Aachen,Brussels,CERN,Ecole Polytechnique,Milano,LALOrsay,UCL

A.Pullia 25 November 2009 Milano-Bicocca

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Aachen,Brussels,CERN,Ecole Polytechnique,Milano,LALOrsay,UCL


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1)During the 1960’s there were good reasons to disbelieve the existence of Weak Neutral Currents:

Processes as:

were highly suppressed

(B.R. < 5x 10-5).

Many experiments placed other,similar limits on strangeness-changing neutral currents.

PERSONAL REMARKS


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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 reachedwas 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±0.06and (+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 WeinbergSalam theory concerned only LEPTONS and QUARKSplayed no role at all.


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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!


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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

1)A. Pais and S.B. Treiman (Phys.Rev. D 6(1972) 2700

2)E.A. Paschos and L.Wolfenstein (Phys. Rev. D 7(1973) 91 )

3) L.M. Seghal (Nucl. Phys. B65(1973)141 )


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REMARKS ON GARGAMELLE (Wife of Grangousier andMother 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 .


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(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 theGGM 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)

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)(

)(

R

MEG

dxxFQ

eN

2

22

4

)3

)(

=0.29±0.

03


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•Elastic scattering on pointlike constituents

(See the presentations of D. Cundyand M. Hagenauer at the LondonHEP Conference of 1974)


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The ratio≈1/3indicates a spin ½ (any other target spin would give R≈1.


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ELECTRONS AND “”SEE”THE SAME STRUCTURE INTHE NUCLEON! AND THE TWO SETS OF MEASUREMENTS CONFIRM<Q2>=5/18 AS FORESEENFOR QUARKS.


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• 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).


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•The Gross Llewellyn Smith sumrule GGM results:

3 valence quarks


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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.


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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.


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+n=+n+

n


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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:I) 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


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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 %)).


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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.


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Results reportedby myself in HEPLondon Conf. 1974Showing a backgr.at the level of 15%


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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:

PURELY LEPTONIC NEUTRAL CURRENTS

ee

PURELY LEPTONIC NEUTRAL CURRENTS


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The background for this process was really very small andat this point the overall collaboration was excited and the search of neutral currents then stood at the center ofeveryone’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.


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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)


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e-

+p=c

⇓ c

++

⇓ e+

+e

d=+c ⇓ e++e+s


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ee XN


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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 Deuterium3) Right and Left handed muons (±) on C4) etc. etc.

....)()( ssdduu

....)()( ssdduuee

......),,()( ssdduu


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Aachen,Brussels,CERN,Ecole Polytechnique,Milano,LALOrsay,UCL

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