共查询到20条相似文献,搜索用时 26 毫秒
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2.
A. Gehrmann-De Ridder T. Gehrmann E. Poulsen 《The European Physical Journal C - Particles and Fields》2006,47(2):395-411
The production of final state photons in deep inelastic scattering originates from photon radiation off leptons or quarks
involved in the scattering process. Photon radiation off quarks involves a contribution from the quark-to-photon fragmentation
function, corresponding to the non-perturbative transition of a hadronic jet into a single, highly energetic photon accompanied
by some limited hadronic activity. Up to now, this fragmentation function was measured only in electron–positron annihilation
at LEP. We demonstrate by a dedicated parton-level calculation that a competitive measurement of the quark-to-photon fragmentation
function can be obtained in deep inelastic scattering at HERA. Such a measurement can be obtained by studying the photon energy
spectra in γ+(0+1)-jet events, where γ denotes a hadronic jet containing a highly energetic photon (the photon jet). Isolated
photons are then defined from the photon jet by imposing a minimal photon energy fraction. For this so-called democratic clustering
approach, we study the cross sections for isolated γ+(0+1)-jet and γ+(1+1)-jet production as well as for the inclusive isolated
photon production in deep inelastic scattering. 相似文献
3.
Time-resolved two photon photoemission electron microscopy 总被引:1,自引:0,他引:1
O. Schmidt M. Bauer C. Wiemann R. Porath M. Scharte O. Andreyev G. Schönhense M. Aeschlimann 《Applied physics. B, Lasers and optics》2002,74(3):223-227
Femtosecond, time-resolved two photon photoemission has been used to map the dynamics of photo-excited electrons at a structured
metal/semiconductor surface. A photoemission microscope was employed as a spatially resolving electron detector. This novel
setup has the potential to visualize variations of hot electron lifetimes in the femtosecond regime on heterogeneous sample
surfaces and nanostructures.
Received: 22 October 2001 / Revised version: 10 January 2002 / Published online: 7 February 2002 相似文献
4.
P. Jankowski M. Krawczyk A. De Roeck 《The European Physical Journal C - Particles and Fields》2002,24(4):547-553
Heavy quark production is studied at the TESLA high energy linear collider (LC) both in its nominal and photon collider (PC) mode. Leading order cross-sections are calculated for the production
of heavy quarks, , at high transverse momenta. The sensitivity of this process to the gluon content in the photon is studied.
Received: 26 November 2001 / Published online: 21 June 2002 相似文献
5.
P. Aurenche Rahul Basu M. Fontannaz 《The European Physical Journal C - Particles and Fields》2011,71(4):1616
We present a next-to-leading order calculation of prompt photon production in deep-inelastic scattering. The calculation involves
direct, fragmentation and resolved contributions. Inclusive as well as isolated photon production cross sections are presented.
The relevance of imposing a transverse momentum cut-off in the virtual-photon proton center-of-mass system rather than in
the laboratory frame is discussed. Whenever possible, a comparison of the theoretical results with recent HERA data is carried
out. 相似文献
6.
We attempt in this paper to deal with some aspects of the direct photon production phenomenon mainly in the Pb+Pb and Au+Au collisions on the basis of a model for production of the same particle species in PP collisions. The results have, thereafter, been converted to those for a few AB/AA interactions through an appropriate mechanism. Comparison of the theoretical results obtained on the basis of model-based calculations with measured data on the relevant observables leads to a fair agreement between them. This reflects modestly the fair achievements attained by the models that are made use of in the present work. 相似文献
7.
A. D. Levin D. M. Gitman R. A. Castro 《The European Physical Journal C - Particles and Fields》2014,74(9):1-7
We show how the photon input parton distribution function (PDF) may be calculated with good accuracy and used in an extended DGLAP global parton analysis in which the photon is treated as an additional point-like parton. The uncertainty of the input photon PDF is relatively small, since the major part of the distribution (which is produced by the coherent emission of the photon from a proton that remains intact) is well known. We present the expected photon PDFs and compare the predictions with ZEUS data for isolated photon electroproduction at negative rapidities. 相似文献
8.
V.A. Khoze A.D. Martin M.G. Ryskin 《The European Physical Journal C - Particles and Fields》2002,24(3):459-468
The rich structure of photon-exchange processes at hadron colliders is studied. We discuss central vector meson production
, W production and production. Each process has distinct, and large, soft pp rescattering effects, which can be directly observed by detecting the outgoing protons. This allows a probe of the optical
density of the proton, which plays a crucial role in the evaluation of the rapidity gap survival probabilities in diffractive-like
processes at hadron colliders. We note that an alternative mechanism for production is odderon, instead of photon, exchange; and that the ratio of odderon to photon contributions is enhanced (suppressed)
for vector meson production.
Received: 1 February 2002 / Revised version: 4 April 2002 / Published online: 22 May 2002 相似文献
9.
E.R. Berger A. Donnachie H.G. Dosch W. Kilian O. Nachtmann M. Rueter 《The European Physical Journal C - Particles and Fields》1999,9(3):491-501
We investigate the reaction where PS denotes a pseudoscalar meson , , , or and X either a proton or resonance or continuum state into which the proton can go by diffractive excitation. At high energies
photon and odderon exchange contribute to the reaction. The photon exchange contribution is evaluated exactly using data for
the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative
QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark
structure as suggested by the small odderon amplitude in pp and forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic PS production cross section.
Observation of our reaction at HERA would establish the soft odderon as an exchange object on an equal footing with the soft
pomeron and would give us valuable insight into both the nucleon structure and the mechanism of high energy diffractive scattering.
Received: 2 February 1999 / Revised version: 22 March 1999 / Published online: 28 May 1999 相似文献
10.
A. Gehrmann-De Ridder E.W.N. Glover 《The European Physical Journal C - Particles and Fields》1999,7(1):29-48
We present a detailed study of photon production in hadronic events in electron-positron annihilation at LEP energies. We
show that estimates of the inclusive photon spectrum using the quark-to-photon fragmentation function determined using the
ALEPH ‘photon’ + 1 jet data agree well with the observations of the OPAL collaboration. This agreement shows that the photon
fragmentation function determined in this way can be used for inclusive observables. We also compare next-to-leading order
and beyond leading logarithm predictions obtained using the numerically resummed solutions of the fragmentation function evolution
equation of Bourhis, Fontannaz and Guillet and Glück, Reya and Vogt with the data. Moreover, in order to check the general
behaviour of the fragmentation function, we consider an analytic series expansion in the strong coupling. We find that the
parameterizations are inaccurate at large x values. While the OPAL data is in broad agreement with estimates based on any of these approaches, the ALEPH data prefers
the resummed BFG parameterization. Finally, there is some ambiguity as to whether the fragmentation function is treated as
or . We show that at present this ambiguity affects mainly the prediction for the ‘photon’ + 1 jet rate at large z.
Received: 9 June 1998 / Published online: 21 August 1998 相似文献
11.
The ZEUS Collaboration S. Chekanov et al. 《The European Physical Journal C - Particles and Fields》2002,23(4):615-631
The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity
of 38.6 pb. The events were required to have a virtuality of the incoming photon, , of less than 1 GeV and a photon-proton centre-of-mass energy in the range GeV. Each event contains at least two jets satisfying transverse-energy requirements of GeV and GeV and pseudorapidity requirements of \mbox{}. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density
of partons in the photon, allowing the validity of the current parameterisations to be tested.
Received: 21 December 2001 / Published online: 5 April 2002 相似文献
12.
D.K. Srivastava 《The European Physical Journal C - Particles and Fields》2001,22(1):129-132
Scaling of single photon production in pp and collisions is studied. It is empirically observed that the available data scales for and for larger . The NLO pQCD predictions for pp collisions at an of 200 and 5500 GeV, relevant for RHIC and LHC energies are seen to closely follow this scaling behavior. Implications for
single photon production in heavy ion collisions are discussed.
Received: 2 February 2001 / Revised version: 28 May 2001 / Published online: 5 October 2001 相似文献
13.
N.N. Nikolaev J. Speth V.R. Zoller 《The European Physical Journal C - Particles and Fields》2002,22(4):637-646
High-energy virtual photon–virtual photon scattering can be viewed as an interaction of small size color dipoles from the
beam and target photons, which makes scattering at high energies (LEP, LEP200 and NLC) an indispensable probe of the short distance properties of the QCD pomeron
exchange. Based on the color dipole representation, we investigate the consequences for the scattering of the incorporation of asymptotic freedom into the BFKL equation which makes the QCD pomeron a series of isolated
poles in the angular momentum plane. The emerging color dipole BFKL–Regge factorization allows us to relate in a model-independent
way the contributions of each BFKL pole to scattering and DIS off protons. Numerical predictions based on our early works on the color dipole BFKL phenomenology of
DIS on protons are in good agreement with the experimental data on the photon structure function and the most recent data on the cross section from the OPAL and L3 experiments at LEP200. We discuss the role of non-perturbative dynamics and predict a pronounced effect
of the Regge-factorization breaking due to large unfactorizable non-perturbative corrections to the perturbative vacuum exchange.
We comment on the salient features of the BFKL–Regge expansion for scattering including the issue of the decoupling of subleading BFKL poles and the soft plus rightmost hard BFKL pole dominance.
Received: 9 January 2001 / Revised version: 25 September 2001 / Published online: 7 December 2001 相似文献
14.
R. M. Godbole 《Pramana》1998,51(1-2):217-228
After giving a very brief introduction to the resolved photon processes, I will summarize the latest experimental information
from HERA, on resolved photon contribution to largep
T jet production as well as to direct photon production. I will point out the interesting role that resolved photon processes
can play in increasing our understanding of the dynamics of the quarkonium production. I will then discuss the newer information
on the parton content of virtual photons as well as thek
T distribution of the partons in the photon. I will end by giving predictions of an eikonalized minijet model for σ
γγ
inel
which crucially uses the experimental measurement of the abovementionedk
T distribution and comparing them with data.
On leave of absence from Department of Physics, University of Bombay, Mumbai 400 076, India 相似文献
15.
F. Jegerlehner K. Kołodziej 《The European Physical Journal C - Particles and Fields》2002,23(3):463-469
We accomplish our efforts to obtain predictions for all four–fermion final states of –annihilation and the corresponding bremsstrahlung reactions which are possible in the framework of the Standard Model. For
this purpose we have developed a program ee4
. Our predictions are valid for fermions of arbitrary masses and we can obtain results for total cross sections without any
collinear cut. Keeping exact fermion masses is of course required for top quark production. We give a detailed phenomenological
analysis of fermion mass effects and real photon radiation for all channels of four–fermion production at LEP-II and next
linear collider energies.
Received: 2 October 2001 / Revised version: 2 January 2002 / Published online: 1 March 2002 相似文献
16.
We examine the possibility of using direct photon production at HERA as a means of obtaining information about the photon structure and fragmentation functions. Estimates of the cross section for inclusive prompt photon production at theep collider HERA are made completely in next-to-leading order QCD. Using parton distributions for the photon evolved in next-to-leading order QCD for the first time, we show that theO(
s
) corrections to the processes involving these functions are significant in the regions where they dominate. This can have important consequences for the possibility of measuring the gluon content of the photon using these processes at HERA. Moreover, we show that it may not be straightforward to separate the various contributions to the cross section in theep lab frame. 相似文献
17.
《中国物理C(英文版)》2018,(11)
As part of a recent analysis of exclusive two-photon production of W+W-pairs at the LHC, the CMS experiment used di-lepton data to obtain an "effective" photon-photon luminosity. We show how the CMS analysis on their 8 TeV data, along with some assumptions about the likelihood for events in which the proton breaks up to pass the selection criteria, can be used to significantly constrain the photon parton distribution functions, such as those from the CTEQ, MRST, and NNPDF collaborations. We compare the data with predictions using these photon distributions, as well as the new LUXqed photon distribution. We study the impact of including these data on the NNPDF2.3 QED, NNPDF3.0 QED and CT14 QEDinc fits. We find that these data place a useful and complementary cross-check on the photon distribution, which is consistent with the LUXqed prediction while suggesting that the NNPDF photon error band should be significantly reduced. Additionally, we propose a simple model for describing the two-photon production of W+W-at the LHC. Using this model, we constrain the number of inelastic photons that remain after the experimental cuts are applied. 相似文献
18.
J.-S. Xu H.-A. Peng Z.-Y. Yan Z.-M. He 《The European Physical Journal C - Particles and Fields》2000,14(2):275-284
We present a study of the diffractive production in direct photon processes at HERA based on the factorization theorem for lepton-induced hard diffractive
scattering and the factorization formalism of the non-relativistic QCD (NRQCD) for quarkonia production. Using the diffractive
gluon distribution function extracted from HERA data on diffractive deep inelastic scattering and diffractive dijet photon
production, we demonstrate that this process is measurable at DESY HERA. The experimental study of this process can give valuable
insight in the diffractive production mechanism and test the color-octet mechanism for heavy quarkonia production in a new
environment.
Received: 13 September 1999 / Revised version: 31 December 1999 / Published online: 6 April 2000 相似文献
19.
M. Glück C. Pisano E. Reya I. Schienbein 《The European Physical Journal C - Particles and Fields》2003,27(3):427-432
The production rates of lepton-photon and dimuon pairs at the HERA collider and the HERMES experiment are evaluated in the
leading order equivalent photon approximation. It is shown that the production rates are sufficient to facilitate the extraction
of the polarized and unpolarized equivalent photon distributions of the proton and neutron in the available kinematical regions.
It is pointed out that these results indicate the possibility of additional, independent, tests
concerning the unpolarized and polarized structure functions F
1,2
N
and g
1,2
N
, respectively, of the nucleon.
Received: 2 October 2002 / Revised version: 9 December 2002 / Published online: 14 February 2003 相似文献
20.
We study the single transverse spin asymmetry of prompt photon production in high energy proton–proton scattering. We include the contributions from both the direct and fragmentation photons. While the asymmetry for direct photon production receives only the Sivers type of contribution, the asymmetry for fragmentation photons receives both the Sivers and Collins types of contributions. We make a model calculation for quark-to-photon Collins function, which is then used to estimate the Collins asymmetry for fragmentation photons. We find that the Collins asymmetry for fragmentation photons is very small, thus the single transverse spin asymmetry of prompt photon production is mainly coming from the Sivers asymmetry in direct and fragmentation photons. We make predictions for the prompt photon spin asymmetry at RHIC energy, and emphasize the importance of such a measurement. The asymmetry of prompt photon production can provide a good measurement for the important twist-three quark–gluon correlation function, which is urgently needed in order to resolve the “sign mismatch” puzzle. 相似文献