Me, walking into a sunny courtyard, then entering a narrow corridor; at its end, a hall, and a blue T-shirt already flying to my face from Leon’s hands. This is the first memory I have of iaps@GranSasso, the very first event organised in Italy by IAPS, alongside the newborn and fast-growing http://jiaps.org/italy-joins-iaps/ - its Italian national committee.

Forty students, from all over Europe and beyond, took part in this five-day event deep within the heart of central Italy. Main theme: astroparticles - but much more was in plan.

We gathered on the first day, May 5th, at a cozy hostel in the center of Rome, many already knowing each other, thanks to different IAPS events such as CERN visits or ICPSs; and a few newcomers including myself, thrilled to jump in the blue of this new experience. After a little walk to explore the surroundings, we all moved to a nearby pizzeria (i.e. place where they make pizza) to taste some local specialities (and a lot of French fries), everything being payed for by our sponsors, then moved back to the hostel: we knew the following day was to be an intense one.

## Frascati

On May 6th, first full day of our tour, we left early in the morning for Frascati, a small center in the outskirts of Rome. There, a series of blocks host some of the most important labs of the National Institute for Nuclear Physics (INFN), the Italian agency responsible for coordinating research in many fields of fundamental physics. Right in front of those, our destination: ENEA laboratories.

ENEA is the Italian National Agency for New Technologies, Energy and Sustainable Economic Development. It leads cutting-edge research in several topics, which stand out for their great public interest: one of the most intriguing is certainly nuclear fusion.

The basic idea is pretty simple: when light atomic nuclei get very close to each other, they may fuse to give new species of higher atomic number; when the colliding elements come before iron in the period table, a mass defect exists between reactants and products, and the reaction is exothermic. Yet, in order for the reaction to have a large enough cross section - that is, to happen with sufficiently high likelihood - reactants must be strongly energetic. In Frascati two different research paths are explored, both involving deuterium and tritium (D-T) as reactants. In the first one, called inertial confinement, a pellet target containing D-T is hit by a powerful laser beam: when the surface of the target evaporates, the rest of the pellet gets compressed and heated; thus a sufficiently dense plasma may form, though for a short time. In our visit we had the chance to see the ABC Laser facility, which investigates this method using a room-long laser beam and impressive diagnostics.

The second technique, on the other hand, guarantees longer confinement times despite being more elaborate. In the case of magnetic confinement a D-T plasma is kept in place and heated by means of varying magnetic fields and EM waves. The machine hosting the vacuum chamber, in which the plasma moves, has the shape of a torus and is technically called Tokamak: when we got there we found it not functioning, hence we could walk around and under it freely. Such a machine requires parts with peculiar electromagnetic properties, for instance superconducting ones. ENEA researches and develops many of the components it needs, thus we had the chance to see the cryogenic equipments kept in dedicated labs.

After lunch in the labs canteen, alongside the researchers who guided us through the visit, we took a great group photo in the lawn in front of the center, then hopped on the coach heading to L’Aquila - second step of our tour.

## Gran Sasso National Laboratory

The beautiful and historical city of L’Aquila lies at the bottom of a wide valley surrounded by snowcapped mountains; in 2009 it was almost destroyed by a disastrous earthquake which caused more than 300 victims. It only takes a few minutes to get from its still crumbling monuments to one of the most important research centers for astroparticles and neutrino physics: the Gran Sasso National Laboratory (LNGS). The labs, whose construction begun in the late 80s, take their name after the mountain under which they are built, literally meaning “Big Stone” - that is pretty much what it is: 1400 m of solid rock providing a perfect shielding from cosmic rays.

We started on May 7th with a series of talks to introduce us to the main research areas covered at LNGS and describe in detail some of the experiments we would have seen underground.

### Dark Matter Hunt

The great shielding offered by rock - equivalent to more than 3 km of water at Gran Sasso - allows experiments to work at very low level of background noise, which puts LNGS and other underground facilities in the front run for the search of very rare events, such as Dark Matter (DM) particles detection. Indeed, as most physics students will know, there has been growing evidence that the amount of matter we see in the Universe is not sufficient to account for the entire gravitational interaction we measure. Therefore, there must exit some kind of “dark”, meaning not light emitting, matter; furthermore, we know that DM cannot be baryonic and none of the Standard Model’s particles can do the job. Many theoretical proposals have been put forward, but no direct observation has yet been done and very little is overall known about this subject. For this reason any clue regarding DM’s behaviour is of great interest: such hint came, for instance, from the DAMA experiment at LNGS, which found an annual cosine-like modulation in DM flux - a particularly relevant result for it did not require any model dependent assumption regarding the phenomenology of its interactions.

Meanwhile, a whole set of experiments at LNGS aims at directly detecting DM candidates in the form of Weakly Interacting Massive Particles (WIMPs), via their low-energy interactions with ordinary matter: different targets are being used to explore many possible WIMPs mass regions. Stay tuned for further news.

### Neutrinos

Low backgrounds offer as well a great chance to perform very fine measurements on highly elusive, though more easily detectable, particles, namely neutrinos: electrically neutral elementary particles, assumed to be massless within the Standard Model.

Since their electrical charge is zero, one may well wonder whether neutrinos and antineutrinos are indeed the same particles. The question turns out to be all but trivial and may be rephrased as follows: is the neutrino a Dirac ($\nu \neq \bar{\nu}$) or a Majorana ($\nu = \bar{\nu}$) particle? In the latter case, one should be able to observe a particular double $\beta$ decay, though a neutrinoless one, thus violating lepton number conservation: indeed the standard version of this decay, which is ordinarily detected, results in two $\beta$ particles and two neutrinos1.

Many experiments at LNGS aim at detecting such decay. One of those I’d like to mention, because of a minor detail that nonetheless surprised me: CUORE. Its inner shield, built to ensure a further protection from spurious radioactivity, is made of true Roman lead, 2000 years old, taken some years ago from a sunk ship in the Mediterranean Sea. Not exactly something you’d find at a hardware store.

We said neutrinos are assumed to be massless, yet a peculiar phenomenon has been observed which proves that they do have mass. Like leptons (electrons, muons and taus), also neutrinos come in three species, or flavours: electronic, muonic and tau. Unlike leptons, neutrinos have a certain probability to “oscillate” between different flavours. This means that a neutrino which is born, say, electronic, after traveling for some time, may end up being detected as muonic. The existence of this phenomenon, labelled neutrino oscillation, guarantees that the mass difference between flavours is non-zero2. Neutrino oscillations have been studied at LNGS by OPERA, an experimental set-up now in the dismantling phase designed to measure neutrinos shot from CERN to Gran Sasso: just a few days ago, on June 16th, the OPERA spokesperson announced in a press conference the detection of the fifth ever tau neutrino in that beam, thus reaching a $5\sigma$ confidence level for $\nu_{\mu} \to \nu_{\tau}$ transitions [1]  in fact, $\nu_e \to \nu_{\mu}$ transitions had already been confirmed.

In the late afternoon we moved to the underground facilities, by coach: the whole area can be easily reached from the nearby highway tunnel, a distinctive and very useful feature of the Gran Sasso labs. We were guided to see all the experiments mentioned above an many more. Overall a very impressive visit.

The following day we were hosted by the Gran Sasso Science Institute (GSSI), a newly founded multidisciplinary PhD school based in L’Aquila. We found a truly warm welcome there, and the commitment its funder show towards the city is certainly admirable. Indeed their activities seem really interesting: I strongly suggest to take a look at their website [2].

After a few interesting talks by experts of the Institute, the floor was given to the members of our students’ group: first with a poster session, then with a few specific talks about the respective research interest. Although my opinion may not be of great relevance, I have to say I really got interested by each and every talk or poster alike. Moreover, many researchers there wanted to congratulate with the students for the high quality of their work - something really to be proud of!

That was the last day of our tour: the day after we moved back to Rome. We spent the last hours sightseeing around the city together, waiting for everyone to set off.

## Conclusions and thoughts

The scientific program of this event was extremely interesting: all the talks were technical yet tailored to our possibilities, the language was precise yet not still a lingo; we truly had the chance to learn about the different aspects of hard core physics we encountered. Also, researchers effectively evoked the feeling of being at the edge of sound scientific knowledge and inspired in us the will to get a few steps further.

Yet, I have to admit my fairly limited preparation, that of a second year bachelor student, did not allow my comprehension to be deepened as much as I wished. What really struck me, instead, were my group mates: their passion, along with their competence and professionalism, deeply stimulated me and boosted my determination to deepen my studies.

The same eagerness seemed to be fully shared by our hosting institutions: not only they welcomed us warmly, but sponsored our stay too. Anyone who ever tried to organise such a complex event will understand how important this contribution may be.

For my part, I invite everyone to join the second edition of this event, which many (including myself) hope will take place next year. Should you be interested in the scientific activity of the institutions that hosted us, you will find the links to their web pages among the references; also, you can find all the event materials, both by researchers and students, online at [5] - I made great use of them for writing this article. Lastly, I would like to draw your attention to their thesis and PhD proposals: they are willing to welcome students from all countries and backgrounds, to share an investigation which may bring us back to the Big Bang and forward to a brilliant future of advances in Physics.

## References

[1] OPERA Collaboration. “A Fifth Tau Neutrino Detected at Gran Sasso”, press release.
http://operaweb.lngs.infn.it/spip.php?article66, June 2015.
[2] Gran Sasso Science Institute (GSSI). Homepage. http://www.gssi.infn.it/.
[3] Energy Italian National Agency for New Technologies and Sustainable Economic Development (ENEA). Enea fusion.
http://www.fusione.enea.it/index.html.en, June 2015.
[4] Energy Italian National Agency for New Technologies and Sustainable Economic Development (ENEA). Homepage.
http://www.enea.it/en/home?set_language=en&cl=en, June 2015.
[5] Italian National Institute of Nuclear Physics (INFN). iaps@gransasso timetable. https://agenda.infn.it/conferenceDisplay.py?ovw=True&confId=9213, May 2015.

1. The nuclear reaction is of the kind $(A,Z) \to (A, Z+2) + 2 \beta + 2 \nu$
2. The amplitude of the oscillation depends on $\Delta m^2$