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Three score years and ten!

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Three score years and ten!

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Three score years and ten!

Colin Wilkin

University College London

University

College

London

(UCL)

In the rain!

The first university in England to admit students of any race, class or

religion, and the first to welcome women on equal terms with men.

The first undergraduate teaching laboratories in physics and chemistry.

The days of our years are threescore years and ten;

and if by reason of strength they be fourscore years,

yet is their strength labour and sorrow;

for it is soon cut off, and we fly away.

(Psalms 90 in the authorised King James version of the bible.)

The days of our years are threescore years and ten;

and if by reason of strength they be fourscore years,

yet is their strength labour and sorrow;

for it is soon cut off, and we fly away.

(Psalms 90 in the authorised King James version of the bible.)

[For the ignorant, 1 score = 20.]

This suggests that you should soon start looking for a replacement “tame” theorist with whom to collaborate since I am likely indeed to be fourscore by the opening of FAIR (provided that I haven’t “flown away”).

Shakespeare, however, may give more grounds for hope!

Three score and ten I can remember well:

Within the volume of which time I have seen

Hours dreadful and things strange;

but this sore night hath trifled former knowings.

(Macbeth: Act 2, Scene 4)

Three score and ten I can remember well:

Within the volume of which time I have seen

Hours dreadful and things strange;

but this sore night hath trifled former knowings.

(Macbeth: Act 2, Scene 4)

This suggests that the old man was still on the lookout for new phenomena (and possibly even writing papers) into his seventies.

He also went on to give advice to the younger people (including Macduff, who eventually kills Macbeth). I will therefore spend half an hour giving wise counsel!

Advice to younger Physicists

A series of aphorisms

Sometimes a theory works better than it should do!

The Glauber multiple scattering scheme has proved VERY successful in the description of the scattering of high energy hadrons from nuclei. It is based upon the assumption that the S-matrix for the scattering

from a composite object is product of all the individual S-matrices at shifted impact parameter

Basically the optical limit – propagation in straight lines

Assume also that

Hand-waving explanations are useful

x

y

Consider two arbitrary non-overlapping potentials in 1-d, with transmission and reflection coefficients Ti and Ri.

Glauber needs T=T1T2; not valid unless Ri are small.

However, when one averages over the “nucleon” separation x-y, the reflections in the denominator get washed away if k(nuclear size) >> 1. Averaging saves Glauber theory.

A paper doesn’t have to be right to be influential

A paper doesn’t have to be right to be influential

Abers et al. tried to derive Glauber theory for scattering from the deuteron from Feynman diagrams.

Double scattering

Single scattering

where we put in Regge pole amplitudes for the blobs a and b.

But this diagram, calculated in full detail, actually gives a negligible contribution at high energies – it has a spurious Regge cut. Hence WE concluded that the Glauber shadow effect would vanish as E ∞.

We therefore suggested inelastic contributions to the shadow term

But this diagram, calculated in full detail actually gives a negligible contribution at high energies – it has a spurious Regge cut. Hence we concluded that the Glauber shadow effect would vanish as E ∞.

Glauber was much smarter than us since, in his theory, there was a cancellation twixt the off-shell part of the double scattering and higher order scatterings.

We therefore suggested inelastic contributions to the shadow term

But this diagram, calculated in full detail actually gives a negligible contribution at high energies – it has a spurious Regge cut. Hence we concluded that the Glauber shadow effect would vanish as E ∞.

Glauber was much smarter than us since, in his theory, there was a cancellation twixt the off-shell part of the double scattering and higher order scatterings.

BUT THIS REMAINED FOR THE FUTURE!

We therefore suggested inelastic contributions to the shadow term

Exploit your ideas to the full – or, if you run out of new ideas, repackage the old ones for sale to the new reader!

Exploit your ideas to the full – or, if you run out of new ideas, repackage the old ones for sale to the new reader!

Standard Glauber model does not give (+d) = (0d) because it neglects the possibility of charge exchange in the double scattering.

This is the simplest and most compelling example of an inelastic intermediate state.

It is only actually significant in the region of the (1232), where charge exchange is large.

Normal Glauber double scattering

Charge-exchange double scattering

A person and the wider community might not agree as to what the person’s best work is.

“Best” is a very ambiguous word. Perhaps I mean the paper for which the person has a special affection.

Göran has already talked about “the formula” (but that had popular success as well).

One paper that got only six citations (including 2 from me) was

A person and the wider community might not agree as to what the person’s best work is.

Time-independent perturbation theory

Second (and higher) order shift does not depend upon the spectrum or the transition matrix elements, but only upon the perturbation and the unperturbed density. Can be used for bound or scattering states – or for perturbing in the energy.Calculate the np triplet scattering length from the deuteron wave function (needs also the F-W theorem).

It is inevitable that you will rediscover somebody else’s results independently – the literature is now too vast!

Time-independent perturbation theory

It turned out that Milward and I were about the fourth group to find and publish the above result as a new formula (2nd Aharanov, 3rd Carl Bender), without being picked up by the referees!

The formula is, nevertheless useful and instructive and should be in any undergraduate QM textbook.

It is inevitable that you will rediscover somebody else’s results independently – the literature is now too vast!

Time-independent perturbation theory

It turned out that Milward and I were about the fourth group to find and publish the above result as a new formula (2nd Aharanov, 3rd Carl Bender),

without being picked up by the referees!

Refereeing is a random process

There is no automatic link between the amount of work that you put into a paper and the success of the outcome.

In 1992, the Journées d’Études Saturnes were held at Mont Ste Odile in Alsace. On the five hour train journey from Strasbourg back to Paris, I developed the idea of the quasi-bound state, taking the available data and a pocket calculator.

There is no automatic link between the amount of work that you put into a paper and the success of the outcome.

In 1992, the Journées d’Études Saturnes were held at Mont Ste Odile in Alsace. On the five hour train journey from Strasbourg back to Paris, I developed the idea of the quasi-bound state, taking the available data and a pocket calculator.

Use for one problem what you have learned from another

Liu and collaborators had postulated the existence of states where the -meson is bound to a nucleus (A 12).

But consider the production amplitude

The experimental data showed a strong variation with p.

This looked similar to the situation of neutron-proton charge exchange. There had to be a nearby singularity in the complex plane near p= 0.

If is almost bound then surely is so that there is no real hope to detect heavier nuclei where levels overlap.

Encourage experimentalists to “work even harder”!

Black points = ANKE Grey triangles = SPESII Grey squares = SPESIV Red line = ANKE fit Grey line = SPESII fit

[COSY-11 data very similar to the ANKE points]

Cross section reaches a plateau within 1 MeV of threshold.

Pole must be in complex plane with |Q| < 1 MeV.

Extract the maximum from the data – before somebody else

The ANKE and COSY-11 pd 3He are linear in cos

But this linearity only starts at Q 4 MeV

arises from s-p interference. This behaviour can only come about if the phase of the s-wave amplitude is varying tremendously fast – as it would from a nearby pole.

You cannot force successful collaborations

You cannot force successful collaborations

People have to fit together by being complementary

Jean-François Germond and Göran Fäldt are both people who understand and handle formalism very well. I rely completely on intuition (experience) and need somebody like Jean-François [24 papers] or Göran [29 papers] to put the ideas onto firm foundations.

You cannot force successful collaborations

People have to fit together by being complementary

Jean-François Germond and Göran Fäldt are both people who understand and handle formalism very well. I rely completely on intuition (experience) and need somebody like Jean-François [24 papers] or Göran [29 papers] to put the ideas onto firm foundations.

Collaborating with Torleif Ericson was a disaster: we were both thinking intuitively in the one paper we wrote together.

It reads like a coffee room discussion.

You cannot force successful collaborations

People have to fit together by being complementary

Jean-François Germond and Göran Fäldt are both people who understand and handle formalism very well. I rely completely on intuition (experience) and need somebody like Jean-François [24 papers] or Göran [29 papers] to put the ideas onto firm foundations.

Collaborating with Torleif Ericson was a disaster: we were both thinking intuitively in the one paper we wrote together.

Collaborations should avoid at all costs folie à deux

“a form of mental illness in which two people, generally close to one another, share the same delusion”. [Chambers]

Leads to wild unrestrained speculation

Beware of the Wager of Pascal

Le pari de Pascal: « Pesons le gain et la perte, en prenant choix que Dieu est. Estimons ces deux cas : si vous gagnez, vous gagnez tout; si vous perdez, vous ne perdez rien. Gagez donc qu'il est, sans hésiter. »

A person should “wager” as though God exists, because so living has everything to gain, and nothing to lose.

This maladie was very evident at Saturne in the search for anomalous pion production or strange nuclear fragments of large size, but most especially in the hunt for the dibaryon. Pascal’s wager was then presented in the form that, although it was highly unlikely that dibaryons existed, if one found them then one became famous overnight.

(Cold fusion is a much worse example of the disease.)

Keep hold of Occam's razor

One should select the hypothesis that introduces the

fewest assumptions and postulates the fewest entities.

Before assuming that the above represent evidence for dibaryons, all other standard explanations (including experimental artefacts) have first to be ruled out.

But: dibaryons have 29,000 hits in Google

Look first what the experimental data tell you

pd n{pp}(before Andro)

The pp excitation spectrum clearly has two components, one at Qpp M- MN.

First real “proof” that virtual pions or isobars were crucial in the description of nuclear reactions.

Tp = 1 GeV 0.1<|t|<0.3 (GeV/c)2

interference?

virtual pion production

pn np

Two almost equivalent descriptions

But what happens when Qpp gets so large that the pn get close and perhaps bind to be a deuteron?

Try to link experimental results together – I

Limit of large Qpp is pd backward scattering

Conventional nuclear physics

(p=180o)

Craigie-Wilkin model

Virtual excitation of the -isobar

Whenever we look for rare events at intermediate energies, BEWARE! The (1232) is lurking behind every bush!

Try to link experimental results together – II

If so, the cross sections should be related. Within a naive dynamical model, where the coupling is via a separable potential, the two invariant mass distributions are reproduced and the relative cross section to factor of two.

Still an intuitive model – Göran will firm it up!

You cannot teach intuition

You cannot teach intuition

Physics is the art of finding the good approximation

As an example, consider the reaction pp {pp}+-, where the pp system is in the 1S0 state. Six amplitudes:

COSY

TOF

is the spin of an initial pp system, the relative momentum and the momentum of the dipion with respect to the {pp}. The beam direction is along

Too much freedom!

Let the model guide you

Risser & Shuster model

The dominates single-pion production and this gives p-wave pions, each with a momentum factor.

Mechanism will be largest for S-wave pairs.

In terms of the COSY-TOF notation,

ansatz suggests momentum dependence in Ss[s] amplitude

Don’t be frightened to throw the model away if it doesn’t work!

ANKE results for Epp < 3 MeV, pp < 18o.

AS gives two-hump structure ADgives a single hump (for the ANKE kinematics).

(Bactrian) camel or dromedary

By adjusting AS/AD one can fit data semi-quantitatively. Seem to have the essential Physics elements and so one should not yet jettison the model. But, will it fit exclusive measurements?

800

1100

best fit

1400

2000

AS=0

AD=0

Store away information on data – but remember it!

ANKE recently published small angle data on pp {pp} at 353, 500, and 550 MeV. But CELSIUS data at 310 MeV (with enormous statistics) were never published.

ANKE 353MeV

backward

Fit shows that |E2| 0 and that |E1| |M2|.

Theory says E2 should dominate at 310 MeV. ANKE finds evidence for E2 at 500 and 550 MeV.

forward

Don’t understand hard bremsstrahlung

Listen patiently when experimentalists explain their problems

In BNL 1965-67 Harry Palevsky was studying 1GeV proton scattering from light nuclei. He tried to convince me that the inelastic sum rules would allow him to investigate nucleon correlations in nuclei – as for low energy neutrons in solids.

The flaw in the idea is that at 1GeV the NN interaction is strong compared to the inter-nuclear separation. Need a multiple scattering scheme to handle this.

First application of Glauber theory to a medium weight nucleus (16O).

Influenced the Saturne-I programme

Listen to experimentalists – but keep an open mind!

The Oxford group working at the CERN SC measured the total cross sections for interactions with light nuclei.

The Glauber calculations of the average cross section are not perfect (Fermi motion?) but all the trends are there.

9Be was out of line by about 3%. Experimental or theoretical problem?

The blocks had been made several years previously at the Rutherford laboratory – they were 4”4” and not 1010 cm2. Triumph for theory!

reduced by 500 mb

Not always the smartest student who survives in the long run

One needs good luck and persistence as well as brains

Good luck means meeting the right people at the right time.

Persistence means exploiting the opportunities to the full!

Other influential people

Rudolf Peierls : Best Theory department in the UK.

Gerry Brown: Tutor support through undergraduate years

Stanley Mandelstam: Brilliant PhD supervisor.

Chan Hong Mo: Support in the first post-doc position.

Torleif Ericson: First introduction to Medium Energy Physics.

Vig Teplitz: Saw the connection of Regge cuts & Glauber.

Harry Palevsky: First experimentalist who listened carefully!

Leonardo Castillejo: A delight to discuss with for many years.

Lazare Goldzahl: A nose for Physics – taken in moderation.

Further influential people

Pierre Huguenin: Led to my long collaboration with Neuchâtel

Neil Tanner: First long collaboration with experimental group.

David Bugg: Brought the idea of polarised reaction.

Hellmut Seyfarth & Otto Schult: They brought me to Jülich.

Vladimir Petrovich Koptev: For sharing with me the culinary delights of Jülich

+ many other people in the room today!

Retirement merely means that one doesn’t get paid!

Statistical fluctuation?

Retirement

Hans & Andro persuaded me to spend more time in Jülich after my retirement

ACKNOWLEDGEMENTS

- Thanks to the whole organising committee, especially Andro, Hans, and Jessica.
- Thanks to all the speakers, especially the present one!
- Thanks to all the collaborators, whether they be present in the room or not.
- Thanks to the cook last night.
- Thanks to the funding agencies.
- We look forward to the party to celebrate the 80th birthday!

Thanks and goodbye!

How many of these exotic phenomena survived?

- Evidence for a narrow resonance at 1530 MeV/c2 in the K0p-system of the reaction pp+K0p from the COSY-TOF experiment
- Signature of a -nn resonance in pionic double-charge-exchange at low energies
- A signal of a narrow NN resonance in pppp+-
- Estimate of d'-production in proton-proton collisions
- Upper limits for a narrow dibaryon in pp collisions at 200 and 310 MeV
- Search for the hypothetical X decay
- Search for narrow dibaryon resonances in neutral pion photoproduction from the deuteron
- Search for a bound trineutron with the 3He(-,+)nnn reaction
- Two-pion production, line and aspects of meson, Bose-Einstein correlations and isospin breaking.