Yes. Okay, good. Can you see my shirt next? Okay. Very good. So let me can you
can put the screen. Yeah. Is there okay? So thank you very much it's honor for me
being here talking about soft probes at the LFC. I have basically two objectives
on this talk. The first one is to demonstrate that the study of soft probes
in heavy ion collisions allowed to make precision measurements on the hot and
dense medium. That we produce in heavier in collisions, which is called GGP. These
because having higher energy densities we can study efficiently collective phenomena
like radio dynamics, a traffic flow, given the fact that we have large multiplicities
we can start with Statistically neutral particle productions with with a
statistical approach which is in its grand canonical formulation, and then we have
large or large systems. So, we can disentangle hydronic phase effects which
can which can be also dialogue through centrality, for example, studying nuclei
formation or kinetic result in case of coalescence or the disappearance of short
living resonances theory scattering. Now, the second objective of this talk is to
show how exploiting exploiting small colliding systems we can have a better
understanding of what happens in heavy iron conditions because recently we
realize that simple hydronic interactions as proton proton are far from being
Elementary, you need multi party interactions to explain multiplicity you
need to make crosstalk between multiple interactions in order to explain the
hardening of the spectra like for example, color recognition mechanisms and you need
the pattern density fluctuations in the initial state in order to explain final
state phenomenon. Now for many of these details, they lead to the talk held
yesterday by Valentina. But this clearly raises two questions. The first one is, if
we can use more systems to better interpret large systems observations, and
I will talk a little bit about this. And if this implies cued up formation is more
systems, I will not address this a Li. Tomorrow in a perilous session. Now let's
start from Hunter abundances. As we probably all know, the production of light
flavor hadrons can be described Yes, it can be described by the statistical
modernization model in central javion collisions in its grand canonical ensemble
formulation
squadrons, basically
can be seen as coming from a hot hardware restaurants gas in thermal equilibrium.
And you have here this famous flood plot from the Alice collaboration, which shows
over nine orders of magnitude to production of particles from fires to anti
Union for that actually the the statistical models can reasonably well
describe these yields and the parameters which come from these feet are the
biochemical potential which has a DHCS zero and a chemical result temperature
which is around 153, which is by the way compatible with the Kira crossover
transition temperature from like Sq CD. Now, there are details in this description
for example, the fact that short living resonances cannot be described, and so
they are not included in in the thermal fit because of the influence of a drink on
Ronnie Chris gatoring. For restaurant for short living residences, Denver is of
friction with protons like you can visualize here which is being addressed
through the s matrix approach in order to take into account piezocone interact
interactions and other approaches actually try to solve the proton at the same time
the Xi issue with the flavor dependent chemical freeze out temperatures. Now,
another notable point is the fact that loosely bound nuclei and anti nuclei are
actually very produced by the statistical model which means that they are they're
compatible with thermal production and and these leads to the question why so,
loosely bound states can survive the chronic phase and they can come also from
coalescence model so, that we will discuss later. Now, how do these yields compared
to what we measure in small systems were here we come to the famous blog which was
also showed nicely by Wilk in the first talk, which is the high turnover pion
ratio as a functional multiplicity for different particles for different hadrons
from broken proton at very low multiplicity to heavy ions of high
multiplicity. And what one can observe is that the hovering over biracial smoothly
evolves across multiplicity reaching the terminal values in that lead. Now, these
behavior is not square root of as the pendant down actually to topic energies.
And this is also shown by this new measurement for this conference from the
Atlas collaboration which shows the study of size as a function of multiplicity in
proton proton collisions at five TV as compared to the seven and 13 TV show we
know the final square root of s and it depends on the hadron that we are
considering. So, the stranger the headroom, the steeper the increase and it
is the perfect yarmulke here. Now, there is a caveat here that the fact that also
nuclei in house with multiplicity, but we will discuss this later. So, but this is
why we normally talk about these as strangeness enhancement in small collision
systems. Now, what is also important to show is that for high multiplicity broken
protocol collisions, the Hydra chemistry that we measure is actually roughly the
same as the one that we have in a fully thermalized system. Now, how can we
interpret this trend? Well, we can try to use models which are normally used in
large systems and extend them to lower to smaller systems. Or we can do the other
way around. So use, let's say in backhoe modernization models like PTR DC and
expand them to large systems, or to use the two component models. So, let's try to
go through these possible explanations. So, first of all, is first of all thermal
models statistical idealization models in order to try to describe The multiplicity
of dependence of hydrogen production, what can be done is to consider canonical
suppression which means that the quantum numbers of the system which are charged by
reason and strange numbers are forced to be conserved in smaller and smaller
volumes as the multiplicity decreases. And as you can see here, you can have a
qualitative, let's say, reproduce fraction of what is seen for cyber by an omega or
pi, but there are clear problems for protons counts and especially for files
which do not which are not affected by canonical suppression, but buyers are for
the charge
for charging quantum number, so, this is why this is increasing this way a low
multiplicity. Now another possible way of using the statistical learning is a model
for small systems is to introduce an under saturation parameter gamma is which is can
take into account an incomplete equilibration of the strange quarter. Now,
in this way one fits each data point for each system fits gamma is the the chemical
freezer temperature and the volume and this ends up to be better in agreement
with with cascades for example, but still with the large frictions for protons.
Now, the other way around as I said is to try to use more collision systems as sorry
smaller system MonteCarlo models to describe the evolution with multiplicity
and this is what was tested for PGI, eight and Dipsy and the general. The general
outcome here is that the fact that these models can qualitatively reproduce barrier
enhancement with multiplicity, introducing color ropes, which means that if you have
densely packed strings, these leads to higher strength, tension and solve the
more probable to produce variants with respect to to the masses. Now, this is a
possibility of course, but in this new measurement from the experiment of phi to
new new word for word rapidity as a functional multiplicity and for lo PT
reported here, one sees that actually ropes seem not to be the dominant
contribution at low PT for the yields of five for example, the other way to
describe the Hannover pion ratio is a function of multiplicity is to use two
component models like CT Corona and in these models, you have actually two
regimes a double regime each coalition which is one party can be called core,
which is identified by high density the key GP formation also in small systems,
possibly also small systems and thermalized organization which is dealt
with in the grand canonical limits. And then you can have a Corona which
corresponds to the lower density in the initial state, which hydrolyzes through
jets in a vacuum, and this is dealt with with string fragmentation. Now here I
report two results from models from the equals model on the left and the CCI model
on the right, which shows actually that in these models, the handler firing ratio is
actually flat as a function of multiplicity, but it has two different
values, one for the core and the other one for the corona. And the increase for
example of the omega over pi ratio is a functional multiplicity comes from the
change in the core to Corona ratio as the multiplicity increases. So for high
multiplicity, the core contributes more to the final multiplicity, while for low
multiplicity, the corona contributes more and you can see that these two components
model do a good job in reproducing this, this trends. Now, in order to test these
two component models, what one can do is to try to classify topologically proton
proton events and this is what was tested by Dallas collaboration. You can divide
each event in a two word region and away region and a transverse region towards
means basically the direction of the Jets which is proxied by the ISP t hadron in
the event which we call PT leading. And this has to be larger than five gv because
of the jack pedestal effect which was reported, for example by Alice and Alice
but also from CMS at the LSE, actually, which means basically that when we fix the
BP leading being higher than five gv, then the underlying the event multiplicity is
not any more dependent on this heart scale fixing Okay, so this is why we asked for
bt leading or being larger than five gv and then dividing the event in the toward
region which is the direction of the object in the away region, which is the
direction of the recording jet if you want and then a transverse region which is
mostly dominated by the underlying event, one can start particle production as a
function of multiplicity of the underlying event and the multiplicity Underland
underlying event, we call it R T. And it's the ratio of the charged particle in the
transverse region with respect to its average. So tuning our T means really
going from E like event, having got t equals zero going to lead lead like event
going to RT equals to infinity. And the result here that I selected is the Xi over
pi ratio here is a function of PT, but it's actually valid for across all PT. So
it's also translatable in yours for Xi over by ratio in the transverse in the
right and in the toward regions in the left. So let's first concentrate on the
transverse region, which is dominated by the underlying event. And what you can see
here is that if we go from low multiplicity in red to the high
multiplicity of the underlying event in blue, we see no strangers and how In the
transverse region, so, where the underlying event is selected, we observe
no strangers announcement as a functional multiplicity, while if we go in the region
of the underlying event plus jet saw the toward region here we can see an evolution
and actually this evolution at high multiplicity saturates at the level that
we measure in the transport region.
So, in two components model this could be explained as two different cyber biracial
one in the in the in the jet and one in the underlying event and the evolution
that we observe in the reward region comes exactly from the different importance in
the final multiplicity between core and Corona as a functional multiplicity, of
course, for this we need more measurements to draw a final conclusion. Now, as I said
also, nuclei enhances the functional multiplicity and is shown for the U turn
on left and the new three and then Triton on the right with new original From the
Lab at a TV from Dallas experiment, and in this case you have strangers equals zero.
So, what causes this enhancement? Well, it could be a lifting of canonical
suppression as we discussed before or it could be called lessons probability that
kinetic result and this here you have the comparison with models and you can see
that actually there is a qualitative agreement in the sense that molders can
envisage enhancement as a function multiplicity, but the quantitative
agreement especially for helium three, is really lacking some precision. Now, going
to collective motional particles, well, in a nutshell, it was already explained. So
let me be quick on this. If you have in the Hydra picture, if you have ugp
formation, you expect to have radial flow, which is a common expression velocity of
Barton's and it translates into pity spectrum modification. And then you can
have Anisa tropic flow which means basically translating the initial partial
result trapeze into final momentum on his Trapeze and the characteristics of the
medium the properties of the medium affect how efficiently this translation is done.
So, low balk and sheer viscosities can translate into larger rajal and unlimited
tropic flows. And then so, tropic flow is measured through Fourier expansion
coefficients of the t distribution with this values that we call v n. So, v two v
three before and so on. So, one thing which is important to note is that initial
anisotropy can come from geometry. So, for example, so, the centrality of the
collision in a V is but also from parts of massive fluctuations in the initial state.
So, let's start from radial flow we know from the IHC and also from break actually
that when when we go to more central collisions, the spectral identify particle
and identify particle in this case of problems for example, for lead collision
or fight TV get harder, okay. So, the average As a functional multiplicity in
this case for the different species increases, and this can actually be
described by hydro calculations and another observable in this case here on
the right is the vanover Mason ratio is a function, which is actually more like a
higher to lower mass ratio as a function of PT, which shows this bound by the
intermediate PT, whose increase is actually fairly well described by hydro
calculations. So, we have this hundred over with this burden over measuring ratio
which is described by hydrotherapy in large systems. Now, we can go to small
systems and this is the new result from the collaboration in a BP five TV versus
multiplicity for size and omegas. And you can see that actually you observe on
hardening of the spectra also is more systems. This is also verified across
energies. And also in pilot. So, one can also plot the lumber case you're short as
a function of BDS it was done before, but now for VP on left p lead on middle plot
and lead lead on the right. And you can see that qualitatively you have the same
behavior, but with different magnitudes, but then if you select specific key
regions, so, in blue, the low PT in red, the intermediate PT and in green the high
PT and the evolution of this lambda work is your short ratio as a functional
multiplicities moves which makes the call
is there radial flow is more collision systems. Now, the application of hydro far
from equilibrium is under study Actually, there was this nice presentation from work
at the beginning. But considered it also PCI with color connection can describe the
low PT trend observed MPP. Now, an important thing is that actually this
lambda work is zero short ratio has this evolution only In the underlying event is
more system. So, you can see this in blue, when measured in the underlying event this
super imposes very well to the inclusive measurement while the inject lambda
lowercase your short has a much milder evolution to more evolution also in led
led collisions that you can as you can see here, so this is actually characteristic
of the underlying event is more system and call it that the bulk of the event also in
large systems. Now another important point which was underlined yesterday by was
discussing for the chance sector by john McCallum before me is the fact that there
are striking similarities between light and heavy flavors for the London London
work is your short compared to the lambda see over the zero. Now, this is an
intriguing observation because this could point for example, to a perfect
hybridization, let's say I hide unification say of charm, but it is
actually hard to believe small systems and it's probably not even support By what we
observe in large systems, where we see here see at low p d for the v2. So, we
have the v2 of her charges hadrons which is larger than the V q of dimensions and
larger than the v2 of of jPi for example, and also the lambda work is your short
ratio is larger than the lumberyard is zero in javion, which points in heavy ions
to our non perfect equilibration of charge in the system. So does so why is most
systems this could lead to this very same bar in our Mason ratio. Now this probably
challenge and also the hypothesis for light flavors MPP for this for this
specific measurement, is it called SSL intermediate equally be explained by
choleric connection. Now this this is of course, on the development and also on the
server this zero results with smaller security would actually
be very profitable.
Now coming to an Enzo tropic flow on The left you have a figure which is quite an
old one, but it's a nice combination of first results from LSE. Together with Rick
results which shows v n v two v two v three and V for now we are up to eight
more, which is different from zero and it's specifically in cemetery for
collisions as in the Hydra picture. And actually this can be reproduced by hydro
calculations for the different centrality This is for from the Atlas data points for
the v2 v3, v4 and B five and this can be reproduced by hydrocarbon nation with an
almost perfectly we don't eat over so 0.2 now, we can also measure the v2 for
different particle species. And what we observe is that at low PT we have mass
ordering. So the higher the mass the lower the v2, and this is known as an interplay
between rather than electric flow and if you go to intermediate, PT or large Pity
if you want you have an approximate article by grouping which means that if
you have higher number of Quark content, then you have higher v2. And this is a
compliant with a core coalescence as dominant particle production mechanism in
this video reach. Now, the fine mesons peeve also here because it follows the
mass ordering at low PP bunching with protons with very similar mass and mass
which is lying to mass on so for higher VP. Now the mass ordering is also verified
at the LSE up to the neutron and even three as reported in this plot here from
the eyes collaboration. Now, in small steel, you got four minutes left, thank
you very much. So in small condition systems, the v2 was measured quite some
time ago by the CMS collaboration and the Atlas collaboration as well here is a
combination of PPP LED and lead lead results for the sole for the v2
measurement. Also very recently, a very interesting publication came out from
Dallas collaboration reporting, v2, v3 and v4 as a function of the multiplicity for
led lab seen on Xenon v LED and BP Coalition's and what is shown is that
actually there is the here RCO v2 larger than v3 larger than before as expected by
hydro that in proton proton collisions, this The v2 was measured with different
techniques in order to reduce the influence of non flow and actually, it was
measured to be different from from zero. So,
we have v2
in in small systems and the higher that there we go in multiplicity at some point
there is a drift in in v2 from heavy ion collisions when eccentricity starts to hit
in So, when Esther says that starts to play a role, the v2 in large collision
systems start to be larger than in small collision systems where, of course, you
don't have a very big factor in eccentricities in the initial system. Then
if we measure if we look at v3 and v4, which are more sensible to part on density
fluctuations in the initial system, then you can see that actually, the comparison
between the lead lead and Pipi and V lab is, is much better in the common multiplex
to regions. It's important to say that normal that up to now can clearly
quantitatively describe the data over the food multiplicity range nor hydro, not
even, for example, PTO systems. Now, talking about let's say collective
phenomena. It's also very interesting to study magnetic field effects. As you know,
in semi central collisions in heavy ions you have extreme magnetic fields which are
generated by the spectrum nucleons which actually quickly decay, but the
but of course is conserved
which which means that if you have a system of free patterns are not free, but
let's say of atoms of quarks and gluons interacting in the system, you can develop
some spin momentum bearing which basically turns out to have an effect on the spin
matrix for for example vector measurements. So, some some values of the
spin matrix like overall 00 can be measured which correspond to third
component of the spin equal to zero with respect to our given direction. And in
this case, the relevant direction is the normal to the event plane because indirect
is the direction where the B initially is pointing. And actually this this
measurement from the artist collaboration shows For vector meson k star, you have an
effect going lower than the one third value which would be no polarization,
which you observe only in heavy ion collisions and not in proton proton
collisions, and which you don't observe as a cross check for zero spin particles like
zero short. So this is very interesting because it's consistent with the attorney
ization through recombination of Q bar from the Q GP since you see if you have a
polarized plasma, this translates into polarize of polarization or vector
methods. Now, in the last part of the talk, I will not go along in the
discussion since this was pretty much covered by wicked at the beginning, but we
can try to quantify one minute left. Yes, very, very good. Thank you very much. You
can quantify the characteristic of the acuity system in heavy ions Bye bye, Asian
fitting many observables from the experiments from this specific work from
Alice and CMS, for example yields average bt average speedy fluctuation, v2, v3 and
v4. I don't go into details of the model. Basically, it's a parameterization of many
of the of the important characteristics of the system, also initial conditions, and
then you can try to have posterior probabilities of this. Below deliverables.
Yes. Can you hear me?
Yes. Yes.
Can anybody hear me?
If you can, okay.
Okay, so, No, why? No theory. Well, I'm basically at the end of my talk, I want to
just to underline something that was already covered by Wilker that actually up
to the 10% level, there is a very good agreement of this only comprehensive model
With with the observation from Alison CMS, and that you can actually measure for
example, the temperature or evolution of the shear viscosity over entropy density
which turns out to be very near to the ADF CFT lower limit to one over four pine and
natural units and which has a mild dependence of the temperature and compared
to any kind of other known fluid in nature, this is the one which is the
nearest to the almost perfect fluid condition. So, coming to the conclusions I
hope I convinced you the soft probes in IBM collisions allow to characterize the
medium with precision. It's a quarterback confined caramelized medium with an eight
arise which is slightly okay or slightly lower than 0.2 and which is mildly
dependent on T on the temperature of the system. And this system undergoes chemical
result at a temperature which is between 150 or 100 and 160 bV and that
nucleosynthesis actually from large medium is consistent with thermal production
looking at small colliding system so, I think that I convinced you that it's they
are properly article to a deeper understanding of the cutiepie phenomenon
that hydro chemistry and collectivity at higher multiplicity in proton proton
collisions do match what observed in a collisions when we look at variables which
are not strongly connected to the collision geometry. And the description of
this observation is more systems is very challenging for any theoretical models.
So, it says thank you very much. And if you want to have private discussion, I
will be for roughly half an hour in this zoom. Thank you. Thank you, Olivia. Sorry
I stuck. So, we'll have time for
your question questions. Please.
Shut up.
Go
sorry. No, I didn't raise my hand.
At least not willingly.
Sorry. Anyway, buddy. Nice talk