Deep Inelastic Electron-Nucleon Scattering at the LHC

Abstract

The physics, and a design, of a Large Hadron Electron Collider (LHeC) are sketched. With high luminosity, 10^{33}cm^{-2}s^{-1}, and high energy, \sqrt{s}=1.4 TeV, such a collider can be built in which a 70 GeV electron (positron) beam in the LHC tunnel is in collision with one of the LHC hadron beams and which operates simultaneously with the LHC. The LHeC makes possible deep-inelastic lepton-hadron (ep, eD and eA) scattering for momentum transfers Q^2 beyond 10^6 GeV^2 and for Bjorken x down to the 10^{-6}. New sensitivity to the existence of new states of matter, primarily in the lepton-quark sector and in dense partonic systems, is achieved. The precision possible with an electron-hadron experiment brings in addition crucial accuracy in the determination of hadron structure, as described in Quantum Chromodynamics, and of parton dynamics at the TeV energy scale. The LHeC thus complements the proton-proton and ion programmes, adds substantial new discovery potential to them, and is important for a full understanding of physics in the LHC energy range.

Figures (31)

• Figure 1: Kinematic regions in Bjorken-$x$ and momentum transfers $Q^2$ covered by fixed target unpolarised lepton-proton scattering experiments, the H1 and ZEUS experiments at HERA and the proposed electron-proton collider LHeC.
• Figure 2: Summary of existing (dark, blue boxes) and proposed (grey, red boxes) facilities for unpolarised lepton-proton deep-inelastic scattering investigations in terms of the luminosity and centre-of mass energy. The Jlab fixed target programme is directed to high statistics physics at low $Q^2$ and very large $x$. The SLAC box indicates the luminosity of the classic $ep$ experiment at the 2 mile linear accelerator. BCDMS and NMC have provided the most accurate DIS muon-proton structure function data using 30 m and 3 m long unpolarised hydrogen targets, respectively. The large luminosities envisaged at eRHIC and ELIC (hollow boxes), which is desirable for polarised $ep$ physics, are based on energy-recovery linac technology. HERA has reached peak luminosities of up to $5 \cdot 10^{31}$cm$^{-2}$s$^{-1}$ with a luminosity upgrade. The linac-ring accelerator designs of THERA (TESLA/ILC-HERA) and the QCD explorer (CLIC-LHC) barely provide luminosity above $10^{31}$cm$^{-2}$s$^{-1}$. The LHeC is designed for the highest energy at the largest luminosity.
• Figure 3: Kinematics of $ep$ scattering at the LHeC at high $Q^2$. Solid (dotted) curves correspond to constant polar angles $\theta_e$ ($\theta_h$) of the scattered electron (hadronic final state). The polar angle is defined with respect to the proton beam direction. Dashed (dashed-dotted) curves correspond to constant energies $E_e'$ ($E_h$) of the scattered electron (hadronic final state). The iso-angle and iso-energy lines are derived from Eq. 4, Section 5. The shaded area illustrates the region of kinematic coverage in neutral current (NC) scattering at HERA. In $ep$ scattering electron-quark resonances can be formed with mass $M = \sqrt{xs}$. Due to luminosity and energy range, the search limit at HERA has been at about 290 GeV while the LHeC extends to large $M$ values of about 1300 GeV.
• Figure 4: Mass-dependent upper bounds on the LQ coupling $\lambda$ as expected at LHeC for a luminosity of $10 \hbox{\rm fb}^{-1}$ (full red curve) and at the LHC for $100 \hbox{\rm fb}^{-1}$ (full blue curve) filip. These are shown for an example scalar LQ coupling to $e^- u$.
• Figure 5: (Left) Single LQ production cross section at the LHeC (top) and LHC (bottom), for a scalar LQ coupling to $e^+ d$ with a coupling $\lambda=0.1$; (Right) Asymmetries which would determine the fermion number of such a LQ, the sign of the asymmetry being the relevant quantity. An integrated luminosity of $100 \hbox{\rm fb}^{-1}$ ($10 \hbox{\rm fb}^{-1}$ per lepton charge) has been assumed for the LHC (LHeC).