We discuss the physics of large impact parameter interactions at the LHC: ultraperipheral collisions (UPCs). The dominant processes in UPCs are photon–nucleon (nucleus) interactions. The current LHC ...detector configurations can explore hard phenomena at small
x
with nuclei and nucleons at photon–nucleon center-of-mass energies above 1 TeV, extending the
x
range of HERA by a factor of ten. In particular, it will be possible to probe diffractive and inclusive parton densities in nuclei using several processes. The interaction of small dipoles with protons and nuclei can be investigated in elastic and quasi-elastic
J
/
ψ
and
Υ
production as well as in high
t
ρ
0
production accompanied by a rapidity gap. Several of these phenomena provide clean signatures of the onset of the new high gluon density QCD regime. The LHC is in the kinematic range where nonlinear effects are several times larger than those at HERA. Two-photon processes in UPCs are also studied. In addition, while UPCs play a role in limiting the maximum beam luminosity, they can also be used as a luminosity monitor by measuring mutual electromagnetic dissociation of the beam nuclei. We also review similar studies at HERA and RHIC as well as describe the potential use of the LHC detectors for UPC measurements.
Proton-nucleus (p+A) collisions have long been recognized as a crucial component of the physics program with nuclear beams at high energies, in particular for their reference role to interpret and ...understand nucleus-nucleus data as well as for their potential to elucidate the partonic structure of matter at low parton fractional momenta (small-x). Here, we summarize the main motivations that make a proton-nucleus run a decisive ingredient for a successful heavy-ion program at the Large Hadron Collider (LHC) and we present unique scientific opportunities arising from these collisions. We also review the status of ongoing discussions about operation plans for the p+A mode at the LHC.
Thermal photon production at mid-rapidity in Au+Au reactions at is studied in the framework of a hydrodynamical model that describes efficiently the bulk identified hadron spectra at RHIC. The ...combined thermal plus NLO pQCD photon spectrum is in good agreement with the yields measured by the PHENIX experiment for all Au+Au centralities. Within our model, we demonstrate that the correlation of the thermal photon slopes with the charged hadron multiplicity in each centrality provides direct empirical information on the underlying degrees of freedom and on the form of the equation of state, s(T)/T3, of the strongly interacting matter produced in the course of the reaction.
Experimental results on high transverse momentum (leading) hadron spectra in nucleus-nucleus collisions in the range \(\sqrt{s_{NN}}\approx\) 20-200 GeV are reviewed with an emphasis on the observed ...suppression compared to free space production in proton-proton collisions at the corresponding center-of-mass energies. The transverse-momentum and collision-energy (but seemingly not the in-medium path length) dependence of the experimental suppression factors measured in central collisions is consistent with the expectations of final-state non-Abelian parton energy loss in a dense QCD medium.
In these introductory lectures, we present a broad overview of the physics of hadron and jet production at large transverse momenta in high-energy nucleus–nucleus collisions. Emphasis is put on ...experimental and theoretical “jet quenching” observables that provide direct information on the (thermo)dynamical properties of hot and dense QCD matter.
The single inclusive spectrum of charged particles with transverse momenta
p
T
= 3 – 150 GeV/
c
measured at midrapidity by the CDF experiment in proton-antiproton
collisions at
is compared to ...next-to-leading order (NLO) perturbative QCD calculations using the most recent parametrizations of the parton distributions and parton-to-hadron fragmentation functions. Above
p
T
≈ 20 GeV/
c
, there is a very sizeable disagreement of the Tevatron data compared to the NLO predictions and to
x
T
-scaling expectations, suggesting a problem in the experimental data. We also present the predictions for the
p
T
-differential charged hadron spectra and the associated theoretical uncertainties for proton-proton (
p
-
p
) collisions at LHC energies
. Two procedures to estimate the charged hadron spectra at LHC heavy-ion collision energies
, 5.5 TeV) from
p
-
p
measurements are suggested.
The Future Circular Collider is a new proposed collider at CERN with centre-of-mass energies around 100 TeV in the pp mode. Ongoing studies aim at assessing its physics potential and technical ...feasibility. Here we focus on updates in physics opportunities accessible in pA and AA collisions not covered in previous Quark Matter contributions, including Quark-Gluon Plasma and gluon saturation studies, novel hard probes of QCD matter, and photon-induced collisions.
We present preliminary results of the performance of prototype III of the CASTOR quartz-tungsten sampling calorimeter, to be installed in the very forward region of the CMS experiment at the LHC. The ...energy linearity and resolution, as well as the spatial resolution of the prototype to electromagnetic and hadronic showers are studied with E= 10−200 GeV electrons, E= 20−350 GeV pions, and E= 50, 150 GeV muons in beam tests carried out at CERN/SPS in 2007.
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