共查询到20条相似文献,搜索用时 31 毫秒
1.
on behalf of the ATLAS Collaboration N. Grau 《The European Physical Journal C - Particles and Fields》2009,62(1):191-196
Full jet reconstruction in relativistic heavy ion collisions provides new and unique insights to the physics of parton energy
loss. Because of the large underlying event multiplicity in A+A collisions, random and correlated fluctuations in the background can result in the reconstruction of fake jets. These fake
jets must be identified and rejected to obtain the purest jet sample possible. A large but reducible fake rate of jets reconstructed
using an iterative cone algorithm on HIJING events is observed. The absolute rate of fake jets exceeds the binary-scaled p+p jet rate below 50 GeV and is not negligible until 100 GeV. The variable Σj
T
, the sum of the jet constituent’s E
T
perpendicular to the jet axis, is introduced to identify and reject fake jets at by a factor of 100 making it negligible.
This variable is shown to not strongly depend on jet energy profiles modified by energy loss. By studying azimuthal correlations
of reconstructed di-jets, the fake jet rate can be evaluated in data.
All results presented use modified versions of ATLAS software and should be considered “ATLAS preliminary”. 相似文献
2.
Hanzhong Zhang Jeff Owens Enke Wang Xin-Nian Wang 《The European Physical Journal C - Particles and Fields》2009,61(4):825-828
High-p
T photon–hadron correlations are studied within the next-to-leading order (NLO) perturbative QCD parton model with modified
parton-jet fragmentation functions due to jet quenching in high-energy A+A collisions. In central A+A collisions, the away-side hadrons with large z
T=p
T
h
/p
T
γ
are controlled mainly by the surface emission of the gamma-jet events, while a small z
T region will be volume emission bias. In other words, gamma jets for a small-z
T region probe the dense matter deeper than those gamma jets for a large-z
T region, so the small-z
T gamma jets are found to be slightly more sensitive to the properties of the dense matter than the large-z
T gamma jets. 相似文献
3.
Generalization of z-scaling observed in the inclusive high-p
T-charged hadron and jet production is proposed. Scaling function ψ(z) describing both charged hadrons and jets produced in proton-(anti)proton colisions for various multiplicity densities and
collision energies is constructed. Anomalous fractal dimensions and parameters characterizing an associated medium for both
classes of events are established. The basic features of the scaling established in minimum bias events are shown to be preserved
up to the highest multiplicity densities measured in the experiments UA1, E735, CDF, and STAR. The obtained results are of
interest for use of z-scaling as a tool for searching for new physics phenomena of particle production at a high transverse momentum and in the
high-multiplicity region at U70, Tevatron, RHIC, and LHC.
The text was submitted by the authors in English. 相似文献
4.
The canonical statistical model analysis of strange and multistrange hadron production in central A–A relative to p–p/p–A collisions is presented over the energy range from GeV up to GeV. It is shown that the relative enhancement of strange particle yields from p–p/p–A to A–A collisions substantially increases with decreasing collision energy. It is largest at GeV, where the enhancement of and is of the order of 100, 20 and 3, respectively. In terms of the model these results are due to the canonical suppression
of particle thermal phase space at lower energies, which increases with the strangeness content of the particle and with decreasing
size of the collision fireball. The comparison of the model with existing data on the energy dependence of the kaon/pion ratio
is also discussed.
Received: 25 October 2001 / Published online: 5 July 2002 相似文献
5.
The study of very high transverse-momentum jets will be an important issue at the LHC, in particular since the corresponding
cross sections will be considerably larger than at RHIC energies. Jets are expected to provide information on QGP formation,
due to the energy loss of fast partons in the medium. Jet cross sections can in principle be compared to simple pQCD calculations,
based on the hypothesis of factorization. But often it is useful or even necessary to not only compute the production rate
of the very high-p
T jets, but in addition the “rest of the event”. The proposed talk is based on recent work, where we try to construct an event
generator—fully compatible with pQCD—which allows one to compute complete events, consisting of high-p
T jets plus all the other low p
T particles produced at the same time. Whereas in “generators of inclusive spectra” like Pythia one may easily trigger on high-p
T phenomena, this is not so obvious for “generators of physical events”, where in principle one has to generate a very large
number of events in order to finally obtain rare events (like those with a very high-p
T jet). We shall discuss how we overcome these difficulties in the framework of the EPOS model. 相似文献
6.
E. V. Khramov A. N. Tonoyan V. A. Bednyakov N. A. Rusakovich 《Physics of Particles and Nuclei Letters》2008,5(6):515-519
The possibility of discovering top-antitop resonances with masses of 700, 1000, 1500, 2000, and 3000 GeV/c 2 at proton-proton collision energy of 14 TeV in the center of a mass system is considered. The minimum cross sections for the resonance production necessary for their detection in a lepton + jets channel of $ t\mathop t\limits^ - The possibility of discovering top-antitop resonances with masses of 700, 1000, 1500, 2000, and 3000 GeV/c
2 at proton-proton collision energy of 14 TeV in the center of a mass system is considered. The minimum cross sections for
the resonance production necessary for their detection in a lepton + jets channel of pair decay with a 5σ confidence level is estimated. The analysis is performed both with and without taking into account the
possibility of hadronic jets reconstruction from b quarks (b-tagging).
Original Russian Text ? E.V. Khramov, A.N. Tonoyan, V.A. Bednyakov, N.A. Rusakovich, 2008, published in Pis’ma v Zhurnal Fizika
Elementarnykh Chastits i Atomnogo Yadra, 2008, No. 6 (148), pp. 865–873. 相似文献
7.
A. A. Kuznetsov Yu. A. Panebrattsev R. Togoo B. Baatar 《Physics of Particles and Nuclei Letters》2006,3(2):99-112
The charged π-meson and proton mixed hadronic jets in the fragmentation regions of π− + p and π− + C interactions at 40 GeV/c are extracted and their properties are investigated. It has been shown that the characteristics of the jets in the π−-meson fragmentation region are universal in jet events, do not depend on the type of the target and are defined only from
the quark contents of the π− meson. The jet characteristics in the proton fragmentation region are different and depend upon the quark contents of the
proton. Mixed hadronic jets with defined values of the electric charge were studied. The resonance structures related to the
Δ isobars are discovered in the effective mass distributions of the jets. It has been shown that the small azimuthal angle
high-p
T
correlations are observed and strong back-to-back correlations exist.
The text was submitted by the authors in English. 相似文献
8.
9.
A. V. Bobylev 《Journal of statistical physics》1996,88(5-6):1183-1214
Some inequalities for the Boltzmann collision integral are proved. These inequalities can be considered as a generalization
of the well-known Povzner inequality. The inequalities are used to obtain estimates of moments of the solution to the spatially
homogeneous Boltzmann equation for a wide class of intermolecular forces. We obtain simple necessary and sufficient conditions
(on the potential) for the uniform boundedness of all moments. For potentials with compact support the following statement
is proved: if all moments of the initial distribution function are bounded by the corresponding moments of the MaxwellianA exp(−Bv
2), then all moments of the solution are bounded by the corresponding moments of the other MaxwellianA
1 exp[−B
1(t)v
2] for anyt > 0; moreoverB(t) = const for hard spheres. An estimate for a collision frequency is also obtained. 相似文献
10.
Maitreyee Saha Sarkar 《Pramana》1999,53(3):431-435
Neutron-rich isotopes of Mo (Z=42) around A ⋍ 100 have been investigated within the formalisms of cranked Nilsson Strutinsky and CHFB, to study several interesting features
of nuclear structure in this mass region. The total energy/routhian surfaces have been generated for the isotopes of Mo ranging
from A ⋍ 96 − 112, as a function of deformation (β
2 and γ) for ground state and higher angular momentum states. Results of calculations using two different formalisms have been compared
and combined to have a better understanding of the underlying mechanism of shape evolution. 相似文献
11.
The production of heavy quarks in heavy-ion collisions is important because it is expected to give information about high-density
QCD matter. One interesting channel of heavy quark measurements at LHC is the decay of B to J/ψ. The J/ψ mesons from this channel can be separated from the primary J/ψ (produced at collision vertex) by using the secondary vertex which is efficiently reconstructed with the CMS tracker. In
this work, the generator level results for the primary and secondary J/ψ obtained through dimuon pairs are presented for pp and PbPb collisions at $
\sqrt {s_{NN} }
$
\sqrt {s_{NN} }
= 5.5 TeV. 相似文献
12.
Matteo Cacciari Gavin P. Salam Gregory Soyez 《The European Physical Journal C - Particles and Fields》2011,71(6):1692
Recent LHC results concerning full jet-quenching in Pb Pb collisions have been presented in terms of a jet asymmetry parameter,
measuring the imbalance between the transverse momenta of leading and subleading jets. We examine the potential sensitivity
of this distribution to fluctuations from the heavy-ion background. Our results suggest that a detailed estimate of the true
fluctuations would be of benefit in extracting quantitative information about jet quenching. We also find that the apparent
impact of fluctuations on the jet asymmetry distribution can depend significantly on the choice of low-p
t
threshold used for the simulation of the hard pp events. 相似文献
13.
S. Lupia A. Giovannini R. Ugoccioni 《Zeitschrift fur Physik C Particles and Fields》1993,59(3):427-435
Theoretical basis of void scaling function properties of hierarchical structure in rapidity andp
T intervals are explored. Their phenomenological consequences are analyzed at single jet level by using Monte Carlo methods ine
+
e
– annihilation. It is found that void scaling function study provides an interesting alternative approach for characterizing single jets of different origin.Work supported in part by M.U.R.S.T. (Italy) under Grant 1992 相似文献
14.
OPAL Collaboration G. Alexander J. Allison N. Altekamp K. Ametewee K. J. Anderson S. Anderson S. Arcelli S. Asai D. Axen et al. 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):543-560
Symmetric three-jet events are selected from hadronic Z0 decays such that the two lower energy jets are each produced at an angle of about 150° with respect to the highest energy
jet. In some cases, a displaced secondary vertex is reconstructed in one of the two lower energy jets, which permits the other
lower energy jet to be identified as a gluon jet through anti-tagging. In other cases, the highest energy jet is tagged as
a b jet or as a light quark (uds) jet using secondary vertex or track impact parameter and momentum information. Comparing
the two lower energy jets of the events with a tag in the highest energy jet to the anti-tagged gluon jets yields a direct
comparison of b, uds and gluon jets, which are produced with the same energy of about 24 GeV and under the same conditions.
We observe b jets and gluon jets to have similar properties as measured by the angular distribution of particle energy around
the jet directions and by the fragmentation functions. In contrast, gluon jets are found to be significantly broader and to
have a markedly softer fragmentation function than uds jets. For thek
⊥ jet finder withy
cut=0.02, we find
as the ratios of the mean charged particle multiplicity in the gluon jets compared to the b and uds jets. Results are also
reported using the cone jet finder. 相似文献
15.
We show that in the collapse of a Bose–Einstein condensate (BEC)4certain processes involved and mechanisms at work share a common origin with corresponding quantum field processes in the
early universe such as particle creation, structure formation, and spinodal instability. Phenomena associated with the controlled
BEC collapse observed in the experiment of Donley et al. (Donley, E., et al. (2001), Nature 412, 295; Claussen, N. (2003), PhD Thesis, University of Colorado; Claussen, N., et al. (2003), Physical Review A 67, 060701(R))(they call it “Bose–Nova,” see also Chin, J., Vogels, J., and Ketterle, W. (2003), Physical Review Letters 90, 160405) such as the appearance of bursts and jets can be explained as a consequence of the squeezing and amplification of
quantum fluctuations above the condensate by the dynamics of the condensate. Using the physical insight gained in depicting
these cosmological processes, our analysis of the changing amplitude and particle contents of quantum excitations in these
BEC dynamics provides excellent quantitative fits with the experimental data on the scaling behavior of the collapse time
and the amount of particles emitted in the jets. Because of the coherence properties of BEC and the high degree of control
and measurement precision in atomic and optical systems, we see great potential in the design of tabletop experiments for
testing out general ideas and specific (quantum field) processes in the early universe, thus opening up the possibility for
implementing “laboratory cosmology.”
This essay has the same content as v2 of Calzetta and Hu (2002), with a few references updated. For more details, see Calzetta
and Hu (2002).
4For an excellent introduction to BEC theory, see Pethick and Smith (2002). 相似文献
16.
基于我们最近所构建的Ar+H+2→ArH++H(12A′)反应的新势能面,采用准经典轨线法研究了碰撞能分别为0.48,0.77,1.24 eV以及能量为0.48 eV时反应物不同振动态下Ar+H+2→ArH++H反应的立体动力学性质.结果显示在给定的碰撞能情况下,以及当反应物振动量子数由0变到2时计算的积分反应截面与实验值符合得较好.通过比较发现,碰撞能对此反应k-j′关联函数P(θr)分布的影响大于其受振动激发的影响,并且关于k-k′-j′三矢量相关的函数P(?r)分布以及极化微分反应截面对碰撞能较敏感,同时发现振动激发对P(?r)分布和极化微分反应截面也有较大的影响. 相似文献
17.
We derive the nonlinear k
⊥ factorization for the spectrum of jets in high-mass diffractive deep inelastic scattering as a function of three hard scales—the
virtuality of the photon Q
2, the transverse momentum of the jet, and the saturation scale Q
A
. In contrast to all other hard reactions studied so far, we encounter a clash between the two definitions of the glue in
the pomeron from the inclusive spectrum of leading quarks and the small-β evolution of the diffractive cross section. This
clash casts a further shadow on customary applications of the familiar collinear factorization to a pQCD analysis of diffractive
deep inelastic scattering.
The text was submitted by the authors in English. 相似文献
18.
New experimental data on fluctuations in the multiplicities of negatively charged particles in interactions of light nuclei
(p, d, 4He, 12C) with carbon nuclei at a momentum of 4.2 A GeV/c in 4π geometry are reported. The data indicate a behavior similar to that earlier observed by the NA49 Collaboration. The
cascade evaporation model, FRITIOF model, and UrQMD 1.3 model are used to analyze the data. The dependence of the fluctuations
on nuclear collision centrality is theoretically described without any exotic assumptions. According to the FRITIOF model,
the dependence of the multiplicity fluctuations on the collision centrality is to a large extent governed by fluctuations
in the number of “wounded” nucleons that are associated with the experimental observation conditions. The NA49 Collaboration
data are also described. 相似文献
19.
J. Benlliure P. Armbruster M. Bernas C. Böckstiegel S. Czajkowski C. Donzaud H. Geissel A. Heinz C. Kozhuharov P. Dessagne G. Münzenberg M. Pfützner C. Stéphan K.-H. Schmidt K. Sümmerer W. Schwab L. Tassan-Got B. Voss 《The European Physical Journal A - Hadrons and Nuclei》1998,2(2):193-198
Projectile fragmentation of 238U in a lead target was investigated at a bombarding energy of 750 A MeV. Isotopic production cross sections of about 250 different projectile fragments in the element range Z= 30–53 were measured with the FRagment Separator (FRS). The magnetic selection and the kinematical analysis of the measured
isotopes allowed to disentangle fission and fragmentation residues. The mass loss of these residues indicates a violent collision
where a large amount of energy is dissipated. The position of the fragmentation corridor defined by the measured residues
was used to determine an effective proton-evaporation barrier.
Received: 3 October 1997 / Revised version: 27 February 1998 相似文献
20.
Gábor Hofer-Szabó 《International Journal of Theoretical Physics》2006,45(7):1308-1322
A pair (A, B) of events in a classical probability measure space (Ω, p) is called exchangeable iff p(A
) = p(
B). Conditionally identical common cause system of size n for the correlation is an n-partition of Ω such that (i) any member of the partition screens the correlation off and (ii) for any member {C
i
}
i ∊ I
of the partition p(A|C
i
) = p(B|C
i
). The common cause system is called proper if p(A|C
i
)≠(A|C
j
) for some i ≠ j. In the paper it is shown that exchangeable correlations be explained by proper conditionally identical common cause systems in the following sense. (i) Given a proper conditionally identical common cause system of size n for the two events A and B in Ω, then the pair (A, B) will be an exchangeable (positively) correlating pair. (ii) Given any exchangeable (positively) correlating pair of events in Ω and given any finite number n > 2, then the probability space can be embedded into a larger probability space in such a way that the larger space contains a proper conditionally identical common cause system of size n for the correlation. 相似文献