okay, so I will start now. so I'm going to present today about what we have learned
on the Higgs sector in terms of production, decay properties and differential
distribution at LHC. so first of all a small reminder that the Higgs sector
was introduced in the Standard Model, thanks to several seminal papers, which
here you have a small selections, and that the Higgs boson was discovered
in 2012 by the ATLAS and CMS collaborations at LHC. so if now we
look into the Standard Model Lagrangian, the first thing that strikes out is that
the Higgs boson is the only fundamental particle of spin zero the standard model
that it appears in several of its terms. so for example, we have here the terms
that describe the interaction of the Higgs boson to the fermions, which in
particular, the term which is proportional to the fermion mass, and also we have the
kinematic term that also include the so called, let's say, standard interaction
with the gauge bosons of the Higgs, and as well as the finally the Higgs potential, which is
responsible for the electroweak symmetry breaking, and makes the Higgs field
special. so then, what I'm going to talk today about is mainly about the
precision measurements that you see here, the couplings, differential cross section,
the interpretation, the mass, and the spin CP, as well as the Yukawa interaction with the
third generation fermions. and the other topics in orange will be covered by
Giovanni talk later in the session. I also like to point out the specific talks are
in the parallel session that where you can see these topics expanded in more details
if you're interested. so let's start now with the what are the predictions in
terms of production and decay for the Higgs bosons so when we look at 13 TeV,
which is the energy in the center of mass of the LHC during Run two. we see that
the gluon-gluon fusion production is by far the dominant production mode of the
Higgs boson followed by the vector fusions and the associated production with
the vector bosons. and finally, the ttH associated production. we also
have other production modes not least here like bbH and single-top Higgs productions
that are also in in this plot. also I would like to point out that the first two
that gluon-gluon fusion and the VBF production were observed already during Run one of the LHC
while the the associated production with vector boson and ttH were observed
on the during Run 2. so, the in terms of the decay modes, the b b-bar is the
dominant decay of the Higgs bosons but not the easiest one at the LHC. and, in
fact of the case of in two photons and two Z and even in particular the case
where the Z the decays to four leptons were in fact among the first to be discovered,
despite their low branching ratio, thanks to the good signal to background ratio
together with the WW, which is also the other bosonic channels that contributed to
the first observation of the Higgs boson. at the end of Run two, Run one, the Higgs to tau tau was
also observed, and Higgs to b b-bar was later observed during the Run two of the LHC.
now the the just a small slide on the ATLAS and CMS detector that in particular
during the run one and run two had very good performance and the LHC as well in
fact, already past their design performance in terms of peak luminosity,
as you can see, that LHC already doubled the nominal peak luminosity of 10 to
the 34. and also in terms of number of interaction per bunch crossing. the average
in Run two was 34 compared to the design value of about 23. and that they
delivered luminosity by the accelerator was around 30 inverse femtobarns during Run one
then 160 during Run two. so, quite good performance, I would say.
now discussing the the measurement of the Higgs bosons, I would like to start with
the cross sections one if we believe the Standard Model, there should be about
56,000 Higgs bosons produced per inverse femptobarn for each of the
experiments in each of the interaction point of the LHC and the ATLAS and CMS
experiments can reconstruct about 200 per inverse femtobarn. so the this
allows to make, especially during Run two, precise measurement of the Higgs boson's cross
section. and you have here an example of this measurement by ATLAS, where this is
done by production mode and by in decay channel and you see that several of
these measurements are still limited by statistic which is highlighted by this yellow
band and the table is a is also quote complete. and a way also to make the cross
section to to present the cross sectional measurement was already established
by the during Run one by the first measurements. these are the so called
signal strength which is basically the cross section divide the Standard Model
prediction and you have in this CMS summary a good example of how the
experiment is able to cover very well the the all the production modes and the decay
modes also here the mu mu is a for which we only have upper limits is also
included here. and finally, you have here in in this part, the common signal
strength measurement by the two experiments, the most recent ones. okay,
so, then new somehow measurements are not in any way satisfactory from
several point of view. so, already doing Run one, a new framework was developed
especially for the combination of the measurements by the two experiments and
from different channels. so, this first attempt was the so called Kappa framework,
which is basically modification of the Higgs coupling's vertex at the leading
order, where one can express the production and the decay of the Higgs bosons
in terms of Kappa modificators and then feed these parameters. so, you have here
one of these results by CMS for run two data which were in fact, no undetectable
invisible decays of the Higgs bosons are allowed. so, basically only standard
model, decays to standard model particle, coupling to standard model particles are allowed
here. and you see that the agreement with the Standard Model expressed by the p value
is very high. and also you have in a similar example, by ATLAS of the
measurement of the couplings where here you have three different interpretation in
case of only a coupling to Standard Model and also when you allow Higgs decays
to invisible final states, from Higgs to invisible searches, and also when you allow
modification of the total width of the Higgs, of the Higgs width from off-shell width
measurement searches, and you see, in particular that the Kappa modifiers have a
typical accuracy which is of the order of 10 to 20% for most of these parameters.
now, more recently, a way also to measure the Higgs cross sections and make possible
investigations on the B, beyond Standard Model contributions has been to measure
the Higgs cross section in exclusive fiducial regions of phase space so called bins. so,
under the simplify template cross section. later STXS. so, in these
cases, what happens is that the measurements are done in reconstruction
event categories as you can see on this part of the slide, and then these are
unfolded at particle level in order to couple to the phase space bins that we
want to measure. so, why this is important is because, these definitions are common
between the experiments and the theory. so, this helps, especially in the
combinations and minimize the theoretical uncertainties and improve the experimental
sensitivity to this final state. now, I'd like to present you an example of these
kinds of STXS measurements by ATLAS of a from a measurement that was being released
in April. and you can see for example, in in this plot here, as a function of the
reconstructed event categories here, the purity of the different production mode
bins that we have seen in the previous slides. and in this in this analysis
actually the number of
categories is not particularly high because a neural network is used to to
discriminate the different production modes. and in this particular search as
you can see from the bottom summary, the uncertainties are still dominated by
statistical uncertainties. the the STXS measurements can be done on different
stages from stage 0 to up to stage two. and this particular depending on the number of
bins and the granularity used for the fiducial bins, and you can see that this
result is done in terms of the so called reduced stage one point one. in general, the
agreement with the standard model is good as again shown by the p value of a
standard model agreement. so, finally, a way also to extract information about new
physics, from the Higgs measurements is the possibility to, to use effective field
theories EFT and these allows to interpret the measurements extending the
Standard Model Lagrangian with higher order operators of order six or above. and
this is done for example in the in with the Higgs effective Lagrangian that uses
the strong interaction light Higgs basis. and you have here an example of how the
Wilson's coefficient related to these operators, higher order operators, can modify
simplify template cross sections quite significantly, and that there is also an
alternative let's say EFT model that can be used which is a standard model EFT
based on the Warsaw basis. and this, for example, is in yeah in a show this plot
show an example of how the electroweak Higgs production with two quarks can be
modified in terms of PT of the leading jet by this by the by these higher order operators
action. so, these in fact the STSX and the differential measurements are particularly
interesting for these kind of operations and we are going to see now, some example
of these. the first example is about the measurements coming from the in terms of
Standard Model EFT coming from the Higgs to four leptons measurement that we have
seen before and these he is in these cases the the measurement is not necessarily
sensitive to all the possible operators. therefore, only the Wilson's coefficient
to which the analysis more sensitive are fitted and the others are just set to
nominal zero value. therefore, here you have a an example of the fit where only
the relevant relevant Wilson coefficients are fitted. and then you can see in the
bottom plot the what will be the effect of these operators if they're different from
zero by these quantities. and this depends of course, depending on the category you
can have one operator which is more important than others, and in particular,
the ones that are related to the gluon-gluon fusion are more sensitive to hg coefficient and and
then the ones that for example are in the ttH bin are of course a you are more
sensitive to the couplings to the up type quark. a similar measurement can also be
done from the combination of different from all he combination of the measurement This is
done by this ATLAS result. in this case in terms of the Higgs effective Lagrangian
and therefore a different basis but equivalent and here you can see the
results that are obtained for for these operators again, only the important
the operator which to which analyses are sensitive is are shown. okay, so Now, I
also would like to show you a result from a differential cross sections. and again
we have a new results, which was released in in April by ATLAS. and both
experiment have done measurement in fiducial cross sections defined in terms
of Higgs boson kinematics, jet, multiplicity etc. and the here from from
this ATLAS measurement, you have an example of differential cross sections,
double differential cross section, in terms of the PT Higgs candidate and the number of
jets. so you see here that it's possible not only to make a differential cross sections
in terms of one viable but even more than one. and also in in this case also from an
Higgs to four lepton analysis, you can see instead, the differential cross
sections done in terms of the rapidity distribution of the of the Higgs, which as
you've seen from Sally talk before, is sensitive to the perturbative QCD
prediction.
so, then, another way to exploit the differential measurement is also to try to
set limits on some of the Kappa parameters which are not easy to access directly. one
of these example is the Kappa C so the couplings to the C quark. so this for
example, is an example of how to use the PT Higgs distribution differential
distributions in order to set limits on Kappa C and Kappa B. because these
are two Kappa parameters can modify quite strongly the PT Higgs distribution as
shown in this in this block here. so, therefore, these measurements can can be
constrain can be set under different number of assumptions. here you have one
of these limits, which actually is the most restrictive one that use the largest
number of assumptions, where the modification not only to the shape of the
PT of the Higgs, but also to the branching ratios. coming from these two Kappa parameters
are are exploited and therefore, you have a better limit, but even if we only assume
the modification only to the shape of the PT of the Higgs, still, in this
indirect way we can still put limits on kappa C which is comparable from what
we get from direct searches. okay, so, then there is still one more differential
measurement I would like to talk about which is t CMS measurements from Higgs to WW
in the leptonic final statse where the categories are defined according to this
sub-leading lepton flavor electron or muon and the PT. and in this case the
measurements, the differential measurement, is done in terms of
the PT of the Higgs up to last bin goes above 200 GeV and also number of jets above four
four jets and then you see that the uncertainty on the fiducial cross section
is of the order of 20 percent and on the last the bin the the limitation is still
mostly statistics, but still we are getting we are getting there
okay now,
I will discuss a bit more the Yukawa couplings. that as I said before is a
new kind of introduction that can can reveal a novel feature which are not seen
in gauge boson interaction and therefore, is something that is been
receiving a lot of attention in the Higgs measurements. the first one will be the
discusses the Higgs tau tau where we have the latest Higgs ATLAS analysis in the Higgs tau tau
final state where six channels are analyzed and the cross section is obtained
from the fit of the di-tau invariant mass. and you see that this result has been
interpreted also in terms of simplified template cross sections for gluon-gluon fusion and
VBF. and in particular for the VBF production model. this channel is
particularly important thanks to its sensitivity. CMS has also shown the
results which also include more data than the ATLAS up to 2017. and in this
case four channels has been analyzed and the Z tau tau is modeled in a data driven
way. and instead of the m tau tau fit the the cross section is extracted from the neural
network distribution from a neural network distributions. in this case CMS provided a
stage one simplified template cross sections for these channels. and you can
see here the bins in terms, for gluon-gluon fusion , in term of PT Higgs and for VBF
terms of VBF topology and etc. alright, so, the other fermionic final state is the
the Higgs decaying to b quarks and the here they in order to reduce the
background, usually they associated production with a vector boson is
exploited. and you see a recent results by ATLAS from this year where in fact the
exploits a large number of signal regions and the control regions with a different
charged leptons multiplicity in order to be sensitive to several final states and
also a dedicated b-jet algorithm is used in order to improve the b b-bar mass
resolutions. in particular the these dedicated energy recalibration
algorithm improves by more than 40% the b b-bar mass resolution with respect to the
standard jet calibration case. and the in this case of a simplified template cross
section is provided in terms of the vector boson PT from in two bins from
150 to 250 and above 250. and this analysis is also quite sensitive to
the these two production modes as you can see that in fact can achieve the
observation of the ZH production with more five sigma significance and also in the
case of WH it gets it achieves a very strong evidence of a four sigma. so, now we'd
like to discuss also a different way to also target the Higgs to b b-bar decay,
which is to look for, instead of resolving the, the, the jet from the b quark
from the Higgs decay, reconstructing a large R parameter Jets and
then look inside of it for the signature of it two b jets. so this is done by ATLAS
and CMS with a slightly different target in the case of ATLAS the target
production mode is VH. like in the previous case, and the PT of the Jets has
to be above 250 GeV. and you see [Chair: Luca
you have just under five minutes.]
Yes, thanks. and you can see here that allows to give to achieve to extend their
sensitivity in PT up to 400 up to 400 GeV. in the case of CMS, this is an inclusive
search so mainly for targeting gluon-gluon fusions, and here the PT
requirement of the jet is 450 GeV . but in and in this case CMS also try
first attempt of differential cross section for the PT Higgs in this in this final
state. and as again as you have seen from Sally talk before, this can be quite
interesting in the future because while at low PT we are sensitive to the gluon-gluon fusion
when we go after these bin of large PT we start to be sensitive also not only to
gluon-gluon fusion but also to other production modes and therefore is this
become quite interesting.
okay, I just have one slide here about ttH for completeness, but I'm going to discuss
more about these production more later, I just want to say that for this for the for
this production model, that is from which we can extract the Higgs to top
couplings directly, we are exploiting several decay modes of the
of the top anti top as well as Higgs decay modes. as you can see from this
table from ATLAS and and CMS. so, now I will talk about the properties. so the
first property I talk about is the Higgs mass measurements. and the Higgs mass is
you know, is a question of the naturalness of the Standard Model, since these
are the the basis of the so called hierarchy problem but it's also an important
parameter for the what concern of the importing agreement for the electroweak
fits. and also for the understanding of the stability of the vacuum as well as to
understand if the Higgs has a role as inflaton candidates. at LHC the
measurement is performed in the two photons and four leptons final states because they
have by far the best resolution and remind you that at the end of Run one, the
combination measurements of the two experiments had a precision of 240
MeV. so I want to now to show you a new measurement by ATLAS that improves the
techniques used previously by relying on event by event resolution method instead of
average resolution. and also use a kinematic fit by constraining the invariant mass of the
leading lepton pairs to the Z mass in order to improve the precisions and use a
double sided crystal ball to fit the signal, as you can see here. so, this is
result is summarized in this table, and is a still limited by far by Statistics
uncertainty in all the channels. and but I would like to point out that the systematic
uncertainty on this measurement is quite low is only 90 MeV and 60 minus 60 MeV,
which is mainly coming from the muon momentum scale. and also CMS has recently
provided a Higgs mass measurement, this time on the di-photon using the di-photon
channel with 36 inverse femtobarn of data and it's both in several categories. and
in these cases, the signal is modeled with a sum of up to four Gaussian
function depending on the actual category and by itself this measurement has an
accuracy of 260 MeV, but when it is combined with the Run one CMS result, it
achieve a total uncertainty of 140 MeV, Which is a very low is only about one point one
per mill uncertainty. okay the last topic I'm going to talk about is the spin achieve a total uncertainty of 140 MeV, Which is a very low is only about one point one
per mill uncertainty. okay the last topic I'm going to talk about is the spin
CP of the Higgs boson which, as you know, the prediction on the standard model is
that the Higgs boson is a 0 plus plus state and that already during Run one
the coupling to the vector boson has been studied at length, where the zero plus
state was favored with respect to different alternatives, but anyway is
true that the Higgs to fermions couplings can also give us some more hints
because in this case, the CP odd contribution can be on the same level of
the CP even ones while in the case of the vector boson couplings are suppressed by
the scale of new physics to the second power to the Second power. so, now, just
to finish the results from the two experiments, which are done in the ttH
where the Higgs decay to the photons final state. both results are very new coming
out came out in in March for CMS and April for ATLAS. and this result is a
basically the parameter of interest is a is there a difference between different
definition by to explain, but they are equivalent in the case of ATLAS is the
alpha angle here which 90 degrees is a full is a complete the CP odd state and
in the case of a CMS instead the Kappa T tilda parameters is used and in
particular, this is used to define the fractional CP even contribution FCP. that is
fitted here. so, Kappa T tilda 00 will be the Standard Model. okay, so here they
in both cases the m gamma gamma is fitted in all categories and this is a
summary of the results where both experiments can have excluded the pure CP odd
couplings with more than three sigma 3.9 for ATLAS and 3.2 for CMS. and also,
in the the case of ATLAS a fit of tH to ttH fraction has been performed or
giving a limit of 12 times standard model on the single [Chair: Luca your
time is up.]
yeah. and last slide. so just to conclude the, also ATLAS has a sensitivity to the
Kappa T cosine of alpha sign and the combining with the with the combination of
the Higgs measurements. and and then I would like just to give you the summary,
saying that thanks to the outstanding performance of the LHC and experiments we
run two, was possible to improve significantly our understanding of the
Higgs bosons both in terms of production mode and as well as a CP structure and the
Mass measurements and that run three and run in the future run four etc.
looks bright, as you can see from these projections by the two experiments. thank
you.
Chair: great, thanks a lot Luca
any questions?
please, if you have any questions, feel free to raise your hand.
all right. if not, then I had one. back when you were talking about the EFT
interpretations. I was trying to sort of understand the differences between the
ATLAS and the CMS results that you showed. in particular, like trying to compare I was
looking at hw and noticing that it seems that there was quite different precision.
but you mentioned that these were coming from two quite different analyses. could
you say a little bit more about the differences.
the slide was Let me just get the number it was slide 15.
Luca: yeah, unfortunately, okay with the full screen mode. I think I'm a bit lost with a
slide. but , I think the point is that one has to realize that this
were done under the different bases. so in one case, it was a SM EFT. and the
other case was the Higgs effective Lagrangian, therefore, the parameters don't have the
same meaning. so they are not directly comparable, let's say
in [chair: Okay], so,
yeah. Chair: so that's the main reason now, I was just noticing that you had the comment
that there was some strong anti correlation from the inputs in the CMS
case. but I guess it's really the differed basis that are making the main
differences.
Person: then you're also
comparing I mean, the one on the right is from a combination of all the channels
where the one on the left is essentially
only ZZ four leptons. so
Luca: yes, they in the case of the let's say, on the left, you are mainly sensitive to the
Higgs to ZZ. therefore, here you have a strong Let's say sensitivity to the b, which
is basically the the gauge field rate to the close more closely related, let's say
to the Z. while instead yeah, the CMS case you have the combination This is coming
from the combination of the channels, therefore, you have a more complete view a
complete pictures of the couplings. yeah.
Chair: Okay, thanks. other questions?
I see two hands are up. but somehow, okay, I'm Michael spirit. you want to go ahead.
Michael: okay, because it was, I'm not really sure if I got it right. for the determination
of Kappa C for the charm Yukawa coupling , do you extract it from the
gluon fusion cross section or from c c-bar to Higgs.
Luca: in, well, this limit is extracted from the differential measurements from
the PT Higgs. but, this also includes somehow the effect of the modification not
only to the spectrum, but also to the branching ratios. therefore, has a bit more
of assumption in the big Kappa, have somehow the limits when instead you
only consider the, the, the limit from the, from the, from the shape. now, I'm
sorry, I'm a bit slow moving through slides, but they maybe can jump quickly to
to these results, just to show you.
oops, I think I went too much.
okay, looks like I'm a bit
a bit slow with moving through the slide. so, but
Michael: because the real reason why I'm asking is that I don't understand why the fit is
symmetric for positive negative Kappa C
Luca: well yeah the fit is indeed quite symmetric Now the about the sign I
Well, I mean it's symmetric in the sense that there is no sensitive to the to the
sign Yeah. yes I think only because enter quadratically it only enters
quadratically in the fit.
Michael: yeah, but then of course, this cannot be the gluon fusion. this because this must
be done with c c-bar to HIggs.
Luca: well, these are these also there is also Yeah, okay. there are also box of course
there is a box contribution as well. you have to consider this also is very
sensitive to the Higgs plus jet diagram. Yeah, which is, let's say, box related. so yeah,
it's not only
Michael: but again in the gluon fusion.
Luca: yeah, mainly I would say gluon fusion.
Michael: I'll bet you are fitting an interference term basically, which is sensitive to the sign. Luca: yeah, mainly I would say gluon fusion.
Michael: I'll bet you are fitting an interference term basically, which is sensitive to the sign.
Luca: okay, on this, maybe somebody can answer better than me. I'm, I'm really not expert
only tell you about the if the interference is a [] or not
Michael: because that's one of the deeper reasons of my question that I don't understand.
Then I don't understand this fit is symmetric with respect to the sign if this
is coming from the gluon field. so this must be coming from cc bar to Higgs
plus jets.
then it's quadratic.
Luca: well, I'm sure that all the contributions are considering here. I am pretty sure
that the gluon gluon fusion is one of the main ones to be honest.
Michael: but then it must be asymmetric because then it's sensitive to the sign.
Chair: I think Karsten might want to answer
perhaps
maybe he can't unmute
Luca: mean I know that the the limit Karsten: now I can
[several people at once]
Chair: yeah perfect Go ahead.
Karsten: so, the charm charm to Higgs is is included here. so this is really the using the
fully unfolded kinematic PT Higgs distribution or PT four lepton I should say, but the
thing is
due to low
resolution we had a have a rather large bin from zero to 10 GeV. if you go back to
your original slides you see from like the theory plot that a large fraction of the
sensitivity comes even if you would split it even further from zero to
five and five to 10 however, we didn't have the experimental statistics and
resolution to do that. so so this is something maybe for the future or for
gamma gamma channels and these kind of things. so in that sense it's it's all
included here, but yeah, we use We only have a certain sensitivity with the
current statistics.
Michael: because it is also interesting because in the plots on the upper right, you'll see
if you are comparing the green with the red curve that you are indeed sensitive
to the sign.
Karsten: yes, but that's exactly the issue here and if you look at the upper right, the the
main sensitivity from the sign is from if you compare zero to five and five and
above GeV in PT Higgs. and exactly what we are watching out by because we integrate from
zero to 10. because the limit limited statistics and resolution in this and here
the gamma gamma channel and if you try with a combination and also with a
combination with CMS can help if we, if we make this experimental binning finer
here, we will have still quite experimental anti correlations between
those but hopefully it's good enough to make a better statement.
Chair: okay, I think let's leave the rest of this. discussion for the coffee break. I
think there was another question from Makkah. scalia. you want to go ahead?
Makkah: hello, if you could go on page 26
Okay, so so so I guess that the mass age pole and the mass top pole is different to the
experimental measurement it means that probably you are doing some additional
treatment and so the question is, when will theorist update this kind of plot with
the most recent one
Luca: Okay, I think this is not a question for me, but maybe it's an open question for
the theory at least in the in the room. what we know well the difference between
the top pole and the so called Monte Carlo, experimental top mass. okay, a I leave it
any experimenters want to take this question. I will leave it to you
them.
any theoretists
Chair: I don't see any hands.
Chair: spira you'd like to take the question?
Michael: I think that impossible this issue is related to the because this related
to the final fit of consistent top quark mass and this is an enterprise that's now
starting from the experimental side, because I think what you really have to do
it this is one of the possible ways to fit the msbar top mass, or it was some consistent
definition of the top quark mass and this is now starting. the Higgs mass itself doesn't
play such a big role. but of course, I agree that the fit of the value of the
top quark mass really is crucial here. and the first fits of as far as I remember is []
consistent top quark mass are pointing towards the point that this ellipse moves
a little bit more towards the absolute stability region but it's really in the
vicinity of the border between absolute stability and meta stability.
Chair: thank you Okay.