共查询到20条相似文献,搜索用时 862 毫秒
1.
Yaxian Mao Gustavo Conesa Balbastre Masato Sano Yves Schutz Daicui Zhou 《The European Physical Journal C - Particles and Fields》2008,57(3):613-619
The possibility to study the fragmentation function of jets with energies below 50 GeV, which cannot be reconstructed in the
heavy-ion environment, is explored. We propose to measure the imbalance distribution between prompt photon and charged hadrons
with the ALICE experiment at LHC. In the present article, the case of proton–proton collisions at
TeV is examined with Monte-Carlo simulations. Performances for prompt photon identification and rejection of the π
0 decay photons are presented. We find that the measurement in proton–proton is meaningful with respect to statistical and
systematic errors for photon energies larger than 20 GeV. 相似文献
2.
F. Benedosso 《The European Physical Journal C - Particles and Fields》2007,49(1):61-64
We present measurements of azimuthal correlations between photons (from π0 decay) and charged hadrons in d+Au collisions at =200 GeV. We use di-hadron correlations to study parton fragmentation in d+Au collisions at RHIC. Specifically, the near-side
and away-side peaks of the azimuthal angular difference distribution are used to measure the root-mean-squared (RMS) fragmentation
transverse momentum and the mean intrinsic parton transverse momentum . The measurements with leading photons are compared to results using leading charged particles.
PACS 25.75.-q 相似文献
3.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2006,45(2):291-305
The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies
in the range
≃ 189–209 using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles
in hadronic decays of . Measurements of inclusive charged particle multiplicities, and of their angular distribution with
respect to the four jet axes of the events, are used to test models of colour reconnection. The data are found to exclude
extreme scenarios of the Sj?strand-Khoze Type I () model and are compatible with other models, both with and without colour
reconnection effects. In the context of the model, the best agreement with data is obtained for a reconnection probability
of 37%. Assuming no colour reconnection, the charged particle multiplicity in hadronically decaying W bosons is measured to
be
=19.38±0.05(stat.)±0.08(syst.).
Arrival of the final proofs: 28 November 2005 相似文献
4.
O. Kodolova I. Vardanyan A. Nikitenko A. Oulianov 《The European Physical Journal C - Particles and Fields》2007,50(1):117-123
A jet reconstruction algorithm is developed for events with a high particle density in the calorimetric system. The performance
of the reconstruction of hard QCD jets with initial parton energies 50–300 GeV is studied in central Pb–Pb collisions with
a modified cone jet finder which includes an algorithm for event-by-event background subtraction. The heavy ion background
is simulated using the HIJING Monte Carlo generator with . Results on the achieved jet reconstruction efficiency, purity, energy and spatial resolution are presented. 相似文献
5.
T. Chujo 《The European Physical Journal C - Particles and Fields》2007,49(1):23-28
The baryon production mechanism at the intermediate pT (2–5 GeV/c) at RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au systems at RHIC may provide us a further
insight on the origin of the baryon anomaly and its evolution as a function of . In 2005 RHIC physics program, the PHENIX experiment accumulated the first intensive low beam energy data in Cu+Cu collisions.
We present the preliminary results of identified charged hadron spectra in Cu+Cu at and 62.4 GeV using the PHENIX detector. The centrality and beam energy dependences of (anti)proton to pion ratios and the
nuclear modification factors for charged pions and (anti)protons are presented.
PACS 25.75.Dw 相似文献
6.
Y. Chen V. Chetluru Y. J. Lee C. Loizides C. Roland G. Roland M. B. Tonjes Y. Yilmaz A. S. Yoon 《The European Physical Journal C - Particles and Fields》2009,61(4):649-658
The energy loss of fast partons traversing the strongly interacting matter produced in high energy nuclear collisions is one
of the most interesting observables to probe the nature of the produced medium. The collisional and radiative energy loss
of the partons will modify the fragmentation functions depending on the path length in the medium. Pb + Pb collisions at
GeV at the LHC will allow detailed measurements of the in-medium modifications of fragmentation functions of parton initiated
jets, using the γ-jet channel. Since the photon does not strongly interact with the medium, the initial transverse energy of the fragmenting
parton can be related to the photon transverse energy. This in turn allows for precision studies of the fragmentation function
underlying these jets. 相似文献
7.
A. Marín 《The European Physical Journal C - Particles and Fields》2009,61(4):735-740
Heavy-ion collisions will enter a new era with the start of the CERN Large Hadron Collider (LHC). A first short run with proton-proton
collisions at the injection energy of 0.9 TeV will be followed by a longer one with pp collisions at 10 TeV. First Pb-Pb collisions at
TeV will take place in 2009. Three experiments (ALICE, ATLAS, and CMS) will study both pp and Pb-Pb collisions. A selection of results showing the capabilities of the three experiments for the study of the LHC medium
with direct photons is presented. 相似文献
8.
A.A. Bagneid 《The European Physical Journal C - Particles and Fields》2008,54(4):547-553
We examine distributions of leptons produced in e+e- collisions, by a family nonuniversal extra gauge boson Z′, suggested by the model, and by other neutral gauge bosons occurring in left–right symmetric models and in superstring-inspired E6 models. We discuss how to distinguish the models by examining the couplings to fermions of the extra Z-boson through its
leptonic production cross sections and asymmetries. We show how the universality violation inherent in the model enhances the discovery potential of Z′ at future planned and proposed e+e- colliders. 相似文献
9.
P. Romatschke 《The European Physical Journal C - Particles and Fields》2007,52(1):203-209
Causal viscous hydrodynamic fits to experimental data for pion and kaon transverse momentum spectra from central Au + Au collisions
at are presented. Starting the hydrodynamic evolution at 1 fm/c and using small values for the relaxation time, reasonable fits up to moderate ratios, η/s≃0.4, can be obtained. It is found
that a percentage of roughly 50 η/s to 75 η/s of the final meson multiplicity is due to viscous entropy production. Finally,
it is shown that with increasing viscosity, the ratio of HBT radii Rout/Rside approaches and eventually matches the experimental data. 相似文献
10.
Redamy Perez-Ramos 《The European Physical Journal C - Particles and Fields》2009,62(3):541-545
The energy evolution of average multiplicities and multiplicity fluctuations in jets produced in heavy-ion collisions is investigated
from a toy QCD-inspired model. In this model, we use modified splitting functions accounting for medium-enhanced radiation
of gluons by a fast parton which propagates through the quark–gluon plasma. The leading contribution of the standard production
of soft hadrons is enhanced by a factor
while next-to-leading order (NLO) corrections are suppressed by
, where the parameter N
s
>1 accounts for the induced soft gluons in the medium. Our results for such global observables are cross-checked and compared
with their limits in the vacuum. 相似文献
11.
A. K. Chaudhuri 《The European Physical Journal C - Particles and Fields》2009,61(2):331-338
In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy,
GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T
J/ψ
. Sequential melting of charmonium states (χ
c
, ψ
′ and J/ψ), with melting temperatures
, T
J/ψ
≈2T
c
and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ
p
T
spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts
the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ
p
T
spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,
GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ
p
T
distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC. 相似文献
12.
Sevil Salur 《The European Physical Journal C - Particles and Fields》2009,61(4):761-767
We present the first measurement of reconstructed jets in ultra-relativistic heavy ion collisions. Utilizing the large coverage
of the STAR Time Projection Chamber and Electromagnetic Calorimeter, we apply several modern jet reconstruction algorithms
and background subtraction techniques and explore their systematic uncertainties in heavy ion events. The differential energy
spectrum for inclusive jet production in central Au+Au collisions at
is presented. In order to assess the jet reconstruction biases, this spectrum is compared with the jet cross section measured
in
GeV p+p collisions scaled by the number of binary N–N collisions to account for nuclear geometric effects. 相似文献
13.
T. Lappi 《The European Physical Journal C - Particles and Fields》2011,71(8):1699
A natural framework to understand the energy dependence of bulk observables from lower energy experiments to the LHC is provided
by the Color Glass Condensate, which leads to a “geometrical scaling” in terms of an energy-dependent saturation scale Q
s. The measured charged multiplicity, however, seems to grow faster ( ~ ?s0.3{\sim}\sqrt{s}^{0.3}) in nucleus–nucleus collisions than it does for protons ( ~ ?s0.2{\sim} \sqrt{s}^{0.2}), violating the expectation from geometric scaling. We argue that this difference between pp and AA collisions can be understood
from the effect of DGLAP evolution on the value of the saturation scale, and is consistent with gluon saturation observations
at HERA. 相似文献
14.
M.W. Krasny F. Fayette W. Płaczek A. Siódmok 《The European Physical Journal C - Particles and Fields》2007,51(3):607-617
In this paper we propose a strategy for measuring the inclusive W boson production processes at LHC. This strategy exploits
simultaneously the unique flexibility of the LHC collider in running variable beam particle species at variable beam energies,
and the configuration flexibility of the LHC detectors. We propose their concrete settings for a precision measurement of
the standard model parameters. These dedicated settings optimise the use of the Z boson and Drell–Yan-pair production processes
as “the standard reference candles”. The presented strategy allows one to factorise and to directly measure those of the QCD
effects that affect differently the W and Z production processes. It reduces to a level of the impact of uncertainties in the partonic distribution functions (PDFs) and in the transverse momentum of the quarks on
the measurement precision. Last but not the least, it reduces by a factor of 10 the impact of systematic measurement errors,
such as the energy scale and the measurement resolution, on the W boson production observables. 相似文献
15.
A. Morsch 《The European Physical Journal C - Particles and Fields》2005,43(1-4):333-336
In central Pb-Pb collisions at the LHC, jet rates are expected to be high at energies at which ALICE can reconstruct jets
over the background of the underlying event. This will open the possibility to quantify the effect of partonic energy loss
through medium induced gluon radiation, jet quenching, by detailed measurement of the modification of the longitudinal and transverse structure of identified jets. In order to
obtain probes sensitive to the properties of the QCD medium, it is mandatory to measure the high-
parton fragments together with the low-
particles from the radiated gluons. Hence, the excellent charged particle tracking capabilities of ALICE combined with the
proposed electromagnetic calorimeter for ALICE, EMCAL, represent an ideal tool for jet quenching studies at the LHC.
Electronic Supplementary Material Supplementary material is available for this article at
PACS:
25.75.Nq, 24.85. + p, 13.87.-a 相似文献
16.
M. V. T. Machado C. Brenner Mariotto 《The European Physical Journal C - Particles and Fields》2009,61(4):871-878
We investigate the rapidity and transverse-momentum distributions of the prompt photon production at the CERN LHC energies
considering the current perturbative QCD approaches for this scattering process. Namely, we compare the predictions from the
usual NLO pQCD calculations to the color-dipole formalism, using distinct dipole cross sections. Special attention is paid
to parton-saturation models at high energies, which are expected to be important at the forward rapidities in pp collisions (
TeV) at the LHC. 相似文献
17.
D. Molnar 《The European Physical Journal C - Particles and Fields》2007,49(1):181-186
There are several indications that an opaque partonic medium is created in energetic Au+Au collisions at the relativistic heavy ion collider (RHIC). At the extreme densities of ∼10–100 times normal nuclear density reached,
even heavy-flavor hadrons are affected significantly. Heavy-quark observables are presented from the parton transport model
MPC, focusing on the nuclear suppression pattern, azimuthal anisotropy (“elliptic flow”), and azimuthal correlations. Comparison
with Au+Au data at top RHIC energy indicates significant heavy-quark rescattering, corresponding roughly five times higher opacities than estimates based on
leading-order perturbative QCD. We propose measurements of charm–anticharm, e.g., D-meson azimuthal correlations as a sensitive,
independent probe to corroborate these findings.
PACS 25.75.-q; 25.75.Ld; 25.75.Gz 相似文献
18.
We study the process e+e-→νν̄γ to search for its sensitivity to the extra gauge bosons Z2, Z3 and W2
±, which are suggested by the little Higgs models. We find that the ILC with and CLIC with cover different regions of the LHM parameters. We show that this channel can provide a determination of the parameters, complementary
to measurements of the extra gauge bosons obtainable at the upcoming LHC experiments.
PACS 14.80.Cp; 12.60.Fr; 12.60.Cn 相似文献
19.
J. Bielcikova 《The European Physical Journal C - Particles and Fields》2007,49(1):321-326
We present results on two-particle azimuthal correlations of neutral strange baryons (Λ, Λ̄) and mesons (KS
0) for pT=2–6 GeV/c associated with non-identified charged particles in d+Au and Au+Au collisions at =200 GeV measured by the STAR experiment. We investigate in detail the associated yield of charged particles as a function
centrality of the collision and transverse momentum of trigger and associated particles to look for possible flavor, baryon/meson
and particle/anti-particle differences. We compare our results to the proton and pion triggered correlations as well as to
a fragmentation and recombination model.
PACS 25.75.-q; 25.75.Gz 相似文献
20.
S. Heinemeyer V.A. Khoze M.G. Ryskin W.J. Stirling M. Tasevsky G. Weiglein 《The European Physical Journal C - Particles and Fields》2008,53(2):231-256
We show that the use of forward proton detectors at the LHC installed at 220 m and 420 m distance around ATLAS and/or CMS
can provide important information on the Higgs sector of the MSSM. We analyse central exclusive production of the neutral
-even Higgs bosons h and H and their decays into bottom quarks, τ leptons and W bosons in various MSSM benchmark scenarios.
Using plausible estimates for the achievable experimental efficiencies and the relevant background processes, we find that
the prospective sensitivity of the diffractive Higgs production will allow one to probe interesting regions of the MA–tanβ parameter plane of the MSSM. Central exclusive production of the -even Higgs bosons of the MSSM may provide a unique opportunity to access the bottom Yukawa couplings of the Higgs bosons
up to masses of MH≲ 250 GeV. We also discuss the prospects for identifying the -odd Higgs boson, A, in diffractive processes at the LHC. 相似文献