LBL—29405
DE91 000168
FROM THE NEUTRON TO THREE LIGHT NEUTRINO SPECIES: SOME HIGHLIGHTS FROM SIXTY YEARS OF PARTICLE PHYSICS
Talk presented at the Dalitz Conference in Oxford. 111175,1990
Gerson Goldhaber Physics Department University of California at Berkeley and Lawrence Berkeley Laboratory
This work was supported by the United States Department of Energy, contract number DE-AC03-76SF00098.
This report has been produced directly from the best available copy.
**!»?% ^ 1 LI * <- DISTRIBUTION OF THIsMlteT IS UNUMITE8 From the Neutron to Three Light Neutrino Species: Some Highlights from Sixty Years of Particle Physics
Gerson Goldhaber Physics Department University of California at Berkeley and Lawrence Berkeley Laboratc '
Introduction I would like to dedicate this survey to Dick Dalitz with my admiration. We are about the same age, so it is true that the entire development of modern particle physics - as we know it today - occurred during the course of our lives.
I consider the beginning of modern particle physics to be in 1932-33, when James Chadwick discovered the neutron at Cambridge, /England, and Carl Anderson discovered the positron in Pasadena, California. (See Figures 1 - 3.) I leave out the discoveries of the electron by J. J. Thomson, the nucleus and the proton by Ernest Rutherford, as well as the photon introduced by Albert Einstein and the neutrino as hypothesized by Wolfgang Pauli, as having occurred "before my time."
I was thus able to follow - and sometimes participate in - all the developments of modern particle physics.
The story I will tell is as the unfolding of the field looked, to me - an experimental particle physicists. As with Rashomon, this is as I see it. To get a different point of view, and no doubt there are many, you need a different observer.
One might ask, what did I know about physics in the 1930s, anyway? It so happens that I did hear about Chadwick's discovery at the time, mainly because my brother Maurice was working with him in 1934 on the photo- disintegration of the deuteron, and on the first good measurement of the neutron mass.
I will concentrate on the thirty years, 1930 to 1960 which include Dick Dalitz' important early contributions. I will then skip most of the next thirty years for lack of time, and end up with the study of the Z° in e+e" annihilation. For more details, and explicit references to published papers, I will refer the reader to a recent book by Robert Cahn and myself.^)
l Experimental Results. The first indication for the neutron was observed by Bothe who observed penetrating radiation from the a + Be reaction. Madame Curie-Joliot and M. Joliot followed this up by observing that the ionization produced by this radiation was greatly enhanced when material containing hydrogen was introduced. They ascribed this effect to the ejection of protons by energetic y- rays. It was Chadwick who showed by experiment and logic that fifty MeV y- rays could not be. responsible for the protons observed, but rather that a neutron giving rise to elastic np scattering was responsible. (See Figure 2.) During the 1940s, while I was studying physics at the Hebrew University in Jerusalem, and later, as a graduate student at the University of Wisconsin in Madison, Wisconsin, I became aware of Heideki Yukawa's prediction in 1935 that the nuclear force was transmitted by a particle of mass « 200 mp, the mesotron. Furthermore, a particle of such a mass, now known as the u, was observed in a Cosmic Ray cloud chamber experiment by Seth Neddermeyer and Carl Anderson in 1936 (see Figure 4,5), and confirmed by J. C. Street and E. C. Stevenson shortly thereafter. (See Figure 6.) It took another decade to show that the u did not fit the picture of a strongly interacting particle. (See Figure 7.)
The 1940s were, of course, overshadowed by Woiid War II. All the same, Le Prince-Ringuet and L'Heritier managed to observe a positive particle that gave a d-ray in a cloud chamber experiment in the Haute-Alps. From their measurements, they concluded a mass of 990 me to an accuracy of 12%, presumably a K+! Unfortunately, the particle was positive which left the lingering doubt that it could have been a mismeasured proton. (See Figure 8.)
The year 1947 brought a veritable explosion of data! M. Conversi, E. Pancini, and O. Piccioni published their remarkable experiment - carried out under very difficult conditions in Italy during the War. The experiment consisted of a measurement of Cosmic Ray u decay rates for positive and negative muons at rest which had been separated with suitable magnets designed by B. Rossi. Tomanaga and Araki had calculated that negative "mesotrons" stopping in Carbon would interact rather than decay. The experiment showed, however, that the Cosmic Ray particles - now known as muons - did decay. They could not be Yukawa's Mesotron! (See Figure 9.)
That same year, Don Perkins - then at Imperial College in London - observed an example of a JJ~ which gave a a-star in photographic emulsion, and hence behaved as Tomanaga and Araki had predicted for the mesotron. (See Figure 10.) Soon thereafter, Powell's group at Bristol discovered a number of examples of the jt+ -* ji+ decay in photographic emulsions, showing clearly that two different "mesons" were involved. (See Figure 11.) H. Bethe and R. Marshak in the U.S., as well as S. Sakata, T. Inoue, and Y.
2 Tanikawa in Japan had actually come up with the suggestion that two kinds of mesons might be the origin of the mesotron puzzle. To top off the year, G. D. Rochester and C. C. Butler discovered two examples of "forked tracks" in a cosmic ray cloud chamber experiment at the University of Manchester. This was clearly the beginning of strange particles. (See Figure 12.) Two years later, the x meson - which is central to our discussion today - was discovered in photographic emulsions as well. See Figure 13.
Cosmic Ray discoveries followed fast and furious, well into the 1950s. An important technical development was the discovery by Ed McMillan and independently by V. I. Veksler: the principle of Phase Stability. This allowed the construction of the Synchrotron and Synchrocyclotron, and eventually led to the Cosmotron at Brookhaven, the Bevatron at Berkeley and the Phasotron at Dubna.
The 1950s saw the application of these devices to the study of pions. See Figure 14. Jack Steinberger, W.K.H. Panofsky, and J. Stellar, as well as Burton Moyer and coworkers at Berkeley contributed to the discovery of the it°, simultaneously with the Cosmic Ray emulsion experiment of A. G. Carlson (now known as A. G. Ekspong), J. E. Hooper, and D. T. King which gave a lifetime limit. Furthermore, Panofsky and coworkers measured the spin and parity of the pion: Jp = O".
Dalitz pairs. This brings me to Dick Dalitz. I first became aware of Dalitz' contribution to Particle Physics in connection with Dalitz pairs; that is, a form of internal conversion in ic° decay where one of the gammas converts into an e+e_ pair. This has a probability of 1/80. The possibility also exists for both photons to convert into Dalitz pairs which has then a probability of (1/160)2, or about 4 x 10-5. These Dalitz pairs were observed in photographic emulsion experiments, as pairs essentially coming from the origin of a n or K interac tion or decay. An important application of the double Dalitz-pair decay occurred in 1959, in an experiment by Piano and coworkers, that measured the parity of the Jt°; Figure 15 shows the angular distribution which they observed. For a scalar n° particle, an angular distribution proportional to ei»e"2 which results in cos29 or l+cos2q> is expected. For a pseudoscalar p° particle, we have the triple scalar product: eixlg«lc, etc. which gives rise to a sin2? distribution, or
3 l-cos2 The Cosmic Ray results became clearer and more quantitative at the 1953 Bagneres-de-Bigore (France) Conference. The hyperons A° and Z± and sT, and the mesons 8°-» jt+7t",t+ -> TC+ Jt+it", K+ -* u+v etc. were clearly and distinctly identified. At that same conference also, Dalitz introduced his plot to determine the spin and parity of the t+. In Figure 18,1 show Dalitz' paper where he had collected the available world's data on t decay. The 1950 Pisa Conference. All this came to fruition at the 1955 Pisa Conference. (See Figure 19.) Neither Dick nor I actually came to that conference - but our data was presented, and played an important part. This was the first conference at which results from the newly operational Bevatron were presented. Edoardo Amaldi presented a very considerable compilation of x meson events displayed on a Dalitz plot. (See Figure 20.) It became clear, as was already suspected earlier, that the t mesons corresponded to a uniform distribution on the Dalitz plot. For a three body decay, the feature of the Dalitz plot is that dr ^ IM12dEj dE2. Thus, if IM12 the square of the ma trix element is constant, then the distribution on the plot is uniform. See Figure 21. The decay of the 8+—> Jt+Jt° where the pions are pseudoscalars can have the spin parity values Jp = 0+, 1", 2+... The question was, can the t- meson which decays to three pions have any of these quantum numbers? We can immediately rule out 0+ as being forbidden for three pseudoscalars. Dalitz thus examined whether t decay could correspond to Jp = T, 2+... As shown in Figure 21, these decays require the vanishing of IM12 4 for TJJ—» o, and were thus ruled out by the uniformity of the Dalitz plot observed experimentally. Furthermore, all experimental evidence pointed to the x and 8 having nearly equal masses and lifetimes. This evidence came from Cosmic ray experiments (the G stack) (Fig. 22), but in particular from the Bevatron experiments then in progress. (Birge, et al., Fig. 23, Chupp, et al.. Fig. 24, Iloff, et al., and L. Alvarez and S. Goldhaber, Fig. 25). The x - Q pilule and parity violation. This established the x - 6 puzzle: How could two particles have nearly the same masses and lifetimes, and yet, have different quantum numbers? One possibility - as discussed by M. Gell-Mann at the same conference (Figure 26) was a close mass doublet. The puzzle persisted for nearly two years. Then, T. D. Lee and C. N. Yang came up with the correct suggestion, namely parity nonconservation in weak interactions. Not only did they offer this suggestion, but they also showed various ways in which it could be tested experimentally. This set off a flurry of activity, and Mme. C. S. Wu and E. Ambler, et al. were the first to demonstrate parity violation in the weak decay of aligned Co60 nuclei. This was followed in short order by two experiments which demonstrated parity violation in n - u- e decay. R. L. Garwin, L. M. Lederman, and M. Weinrich converted, practically overnight, a running experiment on m decay at the Columbia University Nevis Cyclotron into an elegant experiment using the precession of muons which were brought to rest in carbon to demonstrate parity violation. J. I. Friedman and V. L. Telegdi had started a m decay experiment in emulsions at the Chicago cyclotron considerably earlier. However, it is the nature of emulsion experiments (or, for that matter, any experiment that needs scanning and measurements) that it takes time to analyze the data and collect statistics. They observed an asymmetry in the decay process in emulsions. Thus, by this circuitous route, the Dalitz Plot analysis led to the discovery of the decade - parity and charge conjugatio violation! A new application of the Dalitz Plot. Just at the end of the decade of the fifties, a new and exciting development occurred at Berkeley - in a Hydrogen Bubble chamber experiment at the Bevatron. Shortly after Don Glaser invented the Bubble chamber in 1953, Luis Alvarez and the group he assembled started to demonstrate that Hydrogen was feasible as a Bubble Chamber liquid. They went from a two- inch to a seventy-two-inch chamber with a series of intermediate steps. The first resonance n+p -> A++ was observed in 1953 by E. Fermi and coworkers at the Chicago Cyclotron. Alvarez and coworkers at LBL discovered a series of new resonances. The first was the Y*(1385), now called Z (1385). See Figure 27. The reaction was K'p -» An+Jt". 5 Displaying the three final state particles on a Dalitz Plot played an important role in recognizing the Y* -* An* resonances. More on Dalitz Plots. With the discovery of the to -* jt+jn°, by B. Maglic' et al., in a hydrogen bubble chamber at the Berkeley Bevatron, a new three pion decay could be analyzed. Here the spin parity value J = 1* gave rise to a more interesting shape. M. Gell-Mann had supplied the equations for various Jp values - see Table I and Lynn Stevenson developed some aesthetic-looking plots (Figure 28). C. Zemach extended the list of matrix elements (Figure 29) which inspired me to construct contour plots for a series of these matrix elements (Figure 30). This led to a method I developed for analyzing mass plots by cutting the data at contours on the Dalitz plot corresponding to specific Jp values. This is illustrated for the co° in Figure 31 for contours increasing by twenty percent steps for Jp = 1". The lowest contour X(l") < 0.2 shows essentially no ca signal, while a very large signal is noted for X.(1") > 0.8. An alternative analysis was carried out by Alff, et al. (Fig. 32), where the data for the various pp masses in the co peak is shown normalized by the matrix ele ment. A few highlights from the intervening years. To do justice to the fantastic developments in particle physics from the sixties to the present, I would need an entire lecture series. I will thus mention just a few points related to my interactions with Dick. Figure 33 shows the cover page of the 1963 Athens, Ohio Conference that both Dick and I attended. Here, side by side, we see a Dalitz plot and a triangle plot I introduced for four particle decays. This enabled us to observe double resonance production K+p -» K*° + A++ K+Jl" p+It- A "pion exchange process" which allowed us (W. Chinowsky, et al.) to measure the K spin. In 1967, Dick and I both lectured at the Hawaii Summer School (Figure 34 shows San Fu Tuan, the director, Val Fitch, myself, T. D. Lee and Dick, the lecturers, and Mrs. Carolyn Chung, the conference secretary, in the front row. 6 In 1977,1 had to again call on the Dalitz plot to perform a measurement. After we discovered charmed mesons with the SLAC-LBL Mark I detector at SPEAR, we had the task of measuring their properties. In particular, the problem was to show that these new particles which decayed to K"JI+ and K_Jt+Jt+, respectively, were indeed the charmed particles predicted by Shelly Glashow, J. Iliopoulos, and L. Maiani, as opposed to another K*. Here we had the T-6 puzzle all over again. Ben Lee, Chris Quigg, and Jon Rosner had computed the shapes on the Dalitz plot for various Jp values (Figure 35). The experimental distribution for D+ -» K~ *+*+ (exotic) and the non-exotic (and nonresonant) distribution X+ -» K+ x+it~ are shown in Figure 36. Here again, as for the 0, D° -* K"7t+ can only have Jp = 0+, 1", 2+... By utilizing the contour method, I illustrated for the ©° earlier, we obtain for the three body D+ decay the result given in Figure 37a,b which shows the test for Jp = 1". Here the contour was chosen with nearly equal areas on the Dalitz plot to give a ratio of 1:8-2 for Jp = 1". Experiment gave » 1:1. Figure 37c,d shows the contour for Jp = 2+ where 1:6-5 was expected, and again « 1:1 was observed. Thus we demonstrated parity violation in D decay - hence we are dealing with a charmed meson, and NOT a K* resonance! This brings me to the present (1990). Here I reluctantly skip the decades of the sixties; seventies, and in particular the eighties with the exciting developments at CERN of W and Z discovery and come to: The study of the Z° from e+e" -» Z° annihilation. We have now been studying the properties of the Z° at e+e" colliders for just over one year. The first such event was observed in the Mark II detector at the SLC on April 11,1989. The four LEP experiments started a few months later. The primary lessons we have learned are that the people who introduced the electro-weak theory, or what is now called the Standard Model, are to be congratulated. We have tried as hard as we could to find deviation from this model - so far, there are none. To mention a few names: Shelly Glashow, Abdus Salam, Gerard t'Hooft, and Steve Weinberg, as well as many others, were responsible for this magnificent theoretical development. The first important result to emerge from these studies is the fact that there appear to be only three species of light neutrinos. Of course, our colleagues in Astrophysics and Cosmology have expected this for a long time! They are also to be congratulated. A new trend in particle physics. With the advent of large electronic detectors, a new phenomenon has entered particle physics. Large collaborations are needed! The attack on the 7 Z° properties required electronic detectors attached to their own computers. To design, build, test, write the on-line programs, and analyze the river of data produced by these new detectors requires an entirely new approach to experimental particle physics. Figures 38 to 42 give the authors in our Mark II experiment at the SLC, where we have ~ 1/a physicists, as well as those for the four LEP experiments where each experiment has nearly 100 x it and more physicists! This is a far cry from the one-to-five-people teams of the 1930s and 40s! Comments on precision Z mass measurements. Figure 43 shows a recent compilation by the particle data group of our data, together with the results from the four LEP experiments - their points are the ones with the smaller error bars! As we noted, the number of neutrino species which is related to the total width r of the Z° resonance (where each v species contributes 177 MeV to Dis most accurately determined from the value of the peak cross-section. Since the Z mass is one of the three fundamental constants of the electro- weak theory, viz, GF, ce, and Mz, one wants to measure it as precisely as possible. With high statistics, the final limitation of such a measurement is the systematic error. At the SLC, the absolute energy in the center of mass is obtained by a precise momentum measurement for both the electron and positron beams for each pulse. Figure 44 is a sketch of one of the spectrometers which act on the beam after the collision and before the beam reaches the beam dump. The momentum measurement is carried out with a vertical bend. The direction of the beam before and after this bend is determined in a novel fashion by two small horizontal bends. These give rise to synchrotron radiation which is then observed on a fluorescent screen. The measurement consists of measuring the displacement of the vertically deflected beam on the screen with a television camera. The systematic error for each beam measurement is 20 MeV. Combining these quadratically, and including an allowance for beam offsets with finite dispersion, we get an overall systematic error on Mz of ± 35 MeV. Figure 45 shows the predicted error in Mz as a function of the integrated luminosity or, equivalently, the observed number of Z° events. With our current data, based on five hundred events, the predicted error is in agreement with our measured error of 120 MeV. The four LEP experiments have smaller statistical errors, but finally came up against the common systematic error of ± 30 MeV, based on sending a proton beam through the LEP accelerator. 8 When the statistical errors become negligible, the residual systematic errors for the SLC and LEP experiments, which at present are comparable, will determine the accuracy to which Mz is known. At that time, it will be important to have two totally independent sources of systematic errors. Measurements of the number of light v species. I will illustrate the measurement of the Z° decay parameters for the Mark II at the SLC. The procedures for the four LEP experiment were similar and with higher statistics achieved higher accuracy. Figures 46-52 present the steps taken in a self-explanatory form. I will also show examples of the results from LEP experiments. Figures 53-55 gives ALEPH results and Figure 56, 57 those of the L3 experiment. Figure 58 summarizes all the data on the number of v species. The search for new particles. In 2° decay, any new particle that couples to the neutral weak current, and for pair production, with a mass References See "The Experimental Foundations of Particle Physics," Robert N. Cahn and Cerson Goldhaber. Cambridge University Press, 1989, for references to results quoted in this paper. Acknowledgement This work was supported in part by the United States Department of Energy, contract numbers DE-AC03-76SF00098. 9 1930s Developments in Accelerators, Nuclear Physics, and Cosmic Rays 1930 *P. A. M. Dirac suggests antiparticles. •Wolfgang Pauli Suggests Neutrino. 1932 James Chadwick's discovery of the neutron. *Werner Heisenberg introduction of Isospin. 1934 *Enrico Fermi Theory of P decay 1935 *Heideki Yukawa Suggests mesotron M * 200me to account for nuclear force. 1936 Seth Neddermeyer and Carl Anderson Discovery of the |X M » 200me. Accelerators: J. D. Cockroft, E. T. S. Walton - Voltage doublers R. J. Van de Graaf - Electrostatic Generators E. O. Lawrence - Cyclotrons Figure 1 FIG. 26 SPUTTER YIELD 1.3 MeV D+ ON COPPER Calculated using TRIM V4.2 l\ < ANGLE LBL - C.F.A. van Os to August 1990 ft 7 k /• 8 80 82 84 86 88 90 ANGLE FROM NORMAL - Degrees 53 CARL D. ANDERSON Tracks of electron-positron pairs produced by 300-MeV synchrotron x rays. (Courtesy of Lawrence Radiation Laboratory, . A 63 million volt positron (tfj-I.lXlO1 gauss-cm) passin* through a 6 mm lead plate rging asa 23 million volt positron (//*« 7.5x10* gauss-cm). The length of this latter path University of California, andemi ir_ te _n times greater than the possible length of a proton path of this curvature. is at let »c ten times greater Berkeley.) — h T - ./•••• / . Figure 3 MAY 15. HJ! PHYSICAL REVIEW VOLUME 51 Note on the Nature of Cosmic-Ray Particles SKTH H. NEDDEKMEVEH AND CARL D. ANDERSON California Institute of Ttclmoloty, Pasadena, California (Received March 30, 1937) EASUREMENTS' of the energy loss of massive than protons but more penetrating than M particles occurring in the cosmic-ray electrons obeying the Bethe-Heitler theory, we showers have shown that this loss is proportional have taken about 6000 counter-ti ipped photo to the incident energy and within the range of graphs with a 1 cm plate of platinum placed the measurements, up to about 400 Mev, is in across the center of the cloud chamber. This plate approximate agreement with values calculated is equivalent in electron thickness to 1.96 cm of theoretically for electrons by Bethe and Heitler. lead, and to 1.86 cm of lead for a Zr absorption. These measurements were taken using a thin The results of* 55 measurements on particles in plate of lead (0.35 cm), and the observed indi the range below 500 Mev are given in Fig. 1, vidual losses were found to vary from an amount and in Fig. 2 the distribution of particles is below e.vperimental detection up to the whole shown as a function of the fraction of energy lost. initial energy of the particle, with a mean frac The shaded part of the diagram represents parti tional loss of about 0.5. If these measurements cles which either enter the chamber accompanied are correct it is evident that in a much thicker by other particles or else themselves produce layer of heavy material multiple losses should showers in the bar of platinum. It is clear that the become much more important, and the probability particles separate themselves into two rather of observing a particle loss less than a large well-defined groups, the one consisting largely of fraction of its initial energy should be very small. shower particles and exhibiting a high absorb For the purpose of testing this inference and also ability, the other consisting of particles entering for checking our previous measurements2 which singly which in general lose a relatively small had shown the presence of some particles less fraction of their initial energy, although there are four cases in which the loss is more than 60 M Sinflt particles percent. A considerable part of the spread on the h) Shower particles negative abscissa can be accounted for by eirors; M Produce sliavrrs it seems likely, however, that the case plotted at the extreme left represents a particle moving upward. Particles of both signs are distributed over the whole diagram, and moreover, the initial energies of the particles of each group are dis tributed over the whole measured range. FIG. 1. Energy IOM in 1 cm of platinum. 1 Andenon and Neddermeyer. Phya. Rev. SO, 263 (1936). n •*, •*r 4 .* * An^eno.1an d Neddermeyer, Report of London Con- +AE/E. feience, Vol. 1 (1934), p. 179. FIG. 2. Distribution of fractional li in 1 cm of platinum. 884 Figure 4 A niuon enters the cloud chamber from above with a momentum of 52 MeV/c. It passes through a Geiger counter and comes to rest. From the measured range the mass was determined to be 220 ± 35 electron masses. S. H. Neddermeyer and C. D. Anderson, Phys. Rev. 54, 88 (1938). Figure 5 J. C. STREET XtKarch Laboratory of Phytic* E C. STEVENSON Harvard Unlvmiiyr rtvwg§t Uinbridic MauachuKita, October 6. »J7. Hew Evidence for the Existence of a Particle of ft Intermediate Between the Proton and Electron O/ Q2 rO ft I 10 03 20 CU>v> Oram. J j-O* Cm ^ 2^/c _^-J^O Ftti, J. Tract if. 0*^ oQo 4 Fie. I. GMinntiral .rrawment of MMuratm. -r^ ** PR&TON' 3>X* •X=2.41P 2.x i** G-au«-0 KIR. 2. Track -I. -fO E*HA«>CE .OMtETCPf"! Figure 6 1940s The Decade of Cosmic Ray Studies 1944 Le Prince Ringuet K+Observation in cloud chamber Cosmic Rays. 1947 Conversi, Fancini, and PiccionL- The p. is not Yukawa's mesotron. Don Perkins: 1C observation in emulsions. Lattes, Muirhead, Occhialini, and Powell Observation of ft* —» |1+ decay in emulsions. Rochester and Butler: Observation of a charged and a neutral strange particle in cloud chamber. 1948 E. McMillan and V. I. Veksler - Synchrotron and Synchrocyclotron. 1949 R. Brown, et al. discovery of She X meson Figure 7 6l8 ACADEMIE DES SCIENCES. SEANCE DU 13 DECEMBRE ig44. PHYSIQUE NUCLEAIRE. — Existence probable d'une particule de masse ggom, dans le rayonntmeni cosmique. Note (') de MM. Loois LBPKIXCE-RI.VSIJKT et MICHEL LHEMTIER. Nousavons pris, au cours de l'annee ig43, dans le laboratoire de Largentiere (Hautes-Alpes) situe a IOOO1" d'altitude, une serie de ioooo cliches de trajec- toires cosmiques commandees par compteurs. Les rayons, nitres par ioc" de plomb, traversaient une chambre de Wilson de -5" de hauteur, placec dans un champ magnetique H de 25oo gauss environ. Nous nous sommes places dans lcs conditions experimentales les plus favorables [discutees precedemment (3), ('),(*)] pour profiter au mieux des cliches de collision entre particules pencj- trantes et electrons du gaz de la chambre, dans le but de determiner la masse au repos de la parlicule incidente. Nous avons obtenu une dizaine de cliches interessants. Le plus remarquable represente une collision dans le gaz pour laquelle d'excellentes conditions sont realisees : le secondaire fait avec le plan median de la chambre un angle I tel que tang? = o,32 et son rayon de courbure projete (i*"^), ainsi que la fleche dont il s'ecartc du primaire sont mesurables avec precision. Le (Hp) du pri- maire =1,7x10* gauss x cm. La formule de collision elastique donne pour le primaire,-qui est positif, la masse au repos k fi0 = 99o±i3 % (limites extremes de Tcrreur) ( ). La masse ainsi obtenue peut surprendre. Les indications suivantes, qui donnent des garanties de la validite de la mesure, nous ont pousses a publier ce . resultat. Destin itirioscopique de la colliiionV. Figure 8 PHYSICAL REVIEW VOLUME 71, NUMBER J FEBRUARY 1. 1947 Letters to the Editor PUBLICATION of brief reports of important dis- JT coveries in physics may be secured by addressing them to this department. The closing date for this department is, for the issue of the 1st of the month, the 8th of the preceding month and for the issue of the 15th, the 23rd of the preceding month. Xo proof vill be sent to the authors. The Board of Editors does not hold itself responsible for the opinions ex pressed by the correspondents. Communications should not exceed 600 words in length. FtC 1. Disposition of cousin*, absorber, ud marnetixed iron pJatc*. All countess "D" are connected in ptraUeJ. On the Disintegration of Negative Mesons ments using, successively, iron .ind carbon as absorbers. M. Cosvitst. E. PANCINI, AND O. Picaom* The recording equipment was one which two of us had previously used to a measurement of the meson's mean December 21, 1946 life/ It gave threefold (III) and fourfold (IV) delayed coincidences. The difference (III) —(IV) (after applying a N a previous Letter to the Editor,1 we gavea first account slight correction for the lack of efficiency of the fourfold I of an investigation of the difference in behavior between coincidences) was owing to mesons stopped in the absorber positive and negative mesons stopped in dense materials. and ejecting a disintegration electron which produced a Tomonaga and Araki1 showed that, becuast- of the Coulomb delayed coincidence. The minimum detected delay was field of the nucleus, the capture probability for negative about 1 psec and the maximum about 4.5 >*sec. Our calcu mesons « rest would be much greater tAan their decay lations of the focusing properties of the magnetized plates probability, while for positive mesons the opposite should (20 on high; 0-15,000 gauss) and including roughly the be the case. If this is true, then practically all the decay effects of scattering, showed that we should expect almost processes which one observes should be owing to positive complete cut-off for the "mesons of the opposite sign." mesons. This ig confirmed by bur results, since otherwise it would Several workers1 have measured the ratio if between the be very hard to explain the almost complete dependence number of the disintegration electrons and the number of on the sign of the meson observed in the case of iron. mi'sons stopped in dense materials. Using aluminum, brass, The results of our last measurements with two different and iron, these workers found values of it dose to 0.5 absorbers are given in Table I. In this table "Sign" refers which, if one assumes that the primary radiation consists to the sign of the meson concentrated by the magnetic of approximately equal numbers of positive and negative field. A/-(III)-(IV)-P(IV), the number of decay elec mesons, support the above theoretical prediction. Auger, trons, is corrected for the lack of efficiency (p) in our Maze, and Chaminade,1 on the contrary, found if to be fourfold coincidences (~0.046). close to 1-0, using aluminum as absorber. The value if- (5 cm Fe) is but slightly greater than the Last year we succeeded in obtaining evidence of different correction for the lack of efficiency in our counting, so Iwhavior of positive and negative mesons stopped in 3 cm that we can say that perhaps no negative mesons and, »t of iron as an absorber by using magnetized iron plates to most, only a few (^5) percent undergo 0-decay with the concentrate mesons of the same sign while keeping away accepted half-life. mesons of the opposite sign (at least for mesons of such The results with carbon as absorber turn out to be quite energy that would be stopped in 3 cm of iron). We obtained inconsistent with Tomonaga and Araki's prediction. We results in agreement with the prediction of Tomonaga and used cylindrical graphite rods having a mean effective Araki. After some improvements intended to increase the thickness of 4 cm because we were unable to procure a counting rate and improve our discrimination against the graphite plate. In addition, when concentrating negative "mesons of the opposite sign," we continued the measure- mesons, we placed above the graphite a 5-cm thick plate of iron to guard against the scattering of very low energy mesons which might destroy the concentrating effect of our magnets. We alternated die following three measure- menu: Sin Absorber 111 rv Hours 1*7100 boun u . <»> + 5 cm Fe 213 106 155.00' A. Negative mesons with 4 cm C and 5 cm Fe, (b) - San Fe 172 15S 206.00' B. Negative mesons with 6.2 cm Fe (6.2 an Fe is ap Nuclear Disintegration by Meson Capture RECENTLY, multiple nuclear disintegration 'stars', produced by cosmic radiation, have been investigated by the photographic emulsion technique. Plates coated with 50 *t Ilfnrd B.l emulsions1 were exposed in aircraft for several hour* at 30.000 ft. One of these diaintcgrnt ions WAS of part icular interest, for whereas all stars proviously observed had boon initiated by radiiition not producing ionizing tracks in the emulsion, llio one in question appear* to be due to nuclear capture of a charged particle, presumably a •low meson. •»• y- .:r.yy -A / 7 .l t. :/. i „ J* •.• ?/. \ 7 / I lun indi-bted lo tin- AiO.C, Knyal Air Force, Bi'iwnn, Ox»n., for kindly exposing the plutes. D. H. PERXINS Figure 10 lin|H»riul College of Scicnrf* and Technology, L"ndnn, S.W.7. Jun. 8. Discovery of the Decay it -» /& No. 40*4 October 4. 1947 NATURE 453 OBSERVATIONS .ON THE TRACKS OF SLOW MESONS IN PHOTO . Bsaca Is easkloe in BkTBSi BnalXe. Friasr/Bn De SMoodsrfi GRAPHIC EMULSIONS' f m •11 n M MS m I0W ttl nr in HI By C M. G. LATTES. OR. G. P. S. OCCHIALINI v 117 OS TI 41 MS ird On. C F. POWeLL Til 4S0 H. H. Wills Physical Lssorstorr. Uninnitr of Bristol nii •00 «•10• IX t» *M x 1M •37 XTRODUCTiOS. In recent experiments, it has XI / bean shown that charged mesons, brought to rest MKB naf- 614 ± *£*. StiBdllDf ootfflcient VTS77» - 4- m photographic emulsions, sometimes lead to the &i " K - it, *k l»lQf tlM mute of % ••ooodtrjr i production of secondary mesons. We have now JEttw IOMD vmlua for • puticla. of thto typ*. extended these observations by examining plates exposed in the Bolivian Andes at a height of 5,300 m., and have found, in all, forty examples of the process leading to the production of secondary mesons. In eleven of these, the secondary particle is brought to rest in the emulsion so that its range can be de termined. In Part 1 of this article, the measurements ^\ made on these tracks are described, and it is shown that they provide evidence for the existence of mesons Bstage tm nkrou of different mass. In Part 2, we present further Fit. 3. OifTUamorT n BAKOB OP TBK IBOOIT&ABT nun. TMO*l MABUD • STOP U TBI BBULIJOS; TBI HUI evidence on the production of mesons, which allows MAKSBD D UUYB THI BMULMOK «HB!t IUI T» WD Of us to show that many of the observed mesons are TUB* EAXOB. HUN BA50B OF IECOHDABT HBMim. «M locally generated in the 'explosive* disintegration of SnCKOXt. TMB BBBCLTB fill 1VBHTB \OB. VIII SO XI ABB nuclei, and to discuss the relationship of the different ROT IBOLUDaS IS IBS PIODBB types of mesons observed in photographic plates to the penetrating component of the cosmic radiation investigated in experiments with Wilson chambers and counters. Fl|. I. OsWRHVATIOS BV 11IU. 1. VOWBLL. (OOKB X 64 ACHBOKATIC 0BJSCT1TB; Ct IlfOBS KtCUUB RBtBABCH BBTUIOK LOADBD •mm BCBUN. TMJS TBACE Or THE *-Bl*OS U OITBK IB TWO PARTS, Till; POINT OP -UJICTIO* BBUQ UDICATBD BT m AMD AX ABBOW Figure 11 No. «077 December 20, 1947 NATURE 855 EVIDENCE FOR THE EXISTENCE OF NEW UNSTABLE ELEMENTARY PARTICLES By D». G. D. ROCHESTER AND Da. C. C. BUTLER ffijrslraJ Libontorlos, University, M&nchistcr MONG aome fifty counter-controlled cloud- chamber photographs of penetrating ehowera Awhich we have obuinod during the put year •• part of an investigation or the nature of penetrating particle* occurring in cccmic ray ahowen under lead, there are two photograph* containing forked traclu of a very atruung character. |fe t tlWWCOHCMOTOWAMWM0W1!,8 AX WUWA* M1E<•*>. TDHU ** * tuncu «OKUO DOW*WAM» u «un n A Figure 12 ?I,T. 1. Sriuotcoiia namumIMOWWO A* uvnvxl rou (•*) wTII au. TH»DIMCTIOK or nl Mioiana nu ancn TMAT A MARTO MTKll COKXYQ WtnilH B SITUHB U» AN AVTICLOCKWUa DUSCT10N 82 NATURE January IS.*I949 vbi. IU OBSERVATIONS WITH ELECTRON-SENSITIVE PLATES EXPOSED TO COSMIC RADIATION' Bv Mm R. BROWN, U. CAMERINI, P. H. FOWLER. H. MUIRHEAD ind P«e». C F. POWELL H. H. Willi Physiol Ubontotr. University of Irinol and 0. M. RITSON Clirtfldon Ltbontery, Oxford PART 2. FURTHER EVIDENCE FOR THE EXIST- ENCE OF UNSTABLE CHARGED PARTICLES. OF MASS ~ 1,000 tn„ AND OBSERVATIONS ON THEIR MODE OF DECAY :^S-* ••*• CO i 1 Figure 13 1950s FROM COSMIC RAYS TO HIGH ENERGY ACCELERATORS • Pion spin parity W. Panofsky, et al. • w observations B jorklund, et aL Synchrocyclotron Steinberger, et al. Synchrotron Carlson, et al. Cosmic Rays. • A. Pais and Y. Nambu, et al. suggestion of associate production • M. Gell-Mann - K. Nishijima - Strangeness • E. Fermi, et al. A++ resonance • Hyperfragments • Hyperons • R. Dalitz T- 8 puzzle • W. B. Fowler, et al. Observation of associate production • Don Glaser Bubble chamber • Antiprotons, Antineutrons at Bevatron • T. D. Lee and C. N. Yang - Parity violation Experiments: P and C violation observed: C. S. Wu, E. Ambler, et al. via Polarization in B decay. R. L. Garwin, L. M. Lederman, M. Weinrich in ll decay. J. I. Friedman and V. L. Telegdi in u decay. • Observation of v~ interactions by F. Reines - C. L. Cowan 1960 Resonances in Hydrogen Bubble Chamber Luis Alvarez group, a new application of the Dalitz plot Figure 14 DALITZ PAIRS n° -> y e+e~ 7C° —> e+e~~ e+e" ~ (1/160)2 Utilized in 1959 by Piano and Steinberger, et al., to measure the parity of the n°. 1 ' 1 1.40 1.20 F- (I-.75 COS 2 + ' / 1.00 / .80 R. Piano, et al. PRL 3,525 (1959) 1 .CO based on theoiy by C. N. Yang and N. Kroll, and W. Wada. .40 - - .20 - _^ , 1 1 . 15" 30* 4S« 60* 75* 90* . Plot of weighted frequency dietrlbution of angle oetween planes of polarization. Figure 15 U53 M DANYSZ & j. PNIEWSKI Phil. Mig. Ser. 7. Vol. 44, PI. 13. >'" SOp Figure 16 PROIJTCTION OF HEAVY INSTABLE PARTICLES S62 FOWI.KR. SHITT, THOKMHKE, AM) WHITTKMORK Ftu. 1. Cue C. Diffusion cloud-chamlwr photograph of two neutral I' particles (a) and (b), whose lines of flight are almost colincar. (i) is believed in lie a \* decaying into a proton (lut and a negative » mewn (2a). Tracks la and 2a prac tically coincide in ihc right view. <\t) is prolwiily a iJ* decaying into r* (lit) and w- (2W. Examples of Associate . Photograph of a 1.5-ltev * prodming two nrulnil I" particles in a collision with a proton Tracks la and 2a. 7C- + p lietieved In he proton and r , m.|icclivi'ly. an- iht- decay products of a A". A if" is prutialily sw-n to decay into w' < HH and r" (2b>. Hecause. of the ratht-r "foggy" i|ualiiy of this piclurc tracks 11), 2a, and 21J have been retouched for better reproduction. ->A + e° Figure 17 IMIYSICAL RKVIEW VOLUME 94, NUMBER « MAY 15 Decay of * Mesons of Known Charge*f R. H. DAUTZ} laboratory of Nuclear Studies, Cornell University, Ithaca, New York (Received February 9,1954) The experimental data on the 3r decay of r mesons is summarized on a convenient two-dimensional plot, both (a) when the ir-meson charges are known and (b) when they are not. Some events may be included in plot (a) only if the parent r meson is assumed positive and arguments supporting this identification for r mesons decaying in an emulsion are discussed. The dependence of this plot on the r-meson spin (J) and parity (tv) is discussed in general terms and those features depending particularly on u> and on its relation with / are emphasized—for example, if the density of events does not vanish at the bottom of the plot, the r meson must have odd parity and even spin. Simple estimates of the distribution, using only the lowest allowable angular momenta and a "short range" approximation, may be modified by final-state meson- meson attractions, whose effects are discussed qualitatively. The available data are insufficient for any strong conclusion to be drawn but rather suggest even spin and odd parity for the r meson; the need (or careful assessment of geometrical bias in the selection of experimental material is stressed. -Completely identified emulsion events • - Cloud chamber event's O- Events identifisble if assume T+ decay X- Events ambiguous even if assume T+ decay FIG. 3. The data on r-meson decay events in which the signs of T-meson charges are established. Figure 18 1955 PISA CONFERENCE SUPPLEMENTO AL VOLUME IV, SERIE X, DEL NUOVO CIMENTO A CL'HA DELLA SOCIETA ITALIANA DI FISICA 19 68 2° Sementre N. 2 CELEBRAZ10NE DEL CEXTENARIO DFX GIORNALF. IL NUOVO CLMENTO C0XFEEBK2A IKTEBS AZIONALE SULLE VABTICELLE ELEMENTAEI E XLI COKGEESSO KAZIOKALE DI PISICA ORGAKIZZATI DALI.A SOCIETA ITALIA.NA DI FISICA 80TTO GLl A1\«P1C1 E COL CONCOUSO DF.LL'UNIONF. I.VTERXAZIO.NALE DI FISICA DEL CONSIGLIO XAZIONALE DELLE KICERCHE DELL'TKIVERSITA DI IMSA E DEL CO.MITATO P1SANO DI OSI'I'I'ALITA 77*'.l. 12-1S (J1VIIKO J9SS SEXniCONTJ Figure 19 2«tt E. AIMUH The experimental data collected in Table 1 are still rather scarce; one can however try to compare them with the theoretical results in the 5 simple eases mentioned above. A general view of the available experimental data can be obtained by plot ting them in the triangular diagram of Fig. 3, Fig. 4, similar to Fig. 3, refers to 10 t-mesons observed in cloud chambers; it was pre pared and kindly sent to me \ by Dr. DALITZ shortly before the 1 Conference. In such a represent ation the height of the triangle is VT~ « taken equal to theQ-valuo (751IcV) ••^W\. of the T-meson, so that the three « ''. * distances of a point P internat to *t ( * ""i-X- » * ; v? *V the triangle (whose sum is always 10 "• 9< * *' • i\ equal to its height; correspond to » V. ' " 1 \ the kinetic euergies of the 3 emitted .*$. pions [29]. Momentum conservation Jr . "• • • "• * // \ * * '» •// \ imposes a further restriction to the » points representing T-meson-decays: IS "S. * . * ^[%J \ in the non-relativistic approxima • tion they can fall only inside the ^ ^r \ inscribed eircle whose diameter is * t * (2/3)C (50 3IeV). The relativist*- Pig. 3. - RepreautUtum of T-me«>n decays corrections restrict somewhat more observed iu emulsioas. the permitted region whose boun dary remains tangential to the sides, while the distance from the center is reduced by 8% in correspondence to its intersections with the heights of the triangle [30]. In such a representation the statistical factor, relative to a given elementary energy interval of the emitted pious (i.e. to a given element of sur face inside the permitted reginn), is constant [31] and the relativistic corrections never exceed 2% [30]. In Fig. 3 the kinetic ene»gy JL of the negative pion is represented by the distance from the side All. while the distance from the side CB corresponds to the kinetic energy £" • ULHC* a ittoiwt A BEBHSUr a Piatt Fig. 4. - Representation of T-raeaou decays observed in cloud chamber (DAUTZ, private communication). Figure 20 DALITZ PLOT 2 oT~ |M| dEidE2 . uniform if M 2 = constant Spin and parity of the pion was known: J = O" for n Thus 9 decay (or K+ decay) jp = o+,r,2+,... From the Dalitz plot we can ask the question: Can the T+ have these quantum numbers? x+ —> n+ 7C+ 71" Here L = even (Bose statistics) J = L + I at Tn- -> O fc = o P _ _ orJ = 0 /2 /... Thus we expect a zero in the Matrix elements when P + J (T) = r,2 /..- Here 0+ is ruled out for 3 Pseudoscalars. Result: No vanishing of IM 12 was experimentally observed. Conclusion: x - 6 puzzle Figure 21 SUPPLEMENTO AL VOLUME IV, SERIE X N. 2, 195Q DEL KDOVO CIMENTO 2° SenieBtre COSMIC RAY RESULTS Observations on Heavy Mesons Secondaries. (G-Stack Collaboration) J. H. DAYXES, D. EVANS, P. H. FOTVLEK, P. E. FRANCOIS, M. W. FKIEDLAKDER. R. HTT.T.TER, P. IHEDALE, D. KEEFE, M. G. K. MENON, D. H. PERKINS and C. F. POWELL H. E. Wills Physical Laboratory - Brittol (Br) L. CRANE, B. H. W. JOHNSON and C. O'CEALLAIGH Institute for Advanced Studies - Dublin (DuAfc) F. ANDERSON, G. LATYLOR and T. E. KEVIN University College - Dublin (DuVC) G. ALYIAL, A. BONETTI, M. DI CORATO, C. DLVWOBTH, B. LEYI-SETTI, A. MLLONE, G. OCCHXAUXI, L. SCARSI and G. TOMMASINI letituto di Fiaica delVUmversitd di Genova Ittituto di Fitica delVUnAversitd di Milano (Ge-Mi) Sezione di Milano delVIttituto Naziotutle di Fiaica Rucleare M. CECCARELLI, Jf. GRIUJ, M. MERLIN, G. SALANDIN and B. SECHI Ittituto di Fitica delf Univereita • Padova .p. Sezionc di Padova delVJstituto Nazionale di Fisica Nuclcare {Vita jiiii )iurtifr>]iire«rpa1a e eompMa reluzioiu- di qnesiu lavoro e Mnta pubblirata lie] Sumo Ciineuto, 2, 1063 (1955). -Y. d. Jf.]. CONTENT.-. — 1. Introduction (C. F. POWELL). - 2. Tin- K^-dccay (reported by M. MERLIN). - 3. The y-deray (reported by C. (I'CEALI.AIOH). - 3a. Vniu-ual decay of a /•inenoii (reported by D. KEEFE, on behalf of the V Diversity College, Dublin group). - 3fc. A determination of the mans of a //meson by the analysis of a collision of it* secondary with a proton (M. in COHATO and L. SCARS], reported by M. «i COKATO). - 4. The x- and Kp-partieles (reported by M. \V. FRIEDLANUER). - 5. On the compo sition of the K-paTticle decay spectrum (reported by A. BOKETTI). Figure 22 STJPPLEilENTO AL VOLUME IT, SERIE X Xi2, 19B6 DEL KtOTO CIUEXTO 2° Bemestre Positive Heavy Mesons Produced at the Bevatron. K. W. BlRGE, R. P. HADDOCK, L. T. KEHTB, J. K. PETERSON. J. SANDWEISS, D. H. STORK, and M. X. 'WHITEHEAD Radiation Laboratory • Berkeley, California (Pre»ented by D. H. STORK.) MK ^{<193>-2 ±2.o) Suelear emulsions have been exposed to 111, 135, .aud 170 MeV positive heavy mesons produced at 90° by 5-7 GeV protons striking a copper target. The exposures were made using the strong-focusing spectrometer [1]. 1. - The strong-focusing spectrometer. The principal features of this apparatus ccusist of a strong-focusing quadru- pole-magnet lens system followed by a conventioual momentum-analyzing magnet. The arrangement is shown in Fig. 1. It can he shown that the flux of heavy mesons at the stack position is (1) A.A ' 'o&QAE M^lksSs where d-Vj,/d.4 is the number of heavy mesons per unit area. .V, is the total number of protons traversing the target, Nt is the number of target nuclei per cm* in the proton beam direction, d*a/di?dE is the cross-section in em8* Btei-1 MeV"1, flc is the velo city of the heavy mesons, dJ'/d-Hs the momentum dis tt'«30* if WW fUGHET (SH"Ol''> persion of the analvzim? |rt-966-'14.7 _& o_ Fig. 1. Fie. 3. Figure 23 SUFPLEUEXTO Ah VOLUME IV, K. 2, 1956 DEL NUOVO CIMEXTO 2° Semestre 2>£V f\TP-0M £.&•<>V LTS K-Meson Mass from a K-Hydrogen Scattering Event [l], W. W. CHUPP, G. GOLDHABEK, S. GOLDHABER, W. E. JOHNSON and J. E. LAX.NUTTI Badiation Laboratory, Deparimtnt of Physica Univcrlity of California • Btrl-eley, California A K-Hydrogen scattering event observed in a stack of nuclear emulsions exposed to tlie focused K+ beam [2] enabled us to get a mass measurement 10/1 AT^ : S Fig. I. - A photomicrograph of a K-bydrogen chattering event J2K = 102 MeV. Both outcoroiup particles come to rest (endings arc sketched in) in the emuhion. J?E< = = 32.21 mm. J.'p = 2.427 mm. (Observer: S. LIVINGSTON, Photomicrograph: R. P. MK'UAELIS). Figure 24 SUPPLEMENTO AL VOLUME IT, SERIE X K. 2, 1956 DEL xrovo CTMEKTO 2° Semestre BEVATRON RESULTS Interactions and Decay of Positive K-Particles in Flight. W. W. CHITP, G. GOLDHABEB, S. GOLDHABER, E. L. ILOFF and J. E. LATSMTTI Radiation Laboratory, Department of Phytic* University of California - Berkeley, California A, PEVSNER and D. BITSON Department of Physics, Massachusetts Institute of Technology - Cambridge, XaesaehusetU r^ - [\.\ ±0'3,)x\D~ See- To pain further information on the nature of K-particles, we have embarked on a program of study of K-partiele interactions. The ideas on the nature and behavior of K-particles and hyperons as expressed by GELL-MASN and t'Ais [1] and those of M. GOLDHABER [2] and K. G. SACHS [3] make rather de- 4e predictions about t1"" "••,"~*"+»ons of K-particles. The Lifetime of the T-Meson. W". ALVAREZ and 3. GOLDHABER Radiation Laboratory, Department of Phytic*. Vnirtreity of California, Berkeley (Reported by D. H. .STOHK.) ! II teMo conipk*lo di quest u hivuro e Btato gia pubblioalo conic lettera alia Redazione nel Kvoro Cimento, 2, 344 (1955). Qui lie pubbli- chinmo mi breve riassunlo. X.d.R.]. .8 Summary. — Slaekh of nuclear emulsions were exposed to the positive K-mesusn beam at two different distances from the target of the Berkeley Bevatron {proper time of flight-f slowing-down time: l.B*IO~fe and 1.3-10-Bs respectively). The mean life- time of T-mesm. determined from these exposures is (1.0+Jjl-10-'s. Figure 25 3UWI.EME.ro Al VOllJIE IV, 3EBIB X M. 2, 1956 MI. svovo CIMEXTO 2° Semeatre The Interpretation of the New Particles as Displaced Charge Multiplets. M. GEIX-MANK (*) Institute for Ailmnctil fllmhj, Pritmlou, S. J. 1. - Introduction. The purpose of this communication is to present a coherent summary of the author's theoretical proposals [1] concerning the new unstable particles. Section 2 is devoted to some background material on elementary particles; the object there is to introduce the point of view adopted in the work that follows. In Section 3 the fundamental ideas about displaced multiplets are given, aud in the succeeding section these are applied to the interpretation of kuowtt particles. A sche*me is thus set up, which is used in Section 5 to predict certain results of experiments involving the new particles. The work of DALITZ on the -r-meson decay spectrum indi cates that the 6 and T have different parity and/or spin and thus cannot be merely two decay modes of the same particle. Thus we expect a second pair of doublets, •:*, T"", T™, and T, with strange ness ±1 like the 8. The neutral partners, if they are as long-lived as the charged ones, could easily have escaped definite identification. The reason for the similarity in mass of the T and 8 is of course completely unknown, but there is a further puzzle. The masses are presumably not exactly equal, and there is the possibility of electromagnetic decay of the heavier into the lighter, fully allowed by conservation of strangeness. Since both the T aud 9 are metastable, something must inhibit such electromagnetic decay so that it takes at least 10-* 8 to occur. It may be that the mass diffe rence is very small, considerably smaller than 1 MeV, say; or it maybe that the - and 0 are both spinless (the t pseudoscalar and the 8 scalar), in which case we are dealing with »0-»0 transition. Figure 26 VOLUMI 5, NUMBIl 11 PHYSICAL REVIEW LETTERS DICIMBIB 1, I960 A NEW APPLICATION FOR THE DALITZ PLOT RESONANCE IN THE Ai SYSTEM Margaret Alston, Luis W. Alvarez, Philippe Eberhard.t Mjrron L. Good,! William Grazlano, Harold K. Tlcho,ll and Stanley G. Wojclckl Lawrence Radiation Laboratory and Department of Physics, University of California, Berkeley, California (Received October 31. 1980) We report a study of the reaction Km*p-\'*** + *- (1) produced by 1.15-Ber/c K' mesons and observed In the Lawrence Radiation Laboratory's lS-in. hydrogen bubble chamber. A preliminary report of these results was presented at the 1S80 Roch ester Conference.' no. 1. Energy distribution of the two plona from the reaction Jt"+»— A*»*+i". Each event la plotted only once on the Dalltt plot, which should be uniformly populated If phaae apace dominated the reaction. The two en ergy blatograma are merely one- dlmenalonal projections of the two- dimensional plot, and each event is represented once on each histogram. The solid lines superimposed over the histograms are the phaae-epsce 0 40 SO 12) ItOrDOMOSSO 110 J00400 Figure 27 Tr*|Hs>) TABLE I The Square of the Matrix Elements for the Angular Momentum-Parity States7 = 0,y = 0-, 1 -, l\ 2", 2* A(O-) = [(£, - £,)(£, - £,)(£, - £„)la A(l") = (Pi »P. + P.*P. + P3« PJ)2 = ?" 2 A(l •) = [P,(£a - ft) + Pa(ft - £,) + P3(£i - £a)] A(2") = 2 PME, - G.W + 2(£, - £„)(£„ - £,XP.-P,)a - '/aWl A(2") = qHE.P, + ftP, + £:,/>:,>* 68$ STEVENSON, ALVAREZ, MAGLlC, AND ROSE.VFELD 1* Mewn CoKtrol Rccion __ d FIG. 1. (A), (b), and (c): Isometric drawings of the square of matrix elements for the J+, 0", and 1" mesons expressed in terms of the normalized Dalits variables t-(T.-T+)/y/3Qt and y-ZVC (Q-T++T„+T,-}f3-3). (d) and (e): Dalit* plots. VV folded six times, (d) displays 241 triplets in the control region and (e) displays 270 triplets in toe peak region. The contour lines V represent the projection of the contours of (c) (1~ meson). C. ^ehf^cH, Zeaos ow bMtT-Sr PUTS Spin 1=0 i=i i = 2 i=i (37r0 only) (except 3ir0] TT+ ir_ ir0 other modes andl=3 0" ® Q Figure 29 I ";»' iii.;;;:;•••"-«....I '•'iiitiH ..iiH"''"' iififteh. 'I : 'ill Si IV . ' ii I' ii / \l .I1 E* » #; | , |l ,!v%|l | P'''\iliii ' .lii ifi ^^v ! ;^n ^iiH«'',,;;;.i.^l:;.^Z:!:;:.^niii! J!::::::;;i€;^:::i'::;:;:yiiM;:il -J::!!;:::I»;.V!:»S''« i i Contour maps for the square of the matrix elements of / = 0 »*w-w° decay. The contours are given in 5% steps by the letters A—rwith every other letter omitted for clarity. The figures give the right-hand half of the Daiitz plot. ilj ' "ii/'llIWi!^ llilll III. ' II, II I, ii!.- 'll.,••!!.=!=.''I! 'I, 05-; Hill: I!!!;"' i^m !i •'Hi Mil. '' I liii'"'"/I '• iiiniHiiiiiiiiin.iij,,,, J"".,!:;:!.",;II,I",I,I«IIIIIIII.. t:!:;!::::»i:-'i»;::"S Figure 30 """IliHi!!!;^:; I.ii'.ii •mmm Location of the 507o coniours in the Daiitz plot for the preceding matrix el?ments. For any given J* value 507o of the events for the corresponding resonance lie inside the contours indicated. 1 3.6SGtf. 09 X(1-» V »> Q, Q5 09 13, 1.7 n M (7r + 7r_7T0 ) Figure 31 VOIUMI 9, NUKBBR 7 PHYSICAL REVIEW LETTERS • OCTOBM 1,1962 DECAYS OF THE w AND n MESONS C. Alff, D. Berley, D. Colley, N. Gelfand, U. Nauenberg, D. Miller, J. Schultz, J. Steinberger, and T. H. Tan Columbia University, New York, New York and H. Brugger, P. Kramer, and R. Piano' Rutgers University, New Brunswick, New Jersey (Received September 7, 1B62) The experiment described In the previous Let the Dalltz plot of Fig. 1. They divide the plot ter* also yields Information on the decay products Into regions of "qua! area along lines of equal of the <*> and IJ mesons. We present here studies matrix elements under the assumption of spin on correlations among the decay products, and one, parity minus following the model outlined branching ratios of competing decay modes. in reference 1. Tht distribution in this "radius" (A) Energy correlations in the ir+a'iT0 decay (also Fig. 1) is in agreement with the 1~ assign modes. -The Dalltz plot (kinetic energies of the ment. This only confirms the now well-estab three pions in the center of mass of the decay on lished 1— quantum numbers of the T = 0 a". Fig a triangular plot) for the to is given in Fig. 1. ure 1 also includes a plot of the distribution in This represents 1100 events, of which an esti the combined masses of all pairs of pions in the mated 34 % are nonresonant background (see Dalitz plot (3 pairs per event). In this plot the Fig. 1 of reference 1.) As was shown already in background has been subtracted with the assump the original contribution2 on the u, this distribu tion that It follows the phase-space distribution 2 tion can determine the spin and parity of the u>. and the matrix element, l?t-xj.| , has been di For this purpose the dashed lines are drawn in vided out. The remaining distribution should 1 % * ... j 1..M.L rrr 1 i -'-S-f- "i . 2 300 400 900 WO 5 TTTr MASS IN KEV i (c) FIG. 1. (a) The Dallti plot for 1100 omegas (including a background of 375 nonresonant triplets), (b) The density of points on the Dalltz plot compared to the expected density for a 1" tu plus a uniformly distributed background, (c) The dependence of the »» interaction in the T-1 J' 1 state as a function of energy. This was obtained by summing the I+J", a*!*, and »"»' moss spectra for pion pairs from the u) decays, subtracting a background, and dividing by the distribu tion expected for 1" decay into t*t"r. Since two of the three mass combinations are Independent, an error corresponding to (^N)"', where H is the number of Figure 32 pairs per Interval before background subtraction, was assigned to each piont. 325 sm£l POD 71-~ !WS m'^ T rra- » -p 4«a CMM ~^5 5± • i |- -fir J . ±HE:; A =T' * - i "Ta •h+ .• iur-i St - ••= J z£-i- ? v. y.' «! 1 • ;:±: ..i 4- •= g::z j*±: _: -.Jt J.I •, i"i iZ±L „..f 2 ±1 ^iiE7 T" • r 3, ' --•'I• l'•' " "r ~~:£: •1+,--* ' ••iff - r t ach; j E. ,1 - f 't* MU ~::^ •, - EDITED BY n - iDXE (-.- • - •• T SoE ±^E .- -;f "t' TOAT r 7^ -h•{-- T' i* JLSZZ M'. • ±±j .1- -f. <•[«<;«>» aS •• ; ir^r • , L. ••M ---+ • -i ' f'" ' Js ifes =uM !• „'-i-f! fis isiiii ES! Figure 33 no Ko wo coo too Figure 34 — 6.LE&, + + + K~7T 77- Ks 7T 7T" £)+ p>R.tu>De " 1^- \77 A/ fa KTTlT Figure 35 \7 + KT 0 , I'; Z' WKTVRKL spt*J-p*&ny 0.5 i—«—r "1 r (a)Exotic K-irir • • • • • .*•_• »*"x. 0.3 • • • ij • • •• *" •• • • 0.2-•. " • • ••»y< • ••/ 0.1 > • (b)Nonexotic Kirir oL j I i I i_ 0.1 0.2 0.3 0.4 IXMTT.-TJA/SQ XBL 7610-4116 Figure 36 H H Events /0.02 GeV/c' v_Z- JO x. A r in y P> jf * irf CI » 1,I 5*1 f^ tf VOLUME6J, NUMBER? PHYSICAL REVIEW LETTERS 14AUQUST1989 Initial Measurements of Z-3oson Resonance Parameters me*e~ Annihilation G, a Abrams,0' C. E. Adolphsen,"1 R. Aleksan,0' I. P. Alexander,"' M. A. Allen,"' W. B. Atwood,"' D. Averill,'4' J. Ballam,"' P. Bambade,'3' B. C. Barish,"' T. Barklow,"' B. A. Barnett,"' }. Bartelt,'3' S. Bethke,"' D. Blockus,'4' W. de Boer,"' G. Bonvicini,"' A. Boyarski,0' B. Brabson,<4' A. Breakstone,"' M. Breidenbach,'3' J. M. Brom,'4' J. L. Brown,"' K. L. Brown,0' F. Bulos,"' P. R. Burchat,'2' D. L. Burke,"' R. J. Cenee,'"' J. Chapman,"' M. Chmeissani,1" J. Clendenin,0' D. Cords,01 D. P. Coupal,"' P. Dauncey,'6' N. R. Dean,0' H. C. DeStaebler,"' D. E. Dorian,'2' J. M. Dorian,"' P. S. Dretl,'" D. C. Drewer,'6' F. Dydak,"' S. Ecklund,"' R. Etia,0' R. A. Erickson."' X. Fay,(" G. J. Feldman,0' D. Fernandes,"' R. C. Field,"' T. H. Fieguth,"' G. E. Fischer."' W. T. Ford,"' C. Fordham,"' R. Frey,"' D. Fujino,0' K. K. Can,"' C. Gatto,'2' E. Gero,"' G. Gidal,(" T. Glanzman,'3' G. Goldhaber,'" J. J. Gomez Cadenas,'2* G. Gratta,'2' G. Grindhammer,"1 P. Grosse- Wiesmann,"' G. Hanson,01 R. Harr,(" B. Harral,'6' F. A. Harris,"' C. M. Hawkes,"' K. Hayes,"' C. Hearty/" D. Herrup,'" C. A. Heusch,'2' M. D. Hildreth,"' T. Himel,01 D. A Hinshaw,"' S.-O. Holmgren,0' S. J. Hong,"' D. Hutchinson,"' A. Hutton,"' J. Hylen,'6' W. R. lnnes,"' R. G. Jacobsen,"' M. JarTre,"' J. A. Jaros,"' R. K. Jobe,'31 C. K. Jung,"' J. A. Kadyk,'" D. Karlen,"' J. Kent,<2> M. King.'3' S. R. Klein,"' D. S. Koetke,"' S. Komamiya,"' W. Koska,01 L. A. Kowalski,'3' W. Kozanecki,"' J. F. Krai/" M. Kuhlen,<5' A. V. Kulikov,"1 L. Labarga,<2) A. JL Lankford,"' R. R. Larsen,"' F. Le Diberder,0' M. E. Levi,"' A. M. Litke,'2' T. Lohse,"' V. Liith,01 G. R. Lynch,"' J. A. McKenna,"' J. A. J. Matthews,'6' T. Matt^n,"' B. D. Milliken,'51 K. C. Moffeit.'3' C. T. Munger,'3' J. J. Murray,'3' W. N. Murray,'4' i. Nash,"' H. Ogren,'4' R. A. Ong,0' K. F. O'Shaughnessy,"' S. I. Parker,'8' C. Peck,'5' M. L. Perl,'1' F. Perrier,"' A. Petersen,"' M. Petradza,0' N. Phinney,"' R. Pitthan,*3' F. C. Porter,"1 P. Rankin."' J. R. Rees,"' J. D. Richman,"' K. Riles,'3' L. Rivkin,'3' M. C. Ross,'" F. R. Rouse."' D. R. Rust,'4' H. F. W. Sadrozinski,'2' M. W. Schaad,"' T. L. Schalk,'2' B. A. Schumm,'" A. S. Schwarz,'2' J. T. Seeman,'3' A. Seiden,'2' J. C. Sheppard,"' J. G. Smith,"' A. Snyder,'4' E. Soderstrom,'5' R. Stiening,'1' D. P. Stoker,*6' R. Stroynowski,'3' M. Swartz,"' R. Thun,'" N. Toge,13' G. H. Trilling,'" R. Van Kooten,'3' P. Voruganti,'3' S. R. Wagner."' S. Watson,'2' P. Weber,"' A. Weigend,"' A. J. Weinstein,'51 A. J. Weir,'5' S. L. White."' E. Wicklund.'5' R. C. Wolf,"' D. R. Wood,'" M. Woods,'3' G. Wormser,'3' R. Wright,0' D. Y. Wu,'5' M. Yurko,'4' C. Zaccardelli,'2' and C. von Zanthier'2' ,n'Lawrence Berkeley Laboratory and Department of Physics, University of California. Berkeley, California 94720 '"University of California, Santa Cruz, California 95064 "'Stanford Linear Accelerator Center, Stanford University. Stanford. California 94309 w Indiana University. Bloomington, Indiana 47405 "'California Institute of Technology, Pasadena, California 91125 161'Johns Hopkins University, Baltimore. Maryland 212IS '""University of Michigan, Ann Arbor. Michigan 48109 «„ '"University of Hawaii. Honolulu. Hawaii 96822 M«u>*e « '"University of Colorado. Boulder. Colorado 80309 (Received 24 July I9B9) nmjnuTTusi ALEPH^UtMaiiM D. DECAMP. B- DESCHiZEAUX.J.-F. LIES.M.-N.MINARD l^wmw~Hrr*n*mmfvHt*n(Htn M'.Vi-CAJl AMtl««n« i kRCLLANTONLJ.F.ROUOREAL'.D.aNAlRO.JJ.CONWAY.OXCO»EN.2.FENC. J.L HARTON. J. HILGART. R.C. MREO *. R.P. JOHNSON, B.W. LECUIRE. V.B. PAN. J.M. CKE5PO. M. DELF1NO. L FERNANDEZ'. M MART IN £2. ft MIQUEL. UM. MIR. T. PAJIICE1LJ.1L PATER. V. SAADI. V. SHARMA J. A. WEAR. F.V. WEBER S*U UN WU. S. ORTCU. A. PACHECO. J.A. PERLAS. E.TUBAU IT. XUE mm a ZOBERNIC i if 111 m rn iff -•—*—[ M •- -t\ttt Tin ••• > ••mijii mm a. *mm* Htmxm Wllt\t til" M.G.CATANESI,M.D£PAWA.A.FAR]UAGlAStlJJ.aMAGCI.A,MASre^ ••ODKCK.AJ nNni r mem .- unrurt u. „rurt aMWHtt WDttR iNATAU.iNuz2aA.(UN»EiiLG.iusar.R0i V. CHEN. H. HU. D. HUANG. J. UN. T. RUAN.T. WANG. W. W. Y. XIE. D. XV. K XV. T. BARCZtWSXLLA.T. BAUERDICK. X. KLEINKNECHT *. t. RENR.S ROEHN. J. ZHANG. W.ZHAO M.-G. SANDER. M. SCMMELUNC. F. STEEG Immnmr *M*+-£mmn *M—. tmmmm *••» m*mm> PX Q— » H. ALBRECHT * F. BIRD. E. BLUCHER, T. CHARITY, H. DREVERMANN. U GARRIDO. J-P. ALBANESE . J-J- AUBERT.C. BENCHOUK, A BONISSENT. F. ET1ENNL. R. NACASCH. C. GRAB. R. HAGELBERG. S. HAYWOOD. S. JOST. M. KASEMANN. G. kELLNER. P. PAYRE. B. P1ETXZYK '.Z Of AN J.KNOBLOCH.A.LACOURT.Ll£HRAUS.T.LOHSE.D.LtfU*.AMARCHIOHO.P.MATO. 0-w*»j-iw*»l*"«*. rm^m*Snrmmmitmmmt.V Z AJALTOONI. M. 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L MIRABTTO. E. MONNIER. P. PEREZ. F. PERRIER. J. BANDER. J.-F. RENARDY. M. CORDEN. C GEORGlOfOULOS. J.H. GOLDJ4AN. MIKEDA, J. LANNUTTI. A. ROUSSAR1E, J.-P. SCHULLER D. UVINTHAi'. M. MERMIKJDES. L SA«*YER m.CXS**mi.r.*miC*mw.rmnrCntn.rmmv tmi !»»*•• Ci )w»il»«itl—wftpMw^H^fWTiwtfcwit. Tmm*mim « JlMm. \OA ""-" JO ASHMAN. CN. BOOTH. F. COMB1XY. M. DINS DALE. J. MARTIN. D PARKER. A. ANTONELLL R. BALOIN1.G. BENavENNl.G. BOLOGNA ". F. BOSS1. P. CAM PAN A LF. THOMPSON G. CAPON. V. CHIARELLA. G. OE NINNO. R OTTTORRE-PIAZZOU M. G. FEUC1. Mno^AM Urn***,****** Sm+mSJ 1IIM. VX * P. LAURELU. G. MANNOCCH1 M.T. MURTA1.CP. MURTAS.G. NtCOLETTl. P. PICCHI» 1 BRANDT.H. BURUURDT. C GRUPEN. H. ME1NHARD. E. NEUGEBAUER. U. 5CHAFEf P. ZOGRAFOU L—m *mimm*>+ri*rntUir-tlirm MHHAm tmtt H. SEYWERD, K, STUPP ERICH rm\mt,nH*rtmm,Ummimll3m*m,»imSmm*.rMC,t B. ALTOON. O. BOYLE. A J FLAVELL. A.W H^UZY. 1. TEN HAVE. J.L. H EARNS. n 8 GOBBO. F. UELia E. MILOTTI. F. RAGUSA . L ROLAND1' IS HUGHES. JG. 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UACDEKMOrr'.R. MAOAHE'.. JAIRE'. P. K. MALHOTRA •. KHAUNIN".CMANA".D.N.aAO»,Y.F.MAO* M.MA0UNEAY*.P.MARCHES1NI*. A>MARCHI0NNI>.J.(i.MARTUI,.LMAinTNE2>.F.MARZAN0>.G.aaMASSAR0-. X MATSUDA •• K. MAZUMDAR •. P. MclRIDC •. Tk. MBNHOLZ •. M. MIRK •. 1. MEROLA •. U. MESCHINI'. W.). UZIZGEB -. Y. Ml •. M. MKKE \ U. MICXE •, G. B. MILLS •. Y. MIR •. 1L MIRABf LU *. J. MNKH *. L. MONTANET •. •. MONTELEONI *. a MORAND *. <.MORAHD'.S.MORGANTI«.V.MORGUNOV>R.MOUNT>.E.NAGY>'. RL NAPOUTANO •. a NEWMAN \ L. NIESSEN \ W. D. NOWAK'. J. ONVLEE -. D. FANDOULAS'. 0. FATERNOSIHl". S. FATRKEUI •. Y.). HI •. Y. FENO •. 0. FOULET.OAUW'. I. PERRIER \ t FERRK •. A PEVSNER '. M. FIERI •, F. A FIROUE '. Y.FlYASKJN-.M.POHL'.V.FOnDAEV.Cl.AFOLS-.N.FRODUIT'.J.M.QIAN'". XN.OURESHI-.R. RAGHAVAN •. G. RAHALCALLOT^. J. VON RANGO'.P. RAZB'. JLREAD'.D.RIN'.Z.RENVS.REUCROFT'.T.RlEUANNl.CIUPflCH'.S.RODiUCUE:-. A F. ROE •. M. ROHNER'. Tk. ROMRACH •. L ROMERO'. J. ROSE'. 1 ROSIER-LEES'. I*. ROSSELET». I. A. RURIO -. W. RUCKSTUHL \ H RYKACZEWSKI •. M. SACHWTTZ«. XS«LJCK>,.QSAUVAGE\ASAVIN".V.SCHEGELSKY'.F.SCHMITT-.O.SCHMITZ-. UColuaemtem R SCHMJTZ \ M. SCHNEEGANS •. M. SCHONTAG •, R SCHOPPER ». D. J. SCHOTANUS ". XJ.SCHRElBER«.R.SCHUL-re'.SSCHum'.K.SCHULTZEM.SCHimf. ISCHWENKE". G. 5CHWERING •. C. SC1AOCA •. P. 0. SEILER •. 1. C SENS -. I SHEER". B. ADEVA'. O. AORIANI •. M. AGUILAR-SENITEZ-. H. AKFARI *. 1. ALCAIUZ\ A. ALOISJO V.SHEVCHENKO-.S.SHEVCHENKO-.X.R.SHI'.K.SHMAK0V-.V.SHOUTKO-. 0. ALVERSON '.MO. ALV1GG1 •. Q. AN •. H. ANDEJLHUR', A. L ANDERSON'. V. P. ANDREEV'. T. ANGELOV'. L ANTONOV». D. ANTREASYAN'. A. AREF1EV - t SHUMILOV -. N. SHIRNOV'. A SOPCZAK •. C SOUYRI'. T. SFICKIRMANN \ R SFIESS •. T. AZEMOON •. T. AZIZ •. P. V. K. s. BABA •. p. BACNA1A '. J. A. BAKKEN M. BAKSAY', F. SPIHAMTOI •• R. STAROSTA •. M. STEUER «. D. F. SUCKLAND'. R. StOHR •. H. STONE-. R. CBALL \ S. BANERJEE •*. J. EAO •. L RARONE'. A. RAY'. U. IECKER ". 1, STRAUCH ". K. SUDHAKAR ". G. SULTANOV •. R. L SUMNER \ H. SLTTER », R. R. SUTTON \ A A SYED •. X. w. TANG '. E. TARKOVSKY *. J. M. THENARD'. S.REINGESSNERVOy.LBENCZE-'.J.BERDUGO'.P. RERGES'.EBERTUCCI'. •.THOMAS'.C TIMMERMANS-.Siiim) C C TINO-.S. M. TING'. Y. F.TONG'. • L, RETEV '. A- IILAND *. R. BIZZARRI •. 1.1. RLAISING'. P. RLOMEKE'. M. TONUTTI •. S C TDNWAR •.). TOTH -. K. L TUNG *. I, ULBR1CHT •. L. URBAN -. a RLUMENFUD". G. J. BOBBINK •, M. BOCCKHJNI». W. BOHLEN •. A. ROHM'. O.UWER-. E VALENTE'. R. T. VAN DE WAU£".H VAN DERGRAAF-, L VETUTSXY-. T. ROKR1NGER •. R, RORGU'. D. ROUULXOV •. u. ROURQUIN'. D. ROirnGNY'. HYHRTtL'.r VIKAS'.M.V1VARGENTU.R VOGa'.H. VOGT'.M.VOUMAR\ J. G. BRANSON •. IC. BROCK •. F. BRUYANT •. C1U1SSON ». I. D. BURGER \ J. P. RURQ • llVONDARDELMVOROBIEV-.AAVOROBYOV'.AlAVOROBYOV'. X D. CAI •. D CAMPANA •. C CAMPS'. M. CAPEU-. F. CARRONARA •, F. CARMINAT1 •. liViriLlEUMIER'.W. WALK'. W.WALUIAF?-.CR.WANO'.G. HWANG'. J. R WANG*. A. M. CARTACCI'. M. CERPADA •. F. CESAKONI". Y. H. CHANG'.UK, CHATURVEDI >. CJ.F.WAN0-.X U WANG'.Y.F. WANO'.Z. M.WANG".J. WEBER'. R. WEILL.'. M.CHEMARIN* A CHEN*. C CHEN*. G.M. CHEN*. RF. CHEN*. H.S. CHEN*. M.CHEN-. XJ.-ENAL!S\ 1. WENNINGER-. M. WHnE'.R. WtlHELM -. CWILLMOTT'. M. L CHEN •. G. CHIEFARI •. C Y. CHIEN *. C C1Y1NINI *. I, CLARE'. R. CLARE'. JF.WHILiEN>HIW.D.WRIOIff.R.i.WU*S.I.W.S.X.WU'.Y.O.WU'. 0. COIGNET'. N. COUNO*. V. COMMICHAU •. G. CON PORTO '. A CONTIN •. F. CRDNS •. ».WYSLOUCH».Z.Z.XU-.ZLXUE,.D.S.YAN'.RZYANG-.CG.YANG'. -YANG'. X. Y. CU1 •. T. S. DAI'. R. D-AUSSANDRO'. A. DEGRE'. (. DETTERS >. E. DENES •. >iJ.YANG•.Q.Y.YANa'.Z0.YANG^O.YE•.CRYE'.iCYEH'.ZW.YrN•. P. DENES •. F. DENOTAPJSTEFANI». M. DHINA '. M. DIEMOZ ". H. R. DIMTntOV '. J.M.YOU".CZA»OUN1DO'.1.ZEHNDER'.M.ZENO',Y.ZENG-.D.ZHANG-. C DION151•. F. DfTTUS V R. DOUN'. E ORAOOV T. DRIEVER \ P. DU1NXER. —. aH.ZHANG-.S.Y.ZHANG'.Z.F.ZHANG*.J.F.ZHOU'.R.Y.ZHU".A21CHlCHl-» *js.ww.at.itnu mrntmiii. jwftn* CJ mil tut tkniuntOi *MOC • nimitiii Figure 41 mV3K3 LETTERS! OPAL OiUaboration Mi AKRAWY -.0. ALEXANDER '.J. ALLISON '. P.P. ALLPORT*. KJ. ANDERSON •. J.C. ARMITAGE \ G.TJ. ARNISON •. P. ASHTON'. G. AZUELOS ". J.T.M. BAINES'. AH. BALL'. J. BANKS'. G J. BARKER '. R J. BARLOW •. JR. BAILEY 'J. BECKER'. T. REHNKE'.K.W BELL'.G. BELLA'. S. BETHKE'.O. BIEBEL-. U. BINDER'. IJ. BLOODWORTH •. P. BOCK'. H. BREUKER'. R.M. BROWN •. R. BRUN'. A. BUUS'. HJ. 8URCKHART'. P. CAPILUPPI •. R.K. CARNEGIE'. A.A. CARTER •. J.R. CARTER *. CY. CHANG'. D.G. CHARLTON', J.T.M. CHRIN\ I. COHEN ". WJ. COLLINS '. J.E. CONBOY '. M. COUCH •, M. COUPLAND •. M. CUFFIANI •. S. DADO'. G.M. DALLAVALU •. P. DEBU'. M.M. DENINNO •, A. DiECKMANN', M. D1TTMAR'. M.S DIXIT •. E- DUCHOVN!'. LP. DUERDOTH u. D. DUMAS'. H. EL MAMOUNI'. P.A. ELCOMBE '. P.O. ESTAIROOK5', E_ ETZION V F. FABBRI •, P. FARTHOUATV H.M. FISCHER -. D.G. FONG', M.T. FRENCH •• C. FUKUNAGA *, A. GAIDOT'. O. GANEL -. J.W. GARY'. J. GASCON'. NJ. GEDDES •• CN.P. GEE •. C. GEICH-GIMBEL -, S.W. GENSLER'. FJC. GENTTT'. G. GUCOMEU1', V. GIBSON *, W.R. GIBSON '. J.D. GILUES '. J. GOLDBERG'. M J. GOODRICK'. W. GORN'. D. GRANITE'. E. GROSS'. P. GROSSE-WIESMANNVJ.GRUNHAUSVH. HAGEDORN'.J.HAGEMANN*. M. HANSROUL'. C.K. HARGROVE'. J. HART '. P.M. HATTERSLEY •. M. HAUSCHILD*. CM. HAWKES'. E HEFUN'.RJ. HEMINGWAY'.JLD. HEUER'..' C. HILL'.SJ. HILUER •. C HO', J.D. HOBBS'. P.R. HOBSON *. D. HOCHMAN •. B. HOLL'. RJ. HOMER '.S.R. HOU'. C.P. HOWARTH '. RE. HUGHES-JONES'. P. IGO-KEM.ENES'. H. IHSSEN'. DC. IMRIE'. A. JAWAHERY '. P.W. JEFFREYS •. H. JEREMIE ". M. JIMACK '. M. JOBES ". R.W.L JONES '. P. JOVANOVIC '. D. KARLEN'. K. KAWAGOE". T. KAWAMOTO*. R.G. KELLOGG'. a.W. KENNEDY ». C. KLEINWORT '. D.E. KLEM •. G. KNOP -. T. KOBAYASHI -. T.P. KOKOTT ". L KOPKE\ R. KOWALEWSKJ'. H. KREUTZMANN -. J. VON KROGH *. J. KROLL'. M. KUWANO *. P. KYBERD •. G.D. LAFFERTY'. F. LAMARCHE\ WJ. LARSON'. M.M.B. LASOTA •. J.G. LAYTER'. P. LE DU •. P. LEBLANC'. A.M. LEE'. D. 1FIIOUCH\ P. LENNERT'. L. LESSARD *,L. LEVINSON'. S.L LLOYD". F.K. LOEB1NGER'. JJH. LORAH'. B. LORAZO ". MJ. LOSTY ", J. LUDWIG'. N. LUPU'. J. MA •J. AJL MACBETH". M. MANNELU *. S. MARCELLINI *. G. MARINGER •. AJ. MARTIN *. J.P. MARTIN >. T. MASHIMO\P. MATTTG*,U. MAUR".TJ. McMAHON•. AC. McPHERSON ", F. MHJERS'. D. MENSZNER '.Fi MERRITT*. H. MES -. A. MICHEUNI'. R.P. MIDDLETON«. G. MIKENBERC •. DJ. MILLER •, C. MILSTENE •. M. MINOWA -. W. MOHR'. A. MONTANARI •. T. MORI -, M.W. MOSS '. P.G. MURPHY «. WJ. MURRAY *. B. NELUjN -, H.H. NGUYEN \ M. NOZAK1-. AJ.P. OTXJWD*. S.W. O'NEALE ". B.P. O'NEILL'. F.G. OAKHAM '. F. ODORIO •. M. OGG'. H. OH'. MJ. ORECUA •.£ ORITO •. J.P. PANSART •. G.N. PATRICK •. SJ. PAWLEY'. P. PFISTER'. J.E. PILCHER •. J.L PINFOLD •. D.E. PLANE >, 8. POU ". A POULADDEJ '. T.W. PRITCHARD •. G. QUAST ". J. RAAB". M.W. REDMOND \ O.L. XEES '. M. KEGIMBALD *. K. RILES'. CM. ROACH • SA. ROBINS •. A. ROLLNIK • l.M. RONEY •. S. ROSSBERG'. A.M. ROSSI". P. ROUTENBI IRC.' K RUNGE'. O. RUNOLFSSON'. S. SANGHERA '. R.A SANSUM '. M. SASAKI". BJ. SAUNDERS'. A.D. SCHAILE'. O. SCHAILE'. W. SCHAPPERT '. P. SCHA.-.FT-HANSEN '. H. VON DER SCHMITT •. S SCHREIBER -. J. SCHWARZ'. A. SHAPIRA •. B.C. SHEN'. P. SHERWOOD '. A SIMON -. G.P SIROLI *. A. SKUJA '. A.M. SMITH '. TJ. SMITH ". G.A SNOW'. EJ. SPREADBURY "•'. R.W SPRINGER '. M. SPROSTON •. K. STEPHENS'. HE. STIER'. R STROHMER'. D. STROM • H TAKEDA -. T. TAKESHITA -. T. TSUKAMOTO -. M.F. TURNER '. C. TYSARCZYK-NIEMEYER'. D. VAN DEN PLAS \ GJ. VANDALEN '. 0. VASSEUR \CJ. VIRTUE•. A. WAGNER '. C. WAHL'. C.P. WARD".DR. WARD". J. WATERHOUSE '. P.M. WATK1NS •. AT WATSON ". N.K. WATSON ". M. WEBER '. S. WSISZ\ N. WERMES'. M WEYMANN '. G.W WILSON MA. WILSON \ I. WINGERTER '. V-H. WINTERER '. N.C. WOOD '. S. WOTTON '. B WUENSCH -. T.R WYATT'. R. YAARI \ Y. YANG ". G. YEKUTIELI \ T. YOSHIDA •. W ZEUNER ' ind C.T. ZORN ' • QtrnMan—d Hmfiri4Collnt.rm*mtr*iU»d.«. tnm*mkl ASS <'A k OmnmematnnwtAitmitomv 1*1 Am t'aitmiii. TriAtt'tW'i tuAri * DttmmtMeinvun. StAuiitt LrferaM]. nelmitnm HaMtmrr Af 11WL. VX * CIWHAJA Utnrvory. CAmtAiAtfCHOHF Ik Ettm Ftmu Imiimt *nd Onmnmna tf nwn t «i»»ii(r o/C*«nf. I Altai* M.MJBJ7. L'SA ' Otm%nmiM Affirm. CArttto* L'nttetmn. Cammtiii Drift, OUAAA GMIAIIO. CAAAAA kli tin tot*r^Aii*ttmlm*miwy. mgSo/iel'Mrmiir.KAlirtfr.jAMA -. rn AT • irwtH t'mrmm ttfAMlit MMinAil'Uim IA figure -**• e+e~ Annihilation Cross Section in Vicinity of Mz -cm (GeV) Data from the Mark II, ALEPH, DELPHI, L3, and OPAL Collaborations (fiefs. 1-5) for the cross section in e+e~ annihilation into hadronic final states as a function of cm. energy near the Z. The curves show the predictions of the Standard Model with three species (solid curve) and four species (dashed curve) of light neutrinos. The mass of the Z was iixed by the data to be 91.157 GeV, and there were no other free parameters. The resulting widths are respectively 2.488 GeV and 2.653 GeV, which include QCD corrections for the hadronic channels and assume no (-quark contribution. The asymmetry of the curves is produced by initial-state radiation. 1. Mark II—G.S. Abrams et at., Phys. Rev. Lett. 63, 2173 (1989). 2. ALEPH—D. Decamp et a/., to be published in Phys. Lett. B (1990). 3. DELPHI—P. Asrnio et o(„ Phys. Lett. B231, 539 (1989). 4. L3—B. Adeva et at, submitted to Phys. Lett. B (1990). 5. OPAL—M.Z. Akrawy et at., to be published in Phys. Lett. B (1990). Energy Spectrometer Precise measurements are made of the energy of both e- and e+ bunches every crossing. The bend angle of the beam through a precision magnet is determined using synchrotron radiation. Spectrometer Quodrupole Mogne t Doublet Verticol Dump Synchrotron Light Monitor Figure 44 EXPECTED UNCERTAINTY IN Mz AND Tz FOR THE-MARK II 4Q I I ) I I I I ! I I 1 I I I) I 50 100 500 1000 INTEGRATED LUMINOSITY (nb'1) Figure 45 Measuring the Z Resonance For each scan point (SLC energy setting), measure: • SLC energy • Luminosity • Number of Z*s produced Determine the Z cross section (oz) using: Number of events = Luminosity x az Then derive resonance parameters by fitting expected shape to data. Figure 46 Luminosity Measurement Count Bhabha events (e+e'—-e+e') in two different detector components. (Rate doesn't depend on creating a Z). Number of events = Luminosity x OB I t count calculate for each energy Figure 47 Selecting Events Z events are almost background-free. It is sufficient to require: • three charged tracks from the interaction point (average is 20 per event). • 5% of the center-of-mass energy in both the forward and backward hemispheres. (Background events tend to give energy in only one hemisphere). Figure 48 Z Resonance Shape Three parameters of the resonance shape: Energy Width increases with the number of different types of particles to which the Z decays. • Height is interpreted in terms of the number of species of neutrinos. Figure 49 We perform a maximun-likelihood fit using Poisson statistics to a relativistic Breit- Wigner line shape: Radiative effects, [1 + b(£f], are calcu lated using an analytic form by Cahn. A Breit-Wigner shape has 3 parameters: position, width, and height. We fit for these as m, T, and T /nv or Nv. Figure 50 Run I79i« Evtnl6$6 E-»1lG*V IS ProrgHatUonc Evani Tf«o#f» Cha'QM Neutral (SST only) M»ffcU*iSLCUar 1.1969 6 30 Figure 51 Results St-C mass = 91.14 +/- 0.12 GeV Width a 2.4 +/- 0.4 GeV (Expect 2.45 GeV if no new particles) N = 2.8 +/- 0.6 =* N < 3.9, 95% CL -r-j—r 88 89 90 91 92 93 94 Figure 52 EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN-EP/89-169 December 19th, 1989 A Precise Determination of the Number of Families with Light Neutrinos and of the Z Boson Partial Widths. IS December 1988 The ALEPH Collaboration Abstract More extensive and precise results are reported on the parameters of Z decay. On the basis of 20 000 Z deca"- collected v.. Mz = 91.182 ± 0.026 (exp) ± 0.030 (beam) GeV Tz = 2.541 ± 0.056 GeV and o°had = 41.4 ± 0.8 nb. The partial widths for die hadronic and Ieptonic channels are: Thad = I804±44MeV re+e- = 82.1 ±3.4 MeV rM+u. = 87.9 ±6.0 MeV and rT+x- = 86.1 ±5.6 MeV, in good agreement with the standard model. On the basis of the average leptonic width 1*1+1" = 83.9 ± 2.2 MeV, the effective weak mixing angle is found to be sin26w(Mz) = 0.231 ±0.008. Using the partial widths calculated in the standard model, the number of light neutrino Figure 53 families is Nv = 3.01 ± 0.15(exp) ± 0.05 (theo). ALEPH O I • • • • i • • • . i • • • • i • • • • i • i i • i • • • i i • • t . i . . i i 88 89 90 91 92 93 94 95 ENERGY (GeV) Cross-section for e+e- -> hadrons as function of LEP energy. The Standard Model predictions for Nv = 2, 3 and 4 are shown. Figure 54 . ALEPH • 2.8 - 9955 C.L N,=4 * ( 6855CJLX 2.6 - • \voN 2.4 N.=2 2.2 - I.I, i . _ i '36 38 40 42 44 46 48 W0N0H (nb) 2 Contours of constant x in the o°had - T2 plane, and the Standard Model predictions for Nv = 2, 3 and 4. Figure 55 Measurement of Z Decays to Hadrons, and a Precise Determination of the Number of Neutrino Species The L3 Collaboration ABSTRACT We have made a precise measurement of the cross section for e+e" —* Z° —• hadrons with the L3 detector at LEP, covering the y/s range from 88.28 to 95.04 GeV. From a fit to the Z° peak, we determined the Z° mass, total width, and the hadronic cross sec tion to be Mz° = 91.160 ± 0.024(experiment) ± 0.030(Z,£P) GeV, TZo = 2.539 ± 0.054 GeV, and ah{MZo) = 29.5 ± 0.7 nb. We also used the fit to the Z° peak cross section and the width to determine ^invisible = 0.548±0.029 GeV, which corresponds to 3.29±0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4 L3 Preprint #004 December 24, 1989 Flgure 56 The measured cross section for e+e -» hadrons as a function of ^/s, for the Run 2 data as described in the text. Data are shown with statistical errors only. The solid curve is a fit to the formula of Borelli ei al. [17] in which Mz« and TinvuMt were left free. The partial widths r„, T^, TTU and Thitron, were taken from trw standard model. The dotted and dashed curves are the 57 standard model curves corresponding to N„ = 2 and 4 respectively. The curve for N„ = 3 is nearly indistinguishable from the fitted curve in the figure. LATEST MEASUREMENTS OF NUMBER OF LIGHT 1) SPECIES N = 2.8 ± 0.6 (MARK II) N = 3.01 ± 0.16 (ALEPH) N = 2.97 ± 0.26 (DELPHI) N = 3.32 ± 0.17 (L3) N = 3.09 ± 0.19 (OPAL) Figure 58