OK sorry. So it's a pleasure for me to present the highlights and perspectives from ATLAS. And
okay we have a superb data set with 139 inverse femtobarn good for physics at the
highest center of mass energy up to now. And in addition, we have some extra data
with heavy ions: lead lead, proton lead and xenon xenon, some high beta star
measurements and some low pileup. We have a 94% data taking efficiency of which 95%
are good for physics. The total luminosity is already known preliminarily with a
precision of 1.7%. And we have already 57 public results with the full run two
data set among which 36 are papers and in this talk I will completely concentrate on full
run two results. Let me start with a few words on detector performance. So, the
reconstruction of physics object, which means electron, muons, taus, jets and so on,
is precisely known from careful data driven calibrations, for example at the per mille level
for lepton efficiencies. We have several improvements during the last year using
machine learning techniques. For example, in b-tagging and tau identification,
and in the upper right plot you see the light flavor rejection
versus the b tagging efficiency in .. in red for our old taggers and in blue for the new
ones and you see that we improve by typically 50% or more. And below you
see the Monte .. the data to MonteCarlo scale factors and this is nicely
consistent with one in the intermediate range of the jet pT,
the error is also in the percent region and a similar plot you see for tau
ID with RNNs in the left plot. We push towards lower energies for electron,
muons and b's to search for scenarios with smaller mass splitting and we have
further improvements in efficiency and precision still to come. So, let me
start with the physics of the Higgs boson now, and let me start with H to
ZZ. So, we use the yield of the H to 4l decay to measure the differential and
the double differential cross sections, to measure the simplified
template cross sections, and to measure the mass. You see on the left plot nicely
the spectrum now for the .. for 4l, where you see that irreducible
background is is very small and the reducible background almost not visible
anymore. So all measurements agree well with standard model prediction, where the total
cross section is being measured witha 10% precision now. You see in the middle
plot the differential cross section with respect to the Higgs boson pT, where the
black points are our data and the different .. the different colored lines are
different Monte Carlo calculations and you see that the agreement is extremely good.
And then the data have been fitted with EFT parameters where we choose the EFT
parameters that modify the Higgs couplings to gauge bosons, quarks and gluons. And
again, you see the in the right plot that, that all EFT parameters are consistent
with zero as they should be within the standard model. And also here the
precision is already getting pretty impressive. In addition, we measure the
Higgs boson, we measure the Higgs boson mass. So also in the 4 lepton
channel the nice thing with this channel is it is completely statistic dominated,
and the systematics is almost exclusively from the muon momentum scale. And you
see again the mass spectrum together .. together with the mass fit in the right
plot, and the mass has been measured to be 124.92 GeV where the error is about
200 MeV now.
Let me come to Higgs to b bbar now where we have two analyses: a resolved analysis for low
and medium Higgs pT and a boosted analysis for high Higgs pT, and you see the background
subtracted mass spectra in the two .. in the two upper plots left for the resolved
and right for the boosted and with the resolved analysis alone the ZH
production mode is established with 5.3 sigma where 5.1 is expected and the WH
mode with 4.0 sigma, expected 4.1. The total cross sections agree well with the next
to next to leading order predictions as shown in .. as shown in the two lower plots and
especially there is a nice nice agreement at higher pT where new
physics effects should show up. And let me show you this nice event display of a
candidate for a boosted WH to b bbar event where you see nicely on one side a high a
high energy muon and ETmiss which forms a W which is recoiling against,
against a fat jet where you can, where you can actually see nicely the substructure
of this jet in two prongs, which would be the two the two b quarks. Let me come
to Higgs to Z gamma now. So Higgs to Z gamma is a loop decay sensitive to, to new
physics different from Higgs to gamma, the branching ratio is very small, it's 5.7
times 10 to the minus six, for Higgs to Z gamma if you then also require that
that the Z decays into two leptons, but this decay actually gives you a very clean
signal, and the data sets have been analyzed with in six categories to enhance
the significance. And in the right you see the .. you see the combined mass spectrum
where the events have been, have been weighted with their purity within the .. within the
category and you you see sort of an enhancement exactly at the Higgs mass. And
so this leads then to a to a cross section normalized to the Standard Model prediction
of 2.0 plus 1.0 minus 0.9, which is also statistically dominated. And then you can
take this, this number and either interpret it as an evidence where I've put
evidence in in quotes because it's still below three sigma but it's it's 2.2 sigma
or you can interpret it as a, as a limit on the cross section which is less
than 3.6 times the standard model expectation, which corresponds to a
branching ratio of Higgs to Z gamma of less than 0.55%. Let me come to
ttH now with with Higgs to gamma gamma. Already some months ago we have we have
analyzed this mode for the for the cross section only, now it has been re analyzed
in terms of the Higgs, the Higgs CP structure. In the first stage ttHiggs and
tH events are identified with a boosted with a boosted decision tree and
you see in the upper plot the gamma gamma mass spectrum after this BDT where
you see a nice peak on the, on the Higgs mass, and then in the second stage the CP
properties are examined with a second BDT using CP sensitive variables. So, the
analysis establishes the ttH production mode with 5.2 sigma and it excludes a CP
mixing angle of larger than 45 degree leaving the total normalization
k_t free and this actually where you see in the in the right in the in the
lower plot, you see the allowed area in k_t times cos
alpha versus k_t times sine alpha and a pure CP-odd Higgs would have an alpha of
90 degree which is clearly outside our limits. So, a pure CP-odd Higgs is
excluded with 3.9 sigma and for the definition of alpha and k_t I've
written down for you here, the Lagrangian that we are using.
As a last Higgs analysis let me now report on the search for invisible Higgs decays
In the VBF channel, the invisible Higgs boson decay can be tagged selecting two
forward jets and missing transverse momentum, which you can see from the from
the Feynman diagrams here where the two, the two quarks radiate a vector boson,
which then fuse into, fuse into a Higgs. And in the standard model, the Higgs to
invisible decay is very small, it only consists of Higgs to two Z where both
Z decay into neutrinos. However, in the analysis, there is a large background from
Z to nu nu decays and from W to l nu, where the lepton is lost. But both backgrounds
can be measured either in the two lepton or in one lepton control region, which
allows then in the end a statisticss limited measurement, and in the plot in
the plot on the right, you can see, you can see the data and the and the prediction
after the fit through the control region and you see a perfect, you see a perfect
agreement. And then this leads to a limit in the branching ratio Higgs to invisible
of less than 13% observed and expected and this is the best limit that exists at
present. And then if you assume that the Higgs decays into two dark matter
particles, this also can set strong constraints on the wimp nucleon cross
section, you see in the right plot, and actually the LHC analyses are sensitive
more to the low masses, which is exactly the region where the direct searches are,
are insensitive. Okay, let me come now to standard model measurements. So first
evidence for four top production. The four top production has been searched for in the
two same sign and in the three lepton channel. The Standard Model prediction for
this process is twelve femtobarn at next to leading order with an error of about
20%. Events are classified again in a boosted decision tree using additional
information on jet multiplicity, b-jet multiplicity, the angles between the
leptons and visible energy. And then the main backgrounds are constrained in the
special control region and extracted in a common fit with the signal. In this in
this fit actually ttW turn.. comes out to be higher than expected, 60 plus or minus
30%. But this is consistent with other ATLAS multi lepton plus b jet
measurements. And on the on the right on the right in the right plot, you can
actually see the BDT output score for the data and the
prediction separated by the different components. And you see already by eye a nice
enhancement coming from the four top signal. And so then for the four top signal the
cross section is measured to be 24 plus plus seven minus six femto barn which
which is something like 1.7 sigma higher than the standard model prediction. And this
corresponds to an evidence for four top production of 4.3 sigma, where 2.4 sigma
are expected. In t tbar events we also looked for lepton flavor violation in W
decays. This ratio W to tau nu to W to mu nu was 2.7 sigma high at LEP, but
clearly t tbar events are a rich source of W pair production. And then if one W
decays leptonically, which you can use for the trigger, and you have two
more b tags in the event, you you can really tag the second W very cleanly and
and unbiased so then if the second W decays into a muon and one or more neutrinos, the
muon impact parameter distribution and the pT distribution can be used to measure the
rate of prompt muons and muons from tau decays, allowing to extract this ratio
of branching ratios. And the upper plot shows you for one pT bin and in the emu case,
the impact parameter distribution. And you see first that the background is pretty
low. You see in light green, the contribution from prompt decays and in dark
green, the contribution from from cascade decays. And this impact parameter
distribution actually can be calibrated using Z to mu mu events. And then the
ATLAS measurement is about a factor to more precise than the combined LEP
measurement. And it's consistent, it's perfectly consistent with one. Again
another eccess over the standard model that seems to be gone.
Okay, let me come now to electroweak jjZ production. Again, this is a, this is
largely dominated by vector boson fusion, which is sensitive to the triple
gauge, to the triple gauge bosono couplings. It is characterized by a high
mass high delta rapidity di-jet system. It can be further separated from strong
production by a veto on central jets and requiring the Z to be central with respect
to the di-jet system. And this actually allows to construct QCD control regions
and then the electroweak component can be extracted, can be extracted from data
in a sort of ABCD method. So, the differential cross section of the, of this
production mode has been measured for several variables and compared to
Monte Carlo generators. And you see here as two examples, as a function of the di-jet
mass and as a function of the azimuthal angle between the two jets and
you see in general, quite a good, quite a good agreement. And then these
distributions can be used to measure EFT parameters that modify the triple gauge
couplings and the right block shows you now for all for the different
variables that we have measured the sensitivity to the EFT parameters and
this sensitivity is splitted in in red in red the interference between the EFT and
the standard model which is the which is the lowest order contribution and in blue
the the higher order contribution one over lambda to the four which is from the pure
EFT and you see that especially delta delta phi j j is very sensitive to
all EFTs and at the same time it's basically only sensitive to the to the
interference contribution. So, to the lowest order one where no higher orders are
mixing in. And so this observable was used for our EFT fits. And you see here the
results for the different parameters, which agree in general well with the
standard with the Standard Model. And you also see that including or not including the
one over lambda to the four term doesn't make any difference to the results.
Okay, let me come now to light by light, light by light scattering. This was
already observed with the 2018 data at 8.2 sigma, you see here one plot from
the analysis and you also see a nice event display which shows you how clean
lead lead collisions can can be. But now, now using the full the full data set, we
have used we have measured the differential cross section for light by
light scattering. So to remind you proton proton collisions are at large impact
sorry lead lead collisions at large impact parameter effective effectively act as a
photon collider, where the where you have in the events a lead comes in,
radiates a photon and then a lead or an excited lead ion goes out. And then
light by light scattering appears at loop level within within QED and the results
the results of this differential cross section measurements are in reasonable
agreement with leading order Monte Carlo predictions and we have we have used the
mass spectra also to, to search for resonances and this actually sets the world
best limit for medium mass axion like particle as you can see in the lower
plot. A couple of heavy ion results. So, we have measured the suppression for
several probes in lead lead collisions with respect to proton proton, they are all reported
here in the in the right plot, and what you actually can see is that in general, if
the probes are strongly interacting, they all agree reasonably well. However, for
weakly interacting probes, W and Z, we see exactly no no suppression. Okay, let
me come now to a few searches. We search for new resonances so new gauge
bosons have been searched for with decays into t tbar fully hadronic, VV semi
leptonic and VH fully hydronic. These searches do not only profit from the
full run two luminosity, but also from much improved tagging algorithms as you see
here for the top case, where the black line is what we used for our
earlier publications and the purple line here is where we are now and you see that
we again gain almost an order of magnitude. In all cases, the background is
derived from from data and then the resonance is searched for in the mass
spectrum, where these are the mass spectra for the three cases and V prime
mass limits of typically three to five TeV have been derived depending on the model,
and the table here shows you the best, the best limit so the model that gives the
best limit that we have from the different analyses. And here you see a
nice, high pT t tbar candidate where within the liquid argon
calorimeter you can see the the three prong substructure already by eye. Let me
come now to supersymmetry. So ATLAS has released already 15 results with the full
data set. For this conference we have four more results: searches for charginos and
neutralinos with three leptons, sorry, where in the upper plot you can see the
agreement of the off shell signal regions with with the prediction and nothing is seen;
searches for for top squarks in cascades with a Higgs or a Z. And again,
nothing is seen. And let me come in to in some more details to two searches with
R parity violation. So if R parity is violated events can be fully
reconstructed. For top squarks this can lead to events with many jets including
many b jets. And you see in the plots here for our signal regions we go to up to
larger than nine jets of which larger than five more than five are b jets and again,
everything here agrees with the prediction, But charginos and neutralinos you
may actually see in three lepton resonances, as you see in the upper right in the upper
right plot where again you see the prediction, the data, everything agrees, but
you see the nice resonances that you would expect from from a signal and both and
then for both topologies we have set limits as you see in the two lower plots,
which go up to something like a TeV for the for the top squark and for the for the chargino.
Okay, to for the end, let me come briefly to ATLAS perspectives. So
at present
the LHC is in is in a long shutdown, LS2, and ATLAS is implementing important upgrades
for run three, and in view of the high luminosity LHC. The main theme of the
present upgrades is refining the trigger selection. So the liquid argon upgrade for
finer granularity in the L1 trigger, new forward muon chambers, our new small wheels,
for better muon pointing and new feature extractors in the level one trigger to
allow for more sophisticated selection of event topologies. So before the COVID
crisis, the upgrades of liquid argon and trigger and data acquisition were well on
track. For new small wheel we had accumulated some delays. However, the
installation of one wheel in LS2 and the second wheel in an extended shutdown
seemed possible. Now we are reassessing the situation and readiness depends
on the CERN LS2 schedule. So in parallel, lots of work is going on in software,
multi threaded reconstruction and trigger, new data model to to save disk space and
so on. So this leads me to my conclusion. So ATLAS was running successfully in
run two and our data set is already well understood. We had a fast turnaround
to produce new results. Many results in searches and measurements have been made
public already. And several recent analyses have been shown here,
properties of the Higgs boson including its CP structure, evidence for the
production of four top quarks, lepton flavor universality and many more, and ATLAS is
working hard to prepare run three upgrades and software and so on. And we look
forward to an increased sensitivity for multiple important analyses like parameter
measurements, searches, rare decays. Okay, thank you.
Okay, thank you very much Klaus. So we have time for one or two questions, you
can raise your hand.
Okay, so I had the question that on the previous slide, does it mean that there's
now a consideration of not including the new small wheel in the next run?
I mean, even one side.
I said this, this is this is in the this is in the planning because I think for one
for one wheel it looks it looks pretty good, for the second wheel we really have to
see the
details of our
of our possibilities and of the of the LHC. Of course, the problem is the wheel
is produc is produced all around the world. And so we have to take into account
the COVID situation all over the world in the different labs and this is very
difficult to judge at the moment. Right.
Okay, yeah, but I misunderstood the slide. So thank you for the clarification.
So if there are no other questions,
OK thank you Klaus and, Bruno, I will hand the microphone to you.