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Aachen,Brussels,CERN,Ecole Polytechnique,Milano,LALOrsay,UCL. PERSONAL REMARKS. 1)During the 1960’s there were good reasons to disbelieve the existence of Weak Neutral Currents: Processes as:. (B.R. < 5x 10 -5 ). were highly suppressed.
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A.Pullia 25 November 2009 Milano-Bicocca Aachen,Brussels,CERN,Ecole Polytechnique,Milano,LALOrsay,UCL
PERSONAL REMARKS 1)During the 1960’s there were good reasons to disbelieve the existence of Weak Neutral Currents: Processes as: (B.R. < 5x 10-5). were highly suppressed Many experiments placed other,similar limits on strangeness- changing neutral currents. A.Pullia 25 November 2009 Milano-Bicocca
A.Pullia 25 November 2009 Milano-Bicocca Since there was no reason at that time to believe that any relevant distinction existed between strangeness- changing and strangeness-conserving neutral currents, the reasonable conclusion that many physicists reached was that neutral currents simply did not exist. 2)Furthermore experimental upper limits were established also on strangeness conserving neutral current processes. (See results on the Heavy Liquid Bubble Chamber – C. RAMM -1 m long) for: (p =p)/(+p=+n)≤0.12±0.06 and (+p=++n/+p=++p)≤0.08±0.04 and for single production (Columbia Univ. W. Lee at BNL with an Al Spark Chamber) : ((+p=+0+p)+(+n=+n)) /(2(+n=- +0+p)<0.14 3)I would like also to remember that the original Weinberg Salam theory concerned only LEPTONS and QUARKS played no role at all.
A.Pullia 25 November 2009 Milano-Bicocca 4)The experimenters were furthermore and correctly attracted by the new discoveries on partons at SLAC and by the opportunity to measure their quantum numbers by the interactions with neutrinos (see the important role of D. Perkins in GGM). HENCE IN SUCH A FRAMEWORK THE SEARCH OF NEUTRAL CURRENTS WAS NOT IN HIGH PRIORITY IN THE EXPERIMENTS IN THE WORLD!
A.Pullia 25 November 2009 Milano-Bicocca 5)At the beginning of the 1970’s theorists took a new interest in neutral currents ; let me remind: -The very important work of Glashow, Iliopoulos and Maiani postulating a mechanism invoking a fourth quark and suppressing the strangeness-changing neutral currents , but allowing the strangeness-conserving ones (Phys. Rev.D,2,1285 (1970). -The work of t’Hooft providing the renormalization proof of the Weinberg Salam theory(Nucl. Phys. B 35,167(1971). -The calculation of the experimental consequences on the semileptonic neutral currents induced by neutrinos A. Pais and S.B. Treiman (Phys.Rev. D 6(1972) 2700 E.A. Paschos and L.Wolfenstein (Phys. Rev. D 7(1973) 91 ) 3) L.M. Seghal (Nucl. Phys. B65(1973)141 )
A.Pullia 25 November 2009 Milano-Bicocca REMARKS ON GARGAMELLE (Wife of Grangousier and Mother of Gargantua- see F. Rablais ≈1550) 1)The construction of such a large Bubble Chamber (4.8 meters long with an inside diameter of 1.9 m and a capacity of 12 000 litres of heavy liquid ) was really the key to investigate experimentally the neutrino interactions at the CERN beam and to distinguish interactions of hadrons ( ≈ 7 Interaction lenghts) from that of neutrinos. This was the great merit of the Ecole Polytechnique (A. Lagarrigue et al.) and the Linear Accelerator Laboratory of the Ecole Normale Superieur (Orsay) 2) As I told before the Collaboration at the beginning was strongly interested to study the Charged Current interactions to determinate the “partons” quantum numbers .
A.Pullia 25 November 2009 Milano-Bicocca (The mean square charge of quark-parton constituents, the comparison of the structure functions F2(x) measured in electron and neutrino scattering on nucleons, the Gross-Llewellyn Smith sumrule , etc.) Let me remember the important results obtained by the GGM Collaboration during 1972-73 : • Linearity of the cross sections and on energy (Scattering from point-like targets) • The Ratio (Spin ½ of partons ) • Mean square quark charge: (Prediction of GMZ and GIM 5/18 =0.28) =0.29±0.03
A.Pullia 25 November 2009 Milano-Bicocca • Elastic scattering on pointlike constituents (See the presentations of D. Cundy and M. Hagenauer at the London HEP Conference of 1974)
A.Pullia 25 November 2009 Milano-Bicocca The ratio≈1/3 indicates a spin ½ (any other target spin would give R≈1.
A.Pullia 25 November 2009 Milano-Bicocca ELECTRONS AND “”SEE” THE SAME STRUCTURE IN THE NUCLEON! AND THE TWO SETS OF MEASUREMENTS CONFIRM <Q2>=5/18 AS FORESEEN FOR QUARKS.
A.Pullia 25 November 2009 Milano-Bicocca • x Distribution: (Fractional momentum carried by quarks and antiquarks ; the areas under the each distribution measure the relative contributions to the the scattering from quarks and antiquarks constituents).
A.Pullia 25 November 2009 Milano-Bicocca • The Gross Llewellyn Smith sumrule GGM results: 3 valence quarks
A.Pullia 25 November 2009 Milano-Bicocca Coming back to Neutral Currents………. In such a frame of interest for the CC interactions, the Milano group started to measure events with at least one pion and without muon or electron candidates , and in a meeting of the Gargamelle Collaboration in Paris (Ecole Polytechnique – March 1972) I offered on behalf of the Milano group preliminary evidence on the neutral currents existence; similar spatial distributions for such events (without charged leptons) and for events with a clear muon. see the minutes of the meeting by D.C. Cundy and M. Hagenauer.
A.Pullia 25 November 2009 Milano-Bicocca Just for fun , I remember that people of the Milano group found themselves out of their office at the via Celoria , as students had occupied the Institute (Students Protest!). We had so an internal meeting in my house to prepare the Paris meeting of the collaboration! Immediately after the Paris meeting P.Musset,D.Haidt,etc.at CERN, V. Brisson, P. Petiau et al. in the Ecole Polytechnique, A. Lagarrigue, J.P. Vialle et al. in Orsay strongly pushed the measurements of the events neutral current candidates.
A.Pullia 25 November 2009 Milano-Bicocca n +n=+n+
A.Pullia 25 November 2009 Milano-Bicocca The longitudinal and radial distributions of CC and NC events and the energy distribution of the hadronic part were perfectly consistent,……… BUT.. the collaboration had to dissipate the doubt that the NC events were not induced by neutrons incoming the chamber from the sides (magnet) ; THE NEUTRON WAS DISCOVERED 40 YEARS BEFORE BY J. CHADWICK !!! Many attempts were done in such a direction: In ORSAY (Blum and J.P. Vialle) a simulation of M.C. type was not able ,in the neutron hypothesys, to reproduce the observed spatial distributions
A.Pullia 25 November 2009 Milano-Bicocca II)To evaluate better the cascade determined by a neutron incoming the chamber , special runs of protons at different momenta (4,7,12 and 19 GeV) were made in Gargamelle and the behaviour of the produced neutrons was investigated. A second M.C. simulation was done at CERN (D. Haidt, J. Fry and U. Camerini). The results were convincing that the N.C. events were not due to neutrons. III)Another approximate method was introduced by A. Rousset ; it was based on general properties of equilibrium in an “infinite region of space” between neutrino’s and neutron’s interactions. The estimated neutron’s background (B) in the NC events was of the same order of the AS ( neutrons ASsociated to interactions (≈15 %)).
A.Pullia 25 November 2009 Milano-Bicocca IV) Another approach (done by myself) was based on the use of a modified Bartlett method applied to the NC,CC and AS spatial distributions. The apparent interaction lenghts of CC and NC are quite similar and that of the AS events is much shorter as we can see in the following figure.
A.Pullia 25 November 2009 Milano-Bicocca Results reported by myself in HEP London Conf. 1974 Showing a backgr. at the level of 15%
A.Pullia 25 November 2009 Milano-Bicocca PURELY LEPTONIC NEUTRAL CURRENTS PURELY LEPTONIC NEUTRAL CURRENTS 1)I well remember a colloquium held in the small library of the Gargamelle Building at CERN with P. Musset , B. Zumino, J. Prentki and M.K. Gaillard(1972). Zumino explained us the theoretical fascination of the new renormalizable theory of Glashow, Salam and Weinberg , suggesting the search of the muon neutrino and antineutrino scattering on electrons. 2)In early January 1973 the Aachen group (H. Faissner, J. Morfin et al.) observed the famous candidate for the reaction:
A.Pullia 25 November 2009 Milano-Bicocca The background for this process was really very small and at this point the overall collaboration was excited and the search of neutral currents then stood at the center of everyone’s attention. 3)Let me finally recall the strong pressure exercised by A. Rousset and A. Lagarrigue to finalize the analysis of the semileptonic events (done mainly by J.P. Vialle) and to pubblish a letter (July 1973). I PERSONALLY BELIEVE THAT WITHOUT THEIR STRONG BELIEF THE COLLABORATION WOULD HAVE DELAYED THE PUBBLICATION OF THIS VERY IMPORTANT DISCOVERY.
A.Pullia 25 November 2009 Milano-Bicocca 4)-Bonn “Electron and Photon “conference August 1973 First official presentation done by. F. Bullock; together with the results of the HPWF (Harward,Pensil- vania ,Wisconsin ,Fermilab) collaboration -The positive results of HPWF were not confirmed by themselves for a few months. -London “XVII Conference on High Energy Physics (July 1974) DEFINITIVE CONFIRMATION by the CITF experiment (California Institute of Technology- Fermilab)
A.Pullia 25 November 2009 Milano-Bicocca e- +p=c ⇓ c++ ⇓ e++e d=+c ⇓ e++e+s
A.Pullia 25 November 2009 Milano-Bicocca The discovery opened a new wide class of experimental effects well described in the famous SAKURAY TETRAGON : 1) Scattering on protons and neutrons (BEBC) 2) Parity violation in atoms Scattering of polarized eletrons on Deuterium 3) Right and Left handed muons (±) on C 4) etc. etc.
