ECFA HF WG1: 1st Workshop of the WG1-SRCH group

Wednesday 25 May 2022, 09:00 → 19:00 Europe/Zurich

Aleksander Filip Zarnecki (University of Warsaw (PL)), Rebeca Gonzalez Suarez (Uppsala University (SE)), Roberto Franceschini (Rome 3 U.)

First workshop of the group, virtual only.
Focus is set on searches for new scalars. Talks are a mix between invited and contributed.

The WG1-SRCH group is centered around direct discovery potential.

It is devoted to the broad exploration of the new physics discovery potential of the future Higgs and top/EW factory, including the search for Feebly Interacting Particles also in connection with “Physics Beyond Colliders” activities.

If you would like to contribute to this effort, or just be informed about the activities of our group, please join the dedicated email list (ecfa-whf-wg1-srch@cern.ch) via this link, or send an email to group conveners.

09:00 → 10:30 Session 1

Convener: Aleksander Filip Zarnecki (University of Warsaw (PL))

09:00 Possible experimental opportunities at the ILC beam dumps

Speaker: Yasuhito Sakaki (KEK)

Sakaki_ECFA.pdf

09:30 Near or Far Detectors? Optimizing Long-Lived Particle Searches at Electron-Positron Colliders

In this talk, I will explore the discovery potential for long-lived particles at the 250-GeV ILC. I will discuss possible gains of a dedicated far detector over the main detector for sub-GeV axion-like particles a, produced via e+ e− → aγ or e+ e− → Zγ → (aγ)γ and decaying into pairs of charged leptons. Our conclusions can also help optimizing long-lived particle searches at the FCC-ee and other high-energy e+ e- colliders. [2202.11714]

Speaker: Ruth Schäfer

Near_v_Far_Ruth_Schaefer.pdf

09:50 New physics search at ILC-BDX experiment

We study capability of the ILC beam dump experiment to search for dark matter particles, comparing the performance of the electron and positron beam dumps. The dark matter particles involving the dark photon are considered as benchmark models, where electron recoil processes and decays of heavier dark matter particles are included as signal events.
We find that the ILC beam dump experiment has higher sensitivity than past beam dump experiments, with the positron beam dump having a better performance for dark matter particles which are produced by the electron-positron pair-annihilation.

Speaker: Daiki Ueda

ECFA_daiki.pdf

10:10 Observing Axion Emission from Supernova with Collider Detectors

We consider a possibility to observe the axion emission from a nearby supernova (SN) in the future, which can be known in advance by the pre-SN alert system, by collider detectors like the LHC detectors (i.e., the ATLAS and the CMS) and the ILC detectors (i.e., the ILD and SiD). The axion from the SN can be converted to the photon by the strong magnetic field in the detector and the photon can be detected by electromagnetic calorimeter. We estimate the numbers of signal and background events due to a nearby SN and show that the number of signal may be sizable. The axion emission from a nearby SN may be observed if, at the time of the SN, the beam is stopped and the detector operation is switched to the one for the SN axion search.

Speaker: Yoshiki Kanazawa (University of Tokyo)

ECFA_Kanazawa.pdf

10:30 → 11:00 Break

11:00 → 13:00 Session 2

Convener: Rebeca Gonzalez Suarez (Uppsala University (SE))

11:00 Extended scalar sectors of interest for Higgs factories

Speaker: Tania Natalie Robens

robens.pdf

11:30 Results and prospects from ATLAS

Speaker: Theodota Lagouri (Instituto De Alta Investigación - Universidad de Tarapacá (CL))

Theodota-Lagouri-ECFA-Talk-v2.pdf

12:00 Results and prospects from CMS

Speaker: Agni Bethani (University of Maryland (US))

ECFA_WG1SRCH_Agni.pdf

12:30 Light Higgs Bosons at Future e+e- Colliders

I will review possible evidences for a light Higgs boson. Based on the experimental data the possibilities to test such a BSM Higgs scenario at future e+e- colliders will be discussed.

Speaker: Sven Heinemeyer (CSIC (Madrid, ES))

sven.pdf

14:00 → 15:30 Session 3

Convener: Roberto Franceschini (Rome 3 U.)

14:00 Global interpretation of LHC indications within the Georgi-Machacek Higgs model

The SM Higgs discovery has relied on the following ingredients:

• An “effective theory”, the SM, which predicted the mass and the couplings of the Higgs particle

• A > 5 s.d. evidence of signals coincidentally observed by ATLAS and CMS for this particle (FNAL started with a ~3 s.d. indication)

The dominant phenomenological framework remains MSSM but, in absence of evidence for SUSY, one needs to allow for alternates

In a bottom up approach I will show that while not yet reaching 5 s.d. – although not so far from it – there are various indications close by, which do not seem to match MSSM but can be accommodated with an extension proposed in 1985 by Georgi and Machacek

Some of these indications are not “far fetched” and belong to the gold plated channels of LHC

Not to be forgotten: (g-2)µ suggests that BSM physics is made out of light particles and could be within reach

Accordingly I will restrict myself to Pseudo Nambu-Goldstone bosons which in large class of models are the lightest objects in similitude with the pions of QCD, the SM h being one of them

Speaker: Francois Richard

Talk-ILCX21-next.pdf

Talk-ILCX21-next.pptx

14:30 Light scalars beyond the SM: collider searches and astrophysical constraints

A light CP-even scalar is very common in the beyond SM physics. It can be searched at the high-energy colliders or high-intensity experiments via long-lived particles or flavor signals, for instance future $e^+ e^-$ colliders, FASER and DUNE. The signatures might depend on the underlying theories. If sufficiently light, a scalar can also be produced copiously in supernovae, neutron stars, the Sun, white dwarf and red giants, etc. Therefore its couplings could be constrained by relevant astrophysical observations, e.g. the luminosity limits. In this talk, we will report some recent progress in these directions.

Speaker: Yongchao Zhang (Southeast University)

light_scalar_ecfa_hf_wg1.pdf

14:50 New physics hints with 2HDM under the Higgs Boson Precision Measurements

We perform comparative studies for four types of the two Higgs Doublet Models (2HDMs) under the precision measurements of the Standard Model (SM) Higgs observables at the proposed Higgs factories. The exploration for the discovery potential is up to one-loop level. We find 5σ observability from the global fitting in a significant theory parameter space at future Higgs factories. We also examine the extent to which the different 2HDM theories may be distinguishable from one to the other at the 95% Confidence Level with four benchmark points as case studies. It confirms that the impacts of loop corrections are found to be significant in certain parameter regions.

Speaker: wei su (university of Adelaide)

2022WG1-SRCH-weisu.pdf

15:10 Probing the Electroweak Phase Transition with Exotic Higgs Decays

An essential goal of the Higgs physics program at the LHC and beyond is to explore the nature of the Higgs potential and shed light on the mechanism of electroweak symmetry breaking. An important class of models defining the strength and order of the electroweak phase transition is driven by the Higgs boson coupling to a light new state. This Snowmass white paper points out the existence of a region of parameter space where a strongly first order electroweak phase transition is compatible with exotic decays of the SM-like Higgs boson. A dedicated search for exotic Higgs decays can actively explore this framework at the Large Hadron Collider (LHC), while future exotic Higgs decay searches at the high- luminosity LHC and future Higgs factories will be vital to conclusively probe the scenario.

Speaker: Ke-Pan Xie

ECFA_HF_WG1_online.pdf

15:30 → 16:00 Break

16:00 → 19:00 Session 4

Convener: Aleksander Filip Zarnecki (University of Warsaw (PL))

16:00 2HDM Neutral Scalars under the LHC

Two Higgs Doublet Models (2HDM) provide a simple framework for new physics models with an extended Higgs sector. The current LHC results, including both direct searches for additional non-Standard Model (SM) Higgs bosons, as well as precision measurements of the SM-like Higgs couplings, already provide strong constraints on the 2HDM parameter spaces. In this paper, we examine those constraints for the neutral scalars in the Type-I and Type-II 2HDM. In addition to the direct search channels with SM final states: H/A → ff, VV, Vh, hh, we study in particular the exotic decay channels of H/A → AZ/HZ once there is a mass hierarchy between the non-SM Higgses. We found that H/A → AZ/H Z channel has unique sensitivity to the alignment limit region which remains unconstrained by conventional searches and Higgs precision measurements. This mode also extends the reach at intermediate tan beta for heavy mA that are not covered by the other direct searches.

Speaker: Shufang Su (University of Arizona)

2HDM_Neutral_LHC_ECFA_HF_WG1_Su.pdf

16:20 Inert Doublet Model at future e+e- colliders

The Inert Doublet Model (IDM) is one of the simplest SM extensions and introduces four new scalar particles: H$^\pm$, A and H; the lightest, H, is stable and hence a natural dark matter (DM) candidate. A set of benchmark points has been proposed, which are consistent with theoretical and experimental constraints and promise detectable signals at future colliders. Prospects for observing pair production of neutral or charged IDM scalars were studied for the leptonic final state, for different running energies of future e$^+$e$^-$ colliders. The expected significance is mainly driven by the signal production cross section.
For high mass scenarios, discovery reach for the IDM charged scalar pair-production can be significantly increased when using the semi-leptonic final state. This was studied for the two high-energy CLIC stages using fast and full detector simulation. Taking into account the pile-up contribution from the beam-induced $\gamma\gamma$ events is crucial for the realistic estimate of the experimental sensitivity.

Speaker: Jan Franciszek Klamka (University of Warsaw (PL))

idm_future_epem_v4.pdf

16:40 Sifting through the SM for the hints of an ALP

Axion-like particles (ALPs) are at the forefront of physics research, especially at the intensity frontier, dealing with light weakly coupled particles. A plethora of different experiments search for signals of the ALP in many different final states using innovative search strategies. We present a different perspective on ALP searches, concentrating on the modifications that such a particle causes to the known Standard Model (SM) results. The presence of a low lying ALP modifies the SM in non-trivial ways. We systematically derive the leading order chiral lagrangian in the presence of an ALP (A𝛘PT). Then, using the derived A𝛘PT, we systematically discuss three distinct modifications to SM physics---which arise at the tree level itself: i) those to the meson mass spectrum, ii) those to hadronic form factors, leading to modified to partial decay rate distributions of the mesons, and iii) those to the sum rules constructed out of meson decay amplitudes. As a proof of concept example of our program, we analyse semi-leptonic Kaon decay data collected by the NA48/2 collaboration to find bounds on the ALP parameter space.

Speaker: Triparno Bandyopadhyay

triparno_ECFAHFWG1.pdf

17:00 Searching for light dark bosons in Z decays

We analyze the Z-boson decay $Z \to \gamma ~ X$ into a photon ($\gamma$) plus a hypothetical light boson (X) belonging to a dark or secluded sector. The dark boson is assumed to behave as missing energy in the detector. We consider for X the cases of spin-1 (massless dark-photon), spin-0 (axion-like), and spin-2 (graviton-like) particles and explore the way to untangle its spin origin. All these scenarios predict a universal signature for this decay, characterized by a single mono-chromatic photon in the Z center of mass, with energy about half of the Z mass, plus a neutrino-like missing energy associated to the X boson. We analyze first the possibility of searching for a massless dark photon at the LHC, HL-LHC and future lepton colliders, and compare the respective sensitivities. As expected, the best result is found for the lepton colliders running at the Z mass, FCC-ee and CEPC, with a final sensitivity to branching ratios of order ${\cal O}(10^{−11})$. Then, we discuss how to use the photon angular distribution of the events in lepton collisions to discriminate between the dark photon and a light invisible axion- or graviton-like particle.

Speaker: Dr Emidio Gabrielli (Nat. Inst. of Chem.Phys. & Biophys. (EE))

Talk_ECFA_HTE-EG.pdf

17:20 Tera-Zooming in on light (composite) axion-like particles

The Tera-Z phase of future e+e− colliders, FCC-ee and CepC, is a goldmine for exploring Z portal physics. We focus on axion-like particles (ALPs) that can be produced via Z decays with a monochromatic photon. As a template model, we consider composite Higgs models with a light pseudo-scalar that couples through the Wess-Zumino-Witten term to the electroweak gauge bosons. For both photophilic and photophobic cases, we show that the Tera-Z can probe composite scales up to 100s of TeV, well beyond the capability of the LHC and current precision physics. Our results also apply to generic ALPs and, in particular, severely constrain models that explain the muon g−2 anomaly. We will also comment on the possibility to disentangle composite versus elementary origins of the ALP and the impact of the new W mass measurement at CDF.

Speaker: Giacomo CACCIAPAGLIA

Cacciapaglia_TeraZooming.pdf

17:40 Discussion

Speakers: Rebeca Gonzalez Suarez (Uppsala University (SE)), Roberto Franceschini (Rome 3 U.), Aleksander Filip Zarnecki (University of Warsaw (PL))