FASER ForwArd Search ExpeRiment at the LHC Sebastian Trojanowski National Centre for Nuclear Research, Poland (& UC Irvine) New Physics with Displaced Vertices NCTS, Hsinchu, 21 June 2018 (FASER group see https://twiki.cern.ch/twiki/bin/viewauth/FASER/WebHome) arXiv:1708.09389, 1710.09387, 1801.08947, 1806.02348 (with J.L. Feng, I. Galon, F. Kling) FASER OUTLINE • Motivation and idea of the FASER experiment • Location of the experiment • Detector layout • Models of new physics in FASER -- dark photons, -- dark Higgs bosons + invisible decays of the SM Higgs, -- heavy neutral leptons at GeV scale, -- axion-like particles, -- inelastic dark matter. • Background: simulations & in-situ measurements • Conclusions 2 FASER MOTIVATION AND IDEA ● Traditionally, new physics particles have been searched for in the high-pT region Focus on heavy and strongly-coupled particles, e.g., Higgs, SUSY, extra dim, … 7 -1 σ ~ fb – pb, e.g., NH ~ 10 at 300 fb energy frontier ● However, light and weakly-coupled new particles typically escape such detection, they can be produced e.g. in rare meson decays, and typically go in the far forward region pT ~ ΛQCD, θ ~ ΛQCD /E ~ mrad, new particles are highly collimated along the beam-axis ● FASER – newly proposed, small (~1 m3) and inexpensive (~1M$) detector to be placed few hundred meters downstream away from the ATLAS/CMS IP to harness large, currently „wasted” forward LHC cross section intensity frontier 17 -1 σinel ~ 75 mb, e.g., Nπ ~ 10 at 3 ab FASER new SM π, K, D, B, … physics LHCf, TOTEM, ALFA, CASTOR 3 FASER FASER LOCATION FASER 4 FASER FASER LOCATION – TUNNEL TI18 thanks to Mike Lamont ATLAS IP FASER TI18 •promising location in a side tunnel TI18 (former service tunnel connecting SPS to LEP) • about L ~ 480m away from the IP along the beam axis • space for a few-meter-long detector • precise position of the beam axis in the tunnel up to mm precision (CERN Engineering Dep) • corrections due to beam crossing angle (for 300μrad the displacement is 7 ~ cm) 5 FASER FASER LOCATION PHOTO (1) thanks to Mike Lamont TI18 New physics hidden in the dark… beam pipe 6 FASER FASER LOCATION PHOTO (2) thanks to Mike Lamont …can be brought to light 7 FASER LHC INFRASTRUCTURE AROUND LLP – Light Long-lived Particle TAN LLPs produced absorber for Some LLPs decay in FASER at the IP neutral particles two (~TeV) charged tracks e.g. e+e- LHC magnets Other LHC infrastructure effectively deflect + ~90m of rocks charged particles (shielding from the IP) 8 (reduced μ BG) FASER BASIC DETECTOR LAYOUT •ongoing GEANT4 studies for optimization of: - lenght of decay volume, - number and placement of tracking layers, - strength and region of B field. E.g., 1 TeV A’ e+e- : Dave Casper (UCI/ATLAS) - 0.5 T magnetic field over 1m length, Asymmetric decays - sufficient to separate ~50% of the charged tracks by > 1 mm, - much larger separation possible for asymmetric decays. In the following we assume separation Track 100% detection efficiency 9 Decay angle in A’ frame FASER FASER – BENCHMARK SETUP(S) L • convenient for pheno modelling – cylindrical detector beam R axis • 2 stages of the project: FASER 1: L = 3 m, R = 10 cm, V = 0.1 m3, 150 fb-1 (Run 3) cost ~ $1M Ongoing efforts: state-of-the-art BG simulation (done by CERN Engineering Dep), scheduled in-situ BG measurements (CERN approved), (THIS WEEK !!!) ongoing GEANT4 studies – detector design FASER 2: L = 5 m, R = 1 m, V = 16 m3, 3 ab-1 (HL-LHC) 10 FASER DARK PHOTON (pp→pA′X) •typical decay length -7 -3 for ε~10 -10 and mA′~10MeV-1GeV in the range of FASER • production rates suppressed by ε2 0 e.g. in π decays 0 2 2 2 3 BR(π →A′γ) = 2 ε (1- mA′ /mπ ) 11 J. Alexander et al., Dark Sectors 2016 Workshop: Community Report FASER 1708.09389 DARK PHOTONS AT FASER -- KINEMATICS pions at the IP A’s at the IP A’s decaying in FASER p 0 [GeV] π p [GeV] d [m] 0 A' pA' [GeV] d [m] 4 π EPOS- LHC 0 10 4 π →γA' EPOS- LHC 3 0 3 10 10 104 π →γA' 10 mA'=100 MeV mA'=100 MeV 3 - 5 2 2 10 103 ϵ=10 10 103 ϵ=10- 5 10 2 10 102 10 102 10 16 p p 10 10 T 5 T 1 p 10 10 , T 1 = A 10 10 ,A 15 Λ ' = ' = 10 Q Λ Λ C Q D 4 C - 1 Q - 1 1 10 D 10 1 C 1014 1 1 D 10 3 - 1 m - 1 13 - 1 10 - 2 10 c - 2 10 10 10 10 - 1 0 10 10 2 12 2 - 2 = 10 R 10 - 3 10 - 2 - 2 10 - 2 Lmax=480m - 3 10 - 5 - 4 - 3 - 2 - 1 π 10 - 5 - 4 - 3 - 2 - 1 π 10 10 10 10 10 10 10 1 10 10 10 10 10 1 10- 5 10- 4 10- 3 10- 2 10- 1 1π 2 2 2 θ 0 θ π A' θA' •Monte Carlo fitted to • π0 →A′γ •only highly boosted A′s experimental data (LHCf, ALFA) survive until FASER 0 •high-energy π EA′ ~TeV •typically pT ~ ΛQCD collimated A’s •further suppression from decay in volume probability 2 -10 •for E~TeV pT/E ~0.1 mrad •ε ~10 suppression •still up to NA′ ~100 events but still up to in FASER, 15 • even ~10 pions per (θ,p) bin 105 A′s per bin mostly within r<20cm 12 FASER 1708.09389 DARK PHOTONS AT FASER -- SENSITIVITY 10- 3 10- 3 FASER LHCb D* int - 1 L =3ab , EA'>100GeV HPS Lmax=480m, Δ=5m, R=1m - 4 B - 4 10 rem 10 LHCb A'→μμ ss tra hlu ng 10- 5 10- 5 4 3 ϵ 10 ϵ SHiP 1 1 F 3 AS g E 10 g R 1 γ γ g - 6 102 g - 6 10 10 10 10 FAS 3 ER 2 π0→γA' 3 η→γA' SeaQuest - 7 - 7 10 10 NA62 FASER 10- 8 10- 8 10- 2 10- 1 1 - 2 - 1 1 10 10 1 ' 1 mA [GeV]gγg mA' [GeV]gγg direct (QCD) •both FASER 1 and FASER 2 can have world-leading sensitivity at the time of operation, production -7 -6 currently •in FASER 2 the reach extends to mA’ > 1GeV for ε~10 -10 , -4 -6 not included •for ε~10 -10 contours with NA′=const are very densely spaced (exponential suppression for decay length << L~480m) • the reach is then similar for FASER and much larger experiments, • also reach there is very mildly sensitive to the exact number of BG events, detector efficiency etc. 13 FASER DARK HIGGS BOSONS AT FASER 1710.09387 ф 10- 2 F A S •Important production channel: B→Xsф E R NA62 at FASER energies: N /N ~10-2 1 B π - 3 SeaQuest -7 10 for beam-dumps typically NB/Nπ < 10 1 ~ g •FASER’s reach is complementary γ - 4 LHCb g 10 θ to other proposed experiments F AS ER (large boost allows to probe lower lifetime) 2 - 5 C 10 OD EX - b • Typical p ~m SHiP T B MATHUSLA improved reach for FASER 2 (R=1m) FASER 10- 6 10- 1 1 10 1 14 mϕ [GeV]gγg FASER 1710.09387 PROBING INVISIBLE DECAYS OF THE SM HIGGS f h f • trilinear coupling invisible Higgs decays h → фф • far-forward region: efficient production 10- 2 via off-shell Higgs, B → Xsh*(→ фф) - 3 10 B→Xsϕ -6 • can extend the reach in θ up to 10 10- 4 1 g γ for B(h → фф )~0.1 g θ F A - 5 S 10 E R 2 • up to ~100s of events 10- 6 FASER B(h→ϕϕ)=0.1 10- 7 10- 1 1 10 1 15 mϕ [GeV]gγg FASER HEAVY NEUTRAL LEPTONS 16 FASER HEAVY NEUTRAL LEPTONS AT FASER 1801.08947 FASER 2 Decay modes: FASER 2 17 FASER ALPS AT FASER – 1806.02348 LHC AS A PHOTON BEAM DUMP Dominant „aγγ” coupling – production modes: a) Primakoff process (γN→aN) 0 b) Rare decays of π and η 18 FASER 1806.02348 ALP DIPHOTON COUPLING – FASER REACH •signal = 2 high-energy photons (γγ), 10- 2 • need of calorimeter; existing technology e.g. LHCf calorimeter: 10- 3 -- 23cm long, 1 -- 5% energy resolution for E>100GeV g γ g - 4 FA ] 10 S (used also for a few TeV energies) E 1 R 1 Belle- II 3γ - F V A -- 2 photons reconstructed with 90% efficiency SE e R 2 if they are 1mm away from each other G - 5 [ 10 γ γ Belle- II γ+inv a g NA62 •Ea~ few hundred GeV, SeaQuest 3 10- 6 for ma~100MeV γLor = Ea/ma~few x10 typical opening angle θγγ~2/γLor < 1 mrad FASER SHiP after >1m both photons are separated ~1mm 10- 7 10- 2 10- 1 1 (more details see 1806.02348) 1 ma [GeV]gγg + - • possible conversions in the tracker layers (γe e ) 19 FASER INELASTIC DARK MATTER AT FASER For more details see : A. Berlin, F. Kling, 1806.xxxxx (also MATHUSLA, Codex-b, LHC) Pseudo-Dirac pair χ1 and χ2 nearly degenerate in mass small mass splitting FASER 2 PRELIMINARY A’-portal, dominant off-diagonal coupling to A′ Production pp→A′→χ1χ2 goes through A′/Z: -- meson decays, -- dark Bremstrahlung, -- Drell-Yan χ2 decays are delayed by adjusting Δ: up to 100s of events in FASER 20 reach can go up to mA′=3m1 > 30GeV ! m1 [GeV] FASER BACKGROUNDS – SIMULATIONS (1) Spectacular signal: -- two opposite-sign, high energy (E > 500 GeV) charged tracks, -- that originate from a common vertex inside the decay volume, -- and point back to the IP (+no associated signal in a veto layer in front of FASER), -- and are consistent with bunch crossing timing.