arXiv subjects

Shigeru Odaka

Publications and source records attributed to Shigeru Odaka.

14 recordsLinked to original sources

arXiv2018

GR@PPA 2.9: radiation matching for simulating photon production processes in hadron collisions

We release an event generator package, GR@PPA 2.9, for simulating the direct (single) photon and diphoton (double photon) production in hadron collisions. The included programs were used in our previous studies, in which we have explicitly shown large contributions from parton-associated processes. The programs consistently combine simulations based on matrix elements with parton-shower simulations that reproduce the multiple parton radiation and quark fragmentation to photons. The matrix elements include associated parton production processes up to two partons. We provide instructions for the installation and execution of the programs in this article. The practical performance is also presented.

hep-ph↗

arXiv2017

Discovery of a big void in Khufu's Pyramid by observation of cosmic-ray muons

The Great Pyramid or Khufu's Pyramid was built on the Giza Plateau (Egypt) during the IVth dynasty by the pharaoh Khufu (Cheops), who reigned from 2509 to 2483 BC. Despite being one of the oldest and largest monuments on Earth, there is no consensus about how it was built. To better understand its internal structure, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone. The resulting cosmic-ray muon radiography allows us to visualize the known and potentially unknown voids in the pyramid in a non-invasive way. Here we report the discovery of a large void (with a cross section similar to the Grand Gallery and a length of 30 m minimum) above the Grand Gallery, which constitutes the first major inner structure found in the Great Pyramid since the 19th century. This void, named ScanPyramids Big Void, was first observed with nuclear emulsion films installed in the Queen's chamber (University of Nagoya), then confirmed with scintillator hodoscopes set up in the same chamber (KEK) and re-confirmed with gas detectors outside of the pyramid (CEA). This large void has therefore been detected with a high confidence by three different muon detection technologies and three independent analyses. These results constitute a breakthrough for the understanding of Khufu's Pyramid and its internal structure. While there is currently no information about the role of this void, these findings show how modern particle physics can shed new light on the world's archaeological heritage.

physics.ins-det↗

arXiv2016

Consistent simulation of non-resonant diphoton production in hadron collisions including associated jet production up to two jets

An event generator for diphoton ($γγ$) production in hadron collisions that includes associated jet production up to two jets has been developed using a subtraction method based on the LLL subtraction. The parton shower (PS) simulation to restore the subtracted divergent components involves both QED and QCD radiation, and QED radiation at very small $Q^{2}$ are simulated by referring to a fragmentation function (FF). The PS/FF simulation has the ability to enforce the radiation of a given number of energetic photons. The generated events can be fed to PYTHIA to obtain particle (hadron)-level event information, which enables us to perform realistic simulations of photon isolation and hadron-jet reconstruction. The simulated events, in which the loop-mediated $gg \rightarrow γγ$ process is involved, reasonably reproduce the diphoton kinematics measured at the LHC. Using the developed simulation, we found that the 2-jet processes significantly contribute to diphoton production. A large 2-jet contribution can be considered as a common feature in electroweak-boson production in hadron collisions although the reason is yet to be understood. Discussion concerning the treatment of the underlying events in photon isolation is necessary for future higher precision measurements.

hep-ph↗

arXiv2016

Consistent simulation of direct-photon production in hadron collisions including associated two-jet production

We have developed an event generator for direct-photon production in hadron collisions, including associated two-jet production in the framework of the GR@PPA event generator. The event generator consistently combines $γ$ + 2-jet production processes with the lowest-order $γ$ + jet and photon-radiation (fragmentation) processes from QCD 2-jet production using a subtraction method. The generated events can be fed to general-purpose event generators to facilitate the addition of hadronization and decay simulations. Using the obtained event information, we can simulate photon isolation and hadron-jet reconstruction at the particle (hadron) level. The simulation reasonably reproduces measurement data obtained at the LHC concerning not only the inclusive photon spectrum, but also the correlation between the photon and jet. The simulation implies that the contribution of the $γ$ + 2-jet is very large, especially in low photon-$p_{T}$ ($\lesssim$ 50 GeV) regions. Discrepancies observed at low $p_{T}$, although marginal, may indicate the necessity for the consideration of further higher-order processes. Unambiguous particle-level definition of the photon-isolation condition for the signal events is desired to be given explicitly in future measurements.

hep-ph↗

arXiv2015

ME-PS matching in the simulation of multi-jet production in hadron collisions using a subtraction method

The subtraction method for the matching between the matrix element (ME) and parton shower (PS), that has been developed for combining 0-jet and 1-jet production processes in association with electroweak-boson production in hadron collisions, is extended to multi-jet production. In order to include multi-jet MEs, we have to address the soft-gluon divergence together with the collinear divergence. We introduce an approximation which simultaneously reproduces both divergences in a form suitable for application to our subtraction method. The alteration in the subtraction can be compensated by applying an appropriate correction to corresponding non-radiative events. We demonstrate that $W$ + 0, 1, and 2 jet production processes can be consistently combined using the developed matching method.

hep-ph↗

arXiv2013

Precise simulation of the initial-state QCD activity associated with $Z$-boson production in hadron collisions

The $ϕ_η^{*}$ distribution of the $Z/γ^{*} \rightarrow \ell^{+}\ell^{-}$ production in hadron collisions is simulated using a leading-order event generator, GR@PPA. The initial-state parton shower, which simulates the multiple QCD-radiation effects in the initial state, plays the dominant role in this simulation. The simulation in the default setting agrees with the high-statistics measurement by ATLAS at LHC with the precision at the level of 5%. The observed systematic deviation, which can be attributed to the effects of ignored higher-order contributions, can be reduced by adjusting the arbitrary energy scales in the simulation. The agreement at the level of 1% can be achieved over a very wide range without introducing any modification in the implemented naive leading-logarithmic parton shower.

hep-ph↗

arXiv2012

Simulation of $Z$-boson $p_{T}$ spectrum at LHC and Tevatron using GR@PPA

Predictions from the GR@PPA event generator concerning the transverse-momentum ($p_{T}$) spectrum of $Z$ bosons are compared with recent measurements at LHC and Tevatron. The simulation results are in reasonable agreement with the measurements, although marginal discrepancies are observed in high-$p_{T}$ regions. The principal agreements imply that the leading-order simulation with a primitive parton shower based on the leading-logarithmic approximation still provides a reasonable description of the transverse motion of the hard-interaction system in hadron collisions, without the need to introduce noble techniques to incorporate higher-order corrections.

hep-ph↗

arXiv2012

Consistent simulation of non-resonant diphoton production at hadron collisions with a custom-made parton shower

We have developed a Monte Carlo event generator for non-resonant diphoton ($γγ$) production at hadron collisions in the framework of GR@PPA, which consistently includes additional one-jet production. The jet-matching method developed for initial-state jet production has been extended to the final state in order to regularize the final-state QED divergence in the $qg \rightarrow γγ+ q$ process. A QCD/QED-mixed parton shower (PS) has been developed to complete the matching. The PS has the capability of enforcing hard-photon radiation, and small-$Q^{2}$ photon radiations that are not covered by the PS are supplemented by using a fragmentation function. The generated events can be passed to general-purpose event generators in order to perform the simulations down to the hadron level. Thus, we can simulate the isolation requirements that must be applied in experiments at the hadron level. The simulation results are in reasonable agreement with the predictions from RESBOS and DIPHOX. The simulated hadron-level events can be further fed to detector simulations in order to investigate the detailed performance of experiments.

hep-ph↗

arXiv2012

GR@PPA 2.8.3 update

GR@PPA 2.8 is a program package including event generators for single and double weak-boson production processes at hadron collisions, in which a jet matching method is implemented for simulating the weak-boson kinematics in the entire phase space. Since the initial release in November, 2010, several improvements have been applied to the program components. This report describes the improvements and changes applied so far, up to the 2.8.3 release.

hep-ph↗

arXiv2012

GR@PPA 2.8: initial-state jet matching for weak boson production processes at hadron collisions

The initial-state jet matching method introduced in our previous studies has been applied to the event generation of single $W$ and $Z$ production processes and diboson ($W^{+}W^{-}$, $WZ$ and $ZZ$) production processes at hadron collisions in the framework of the GR@PPA event generator. The generated events reproduce the transverse momentum spectra of weak bosons continuously in the entire kinematical region. The matrix elements (ME) for hard interactions are still at the tree level. As in previous versions, the decays of weak bosons are included in the matrix elements. Therefore, spin correlations and phase-space effects in the decay of weak bosons are exact at the tree level. The program package includes custom-made parton shower programs as well as ME-based hard interaction generators in order to achieve self-consistent jet matching. The generated events can be passed to general-purpose event generators to make the simulation proceed down to the hadron level.

hep-ph↗

arXiv2011

A consistent event generation for non-resonant diphoton production at hadron collisions

We have developed a Monte Carlo event generator for non-resonant diphoton ($γγ$) production at hadron collisions in the framework of GR@PPA, which consistently includes processes having additional one jet radiation. The possible double count problem in the generation of radiative processes is avoided by using the LLL subtraction method that we have applied to the weak-boson production processes. The subtraction method has been extended to the final-state QED divergence that appears in the $qg \rightarrow γγ+ q$ process. Because a parton shower (PS) which regularizes the subtracted QED divergence is still under development, we tried to use PYTHIA for the generation of the fragmentation events to restore the subtracted components. The simulation employing the "old" PS of PYTHIA shows a reasonable matching with the GR@PPA events, and the combined event sample shows a result in reasonable agreement with ResBos. We found that the contribution from $qg \rightarrow γγ+ q$ is significant in the LHC condition. This event generator must be useful for the background studies in low-mass Higgs boson searches at LHC.

hep-ph↗

arXiv2010

GR@PPA Event Generator

The history and the present status of the GR@PPA event generator are briefly reviewed. The development of GR@PPA started in 2000 in order to provide a framework of NLO event generators for hadron collision interactions. After the first release of the package (GR@PPA\_4b) in 2002, which supported four bottom quark production processes, many multi-particle production processes have been added to the package: GR@PPA\_ALL in 2004 and GR@PPA 2.7 in 2006. Now we are going to release a new package (GR@PPA 2.8), which supports single and double weak-boson production processes with an initial-state jet matching. Though the matrix elements presently included are still at the tree level, this new release is an important step towards constructing consistent NLO event generators.

hep-ph↗

arXiv2010

Simulation of $Z$ boson $p_{T}$ spectrum at Tevatron by leading-order event generators

We show that the transverse momentum ($p_{T}$) spectrum of $Z$ boson production measured at Fermilab Tevatron can be well reproduced by leading-order event generators if $Z$ + 1 jet processes are included with a proper solution for the double-count problem and if the parton shower (PS) branch kinematics are defined appropriately. The choice of the PS evolution variable does not definitely determine the low-$p_{T}$ behavior. Our new event generator employing the limited leading-log (LLL) subtraction and a built-in leading-log PS reproduces the spectrum very well, not only in large $p_{T}$ regions but also at low $p_{T}$ down to $p_{T}$ = 0.

hep-ph↗

arXiv2006

A simple method to simulate W/Z + jet production at hadron collisions with PS-ME matching

We propose a simple method to simulate $W/Z$ + jet productions at hadron collisions. The simulation can be done by using existing tools with some modifications allowed to users. $W/Z$ + 1 jet events are generated using an ME-based event generator at the tree level. The divergence at low $p_{T}$ is suppressed by using the Sudakov form factor. PS is added with an appropriate consideration for PS-ME matching. The simulation for the $W$ + 1 jet production shows a smooth matching with the $W$ + 0 jet simulation at low $p_{T}$s. The $Z$ + 1 jet simulation in the Tevatron Run I condition well reproduces the experimental measurement on the $p_{T}$ spectrum of $Z$.

hep-ph↗