Dear NA61 Leaders,
It became clear on the last SPSC meeting that your light ion proposal
would require significant strengthening, although the physics cases for
light ions seem interesting. This has two parts:
The arguments based on "projections" of various particle ratios and
observables (regarding the strong interaction program) with various ions
did not really meet with unanimous support in the SPSC. It would
probably help to find more theoretical comparisons and stronger physics
arguments around those observables, including the isospin symmetry
violation. It would be nice to find clearer and stronger arguments about
how the expected results clarify, support, falsify theoretical
scenarios, what is to be learned, how the expected uncertainties are
estimated and are they small enough to lead to a breakthrough, and what
are the consequences of succeeding or not, with these planned light ion
measurements.
The arguments based on cosmic ray physics, if possible, also should be
worked out more clearly and perhaps more qualitatively, describing how
these measurements contribute to a better modeling of cosmic ray related
processes in general and also in particular. A few illustrative plots or
more specific arguments would help the case of these requests
significantly. The proposed QCD program is also apparently useful for
the cosmic ray and radiation programs in terms of input for Monte-Carlos
used for air showers or hadronic interactions in general (like FLUKA).
Perhaps Tanguy could advise/contribute here in more detail.
Finally, the small window of opportunity for light ions is probably
there in the SPS after this LS, and we believe and support that it
should be ideally used, by NA61, to take light ion data. In order to
maximize chances, we may need a bit more than usually requested for a
simple beam request, that is why we collected the above advices. It
would be also important to prioritize the beam requests, so if they need
to be shortened, we know already what is most important. This means we
would need to know which ion species and which energies are most
important, how much statistics is minimally needed per species and
energy, and what is the absolute minimum set of runs needed below which
the whole programme would not make sense any more. We also need to
understand more precisely some details about what drives the length of
each request (for a given ion and energy), i.e. how much is it setup
time, real data taking time, and safety margin; and whether it is better
to express the requests in terms of days, or collected data volume
(number of events), or both (and how much can be collected in how much
time), and what are the statistical limitations and consequences of
smaller data volumes. Also, it would be nice to express clearly the
distinction between the readiness to take and analyze the planned data
for the planned observables, from the apparent long delays and serious
difficulties related to the open charm analysis in the large Pb+Pb
dataset, such that SPSC members do not unfairly connect the two. Still,
any good progress on the latter open charm program would very probably
have an indirect, but quite positive effect on the discussions about the
future beam requests.
As always, our aim is to understand and also to support better your
requests, since we think that the NA61 program, with its diversity, is a
valuable asset to preserve, and in particular, for the light ion beam
opportunity we are supposed to discuss.
We are open to discuss along these lines even much before you prepare
something in writing, which is then, after submitted, is much more
difficult to shape/optimize/change before the SPSC meeting.
Thank you, and best regards,
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I suggest that we organize our work around four main topics:
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Physics motivation and theoretical predictions – Strengthen comparisons with theoretical models and demonstrate how the proposed measurements can distinguish between different physics scenarios, including isospin symmetry violation.
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Cosmic-ray and radiation physics – Develop more specific arguments and illustrative plots showing how our measurements could improve hadronic interaction models and cosmic-ray simulations.
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Beam request priorities – Establish a clear ranking of ion species and energies, determine the minimum and optimal statistics, and prepare realistic estimates of the required beam time. We should also define the minimum scientifically meaningful program.
-
Analysis readiness – Demonstrate our ability to analyze the proposed light-ion data and clarify how this program differs from the ongoing open-charm analysis.
