Responsible: Grégory Moreau [TH](moreau@th.u-psud.fr), Susan Gascon-Shotkin [EXP](smgascon@mail.cern.ch)
Participants (please add your name and your email): Jérémie Quevillon (jeremie.quevillon@lpsc.in2p3.fr), Antoine Lesauvage (antoine.baptiste.lesauvage@cern.ch), Aoife Bharucha (aoife.bharucha@cpt.univ-mrs.fr), Bill Murray (bill.murray@cern.ch), Nishita Desai (nishita.desai@umontpellier.fr) Jose Miguel No (josemiguel.no@uam.es), Jon Butterworth (J.Butterworth@ucl.ac.uk), Natascia Vignaroli (vignaroli@pd.infn.it), Kohsaku Tobioka (ktobioka@fsu.edu), Giacomo Polesello (giacomo.polesello@cern.ch), Sophie Williamson (swilliamson@lpthe.jussieu.fr), Shilpi Jain(shilpi.jain@cern.ch), Shankha Banerjee (banerjeeshankha@gmail.com), Biplob Bhattacherjee(bbhattacherjee@gmail.com), José Zurita (jose.zurita@kit.edu), Thomas Flacke (flacke@ibs.re.kr)
⇒ First MEETING Friday June 21 at 17:00pm in the QCD Room.
⇒ Second MEETING Saturday June 22 at 14:30pm in the Library.
⇒ Dedicated MEETING on Exotic Higgs decays $h \to Z \phi$ Monday June 24 at 16:00 in the Auditorium
⇒ Third MEETING (on all possible light scalar subjects) on Tuesday June 25 at 14:30 in the QCD Room
⇒ IMPORTANT: Please see the 'EXECUTIVE SUMMARY' of potential subjects for the proceedings AT THE END OF THIS WIKI and recommendations for preparation of contributions to Friday's summary talk (please send to Gregory, Susan and Jose by Thursday morning)
Down to which masses the LHC can test (pseudo-)scalars? And how?
Below 80-90GeV, for a generic (pseudo-)scalar $\phi$ (light Higgs, radion, dilaton, axion, ALP's…), the decay $\phi$ → Z*Z is kinematically closed and $\phi$ → $\gamma\gamma$ becomes challenging to trigger on, so that the gluon-gluon Fusion mechanism to produce $\phi$ is not promising anymore (see for instance 1607.08653).
For instance, Higgs composite models with additional light scalars:1710.11142, 1902.08690.
Motivation: the produced Vector boson V helps to trigger on the signal (for example: Radion+Z production within the RS model studied in 1702.03984).
Context here: EFT with on-shell scalar ($\phi$) and scalar couplings to vector bosons only so look at the decay $\phi \to \gamma \gamma$ [here $\phi$ is not a stable DM candidate leading to missing $E_T$]. Looking at scalar couplings to fermions, other production and decay modes ($\phi \to \tau \tau$ or $\phi \to b \bar b$ [reconstructing the invariant scalar mass]) could be studied as well.
Gauge invariant (pseudo-)scalar couplings to ZZ, WW, $\gamma\gamma$, $\gamma$Z, gluon-gluon: $$\frac{\phi}{\Lambda_1}\vert D_\mu H\vert^2 \ \ (for \ scalars \ only) \ \ and \ \ \frac{\phi}{\Lambda_2} Tr[V_{\mu\nu} \tilde V^{\mu\nu}] \ .$$
Two other effective parameters: $\phi$ mass ($m_\phi$) and Branching for $\phi \to \gamma \gamma$ ($B_\gamma$).
Exhaustive list of hard PROCESSES (no focus on W production for EXP reasons):
$e^+e^-$ → Z* → Z$\phi$ or $\gamma$ $\phi$ at FCC [names: GP?]
$qq$ → Z* → Z$\phi$ interfaced to DELPHES [names: SG, AL]
Z → $\gamma\phi$, $\phi\to\gamma\gamma$. Triphoton final state [names: GP?]
Exotic Higgs decays in $h \to Z \phi$
Promising DECAYS: $\phi\to\gamma\gamma$ (and $\mu\mu$, $bb$, $\tau\tau$, Missing E_T ?) [names: TF, JZ]
General comment: If the particle is lighter than hadronic threshold ($m_a <3m_\pi<450\rm MeV$ for CP-odd scalar), the particle is easily long-lived in the reasonable parameter space. Many literature ignores loop-factor $16\pi^2$, which sometimes leads to less physical parameter space. A scale $\Lambda/C_{\gamma\gamma}=1\rm TeV$ in 1708.00443 parameterization corresponds to a scale $f_a =6\rm GeV$ in the decay constant (SSB scale).So ALP being invisible is quite possible with sub-GeV mass and $f_a >100\rm GeV$. Estimates with ALP as missing energy in 1409.4792 (mono-jet), 1701.05379 (mono-W, mono-Z, mono-Higgs) and 1901.03061.
For boosted configurations: for example gamma gamma + j(l)etc, 'fat' photon ids…
ALP UFO file from Bauer, Neubert, Thamm with fix for the ALP mass / Higgs/ Z mass bug from Peter Richardson.
ALP UFO file from 1701.05379 (Brivio, Gavela, Merlo, Mimasu, No, del Rey, Sanz) (with fix for the ALP width).
ALP linear UFO file from Brivio, Gavela, Merlo, Mimasu, No, del Rey, Sanz (also with fix for the ALP width - GP).
Readme file Conversion of couplings between two UFOs above - GP.
fat_photon_phenomenology from https://arxiv.org/pdf/1210.3657.pdf
$h^* \to Z \phi$ [UFO files from effective ggh coupling for kinematics and rescale rate with ggF cross section?]
A model apart from ALP for $h\to Z\phi$ is flipped 2HDM by0904.0705. However, the model with light A seems to be very constrained by Higgs mass and Higgs coupling measurements. Another straightforward model is 2HDM plus singlet but in this case the Higgs portal (SM+singlet) is simpler (refs).
'Executive Summary' of possible project list for the proceedings and input needed for the Friday summary talk:
Contributions on the above projects to the Friday closing talk (by the Higgs convenors) should include (~1-2 slides):
Please send to Gregory, Susan and Jose by Thursday morning (so we can give a synthesis to the speaker by ~Thursday noon and also circulate among us)
Thank you all for all the work, and let's not stop here! Here are the slides shown in the summary session on June 28, 2019.