Laboratory of nuclear & subnuclear physics - Neutrinos part

Event topologies: we can identify neutrino the beam is at 250 km from Superkamiokande;

interaction types by topology: with GeV neutrinos, the best distance would be

➢ + → + .

v CC events: Mostly 500 Km to have the max oscillation probability.

µ →

produce a muon inside the detector. in Event selection: in general, when we have a

the detector we see a long µ track + neutrino beam we can relax our selection cut

hadronic activity at the vertex – The because you know when the events happen:

energy of the muon can be reconstructed usually v are produced in bunch with a width of 1

very easily in two ways: if the event is FC µs and this is the time at which the p are sent to

the e is driven by the range of the muon →

the target so we can fix the time window in a

in the material; if the event is PC here very narrow time window.

comes the importance of magnetic field,

used to bend the trajectory. Energy reconstruction: in this case we have 2

types of events Quasi-elastic scattering and non

➢ →

+ → + .

NC events: in the quasi elastic scattering for the background. Due to

detector we see short event, often the fact that the direction of the neutrino (from

diffuse. the reactor) and for quasi-elastic events we know

the energy of the muon and also the scattering

➢ + → + .

v CC events: In this case angle, we can easily reconstruct the energy of

e

we have e in the final state so the creation neutrinos.

Results: even if the statistical error is large, they mass of the detector and the so the probability to

saw a deficit of events consisted with oscillations have a neutrino interaction. In the brick the

hypothesis. With Superkamiokande we have the interaction are seen as black dots.

proof of oscillations, but we don’t know in which

flavour v goes, we know only they don’t go into v

µ e

channel. Event selection: we are looking for a τ decay.

Being τ very massive, it decays producing an high

energy kink between tau and its daughter, that

what we search for. Otherwise, we have straight

lines and is not an indication of tau decay.

They expected 1 v detected per year!

τ

MINOS experiment

opera experiment MINOS = main injection neutrinos oscillation

The goal of OPERA is providing significant search. The muon neutrino beam is produced by

→

evidence for in the region of atmospheric

129 GeV/c main injector at Fermi lab. The goal is

neutrinos by detecting the appearance in the v µ

measuring the disappearance of v .

µ

beam. Detector: similar to K2K experiment. We have 2

Two requirements: large mass (kton) and signal functionally identical detectors, separated by 735

→

selection background rejection achieve by km (one near and one far).

granularity. Results: looking at the survival probability

Detector: the way is use nuclear emulsion in an 2 2 2

( → = 1 − sin 2 sin (1.267∆ /)

)

emulsion cloud chamber (ECC): a charged particle

travels this emulsion and produce and excitation Looking at v spectrum we saw oscillation, so low

µ

that can be developed and seen. It’s an hybrid number of events. We have predict unoscillated

detector with ECC, some scintillator tracker and CC spectrum at Far detector and we compare it

WS, in this way we can see if there is an with measured spectrum to extract oscillation

interesting interaction and selecting the right film. →

parameter if we compare the

For this reason it’s not a real time detector: we oscillated/unoscillated vs energy we can see a

need to develop the film only at the end. minimum: the depth of the minimum tells about

the mixing angle (the angle is related to how large

→The ECC target brick consists of 150000 bricks; are the oscillations), the position of the minimum,

each brick is made by 57 films interleaved with so the E at which the minimum happens, tells the

1mm thick lead plates, the lead to increase the 2

value of Δm . NB: L is fixed! Se we can do these

measurements very well if we reconstruct the interacts create x ray and it distorted and

energy. slowed down, and the matter distribution

that can be reconstructed using

→ The results: we observe an energy dependent gravitational lensing, which isn’t distorted.

deficit and below 10 GeV a 49% of deficit id

observed. The values are compatible with ➢ Cosmology: comes from the CMB. Looking

Superkamiokande results. at the distribution of intensity of the CMB

we can see some anisotropies which can’t

be explained by normal matter.

Composition of DM: the particle that can explain

the DM must be:

✓ →

Massive to explain gravitational effects.

✓ →

Neutral no EM interaction.

✓ →no

Stable to have decayed by now.

✓ Cold (moving non-relativistically) or wam.

The neutrino fulfil most of these but it’s too small,

so there must be model beyond the SM that

→

predicts new particles the hypothesis are the

WIMPS (Weakly interacting massive particles).

Dm searches: the search is mainly concentrated

dark matter detection in: ➢ + → ̅ +

Production at LHC:

DM proofs: Dark matter exists and we have

different proofs which come from: ➢ Indirect detection: we look at the centre

of the start, where we can have an

➢ Astronomy: if we look at the rotation accumulation of wimps and we search for

velocity, which can be measured with the the annihilation, we look for antiparticles

doppler shift of the 21 cm hydrogen line, emitted from massive objects. In this type

we expect a decrease of the rotation we have ground-based detector (large

velocity with the increasing of the radius, neutrino detectors and Cherenkov

but what we measure is a constant telescopes) and in space from AMS we

behaviour. found a large excess of e+ but not for the

antiproton.

➢ Gravitational lensing: the photon

trajectory is curved around big masses. ➢ Direct detection: looking at the scatter of

Although astronomers cannot see dark →

wimps with standard matter our focus.

matter, they can detect its influence by

observing how the gravity of massive

galaxy clusters, which contain dark matter, Dm signal and backgrounds

bends and distorts the light of more-

distant galaxies located behind the cluster. We live in a DM halo; we know that the density of

−3

➢ ~ 0.3

DM at our position is we

Galaxy-cluster collision: we have 2

know also the velocity distribution of the wimps:

observables: the baryonic matter which

supposing we are not moving in the galaxy, wimps Signature of the signal:

are coming to us with a thermal velocity of 200 ➢ Spectral shape: we expect a precise

km/s. energy distribution which can be tested

Moving through the halo of the galaxy we expect a using different elements.

scatter between wimps and ordinary matter, since ➢

the velocity is not high, the interaction is not Annual modulation: the earth rotates

relativistic with a recoil energy of KeV. around the sun and the relative speed of

DM particles is larger in the summer, so

Cross section and mass: The rate of wimps is: the rate is larger, so we have many nuclear

recoils in summer.

0

∝ <>

➢ Directionality: there is a preferential

Where the density and the velocity are known, direction for the wimps; if we are able to

and we are interested in the mass and in the cross detect the direction of the event, we can

section. distinguish the signal from the

background.

In general, interactions leading wimps-nucleus

scattering are parametrized as spin-independent

interaction because the velocity is so low that the

wimps can’t se the nucleons but only the whole

→

nucleus the cross sections goes as the squared Backgrounds: we can divide the background into

of the atomic mass so heavy nuclei are favoured, two families:

but we need to take care about the form factor for 1. Electron recoil: photons and electrons

which for heavy nuclei we can have large energy scattered from atomic electrons.

scatter, so low energy threshold is essential to 2. Nuclear recoil: wimps and neutrons

minimize the form factor suppression of rate. scattered from atomic nucleus.

Energy spectrum: Looking at the energy We have many sources of backgrounds:

distribution of nuclear recoil for different wimp ➢ →

masses we can see: if the mass is high (50 GeV) Cosmic rays we can go underground.

the energy can go up to 50 KeV, otherwise if the

→ ➢

mass is small the energy goes up to few KeV External photons from natural

this is crucial for the detection because each radioactivity: the main elements are K40,

detector has its own threshold and if the energy is which produces photons and beta decays,

lower the threshold we can’t detect the event. U238 chain and Th232, which produces

alfa and beta. Every time we have a

If we fix the wimp mass but we change the target, nucleus in an excited state, when we have

we can see that the heavy nuclei are better the de-excitation we have an emission of

because we have large number of interaction, but photons, which can penetrate a lot in the

the form factor kill the rate at high energy. matter. Among them there is the Radon,

Detector requirements: that is important because it’s a gas and

can change the equilibrium of the chain.

➢ →

Large mass the interaction is weak. →

The main problem are the photons if

➢ →

Low energy threshold sub-kev to few we can see the position of the interaction,

kev. we can see that the background mostly

➢ Very low background and/or background populate the outer layer of the detector,

→

discrimination the interaction is simply so we can select only the inner part;

a scatter. another solution is the rejection of

➢ →

Long term stability we expect one multiple scattering: the signal of the

event per ton per year! wimps is a single scatter nucleus recoil,

single scatter because the cross section is mass the cross section can’t be smaller than the

so small that we can’t have multiple line): if the mass is big, we have smaller rate, so

scattering. Another solution is the less interaction and otherwise; the fact that we

capability to distinguish between nuclear have a steep decrease with a minimum means

and electron recoil because our signal in that in that region, before the minimum, we are

→

the nuclear recoil region (valid for not sensitive this is related to the threshold of

photons but not for neutrons). the detector, we can’t see the signal if the mass is

too small.

➢ External neutrons: muon-induced and We can increase wrt the reference limit: increasing