Long Lived Particles at Future Colliders - Rebeca Gonzalez Suarez - Uppsala University - CERN Indico
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Long Lived Particles at Future Colliders Rebeca Gonzalez Suarez - Uppsala University
It is normal to live different lives • The Standard Model is already an example of that How long a particle lives depends on many things: • Mass • Virtual mediators • Mass Splitting • Couplings Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 2
https://www.particlezoo.net/ What is a long-lived particle? ? Long-Lived Sort-Lived 2.2µs Lives literally forever (stable) 10-22 seconds Feels like it could be short-lived (As far as we know) You blink and you miss it! Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 3
I’m out of here Detector stable Long-lived Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 4
What is a long-lived particle? • Long-lived particles: umbrella term to cover lifetimes long enough to travel measurable distances inside the detectors before decaying, long enough to have distinct experimental signatures Long-lived Long-Lived 2.2µs Stable (As far as we know) And thought these two are technically long-lived particles, we tend to use the term to refer to NEW particles that we have not discovered yet Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 5
New, long-lived particles • LLPs are not a prediction of a single new theory, they fit into virtually all proposed frameworks for BSM physics • Typically Feebly Interacting • Theoretically, their presence is strongly motivated Featured in (including but not limited to): • SUSY • Compositeness • Exotic decays (H, Z, hadrons) • Hidden sectors This is the case at the LHC, and beyond Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 6
Three examples interconnected
Previous talk: The Search for Right-Handed Neutrinos - Marco Drewes 1 - Heavy Neutral Leptons • New heavy neutral leptons could give answer to central Marco Drewes (FCC-ee LLP informal team) open questions of the SM • How do Neutrinos get mass (right-handed neutrinos) • The net lepton number in the early Universe (leptogenesis) • Matter/antimatter unbalance in the Universe • Dark Matter (Sterile Neutrinos) Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 8
Long-lived HNL • Most of the current limits cover high neutrino mixing values • For low values of the neutrino mixing angle, the decay length of the heavy neutrino can be significant (a LLP) • Z → νN, N → lW (displaced vertex search) • For HNL with long enough lifetime → oscillations can also be studied arXiv:1709.03797 • Current constraints on the electron neutrino-sterile neutrino mixing | |2 as a function of the sterile neutrino mass [Ref] Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 9
2 - Hidden Sectors • At the moment, we know there is more to Nature than the SM • But we have no idea of the energy scale where new physics may live • They could in fact be right here, but just not interact or doing it very weakly with us • There could tiny couplings of these new collections of particles and forces with SM particles (the Higgs boson being one of the prime candidates) called “portals”, that would give us subtle signs to follow • When there is a small coupling → Long-lived signature! Hidden Sector Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 10
Hidden Sectors poster-child: Dark Sectors • Matter-Energy content of the Universe: ~27% dark matter, ~5% normal matter • Dark Matter makes up > 80% of all matter Regular matter is very complex • We don’t know much about Dark Matter, but a Dark Sector which almost does not interact with the SM but is similarly complex, would not be very far-fetched • In the context of Dark Sectors there are many Long-lived signatures that arise, some of them quite exciting, like dark showers Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 11
ALPs • “Axion-Like Particles” (ALPs) are very-weakly-coupled window to the dark sector • For small couplings and light ALPs, the ALP decay vertex can be considerably displaced from the production vertex → LLP arXiv:1808.10323 Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 12
3 - the Higgs boson itself • We are still getting to know the Higgs boson • It does look pretty much as expected from where we stand but it still could be exotic and provide us with indications of what can lie beyond the SM • This is why a Higgs factory is the first priority for the European Strategy for particle physics for example • Exotic Higgs decays to long-lived particles (LLPs) can be explored at future lepton colliders • Some related to Hidden sectors, like Twin Higgs and Hidden Valley models Projected 95% h→XX branching ratio limits as a function of decay length for a variety of X masses. Blue lines are for CEPC and orange lines are for FCC-ee, and where only one is visible they overlap. [arXiv:1812.05588] Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 13
The technical challenges
Detecting particles at colliders nowadays We push the energy frontier → we produce heavier and heavier particles → short lived - The Higgs boson at the LHC: - A Higgs boson is produced and decays 10-22 seconds after - It often decays into two Z bosons, each of them decaying in about 10-25 s in e.g. a couple of muons each - In practice this means that we see 4 muons coming from the collision point Our detectors, trigger, and reconstruction are made for that! Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 15
LLPs are not like that • New, long-lived particles display a collection of different signatures which are quite weird • Displaced tracks/vertices • Disappearing/kinded tracks • Anomalous tracks (dE/dX) • Slow/stopped particles (out of time) • Emerging signatures … • Which means • Little/no backgrounds • Potential instrumental background (how to model?) • Dedicated techniques • Reconstruction, Trigger, and Detector Design https://hrussell.web.cern.ch/ Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 16
This won’t be different at future colliders • At this point we have two ways to go: arXiv:1604.02420 • Design the future detectors as usual and then try to make the best out of them for LLPs • which can be done but won’t be easy as we know from the experience at the LHC -and before- • Design the future detectors with LLP in mind, prioritising for example displaced tracking and timing, and budgeting for unexpected Sensitivity of different detector components to HNL signals as a function of the mixing • which can bring up not only a boost for parameter and mass these searches but also innovation Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 17
Complementarity • Different colliders offer sensitivity to different parameters in different models • The key word is complementarity • Certain colliders offer higher energy, other cleaner environments, access to different ranges of mass/couplings • Many challenges related to Exclusion limits for ALPs coupled to photons. All curves correspond to 90% LLP will be common CLexclusion limits, except for LHeC/FCC-eh (95% CL exclusion limits), FCC-ee (observation offour signal events) and FCC-hh (observation of 100 signal events). From the Briefing Book Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 18
Ryu Sawada • It is a good time to plan our dream LLP detector, following Ryu Sawada first example at the latest LLP workshop in November (link) Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 19
The next collider
HL-LHC: the LHC upgrade https://hilumilhc.web.cern.ch/ • New functionalities • Track triggers (arXiv:1907.09846): e.g. trigger on displaced muons from the same vertex to find dark photons (arXiv:1705.04321) • Better timing information: using timing information to target pair-produced LLPs significantly delayed (arXiv:1805.05957) Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 21
HL-LHC: Dedicated experiments • Complementary instrumentation in the caverns offering low background environments • FASER: (approved) ∼1 m3 480 m downstream from the ATLAS interaction point (on-axis) • MATHUSLA: (proposed) large-scale surface detector instrumenting ∼8×105m3 above ATLAS or CMS (off-axis) • CODEX-b: (proposed) ∼103m3 detector in the LHCb cavern (off-axis) • AL3X: (proposed) cylindrical∼900 m3 detector inside the L3 magnet and the time-projection chamber of the ALICE experiment • ANUBIS: (proposed) 1×1 m2 units on top of ATLAS/CMS (off-axis) Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 22
And then?
Lepton colliders • The European Strategy Update highlights the need to pursue an electron- positron collider acting as a Higgs factory as the highest-priority facility after the LHC • Clear case: Higgs decays to LLPs (Ref.) • But much more than that Linear: energy Circular: precision See more: Ref. Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 24
Ref: Ryu Sawada Linear e e Colliders + - • CLIC: From (https://agenda.linearcollider.org/event/ 8217/contributions/44770/) • Hidden valley searches in Higgs boson decays with displaced vertices (Ref) • Degenerate Higgsino Dark Matter → chargino pair production (disappearing tracks) (arXiv:1812.02093) https://clic.cern/ CLIC@CERN [380 GeV] ILC@Japan [250 GeV] Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 25
Circular e e Colliders + - CEPC@China [90-240-(350) GeV] https://fcc-ee.web.cern.ch/ FCC-ee@CERN [90-365 GeV] http://cepc.ihep.ac.cn/ Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 26
FCC-ee: Heavy Neutral Leptons • The FCC-ee will offer an unbeatable reach for HNL at the Z-Pole, making it the flagship of LLP searches in this collider Courtesy of Alain Blondel Reference Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 27
FCC-ee: ALPs • Specially sensitive final states at the FCC-ee : arXiv:1712.07237 • + MET for very light a • for light a • for heavier a • Orders of magnitude of parameter space accessible Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 28
Extra detectors! • Following the plans for different additional LLP experiments at the HL-LHC it is possible to also envision similar concepts at other future colliders • HADES: A long lived particle detector concept for the FCC-ee or CEPC • arXiv:2011.01005 • The civil engineering of the FCC-ee will have much bigger detector caverns than needed for a lepton collider (to use them further for a future hadron collider) • Then we could install extra instrumentation at the cavern walls to search for new long lived particles Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 29
More on circular e e Colliders + - • Finding valid motivations for LLP at the FCC-ee/CEPC is certainly not a problem • As previously discussed: Twin Higgs models with displaced exotic Higgs boson decays, Hidden Valley models with neutral, long-lived particles that the Higgs boson can decay to (arXiv:1812.05588) • Higgs portal, dark glueball (arXiv:1911.08721) • Neutral naturalness (arXiv:1506.06141) • Folded SUSY (arXiv:1911.08721) • Neutralinos (arXiv:1904.10661) • … arXiv:1904.10661 Rebeca Gonzalez Suarez - Uppsala University - November 11, 2020 30
Ref: Ryu Sawada RGS FCC workshop Future Hadron colliders LLP in Higgs decays arXiv:1712.07135 • Options on the table (ep, pp) • LHeC@CERN • HE-LHC@CERN [27 TeV] • FCC-eh/hh@CERN [3.5/100 TeV] • SppC@China [75-150 TeV] Dark photon: arXiv:1909.02312 Eur.Phys.J C (2019) 79:469 FCC-hh Wino and higgsino dark matter HL-LHC with a disappearing track FCC-eh signatures LHeC FCC-hh FCC-ee … HNL complementarity arXiv:1612.02728 Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 31
Summary • LLP searches are a very attractive alternative to mainstream new physics searches at colliders • But challenge conventional reconstruction and trigger methods • There are many interesting lines to explore at future colliders • Heavy Neutral Leptons, Hidden sectors, exotic Higgs decays… • Different colliders have different sensitivities but many things in common • Organize and properly benchmark the most interesting options • Dive-in into dedicated detector design • Not only to just “see” LLPs at future colliders, but to maximize coverage and fully exploit the phase space Rebeca Gonzalez Suarez (Uppsala University) - The Cracow Epiphany Conference 2021 32
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