1,456 research outputs found
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
Energy Dependence of Jet Quenching and Life-time of the Dense Matter in High-energy Heavy-ion Collisions
Suppression of high hadron spectra in high-energy heavy-ion collisions
at different energies is studied within a pQCD parton model incorporating
medium induced parton energy loss. The dependence of the nuclear
modification factor is found to depend on both the energy
dependence of the parton energy loss and the power-law behavior of the initial
jet spectra. The high hadron suppression at GeV and its
centrality dependence are studied in detail. The overall values of the
modification factor are found to provide strong constraints on the lifetime of
the dense matter.Comment: 6 pages in RevTex with 3 postscript figure
Sensitivity of the correlation between the depth of shower maximum and the muon shower size to the cosmic ray composition
The composition of ultra-high energy cosmic rays is an important issue in
astroparticle physics research, and additional experimental results are
required for further progress. Here we investigate what can be learned from the
statistical correlation factor r between the depth of shower maximum and the
muon shower size, when these observables are measured simultaneously for a set
of air showers. The correlation factor r contains the lowest-order moment of a
two-dimensional distribution taking both observables into account, and it is
independent of systematic uncertainties of the absolute scales of the two
observables. We find that, assuming realistic measurement uncertainties, the
value of r can provide a measure of the spread of masses in the primary beam.
Particularly, one can differentiate between a well-mixed composition (i.e., a
beam that contains large fractions of both light and heavy primaries) and a
relatively pure composition (i.e., a beam that contains species all of a
similar mass). The number of events required for a statistically significant
differentiation is ~ 200. This differentiation, though diluted, is maintained
to a significant extent in the presence of uncertainties in the phenomenology
of high energy hadronic interactions. Testing whether the beam is pure or
well-mixed is well motivated by recent measurements of the depth of shower
maximum.Comment: Accepted for publication in Astroparticle Physics, LA-UR-12-2008
Dihadron Correlation in Jets Produced in Heavy-Ion Collisions
The difference between the structures of jets produced in heavy-ion and
hadronic collisions can best be exhibited in the correlations between particles
within those jets. We study the dihadron correlations in jets in the framework
of parton recombination. Two types of triggers, and proton, are
considered. It is shown that the recombination of thermal and shower partons
makes the most important contribution to the spectra of the associated
particles at intermediate . In collisions the only significant
contribution arises from shower-shower recombination, which is negligible in
heavy-ion collisions. Moments of the associated-particle distributions are
calculated to provide simple summary of the jet structures for easy comparison
with experiments.Comment: 24 pages in Latex + 5 figure
Large Extra Dimension effects through Light-by-Light Scattering at the CERN LHC
Observing light-by-light scattering at the Large Hadron Collider (LHC) has
received quite some attention and it is believed to be a clean and sensitive
channel to possible new physics. In this paper, we study the diphoton
production at the LHC via the process through graviton exchange in the Large Extra
Dimension (LED) model. Typically, when we do the background analysis, we also
study the Double Pomeron Exchange (DPE) of production. We
compare its production in the quark-quark collision mode to the gluon-gluon
collision mode and find that contributions from the gluon-gluon collision mode
are comparable to the quark-quark one. Our result shows, for extra dimension
, with an integrated luminosity at the
14 TeV LHC, that diphoton production through graviton exchange can probe the
LED effects up to the scale for the forward
detector acceptance , respectively, where
, and .Comment: 25 pages. 7 figs. Change some grammatical error
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
-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
Probing the QCD equation of state with thermal photons in nucleus-nucleus collisions at RHIC
Thermal photon production at mid-rapidity in Au+Au reactions at
= 200 GeV is studied in the framework of a 2D+1 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 bin provides direct
empirical information on the underlying degrees of freedom and on the equation
of state, , of the strongly interacting matter.Comment: Version to appear in EPJ-C (extended discussion and refs. and a few
corrections
Elliptic flow in proton-proton collisions at 7 TeV
The angular correlations measured in proton-proton collisions at 7 TeV are
decomposed into contributions from back to back emission and elliptic flow.
Modeling the dominant term in the correlation functions as a momentum
conservation effect or as an effect of the initial transverse velocity of the
source, the remaining elliptic flow component can be estimated. The elliptic
flow coefficient extracted from the CMS Collaboration data is 0.04-0.08. No
additional small-angle, ridge-like correlations are needed to explain the
experimental data
High-mass dimuon resonances in Pb-Pb collisions at 5.5 TeV in CMS
The measurement of the charmonium (, ) and bottomonium
(, , ) resonances and boson in
nucleus-nucleus collisions provides crucial information on high density QCD
matter. The observation of anomalous suppression of at the CERN-SPS
and RHIC is well established but the clarification of some important questions
requires equivalent studies of the family, only possible at LHC
energies. The boson will be produced for the first time in heavy-ion
collisions at the LHC and, since its dominant production channel is through
fusion, it is an excellent probe of the nuclear modification of
quark distribution functions. This paper reports the capabilities of the CMS
detector to study quarkonium and production in Pb-Pb collisions at 5.5
TeV, through the dimuon decay channel.Comment: 4 pages 3 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
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