Historical Examples Supporting the Case for Two Complementary Detectors at the ILC

Multiple experiments have been important often in the past, either in establishing new physics, or in providing critically important information on interpreting experimental results.

One important set of historical examples illustrates the importance of confirming results with a second experiment

- The Nobel Prize for the discovery of the W and Z (1984) was awarded

within two years (data 1982/83), thanks to two experiments getting

clean signals

(the prize was only awarded to one, but without the other, it would

not have been awarded so fast)

- The Nobel Prize (2002) for the observation of solar neutrinos

(initially a one experiment show) was only awarded decades later

after the observations had been confirmed by several experiments.

- The Nobel Prize for the J/psi discovery (1976), again observed

simultaneously by two experiments, was awarded within two years

(data 1974)

- The Nobel Prize for the discovery of CP violation, originally observed by

only one experiment in 1964, was awarded only many years later

(1980), despite the very clear initial observation.

Other historical examples:

 (i) TPC and Mark II magnet coils shorted -- other PEP experiments were able to take data while the coils were repaired
 (ii) When Jade's wires broke  Petra was able to continue running
 (iii) High backgrounds in H1 at HERA are not troubling ZEUS
 (iv) UA1 and UA2 at SppS
 (v) BaBar and Belle have greatly exceeded expectations; would this have happened if there had been just one
 (vi) LSND has an anomalous observation; experiment repeated with MINIBOONE
 (vii) Hi-Q^2 jet distributions of CDF and D0 needed both experiments
 (viii) Crystal Ball saw Zeta -> repeat experiment at DESY
 (ix) charm and B lifetimes have needed multiple experiments to sort out observations
 (x) Ab has a history requiring multiple experiments
 (xi) Leptoquark signals at ZEUS and H1 were compared and found to be inconsistent
 (xii) Pentaquark signals cannot be judged by one experiment alone.
 (xiii) Epsilon-prime.
 (xiv) At LEP, Aleph found a 4-jet mass peak at 105 GeV/c^2.  It was not confirmed by the other experiments, an important check.
 (xv)  Kl -> mu+ mu-
 (xvi) QED violation (Pipkin)

(xvii) ARGUS-CLEO competition reduced cost and increase physics

(xviii) CDF and D0 provided significant complementary roles in top quark discovery

(xix) Rising total proton-proton cross section observed directly in Pisa-Stony Brook experiment, confirmed by complementary indication in CERN-Rome experiment measuring elastic scattering at zero angle (optical theorem).

(xx) Eta-c discovered by DASP, rediscovered at different mass by Crystal Ball

(xxi) Unconfirmed top and Higgs discoveries

There are more.