Detecting and Studying High-Energy Collider with FASER --FASER흂--

The FASER Collaboration Coordinators: Akitaka Ariga (Bern), Tomoko Ariga (Kyushu), Felix Kling (SLAC)

arXiv:1908.02310

1 FASER휈

• “Collider neutrinos” have never been directly detected, but we can detect ~20,000 of them in LHC Run-3 at FASER휈 and at TeV energies. • Cross-section measurements at currently unconstraint energy ranges for three flavors. Studying heavy quark production channels. • We have been thinking about possible measurements, which were discussed in the LOI response to the LHCC reviews, and also explicitly in the TP. • The design of the trench that will be dug in early 2020 already includes an area for the FASER휈 detector to be on the LOS.

흂풆 흂흁 흂흉

2 FASER layout ≡ high energy neutrino beamline charged particles (P<7 TeV) forward jets FASER휈 neutrino, dark photon LHC magnets p-p collision at IP 100 m of rock of ATLAS 480 m

Interaction Decay Charged particle stop target=7 TeV p volume sweeping Detector 280 휆𝑖푛푡

Neutrino beam size Expected # of interactions in Run 3 (2021-2023) with 7+7 TeV, 150 fb-1, detector mass 1.2 ton, on-axis

# of CC Mean interacting interactions energy

휈푒 + 휈푒 1296 827 GeV

휈휇 + 휈휇 20439 631 GeV

휈휏 + 휈휏 21 965 GeV 3 Reminder – these studies were included in the FASER TP

In situ background measurements TI18 • Emulsion detectors were installed in two sites in 2018 TI12 • Charged particle flux, angle, momenta were measured (only for on-axis) Angular distribution with from IP different energy cutoff from LHC beamline

TI18

Flux all Flux in main peak [fb/cm2] [fb/cm2]

TI18 data 2.6 ± 0.7 × 104 1.2 ± 0.4 × 104

TI12 TI12 data ퟑ. ퟎ ± ퟎ. ퟑ × ퟏퟎퟒ ퟏ. ퟗ ± ퟎ. ퟐ × ퟏퟎퟒ

FLUKA MC ퟐ. ퟎ × ퟏퟎퟒ

4 FASER휈 detector design Detection efficiency (charged multiplicity>=5) • Emulsion detector with tungsten target • Decades of experiences as (based on GENIE) • Sensitivity to heavy flavor particles, 휈휏, 푐ℎ푎푟푚, 푏푒푎푢푡푦 • Tungsten is chosen due to short 푋0 and low radioactivity

1.2 tons 25 cm x 25 cm x 1.3 m 285 푋0 10 휆𝑖푛푡

Tau decay detection efficiency =75% (휏 → 1 prong) Mean flight charm beauty length ≃ 30 mm heavy quark production channels

• Replace every 15-50 fb-1 to maintain track density low • Challenges: Logistics to transport and replace the 1-ton- 5 scale detector every technical stops (3 times/year). Pilot neutrino detector in 2018 30 kg detector, exposed to data of 12.5 fb-1 at TI18 A few tens of neutrino interactions are expected Vertex search: Tracks emerging from a point 15 kg with lead Reconstructed tracks in 2 mm x 2 were searched for. Several vertex candidates mm x 10 emulsion films 15 kg with tungsten have been found so far.

≃ 3 × 105 tracks/cm2 line of sight mostly muons and associated electrons

This proves that the detector works in the LHC TI18 environment We are learning a lot from this pilot run sample. Track reconstruction algorithm, data processing scheme. Synergy with the DsTau experiment (NA65), as both share similar track density. Background to neutrino events are carefully being estimated. We are aiming to report the first detection of neutrinos from the LHC. 6 FASER휈 + FASER, hybrid detector design

• Combining FASER and FASER spectrometer information understudy • An additional tracking station to be installed at the front of the FASER decay volume • To allow accurate matching of tracks from emulsion vertices to the spectrometer • Baseline, the ATLAS SCT as other FASER tracking stations. (To be installed in 21/22 YETS) • Would allow: • To distinguish 휈휇 and 휈휇 from charge measurement of lepton  Wider physics cases • To improve neutrino energy reconstruction by momentum measurement of outgoing particles in the FASER spectrometer • To reduce backgrounds (e.g. by using event time from spectrometer to see if charged particle entering FASER for that event)

7 Targets in Run 3 (2021-2022) Expected yields in Run 3 (2021-2023), • Firm establishment of “collider neutrino” measurements  open a 14 TeV, 150 fb−1, 1.2 tons. new domain of physics programs in the LHC # of CC Mean • Tau neutrino detection interactions interacting • Charged current cross section measurements energy • Three flavors in an energy range where cross sections are unconstrained 휈푒 + 휈푒 1296 827 GeV • Additional physics studies • Measurement of charm production channels, search for beauty production 휈휇 + 휈휇 20439 631 GeV channels in 휈휇 and 휈푒 CC • Intrinsic charm and “prompt neutrino” study 휈휏 + 휈휏 21 965 GeV • oscillations • More detailed uncertainties on 휈 production / interaction / detector response / energy reconstruction are being studied.

↓ Projected precision of FASER흂 measurement 휈 푙− 휈푒 휈휇 휈휏 d 푐

휈 푙+ u 푏 8 Resources, cost and funding

• Resources • Funding and contribution • We have sufficient personnel with expertise in • Grants from JSPS and the Mitsubishi foundation neutrino physics / emulsion detector technology have been approved to support partially the • Experience and software tools from former FASER neutrino program. In addition, the Japan DONuT, OPERA and recent DsTau(NA65) emulsion group promised to provide part of the 흂 (FASER has similar condition to DsTau) emulsion gel (half of the total). • Fast emulsion scanning systems and raw data • With the already secured funding and processing machines are available. A dedicated contribution, we can prepare 0.6-ton server will be added. Data storage (1PB) would be needed. tungsten/emulsion detector for the whole Run3 (2021-2023, 7 replacements). • Cost • We are seeking for additional funding • Detailed cost estimate in the backup slides • An ERC proposal under review (step1 passed) • Total 595 kCHF for the 1.2-ton tungsten/emulsion detector (7 replacements of • Contacting the Heising-Simons Foundation and the emulsion films) Simons Foundation • Additional 173 kCHF for extra set of tungsten • Other JSPS / SNF grant applications plates (for fast installation / removal of detector), 120 kCHF for interface detector 9 Complementarity with XSEN XSEN info from https://agenda.infn.it/event/19732/contributions/98006/attachments/65435/79655/XSEN_assembleaBo_20190717.pdf

FASERν XSEN Location of detector Centered on LOS Displaced from LOS Space Space on LOS is limited by size of trench and the No digging of trench in TI18. FASER main detector. Less space limitation off axis. Target material Tungsten Lead Other Possibility to couple with the FASER spectrometer

FASERν XSEN

10 Detector position • FASERν: On-axis • Maximize neutrino interaction rate in all flavors • Minimize muon background, which has a strong position dependence. More muon rate off axis. Muon flux measurement in 2018 by FASER was performed only at the on-axis position • XSEN: Off-axis • Decrease total number of interactions for all flavors (enhance tau neutrino fraction) • Predicted muon background is higher (about x10 at 50 cm)

FASER Expected number of neutrino CC interactions Muon background XSEN B2 (estimated with our flux estimation) XSEN B1 FASERν XSEN B1+B2 FLUKA muon (1.2 ton) (assuming 3 tons) flux estimate by STI group 휈푒 1300 1200

휈휇 21500 14000

휈휏 22 34 Hole of muon flux on-axis 11 Tungsten Lead Target material - density 19.30 g/cm3 - density 11.35 g/cm3 - 휆int 9.9 cm - 휆int 17.6 cm

- X0 3.5 mm - X0 5.6 mm FASERν: Tungsten • High density → higher interaction rate, keeping the detector small and the emulsion cost low

• Shorter X0 → higher performance in • the EM shower reconstruction, keeping shower tracks in small radius • the momentum measurement by multiple Coulomb scattering • Low radioactivity • Relatively expensive, but still not the most expensive component XSEN: Lead • Lower density

• Longer X0 • Higher radioactivity • XSEN can re-use the OPERA lead plates for free

12 Summary

• FASER휈: High energy frontier of man-made neutrinos at 1 TeV scale from the LHC, which would open new domain of physics research • Detailed flux simulation, detector design, physics cases were reported in arXiv:1908.02310 • A 1.2-ton neutrino detector in Run 3 (2021-2023) can collect ∼20,000 휈휇, 1000 휈푒 and 20 휈휏 CC interactions • Emulsion-based detector to study different flavors (휈푒, 휈휇, 휈휏, charm and beauty). • An in-situ measurement of background proved that emulsion detector can work at the actual environment. • The 30 kg pilot neutrino detector accumulated 12.5 fb-1 of data in 2018. Hoping to report a first detection of neutrinos from the LHC in this year. • Investigating possibility of combining FASER휈 with FASER spectrometer, would require an additional tracking station that could be installed in 21/22 YETS • Funding available for 1/2 of proposed emulsion detector for full Run-3, actively pursuing additional funds (also for additional tracking station). • Positive review of physics case by the LHCC would likely help funding. 13 To do list

• Mechanical design of FASERν detector support (including being able to raise detector from trench floor to be aligned with crossing angle) • Discussion with CERN transport on installation / removal of detector (needs to be fast/reliable/safe for LHC) (any specific tooling needed) • Discussion with CERN Radio Protection group to understand any RP issues with removal/installation • Support from Physics Beyond Colliders for above studies • Plan to present details at TREX meeting in September and then to the LMC

14 Backup

15 Motivation for high energy neutrinos Muon neutrino cross-sections (PDG) • Neutrino-quark scattering are basic tools to study interactions between leptons and quarks, QE, Res DIS especially in DIS 휈 − 푁 휈 − 푞 • Flavor physics with high energy neutrinos, 휈푒, 휈휇, 휈휏 and charm, beauty

• Few data available at high energy 퐸휈 ≥ 300 GeV • Let’s study high energy “collider neutrino” at the LHC!

흂풆 흂흁 흂흉 흂풆 흂흁 흂흉

16 Emulsion detectors: AgBr crystal = detector 3D tracking device with 50 nm precision 1014 channels/film or 1014 channels/cm3 Cross-sectional view Emulsion film Emulsion layer (≃50 m)

Plastic base (≃ 200 m)

Emulsion layer 200 nm

Residual from fitted track s = 50 nm

Sensitivity 36 grains/100 m 10 GeV/c  beam

20 m 17 A tau neutrino event in OPERA with emulsion-lead detector 휈 detector sensitive to heavy flavor particles Sensitivity to 휈푒, 휈휇, 휈휏 and also charm and beauty

Kink angle = 41 +- 2 mrad Decay length = 1335 +- 35 m An event from OPERA +6 P(daughter) = 12 – 3 GeV +230 t  rt PT(daughter) = 470 -120 MeV 0 Phi angle = 173 +-2 deg r    gg Minv (gg) = 120 +-20 +- 35 MeV 0 +125 +100 Minv (  (r)) = 640 -80 -90 MeV 18 Muon background

There is a hole of muon flux at the line of site due to sweeping effect of the LHC magnets.

Muons has TeV energy scale.

19 Angular distributions of beam backgrounds Projection Y and zoomed particles from ATLAS IP 휎 = 2.3 mrad ≃ measurement resolution  marginal multiple Coulomb scattering in 100 m of rock  the particles are very high particles from the 10 mrad momentum, P>300 GeV. LHC beamline

Projection X

(uncertainty 100%)

Data and the FLUKA beam detector prediction agrees within structure their uncertainties.

tungsten plates, 0.5 mm emulsion films, 0.3 mm 20 Neutrino flux

estimation

04

-

Lhc

tune

tune, tune,

-

2.3c

-

ii

-

-

Epos

Sibyll

Monash

Qgsjet

minimum bias bias A2 minimum Pythia 8

Shaded region = range of predictions

21 Expected # of interactions

• Sizable number of neutrino interactions already in Run 3 (2021 – 2023) • All flavors Expected # of interactions in Run 3 (2021-2023) with 7+7 TeV, 150 fb-1, detector mass 1.2 ton • Narrow beam • FASER휈 = on axis

22 Particle momentum measurement by multiple Coulomb scattering (MCS) • Sub-micron precision alignment thanks to muons. • Our experience = 0.4 μm (in DsTau) • This allow to measure particle momenta by the MCS, even above 1 TeV.

Performance with position Measurable energy vs resolution of 0.4 μm, in 100 position resolution 23 tungsten plates (MC) Example of MCS and fit

track in 100 layers of tungsten x 1 mm Trajectory in Y

Trajectory in X smeared with position resolution

RMS of scattering as a Fitting result function of cell length

2 0.0136 2 푥 퐹 푃, 훿 = 푥 + 훿2 푃 3 푋0

position resolution = 0.4 휇푚 24 Features of neutrino interactions

• GENIE • 휈휇 퐶퐶 events • extended for high energy • MC truth  • Inputs for energy measurement

25 Neutrino energy estimation

Momentum measurement by the Energy resolution Multiple Coulomb Scattering (MCS) • Thanks to high alignment accuracy (~0.4 휇푚), the MCS of charged particle P>1 TeV can be measured

• Sum of visible energy (model independent) already gives a reasonable resolution • ANN can solve problem at high energy and gives about 30% resolution at relevant energy

range. 26 Main background to vertex search • Neutral produced by muons via photo-nuclear interactions • muons interacted in rock  neutral hadrons • muons interacted in tungsten  neutral hadrons • These hadrons are low energy. No lepton at the interaction.

FASER휈 Rock

Produced in rock and Produced in FASER휈 27 enter to FASER휈 CC / NC / hadron separation

• On top of lepton identification, the kinematical features can provide additional separation 휙 • Measurement with 2 휆𝑖푛푡 for track measurement • 휈휇 CC identification eff = 86% HMP Others • purity 푁퐶퐶/ 푁퐶퐶 + 푁푁퐶 + 푁푛푒푢푡푟푎푙 ℎ푎푑푟표푛 = 86%

28 Heavy-flavor-associated channels • Measure charm production channels • Study of quark mixing and QCD • Large rate ~ 10% 휈 CC events

• Search for Beauty production channels • Probe for “flavor anomaly” suggested by collider experiments • Expected events (휈휇 퐶퐶 푏 production) are 2 −5 풪(0.1) events in Run 3, due to CKM suppression, 푉푢푏 ≃ 10

휈 푁 → ℓ퐵 푋

휈푁 → ℓ퐵퐷푋 29 Heavy-flavor-associated channels

• Weak charm production • study of quark mixing and QCD

휈 ℓ charm production via mixing mainly 휈 푑 푉푐푑 푐

휈 ℓ

charm production via partonic 푠 푉 푐 interaction 푐푠 both 휈, 휈 푠

푞 30 Topology of beauty channels t- + t t t

Sea cc c b quarks u b c

Topology in detector t X t X B D D B X X D X

휎 휈 푁 → 휏퐵 푟푒푙 휏 푟푒푙 휎 휈휏푁 → 휏퐵퐷 휎휏 퐵 = 휎휏 퐵퐷 = 휎 휈휏 푁 → 휏푋 휎 휈휏푁 → 휏푋 푟푒푙 푟푒푙 휎휏 퐵 휎 퐵퐷 푅 퐵 = 휏 푟푒푙 푅 퐵퐷 = 푟푒푙 31 휎휇 퐵 휎휇 퐵퐷 CERN WA75 Direct Observation of the Decay of Beauty particles into charm particles Phys. Lett. B158, 186, 1985

32 “Prompt Neutrino” Production and Intrinsic Charm • Forward charm production in 푝-푝 collision is not well understood  Large uncertainty in “prompt neutrino” production. • 14 TeV p-p collision ≡ 100 PeV interaction in lab frame • Intrinsic Charm content in proton could change neutrino production by a factor of 10 at high energy • Important input to extraterrestrial neutrinos measurements, e.g. by IceCube

• FASER휈 would be able to study it in 휈푒, and 휈휏 channels.

IceCube

33 Sterile neutrino oscillation

• Due to unique energy and baseline (small 퐿/퐸), FASER휈 is sensitive to large Δ푚2. • If the effect is enough large, the spectrum deformation may be seen.

34 Neutrino oscillation sensitivity

35 Cost estimate

Tungsten / emulsion detector Interface detector (for the case with SCT modules) Item Cost Covered [kCHF] Remaining [kCHF] [kCHF] Item Cost [kCHF] Tungsten plates, 1200 kg 173 86.5 86.5 SCT modules - Emulsion gel for 440 m2 314 220 m2 157 Tracker mechanics 5 Emulsion film production cost 31 15.5 15.5 Tracker power supply and 15 Packing materialcs 5 5 cooling ventilation

Support structure 12 12 layer) (per Trigger readout board 3

Chemicals for emulsion 20 20 Cabling 2 development Spare 5 Tools for emulsion development 5 5 Total per layer 30 Racks for emulsion film storage 5 5 Total for the current 120 design (3+1 layers) Computing server 10 10 0

Data storage (1 PB) 20 20

Total 595 - 326 36 Complementarity with XSEN XSEN info from https://agenda.infn.it/event/19732/contributions/98006/attachments/65435/79655/XSEN_assembleaBo_20190717.pdf

FASERν XSEN (B2) XSEN (B1)

Detector position: (digging of a trench) (no digging) (no digging) distance from the axis 0 - 12.5 cm 5 - 30 cm 25 - 60 cm

Mean energy 휈푒 827 GeV 휈휇 631 GeV 1.2 TeV(?) 0.7 TeV(?) 휈휏 965 GeV

Target material Tungsten (1 mm thick) Lead (1 mm thick) Lead (1 mm thick) - density 19.30 g/cm3 - density 11.35 g/cm3 - 휆int 9.9 cm - 휆int 17.6 cm - X0 3.5 mm - X0 5.6 mm

Target mass (Run3) 1.2 ton 0.4 ton --> 1.5 ton 0.4 ton → 1.5 ton

Emulsion/target cost Emulsion 314k CHF Emulsion ? Emulsion ? Tungsten 173k CHF Lead 0k Lead 0k

Number of int. 휈푒 1300 with 150 /fb 휈휇 20000 Up to 2000 int.(?) 휈휏 20 Up to 100 휈휏(?)

Muon ID (for 휈휏 detection) 1-m tungsten (10휆int) ? ?

Electronic detector FASER spectrometer - - 37 38 Expected number of neutrino interactions

The expected number of neutrino CC interactions at FASER휈 In FASERν, the charm production and at XSEN (B1+B2) (estimated with the FASER휈 flux) channels are simulated with Pythia 8. However, note that the default Pythia FASERν XSEN B1+B2 FASERν XSEN B2 XSEN B1 (1.2 ton) (1.5+1.5 tons) 푬 GeV 푬 GeV 푬 GeV is found to be not appropriate for the 흂 흂 흂 forward hadron production. Therefore 휈푒 1300 1200 827 650 573 we used Pythia 8 using both the 휈휇 21500 14000 631 524 499

MONASH-tune and A2-tune. 휈휏 22 34 965 791 686

νe νμ ντ

39 Module segmentation Detector must be divided into small pieces, so that people can handle (5-20kg each). FASERν: Aims to reconstruct long tracks for muon identification. Muon ID is fundamental to detect tau neutrinos, because we need to reject background from numu CC charm production. This BG can be killed by identifying muons. Since λint is 10 cm in tungsten, we need to follow at least 2λint (20 cm) to identify muons. We will make many slices of detectors but without a gap (<1mm). FASERν nutau CC BG : numu CC charm prod. tau mu charm particle decay

XSEN: Lead-based OPERA like bricks. 56 x 1mm lead XSEN plates → 0.32 λint, which would be not sufficient for muon identification. XSEN’s structure inevitably have 25 cm x a gap between modules larger than 5 mm, which 25 cm x makes the reconstruction over the modules very 2-3 cm challenging (because of high density of muon tracks). 40