physics experiments based on the AWAKE acceleration scheme

Matthew Wing (UCL / DESY)

• Introduction and motivation • Future beam based on AWAKE scheme • Possible physics experiments • Strong-field QED at the Schwinger field • Search for dark photons, NA64-like

British• High Museum energy electron− collisions, LHeC-like and VHEeP • Summary and discussion

Royal Society Meeting — 5 June 2018 Motivation: big questions in particle physics The Standard Model is amazingly successful, but some things remain unexplained : • a detailed understanding of the Higgs Boson/mechanism • neutrinos and their • why is there so much matter (vs anti- matter) ? • why is there so little matter (5% of Universe) ? • what is dark matter and dark energy ? Does supersymmetry occur at the TeV scale • why are there three families ? • hierarchy problem; can we unify the forces ? • what is the fundamental structure of matter ? • … Colliders and use of high energy particle beams 2 will be key to solving some of these questions Motivation: colliders • The use of (large) accelerators has been central to advances in particle physics. • Culmination in 27-km long LHC (pp); e.g. a future e+e– ? collider planned to be 30–50- t quark km long. W/Z bosons • The high energy frontier is Nν = 3 (very) expensive; can we reduce costs ? Can we gluon develop and use new technologies ? • Accelerators using RF cavities limited to ~100 MV/m; high energies → long accelerators. • The Livingston plot shows a saturation … 3

3 Motivation: wakefield acceleration as a solution • Plasma wakefield acceleration is a promising scheme as a technique to realise shorter or higher energy accelerators in particle physics. • Proton-driven plasma wakefield acceleration is well-suited to high energy physics applications. • Accelerating gradients achieved in the wakefield of a plasma are very high (3 orders of magnitude more than RF acceleration and up to 100 GV/m), but need : - High repetition rate and high number of per bunch; - Efficient and highly reproducible beam production; - Small beams sizes (potentially down to nm scale). • Ultimate goal : can we have TeV beams produced in an accelerator structure of a few km in length ? • Here consider realistic and first applications: - Based on AWAKE scheme of proton-driven plasma wakefield acceleration; - Strong use of CERN infrastructure; - Need to have novel and exciting physics programme. • A challenge for accelerator, plasma and particle physics. 4 An AWAKE-like beam for particle physics

5 AWAKE Run 2 • Preparing AWAKE Run 2, after CERN LS2 and before LS3, 2021–4. - Accelerate electron bunch to higher energies. - Demonstrate beam quality preservation. - Demonstrate scalability of plasma sources.

Preliminary Run 2 electron beam parameters • Are there physics experiments that require an electron beam of up to O(50 GeV) ? • Use bunches from SPS with 3.5 × 1011 every ~ 5 s. • Using the LHC beam as a driver, TeV electron beams are possible.

E. Adli (AWAKE Collaboration), IPAC 2016 6 proceedings, p.2557 (WEPMY008). AWAKE experiment at CERN

• Demonstrate for the first time proton- driven plasma wakefield acceleration. • How can an experiment fit into the CERN complex ?

AWAKE experiment • Advanced proton-driven plasma wakefield experiment. • Using 400 GeV SPS beam in former CNGS target area.

AWAKE Coll., R. Assmann et al., Plasma Phys. Control. Fusion 56 (2014) 084013 7 Possible particle physics experiments I • Use of electron beam for test-beam campaigns. - Test-beam infrastructure for detector characterisation often over-subscribed. - Also accelerator test facility. Also not many world-wide. - Characteristics: ‣ Variation of energy. ‣ Provide pure electron beam. ‣ Short bunches. • Fixed-target experiments using electron beams, e.g. deep inelastic electron−proton scattering. - Measurements at high x, momentum fraction of struck parton in the proton, with higher statistics than previous experiments. Valuable for LHC physics. - Polarised beams and spin structure of the nucleon. The “proton spin crisis/puzzle” is still a big unresolved issue. • Investigation of strong-field QED at the Schwinger limit in electron−laser interactions.

8 Possible particle physics experiments II

• Search for dark photons à la NA64 - Consider beam-dump and counting experiments. • High energy electron−proton collider

- A low-luminosity LHeC-type experiment: Ee ~50 GeV, beam within 50−100 m of plasma driven by SPS protons; low luminosity, but much more compact. - A very high energy electron−proton (VHEeP) collider with √s = 9 TeV, ×30 higher than HERA. Developing physics programme. These experiments probe exciting areas of physics and will really profit from an AWAKE- like electron beam. • Demonstrate an accelerator technology also doing cutting-edge particle physics

Using a new Fixed-target High E ep High E, high technology collider lumi e+e− collider

9 Strong-field QED at the Schwinger field

10 Strong-field QED • Quantum mechanics and QED has been investigated and measured with amazing precision in many experiments and high-precision predictions describe this well. - However the strong-field regime, where QED becomes non-perturbative, has still not been measured. • The strong field regime was already considered by Heisenberg, Euler et al. in 1930s. • Characterised by the Schwinger critical field (1951):

• This has not been reached experimentally, although they are expected to exist: - On the surface of neutron stars. - In bunches of future linear e+e− colliders. • Can be reached by colliding photons with a high-energy electron beam - Pioneering experiment E144 @ SLAC in 1990s.

• Given increase in laser power, investigate QED in an unexplored region. 11 2 3 me c 16 m2 c3 Ecrit = =1.3 10 V/cm E = e =1.3 1016 V/cm e h¯ ⇥ crit e h¯ ⇥ Non-linear QED processes eE ⌘ = eE m !c • Initial interest in two⌘ strong-field= processes in the e interaction of electron beamme !withc high-power laser pulse. 2 E E  = - Non-linear Compton scattering where multiple 2 2 E E me c Ecrit laser photons are absorbed= 2 and a single me c Ecrit E (1 cos ↵) E photon radiated. ⌥= beam m c2 E - One or more such ComptonEbeam scatters(1 cos happen.↵) E e crit ⌥= 2 - Produced photon interacts withme laserc fieldE tocrit produce electron−positron pair e + n e + (Breit−Wheeler) ! + + n e + e e + n e + ! − ! + e− e + n e + e ! n γ n γ

Compton Pair production

12 e− e+ E144 experiment at SLAC

• Used 46.6 GeV electron beam (Final Focus Test Beam) with 5 × 109 per bunch up to 30 Hz. • Terawatt laser pulses with intensities of ~0.5 × 1018 W/cm2 and frequency of 0.5 Hz for wavelengths 1053 nm and 527 nm. • Electron bunch and laser collided with 17∘ crossing angle.

E144 Coll., C. Bamber et al., Phys. Rev. D 60 (1999) 092004; T. Koffas, “Positron production in multiphoton light-by-light scattering”, PhD thesis, 13 University of Rochester (1998), SLAC-R-626. New strong-field QED experiments • New experiments being performed/considered - In LWFA with few-GeV electrons and laser. - Using FACET and EU.XFEL 10−20 GeV electrons and laser. - Using higher-power lasers compared to E144@SLAC. • Could also be an application of an AWAKE-like bunch - Unique feature would be the higher electron energies and hence higher √s. - Sensitive to different processes. - Can constrain more exotic physics (e.g. dark photons).

14 Experiments to search for the dark sector

15 The hidden / dark sector

• Baryonic (ordinary) matter constitutes ~5% of known matter. - What is the nature of dark matter ? Why can we not see the dominant constituent of the Universe ? • LHC Run 1 (and previous high energy colliders) have found no dark matter candidates so far. • LHC Run 2 to continue that search looking for heavy new particles such as those within supersymmetry. • Also direct detection experiments looking for recoil from WIMPs • There are models which postulate light (GeV and below) new particles which could be candidates for dark matter. • There could be a dark sector which couples to ordinary matter via gravity and possibly other very weak forces. • Could e.g. explain g−2 anomaly between measurement and the Standard Model.

16 Dark photons A light vector boson, the “dark photon”, A′, results from a spontaneously broken new gauge symmetry, U(1)D. The A′ kinetically mixes with the photon and couples primarily to the electromagnetic current with strength, εe

Growing field of experiments with many running or starting or proposed at JLab, SLAC, INFN, Mainz, etc. 17 NA64 experimental programme • Initial run in SPS beam focusing on A′ → invisible channel. • Future programme measuring A′ → e+ e− channel. e+ e− χ e− e− e− A’ A’ e− χ γ γ

Signature: Z Z • Initial 100 GeV e− track • Final < 50 GeV e− shower in ECAL • No energy in the veto or HCAL

• NA64 detector for A′ → invisible channel. • Backgrounds essentially zero. • Similar detector for A′ → e+ e− channel with signature of two EM showers after S. Gninenko et al. − arXiv:1604.08432 gap when initial e hits target. 18 Electrons on target

NA64 will receive about 106 e−/spill or 2 × 105 e−/s from SPS secondary beam

➡ Ne ~ 1012 e− for 3 months running. AWAKE-like beam with bunches of 109 e− every (SPS cycle time of) ~ 5 s or 2 × 108 e−/s (1000 × higher than NA64/SPS secondary beam)

➡ Ne ~ 1015 e− for 3 months running. Will assume that an AWAKE-like beam could provide an effective upgrade to the NA64 experiment, increasing the intensity by a factor of 1000. Different beam energies or higher intensities (e.g. bunch charge, SPS cycle time) may be possible, but are not considered in this talk.

19 Sensitivity with increased electrons on target

Have taken plots of mixing strength, ε, versus , mA′, from NA64 studies/proposals and added curves “by hand” to show increased sensitivity. • Considered A′ → e+ e− and A′ → invisible channels.

• In general, but certainly at high mA′ (> 1 GeV) need more detailed calculations (developed in S.N. Gninenko et al., arXiv:1604.08432). • More careful study of optimal beam energy needed. • Evaluation of backgrounds needed; currently assume background-free for AWAKE-like beam. • More careful study of possible detector configurations. • Could consider other channels, e.g. A′ → µ+ µ−. • Note that this idea uses bunches, rather than single electrons. Results shown here should be considered as indicative.

20 Limits on dark photons, A′ → e+e− channel

#2 For 1010 − 1013 electrons on 10 KLOE SINDRUM HADES BaBar target with NA64. WASA 14 16 aΜ ae For 10 − 10 electrons on #3 Dark# A1 10 E774 Light APEX target with AWAKE-like beam. APEX As proposed by NA64 group: 1010 #4 11 HPS • extend into region not covered 10 10 12 E141 10 by current limits. 1013 Ε • similar to and complement #5 Ν-Cal I Π0 10 1014 other future experiments. 15 Ν-Cal I KEK 10 p#Brems Using an AWAKE-like beam #6 1016 ! " 10 Orsay would extend sensitivity further around ε ~ 10−5 beyond any ! " current experiment. #7 NOMAD 10 & PS191 E137 CHARM 10#2 10#1 1 21 mA' GeV

# $ Electron–proton colliders

22 High energy electron−proton collisions

Energy scale or resolution, Q2 = −(k−k′)2 Parton momentum fraction, x Understand hadronic cross sections as a function of these variables.

Deep inelastic scattering is the way to study the structure of matter. When does the complex structure “level out” or “saturate” ? Tells us a lot about the strong force: parton interactions, αs, etc. Is there further partonic substructure ? 23 High energy electron−proton collisions

• Consider high energy ep collider with Ee up to O(50 GeV), colliding with LHC proton TeV bunch, e.g. Ee = 50 GeV, Ep = 7 TeV, √s = 1.2 TeV. • Can “easily” exceed HERA energies (√s = 300 GeV); can consider different detector and probe different physics. • Create ~50 GeV beam within 50−100 m of plasma driven by SPS protons and have an LHeC-type experiment.

• Clear difference is that luminosity* currently expected to be lower <1030 cm−2s−1. • Any such experiment would have a different focus to LHeC. - Investigate physics of the strong force. - Little sensitivity to Higgs physics.

• Consider design further, e.g. luminosity, understanding how to build a plasma accelerator, etc. Can site at CERN with minimal new infrastructure ? 24 *G. Xia et al., Nucl. Instrum. Meth. A 740 (2014) 173. Very high energy electron–proton collisions, VHEeP • What about very high energies in a completely new kinematic regime ?

• Choose Ee = 3 TeV as a baseline for a new collider with Ep = 7 TeV ⇒ √s = 9 TeV.

• Acceleration of electrons in under 4 km. • Can vary the energy. • Centre-of-mass energy ×30 higher than HERA. • Reach in (high) Q2 and (low) Bjorken x extended by ×1000 compared to HERA. A. Caldwell & K. Lotov, Phys. Plasmas 18 (2011) 103101

Idea presented at various workshops and published*. Also had a workshop to expand particle physics case: https://indico.mpp.mpg.de/event/5222/overview

25 *A. Caldwell and M. Wing, Eur. Phys. J. C 76 (2016) 463 Plasma wakefield accelerator • Emphasis on using current infrastructure, i.e. LHC beam with minimum modifications. e ep • Overall layout works in powerpoint.

plasma) • Need high gradient magnets to bend protons dump dump accelerator into the LHC ring. p p • One proton beam used for electron acceleration to then collider with other proton beam. LHC • High energies achievable and can vary electron beam energy. • What about luminosity ? • Assume • ~3000 bunches every 30 mins ⇒ f ~ 2 Hz.

• Np ~ 4 × 1011, Ne ~ 1 × 1011 For few × 107 s, have 1 pb−1 / year of • σ ~ 4 µm running. Physics case for very high energy, but Other schemes to increase this value ? moderate (10−100 pb−1) luminosities. 26 Physics at VHEeP

• Cross sections at very low x and observation/evidence for saturation. Completely different kind of proton structure. • Measure total γP cross section at high energies and also at many different energies; relation to cosmic-ray physics. • Vector meson production and its relation to the above. • Beyond the Standard Model physics; contact interactions, e.g. radius of quark and electron; search for leptoquarks.

• Proton and photon structure, in particular e.g. FL given change in beam energy, and eA scattering. Also related to saturation and low x. • Tests of QCD, measurements of strong coupling, etc.. I.e. all usual QCD measurements can and should be done too in a new kinematic regime. • …

27 Total photon−proton cross section

Data VHEeP reach (mb) p γ 1 2 2 σ ln (W ) Regge fits: DL 1992 DL 2004

-1

Total cross section, 10

2 3 4 1 10 10 10 10 Photon-proton centre-of-mass energy, W (GeV) Energy dependence of hadronic cross sections poorly understood. • Multiple measurements can be made with low luminosities. Equivalent to a 20 PeV • When does the cross section stop rising ? photon on a fixed target. • Relation to cosmic-ray physics. 28 • Great example of where you really gain with energy. Vector meson cross sections

W0.16 Strong rise with energy related to gluon density at low x. Vp) (nb) 10 5 → σtot

p Can measure all particles within the same γ 0.22 ( W

σ experiment. 4 10 Comparison with fixed-target, HERA and ρ LHCb data—large lever in energy. W0.22 ω 10 3 At VHEeP energies, σ(J/ψ) > σ(φ) ! W0.7 φ Onset of saturation ?

0.7 10 2 W J/ψ γ∗ J/ψ c¯ 10 ψ(2S)

W1.0 c kT kT VHEeP reach Υ(1S) 1 H1/ZEUS VHEeP, √s fixed target xx′ ALICE/LHCb -1 10 p p 2 3 4 29 1 10 10 10 10 Martin et al., Phys. Lett. Photon-proton centre-of-mass energy, W (GeV) B 662 (2008) 252 Virtual-photon−proton cross section

• Cross sections for all Q2 are rising; (mb) p γ again luminosity not an issue, will σ

Q2 = 0.25 GeV2 have huge number of events. -1 10 • Depending on the form, fits cross; physics does not make sense. • Different forms deviate significantly from each other.

-2 • VHEeP has reach to investigate 10 this region and different behaviour of the cross sections. • Can measure lower Q2, i.e. lower x HERA/fixed target and higher W. VHEeP reach 2 ∼ x-λ(Q ) • Unique information on form of -3 2 10 ∼ e(B(Q ) √log(1/x)) hadronic cross sections at high 2 2 Q = 120 GeV energy. 2 3 4 10 10 10 10 W (GeV) VHEeP will explore a region of QCD where we have no idea what is happening. 30 Leptoquark production Electron–proton colliders are the ideal e ,ν machinee± to look for leptoquarks. e ± e q ± LQ s-channel resonance production possibleLQ up to √s. q q e ,νe Reachq of LHC± currently about 1 TeV, to P Pincrease to 2 − 3 TeV.

ZEUS λ

/ 90 % upper limit ν (a) ν (b) λ 90 % upper limit λ 1 10 VHEeP

SL 1/2 e ,ν 10-1 e ± e ± 1 ZEUS e±p (498 pb-1) H1 e±p ATLAS pairγ prod.,Z,W -2 -1 10 L3 indirect limit 10 q q 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -2 M (TeV) 10 ZEUS Coll., Phys. Rev. D 86 (2012) 012005P LQ 123456789 MLQ (TeV) Sensitivity depends mostly on(c )√s and VHEeP = 30 × HERA 31 VHEeP Workshop

https://indico.mpp.mpg.de/event/5222/timetable/#20170601

Some highlights: • Observe saturation; theory of hadronic interactions (Bartels, Mueller, Stodolsky, etc.) • Relation of low-x physics to cosmic rays (Stasto); to black holes and gravity (Erdmenger); and to new physics descriptions (Dvali, Kowalski) • Status of simulations (Plätzer) • Challenge of the detector (Keeble) • What understood from HERA data (Myronenko) 32 Summary and discussion • The AWAKE collaboration has an exciting programme of R&D aiming to develop a useable accelerator technology. • [Consider combination of conventional and novel schemes in designs such as upgrade of conventional e+e− accelerator with plasma wakefield acceleration.] • Emphasis what can be done with proton-driven scheme using CERN infrastructure. • Have started to consider realistic applications to novel and interesting particle physics experiments: - Investigation of strong-field QED. - Fixed-target/beam-dump experiments in particular those sensitive to dark photons. - Electron–proton collider up to very high energies. • Work ongoing studying boundary conditions / possibilities from physics, technical and integration side, e.g. de-phasing limit, repetition rate, tunnel space, etc.. • If we want to have cutting-edge accelerators based on new technology for high energy physics at the energy and intensity frontier, we will not get there in one go and this presents a path to try and do it for proton-driven plasma wakefield acceleration.

33 Back-up

34 Plasma wakefield acceleration

+ + " " + + " + +

Short&proton&beam Neutral&plasma

• Electrons ‘sucked in’ by proton bunch • Continue across axis creating depletion region • Oscillation of plasma electrons creates strong electric fields • Longitudinal electric fields can accelerate particles in direction of proton bunch • Transverse electric fields can focus particles • A ‘witness’ bunch of e.g. electrons placed appropriately can be accelerated by these strong fields

35 Proton-driven plasma wakefield acceleration concept*

Ee = 0.5 TeV from Ep = 1 TeV in 300 m

Note proton bunch length, 100 µm; cf LHC, bunch length, ~10 cm 36 * A. Caldwell et al., Nature Physics 5 (2009) 363. Plasma considerations Based on linear fluid dynamics :

2 np e Relevant physical quantities : !p = s✏0 me • Oscillation frequency, ωp 1015 [cm 3] • Plasma wavelength, λp 1 [mm] or p2 ⇡ p v z • Accelerating gradient, E ⇡ u np ⇡ u t 2 where : 1 N 100 [µm] E 2 [GV m ] 10 • np is the plasma density ⇡ 10 z ! ✓ ◆ • e is the electron charge

• ε0 is the permittivity of free space

• me is the mass of electron • N is the number of drive-beam particles

• σz is the drive-beam length High gradients with : • Short drive beams (and short plasma wavelength) • Pulses with large number of particles (and high plasma density)

Plasma wakefield acceleration first proposed by T. Tajima and J.W. Dawson, Phys. Rev. Lett. 43 37 (1979) 267; use of particle beams proposed by P. Chen et al., Phys. Rev. Lett. 54 (1985) 693. Plasma wakefield experiments • Pioneering work using a LASER to induce wakefields up to 100 GV/m. • Experiments at SLAC§ have used a particle (electron) beam :

• Initial energy Ee = 42 GeV • Gradients up to ~ 52 GV/m • Energy doubled over ~ 1 m • Next stage, FACET project (http://facet.slac.stanford.edu) • Have proton beams of much higher energy : • CERN : 450 GeV and 6.5 (7) TeV • Can accelerate trailing electron bunch to high energy in one stage

38 § I. Blumenfeld et al., Nature 445 (2007) 741. Long proton bunches ? Use self-modulation instability where micro-bunches are generated by a transverse modulation of the bunch density. N. Kumar, A. Pukhov, K.V. Lotov, Phys. Rev. Lett. 104 (2010) 255003

Long proton beam

• Micro-bunches are spaced λp apart and have an increased charge density. • Micro-bunches constructively reinforce to give large wakefields, GV/m. • Self-modulation instability allows current beams to be used.

39 AWAKE experimental programme (Run I) Phase 1: understand the physics of self-modulation instability process in plasma

Laser 10m Proton& SPS p beam& protons dump Proton& diagnostics Laser& BTV,OTR,&CTR SMI dump

plasma gas proton& bunch Started laser&pulse ! Start&with&physics&Q4&2016!

0.0 0.20 8.3 meters plasma ρ Propagation direction beam ρ

-0.4 ] ] e0 e0 [n 0.10 [n pe -0.8 radius (r) plasma beam ρ r ρ J. Vieira et al., -1.2 Phys. Plasmas 19 (2012) 063105 Proton&beam&density&

Plasma&electron&density& 0.00 Distance in beam (z) 40 AWAKE experimental programme (Run I) Phase 2: probe the accelerating wakefields with externally injected electrons.

LaserLaser RF&gun e" 10m Proton& SPS p beam& protons dump Proton& diagnostics Laser& BTV,OTR,&CTR SMI Acceleration dump

plasma gas proton* bunch ! Start%with%physics%Q4%2017! electron*bunch laser*pulse

Demonstrate-13.5 GeV acceleration 1.2 (a) (b) (c) 1.0 of-13.6 electrons with proton-driven 25

, cm

GV/m 0.8 wakefields of GV/m 20 z-ct -13.7

z

E, 0.6 15 -13.8

0.4 % /10 GeV 0.2 -13.9 5 0.0 -14.0 0 0 246 8 10 0 246 8 10 1.8 1.9 2.0 2.1 2.2 z,m z,m Energy, GeV 41 AWAKE preliminary results Screen composed of two materials

Laser st nd 10m 1 BTV 2 BTV SPS p Proton& protons beam& dump Laser& Laser& SMI dump dump

M. Turner, CERN Transverse beam profile Transverse beam profile with no plasma with plasma Transverse blow-up of proton beam indicative of strong electric fields. 42 AWAKE preliminary results

Laser st nd 10m 1 BTV 2 BTV SPS p Proton& protons beam& dump Laser& Laser& SMI dump dump

Image of OTR from the proton beam measured with a streak camera

laser 100# ps =#3#cm

K. Rieger, MPP Clear modulation of proton beam, with microbunching on few-mm scale expected. 43 Taking more data right now … Search for dark photons • Several ways to look for dark photons: - A: bump-hunting, e.g. e+e− → γA′ - B: displaced vertices, short decay lengths - C: displaced vertices, long decay lengths

10-4 • Search for dark photons, A′, up to (and beyond) A GeV mass scale via their production in a light- shining-through-a-wall type experiment. • Use high energy electrons for beam-dump and/ Mont's Gap or fixed-target experiments.

Yield e+ B e− e− A’

e− (log scale) (log

2 γ ε

Z Decay Length χ C e− e− A’ -16 10 χ 1 MeV 10 GeV γ A' Mass 44 J. Alexander et al., arXiv:1608.08632 Z Limits on dark photons, A′ → invisible channel NA64 AWAKE-

like beam

1013 14 10 15 10

45 Leptoquark production Electron−proton colliders are the ideal e ,ν machinee± to look for leptoquarks. e ± e q ± LQ s-channel resonance production λ λ possibleLQ up to √s. q q e ,νe q ± P P ZEUS (a) (b) λ 1

e ,ν L e± ± e S1/2 10-1 ZEUS e±p (498 pb-1) γ,Z,W H1 e±p Sensitivity depends mostly on √s ATLAS pair prod. -2 and VHEeP = 30 × HERA q q 10 L3 indirect limit

P 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 M46 (TeV) (c) ZEUS Coll., Phys. Rev. D 86 (2012) 012005 LQ Leptoquark production at VHEeP 10 3 −1 Expectation (100 pb-1) Assumed L ~ 100 pb Measured Required Q2 > 10,000 GeV2 and y > 0.1 Events/bin 2 10 Generated “data” and Standard Model “prediction” using ARIADNE (no LQs). λ

10 / 90 % upper limit ν ν 90 % upper limit λ 10

1

1 -3 -2 -1 10 10 10 x Sensitivity up to kinematic limit, 9 TeV.

-1 As expected, well beyond HERA limits 10 and significantly beyond LHC limits and potential.

-2 10 47 123456789 MLQ (TeV) Leptoquark production at the LHC

g q q LQ

Can also be produced LQ g in pp singly or pair q ` production q¯ LQ

q LQ1LQ1 production `¯ 1

e q) ATLAS

→ 0.9 s = 8 TeV, 20.3 fb-1

(LQ1 0.8 Reach of LHC currently about 1 TeV, to β 2-electrons + 2-jets 0.7 increase to 2 − 3 TeV. All limits at 95% CL Coupling dependent. 0.6 0.5

jj 0.4 ν

0.3 eejj+e expected limit observed limit 0.2 expected ± 1σ expected ± 2σ 0.1 s = 7 TeV, 1.03 fb-1 0 300 400 500 600 700 800 900 1000 1100 1200 48 m [GeV] ATLAS Coll., Eur. Phys. J. C 76 (2016) 1 LQ1 Kinematics of the final state • Simulated events Q2 > 1 GeV2 4 10 10 4 and x > 10−7 Events Events 3 −1 10 10 3 • Test sample of L ~ 0.01 pb

2 • Kinematic peak at 3 TeV, with 10 10 2 electrons scattered at low 10 10 angles.

1 1 • Hadronic activity in central 0 1000 2000 3000 3.11 3.12 3.13 3.14 region as well as forward and

E´e (GeV) θe backward. 3000 • Hadronic activity at low 2500 All x

(GeV) -4 backward angles for low x. Events x < 10 e 4 10 -6 E´ 2000 x < 10 • Clear implications for the 1500 kind of detector needed. 10 3 1000

500 10 2 0 0 0.002 0.004 0.006 0.008 0.01 0123 49 π–θe γhad Sketch of detector

Forward/ Electron/ spectrometer Central/detector Hadron spectrometer spectrometer Dipole Dipole e p

Low$x events High$x$events

High$Q2 events

• Will need conventional central colliding-beam detector. • Will also need long arm of spectrometer detectors which will need to measure scattered electrons and hadronic final state at low x and high x.

50 DIS variables 10 5 3000 • Access down to x ~ 10−8 for 10 4 Events 2500 Events Q2 ~ 1 GeV2. 2000 10 3 • Even lower x for lower Q2. 1500 • Plenty of data at low x and 10 2 1000 low Q2 (L ~ 0.01 pb−1). 500 10 • Can go to Q2 ~ 105 GeV2 for 0 L ~ 1 pb−1. -6 -4 -2 0 0 25 50 75 100 2 2 log10x Q (GeV ) • Powerful experiment for

) 3 low-x physics where 2 luminosity less crucial. 4 2.5 /GeV

Events 10 2

(Q 2

3 10 10 1.5 log

10 2 1 0.5 10 0 0 0.25 0.5 0.75 1 -6 -4 -2 0 51 y log10x