Near-threshold production of W±W^\pm, Z0Z^0 and H0H^0 at a fixed-target experiment at the future ultra-high-energy proton colliders

We outline the opportunities to study the production of the Standard Model bosons, $W^\pm$, $Z^0$ and $H^0$ at "low" energies at fixed-target experiments based at possible future ultra-high-energy proton colliders, \ie\ the High-Energy LHC, the Super proton-proton Collider and the Future Circular Collider -- hadron-hadron. These can be indeed made in conjunction with the proposed future colliders designed to reach up to $\sqrt{s}=100$ TeV by using bent crystals to extract part of the halo of the beam which would then impinge on a fixed target. Without disturbing the collider operation, this technique allows for the extraction of a substantial amount of particles in addition to serve for a beam-cleaning purpose. With this method, high-luminosity fixed-target studies at centre-of-mass energies above the $W^\pm$, $Z^0$ and $H^0$ masses, $\sqrt{s} \simeq 170-300$ GeV, are possible. We also discuss the possibility offered by an internal gas target, which can also be used as luminosity monitor by studying the beam transverse shape

Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-Z targets

In the CERN NA63 collaboration we have addressed the question of the potential inadequacy of the commonly used Migdal formulation of the Landau-Pomeranchuk-Migdal (LPM) effect by measuring the photon emission by 20 and 178 GeV electrons in the range 100 MeV - 4 GeV, in targets of LowDensityPolyEthylene (LDPE), C, Al, Ti, Fe, Cu, Mo and, as a reference target, Ta. For each target and energy, a comparison between simulated values based on the LPM suppression of incoherent bremsstrahlung is shown, taking multi-photon effects into account. For these targets and energies, we find that Migdal's theoretical formulation is adequate to a precision of better than about 5%, irrespective of the target substance.Comment: 8 pages, 13 figure

Near-Threshold Production of ± , 0 , and 0 at a Fixed-Target Experiment at the Future Ultrahigh-Energy Proton Colliders

We outline the opportunities to study the production of the Standard Model bosons, ± , 0 , and 0 , at "low" energies at fixed-target experiments based on possible future ultrahigh-energy proton colliders, that is, the High-Energy LHC, the Super proton-proton Collider, and the Future Circular Collider hadron-hadron. These can be indeed made in conjunction with the proposed future colliders designed to reach up to √ = 100 TeV by using bent crystals to extract part of the halo of the beam which would then impinge on a fixed target. Without disturbing the collider operation, this technique allows for the extraction of a substantial amount of particles in addition to serving for a beam-cleaning purpose. With this method, high-luminosity fixed-target studies at centreof-mass energies above the ± , 0 , and 0 masses, √ ≃ 170-300 GeV, are possible. We also discuss the possibility offered by an internal gas target, which can also be used as luminosity monitor by studying the beam transverse shape

Measurement of electromagnetic cross sections in heavy ion interactions and its consequences for luminosity lifetimes in ion colliders

The limitation of the luminosity lifetime in high energy heavy ion colliders like RHIC or LHC operating in ion mode is set by the very large cross section of beam - beam interactions. One of the dominant processes at relativistic energies is electron capture from pair production in the strong electromagnetic field provided by the high Z of the ions. The capture cross sections for Pb82+ interacting with a number of light and heavy solid targets have been measured using one of the high energy resolution 158 GeV/nucleon beams at CERN. Gas targets Ar, Kr and Xe have also been used. The results, together with results on electromagnetic dissociation, are discussed in terms of beam lifetimes for RHIC and LHC using extrapolations of the measurements to the corresponding collider energies

VLT/X-shooter spectroscopy of the afterglow of the Swift GRB 130606A: Chemical abundances and reionisation at z∼6z\sim6

The reionisation of the Universe is thought to have ended around z~6, as inferred from spectroscopy of distant bright background sources, such as quasars (QSO) and gamma-ray burst (GRB) afterglows. Furthermore, spectroscopy of a GRB afterglow provides insight in its host galaxy, which is often too dim and distant to study otherwise. We present the high S/N VLT/X-shooter spectrum of GRB130606A at z=5.913. We aim to measure the degree of ionisation of the IGM between 5.02<z<5.84 and to study the chemical abundance pattern and dust content of its host galaxy. We measured the flux decrement due to absorption at Ly$\alpha$, $\beta$ and $\gamma$ wavelength regions. The hydrogen and metal absorption lines formed in the host galaxy were fitted with Voigt profiles to obtain column densities. Our measurements of the Ly$\alpha$-forest optical depth are consistent with previous measurements of QSOs, but have a much smaller uncertainty. The analysis of the red damping wing yields a neutral fraction $x_{HI}<0.05$ (3$\sigma$). We obtain column density measurements of several elements. The ionisation corrections due to the GRB is estimated to be negligible (<0.03 dex), but larger corrections may apply due to the pre-existing radiation field (up to 0.4 dex based on sub-DLA studies). Our measurements confirm that the Universe is already predominantly ionised over the redshift range probed in this work, but was slightly more neutral at z>5.6. GRBs are useful probes of the ionisation state of the IGM in the early Universe, but because of internal scatter we need a larger statistical sample to draw robust conclusions. The high [Si/Fe] in the host can be due to dust depletion, alpha-element enhancement, or a combination of both. The very high value of [Al/Fe]=2.40+/-0.78 might connected to the stellar population history. We estimate the host metallicity to be -1.7<[M/H]<-0.9 (2%-13% of solar). (trunc.)Comment: 15 pages, 12 figure

Measurement of pair-production by high energy photons in an aligned tungsten crystal

A new measurement has been made of the rate of pair production in a 3.2 mm thick tungsten crystal, exposed to photons with energies in the range 10 to 150 GeV, for angles of incidence up to 10 mrad from the crystal axis. A strong enhancement of the pair-production rate is observed when the beam is aligned along the crystal axis, as compared to a random orientation. This effect can be exploited in the NA48 CP- violation experiment by using a thin crystal rather than an amorphous material to convert photons, thus minimising the scattering of kaons in the converter