EF10 Contributions
Liantao Wang
      
      >> Phil: All right. Should we go to our next speaker?
      LIANTAO: I'll need to share my screen.
      [ Applause ]
      Can YenJie unshare? Okay. Very good. Okay. I'm going to give you a summary of the work happening EF10, dark matter at the colliders. Work that's happening and the contributions that we received.
      So, here is just a list of our  the focused questions for EF10 that we wanted to address. And the first question is how to best test the WIMP paradigm. This is I think one of the main things that the search for dark matter at Energy Frontier can contribute. And we have the following three approaches. Testing the simple/minimal dark matter model and using  and using simple mediator models and also the Higgs portal scenario. And the second question we wanted to contribute to is that how do we best explore beyondWIMP scenarios?
      So, this is a very big field. And almost, you know, covers the rest of the dark matter field. I think from our point of view we started with portals as dark matter. And then we wanted to see what, again, the search of the Energy Frontier can bring to the table. And we are focusing on lessexplored signatures of dark sector and, you know, highlight future blind spots.
      The third question is, again, we are aware that the dark matter is a very big topic. And it really requires a combination of synergy of many methods. So, we are trying to actively contribute to this effort and see, you know, the complementarities with the different frontiers working group the and the approaches. In terms of different experiments, the observation can be brought together to understand nature of dark matter and also in terms of detector and the data acquisition and the trigger design.
      So far we have received 11 contributed white papers on these questions. And then we are expecting more. I think we are aware of several  at least a handful of them are in working and we are expecting them to come to us. And today I think I will focus on giving you some limited highlights along these three directions. And there are more materials in the backup slides.
      So, let me begin just by the first question, WIMP. So, I don't need to repeat to you the familiar WIMP, the story. The key part of the story is there are a coupling between the dark matter and the Standard Model. Any test of WIMP will have to begin with these two questions. A, is what are actually the WIMP dark matter? Okay. Have to have some model in mind. And how do they interact with the Standard Model?
      So, we'll begin with the simplest case, which is the WIMP is part of the electroweak multiplets. So, this is the scenario. So, this is when the WIMP is part of the electroweak multiplet. On the model, you can see we can classify them in terms of representations under the electroweak group of the Standard Model. These are the fermionic state candidates. So, yeah. And basically they're interactions with the Standard Model. So, this is simple because the two questions that I outlined before are answered simultaneously. Once you decide what is dark matter, interaction is fixed. And the interacting with the Standard Model via the Standard Model weak interaction. And the couplings are standardized by the gauge interactions. And in the minimal modeling with the dark matter mass is the only free parameter. Therefore, it's very, very predictive. What's the abundance and so on. The calculation, you know, showing in that sketch before. It was very  there's only one free parameter there.
      And this leads to a set of target mass. These are the mass that  these kind of dark matter at this mass will give you the right relic abundance. Covering these kinds of models means you would like to search for this dark matter at least up to this kind of masses.
      This also highlights the fact that, you know, the average you see may not have great sensitivity on the dark matter because these are all at least in the TeV range.
      So, there are multiple candidates. And typically the Dirac doublet and the Majorana triplet are the standard benchmarks because they are earlier famous models of supersymmetry. Supper symmetry of the doublet is Higgsino, and the triplet is wino. They are 1.1 and 2.8 respectively. Higher masses can be considered. And typically they have higher target masses.
      And there are two type of signals at the hadron energy colliders. They are well known. One is the X + MET, basically producing a pair of dark matter. And the recoil against one of the Standard Model states. And this is a, you know, a  yeah. The model X scenario, okay? So, and this is a very model independent. And the very inclusive. And, of course, the flipside is the gaining sensitivity on this is more difficult. The second set of signal for this is that it's called a disappearing track. Because this takes advantage of that mass splitting in this kind of electroweak multiplets are quite tiny. And therefore, a charged member of this multiplet after its production will have a long lifetime so it can actually get into the trackers. So, it is a  this is a good distinct signal that you can imagine that the sensitivity is good. Is that the  one only has to be careful about this is a more susceptible to detector design and collider environment. The simulation is actually quite crucial to predict its potential, it must be longlived.
      So, the Higgsino/wino reach at future hadron colluders has been done by the European strategy already. And here is the summary plot in a European strategy update a few years ago. The message  basic message  is that the 100TeV collider will be needed to couple the doublet and the triplet case. And the  for higher multiples, obviously we need a much higher energy proton colliders.
      And I think what's new for this Snowmass study is that there are a lot of studies for high energy lepton colliders. In particular, muon collider. And the  on the lefthand you see a brief summary for the reach for the Higgsino and the wino case, okay? So, the basic message here is that a 10 TeV muon collider will be enough to cover a Higgsino and a wino cases. Actually if you look into details, we don't actually need a 10 TeV collider. I think a 6TeV collider will have enough for the Higgsino case. The plot in the middle, this is for the Majorana case, 14TeV. But it's the same. Between the signals and the disappearing track signals.
      And if you wonder what happens with the higher multiple, it's on the righthand side. Obviously, you need more energies so it's bigger.
      Okay. So, the next type of scenarios that we're considering is the Higgs portals. This is the answering the question that the  how the Standard Model interacting with the dark matter sector. The answer is indicated through this Higgsmediated processes.
      Okay. So, the Higgs portal basically is a coupling between the Higgs and the operator made up of H, H, and the dark matter operator. In the simplest case, the dark matter operator is just dark matter squared and this leads to a Higgs to pair of dark matter coupling. And obvious case to look for, look for Higgs decay to dark matter. In the case, dark matter mass is less than half of the Higgs mass. And many future colliders, hadron collider, lepton colliders, will measure this to higher and higher precision. And yeah. So, on the righthand side is a interpretation of Higgs to invisible decay measurement translated into  translated into this kind of scenarios. And in comparison with dark matter direct detection experiment. And yeah. So, you see this is particularly strong what the dark matter mass is less than half of the Higgs mass and at the lighter dark matter masses.
      So, in the future with the improvement of Higgs invisible decay measurement, this will certainly get stronger. The work we will do is to update  so, they are European strategy plots. I will be working on updating them with newer results from, for example, from muon collider studies. Okay.
      And beyond the simplest models, there are also  has also been explored by some white papers such as I would consider more general couplings between complex singlet and the Higgs boson. And also, the Higgs coupling can be more involved. Okay? So, all right.
      Okay. The third approach in the WIMP category is the simplified models. Okay. So, this is another  yet another way of answering the question I put forward before. In this case, usually the dark matter is just some simple singlet. At the same time, the way they couple to the standard model is through some new particles become mediators. It depends on how the particles couple. This can be divided into the S and the T channel. These are very wellestablished models. In fact, I remember that the last Snowmass, the summary meeting was where the tchannel mediators paper came out. That was around 10 years ago.
      So, yes. There are many results. There are results in this category for the European strategy study already. And again, one can  once we have the constraint on a particular simpler model, it's easy to plot it in this kind of dark matter mass versus direct detection cross section. And then compare with direct detection. And usually the strength is when the dark matter mass is very light. Not surprisingly.
      So, in this Snowmass, we have additional contributions. And also, white papers in this category.
      So, one of the ongoing work within the group and the  is that to generalize the available result that's in the European strategy study. And there the dark matter simplified models have other couplings fixed to the other one. The goal here is to go to generalized  more generalized couplings. And this will allow us to, you know, easier  with a easier interface with the search as approach. So, as you will see later when we talk about complementarity message. Yeah. So, the approach here is basically because the cross section is simple enough, a lot of the things can be done by just simple analytical scaling the limit. And the goal for Snowmass white paper we are writing is to have a reference document for this scaling and then cover different constraints from different topologies such as monojet, dijet and lepton search. And also provide code, you know, for different users with summary plots.
      Okay. Beyond the WIMPs, and again, I will say this is a very big field. And our angle is to see what the high energy collider can bring to this table. We are starting with portals. And dark photon is the most obvious portal. And we see in the dark photon reach. Certainly when the dark photon mass gets heavy. And high energy collider will have nothing is say about it. And also including in the European strategy and also physics beyond the collider study.
      Okay.
      >> 4.5 minutes?
      LIANTAO: sorry?
      >> 4.5 minutes left.
      LIANTAO: Good enough. Sorry. Yeah. Just some highlight of the result we received and the still ongoing work. You know, and so, there is a Belle II experiments. And they will certainly has this  has this new projection of dark photon reach. Which is very interesting. And also, upgraded LHCb can search for dark photon case. In particular in connection to our dark matter focus, we are particularly interested in the dark photon invisibility case. And essentially when dark photons can actually decay to dark matter. And one of the interesting approach is to reinterpret the monophoton, a model X search that happened at the LHCb. And this is the result coming out of that study.
      And there are also additional, you know, signals and approaches we can follow. For example, as was indicated in this white paper. Usually a dark photon means that the kinetic mixing is  can be introduced as integrating out UV particles that charge both under Standard Model and the dark sector. And that those new particles will certainly have new signals. That's something that I think was a very interesting contribution. And, of course, the  also have a additional experimental opportunities in the forward physics as well to look for dark photon.
      Yeah. So, the last thing in the beyond WIMP approach I will mention is dark showers. It's, again, it's the slide here. This is a complicated dark sector. And it goes through a complicated showering process in the dark sector before it comes back to the Standard Model. And there are many, many moving parts in this model. Okay? So, and they are leading to a very different signature space. And I think this is also  I think you will probably hear much more about this in the later presentations, for example, from EF09. And I think from our point of view the Snowmass effort will be concentrating on defining some benchmarks. And from our point of view especially interesting is that they can be more connected with dark matter. And I think this part of the work is still ongoing and that there is a, you know, discussion on Friday. And looking forward to more discussion in this direction.
      Okay. So, again, so, the third aspect I wanted to address is the complementarity ideas from the EF in particular with the cosmology frontier. And so, this is a very important connection in the search of dark matter. Two of our  my coconveners, Antonio and Caterina, they are serving as the liaison between the Energy Frontier and the Cosmic Frontier. They can probably provide better answer.
      So, for example, one of the things that was actively trying to start was the  restart  with the Cosmic Frontier is the dark matter complementarity discussions. The first Snowmass produced some overview picture between  complementarity between different approaches of probing dark matter and the goal for this effort is to improve on that. And bringing new ideas and new approaches. And, for example, the  the  the extension of the  our work into going beyond a fixed 1 coupling between dark matter and Standard Model will certainly facilitate that discussion and make it easier connection with other approaches.
      Okay. So, I will conclude. And I think as I have just briefly showed you some of the these highlights that EF10 has received many great contributions to our  towards our three big questions. How do we test WIMP paradigm? How do we best explore beyond the WIMP scenarios? And how should we build the best synergy and the complementarity between dark matter colliders and other topical groups and frontiers to pin down the dark matter better? And we are certainly happy to receive more. And if you  if there are  I mean, we are aware of there are certainly still several ongoing works. But if you are still working on something that is coming to us soon, please let us know as well.
      And, you know, we will plan to evolve the EF10 materials for the white paper in a very public way. We will have a draft. And our final report will be included in the joint report with EF08 and EF09. Okay. Thank you.
      >> John: Thank you, Liantao, very nice. Do we have any comments or questions from Zoom? It does not appear to be the case. Go ahead, Phil.
      >> Phil: Questions from the room? I saw a hand raised in the middle of the talk. Did you have a comment or question?
      >> No, sorry, just my mistake.
      >> Phil: Okay.
      >> So, I'm sorry if I missed this. But I don't think you discussed the Higgs portal in this talk.
      LIANTAO: I probably discussed too briefly. It's here.
      >> Oh, very good.
      LIANTAO: It's also a very busy slide. I apologize for that. Yeah. So, basically the concrete result here is, you know, the  by measuring the Higgs invisible decay, we can save quite a bit for this scenario when the dark matter mass is lighter than half of the Higgs mass.
      >> Very good. Okay.
      LIANTAO: And the future colliders can measure this better. But they're also like more extended models. So, this is  basically, you can just explore how this dark is.
      >> Please excuse me for sleeping through the slide. When you combine the Higgs portal with the dark showers, there's a lot of interesting information. You have written one of the paper on this, but a lot of it is totally unexplored.
      LIANTAO: Yes, I agree. There should be more work along those lines. Yes.
      >> So, Liantao, you mentioned very appropriately that there's a lot of complementarity between the cosmic frontier and the energy frontier, and two of your convenors are cosmic frontier people. We didn't see that in the talk, will that be part of the summary, or will that be a separate contribution to Snowmass that's like all the different areas working together discussing their complementarity?
      LIANTAO: I think Caterina probably can address this better. I think that the main effort is this complementarity figure that we are going to  the eventual goal is to bring all approaches to showing them on the same figure and seeing which area they can  they can cover. And that they're complementary. Again, maybe Caterina can chime in.
      CATERINA: Sure. We're going to do both. We're going put some plots in our report. Especially ones with the future collider projections. But also, we're going to be part of bigger complementarity discussion that not only involves the Cosmic Frontier, but also the neutrino frontier and other frontiers. Precision as well. And this is the short white papers that mentioned below. Here we projections, we have sketches based on the projection. I want to highlight the story. Not if it's better than another. This is not how the plot should be used. We need to do more rather than less. Because one experiment is better than the other in the projections, right?
      So, we'll have a discussion on Friday where we invited people from the Cosmic Frontier. You're welcome to come to that to see the first interaction on how this discussion will evolve. Because we have just restarted the complementarity discussions after all the white papers came in.
      >> Phil: We have another question in the room.
      >> Hi, Caterina. I have maybe a bit of a technical question about that particular plot. Can we make any statement below 1 GeV?
      >> Phil: Can I answer this question?
      CATERINA: You can answer the question. You can.
      >> We had a long discussion about this in the working group. The concern is not the LHC or the collider bounds, the concern is the direct detection cross section. Once you go below GeV  in principle, once you go below 1 GeV, you have to take into account nonperturbative effects in the cross section. Some say you can push it to 100 MeV, and it's probably fine. But at some point you need to kind of start thinking about how you do these calculations more carefully. So, in the interest of being conservative, we've kind of officially stated that we go to 1 GeV.
      You know I  you know, we can have a discussion. Especially in the context of complementarity. How low do we want to push this? I've seen people push this to 1 MeV. The interesting thing is that the reduced mass squared is in the  is in the calculation of the crosssection for direct detection. So, the LHC bounds, or the collider bounds in general tend to get much, much better. They scale as  the cross section scales as mass squared. If you do down two orders of magnitude, you dropped your cross section four orders of magnitude just for free. It looks very impressive. But there's a number of caveats.
      >> So, if they find a signal we can't correlate?
      >> Yeah. It's not  the concern I think is not  the concern is not on the LHC, the collider side. It's really on the calculation of the cross section. So, if a liquid helium experiment seeing this, you know, right? We can go right away and see we have to search for it. But I don't think we can take theirs and look at the crosssection without some assumptions.
      >> We have to look at it. Makes no difference to us.
      LIANTAO: But this translation, as Phil said, always a lot of assumptions you have to make to actually translate into an LHC cross section.
      >> All right. We don't see any more questions in the room. Sounds like there are no questions online. So, now we have a 30minute break. And I'll see you guys back in 30 minutes. 3:30.
      >> Yeah.
      >> Yeah, let's say 30 minutes past the hour so we don't start too late and finish too late.
      [Break]
      >> Recording stopped.