++,..0 (or vice verla) do not fan into the mass band u8ed in thilanalyah.We conclude that the T/A branching ratio R for the strong decay of the•T =1 Y1 18 at most a few percent and i. consiatent with zero. This result agrees13with the value of R obtained by Baatien et a1. /4.. indicated above. this valueof R does not rule out either tbe global symmetry or the R-N bound-state model•of the Y1 relonal}ce.Next, we wish to report the resulta of our study of the three reactions:- + - " - +K +1'-1:: +w +w +1f (1)- + +K + p- I;':' +,.. + w + 'ft'- (l)- 0 0 + -K + p- I: of w + 'ft' -+ 11' • (3)Reactions (1) and (Z) are readily identified and measured. but reaction (3) cannotbe identified unambiguously. Accordingly, we discuss first the results pertaining-4-to reactions,(l) and (2). In a search for possible 1;-11' resonances, we haveplotted in Fig. Z histograms of the invariant masses of the 1:: and each of thethree pions in reactions (1) and (2). Figure Zb refers to the 1: I and pion oflike charge; Fig. 2a to the 1: and each of the pions of unlike charge. For thisrea.on twice a8 many eventl appear in Fig. Za as in Fig. Zb. The plotted curvesare mas. distributions expected on the balis of a uniform phase-space population.The histogram of Fig. Zb agrees with the phase- apace curve, but the 1: and unlike-charged pion distribution appears to exhibit an anomaly, indicating a concentrationof events with a 1;-11' mass of about 1405 Mev. A more detailed investigation of thedistribution of our events in the four-particle phase space suggests that it is quiteunlikely that we are deaUng with a .tatistical accident. In fact. in practicallyevery event one of the neutral 1;-11' eystema has a male which lies in the reso-nance region. 11 one interprets the observed distribution as a resonance, itspeak corresponds to a mass of 1405 Mev, and its full width at half maximum isabout 20 Mev after unfolding experimental error•.To investigate further the possibility of a I;-1I' resonance, we studied- + -the 39 two-prong events aasociated with a A that did not fit the K -+ P- I\. -+ 11' +tr- 0 + -or K +P - 1: +11' +" interpretations. These events could be:1<- IP + ,,+ + 11'- 0+ p- + trK- A + - +',,,0+p- +,.. of,..K +p- 2:0 + ..+ + ,,- + ,,0 + ,,0• + - + ,..0 + ..0.K- + p- h +" +,..(3)(4)(5)(6 )Identification is very difficult because only reaction (4) is sufficiently over-constrained to permit a kinematical fit. Furthermore, most of the events thatare actually examples of reaction (3) fit hypothesis (4), but generally with aZlarger X value.-5- UCFL-9717•Of the 39 events, 16 had Xl. ~l. when kinematically fitted to the one-constraint hypothesiB (4). MOlt of these events are probably due to reactionl.(3), since !"priori only 17'001 the events due to reaction (4) should have X ?,2.- + - +-Also, only one example of the reaction K +P - A +1r + 1r t 1r ---'IT and no examples:*: +" + - 0of K- -+ P - ~ +,.. + 1r + 1T + 1t' were observed; thus reactions (5) and (6) areprobably rare. Even though a kinematical fit to hypothesis (3) 11 impossible, oneo 0 -can obtain the invariant maslll of the ~ -1r system from the incident K momentumand the measured momenta of the two charged piona. However, since no kinematicconstraints can be imposed on such events, the experimental errors will. ingeneral. be larger than for fitted events and fluctuate more wi.dely. Therefore.the data are better represented by ideograms.Figure 3a shows the ideogram of the mass distribution of the 16 eventswith XZ~Z. The three events with M < 1320 Mev can be interpreted a8 the tailof the xZ distribution of reaction (4); the four evenU with M> 1450 Mev areprobably due to reaction. (5) and (6). The remaining nine events fall into anarrow band centered at about 1386 Mev and are most probably due to reaction(3). The plotted curve is the masl distribution of !:,O _,..0 systems based onphase space and normalized to nine events. It is worth emphasizing that due toour experimental errors of - 20 Mev, the actual peak is expected to be somewhatsharper than shown.Figure 3b shows the corresponding distribution for the events with x2 < 2 .In order to permit a direct comparison with Figure 3a, again only the measuredmomenta of the charged pionlil were u8ed to obtain the mass ideogram. Themeasured distribution appears to agree with that expected from phase space for0-+-A 1r ,.. 1t' events. No anomaly at M -1390 Mev is observed. Thus there does not*0 0 + -appear to be any evidence of the T = 1 Y1 resonance in the A 1f 1r 11' data. Further-0+-more. if one fits all 39 events to the A,.. 1r 11' hypothesis and then calculates the-6- UCRL-9717o iA -tr • A -11' ,and A -11' maS8es from the fitted values, there is still no evidence•for the Y I resonance. In particular, the peak of Fig. 3a vanishes. Thus wecannot attribute the observed peaks in the maet! distribution shown in Figs. Za or 3ato the Y~ resonance, especially in view of the low T/A branching ratio discussed.,above. Because of this and tbe selection criterion used in isolating the events ofo 0Fig. 3a, the nine evente probably represent a I; -11' resonance linked bv charge... - • +ind.ependence to the 1: -11' and 1:: -11' resonance already discussed.It h easy to show that the branching ratio ~=N.J) O!(N-+ +N I),L,~11' L. 11'- r ft'uniquely determines the isotopic spin of the resonance. For T :: 2, 1. or 0,we have ~:: 2, 0, or 1/2, reepectively. Neglecting possible backgrounds, ando 0correcting for neutral decays and escape of the A hyperons in the 1: -11' case,we have ~:: 0.6:t: 0.2. Hence, the isotopic spin of the indicated resonance is zero,•and we will call it YO'One difficulty of our interpretation of the data is the difference in massof 19 Mev:li: 6 Mev between the two peaks of Figs. 2a and 3a. However, sinceathere are two identical pions in the eha rged 1: cases and not in the 1: cases,it i8 po.sible that the effect of B08e Itatistics could cause a shift of the peaks.Abo, from the fact that the cha rged 1: can resonate with either of the two unlikecharged pions, one would expect interference effects between the two resonantampHtudes. Another possibility ia interference between the resonance and non-resonant backgrounds. Both these interferences might alter the observed posi-. • + - --+tions of the peaks. Electromagnetic mass differences in the 1': -ft' , 1: -'II' • ando 01: -11' have a negligible effect on the position of the peaks if' one a8S'.Imee tran-sition probabilities that are proportional to the decay momentum .•The YO could also be produced in the events in which the final state con-sists of a 1': and two pions. If it ia produced, it should appear in the (1':_11')0 massplot given in Fig. lc. No significant peak is obsel'ved; however, the number ofevents in thh region of the mass plot if; uncertain because of the difficulty of. .. .UCRL-9717=... 0 O. *correcting for ~ 11' 11' 11' produchon. The absence of the YO in this final state*(Y0 + 11') could be easily understood if the interaction took place mainly throughthe T :: 0 initial channel. The eqqp.lity of the cross sections for 2::'Z1f reactionsproducing 1:: of all charges (Table 1) is consiltent with this possibility. Astronger te8t of this pOlsibility is provided by the interaction gO+P (a pure T • 14state) currently being studied by Adair.We belleve that our data for I: and three pions are moat naturally inter-preted by invoking aT;; 0 I:-v re8onance. However, both because of the smallnumber of eventa involved and the complexity of the final state, we cannot regardthe evidence as conclusive. Evidence for a U:= - ,,+) resonance has been obtainedby Eisenberg et a1., who have studied K- -meson interactions in emulsion and findo 14a peaking in the (2:-11') maS8 spectrum at 1405 Mev. This peaking could be at-•tributed to a YO' In addition, Schult and Capps have recently invoked aT:: 0resonance at a mass of about 1410 Mev to explain the hyperon branching ratio in- 15low-energy K -d interactions.DaUtz and Tuan have shown that the (b-) solution for the scattering lengthsin R-N low-energy interactions will result in a I:-1r resonance in the T :: 08tate. 9 Recent values for the zero-energy R-N scattering lengths obtained by16 17Dalitz using the data presented by Alvarez at the Kiev Conference, indicatethat this resonance will be at 1-US:t: 3 Mev, with a half-width (r/Z) of about ZO Mev.If thla explanation of the T ;: 0 resonance is correct, it should have J :;; liz. theobserved T :: 1 resonance could be the resonance predicted by global 8ymmetrywith J :;; 3/Z. 18 Dalitz haa pointed out that the values of the (a -) 8olution given inreference 9 are consistent with both aT:: 1 and aT;: 0 Y1r resonance; 19 both ofthese resonances should then have J;: l/Z.The authors wish to thank the many members of the Bevatron and bubblechamber crews and the scanners who made thia experiment possible. We also-8- UCRL-9717. .tbank Profe••ors R. H. Dalitz, A. Pale, B. Sakita. and S. Treiman for severalhelpful dhcu••ionB. One of U8 (PE) wiabea to thank the Philippe'a Foundation,Inc. and the Commieariat a l'Energie Atomique of France for a fellowship .•-9- UCRL-9717Table 1. Crose sections for the E producing interactions at 1.15 B.v/c. ., .Reaction- - +K +p- E+1I'- r:'+ + 11'-+ - 0- E +11' +11'- + 0- 1: +1r +...o + -- E + ... +11'+ - 0 0- 1: +11' +11' +11'- + 0 0- E +11' +11' +11'- 1:++11'+ +11'- +11'-- - + +- E +11' +11' +'11'No. of events(uncorrected)878457541.71391913Cross sections(mb)1.40.0.161.34:t 0.180.97:t: 0.160.83 :t: O.lO0.97:*: 0.1.00.18 * 0.06O.ll .0.050.19:4: 0.060.ll.0.05-10-FOOTNOTESUCRL-9717.~ Work done under the auspices of the U, S. Atomic Energy Commission.t Pr••ently at Laboratoire de Phy.ique Atomique, Collese de France,Parle. France., Pre••ntly at Univer.Uy of Whconeln, Madleon. WleconlJin.•• Pre.ently at the Unlver.lty of California at Los Angelea. Loa Angel.s,California.1. M. Al.ton, L. Alvarez. P. Eberhard. M. Good, W. Graziano. 'H. Ticho,and 5. Wojcicki. Phy•. Rev. Letters~. SZO (1960).Z. O. Dahl, N. Horwitz, D. MiUer, J. Murray, and P. White. Phya. Rev.Letter. 2,. l4Z (1961).3. J.P. Berge. P. BalJUen, O. Dahl. M. Ferro-Luzsi. J. Kirz. D. H. Miller,J. J. Murray, A. H. Roaenfeld, R. D. Tripp. and M. Watson, PhYlJ. Rev.Letter. 6, 557 (1961).4. H. Martin. L. Leipuner, W. Chinowlky, F. Shively, and R. Adair, Phys.F.ev. Letter. 2" Z83 (1961).5. M. M. Block, E. B. Brucker. R. Geaaaroli. T. Kikuchi, A. Kovace.C. M. Melber, R. Kraemer, M. Nua.haum. A. Pevaner. P. Schlein,R. Strand, H. O. Cohn. E. M. Harth, J. Leitner. L. Lendinara, L. Monari,. .. .6.7.and G. Puppi, Cauhmitted to Nuovo cimento).R. Ely, S. Fung, G. Gldal, Y. Pan. W. Powell, and H. White. Bull. Am.Phy•. Soc. !' 291 (1961).M. Gell-Mann. Phy•. Rev. 106, lZ97 (1957).•8. P. Amati, A. StanghelHni, and B. Vitali, Phy•. Rev. Letters 2" SZ4 (1960).Nuovo elmento .!l. 1143 (1959).9. R. Dalitz and S. F. Tuan, Phys. Rev. Letter• .!, 425 (1959).-11- UCRL-9717•10. R. Dalitz, Phy•. Rev. Letters~. 2.39 (1961).11. Ph. Meyer, J. Prentki, and Y. Yamaguchi, Phys. Rev. Letter.,2,. 44l (1960).lZ. J. L. Shaw, University of California at La Jolla (private communication).13. P. Bastien, M. Ferro-Luzzi, and A. H. Rosenfeld, Phys. Rev. Lettersto be pubUshed•14. V. Ellenberg. 0. VekutieH, P. Abrahamson, and D. Keesler, WelzmannInstitute of Science, Rehovoth, llrael, private communication.15. R. L. Schult and R. H. Capps, ~ysical Review, to be pubUshed.16. R. H. Dalltz, On the Strong Interactions of the Strange Particles, LawrenceRadiation Laboratory Report UCRL-9580, January Z7, 1961 (unpublished)17. L. W. Alvarez, paper pre.ented at the 19S9 International Conference onPhysics of High Energy Particle., Kiev, July 1959 (unpublished): TheInteractions of Strange Particles, Lawrence Radiation Laboratory Report. ., .18.19.UCRL-93S4, August 11, 1960 (unpubli.hed) .•A. Pais has pointed out to us that if the Y1 Ihould turn out to be the resonancepredicted by global Iymmetry, the quellion arieee whether the existence of•YO could have anything to do with global symmetry as well. This is certainly• •not the case because, if the YO ia related to the global symmetry h ypotheslS,then there should be a corresponding T :: liZ 1I'-N relonance with 0 - 160 Mev.•Thul the existence of aVO may indicate that the aS8umption of globalsymmetry h wrong. However. another pOSllbiHty h that this symmetrycould be valid in the P·wave but not the S-wave pion-baryon interaction.R. H. Dalltz, Enrico Fermi Institute for Nuclear Studie., University ofChicago, private communication.-12.-FIGURE LECENDSUCRL-9717representing phase ~ .pace distributions.<a) Mass of (1:"'11')", from the reactions: K-•. .. .Fig. 1.Fig. 2.Fig. 3.•Mass plots of the charged and neutral 1:-'11' systems, including curveso ++p-I: +11' +'11'- 0 +-1: +'11' +'11'(b) Ma•• of (1:-11')+, from the reactlon .. : K + p- 1:0 ... 11'+ -t ''tr-- 1:+ + 11'0 ... 'II'o - + - 0(c) Mass of (:E-'II') , from the reactions: K ... p - I: ... " + 'II'-I; +'11'+ +'11'0Mass plots of the neutral and doubly charged I:-1I'systems.Ideograms of the misdng mass for the 39 event. in which a A and twocharged pion. were obee ved and neutral pions were also produced.2 0 + -<a) Events with X ~ 2. for the A'If 11 'Il' hypotheeis. The eupe rimpoaed00.. -curve is the phase- space distribution for the 1: 11' 11' 1T reaction norm-2. 0 ~ -alized to nine events. (b) Events with X < 2. for the A 'If 11' 11' hypothesis.The superimposed curve.is the expected A1I'°" 4- 1T - phase- space distribution.14-13-22(0 I20181& -14Rc· 12:'0• 10·..e~ 8c..,.~ 6:;;4..2Ib)201816RC: 12.il 10§c 8642oL--II.._J......--l._..J...----J._--'---l_-'-_L...L-L.....JJ,..J1300 1340 1380 14l!O 1460 1500 1540 1580 1620 1660 1700 1740Mall (I7T)' (M•• )Ie)1412o..•R 10c·>• 8t 6~z ..21460 1500 1540 1580Mall (I1I")0 I M•• I'fMUS·ISSFig. 1.'7",- .......----;-..--,.-. ,-....,.-- . .__._~.~.~ __~'.....,.~-.';- "":' .. ~-r-----:--.-:-~....,._ .._. _.-.-.-...._..._- "-'--~--•.--.-----'/1- ..-',j0 1 I I I iii I i l=">m i tl ' I I i I I , I -,.......". ,1320 1360 1400 1440 1480 1520 1560 1600 1320 1360 1400 1440 1480 1520 1560 1600++Mass (l.1T")o (Mev ) Ma ss (L1T"r- (Mev)15fA..-c; lor ~l ( a ) ( b) II ~~Q).cE;:)z5:1j 20iii. ii I I .,....--n. i i i i i i i ,.~ .I-~'Il"i'~ '\ ,- j.. -'1I1j!1'I~ 1IIIiI,I\ Fig. 2\-.a MU-23360•. "". ,,-------15- JI event1200 1240 1280 1320 1360 1400 1440 1480 1520Mass of the neutral system (Mev)Fig. 3. MU-23462'f------,....----------.. ~ ~;', .'.-, f,

English

A STUDY OF RESONANCES OF THE Z-7r SYSTEM

A STUDY OF RESONANCES OF THE Z-7r SYSTEM

Abstract

Similar works

Full text

Available Versions

eScholarship - University of California