7 October 2019

Feng 1

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What tools are critical for making progressin cosmology in the coming decades?

Cosmic Controversies Panel
University of Chicago
Jonathan Feng, UC Irvine, 7 October 20197 October 2019

Feng 3DARK MATTER• For dark matter, the question is very timely• New community exercises underway in both
astrophysics and particle physics– Astro 2020
– European Strategy for Particle Physics Update 2020
– Snowmass 2021

• Many new developments in dark matter– WIMPs and other classic candidates not discovered, but remaininteresting– Other DM candidates are rising in prominence– Both facts have implications for what tools and experiments will
be needed for progress
7 October 2019

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WIMP PARADIGM• For decades, the WIMP paradigm has been dominant,bolstered by the WIMP miracle and its many implications

2008• Indirect detection: interesting signals in n, g, e+, pbar, …
• Direct detection: mass matched to scattering off all nuclei• Colliders: almost all BSM signals, mono-X
7 October 2019

Feng 5WIMP STATUS• Many constraints, but still viable. E.g., there are viable
SUSY models with thermal relic neutralinos, and all
squarks/sleptons below a few TeV.

• DM is 200-700 GeV andBino-like, so scatters very
weakly, but freezes out
correctly through cc à t4t4.

Abdullah, Feng, Iwamoto, Lillard ( 2016)• For example: MSSM4G,MSSM + vector-like 4th
generation.

• There remain strong motivations to pursue direct detection
down to the neutrino floor, both in xenon (XENON-nT, LZ,Panda-X, Darwin) and argon (Darkside-20K, ARGO).
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COLLIDER SEARCHES• For the next many years, the energy frontier will continue tobe dominated by the LHC and HL-LHC.
• The LHC is currently inLong Shutdown 2, but will
start up again in 2021 andrun till ~2037. Will we find
new particles throughconventional searches?
• What other approaches
can enhance theprospects for discovering
DM and other newparticles?
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MACHINE LEARNING• Machine learning is now able to optimize searches overconventional methods.
• For example: identifying the originating quark / gloun from a
hadronic shower.

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MACHINE LEARNING• Examples: b-quark tagging (left) and top-quark tagging (right).
Top curves are from neural network, bottom curves are using
expert-curated variables (note log scale).

Guest, Collado, Baldi, Hsu, Urban, Whiteson (2016)7 October 2019

Butter, Kasieczka, Plehn, Russell (2018)
Feng 9AXIONS• The QCD axion
remains a highly
motivated DM
candidate.

ADMX-G2 (2018)• ADMX-G2 has finallyprobed down to thecanonical sensitivity
and mass range.
• Strong motivation tocontinue to higher(and lower) masses.
7 October 2019

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NEW CANDIDATES• Of course, the absence of a compelling DM signal(and, in fact, a compelling BSM signal of any kind)motivates the study of other possibilities.
• In recent years, there has been a huge growth in thenumber of DM candidates under investigation.
• Most exciting, many of these motivate relatively small,cheap, and fast experiments.

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Dark Matter Candidates, Anomalies, and Search Techniques

QCD Axion
Ultralight Dark MatterkeV

MeVGeVSterile Neutrino

TeVWIMPsHidden Thermal Relics / WIMPless DM
SIMPs / ELDERSPeV 30M

≈zeV aeV feV peV neV µeV meV eVBlack Holes

Asymmetric DM

X-ray Line Beryllium-8
Muon g-2
Small-Scale Structure
Coherent Field Searches

Nuclear and Atomic Physics

Microlensing

Direct Detection (Low-Threshold and Spin-Dependent)≈Accelerators

keV
MeV
GeV
zeV aeV feV peV neV µeV meV eV
Cosmic Visions Report (2017)7 October 2019

TeV

PeV 30M
Feng 12clert i sPa xpt
E

THE NEW PARTICLE LANDSCAPEMass
MeVGeVTeVInteraction Strength1Already
Discovered

Strongly Interacting
Heavy Particles

Weakly Interacting
Light Particles

Impossible toDiscover

10-3

10-6

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LIGHT, WEAKLY-INTERACTING PARTICLES•The possibility that new particles are lightand very weakly-interacting also has acosmological motivation.

•The thermal relic density isDM

SM

DM

SM

time

WIMP Miracle: ~100 GeV to 1 TeV
masses, strong couplings à rightabundance•

WIMPless Miracle: lighter particles,
weaker interactions à right abundance
Boehm, Fayet (2003);

WIMP DM

WIMPless DM

Feng, Kumar (2008); Feng, Tu, Yu (2010)•

Pospelov, Ritz, Voloshin (2007); Hooper, Zurek (2008)
7 October 2019

Feng 14clert i s
Pa xptE

THE NEW PARTICLE LANDSCAPEMassMeVGeV

TeVatter

ark
Dight
tobe

10-3

Weakly Interacting
Light Particles

10-6

7 October 2019

Strongly Interacting
Heavy Particles

M

Too Already
Little to be
DiscoveredDark
Matter

JustR

Interaction Strength

1Impossible
Too
Much to tobe
DiscoverDark
MatterFeng 15DARK SECTORS• Light, weakly interacting particles naturally emerge fromgeneralizing dark matter à dark sectors.
• E.g: suppose there’s a dark sector with DM and its own EMforce. It can interact with the SM through a dim 4 operator:

SMU(1)EM

Dark Sector
DM, U(1)
MHoldom (1986)• The result is a weakly interacting (since interactions areinduced by a loop) particle (“mediator”): the dark photon.
• Other mediator possibilities: dark scalar, dark fermion.
7 October 2019

Feng 16STRUCTURE FORMATION WITH SIDM
• The possibility of a dark sector naturally allows DM to bestrongly self-interacting. It is even more motivated by theidea of a light thermal relic with mass around MeV – GeV,
which naturally generates s/m ~ barn/GeV ~ cm2/g.

SM

Dark Sector• From this viewpoint, perhaps “Is a theory beyond Cold Dark
Matter needed to describe structure formation?” should be“What can structure formation tell us about dark matter’s
self-interactions and other properties?”• Strong motivation for N-body simulations with SIDM andDM with other properties.
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LIGHT, WEAKLY INTERACTING PARTICLES• The possibility of light, weakly interacting particles canbe explored without enormous investments.
• It puts a premium on new ideas, new techniques, newcollaborations between theorists and experimentalists.
• Many new ideas in indirect detection and direct
detection, both for existing DM detectors and inproposed experiments (see earlier talks).
• Also many new ideas for collider and accelerator
experiments probing light, weakly interacting particles
and/or long-lived particles
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NEW COLLIDER/ACCELERATOR EXPERIMENTS• A wealth of new experiments, some on very short timescales
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FASER: FORWARD SEARCH EXPERIMENT• New physics searches at the LHC focus on high pT . This isappropriate for heavy, strongly interacting particles, like TeVscale superpartners• However, if new particles are light and weakly interacting, thismay be completely misguided– Light and weakly-interacting à we can be produced in p, K, D, B
decays, but they are typically produced along the beamline, where thedetectors have a blind spot

• Conclusion: we can enhance the LHC’s discovery reach byputting a detector where the pions are: at low pT along thebeamline

Feng, Galon, Kling, Trojanowski (2017)7 October 2019

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FASER LOCATIONATLAS IPSPSLHC

TI12FASER

The view looking west

New Particles(Dark Sector)
7 October 2019

LHC Beamline(Visible Sector)
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FASER DETECTOR
Cylindrical decay volume: L = 1.5m, R = 10cm
Total volume: 5m x 1m x 1m
Main Crate

A tabletop experiment!

Chillers

Tracker Crate

Cable Tray

TR Kk
B ac

bone

Upper Frame
Aluminum + Steel plates(interface to the floor)

7 October 2019

ECAL

Feng 22DARK PHOTON SENSITIVITY REACH••

FASER was approved and funded in early 2019 by CERN and theHeising-Simons and Simons Foundations.
Now under construction with very helpful contributions from LHCb andATLAS SCT Collaborations.
FASER
10-3LHCb D*HPS

10-4

LHCb A'→μμϵ

SeaQuest

1 fb

10-5-1

10 fb -1

SHiP150 fb -1

NA62

3000 f

10-610••Belle-IIb -1

Dark Photon-2

10-1
mA' [GeV]FASER probes new parameter space with just 1 fb-1 starting in 2021
Possible upgrade to FASER 2 for HL-LHC will increase (Lum*Vol) by ~106.

7 October 2019Feng 23

FASER COLLABORATION•

46 collaborators, 18 institutions, 8 countries

Henso Abreu (Technion), Claire Antel (Geneva), Akitaka Ariga (Bern), Tomoko Ariga (Kyushu/Bern), Jamie Boyd (CERN), DaveCasper (UC Irvine), Franck Cadoux (Geneva), Xin Chen (Tsinghua), Andrea Coccaro (INFN), Candan Dozen (Tsinghua), Yannick
Favre (Geneva), Jonathan Feng (UC Irvine), Didier Ferrere (Geneva), Iftah Galon (Rutgers), Stephen Gibson (Royal Holloway),
Sergio Gonzalez-Sevilla (Geneva), Shih-Chieh Hsu (Washington), Zhen Hu (Tsinghua), Peppe Iacobucci (Geneva), SuneJakobsen (CERN), Roland Jansky (Geneva), Enrique Kajomovitz (Technion), Felix Kling (SLAC), Susanne Kuehn (CERN),Lorne Levinson (Weizmann), Congqiao Li (Washington), Josh McFayden (CERN), Sam Meehan (CERN), Friedemann Neuhaus(Mainz), Hidetoshi Otono (Kyushu), Brian Petersen (CERN), Helena Pikhartova (Royal Holloway), Michaela Queitsch-Maitland(CERN), Jakob Salfeld-Nebgen (CERN), Osamu Sato (Nagoya), Kristof Schmieden (CERN), Matthias Schott (Mainz), AnnaSfyrla (Geneva), Savannah Shively (UC Irvine), Jordan Smolinsky (UC Irvine), Aaron Soffa (UC Irvine), Yosuke Takubo (KEK),
Eric Torrence (Oregon), Sebastian Trojanowski (Sheffield), Dengfeng Zhang (Tsinghua), Gang Zhang (Tsinghua)

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FASER LOCATION NOW• In TI12, unused ventilation ducts, cables, etc. have been
removed to prepare for FASER trench excavation andinstallation.

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FASER CONSTRUCTION NOW•

The main component of FASER is the tracker, composed of spare SCT
modules from ATLAS. 8 SCT modules make up a 24cm x 24cm trackinglayer, 3 layers make up a tracking station, and FASER has 3 tracking
stations. Tests of prototype tracking layers have started.

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COMPLEMENTARY EXPERIMENTS AT THE LHCSHiPCODEX-b~1000 m3, ~100M CHF + beam
Alekhin et al. (2015)~1000 m3 ~ 1 mIKEAs
Gligorov, Knapen, Papucci, Robinson (2017)

MATHUSLA~800,000 m3 ~ 1 IKEA, ~$50M
Chou, Curtin, Lubatti (2016)7 October 2019

FASER

~1 m3 ~ 1 µIKEAs
Feng, Galon, Kling, Trojanowski (2017)

Feng 27