Smaller institutes look to gain from scientific fallout

Large laboratories obtain scientific data in vast quantities and usually use this material for rapid research being driven by competition. The majority of important results are collected in as short a time as possible. When new data appear older data lose their importance and are abandoned or placed at the disposal of smaller labs that could make use of them.

This has been the case in the past with data obtained at laboratories such as CERN, Fermilab and JINR, which came in such quantities that they could not be exhaustively analysed by the researchers there. The data were therefore given to various universities and other smaller laboratories, which over a long period of time have analysed the events in question and sometimes made valid discoveries.

More recently, data from the CDF and D0 experiments at Fermilab have become available via the web. A more leisurely analysis phase is also happening with data obtained from experiments at LEP, whose activity is slowing down. Thus it gives the possibility of allowing researchers at smaller scientific institutions to follow up the work and make new findings. For example, institutes in the “Post L3” collaboration are currently analysing some LEP data in their own time and have no obligation to provide results by a specific deadline.

The pictures made in the late 1960s with the CERN 2 m hydrogen bubble chamber show the possible importance of this approach. Its films ended up in various universities, either for further analysis or for didactic purposes, because bubble-chamber pictures are useful for students. Consequently, during the 1970s, the University of Bucharest and JINR in Dubna obtained 125,000 pictures courtesy of CERN. The pictures were found to contain a number of interesting items that had earlier been overlooked because in the principal analysis they had been viewed with different criteria in mind.

In one particular example, V M Karnauhov, V I Moroz, C Coca and A Mihul were able to report on finding a resonance in π^–p interactions at 16 GeV, having a mass of 3520 ± 3 MeV/c² and a width of 7 ⁺²⁰_-07MeV with eight standard deviations (Karnauhov et al. 1992). At the time this seemed very strange, as most physicists were not particularly interested as the resonance corresponded to a five-quark particle (uud ccbar), which did not fit then into any theoretical framework.

During the past year, however, evidence for several exotic resonances has been reported. A real “gold rush” for similar phenomena – the “pentaquarks” – has begun, even though there are few, if any, irrefutable theoretical explanations. Their masses have not yet been calculated due to the lack of a theoretical basis. These include the Θ* (1540 MeV and a width of 17 MeV) and the Ξ (1862) baryon with S = -2, which have still to be established with high accuracy. They appear like states of five quarks (pentaquarks), i.e. four quarks and one antiquark, so yielding a system without colour, which is necessary to be observable.

The 2 m bubble-chamber data suggested long ago that at least one more baryonic exotic state was found with a mass of 3520 ± 3 MeV/c², a width of 7 ⁺²⁰_-07 MeV and S = 0. This was a pentaquark baryon with neutral strangeness. The essential difference between the Θ*and Ξ (1862) and what was found long ago is that the old resonance was formed by quarks including a ccbar pair, while the new ones contain s (sbar) quarks, giving a substantial difference in the final mass. Other teams have also reported possible sightings of pentaquarks in data from the 2 m chamber, and now the H1 experiment at DESY has evidence for a uuddcbar state with a mass of 3100 MeV/c².

So what can we learn from this experience? The distribution of data to smaller institutions, which perhaps have more time to follow different or unfashionable lines of analysis, must continue. Besides the benefits that this activity can bring to the institutes themselves, the long-term process also has the benefit of bringing fresh minds to the analysis as younger physicists, who may bring new approaches, replacing older ones.

The Grid should also be able to overcome some of the difficulties of the past. It aims at providing a global computing facility, which will allow the smaller laboratories to participate in the primary research. However, the Grid is being developed to provide enormous computing power; it will not be able to provide the thinking time that is necessary for the best job to be done. This can only be provided by the researchers performing long-term analysis generally in the smaller laboratories.