The Rise of Large Collaborations

The Rise of Large Collaborations

P. GrannisAPS Panofsky Prize TalkMay 1, 2001

Panofsky Prize citation: “For his distinguished leadership and vision in the conception, design, construction, and execution of the DØ experiment at the Fermilab Tevatron proton-antiproton collider. His many contributions have been decisive in all aspects of the experiment.”

Had not my colleagues succeeded in building a superb detector, and produced a world-class set of measurements, I would not be here today. My thanks to all my DØ colleagues!

Here I comment on the nature and role of large collaborations in particle physics, and other fields of science.

A brief history of DØ

After 2 years consideration of `small, clever’ proposals for the DØ

interaction region, Leon Lederman asked Grannis on July 1, 1983 to form a new collaboration to complement the existing CDF experiment – with `Stage I approval’, sight unseen!

Proposal to Physics Advisory Committee, Nov. 1983 First `Temple’ review Nov. 1984 – proposed experiment was essentially that built (cogniscenti will notice some changes though!) Collaboration funding & building slow in 1984 – 88 due to pressures from other major initiatives at SLAC (SLD), LEP, FNAL (CDF) (the longer you have, the more the tendency to `optimize’ ! )

Roll-in detector Feb. 1992; first collisions May 1992; first physics data Sept. 1992

Tevatron Run I: 9/92 – 1/96

100th publication of full collaboration: early 2001

DØ detector as proposed – 1984

100th paper author list

M. Abolins, M. Adams, L. Ahrens, R. Brock, C. Brown, D. Buchholz, R. Butz, P. Connolly, B. Cox, C. Crawford, D. Cutts, R. Dixon, D. Edmunds, R. Engelmann, H. Fenker, . Ficenic, D. Finley, P. Franzini, E. Gardella, B. Gibbard, B. Gobbi, L. Godfrey, H. Goldman, H. Gordon, P. Grannis, D. Green, H. Haggerty, M. Harrison, D. Hedin, J. Hoftun, R. Horstcotte, R. Johnson, H. Jostlein, S. Kahn, J. Kirz, W. Kononenko, S. Kunori, R. Lanou, J. Lee-Franzini, S. Linn, D. Lloyd-Owen, E. Malamud, P. Martin, M. Marx, P. Mazur, J. McCarthy, R. McCarthy, M. Month, M. Murtagh, D. Owen, B. Pifer, B. Pope, S. Protopopescu, P. Rapp, L. Romero, R.D. Schamberger, W. Selove, T. Shinkawa, D. Son, S. Stampke, S. Terada, G. Theodosiou, P.M. Tuts, R. Van Berg, H. Weerts, H. Weisberg, D. Weygand, D.H. White, R. Yamada, P. Yamin, S. Youssef

List from original 1983 proposal

24 red highlighted are in current author list

386 authors, 62 institutions71 people, 12 institutions

If there is justification for large collaborations, it had better be the PHYSICS!

How did the proposed physics program compare with reality ? (Talked of 5 pb-1 data accumulation! Got 127 pb-1 -- thanks to the Fermilab Accelerator Division)

W/Z boson mass, width, cross-section, study W tb ! (explore Electroweak interaction)

Anomalous trilinear gauge boson couplings (WW) etc.

Search for new quarks and leptons (did not really talk about discovery of top quark in 1983, since it seemed clear it would be discovered before DØ started! )

QCD studies – jets, W/Z, Drell Yan dileptons, photons, S measurement

Searches for beyond-the-SM phenomena: technicolor, leptoquarks, heavier W/Z, supersymmetry, compositeness …

Discussed in proposal, but did not do:

X Centauro events !

X Quark gluon plasma indications

But did many things not envisioned – QCD color coherence; diffractive production of jets/W; magnetic monopole search; large extra dimensions search; J/production; b production; b s transitions, electroweak production of top, – e universality …

Physics highlights – top quark

DØ and CDF discover top quark in March 1995. DØ mass determination 172.1 +/-

7.1 GeV using l + jets and even ll + 2 jets + ET where underconstrained kinematically; 4% precision with only ~40 events!

Cross section measured to ~30%, using ll, l, and even the 6 jet final state where background is 106 X signal.

Top quark is the last matter particle expected in the SM; is astoundingly heavy – its mass is ~ scale of EW symmetry breaking. This seems provocative !!

Physics highlights – Electroweak bosons

W mass measured in e decay : 80.482 +/- 0.091 GeV (~ 1 per mil in one channel)

WW, WWZ, ZZ, Z gauge couplings measured. As with (g-2), couplings probe new physics beyond the SM (1995 demonstration that SU(2)xU(1) couplings required)

Combination of top quark and W mass constrain the Higgs mass through its contributions to loop diagrams. Light Higgs preferred in SM (fit with Susy somewhat better).

Physics highlights – QCD

69.0GeV, 472

69.0GeV, 47522

11

T

T

E

E

Cross sections for jets are the modern analog of Rutherford scattering – measures proton structure, tests QCD and seeks new level of constituents. Jet XS agrees w/ QCD for pT up to ½ beam energy, and rapidity = 3, and gives new constraints on high-x gluon distribution. Highest energy qq scatter

Measurements of W,Z production cross sections agree with QCD and probe non-perturbative effects.

New studies of diffractive production of jets helps illuminate high Q2 colorless-exchange processes.

b-quark production exceeds QCD prediction by factor ~X2

Physics highlights – Searches for New Phenomena

No substructure of leptons/ quarks at scale > 3.3 - 6 TeV from Drell Yan qq e+e-

Limits on scalar leptoquarks to 225 GeV

Dirac spin 1/2 monopole limit of M > 870 GeV

No Supersymmetric equal mass squark gluinos (mSUGRA) M < 260 GeV

Effective Planck scale limit for extra dimensions. qq/gg e+e-/ > 1.4 TeV (nextra=2); > 1.0 TeV (nextra=4-7)

M(ee) M(ee)

M(ee)

cos cos

cos

data

bknd

Signal + bknd

Are large collaborations effective?

DØ ~350 authors; 9 yrs to 1st data, 13 yrs to end of Run I, 18 yrs to 100 papers. Experiment cost $75M.

(typical for large contemporary collider experiments)

3 contemporary fixed target experiments (KTeV, g-2, E706 combined) (~10 yrs duration):

220 members, 32 publications

My thesis experiment: 10 members, 1 publication; (~ 3 yrs duration)

0.02 papers/author/year $750K/publication

Detector Cost ~ $20K/person/year ~ $6.5/lb (good steak)

0.03 paper/author/year

0.015 papers/author/year

Number of papers/participant/year is not so different for large collider experiments, contemporary ‘fixed purpose’ experiments, and experiments of 30 years ago.

But large collider experiments can do physics of a complexity not possible with smaller experiments due to nearly coverage for tracks, energy flow, particle ID & 106 electronics channels . e.g. tt production with 6 final state objects (lepton, , and 4 jets) invokes all aspects of a full detector.

The large collider detectors have proven to be capable of a wide range of measurements not originally envisioned.

Physics justification of large collaborations

Large costly detectors/experiments have the reach to study largest questions before us – not only in HEP, but also in Biology (genome research, xFELs), Astronomy (HST,MAXIMA, CHANDRA, GLAST, …), Nuclear Physics (RHIC, CEBAF), Materials Science (Light sources, SNS, …) etc.

Size in HEP has been essential in understanding the basis for the SM (LEP, SLC, Tevatron exp’ts) and without them we would not have #’s, W/Z bosons, top quark, direct and indirect Higgs indications, confirmation of the gauge structure

of SM. We won’t discover Susy, large extra dimensions, or strong WW scattering without large detectors. We won’t unravel the mystery of neutrino masses, oscillations, proton decay or GUTs and won’t illuminate CP violation in the B sector without them.

The pressing questions of our field are no longer amenable to small limited scope experiments.

Education of young scientists

DØ Graduate students : 136 completed Ph.Ds ; 123 presently in progress. Of those completed: (about 60% of students took HEP postdocs initially)

NOW: 34% HEP postdocs15% Academic10% National Labs32% Technical industry8% Financial industry1% Government

DØ Postdocs : 162 completed postdocs : 67 presently in progress.Of those completed: (some duplication of postdocs and students)

NOW: 31% Academic31% Technical Industry27% National Labs6% Financial, legal 3% Government2% Other

20 of the 44 graduate students at the time of the top discovery paper

The price of being large Organization of large experiments becomes complex. Line authority in project organization; governance documents; rules for authorship; Speakers bureau; Decision processes are complex and involve many constituencies. Extensive review by Labs, funding agencies.

Individual success in large collaborations requires communications skills (often of use in subsequent jobs!)

Size of the enterprise means that most individuals specialize in particular aspects -- software, electronics, detector building (but not so different in smaller collab.)

Few see the experiment from inception of design to final physics.

Nevertheless, many individuals take a series of diverse tasks over the history of the experiment.

Actual research projects (build a trigger, do a physics analysis, design ID code … ) are typically 3 – 4 persons, as in smaller science research.

International collaborationLarge high energy physics collaborations are a driver for developing more effective relationships with scientists across the globe.

Improvement of understanding of the frameworks in various nations. In a collaboration, one needs to understand the special forces at play in each participating nation.

Helps developing nations to build S&T infrastructure at home, and promotes technically competent people for high level positions.

‘developing’ (in science) nations in DØ: Brazil, Colombia, Ecuador, Korea, Mexico, (Vietnam?) Low funding, but very talented people.

Large collaboration dynamics:

HEP collaborations are strange organizations !

Multi-instutional, multinational (DØ has now 68 institutions/ 17 nations)

No line authority – spokespersons/ group heads have no real authority (hires/salary/ reward mechanisms)

Research program, detector choices, etc. are based upon collective decision to collaborate towards a common goal.

It’s a miracle that it works at all !

Indeed some individualists are repelled; there is some degree of peer pressure to conform to group decisions.

Competition with other experiments is intense. (If the competitor has a 1% better measurement, spurred to do better, and the innovations born are often significant.)

For many, the collaboration is the primary loyalty – above that to one’s university, Lab.

Large collaboration publications

The big author lists – what to do about them?

Pressure from APS, European Physical Society, University promotion and tenure committees to reduce the size.

“ Only put on the list those who did the work”

DØ and other collaborations have resisted this:

Take our recent paper on inclusive production of jets at high transverse momentum and all angles:

One student postdoc did the analysis; group of about 5 very closely tied to the particular analysis through closely related studies. The work builds on that of perhaps 30 physicists who developed the jet energy scale, resolutions, errors, underlying event corrections etc. The analysis benefited from 20 or so who made strong critical contributions to the analysis, interpretation. A group of ~30 more contributed to the algorithms for jets, underlying energy from Main Ring beam, vertex determination, event selection,etc. Then there are the critical contributions (another 30?) to the building of the calorimeters, the triggers, the online analysis, beam monitoring, data bases, luminosity determination, offline CPU farms, etc. And what about the 50 or so more who did necessary experiment management, HV power, controls, accelerator interfaces, databases, computer farms, Monte Carlo generation, etc. ?

It is essentially impossible to delineate ‘contribution’ – it is a continuum. Trying to do so would destroy the fabric of the collaborative spirit. DØ and others list the full set of collaborators as authors.

How to reward physicists in large collaborations

The large experiments comprise as many individuals as are in many entire academic fields worldwide – for example DØ comparable to the world set of 19th century Russian historians (and a lot bigger than many ‘fields’).

Typically, in cases of hires or promotions, one asks experts in the field who have not directly collaborated with an individual.

For those working in large experiments, this is thought to be a problem – can’t ask collaborators. But those from other experiments typically have no way to judge the individual – they cannot peer into the internal workings of a collaboration.

One must therefore rely, even more strongly than usual, on the written evaluations of members of a collaboration who have not themselves worked closely with a candidate. They will have seen the person in action – internal talks, internal notes, oral evaluations – and know who has really done a good job. There is no evidence that such evaluations are any more biassed than the ‘outside commentator’. There is just as much pressure in this case to offer the sort of sound advice that one wants and needs at one’s own institution. In my experience, letters from ‘collaborators’ are often more critical and insightful than ‘outsiders’.

Defects of large collaborations

Large collaborations, even more than smaller HEP experiments, tend to foster compartmentalization – individuals gravitate to a speciality.

It is hard for individuals – students in particular – to see an experiment from inception to publication (though this is becoming the norm with ‘smaller’ HEP experiments as well !)

The large general experiments tend to freeze out smaller dedicated experiments. Since they can do many things at least moderately well and have high costs, they tend to saturate the resources available. But there are topics that large experiments cannot attack; speculative new physics can elude the big detectors.

Once started, the large collaborations are hard to stop (DØ started with proposals in 1981 – will continue until at least 2006 [to try to discover Higgs] ). Keeping them vital and responsive to new needs is challenging.

Strengths of large collaborations

o We are in an era where we know many of the most crucial questions, and to answer these, we need large scale experiments.

o The large experiments have given us many high profile results in the past 20 years, and these have percolated to the attention of the general public.

o The large experiments, properly accounted, are less expensive than a set of smaller experiments.

o The flexibility of large detectors is impressive – many topics studied that are not foreseen.

o Large collaborative efforts have helped drive technological advances for all of science – large scale electronics, new detection techniques, large data set organization, the WEB, multivariate analysis techniques ...

ConclusionsConclusions

The nature of the questions we have to ask assures us that large experimental collaborations are here to stay. HEP experiments have led the way, but are not unique.

The large experiments have been remarkably successful in advancing physics.

Seen from the inside, work is not so different from small experiments.

Giving adequate recognition to young physicists is a problem.

Continued effort is needed to keep the environment in large experiments healthy and conducive to innovative ideas.