Forward Physics at the LHC: within and beyond the Standard Model

We review the detection capabilities in the forward direction of the various LHC experiments together with the associated physics programme. A selection of measurements accessible with near-beam instrumentation in various sectors (and extensions) of the Standard Model (SM) is outlined, including QCD (diffractive and elastic scattering, low-x parton dynamics, hadronic Monte Carlos for cosmic-rays), electroweak processes in gamma-gamma interactions, and Higgs physics (vector-boson-fusion and central exclusive production).Comment: 9 pages, 18 figs. Lectures given at the LAWHEP'07 School (Sao Miguel das Missoes, Brazil, 3-7 Dec 2007) to appear in Braz. J. Phys. Also presented in HLPW08 (Spa, Belgium, 6-8 Mar 2008) AIP Conf. Proceeds, to appear; and in HANUC European Grad. School (Jyvaskyla, Finland, 25-29 Aug. 2008

Single inclusive pion pT-spectra in proton-proton collisions at sqrt(s) = 22.4GeV: data versus perturbative QCD calculations

We compare the inclusive transverse momentum spectra of single pions above pT = 3 GeV/c measured in proton-proton (p-p) collisions at sqrt(s) = 21.7 - 23.8 GeV, with next-to-leading order (NLO) perturbative QCD (pQCD) predictions using recent parametrizations of the parton densities and parton-to-pion fragmentation functions. Although the dependence on the theoretical scales is large, the calculations can reproduce the experimental results both in magnitude and shape. Based on the existing data and on a pQCD $\sqrt{s}$-rescaling of the measured spectra, we provide a practical parametrization of the baseline p-p pion transverse momentum spectrum to be compared to nucleus-nucleus collisions data at sqrt(s_NN) = 22.4 GeV.Comment: 16 pages, 7 figure

Low-x QCD studies with forward jets in proton-proton collisions at sqrt{s} = 14 TeV in CMS

Forward (di)jet measurements are a useful tool to constrain the Parton Distribution Functions (PDFs) at low values of parton momentum fraction x, and to study the possible onset of BFKL or gluon saturation QCD evolutions in the proton. We present studies of jet reconstruction capabilities in the CMS Hadron Forward (HF) calorimeter (3<|eta|<5). The expected sensitivity of the inclusive forward jet p_T spectrum to the proton PDF, as well as the azimuthal decorrelation of Mueller-Navelet jets with a large rapidity separation are presented for p-p collisions at sqrt{s} = 14 TeV.Comment: 5 pages, 8 figures. Proceedings Diffraction 2008: International Workshop on Diffraction in High Energy Physics, La Londe-les-Maures, France, 9-14 Sep 200

Study of Higgs boson production and its b-bbar decay in gamma-gamma processes in proton-nucleus collisions at the LHC

We explore for the first time the possibilities to measure an intermediate-mass (mH = 115-140 GeV/c^2) Standard-Model Higgs boson in electromagnetic proton-lead (pPb) interactions at the CERN Large Hadron Collider (LHC) via its b-bbar decay. Using equivalent Weizsaecker-Williams photon fluxes and Higgs effective field theory for the coupling gamma-gamma --> H, we obtain a leading-order cross section of the order of 0.3 pb for exclusive Higgs production in elastic (pPb --> gamma-gamma --> p H Pb) and semielastic (pPb --> gamma-gamma --> Pb H X) processes at sqrt(s) = 8.8 TeV. After applying various kinematics cuts to remove the main backgrounds (gamma-gamma --> b-bbar and misidentified gamma-gamma-->q-qbar events), we find that a Higgs boson with mH = 120 GeV/c^2 could be observed in the b-bbar channel with a 3sigma-significance integrating 300 pb^-1 with an upgraded pA luminosity of 10^31 cm^-2s^-1. We also provide for the first time semielastic Higgs cross sections, along with elastic t-tbar cross sections, for electromagnetic pp, pA and AA collisions at the LHC.Comment: 22 pages, 8 figures. Tiny changes. Version as publishe

The strong interaction at the collider and cosmic-rays frontiers

First data on inclusive particle production measured in proton-proton collisions at the Large Hadron Collider (LHC) are compared to predictions of various hadron-interaction Monte Carlos (QGSJET, EPOS and SIBYLL) used commonly in high-energy cosmic-ray physics. While reasonable overall agreement is found for some of the models, none of them reproduces consistently the sqrt(s) evolution of all the measured observables. We discuss the implications of the new LHC data for the modeling of the non-perturbative and semihard parton dynamics in hadron-hadron and cosmic-rays interactions at the highest energies studied today.Comment: 7 pages, Proceeds. Workshop "30 years of strong interactions", Spa, Belgium, 6-8 April 2011. Elsevier to appea

Jet Tomography in the Forward Direction at RHIC

Hadron production at high-$p_T$ displays a strong suppression pattern in a wide rapidity region in heavy ion collisions at RHIC energies. This finding indicates the presence of strong final state effects for both transversally and longitudinally traveling partons, namely induced energy loss. We have developed a perturbative QCD based model to describe hadron production in $pp$ collision, which can be combined with the Glauber -- Gribov model to describe hadron production in heavy ion collisions. Investigating $AuAu$ and $CuCu$ collisions at energy $\sqrt{s}=200$ $A$GeV at mid-rapidity, we find the opacity of the strongly interacting hot matter to be proportional to the participant nucleon number. Considering forward rapidities, the suppression pattern indicates the formation of a longitudinally contracted dense deconfined zone in central heavy ion collisions. We determine parameters for the initial geometry from the existing data.Comment: 6 pages for Hot Quarks '06 Conferenc

Constraints from the first LHC data on hadronic event generators for ultra-high energy cosmic-ray physics

The determination of the primary energy and mass of ultra-high-energy cosmic-rays (UHECR) generating extensive air-showers in the Earth's atmosphere, relies on the detailed modeling of hadronic multiparticle production at center-of-mass (c.m.) collision energies up to two orders of magnitude higher than those studied at particle colliders. The first Large Hadron Collider (LHC) data have extended by more than a factor of three the c.m. energies in which we have direct proton-proton measurements available to compare to hadronic models. In this work we compare LHC results on inclusive particle production at energies sqrt(s) = 0.9, 2.36, and 7 TeV to predictions of various hadronic Monte Carlo (MC) models used commonly in cosmic-ray (CR) physics (QGSJET, EPOS and SIBYLL). As a benchmark with a standard collider physics model we also show PYTHIA (and PHOJET) predictions with various parameter settings. While reasonable overall agreement is found for some of the MC, none of them reproduces consistently the sqrt(s) evolution of all the observables. We discuss implications of the new LHC data for the description of cosmic-ray interactions at the highest energies.Comment: 25 pages, 12 figures. Minor mods. Matches version to appear in Astroparticle Physic

Event-by-event fluctuations in Mean pTp_T and Mean eTe_T in sqrt(s_NN) = 130 GeV Au+Au Collisions

Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at sqrt(s_NN) = 130 GeV at RHIC. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of non-statistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant non-random fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive p_T or e_T spectra, we exclude a region of fluctuations in sqrt(s_NN) = 130 GeV Au+Au collisions.Comment: 10 pages, RevTeX 3, 7 figures, 4 tables, 307 authors, submitted to Phys. Rev. C on 22 March 2002. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (will be made) publicly available at http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm