Joint Swiss-Bulgarian Project in Neutrino
Physics (BUCHNEU)
1. Summary
[Very important! I would prefer that you write this, Alain!]
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2. Background
2.1.
Participating research teams
[Geneva University group. Alain, this is for you!]
The participating group of scientist from Sofia University works in the Department of Atomic
Physics. The department is among the biggest in the Faculty of Physics. Ten associate
professors, seven assistant professors and seven junior researchers and assistants with
university education work there. The staff is involved in teaching both at undergraduate and
graduate level. The latter includes education at Master level in Nuclear and Particle physics
and training of Ph.D. students. There are nineteen of them at the moment.
Main directions of scientific research encompass:
 Particle and High Energy physics
 Nuclear structure and Nuclear spectroscopy
 Dosimetry, Radiation protection and Radioecology
 Nuclear energy and technologies
 Nuclear electronics
 Modeling of physical processes in nanosystems
 Moessbauer effect
 Biophysics
For the last 5 years members of the department have published more than hundred articles in
international scientific journals.
The team of researchers being involved in this project consists of two associate professors:
Dr. Roumen Tsenov, representative of the team, and Dr. Dimitar Kolev; one head assistant
professor: Dr. Ilko Russinov, one doctoral student, Mariyan Bogomilov and one junior
researcher, Andrei Marinov. Two more doctoral students will join the team starting 1st of
January 2006. There are positions open for them and the names will be known before
Christmas after standard selection procedure.
Dr. R. Tsenov has his habilitation in Particle Physics and Dr. Dimitar Kolev in Nuclear
Physics. Their main research activity is in the field of Neutrino physics. R.Tsenov joined
CHORUS experiment at CERN in 1994; D.Kolev came into it few years later. CHORUS
(http://choruswww.cern.ch) was short base-line neutrino oscillation search experiment in
CERN’s wide band neutrino beam. The collaboration is still producing physics results mainly
on neutrino induced charm production. Dr. Tsenov and Dr. Kolev contributed in running the
equipment during data taking in years 1994-98, in parallel and afterwards they developed
essential parts of its software for off-line analysis: part of CHORUS simulation code, Eficass,
based on GEANT3, interface layers for I/O operations, object-oriented data base for
integrating final results of event processing and others.
Since year 2000 they have joined HARP Collaboration (http://harp.web.cern.ch/harp/) for
building of apparatus and measuring hadronic cross sections in medium energy interval 3 – 15
GeV with sufficient precision to allow reliable design of multi-MW proton driver, the first
stage of future Neutrino factory. They took part in building the detector (specialized system
for monitoring performance of the large gas Cherenkov counter of the experiment), data
taking, basic software development (interfaces to MySQL and Oracle data-bases for
integrating the results of event processing, methods and procedures for calibrating HARP
resistive plate chambers etc.) and now are in charge with physics analysis of data.
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Dr. Ilko Russinov has experience in optics, optical spectroscopy and nuclear electronics. He
has been drawn in HARP collaboration to design and help in building monitoring system of
the large Cherenkov detector.
Mariyan Bogomilov is a doctoral student under supervision of Dr. D. Kolev. He is involved in
HARP, where he contributed in building resistive plate chambers (RPC) of the detector and
simulation of TPC+RPC combined performance. Now he works on off-line calibration of
RPC and analysis of data in the large angle region of interest.
Andrei Marinov is young researcher with some experience in nuclear electronics and data
acquisition systems. He is taking part now in testing at CERN of large number of resistive
plate chambers for one of the experiments (CMS) at the Large Hadron Collider. He will be
available for our project in 2006.
Members of the team participate in neutrino physics oriented experiments CHORUS [1],
HARP[2], OPERA[3]. Recently the team has been accepted in MICE collaboration [4].
2.2.
Account of the state of the research in the field of
Neutrino physics
Neutrino oscillations are the main topic of Neutrino physics today. Compelling evidences in
favor of neutrino oscillations, driven by small neutrino masses and neutrino mixing, were
obtained in the Super-Kamiokande [5], SNO [6], KamLAND [7] and other atmospheric [8],
solar [9] and long-baseline [10] neutrino experiments.
These findings have brought the physics of massive and mixed neutrinos in the front line of
the research in particle physics and astrophysics. For recent reviews see [11].
Left: Rotation of the neutrino mass-eigenstates 1, 2 and 3 into the flavour eigenstates e,  and  .The definitions of the
2
Euler angles 12, 12, and 23 are indicated. Right: Neutrino mass spectra allowed by the present data. m12 is the mass2
squared difference that relates to the solar neutrino data, m23 the one that relates to the atmospheric neutrino data.
The Standard Model of fundamental particles and forces needs to be modified to
accommodate neutrino mass terms, which require either the existence of right-handed
neutrinos to create Dirac mass terms, and/or a violation of lepton number conservation to
create Majorana mass terms. The observation that neutrino masses and mass-splittings are tiny
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compared to the masses of any of the other fundamental fermions suggests radically new
physics, which perhaps originates at the Grand unification or Planck energy scale, or perhaps
indicates the existence of new spatial dimensions. Whatever the origin of the observed
neutrino masses and mixings is, it will certainly require a profound extension to our picture of
the physical world. The first step towards understanding this new physics is to pin down the
measurable parameters, and address the first round of basic questions:
 Are there only three neutrino flavors, or do light sterile neutrinos exist? Are there any
other deviations to three-flavor mixing?
 There is one angle θ13 in the mixing matrix, which is unmeasured. Is it non-zero?
 We do not know the mass-ordering of the neutrino mass eigenstates. There are two
possibilities: the so-called “normal” or “inverted” hierarchies. Which is right?
 There is one complex phase δ in the mixing matrix, which is accessible to neutrino
oscillation measurements. If both θ13 and sin δ are non-zero there will be CP violation
in the lepton sector. Is sin δ non-zero ?
 What precisely is the value of the lightest neutrino mass and are neutrino masses
generated by Majorana mass terms, Dirac mass terms, or both?
All of these questions, with the exception of the last one, can in principle be addressed by
accelerator-based neutrino oscillation experiments. However, getting all of the answers will
not be easy, and will require the right experimental tools.
A Neutrino Factory appears to be the ultimate tool for probing neutrino oscillations. In
particular, with the observations of flavour oscillations of atmospheric neutrinos [5], a
Neutrino Factory based on a high-energy muon storage-ring [12] became the object of great
interest as the ultimate tool to study the neutrino mixing matrix [13]. Recent results on
neutrinos from the sun [6] and from nuclear reactors [7] establish the Neutrino Factory as the
best facility to discover, and study precisely, leptonic CP violation [14].
Neutrino beams at a Neutrino Factory will be produced from the decay of muons circulating
in a storage ring. The primary aim of the accelerator complex is to store as high a muon
intensity as possible. This will be achieved using a high power proton source to create intense
bunches of protons which are fired into a target. As many of the pions created in this collision
as possible will be captured and transported along a decay channel, where they will decay to
muons. The resulting muon beam will have a large size and a large spread in longitudinal and
transverse momentum, i.e., a large emittance, which must be reduced to avoid a large fraction
of the muons being lost during acceleration and subsequent injection into the storage ring. The
reduction of the momentum spread and transverse emittance takes place in two stages, called
respectively phase rotation and cooling. The muons are then accelerated to a final working
energy in a series of accelerators, before being injected into the storage ring.
Neutrino Factory would be the first of a new line of high-brilliance muon accelerators and an
important first step towards a muon collider [15], perhaps the route of choice to multi-TeV
lepton-antilepton collisions. In addition, a Neutrino Factory complex will provide
exceptionally intense beams of protons, pions and muons. These beams can be used to carry
out a very broad spectrum of fundamental research in the fields of condensed matter physics
and chemistry, materials science and medicine as well as nuclear and particle physics [16].
Two feasibility studies [17,18] have shown that a Neutrino Factory could be built using
accessible technologies, with a performance matching the requirements of an exciting physics
programme. Cost estimates, however, are quite high ($1.9 billion in US Feasibility Study II
[18]), and several of the techniques envisaged have never been applied in practice. Several
partially explored alternatives, with significant potential for cost reduction, exist for some of
the subsystems. A sizeable programme of R&D is thus required.
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There are many things that are not known at all, or known with insufficient precision. To
cover one of them, pion production cross sections at relatively low (3-15 GeV) energy region,
HARP experiment at CERN Proton Synchrotron [19] was built and run in years 1999-2002.
The main motivation of HARP experiment was twofold: to acquire adequate knowledge of
pion yields for an optimal design of the Neutrino factory; and to improve substantially the
calculation of the atmospheric neutrino flux which is needed for a refined interpretation of the
evidence for neutrino oscillation from the study of atmospheric neutrinos in present and
forthcoming experiments. Analysis of data is still in progress.
Probably the largest novelty in Neutrino factory accelerator complex is ionization cooling of
muons before their capture, acceleration and decay to produce high intensity neutrino beam.
Proposed more than twenty years ago and generally considered sound, ionization cooling of
muons at minimum-ionizing energy has never been realized in practice. Yet it makes
significant contributions to both the performance and cost of a Neutrino Factory. This
motivates the proposal of MICE [20], a muon ionization cooling experiment. Importance of
such experiment has been recognized by both the US Muon Technical Advisory Committee
(MUTAC) [21] and the European Muon Coordination and Oversight Group [22]. The aims of
the proposed experimental programme are:


to design, engineer, and build a section of cooling channel capable of giving the
desired performance for a Neutrino Factory;
to place this apparatus in a muon beam and measure its performance in a variety of
modes of operation and beam conditions.
A successful demonstration is an important milestone in the R&D towards a Neutrino
Factory. The point is not to demonstrate the principle of cooling, which is expected to result if
all components work as specified, but to learn how to build and operate a device that performs
as desired, and to prove this by measuring its performance in a beam. The experience gained
from this experimental demonstration will provide input to the final design of the Neutrino
Factory cooling channel, and allow the design of a Neutrino Factory Complex to be optimized
with confidence.
2.3.
Account of Geneva University research in the field of
Neutrino physics
[Alain, this is for you!]
2.4.
Account of Sofia University research in the field of
Neutrino physics
Involvement of scientists from the Department of Atomic Physics in neutrino experiments
started as early as in 1994, when Dr. Roumen Tsenov joined CHORUS experiment at CERN.
That time the experiment was in running phase and initially he took part of the responsibility
for operation of the muon spectrometer. Later on he contributed in development of different
parts of the software for the experiment: simulation, track reconstruction in the muon
spectrometer, improvement of general framework, implementation of Objectivity™ objectoriented data base for integration of results of event processing etc. Now he participates in
physics analysis; one Ph.D. student from the University of Sofia prepared part of her thesis in
CHORUS under his supervision. Dr. Dimitar Kolev, coming from nuclear reactions
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community, joined CHORUS in 1998. He contributed essentially in software development
and data analysis.
Next involvement of the group is HARP experiment. Dr. Tsenov and Dr. Kolev are among the
authors of the proposal. They formed a group of about five researchers in Sofia for HARP.
They contributed in building the apparatus, essentially in designing and constructing of
monitoring system for the large gas Cherenkov counter, trigger electronics and resistive plate
chambers (RPC). The group took part in data taking and development of general software
framework. Now they are in charge with physics analysis of events in so called large angle
region. One Ph.D. student is finishing his work in HARP under supervision of Dr. D.Kolev.
One Master student from the group prepares part of his diploma thesis in another neutrino
collaboration, OPERA [3], being involved in development of ORACLE data-base for brickassembling machine there. He is supervised by Dr. D. Kolev.
3. Research plan
3.1.
Objectivities
The aim of BUCHNEU project is to facilitate participation of the partners, especially the
group from University of Sofia, in European network of activities towards building of
Neutrino factory; in construction, running and analyzing data from MICE experiment; and in
ongoing analysis of data from the HARP experiment.
Main objectivities of the project span the following tasks:
 computing simulation of particular neutrino processes at a neutrino factory;
 participation in building, running and analyzing data of MICE detector [4, 19];
 continuation of participation in analysis of data from HARP experiment.
3.2.
Scientific and technical description
Here main tasks of the project will be described in more detail.
1. Computing simulation of particular neutrino processes at a neutrino factory.
One of important tasks in exploitation of a neutrino factory for physical measurements would
be the absolute normalization of neutrino flux (see [23], p138). Of practical interest for
normalization is the measurement of purely leptonic charge-current process
νμ + e- → μ- + νe
Its signature in the detector is a low-angle forward-going muon with no recoil. Using the
standard electroweak theory, this process can be calculated with high precision, and could be
measured with a dedicated detector. Then, knowing the cross-section and having measured
the event rate of this reaction, the muon flux can be calculated.
We plan to develop a simulation tool for this process and its detection by a relatively small
mass near detector. The tool will be based on GEANT4 [24] package. As an outcome
guidelines for design properties and performance of the near detector should be formulated.
Essential prerequisite for that is the experience of the group in development of simulation
software for neutrino detection.
Milestone 1A: Development of a simulation tool for the above process.
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Milestone 1B: Conclusion on feasibility of exploiting it for absolute flux measurements and
formulation of recommendations for design properties of small mass near detector.
2. Simulation of MONOLITH-like detector
One of designs of the far detector (at ~3000 km distance from the Neutrino factory) considers
MONOLITH-like device [23, p.149]. The MONOLITH concept is based on a massive
tracking calorimeter with a modular structure, shown in the figure below. Magnetic field
configuration is also indicated.
Layout of the MONOLITH detector, showing the magnetic field.
Each module would be a stack of 120 8-cm-thick horizontal iron absorber plates (14.5 x 15
m2), magnetized at B ≈ 1.3 T and interleaved with sensitive elements in 2 cm gaps. The
detector height is about 13 m, and a mass of 34 kt can be obtained with two such modules. As
active elements RPCs with glass electrodes are foreseen. They provide x–y coordinates with a
3 cm pitch and a time resolution of about 1 ns. One of directions of possible improvements is
the option with vertical 8-cm plates that would provide better hadronic background rejection.
Our group will be included in simulation of such a device. This will require further
development of existing code and performing massive simulations with different options.
Gained experience with HARP RPCs and software would be valuable ingredient in this effort.
The main task would be investigation of “vertical plates” option, compared to horizontal
design. As a result, recommendations on detector layout and design properties would be
drawn up
Milestone 2A: Installing existing simulation software of MONOLITH in Sofia, testing its
functionality and possible improvements/optimizations.
Milestone 2B: Comparison between “horizontal” and “vertical” design and
recommendations on detector layout and design properties.
3. Involvements in MICE collaboration
One of the main goals of the project is integration of Bulgarian group in the MICE
collaboration [4] and exploiting its expertise there. Planned tasks encompass:
3.1. design, construction and tests of monitoring system (“slow-control”) for beam trigger,
timing and particle identification system. It will monitor the functionality of the
detectors, high and low voltages etc. during data taking. We envisage design of the
system and manufacturing of its components to be done in Sofia;
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Milestone 3.1A: Design of the system.
Milestone 3.1B: Manufacturing the components.
Milestone 3.1C: Installing in MICE and tests.
3.2. simulation of optical collection and design of upstream Cherenkov counter with
liquid fluorocarbon radiator. Using suitable optical ray tracing code coupled with
results from beam properties simulation package would help optimization of light
collection and detection efficiency of this device;
Milestone 3.2: Optimization of counter design.
3.3. manufacturing of mechanical details for the above counter. After finalizing the design
of the counter some mechanical details could be manufactured in the mechanical
workshop of the Sofia University;
Milestone 3.3: Delivering of details.
3.4. development of software for off-line identification of beam particles. It would include
algorithms for determination of calibration constants, off-line monitoring of stability
of the system and methods to achieve design goal of 70 ps time resolution. Parts of
existing HARP software could be re-used here and integrated into the new
framework.
Milestone 3.4A: Defining of user requirements for the code, its functionality, structure
and dependencies.
Milestone 3.4B: Actual coding and integration into MICE software framework
Milestone 3.4C: Tests on real data and optimization.
4. Analysis of data from HARP experiment
Part of the team of this project is currently involved in analyzing data from HARP
experiment, namely particle yields in so called ”large angle” region, where angle and
momentum measurement is done with the cylindrical time-projection chamber (TPC)
situated in solenoidal magnetic field and particle identification is achieved by combining TPC
dE/dx capabilities and time-of-flight measurement from barrel RPCs, surrounding the TPC.
Analysis is already well advanced and preliminary results are expected this summer. Within
the proposed project we would like to continue our participation in this analysis until
complete results are obtained and published for particle yields and production cross-sections
in the “large angle” region over selection of targets and beam momentum settings relevant for
Neutrino factory proton driver design. Envisaged time for this is end of year 2006.
Milestone 4A: Pion yields in the “large angle” region from 5% interaction length Ta and Pb
targets exposed in 3, 5 and 8 GeV/c positive beam.
Milestone 4B: Pion production double differential cross-sections from thin and thick high Z
targets in 3-12 GeV/c beam momentum interval
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4.1.
Planning, coordination and management
Time disposition of milestones, defined in previous section, over the duration of the project, is
given in the following table.
Task
1
Partner
1,2
2
3.1
1,2
1,2
3.2
3.3
1,2
1,2
3.4
4
1,2
1,2
1st year
2nd year
1A
3.1A
2A
3.1B
3rd year
1B
2B
3.1C
3.2
3.3
3.4A
4A
3.4B
3.4C
4B
Geneva University group will have the responsibility for management and coordination of the
activities. On each milestone a written report will be prepared, circulated and discussed by
partners. Workshops will be organized yearly (two in Geneva and one in Sofia), where
participants will present their work, discuss it, further actions and corrections of plans, if
needed.
Usual communication means as phone and video conferences will be used according to needs.
4.2.
Dissemination and exploitation of results, follow-up
[Alain, write something here, please!]
5. Intended impacts of the planned work
5.1.
Impact on strengthening of capacities
The main impacts of the project can be formulated as follows:
 fostering participation of the Bulgarian group in the fast developing field of Neutrino
physics in Europe;
 making use of existing expertise and strengthen it,
 allowing the group to find its place in the international network of activities towards
building of Neutrino factory;
 giving access of young Bulgarian scientists and Ph.D. students to state-of-the-art
research in High Energy Physics and facilitate their integration into the field;
 modernization and improvement of the local equipment available to the group that
will strengthen it capabilities and will allow its further integration in European
fundamental science.
Important condition and guarantee for realization of these goals is the leading role of the main
applicant, Geneva University group of Prof. Alain Blondel, in the field of Neutrino physics in
Europe.
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5.2.
Impact on national and international networking
Successful realization of the project will make Bulgarian group visible in the filed of Neutrino
physics not only at CERN, but also on broader European context. Moreover, building of
Neutrino factory accelerator complex would be intercontinental enterprise, thus the group will
become known internationally. Visits of Swiss partners to Sofia will allow them to get better
feeling and knowledge of the potential of Bulgarian partners and High energy physics
community there for further collaboration, preparation of joint projects, exploiting capabilities
of local enterprises for specialized software development, building of experimental equipment
and/or its components etc.
5.3.
Impact on economy and society of partner countries
In social aspect, the project will give possibilities to a few young people to work on the world
frontier of fundamental physics research just at home university. This might influence the
direction of their scientific careers towards staying at home and working there in stimulating
environment of international collaboration rather than leaving Bulgaria and looking for jobs
somewhere in Europe and USA.
The amount of requested funds for the project is rather small to have noticeable impact on
Bulgarian economy.
References
1. http://choruswww.cern.ch
2. http://harp.web.cern.ch/harp/
3. http://operaweb.web.cern.ch/operaweb/
4. http://hep04.phys.iit.edu/cooldemo
5. Super-Kamiokande
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Publishers, Inc., hep-ph/0310238.
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http://arXiv.org/ps/hep-ex/0008064
M. Apollonio et al, Oscillation Physics with a Neutrino Factory, hep-ph/0210192 October
2002 (ed. M. Campanelli) http://arXiv.org/ps/hep-ph/0210192
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19. HARP Proposal, see http://harp.web.cern.ch/harp/Documents/Proposal/hpeproposal.html
20. MICE Proposal, see http://cern.ch/proj-bdl-nice/proposal.doc
21. C. Wyss et al.,
http://muonstoragerings.web.cern.ch/muonstoragerings/emcog/workingplan.doc
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