How research is done – two examples

1. How research is done – two examples

2. Feynman • "The first principle is that you must not fool yourself--and you are the easiest person to fool. So you have to be very careful about that. After you've not fooled yourself, it's easy not to fool other scientists. You just have to be honest in a conventional way after that." Richard Feynman

3. A step by step guide to research • An individual or (more likely) a collaboration perform a measurement or come up with a theory • The work is summarised in a research paper and released to the community as a preprint. • Simultaneously the work is sent to an academic journal and one or two anonymous referees review it and recommend for publication or rejection. • If its published (and if its interesting) the work is reproduced by independent researchers who also have to publish their findings. • It doesn’t matter how sensational the results are, we never believe anything until it has been reproduced. • Scepticism is good as long one’s views change when thte evidence becomes unbeatable! • In my career I’ve seen 3 Nobel-prize winning ”discoveries” which ended up as non-discoveries.

4. Questions a reviewer or you, as a curious reader, must ask ? • What are the basic principles of the measurement and what are the systematic uncertainties ? • What does theory say about the claim ? • Most important of all - is the measurement in direct conflict with other measurements or are there special experimental/theoretical circumstances allowing this measurement to be right ?

5. Some points • Its usually easy to understand the experimental principles of a measurement • If you don’t understand then the person explaining is probably doing a bad job. • Nothing is too complicatedsuch that the basic principles can’t be properly and easily explained. • The press do a bad job sometimes. Physics blogs are often much better.

6. Case 1 – The rise of faster-than-light neutrinos ! • Why is the speed of light important ? • What is a neutrino ? • How do Opera make the measurement ? • What are the weak parts of the measurement ?

7. Theory – the speed of light • Einsten’s theory of special relativity • if an object can travel faster than light then it becomes possible to send a message back in time • this leads to a problem, eg the grandfather paradox. You arrange to kill your grandfather before he met your grandmother. But then how would you have been around to send the message ? • Our theories are built on the assumption that nature’s speed limit for particles, objects etc. is the speed of light.

9. Theory - neutrinos neutron proton e

10. Neutrino Facts Neutrinos are emitted from , eg, the sun. 50000000000  pass through your thumbnail each seccond. Neutrino from Enrico Fermi for “Little neutral one” The particle is ~massless Neutrinos are among the most bizarre of subatomic particles. Neutrino from sun will pass through 5 LY of solid lead, with 50% chance of interacting

11. The opera experiment • Basic principles • Fire a pulse of protons (10.5 ms) into a target (graphite) at CERN • The interactions with the target lead to short-lived mesons which decay to neutrinos 50 ms Beam intensity time 10.5 ms 10.5 ms

12. The opera experiment • The neutrinos are fired from CERN towards the Gran Sasso lab in Italy ~730km away.

13. Detecting neutrinos in Gran Sasso 150000 ”bricks” of lead plates (in which neutrinos can interact) and emulsion plates (where the interactions can be measured).

14. How does the experiment work Comparison of observed neutrino signal with proton time profile A bunch of protons (neutrinos) leaves CERN and is measured at a later time at Gran Sasso. A GPS system is used to synchronise the two measurements.

15. How the measurement is made ?

16. Final corrections • Make final corrections for electronic delays etc.

17. Discussion • What do we think the systematic errors should be ? • Which is likely to be the largest ?

18. Systematic uncertainties

19. How were the systematic uncertainties combined ? • When is it permissible to add them quadratically ? • What is the systematic error if we add them linearly ?

20. Interpreting the result • What is the probability of the null hypothesis i.e. that neutrinos move at ~light speed and that we were just ”unlucky” in this measurement ?

21. Putting the result in context ? • Has it been reproduced ? What do other measurements say ? • beta decay • v=c from most recent results • but maybe different type/energy v<c v>c

22. Question

23. Summary of faster-than-light neutrinos • Opera reports clear evidence for faster-than-light travel by neutrinos • No other experiment offers clear evidence • these results are not necessarily in conflict with the opera result • Repeat/improved measurement by Opera underway. • We live in interesting times.

24. Case 2 – the rise and fall of magnetic monopoles

25. Magnetic monopoles We observe electric charge. E-field lines ”radiate out” from an electric charge (an electric monopole) A moving electric charge gives a B-field. We do *not* observe magnetic charge. B-field lines do not ”radiate out” from a magnetic charge (a magnetic monopole)

26. Magnetic monopoles - theory • Symmetry • An electric charge exists, why not a magnetic charge ? • Dirac’s argument • The presence of at least one type of magnetic charge allows quantum mechanics to explain why electric charge comes in ”packets”, eg 1e,2e,3e and not 1.1232135e, 1.32435e etc. It explains why the electron charge = -1 x proton charge. • Unified theories • Theories which try to unify the fundamental forces in a single theory predict monopoles. • They should be there but nobody has seen them!

27. How to see monopoles

28. Cabrera’s monopole • Search in 1981-1982

29. Systematics Examination of everything that could cause a ”jump” of just the right size to match the signal of the expected monopole. Several possible causes, thermal noise etc. but nothing definitive. More searches were needed.

30. Lots of people tried to reproduce • The early 1980’s suffered from monopole fever as we’re suffering from neutrino fever now. Publications on searches as a function of date ”My” search

31. The best search to date – back to Gran Sasso Nothing is seen – Cabrera was either very very lucky that a monopole passed his way or he was just wrong.

32. Summary • When you see a new exciting result ask yourself • What are the basic principles of the measurement ? • How does it fit into our present understanding of nature ? • Has the work been reproduced ? Is it in direct conflict with other measurements ?