2,237 research outputs found
Measurement of isolated photon production in pp and PbPb collisions at sqrt{sNN} =2.76$ TeV with CMS
Isolated photon production is measured in pp and PbPb collisions at
nucleon-nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range
|eta|<1.44 and transverse energies E_T between 20 and 80 GeV with the CMS
detector at the LHC. The measured E_T spectra are found to be in good agreement
with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to
pp isolated photon E_T-differential yields, scaled by the number of incoherent
nucleon-nucleon collisions, is consistent with unity for all PbPb reaction
centralities.Comment: Presented at HP2012: Hard Probes 201
Measurement of the charged-hadron multiplicity in proton-proton collisions at LHC with the CMS detector
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 165-173).Charged-hadron pseudorapidity densities and multiplicity distributions in protonproton collisions at [the square root of sigma] = 0.9, 2.36, 7.0 TeV were measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield was obtained by counting the number of hit-pairs (tracklets). The charged-particle multiplicity per unit of pseudorapidity dNch/d[eta] [eta]<0.5 at [the square root of sigma] = 7.0 TeV is 5.78 i 0.01(stat.) i 0.23(syst.) for nonsingle- diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from [the square root of sigma] = 0.9 to 7 TeV is 66.1% ± 1.0%(stat.) ± 4.2%(syst.) and strong KNO violation is observed in the multiplicity distributions. Results are compared with low energy measurements.by Yen-Jie Lee.Ph.D
Heavy quarks and jets as probes of the QGP
Quark-Gluon Plasma (QGP), a QCD state of matter created in ultra-relativistic
heavy-ion collisions, has remarkable properties, including, for example, a low
shear viscosity over entropy ratio. By detecting the collection of low-momentum
particles that arise from the collision, it is possible to gain quantitative
insight into the created matter. However, its fast evolution and thermalization
properties remain elusive. Only using high momentum objects as probes of QGP
can unveil its constituents at different wavelengths. In this review, we
attempt to provide a comprehensive picture of what was, so far, possible to
infer about QGP given our current theoretical understanding of jets,
heavy-flavor, and quarkonia. We will bridge the resulting qualitative picture
to the experimental observations done at the LHC and RHIC. We will focus on the
phenomenological description of experimental observations, provide a brief
analytical summary of the description of hard probes, and an outlook on the
main difficulties we will need to surpass in the following years. To benchmark
QGP-related effects, we will also address nuclear modifications to the initial
state and hadronization effects
Measurement of the charged-hadron multiplicity in proton-proton collisions at LHC with the CMS detector
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 165-173).Charged-hadron pseudorapidity densities and multiplicity distributions in protonproton collisions at [the square root of sigma] = 0.9, 2.36, 7.0 TeV were measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield was obtained by counting the number of hit-pairs (tracklets). The charged-particle multiplicity per unit of pseudorapidity dNch/d[eta] [eta]<0.5 at [the square root of sigma] = 7.0 TeV is 5.78 i 0.01(stat.) i 0.23(syst.) for nonsingle- diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from [the square root of sigma] = 0.9 to 7 TeV is 66.1% ± 1.0%(stat.) ± 4.2%(syst.) and strong KNO violation is observed in the multiplicity distributions. Results are compared with low energy measurements.by Yen-Jie Lee.Ph.D
Data-driven extraction of the substructure of quark and gluon jets in proton-proton and heavy-ion collisions
The different modification of quark- and gluon-initiated jets in the
quark-gluon plasma produced in heavy-ion collisions is a long-standing question
that has not yet received a definitive answer from experiments. In particular,
the relative sizes of the modification of quark and gluon jets differ between
theoretical models. Therefore a fully data-driven technique is crucial for an
unbiased extraction of the quark and gluon jet spectra and substructure. We
perform a proof-of-concept study based on proton-proton and heavy-ion collision
events from the PYQUEN generator with statistics accessible in Run 4 of the
Large Hadron Collider. We use a statistical technique called topic modeling to
separate quark and gluon contributions to jet observables. We demonstrate that
jet substructure observables, such as the jet shape and jet fragmentation
function, can be extracted using this data-driven method. These results suggest
the potential for an experimental determination of quark and gluon jet spectra
and their substructure
Hard probes in isobar collisions as a probe of the neutron skin
We present an estimate of the yield of hard probes expected for collisions of
the isobars Ru and Zr at collision energies reachable
at RHIC and the LHC\@. These yields are proportional to the number of binary
nucleon-nucleon interactions, which is characteristically different due to the
presence of the large neutron skin in Zr. This provides an
independent opportunity to measure the difference between the neutron skin of
Ru and Zr, which can provide an important constraint on
the Equation of State of cold neutron-rich matter.Comment: 5 pages, 6 figures and an appendix. Comments are welcom
Two-particle azimuthal correlations in collisions at 91--209 GeV with archived ALEPH data at LEP-2
We present the first measurement of two-particle angular correlations of
charged particles produced in annihilation up to 209 GeV.
This analysis utilized the archived hadronic data at center-of-mass
energy between 91 and 209 GeV collected with the ALEPH detector at LEP between
1992 and 2000. The angular correlation functions are measured over a broad
range of pseudorapidity and full azimuth as a function of charged particle
multiplicity for the first time with LEP-2 data. At 91 GeV, no significant
long-range correlation is observed in either the beam coordinate analysis or
the thrust coordinate analysis, where the latter is sensitive to a medium
expanding transverse to the color string between the outgoing pair
from the Z boson decays. Results with data at higher collision energy
than 91 GeV, providing higher event multiplicity reach up to around 50, are
presented for the first time. The thrust axis analysis shows a long-range
near-side excess in the two-particle correlation function. We performed Fourier
series decomposition of the two-particle correlation functions. In high
multiplicity events with more than 50 particles, the extracted Fourier
coefficients and magnitudes in data are larger than the MC
reference.Comment: ICHEP2022 Proceeding
Measurements of two-particle correlations in collisions at 91 GeV with ALEPH archived data
Measurements of two-particle angular correlations of charged particles
emitted in hadronic decays are presented. The archived
annihilation data at a center-of-mass energy of 91 GeV were collected with the
ALEPH detector at LEP between 1992 and 1995. The correlation functions are
measured over a broad range of pseudorapidity and full azimuth as a function of
charged particle multiplicity. No significant long-range correlation is
observed in either the lab coordinate analysis or the thrust coordinate
analysis, where the latter is sensitive to a medium expanding transverse to the
color string between the outgoing pair from boson decays. The
associated yield distributions in both analyses are in better agreement with
the prediction from the PYTHIA v6.1 event generator than from HERWIG v7.1.5.
They provide new insights to showering and hadronization modeling. These
results serve as an important reference to the observed long-range correlation
in proton-proton, proton-nucleus, and nucleus-nucleus collisions.Comment: Replaced with the published version. Added the journal reference and
the DO
First measurement of anti-k jet spectra and jet substructure using the archived ALEPH data at 91.2 GeV
We present the first anti-k jet spectrum and substructure measurements
using the archived ALEPH data taken in 1994 at a center of mass energy
of GeV. Jets are reconstructed with the anti-k
algorithm with a resolution parameter of 0.4. It is the cleanest test of jets
and QCD without the complication of hadronic initial states. The fixed
center-of-mass energy also allows the first direct test of pQCD calculation. We
present both the inclusive jet energy spectrum and the leading dijet energy
spectra, together with a number of substructure observables. They are compared
to predictions from PYTHIA6, PYTHIA8, Sherpa, HERWIG, VINCIA, and PYQUEN. None
of the models fully reproduce the data. The data are also compared to two
perturbative QCD calculations at NLO and with NLL'+R resummation. The results
can also serve as reference measurements to compare to results from hadronic
colliders. Future directions, including testing jet clustering algorithms
designed for future electron-ion collider experiments, will also be discussed
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