Lepton Physics at Cern and Frascati

The following sections are included:

• CONTENTS

• FOREWORD

The high precision measurement of the anomalous magnetic moment of the muon was an experiment I wanted to encourage when I joined CERN as Research Director responsible for the SC. Many ideas were proposed. Two of them were the "screw magnet" and the " lat magnet". Here the problem was the complexity of the magnetic field needed: injection, ejection, storage and transition fields. ccording to the SC greatest magnet specialist, Dr. Bengt Hedin, many months of high precision mechanical work were needed in order o produce just one "shape" of a given polynomial field. In order to reach the final correct shape, futher high precision machining was needed. The conclusion was that, in order to shape the "flat magnet", the mechanical preparation of the magnet poles required no less than five to six years. The "screw magnet" started to be built. Meanwhile Nino had the idea of trying a new very simple technique shaping a flat pole with very thin iron sheets, glued using the simplest possible method: scotch tape. In this way, instead of six years, few months of hard work allowed Nino to conclude that polynomial fields of practically any desired form could be built with better than 10^-3 accuracy. The six-metre long magnet containing an injection field, followed by two transitions, a storage, another transition and finally an ejection field, became the core of the high precisiom measurement of the muon (g - 2).

If people would just read our articles on the subject, in particular our article in Nuovo Cimento, they would see more than I could say what Antonino Zichichi contributed to our work. His special responsibility (and HIS ALONE) was the job of producing the bizarre agnetic field in our large storage magnet, which he accomplished with imagination, energy, and efficiency.

A method for trapping muons in magnetic fields it described together with its application to higher accuracy determination of the electric dipole moment of the muon The value found is:

The following sections are included:

• Introduction

• Knowledge of g-2 indirect methods

• Direct g-2 experiment

• Preliminary experiment

• Status

• Acknowledgement

• List of references and notes

No abstract received.

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The following sections are included:

• List of references

• Discussion

The following sections are included:

• list of references

The anomalous part of the gyromagnetio ratio, of the muon has been measured by determining the precession for 100 MeV/c muons as a function of storage time t in a known static magnetic field of the form B = B₀(1+ay+by²+cy³+dy⁴). The result is a_exp=(1162±5)·10⁻⁶ compared with the theoretical value a_th = α/2π + 0.78α^γ/π² = 1165·10⁻⁶. This agreement shows that the muon obeys standard quantum electrodynamics down to distances ~ 0.1 fermi. Details are given of the methods used to store muons for ~ 10³ turns in the field, and of measuring techniques and precautions necessary to achieve the final accuracy. Some of the methods of orbit analysis, magnet construction shimming and measurement, polarization analysis, and digital timing electronics may be of more general interest.

Once Nino came to my office to tell me about his ideas of studying lepton pair production at PS. I was still not Director General, but Research Director at CERN. In addition to (e⁺e^-) and (μ⁺μ^-) pairs, he wanted to search for (e^±μ^∓) pairs as a signature of a new lepton carrying its own lepton number. He told me that if such a lepton existed with one GeV mass, it would have escaped detection in hadron accelerator experiments for two reasons: i) it would decay with a lifetime of order 10^-11 sec and ii) because there is no π → μ mechanism for such a heavy new lepton: for its production a time-like photon would be needed. Time-like photons could be produced in hadronic interactions: for example in () annihilation. This was before Lederman-Schwartz and Steinberger had discovered the two neutrinos. To think of a "sequential" Heavy Lepton and to work out the possible ways to get it in a hadron machine was for me extremely interesting Nino had just finished his first high precision work on the muon (g-2). It was some time after the Rochester Conference in 1960. I gave Nino the following suggestion: if you want to search for something so revolutionary as a Heavy Lepton carrying its own lepton number you should work out a proposal for a series of experiments where the study of lepton pairs (e⁺e^-) and (μ⁺μ^-) could be justified in terms of physics accepted by the community. In addition a high intensity antiproton beam was needed. He came later to tell me that he had two very good friends, both excellent engineers: Mario Morpurgo and Guido Petrucci. A very high intensity antiproton beam could be built to study the electromagnetic form factor of the proton in the time-like region. If the proton was "point-like" in the time-like region, the rate of time-like photons yielding (e⁺e^-) and (μ⁺μ^-) pairs could be accessible to experimental observation, thus allowing to establish some limits on the new Heavy Lepton mass, or to see it, via the (e^±μ^∓) channel.

The "official" theme was: to establish if the proton had a structure or not in the time-like region. Thus a powerful system able to detect (e⁺e^-) and (μ⁺μ^-) pairs could be built. Nino established in 1963 the existence of a time-like structure of the proton studying the (e⁺e^-) channel and in 1964 studying the (μ⁺μ^-) channel. The set up was able to do what he wanted: a simultaneous detection of electrons and μ pairs, therefore (e^±μ^∓) as well. Unfortunately the proton was not a point-like particle in the time-like region and therefore the source of time-like photons originated in () annihilation was very depressed. In fact, using the (e⁺e^-) and the (μ⁺μ^-) channels, Nino established that at 6.8 (GeV/c)² time-like four momentum transfer, the crosssection was 500 times below the expected point-like value. This result had attracted a lot of attention. Bogoliubov was very interested when in 1964 Nino went to Dubna to present the (μ⁺μ^-) results at the International Conference on "High Energy Physics". Yang had a model that predicted a point-like structure of the proton in the time-like region. I called this series of experiments as measuring the "heartbeat of the proton". Of course there were no (e^±μ^∓) events, neither in the () nor in the (μ^–p) channel. Nevertheless a series of experiments was performed on "standard" physics, such as the discovery of many rare decay modes of mesons and the measurement of the (φ-ϕ) mixing.

All these experiments could be done because Nino had invented what is now known as the "preshower" method to reject with high efficiency pions in favor of "electrons". Once it was clear that in hadronic interactions there are very few time-like photons, he asked me if I would give green light in order to consider the use of the (e^±μ^∓) technology in the newly being developed Frascati (e⁺e^-) method would have been the best in order to see if a Heavy Lepton carrying its own lepton number existed. Of course he got the green light and in 1970 he got the first limit on the Heavy Lepton mass together with a series of high precision QED measurements.

But one story I will never forget in connection with the "heartbeat of the proton". After he succeeded with his friends Mario (Morpurgo) and Guido (Petrucci) to build the highest intensity antiproton beam at CERN, Nino came to my office and said more or less the following: "Viki, by changing the voltage of the electrostatic separator and a few other trivial details, in one night, I will be able to establish if the antideuteron exists with the correct expected deuteron mass". I told him that this was an experiment where he would get the Nobel prize if he found nothing. "But, there is a but", I added. "If you do not succeed in one night and if you destroy the beam, then I will not defend you. My green light is only valid if you really can check the existence of the antideuteron in a single night". Next morning, when I arrived at CERN, Nino was there with his graph where the antideuteron signal was exactly where it was expected to be.

I remember the year, 1965, not the day. It was (and is) the birthday of Peter Standley who was at that time the PS Division Leader. I called him in my office and the antideuteron discovery at CERN was my and Nino's gift to our mutual friend Peter. I decided not to have a press-release and Nino agreed. A few weeks later we read in the newspaper that the antideuteron had been discovered by Lederman and Ting in the United States. They had decided to have a press-release. Nevertheless Nino's paper in Nuovo Cimento preceeds Leon's and Sam's publication in Physical Review.

The following sections are included:

• Introduction

• Description and Principle of Operation

• Calibration of the Telescope

• References

An electron detector, which consists of five elements, each one being made of a lead layer followed by a plastic scintillation counter and a two-gap spark chamber, is described. The rejection power of this new detector against pions is of the order of 4·10⁻⁴, the efficiency for electron detection varies from 75% to 85%, and the energy resolution can be as good as 10%, in the energy range 1.1 GeV to 2.5 GeV.

A large electromagnetic shower detector which consists of nine layers, each one made of lead, spark-chamber and scintillation counter, is described. The rejection power against pions is of 6 × 10⁻⁴, the efficiency for electron detection varies from 68 % to 80 % and tie energy resolution from 15 % to 10 % in the energy range 0.4 GeV to 1.1 GeV.

A large electromagnetic shower detector for identification and energy measurements of γ-rays (between 150 and 1600 MeV) and electrons (between 400 and 1100 MeV), in the presence of high pion background , is described.

The detector is based on the principle of simultaneous measurement of the spatial development of the electromagnetic cascade and of its energy release. It consists of 1) two six-gap thin-plate spark chambers for the reconstruction of the incoming particle trajectories ; and 2) nine elements, each made of a lead foil, a spark chamber, and a plastic scintillator , all sandwiched together ; here the shower development is studied . When used for γ-detection, a 0.5 cm Pb foil is placed in front of the thin-plate spark chambers, in order to allow the detection of the γ-corversion process and the identification of the γ-direction. The dimensions of the detector are 60 × 120cm² front face, and 50 cm depth along the electromagnetic shower development.

A pion rejection power of the order of 5 × 10⁻⁴ between 400 and 1100 MeV, for electron efficiencies varying from 70% to 80%, is obtained. The pion rejection efficiency in the γ-case is highly improved by the anticoincidence efficiency factor, while the γ-detection efficiency depends on the precision required in the reconstruction of the γ-ray direction. The y-ray and electron energy resolution is about ± 15%.

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The range of highly relativistic muons has been measured. The results of the experiment are presented and compared with the theoretical expectations. The agreement between experiment and theory is established to be within 2% up to a value af γ as high as 23.

The possibility of achieving relatively high intensity anti-proton beams has prompted some considerations on the rather rare annihilation channels of the proton-antiproton system. We propose i) to study the two-electron mode as a means of investigating the electromagnetic structure of the proton for time like momentum transfers; ii) to study the two-muon mode and compare with the two-electron mode to investigate whether the muon behaves like a heavy electron for large time like momentum transfers; iii) to investigate the existence of weak vector bosons by the modes and . Although no precise theoretical predictions can be made, crude estimates indicate that the cross-section for these four channels could be roughly of the same order of magnitude.

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The following sections are included:

• Introduction and principle of the method

• Experimental set-up

• Electronic logic

• Background

• Results and discussion

The following sections are included:

• Introduction

• Experimental set-up

• Background

• Results and discussion

The following sections are included:

• Introduction

• The four mixing angles

• Vector-meson photon interaction

• The first experimental measurement of the (ω₈ - ω₁) mixing

• Present status and conclusions

• References

≪ … Concerning the discovery of the heavy lepton 𝛕, ADONE beam energy should have been 20% higher: in this case the 𝛕 would have been discovered at Frascati with the same method used later on at stanford and first suggested,then tested at ADONE by Antonio Zichichi. … ≫

The following sections are included:

• Introduction

• Search for leptonic quarks

• Search for heavy leptons

• The electronic logic

• References

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The following sections are included:

• The experimental set-up

• Data taking and analysis

• Reaction (a): e⁺e^- → e^± μ^∓

• Reaction (b): e⁺e^- → μ^± μ^∓

• Reaction (c): e⁺e^- → e^± μ^∓

• Reaction (d): e⁺e^- → e^± μ^∓ + anything

• Reaction (e): e⁺e^- → h^± h^∓

• Reaction (f): e⁺e^- → h^± h^∓ + anything

• Figure captions

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49 e⁺e⁻ non-collinear, non-coplanar events have been observed in a study of 1824 e⁺e⁻ interactions at total centre-of-mass energies from 1.6 GeV to 2.0 GeV. The inadequacy of the peaking approximation in radiative corrections is measured to be (2.8±0.4)%, in these experimental conditions of observation.

A study of the timelike reaction e⁺e⁻ → μ^±μ^∓ and of its comparison with the spacelike dominated reaction e⁺e⁻ → e^±e^∓; allows us to establish the validity of QED in terms of production angular distributions, absolute rates, energy dependence and angular correlations between the pair of final-state leptons, in two very different ranges of invariant four-momentum transfer. No sign of QED break is detected in the electromagnetic interaction of leptons and the muon behaves like a heavy electron, within the accuracy of the present investigation.

A study of 1824 e⁺e⁻→e^±e^∓ events in the total centre-of-mass energy range from 1.6 GeV to 2.0 G-eV, allows one to establish that production angular distributions, a collinearity and acoplanarity distributions, and absolute value of the cross-sections and their energy-dependence, follow QED predictions including first-order radiative corrections. In particular, the absolute value of the cross-section and the power of its energy-dependence agree with theoretical expectations within ± 6% and ± 2%, respectively. The inadequacy of the peaking approximation in our experimental conditions of observations has been measured to be (2.8 ± 0.4%).

Further proof is given for the inadequacy of the peaking approximation in first-order radiative corrections, via the observation of 429 non-coplanar (e⁺e^-) events. The energy dependence of this effects is measured in the s-range 1.44 to 9.0 GeV², and represents another proof of the validity of QED.

The analysis of 12 827 e⁺ + e⁻ → e^± + e^∓ events observed in the s-range 1.44-9.0 GeV² allows measurement of the energy dependence of the cross-section for the most typical QED process, with ±2% accuracy. Within this limit the data follow QED, with first-order radiative corrections included.

A further search for heavy leptons at the ADONE e⁺e⁻ storage ring has revealed no events. This establishes, with 95% confidence, that, if a heavy lepton exists and is universally coupled only to ordinary leptons, its mass must be heavier than 1.4 GeV. If it is also coupled to the hadrons, its mass must be greater than 1 GeV, again with 95% confidence.

We have studied a total of 26,208 events produced in (e⁺e^-) reactions in the energy range from 1.2 to 3.0 GeV. All these events had to have at least two charged particles in the final state with an energy cut-off, depending on the nature of the particle: E_e ≥ 100 MeV; E_π ≥ 130 MeV; E_K ≥ 225 MeV. The above conditions were imposed by the fast electronic trigger.

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The analysis of 1466 events of the type e+e−→ μ^±μ^∓ in the time-like range from 1.44 to 9.00 GeV², shows that the absolute value of the cross-section and its energy dependence follow QED expectations within (± 3.2%) and (± 1.2%), respectively.

The following sections are included:

• Introduction

• The experimental set-up

• Data taking and analysis

• Results

• References

The proof is given for the existence of the reaction e⁺e ⁻→h ^±h^∓ in the energy range 1400–2400 MeV, and its energy dependence is compared with that of e⁺e⁻→e^±e^∓, in the same experimental conditions of observation. The exponent of the s-dependence of the ratio α = (e⁺e ⁻→h^±h^∓) / (e⁺e⁻→e^±e^∓) is measured to be n = 2.08 + 0.45, in the s-range (1.96 - 5.76) GeV², on the basis of 51 e⁺e⁻→h^±h^∓ events and 8918 e⁺e⁻→e^±e^∓ events observed.

The study of 620 hadron pairs produced in the s-range (1.44–9.0) GeV², has yielded 110 collineai hadronic events. Their identification in terms of π and K mesons allows the determination of the time-like electromagnetic from factors of these pseudoscalar mesons in the above time-like range. The total number of (e⁺e⁻) events observed in the same experimental conditions is 18 048.

We have observed 1085 events of the type e⁺e⁻ → hadrons, in the total centre-of-mass energy range to 3.0 GeV. The energy dependence of the total annihilation cross-section, parametrized in the form σ(e⁺e⁻ → hadrons) = A.s¹², is measured to be in the above energy range.

We have measured the cross section for the reaction e⁺e⁻→4π± in the energy range 1.2–3.0 GeV. No statistically significant evidence for a new vector meson in the ρ″ region is found.

The angular distribution of 2720 tracks of 1085 hadronic final states produced from (e⁺e⁻) annihilation has been studied in the 1.2 to 3.0 GeV total centre-of-mass energy range. If we parametrize the angular distribution in terms of f(θ) = 1 + A cos²θ, where θ is the angle between the hadronic track produced and the colliding-beam direction, the results show that A is less than 0.21, with 90% confidence.

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The results obtained by the Bologna-CEBN-Frascati Collaboration during about three years of work at Frascati are reviewed and taken as a basis to show the impact of (e⁺e⁻) physics in understanding the laws of subnuclear phenomena.

The observation of 21 K⁺K⁻ pairs in 38 hadron pair events produced at 1.5, 1.6, and 1.7 GeV total centre-of-mass energies in e⁺e⁻ annihilations, establishes that time-like photons produce K pairs and π pairs with comparable rates in this energy range. The K-meson electromagnetic form factor at a mean s-value of 2.4 GeV² is measured to be |F_K| = 0.50 ± 0.08. The number of e⁺e⁻ pairs observed in the same angular and energy range is 5148.