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Файл:Совр эксперимент на ускорителях (4 сем, мага) / Lecture-2_MEPhI_SHiP_15_02_2024
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Seesaw mechanism
It has two eigenvalues:
The simple mathematical principle behind the seesaw mechanism is the following property of
any 2×2 matrix of the form
and
The geometric mean of and equals , since the determinant .
Thus, if one of the eigenvalues goes up, the other goes down, and vice versa. This is the point
of the name "seesaw" of the mechanism.
In applying this model to neutrinos, is taken to be much larger than Then the larger
eigenvalue, is approximately equal to while the smaller eigenvalue is approximately
equal to:
This mechanism serves to explain why the neutrino masses are so small.
February 15, 2024 Modern accelerator physics, Lecture 2 11
Neutrino mass origin
In the framework of the Higgs mechanism, the particle acquires mass from the vacuum
expectetion value of the sclar Higgs field: m
François Englert and Robert Brout came up with such a scalar field, but it was not clear how to observe
this field. The Scottish scientist Piter Higgs realized that field fluctuation is a particle that can be observed
in experiment. The scalar Higgs boson (m = 126 GeV) was observed at the LHC in 2012. The mass is
forbidden by electroweak gauge symmetry SU(2)×U(1), and can only appear after the symmetry has been
spontaneously broken by a Higgs mechanism, like the Dirac masses of the charged leptons. In particular,
since χ ∈ L has weak isospin 1/2 like the Higgs field H, and right-handed neutrino η has weak isospin 0,
the mass M can be generated from Yukawa interactions with the Higgs field, in the conventional standard
model fashion:
February 15, 2024 Modern accelerator physics, Lecture 2 12
= f v/√2, where v = 246 GeV .
f
Neutrino as a dark matter
Test of the standard neutrino role as a dark matter in the Universe based on LCDM model:
Mν=0.12 eV
February 15, 2024 Modern accelerator physics, Lecture 2 13
SHiP HNL sensitivity
Neutrino portal:
February 15, 2024 Modern accelerator physics, Lecture 2 14
SHiP Axion (ALP) sensitivity
Axion portal:
February 15, 2024 Modern accelerator physics, Lecture 2 15
Neutrino Detector
BGT counters
February 15, 2024 16Modern accelerator physics, Lecture 2
Wall SciFi planes
Iron for the return field
Coils to produce horizontal field
Up to 19 SciFi planes for TT
Up to 6 for MMS
Neutrino Detector
BGT counters
Wall SciFi planes
February 15, 2024 17Modern accelerator physics, Lecture 2
SciFi tracker structure
Conceptual view
SciFi mats
ECC Brick
Honeycomb
CFC skin
February 15, 2024 18Modern accelerator physics, Lecture 2
SciFi tracker structure
SiPMs
SciFi ribbon «X»
SciFi ribbon «Y»
Front-End electronics with
cooling for Plane «X»
ECC CES
Magnet envelope
Envelope
Support
Nomex/
Airex
CarbonFibre
Composit
e (CFC)
February 15, 2024 19Modern accelerator physics, Lecture 2
Conclusion
q
q
The SH iP ex pe rim ent can be c onsid er ed a zero -b ac kg round
experiment with a high level of redundancy to efficiently suppress the
background for a broad spectrum
The SHiP experiment could potentially shed the light on the baryon
asymme tr y origi n an d s olve the m ys t er y of th e d ar k m at t er .
February 15, 2024 Modern accelerator physics, Lecture 2 20
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