C520: Is it gonna record?
C520: Yes, alright. Good.
C520: thanks. Dave, good morning.
C520: Oh, and it's, because of morning cornes
C520: in the meeting yeah, meetings. Now by your messaging.
C520: It's fine.
C520: Right?
C520: It's okay.
C520: Hey? Good morning.
C520: It. Let me see.
C520: Yeah, it's a bifocal crisis. Yeah.
C520: it's nice. I don't need it too crazy.
C520: Oh, yeah. So then we just need yeah.
C520: there we go.
C520: Hey?
C520: Alright, thanks very much. Come to exam. I'm really excited since I met Haran in 2019 for this moment, and has been one of the promising students that been working for many years. And
C520: but well, we really depend
C520: heavy how we start and working on the Phd. Unfortunately, we experience COVID-19. And this did bring quite a few unexpected the arrangement in between.
C520: That's why I really really appreciate that, carry things along and finish several different projects and come to the today. And we will hear
C520: 2 of the selected, the studies from our end and hopefully, that you can learn about what's the journey of the
C520: his research in a with a particular path. But maybe there's more than one Hicks. Right? So thanks for the nice introduction. And do you want to remove the oh, yeah, you can hide
C520: and thank you everyone for make it to attending my final exam. So you know, this is a heavy snow, and there's a Chinese coast like heavy snow. Predictable. 2025. Okay? So without further ado. Let's get started. Okay? So today, my talk will be around the Higgs search with the.
C520: So
C520: so here's how the story starts in back into 2022. I was searching for this topic, but that year it was just the 10th anniversary of the Higgs discovery and people. There are lots of talking about the Higgs, and also the discovery. And then I was just like, Why don't I choose this search for join? The effort to search for new new Higgs particles. And then
C520: this led me to an interest analysis. And today I will get you through this analysis and show you what we've uncovered.
C520: Okay, so here, this is the offline of this talk. I will introduce a lot of the background knowledge to get you started in the 1st part, and then presenting to individual search, and then my contributions as your combination and also improvement.
C520: So first, st that is about theory and the experimental setup. So humanity's understanding of the
C520: fundamental building blocks has evolved over time. So initially, we thought the atomics were indivisible, and then we discovered the atom nuclear, followed by neutrons and protons. And now, finally, eventually, we delved into this subatomic scale, which is like less than 10 to negative 15 meters.
C520: and in this scale the gluons and quarks and electrons make up the visual universe.
C520: and but there are even more types of elementary particles, and they can be described by the standard model of Higgs. So, as you can see, this is a theory up to now, and we have 2 types of particles, fermions, and the Bosons. The fermions are the Constitution particles, and they are spin one half particles. They can be further divided into quarks in orange here, and leptons in green
C520: on the right table. They are bosons. They they are responsible for the interaction.
C520: For example, the glongs
C520: mediate the strong force, the photons mediate electromagnetic force, and the Wz Bosons mediate the weak force. And of course we have this Higgs boson, which is essential to give other particles mass, and together this table summarized all the known particles in an elegant way, and it does explain a lot of phenomena.
C520: But this is not the ultimate theory. For example, the standard model of Higgs Field. It is just the simplest version right now, and it's just the complex doublets. And there is only one neutral Higgs boson predicted. Well, this theory. It does explain some of the math, but it
C520: doesn't explain everything. For example, the neutrino Mass. Where does neutrino mass come from?
C520: That's why people are interested in the extensions to this, then model a sector. So first, st there is no theoretical restrictions for stopping us from adding more and more sectors. And but
C520: another thing is, that if we, for example, we can add more extension, for example, if we add a contract to the model, etc. We can find a way to expand the neutrino mass.
C520: What is more exciting is that introduce this more extension usually will predict more Higgs. If we can find any types of Higgs other than this neutral one that would be a huge sign for physics, we understand model.
C520: So the theoretical model we are talking about today is called Georgia model, or the Jm. Model. So this time talk about its main features.
C520: So this model extends the standard model, except there with 2 additional triplets, one complex triplet, and a real triplet.
C520: So in the standard model does that the Higgs sector is represented by the doublet, where there are 4 degree of freedoms, and with this extension. We have
C520: 9 degrees of extra 9 degree of freedoms. And one key of this GM. Model is that it can preserve the unity of electric load parameter at tree level.
C520: This is the very advantage. So the electric low parameter is defined as MW. Squared over Mz. Squared, cosine squared. It is the relative. It is the relative strength of charge, the current over the neutral current, and experimentally it is measured to be very close to one, and the
C520: there are many other types of extension to the peak sector. They usually they they don't. They violate this relation here. So there will be further fine tuning problems. But the scale model like this relation is kept is satisfied automatically.
C520: and what is more interesting experimentally say is that it predicts other types of charged Higgs with a clear signature. And this is very interesting for experimenters. So we'll go through this later. So I will start with this motivation of introducing 2 Triplet. So if we just introduce a complex triplet, which is this Chi, this can generate the neutrino mass.
C520: But this triplet contributes more mass to the Z boson than that to the W. Boson. So in this row parameter, this
C520: because I sorry this Chi fields will make this row less than one.
C520: so this will break the condition we have.
C520: But if we add another real complexity, and this field only contributes to the W mass, which is the numerator here, so so we can find a way to
C520: introduce these 2 triplets simultaneously altogether, to keep to keep the balance, to keep rho equal to one. And here is here is some more math derivative. So W. And Z. Mass, they are coming from the connected kinetic Liberation terms, and with the introduction of
C520: the place they can express the now in terms of vacuum expectation values. We can see MW. Received contributions from
C520: because
C520: vacancy and the weight. Chi, while this MW. Just became mass from weight. Chi squared. So if we put them together.
C520: this is the expression for low parameter, and we can see if we set the C equal to big Chi. This numerator will be identical to the denominator, so so low equals one automatically and the
C520: experimentally, we have a constraint to the total valve, and it is measured to be 246 gev. So we have this condition here.
C520: and hence we can introduce a very important parameter in this model which is called sine Theta H, which is the fraction of contributed by the triplet.
C520: It's our 1st K Browser.
C520: and then let's take a look at the physics, spectrum after symmetry breaking. So the 1st row is the standard model Higgs. We have 4 degree of freedoms, and the 3 of them are eaten by the golden stained bosons.
C520: That's why they gain mass, and leaving one neutral particle for the doublets for the triplet field, and they transfer as a singlet as a triplet plus a doublet we can see in this tablet we have double charged. This is experimentally interesting.
C520: So we'll focus on this calculate later.
C520: So the feature of this double plate is so. First, st all of these Bosons share the same mass in this bell plate, and second, if we write this state, we can see there is no doublet. Contribution to this bell plate states. That means this bell plate is fermirophobic. That means it does not decay to fermions.
C520: So this makes another unique features of this model. That means the production of this through this vector boson. So vector boson fusion. And we have another.
C520: we set up a framework called the H. 5 Plan, which set which fixed several parameters to make this model easier to be searched experimentally. So in this benchmark scenario we assume the triplet mass is greater than the 5 plate mass, so the decay from H. 5 to H. 3 is totally forbidden.
C520: and in the in this case, H, 5, only coupled to 2 vector bosons at around a hundred percent branching ratio. So the production of H 5 is through the vector boson fusion. So we have 2 incoming quarks. And then they
C520: exchange virtual vector, bosons to form to
C520: the 2 vector Bosons fuse into H 5 doubly charged or singly charged. And then the charger Higgs decay back to the vector, bosons. Well, the original parts, like they're flying away with large angular separation. And they are very high energy. So this is the Bbf signature. This is very helpful for experimental search.
C520: And again, we have 2 free parameters. Here we have the degenerate degenerative State, Mass. M. 5, and also the Sh. The fraction of this triplet of contribution to the total
C520: but the W. And Z. They are not the final state. We can search experimentally. The W. Has a branching ratio of 30% to decay to a lepton plus a neutrino, and the Z. Boson has a branching ratio to decay to a pair of lepton with 10%.
C520: So we are experimenting. We are very interested in the electronic decays because they're they provide a great signal sensitivity.
C520: So again, this is a summary of the final state. So in both 5 doublet and the single charged Higgs production there will be associated with typology, which means 2 forward energetic quarks, and the 2 the doublet charged Higgs has decay to same sign, Ww. Boson, and then followed by the decay to the same sign, Leptons
C520: and the singly charged heats will decay to a W. And the final state is at 3 3 Leptons. We also have a missing transverse energy representing the neutrino.
C520: We will talk about this later.
C520: Okay, so now we're transferring to this experimental part. So the facility we are using to search for charger. Higgs is called Large Hagen Collider. It is the most. It's largest and the most energetic particle accelerator in the world.
C520: It is located in the border of Switzerland and France. It's very long, with a diameter of 8.5 k kilometers, and it's underground around 200 meters. There are 4 main detectors at Hc. And the Uw. Our team is working on this one called Atlas.
C520: And let's take a look. What happened in the collider. So we have a lots of protons. They are divided into the 3,300 bunches, and each space that 7.5 meters, and each
C520: bunch contains like 10 to 11 protons. That's a lot.
C520: And they are accelerating in opposite direction to very high energy, and each bound carry 6.5 TV. So the collision energies is 13 TV in this
C520: high energy environment, new particles will be created. And and we call each collision an event. And the address detector collects this event for physics. Analysis.
C520: Okay.
C520: okay, now, we turn to the act as detector part. So it is a very huge one. It's 44 meters long and 25 meters high. It's designed to search a lot. A wide range of physics, including for search for particles beyond the standard model and it it contains a lot of self detectors.
C520: Sorry. Here we have a lots of sub detectors, and our UN team is contributing to this forward neuro chambers.
C520: or or in this picture we designed and manufactured 1 3rd of this 4 of these tubes, and they are a example here at the Uw. And then shipped to cern. We also contributed to the insertable V layer. And now we are working on the the inner track tracking detector for the lc. For the atas upgrade.
C520: Oh, this is the coordinates used in the in Atlas, so the Z axis is the beam direction and the the origin of the ordination coordinates is the interaction point is nominal collision points.
C520: and we have transverse plan that is perpendicular to the z axis longitudinally, or or on the Z axis. We use another quantity called pseudorapidity, to represent this longitudinal behavior. So it's a function of the polar angle.
C520: and the when it corresponds to the data of 90 degree, which is the transfer transfers plan here, and the forward region means the higher iteration.
C520: Okay, now we turn to how this access detector recognize particles. So there are 2 principles like
C520: 1st wise. Only the stable particles can be captured by the detector, and it is through this stable particles that we infer the physics process happen
C520: in the middle. We have a layout of Atlas detector from innermost to out. We have tracking system which record the charge. The heats sorry charge the particle trajectory, and then we have electromagnetic calorimeter. It stops photons and the electrons to measure their energy, and then we have hydronic calorimeter. It can stop
C520: protons and neutrons to to measure the energies and also have a muon spectrometer is specially designed for neurons, because this red this yellow line
C520: can penetrate. This means can penetrate all the layers before
C520: and on the right. It shows the signature of this, this particles in in the real assets detector.
C520: We have to
C520: 2 signature left, and we'll move on to them. So the 1st is the jet. Another one is neutrino.
C520: So the jet is are the signature of the box and the glass. A jet is basically a bunch of particles that are flying in roughly the same direction. This is because of the color confinement and the quark and carry color charge.
C520: so they cannot exist freely in nature. Instead, they need to form stable and color neutral particles before reaching the detector
C520: and the.
C520: and in this illustration, quantum, it can form, like other hadrons, like pion, and the chaos and pion chaos, they'll deposit the most of energy into a hydron-hydronic calorimeter, and this is the signature of the quantum.
C520: Another object is the neutrino, so neutrino is invisible to the detector. It does not interact.
C520: almost. It doesn't interact with the detector. And we but we can figure out its presence by the conservation law of the transverse momentum. So before and after the transverse before and after the collision, the transverse plan, momentum sum to 0. If we sum up all the visible objects here, and we can infer the momentum transverse momentum of the neutrino.
C520: Okay, so so now, I'm showing an event display of rotation. Here we can see this 2 blue coin that are representing the jet. This is, they have very large separation. Very likely they are from the Vpf technology. And this tower staff.
C520: as you can see, it, shows some tracks here. And also it stopped in this em call. So it's a electron, and this red line. It penetrates all the layers. So it's a muon. And in the transfers plan, actually, there is, there is some dash line.
C520: It's a bit invasive audio to the curtain. But okay, so that is the signature of the neutrino. So in summary, this event represent a collision that's a Www.
C520: Production, and the to a pair for to a laptop and a neutrino.
C520: I also want to talk about about the data analysis here, so I'll go through the the real condition and the information are collected by detector.
C520: And we have another branch from a theoretical part we can model, or we can simulate the so cohesion
C520: through the Monte Carlo techniques. So first, st we have for this matrix and the calculation, it predicts how the particle interact with each other. And then we can simulate the python shower and hydronization procedure where can belong form jet.
C520: And this detected simulation mimic the detector response to to the particles. And then these 2 branch goes through the same event. Selection. At this step the electronic signals are converted to physics. Analysis, object.
C520: then we development selection strategies to to keep more single events while removing the background noise. And finally, we can do statistical interpretation between data and our theory to draw some conclusions.
C520: So let's look at the final part here because the rest of the talk is related.
C520: So
C520: there's 1 physics entity. We are interested. That is called Cross Section. It is a measurement of probability that a certain physics process occurs.
C520: and experimentally it can be measured as the number of observed events minus the number of the background events, and then over the luminosity, acceptance and the efficiency. So luminosity is a amount of
C520: collisions basically. And the acceptance refers to the detector geometry coverage and the efficiency includes the factors, like detector selection, efficiency, the reconstruction, efficiency, etcetera.
C520: And then we can do some feeding on it. The feeding procedure is to is to extract the the information on on the cross section. So we do. Maximum likelihood explanation on some likelihood function. It is the parameter. Here is the mu and the data given some
C520: collision collision events. So mu is the parameter of interest. It is the single strength defined as the measure. The cross section over some standard model prediction cross section.
C520: and we also have other, a lot of systematic uncertainty. They will be included in this nuisance. Parameters. Data, when doing, fitting this nuisance parameter is not our interest. But we also need to de-term the values of this.
C520: So typically likelihood function can be right in this way. It's a accumulated of a sound distribution, and the the event is associated to the event. Rate. Lambda here, and lambda is a function of the signal strength, and as well as the nuisance parameter.
C520: and we also, we constrain this nuisance parameter through measurements, and usually we use Gaussian to constrain this nuisance parameter.
C520: and on the right is a histogram I want to show. So so the basic process is that
C520: of the fitting is we adjust the the backgrounds and the signals to to make it match to the data here, and then we get information of the signal strength. We can interpret it into terms of cross action, and it's related to the model parameters.
C520: Let's take a look at the typical outcome of the new physics. Search either we find it or we cannot find it. So to clearly find it, we perform a discovery test. It is usually associated with this P. Value, which is, means the
C520: which means the on this, no hypothesis that mean no signal present. The the fluctuation is pro is caused by the background, the fluctuation that is defined as the P. Value. The smaller this value we, the more likely we can reject the background background. Only hypothesis.
C520: Usually we define like 5 sigma. It's like 3 times 10 to negative 7, probability
C520: to to claim a discovery if we don't find significant process. Instead, we said, it's put a limit on it.
C520: This bottom plot shows we set a confidence level of 95 on the mass, on the signal strength as a function of mass. Hicks.
C520: And we can see, for example, the mass of 1 5,001 50 gb, the upper limit is point 3. That means the the
C520: the range above this point 3 are excluded for this price point.
C520: Okay, so after this all the basic stuff? Oh, now we can go to the search for W. Chart takes.
C520: I would like to talk about this event is the action procedure and also the background. This is essential for our feeding. So first, st
C520: the main background for this.
C520: for for this double H is the standard model background that's sharing the same final state.
C520: So typical. Spiderman diagrams are shown here. The left one is the standard model Ew. Production.
C520: It shows Ww scatter process and the red plot is the Qcd. Procedure of this, since I Ww. Process, because they're sharing the same final state, and they are called irreducible background.
C520: There the dominant background is accounting for 60% of the total background. But we also have some reducible background. For example, this nonprofit background. It can be reduced a lot.
C520: So the non prompt background means that the they are coming from second-secondary decays of other particles, or they are from the jet freaking laptops. Usually we apply some selection on the laptops in terms of isolation. Criteria, for example, and also some geometrical restriction to remove the non prompts
C520: for this failure on background.
C520: That means a pair of laptop, that, coming from virtual photon or Z. Boson, created from a pair of quark annihilation.
C520: and we can reduce this background by applying some lower mass cuts in this date, left some environments
C520: distribution and also exclude this. Win this window around the
C520: then next we have this wz background. It's it's just the 3 3 laptop in the final state. And if we ask to battle the 3rd laptop, we can reduce this background.
C520: We also have this background related to the top process. One signature of top decay is the B park, and we can do some B tagging techniques, and then better the speed tag to suppress such a background.
C520: Now let's take a look at the distribution of different samples in in this singular region. That means, after we apply in the signal selection criteria. The X-axis is the transverse mass. It is defined as a function of mass and the transverse
C520: activities.
C520: So the wise is the top bottom. The top panel is the distribution, and the bottom is the data over prediction. So from the top panel we can see there is some
C520: access around this 300 Gv. That could potentially mean some new physics. And we can also see the dominant background is the that same side Wwg process from send model as well as the red W. Process.
C520: Oh, I forgot to mention that we also shown some potential signal here which can kind of account for this discrepancy.
C520: Okay, so better constrain the background of this
C520: blue histogram and the red histograms. We further define 2 control regions to
C520: to help us distinguish or model this dominant background. In the signal region we have a Sims and Ww. Control region, and also a Wcd. Region.
C520: They are categorized by number of Leptons and the jet mass.
C520: and the single region is for the digital mask.
C520: In this range, 500 to 3,000 employees.
C520: and the the control region of Ww. Is in 200 500 Gb. Edge.
C520: and then we can take a look, the final state or the results fitting results. So we don't observe significant access. So instead, we set some exclusion upper limit on the parameters as a function
C520: mass of H. 5.
C520: So left subst is the upper limit of the cross section times the branching ratio.
C520: And there's a lot of information going out here. So so this that's the line is to observe the upper limit at 95% confidence level. And this
C520: blue dashed line is the expected upper limit with the uncertainty band in green and yellow. So anything above this black solid line can be excluded.
C520: and on the right side it is a model parameter as a function of Mh. 5, and the again the region above the solid line is excluded. That means the range of point 11 to point 42,
C520: and even though we don't find anything significant, we can still get some conclusion that the viable parameter space that is below this regions, and this can be improved by further analysis. Improvement.
C520: Okay? And then, now we turn to this single, each one his boson search.
C520: So this, this even selection is different from that in the same value channel. Here, instead of use the traditional car based method I've gone through just in last section. Here we design a neural network to help us identify a single event.
C520: So the signal events are the charge hits in the jam model
C520: and the background events we use are the main backgrounds. They are the deposit process from standard model.
C520: So the architecture of the neural network is given below. We have 8 into the features, and we have 2 layers of narrow layers of neurons, and each with 45 neurons, and finally, we out to the score for for each event.
C520: And the this is the score distribution. We can see if the the score is closer to one. It means that events is more single signal like, and it's if it is closer to 0, it means it's background like.
C520: And then we can give a a cut based on this and score to define the signal region and the control region.
C520: and we can see the Dom. In the background are the established process in the screen.
C520: So we so it's better to use a control region to con to constrain the background in the single region.
C520: We also have another control reason called the Dz region, because you can have 4 laptops in the final state, and if if one laptop is missing or out of detector range. This will be very like to our signal
C520: so we use this DC control region to help us constrain this background.
C520: This is the fitting results, and we can see
C520: there is a small access around this 355 Gb. And also but it is not significant enough to claim for discovery or evidence and uplimit are set.
C520: And to from this analysis we can exclude the parameter space of point 3.
C520: So then, let's talk about this contribution I have presented to individual search for this chart of Higgs, and they are all coming from the same theoretical model. Then can we set up some better constraint by
C520: combining these 2 analysis. This is the idea of this. And then I implemented this feasibility study of combination. Basically, if we put 2 upper limit, plot side by side. We can see first, st their exclusion. Lower limits are on the same level. They are both in this point 2 2.3 ranges.
C520: and also we can see small access around this 400 Gb, so this combination is doable.
C520: and we expect to set tighter constraints on this model.
C520: But
C520: to do so we need to ensure there is no event double counting in into analysis. That means we don't want to use some events twice
C520: if we look at the control region, definitions in between channels, the left one channel, the driver is the W. Channel. We can see when
C520: number of laptop equals 3. This wz control region is overlapping with that in the Wz channel, and we decide to drop this Wz control region. And this is the only way to do so, because if we do it the other way around, if we drop this control region.
C520: this control region is A. Since then Ww. Is still overlaps with- with the Wz signal region here. So this is the only choice.
C520: and then we also need to consider the system systematic uncertainty correlation. So usually when
C520: performing this statistical interpretation, or inter
C520: to take into account of the uncertainties, and we can separate all the uncertainties. There are 2 types of uncertainties. One is the statistical uncertainty, another is systematic uncertainty. So statistic uncertainty comes from the nature randomness of the incoherent, inherent random
C520: process, and it usually goes usually decrease with more data, decrease at one over square root of N equal. A single process of collisions, and the systematic uncertainty can be further divided into experimental uncertainty and the theoretical uncertainty, experimental uncertainty there. And they're associated with the measurement process
C520: and also some object identification method like Jack and Laptop and the luminosity is a typical example of the measurement process, and we also have this theoretical uncertainty. They are associated with the assumptions in the theoretical models
C520: like when generating the Monte Carlo simulation. We assume several parameters, and that comes with uncertainties.
C520: And the goal of this combination is that we want to put this 2 individual fitting into a more big fitting and together. And so we can better constrain the jam model. But we need to handle the systematic uncertainty scheme in the fitting set up.
C520: So for this experimental uncertainty, the default, the default choice is to correlate them because they usually come from the same source. For example, the luminosity measurements, because luminosity can impact the 2. Analysis in the same way, by the number of position we collected. And there's a way that
C520: this is the common source, and we should correlate it
C520: for the theoretical uncertainty. The default.
C520: A choice is to unpard them, because they usually probe different face of theory, and one exception is the sentiment. One exception is general model, because they are all coming from the same theoretical framework.
C520: But I would like to emphasize that the combination, the sensitivity, is limited by the statistical uncertainties on this plot. I'm demonstrating this. The Y-axis is the absolute relative difference. It is basically defined as the full setting up
C520: minus the statistics, static sticks, only fitting over the full fitting out. So the numerator is just the the impact of the systematic uncertainty.
C520: and we can see here are 3 lines.
C520: The red is the Wz channel, and the blue line is the since channel and the only the Wz channel is
C520: impacted by this nuisance parameter or systematic uncertainty. A lot up to today, it's around like 7%. But one combination is up to 5% of impact of this systematic uncertainty. So our combination is impact mainly by the statistical uncertainty.
C520: This is the fitting setting up of the combination. And we use some software in address, and the 2 sets of inputs from individual search are used to set up the fitting, and we have 2 single regions of single charge, Hicks and Double charged Hicks, and we have 3 control regions with their own normalization factor to constrain the contributions from.
C520: So all the background in this.
C520: from the control region to the single region, and the multi feed function is used to combine these 2 workspace.
C520: So first, st we perform this discovery, significance test.
C520: And this plot shows the local P value as a function of of Mh, 5, we can see 3 lines and red, and the blue lines are individual search, and the combination is the black line. We can see
C520: the local, the largest. The local significance occurs at 375 Gb. And it co-, it corresponds to a global significance of 2.5 sigma, after correcting the look elsewhere effect.
C520: So this is not significant. Okay, any discovery. And we said, include the upper limit on on the model parameter.
C520: This plot shows the
C520: upper limit on site data H, as a function of Mh. 5. There are 6 lines here set can be grouped into 3 sets, so combination in black, and the wz individual channel in red and the blue we can see in the lower mass of 5
C520: the blue dashed line is always smaller than the red dashed line. That means the Simpson Ww. Process is dominant in in the low low Mass range.
C520: and the the combination is in this black line, so we can see the upper range there included.
C520: And if we compare this, dash the blue line with either of the red or blue dashed line, we can draw a conclusion that improvement is around 10 to 26% depending on different mass points.
C520: We also compare our results from others with the Cms. And we draw conclusion that our fitting is more stringent because it shows a lower upper limit on site data age.
C520: This is due to in our combination. We have.
C520: we have used the W channel, and also we have dedicated control regions to constrain the background in the singular region. Thus it has a better sensitivity.
C520: Now let's move to the last part. This is improvement can be done in this analysis
C520: especially, it's a Sims and Ww. Channel.
C520: So, as you may notice, the current is given set period in the same time that the double channel is just traditional code based method. But we use the in the Double Z channel.
C520: So we are thinking whether we can improve our event selection by by the machine learning techniques in the same. So I've done this feasibility studies. And it shows a great improvement. That's
C520: take a look.
C520: So the machine learning I choose to use is this boosted decision tree. So basically, it's a ensemble of tree like structure, classifier or decision tree is represented here you have some node, and on each branch you set some selection criteria to separate the background and the signal the advantage of this
C520: boosted decision. Trees that it's under easy to understand. And it can use multi variant input, and it can be trained fast.
C520: And then I, for I trained a lot of classifier based on each point, and the background is that is chosen to the standard model background. They are the main contributions to the background, and this not from laptops.
C520: The keyfold hospitalization is used, and the setup of this trees to be shallow with steps of 3 and a hundred. The estimator.
C520: with learning rate of 0 point 1.
C520: This plot shows some input feature I use, and the left one is the transverse mask and the right one is the separation of 2 jets. Both. They show discrimination power between the background and the signal.
C520: This slide is showing the Bdt performance and the left wise is to show we don't have overtraining here.
C520: This can be observed from the distribution from testing data set and the training data set, and we can see overall. They show the similar behavior or be similar distribution. So no overtraining. And the red plot is the your curve.
C520: So we use this to evaluate the performance. The higher the area under the curve the better the classifier. So we see the
C520: the score is point 91. So it means this classifier is great.
C520: and then we compare our
C520: improvement of our new method on terms of this final results
C520: of the scientific age. So here we design this fitting set up one difference that we don't use the score to define single region and control regions. But we just do one d fitting out this Bdt score with similar region control regions set up, and then we assess the expected limit.
C520: and the result is shown here. This is the upper limit on the cross section as a function of Mh. 5. So the lower means the better sensitivity. We can see the Pdt method in blue line here is much lower than the previous card based method. That that means this
C520: utilizing the speedt method can lead to great, much better improvements in the event section, and thus affecting slower upper limit down
C520: cross section.
C520: So this led to my conclusion of my work. So I have presented the combination search for Charger Higgs boson in this topology, and turned to 26
C520: more stringent results are set. This is the the most stringent result up to date, and my results
C520: is was highlighted in this ichap meeting here, and also I gave a poster presentation in this
C520: very important meeting at particle physics.
C520: and I also shown some improvements by introduce the result in the same center, and the people are working on this for future
C520: upgrade.
C520: Analysis of of this.
C520: So on this page, I show my publication other than the physics. Analysis I presented. I also did some object performance study on quantum object, calibration, tiger and calibration, and also I contributed to some inference as a service model for Collider physics.
C520: Yeah. And I would like to thank all of you and all the department team. And the finally, maybe stop here with picture of some.
C520: Yeah of everyone. Yeah. Doing my Phd, journey.
C520: Yeah, I think that's all from my.
C520: which is okay on a previous slide that we found.
C520: So who's that 39, 39.
C520: Thank you for that.
C520: Yeah. Yeah. So probably missed it. But so, okay, you have an access in the spin. And you said, it's not significant, you know.
C520: like what- what, where this mismodeling comes from, if not from the network.
C520: Oh, I think most likely it's from the saturation of random process of the data. That is the most important
C520: doesn't what's the problem of?
C520: And also it could be from
C520: detector performance. For example, yeah, but this is the Mp. Basically, it's not the environments of Wz or anything else. So
C520: so that means you, you don't have. You only come to the visual being seen in this variable. And
C520: yeah, I guess, is there anything special about those events?
C520: Have you tried to look at other features in this specific team?
C520: So
C520: procedure and the companies to Neutrinos, and I think the reconstruction of the Mps is not like that of like MW. For example, so it cannot precisely reflect the transfers activities. And this could lead to some mismatch of the data. And.
C520: for example, you can also see some point here. The data is lower than the Monte Carlo simulation.
C520: And yeah, I think that's
C520: maybe don't match. If you look at those empty around 300 TV, there are 11 events.
C520: Those 11 events also appear weird kinematic behavior. If you look at the other variables.
C520: this is just pick those event events and dump all the variables. Look at the feature more than empty. If I also look at the other feature, do we see anything special?
C520: Yeah, I think in the Mj variable, it also show.
C520: Yeah.
C520: And Jj. Is probably highly correlated to empty.
C520: No Mtg. Is forward.
C520: So the Mt. Is the transverse energy. So there are different.
C520: Okay
C520: of the GM. Model. Probably, if you
C520: so we went a bit faster. Listen with the coupling of these new triplets to ports and left, right there must be some copy, or are they all for business? So that the just to frame the question is one of those couplings, and
C520: so are there low energy constraints, for example, for measuring the case on these. And where do they stand compared to your what you're you're finding. Yeah, I think the assumption here is that this particle in this
C520: their state. They don't contain the standard model doublet, and so they do not couple to fermion. So it's not.
C520: does not interaction with sparks and good ones. Sorry- sorry for the loss. That's a good question.
C520: Mass problem.
C520: Yeah.
C520: thank you.
C520: Yeah. But- but then we can. We can relate now.
C520: So then, you could do the exercise to make it really didn't.
C520: because M. 3 and M. 5 are connected right?
C520: No, they are not connected because we we assume the this mass is the M. 5. So they don't connect. Yeah.
C520: to me, there's no loyal energy
C520: for that. I guess we need to look at other- other plans like fact, or this singlet instead of this.
C520: and usually and then the Qc background probably will affect this search or the section menu.
C520: Yeah, it was. It was about the same thing. So
C520: if you, if you didn't assume
C520: that M. 3 was larger than 5, how would that make?
C520: How would that make things more difficult.
C520: Is it just background?
C520: Yeah. So- so then, this procedure isn't. Maybe if this will indicate, like
C520: like charter hits in the history plan, and then it couples and then does not provide as clean signal as here. So
C520: it's another story. Yeah.
C520: And do we have other questions on Zoom?
C520: Oh, Alex, go on.
C520: Oh.
C520: coming from theory. So basically, it's like, this is a range where the ticket ways of
C520: it's greater than 10% of mass of
C520: massive case. So they are forbidden.
C520: Oh, yeah.
C520: So anyone on the zoom have questions.
C520: Oh, you you can hear us from the zoom. Maybe you can give us a signal.
C520: Yes. Okay. Go ahead.
C520: Do you have any question.
Jenq-Neng Hwang: Oh, yes.
Jenq-Neng Hwang: I like it from the training purpose, from this multi day perception, training, perspective. I like to know how did you find it is a point 8 2 as Us. Threshold for a detail.
C520: Oh, yeah, so so let me see, if we have a formula for the significance definition.
C520: let me pull that up.
C520: Yeah, we have a significant formula here. So at different score, you can define S and B, and then you can use this significance formula to what is the S is the signal event, and the B is the background event. And usually you.
C520: The simplest version of this is like S over square root of B. That means the significance of of
C520: Yeah, and we want to find a value that maximize its significance, and we scan each threshold of a score, and we find that threshold is with point 2. This point 8 2 is the
C520: the maximum, the issue. There's no S in this one has. Oh, oh, sorry. Yeah.
C520: yeah, basically. And can be expressed. As for the discovery test, yeah, it's crazy. Because.
Jenq-Neng Hwang: Okay. But sometimes using this kind of theoretical derivation are based on some specific criterion.
C520: Yeah.
Jenq-Neng Hwang: When the data environment change
Jenq-Neng Hwang: this threshold might also might also switch which cannot be generalized through some testing data.
Jenq-Neng Hwang: So that's why most people when they try to do this threshold selection, they use something like Ozu threshold. I don't know. Are you familiar with that Ozu threshold?
Jenq-Neng Hwang: OSTU.
C520: No. And okay, yeah.
Jenq-Neng Hwang: That's fine. Another question I have is.
Jenq-Neng Hwang: seems to me that you have so many hyper parameters, but
Jenq-Neng Hwang: looks like you. Only try, for example, you have this 45 neurons per layer and 2 hidden layer.
Jenq-Neng Hwang: I'm just curious. Have you done any kind of operation study trying different kind of number of the hidden neurons and a different number of layers. Have you tried that.
C520: Yeah, I think here the problem is that the available event features are not that much. So we- we only have that around 10. So it feels
C520: increase more layers. It doesn't improve a lot. And
C520: so that's-, that's why we start with this. Yeah, yeah, of course. And this is up to more result, right?
Jenq-Neng Hwang: Okay, so 45, 45 is the best result you can get.
C520: Yeah.
Jenq-Neng Hwang: Okay? And one final question I might have is.
Jenq-Neng Hwang: apparently you care a lot about your uncertainty. And you know, if you use this kind of neural network. In fact, you can also have one more output which is called uncertainty.
Jenq-Neng Hwang: and your loss function will be the regular loss function divided by the uncertainty, then your neural network can also automatically generate through the data chain can automatically generate uncertainty. You might want to consider that because if you already decided to perform this kind of data driven, you might as well also use the neural network to give you the uncertainty.
C520: Yeah, yeah, that sounds a very great approach.
C520: Yeah, yeah, for the current analysis. Guess I can forward this to- to people, yeah, okay, yeah.
Jenq-Neng Hwang: That's currently you know the question I have.
C520: Thanks.
C520: Alright.
C520: Any more questions.
C520: Great. Then I think we can conclude a public presentation session and thanks for everyone, and let's keep a pause.
C520: Alright so! And then we'll move to the pro session and everyone who is not in the committee and take your time.
C520: We all do a little. Thank you.
C520: Yeah, stop. Do you want to take a short break?
C520: But the people here on paper?
C520: Yeah, if not, then we can be sure. And you. Okay? So now we are all committee member.