Remembering Jan Nassalski
I was greatly saddened when I heard that Jan Nassalski had died suddenly, and I agree with all of the positive things said about him in the obituary published in CERN Courier (October 2009 p32). But one episode in his career was omitted.
For about a year in the early 1970s he was a visitor at University College London (UCL) where he worked with us on the analysis of film from our heavy-liquid bubble chamber at the NIMROD accelerator of the Rutherford Laboratory. Because of passport restrictions from the Polish Communist government, he was unable to stay in London long enough to do a PhD at UCL. Instead, he copied all of his data onto paper tape, took it with him when he returned to Warsaw, completed his analysis there and submitted it successfully in 1973 for a Warsaw PhD under the supervision of Prof. P Zielinski. The work he did in collaboration with UCL, CERN, Tufts University and Brussels was to search for a possible resonant enhancement in the invariant-mass distribution of pairs of Λ hyperons produced when 2.1 GeV/c K– mesons interacted with nuclei. His thesis title was "Analysis of two Λ0 production in high energy K– interactions with heavy nuclei in a freon–propane bubble chamber".
For a while we believed we had seen such an enhancement in events with an identified K+ in the final state, confirming the production of two units of negative strangeness (P Bellière et al. 1972 Phys. Lett. 39B 671), but when we later scanned the same film for dilambda events with a K0 among the final-state baryons (another possible signature for production of strangeness –2) there was no significant enhancement (G Wilquet et al. 1975 Phys. Lett. 57B p97). Jan was therefore involved in one of the first failures to observe and prove the existence of a dibaryon resonance, and he helped us all to learn how capricious samples with small statistics can be.
Jan worked harder and more thoroughly than any other graduate student I have known, even missing the departmental Christmas party to complete the preparation of the data tape that he took back to Warsaw.
David Miller, University College London.
The NuTev anomaly
NuTeV would like to respond to the article "NuTeV anomaly supports new effect in bound nucleons" (CERN Courier September 2009 p9). The article asserts that, after the new effects are considered, "the NuTeV data turn out to be in excellent agreement with the Standard Model". NuTeV does not believe this claim is justified.
First, we want to clarify a point that may be misinterpreted in reading the article. The NuTeV result is not based on free-nucleon parton distributions but on structure functions measured in our iron target. Thus, a separate EMC correction is not needed in the NuTeV analysis.
Second, the authors of the work described have made a specific numerical choice for asymmetries in the momentum distribution of the strange v antistrange sea that is different and only consistent at the 5% level with our published measurements.
Finally, after the NuTeV publication, the Ke3 branching ratio changed and that change has not been included in this update. The electron-neutrinos from Ke3 decay will cause a small change in the measured neutral current rate, and hence the result.
The NuTeV collaboration plans to update the result with an improved-structure function analysis, an internal measurement of the strange-sea asymmetry and the shift in the Ke3 branching ratio. Before these are completed, it is premature to draw conclusions that NuTeV supports the model to the stated accuracy.
NuTeV measured the ratios of cross-sections in both neutrinos and antineutrinos. We found a shift in neutrinos and essentially none in antineutrinos. New models, including this one, must explain both ratios and the weak mixing angle result simultaneously.
The model presented is intriguing (arXiv:0908.3198v1). We believe it deserves further research but such a post-diction does not justify the claims made in the article.
Robert Bernstein for NuTeV.