Study of high-energy in the FASER experiment at the LHC

Tomoko Ariga Kyushu University / University of Bern on behalf of the FASER Collaboration Physics motivation of the FASERν program

• Study of high-energy neutrinos at TeV scale – First detection of collider neutrinos in far forward location, where high-energy flux is concentrated – Cross-section measurements of all flavors in unexplored energy region – Search for new physics effects in high-energy neutrino interactions

νμ νe

FASERν FASERν

2 Tau neutrino

• Tau neutrino is one of the least ν studied particles τ – Only a few measurements

Direct 휈휏 beam: DONuT

Oscillated 휈휏: OPERA, Super-K, IceCube

FASERν • FASERν aims to measure ντ cross section at the highest energy ever

3 The FASER experiment TI18 TI12 FASER • Current searches for new physics at the LHC focus on high pT (appropriate for heavy, strongly interacting particles) • FASER is a new experiment at the LHC aiming to search for light, weakly- interacting particles – A particle detector will be located 480 m downstream of the ATLAS interaction

point (low pT along the beamline)

ATLAS interaction point pp → LLP + X, LLP travels ~480 m, LLP → e+e-, μ+μ-, …

FASER

0.55T magnet 0.55T magnet 0.55T magnet Signal signature

Decay volume (1.5 m) 4 sensitivity reach The FASER experiment

• FASER LOI, TP reviewed by LHCC • Approved by CERN in Mar. 2019 • Funded by the Heising-Simons Foundation and the Simons Foundation with support from CERN

• FASER installation planned in 2020 – Data-taking in Run3 (2021-2023) (150 fb-1) – Decay volume: R = 10 cm and L = 1.5 m • FASER2 (possible future upgrade) – Data-taking at the HL-LHC (3 ab-1) – Decay volume: R = 1 m and L = 5 m

In addition to searches for new particles, we also aim to study high-energy neutrinos of all flavors No one has ever detected neutrinos at the LHC

5 Expected neutrino rates at FASER

charged particles (p<7 TeV) ~5 m forward jets Neutrino FASER LHC magnets ~100 m of rock p-p collision at IP 480 m of ATLAS

Expected yields in Run 3 (2021-2023)

# of CC Mean interactions energy (GeV)

휈푒 + 휈푒ҧ 1296 827

휈휇 + 휈휇ҧ 20439 631

휈휏 + 휈휏ҧ 21 965

6 with emulsions

Signal topologies Muons AgBr crystal Cross-sectional view e μ 휈푒 휈휇 Emulsion layer

Plastic base Emulsion film Tungsten plate (1 mm thick) (200 m) τ 휈 Emulsion layer 200 nm 휈휏 휈

CC heavy quark production

36 grains/100 m 10 GeV/c  Lepton Lepton 휈 휈ҧ beam 3D tracking device D B 0 with 50 nm precision D 20 m X X 7 In situ measurements in 2018: detector environment TI18 TI12 Particles from Particles from ATLAS IP TI18 the LHC beamline

Normalized flux (fb/cm2) TI18 (2.6 ± 0.7) × 104 TI12 (3.0 ± 0.3) × 104

TI12

8 Test run in 2018: data for possible neutrino detection

• Aims: possible neutrino detection and gamma background measurement • A 30-kg emulsion detector was installed in TI18 and exposed to ~12.5 fb-1

Reconstructed data (2 x 2 mm2) ≃ 3 × 105 tracks/cm2 15 kg with lead 15 kg with tungsten

1000 μm

9 Test run in 2018: data for possible neutrino detection

Vertex candidates

(tilted view) No muon ID in the 2018 run → More background

Neutrino / neutral separation is under study 1 mm 200 μm

Vertex but with parent: Electromagnetic showers pion interaction (partial reconstruction, peak-angle tracks not shown)

500 μm 200 μm 10 Possible detector design for LHC-Run3 (2021-2023)

Total 1000 emulsion films interleaved with 1-mm-thick tungsten plates Muon ID: muons are 휈 1.2 tons identified by their track 25 cm x 25 cm x 1.3 m 285 푿ퟎ length in the detector 10 흀풊풏풕

Muons Expected yields in Run3 e μ τ Lepton # of CC int. 휈푒 휈휇 휈휏 휈 휈 + 휈ҧ 1296 D 푒 푒 X 휈휇 + 휈휇ҧ 20439 Emulsion film Tungsten plate (1 mm thick) 휈휏 + 휈휏ҧ 21

Possibly upgraded to couple with the FASER spectrometer for: • charge measurement • improvement of the energy estimation • background suppression

11 Signal features and backgrounds

νe CC νμ CC ντ CC NC How to identify High energy Muon ID Detection of τ decays electron 0 Background π from ν ・νμ CC charm production Neutral hadron interactions ・Hadron interactions interactions How to suppress Thin target ・Muon ID Topological / kinematical the background ・Topological variables variables

Detection of τ decays: Energy spectrum of neutral flight length / kink angle produced in rocks in front of FASERν

Mean flight length ≃ 30 mm

Kink detection efficiency 75%

12 Neutrino energy reconstruction • Neutrino energy will be reconstructed by combining topological and kinematical variables 퐸 − 퐸 An ANN algorithm was built with 휈 퐴푁푁 topological variables

・ # of charged tracks → 퐸ℎ ・ # of 훾 showers → 퐸ℎ ・ inverse of lepton angle → 퐸ℓ ・ sum of inverse of hadron track angles → 퐸ℎ ・ inverse of median of all track angles → 퐸ℎ , 퐸ℓ kinematical info (smeared)

・ lepton momentum → 퐸ℓ ・ sum of charged hadron momenta → 퐸ℎ ・ sum of energy of 훾 showers → 퐸ℎ Δ퐸 = 25% (RMS) (preliminary) 퐸

Detailed detector simulation under way

13 Prospects for cross section measurements at 14-TeV LHC in Run3 (150 fb-1) using a 1.2-ton tungsten/emulsion detector

νe νμ ντ

Dashed curve: theoretical prediction

Solid error bars: statistical uncertainties. Dashed error bars: also include uncertainties from neutrino production rate corresponding to the range of predictions obtained from different Monte Carlo generators.

14 Summary

• At the LHC-FASER, neutrino cross sections will be measured in the currently unexplored energy range between 350 GeV and 6 TeV. In particular, tau-neutrino cross section will be measured at the highest energy ever. • As a feasibility study, a test run was performed in 2018 at the proposed detector location with a 30-kg lead/tungsten emulsion-based neutrino detector. Data of 12.5 fb-1 was collected and the event analysis is in progress. • For LHC-Run3 (2021-2023), we are planning to deploy a 1.2-ton tungsten/emulsion detector, possibly coupled with the FASER magnetic spectrometer, which would yield about 20000 muon neutrinos, 1300 electron neutrinos, and a few tens of tau neutrinos interacting in the detector. – So far, a JSPS grant and a research grant by the Mitsubishi foundation have been approved to support partially the FASER neutrino program. We are seeking for additional funding. – A paper on the prospects for neutrino studies will be submitted soon.

15 The FASER Collaboration

Henso Abreu (Technion), Claire Antel (Geneva), Akitaka Ariga (Bern), Tomoko Ariga (Kyushu/Bern), Jamie Boyd (CERN), Dave Casper (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), Sune Jakobsen (CERN), Roland Jansky (Geneva), Enrique Kajomovitz (Technion), Felix Kling (UC Irvine), 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), Osamu Sato (Nagoya), Kristof Schmieden (CERN), Matthias Schott (Mainz), Anna Sfyrla (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)

Part of the Collaboration

16 Backup

17 THE FASER DETECTOR

• The entire detector is 5.5 m long. It consists of – veto – 1.5 m-long decay volume – 2 m-long spectrometer – 3 tracking stations – EM calorimeter

0.55 Tesla particles from IP 18 19 DARK PHOTON SENSITIVITY REACH

• Combine ,h → A’g, qq → qqA’, etc., plot NS=3 (10 makes little difference) • FASER: R=10cm, L=1.5m, Run 3; FASER 2: R=1m, L=5m, HL-LHC

FASER -3 FASER and FASER 2

10 * Feng, Kling,Galon, Trojanowski (2017) 10-3 LHCb D *

LHCb D HPS FASER Collaboration (2018) 10-4 LHCb A'→μμ Belle-II HPS 10-4 LHCb A'→μμ 10-5

SeaQuest ϵ SHiP

1 F ϵ ASE g R 1 1 fb-1 γ g -6 -5 10 - SHiP FAS 10 10 fb 1 ER 2 NA62 150 fb-1 SeaQuest -7 10 NA62 3 000 fb-1 -6 10 Dark Photon -8 FASER -2 -1 10 10 10 10-2 10-1 1 1 ' [ ] mA' [GeV] mA GeV gγg • FASER probes new parameter space with just 1 fb-1 starting in 2021

• Without upgrade, HL-LHC extends (L*Volume) by factor of 3000; with possible upgrade to FASER 2, HL-LHC extends (L*Volume) by ~106 20 MORE FASER PHYSICS: ALPS WITH PHOTONS

• FASER can also discover ALPs and other LLPs produced not at the IP, but further downstream • For example: ~TeV photon from IP collides with TA(X)N ~140 m downstream (between beams), creates -Like Particle, which decays through a → gg, detected in FASER calorimeters

10-2 • “Photon beam dump” or “light shining FASER, NS=3 through walls”

SeaQuest

] -3 1

- 10 1

fb -1 V

e 1 0 f -1

G b [ 1 γ 50 f f -1 / b Belle-II 3γ 1 -4 3 = 10 000

γ fb -1

γ

a g

10-5 Belle-II γ+inv NA62 SHiP ALP - Photon Dominance 10-2 10-1

ma [GeV] 21 MORE FASER PHYSICS: DARK HIGGS BOSONS

• SINGLE PRODUCTION • DOUBLE PRODUCTION 10-2

F Feng, Galon, Feng, Galon, Kling, Trojanowski (2017) A S f E R NA62 1

10-3 SeaQuest

1 g γ -4 LHCb

g 10 θ F AS ER 2 -5 C 10 OD EX -b SHiP MATHUSLA FASER 10-6 10-1 1 10 1 mϕ [GeV]gγg • Dark Higgs produced in B decays. • Probes hff trilinear coupling -2 NB/N~10 at FASER • Complementary to probes of exotic -7 (cf. NB/N~10 at beam dumps) Higgs decays h→ff • Reach is complementary to other • FASER probes SM Higgs properties, experiments exotic decays 22 23 Study of neutrino CC interaction with heavy quark production Muon neutrino cross-sections (PDG) • Neutrino-quark scattering are basic QE, Res DIS tools to study interactions between 휈 − 푁 휈 − 푞 leptons and quarks – Those in high energy (DIS regime) tell fundamental interactions between neutrinos and quarks • Flavor physics with high energy

neutrinos, 휈푒, 휈휇, 휈휏 and charm, beauty 휈ҧ + • BSM search, e.g. flavor anomaly 푙 involving heavy leptons and quarks 휈ҧ푁 → ℓ퐵ത푋 u 푏 푙 휈ҧ 휈 − 푏 푙 푐 휈푁 → ℓ퐵퐷푋 Anomalous b semi-leptonic decay 푐ҧ 푏ത 휈 CC 푏 production 24 Neutrino fluxes at 14-TeV LHC

νe νμ ντ

Shaded area: uncertainties from neutrino production rate corresponding to the range of predictions obtained from different Monte Carlo generators. 25 Angular resolution

Align films with tracks (100 tracks/mm2) Angular resolution Reconstructed tracks vs Track length

~4000 tracks in 2 x 2 mm2, 15 films

1000 μm

Residual of track segments to fitted line (RMS) ≃0.4 흁풎

26 Particle momentum measurement by multiple Coulomb scattering (MCS)

• Sub-micron precision alignment using muon tracks – Our experience = 0.4 μm (in the DsTau experiment) • This allow to measure particle momenta by MCS, even above 1 TeV

particle trajectory 푦2 푠

푦1 푦0 푥 푥

Performance with position Measurable energy vs resolution of 0.4 μm, in position resolution 100 tungsten plates (MC)

27 Example of MCS and fit

track in 100 layers of tungsten x 1 mm

Trajectory in X Trajectory in Y smeared with position resolution

RMS of scattering as a function of cell length Fitting result

2 0.0136 2 푥 퐹 푃, 훿 = 푥 + 훿2 푃 3 푋0

position resolution = 0.4 휇푚

28 High-energy EM shower in emulsion/lead chambers

Longitudinal development of the averaged number Astrophys. J. 760 (2012) 146. of shower tracks within a circle of radius 100 μm

Energy resolutions 10.6% at 200 GeV 29