arXiv subjects

Takao Sakaguchi

Publications and source records attributed to Takao Sakaguchi.

At least 19 recordsLinked to original sources

arXiv2019

High density matter physics at J-PARC-HI

Physics prospective of the high density matter using heavy ions collisions is presented. The J-PARC-HI project which is a unique lab to tackle the high density matter physics is described. The world highest rate of heavy ion beam of 10$^{11}$ Hz is aimed at J-PARC-HI which enables us to perform measurements of hadrons, fluctuation of conserved quantities, dileptons, multi-strange hypernuclei. New event selections are also discussed to reach a highest baryon density on the ground.

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arXiv2019

Overview of latest results from PHENIX

An overview of the latest results on the hard probes from the PHENIX experiment at RHIC is given. The results on the measurements of high $p_{T}$ hadrons, hadron-hadron correlations, open heavy flavor and quarkonia, and direct photons from large (Au+Au) to small collision systems ($p$+Al and $p/d/^3$He+Au) provided a deeper insight on the medium created in the large systems and the possible onset of QGP-nization in transition from small to large systems.

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arXiv2017

Systematic study of high $p_{\rm T}$ hadron production in small collision systems by the PHENIX experiment at RHIC

High $p_{\rm T}$ hadrons in the small systems of $d/^3$He+Au and $p$+Al/Au collisions have been measured at the midrapidity ($|η|<0.35$) as well as at the forward and backward rapidities ($1.2<|η|<2.4$) at $\sqrt{s_{NN}}$=200GeV. A clear system and centrality ordering in the $R_{p/d/{\rm HeA}}$ was observed for midrapidity $π^0$ production. Hadron $R_{\rm cp}$ as a function of rapidity in forward and backward regions show an opposite trend to what HIJING++ predicted. Together with the difference of $R_{\rm cp}$ in $p$+Al/Au collisions, the observation can be understood consistently with the measured long-range two-particle correlations, hinting the possible medium creation similar to A+A collisions.

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arXiv2016

Leading Hadron Production in $d$+Au and $^3$He+Au collisions in the PHENIX experiment

Neutral pions have been measured in $^3$He+Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV up to 20 GeV/$c$ in the RHIC Year-2014 run. The nuclear modification factor $R_{\rm AA}$ was measured and compared with that from $d$+Au collisions. The integrated $R_{\rm AA}$ as a function of $N_{\rm part}$ was calculated for $d$+Au, $^3$He+Au and Au+Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV, and found to converge for $N_{\rm part}>$12, while a clear system ordering $R_{\rm dAu}$$>$$R_{\rm HeAu}$$>$$R_{\rm AuAu}$ was observed for $N_{\rm part}<$12. The fractional momentum loss for the most central $^3$He+Au collisions was also estimated.

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arXiv2016

PHENIX results on centrality dependence of yields and correlations in $d$+Au collisions at $\sqrt{s_{_{NN}}}$=200\,GeV

PHENIX has measured the transverse momentum ($p_{\rm T}$) spectra and two particle angular correlations for high $p_{\rm T}$ particles in $d$+Au collisions at $\sqrt{s_{_{NN}}}$=200\,GeV using the RHIC Year-2008 run data. The azimuthal angle correlations for two particles with a large rapidity gap exhibit a ridge like structure. Using the $π^0$ reconstructed in the EMCal, we have successfully extended the $p_{\rm T}$ reach of the correlation up to 8\,GeV/$c$. We find that the azimuthal anisotropy of hadrons found at low $p_{\rm T}$ persists up to 6\,GeV/$c$ with a significant centrality and $p_{\rm T}$ dependence, similar to what was observed in A+A collisions.

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arXiv2015

Detailed study of parton energy loss via measurement of fractional momentum loss of high $p_T$ hadrons in heavy ion collisions

PHENIX measurement of the fractional momentum loss ($d p_T/p_T$) of high $p_T$ identified hadrons are presented. The $d p_T/p_T$ of high $p_T$ pizero which are computed from 39GeV Au+Au over to 2.76TeV Pb+Pb are found to vary by a factor of six. We plotted the $d p_T/p_T$ against several global variables, $N_{part}$, $N_{qp}$ and $dN/deta$, and found global features. It was found that 200GeV Au+Au points are merging into the central 2.76TeV Pb+Pb points when plotting $d p_T/p_T$ against $dN/deta$.

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arXiv2014

Photon and dilepton production in high energy heavy ion collisions

The recent results on direct photons and dileptons in high energy heavy ion collisions, obtained particularly at RHIC and LHC are reviewed. The results are new not only in terms of the probes, but also in terms of the precision. We will discuss the physics learned from the results.

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arXiv2014

Detail study of the medium created in Au+Au collisions with high $p_T$ probes by the PHENIX experiment at RHIC

Recent results on high $p_T$ identified hadrons in Au+Au collisions from the PHENIX experiment are presented. The $R_{\rm AA}$ for $π^0$ and $η$ are found to be very consistent. The second and fourth order collective flow of $π^0$s have been measured and found that $v_4/v_2^2$ is consistent with the one observed in lower $p_T$ region. Assuming the suppression of the $π^0$ yield at highest $p_T$ arises from energy loss of partons, we found that the energy loss is $L^3$ dependent, where $L$ is the path length of the partons in the medium. The $δp_T/p_T$'s of high $p_T$ hadrons are computed from 39GeV Au+Au over to 2.76TeV Pb+Pb, and found that they vary by a factor of six. We have seen a smooth trend in $δp_T/p_T$ from RHIC energy to LHC energy when plotting against charged multiplicity of the systems.

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arXiv2013

Profiling hot and dense nuclear medium with high transverse momentum hadrons produced in d+Au and Au+Au collisions by the PHENIX experiment at RHIC

PHENIX measurements of high transverse momentum ($p_T$) identified hadrons in $d$+Au and Au+Au collisions are presented. The nuclear modification factors ($R_{d{\rm A}}$ and $R_{\rm AA}$) for $π^0$ and $η$ are found to be very consistent in both collision systems, respectively. Using large amount of $p+p$ and Au+Au datasets, the fractional momentum loss ($S_{\rm loss}$) and the path-length dependent yield of $π^0$ in Au+Au collisions are obtained. The hadron spectra in the most central $d$+Au and the most peripheral Au+Au collisions are studied. The spectra shapes are found to be similar in both systems, but the yield is suppressed in the most peripheral Au+Au collisions.

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arXiv2013

Cold nuclear matter effect measured with high pT hadrons and jets in 200GeV d+Au collisions in PHENIX

High pT π^0 and η, as well as jets are measured using high statistics d+Au collision data collected in RHIC Year-2008 run. Both R_{dA} and R_{cp} for three observables are found to be very consistent each other within quoted systematic and statistical uncertainties. It was found that the R_{dA} is strongly centrality dependent as opposed to the expectations from theoretical models. An explanation of the centrality dependence from the experimental point of view is presented.

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arXiv2012

PHENIX Highlights

PHENIX reports on electromagnetic and hadronic observables in large data sets of p+p, d+Au and Au+Au collisions at various cms energies. Initial state effects in cold nuclear matter are quantified by centrality dependent $π^0$, $η$, reconstructed jets and $ψ\prime$ measurements. Using the first run of the new EBIS ion source at RHIC, we report first results for particle flow ($v_1$ and $v_2$) and quarkonium production in U+U and Cu+Au collisions. Hot matter created in Au+Au is characterized using event-plane dependent HBT and dielectrons. Parton-medium interactions are investigated using high $p_T$ single hadrons, $γ$-hadron correlations and heavy flavor decay electrons identified with the newly installed VTX detector.

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arXiv2011

Electromagnetic emission from hot medium measured by the PHENIX experiment at RHIC

Electromagnetic radiation has been of interest in heavy ion collisions because they shed light on early stages of the collisions where hadronic probes do not provide direct information since hadronization and hadronic interactions occur later. The latest results on photon measurement from the PHENIX experiment at RHIC reflect thermodynamic properties of the matter produced in the heavy ion collisions. An unexpectedly large positive elliptic flow measured for direct photons can not be explained by any of the current models.

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arXiv2011

PHENIX photons and dileptons

Electro-magnetic probes such as dileptons and photons are strong probes to investigate the thermodynamical state of the early stages of collisions since they leave the system unscathed. The PHENIX experiment has measured both photons and dileptons in p+p, d+Au and Au+Au collisions. An excess of dilepton yield over the expected hadronic contribution is seen in 0.2-0.8\,GeV/$c^2$ in Au+Au collisions, which is prominent in lower $p_T$ and most central. Direct photons are measured through their internal conversion to electron pairs. We saw a large enhancement in Au+Au collisions over p+p yield scaled by the number of binary collisions. It turned out from the latest results on d+Au collisions that this enhancement is not explainable by a nuclear effect.

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arXiv2009

PHENIX plans for RHIC low energy run

PHENIX plans for low energy running are presented. Current detector setting makes it possible to measure dielectron spectra down to sqrt(s_NN)=39GeV, and photon/high pT hadron spectra down to below sub-injection energy (sqrt(s_NN)=5-10GeV). The upgrade of the trigger scheme after the installation of VTX detector will enable PHENIX to fully explore the sub-injection energy regime, starting 2011.

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arXiv2008

Direct photons ~basis for characterizing heavy ion collisions~

After years of experimental and theoretical efforts, direct photons become a strong and reliable tool to establish the basic characteristics of a hot and dense matter produced in heavy ion collisions. The recent direct photon measurements are reviewed and a future prospect is given.

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arXiv2007

Measurement of electro-magnetic radiation at RHIC-PHENIX

Recent results on direct photons and dileptons from the PHENIX experiment opened up a possibility of landscaping electro-magnetic radiation over various kinetic energies in heavy ion collisions. Results on direct photon measurement in Au+Au collisions at $\sqrt{s_{NN}}$=200GeV are discussed from the point of view of structure function and isospin effect. It is supported by the first measurement of direct photons at $\sqrt{s_{NN}}$=62.4GeV in the same collisional system.

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arXiv2007

Measurement of electro-magnetic radiation at PHENIX

Recent results on direct photons and dileptons from the PHENIX xperiment opened up a possibility of landscaping electro-magnetic radiation over various kinetic energies in heavy ion collisions. A detail discussion is given based on a review of the results.

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arXiv2007

System size and energy dependence of high pT hadron production measured with PHENIX experiment at RHIC

PHENIX has measured high transverse momentum (pT) identified hadrons in different collision species and energies in the last five RHIC runs. The systematic study of the high pT hadron production provides an idea on interaction of hard scattered partons and the matter created in relativistic heavy ion collision. The eta/pi0 ratio is measured in Au+Au collisions, which gives a hint on the system thermalization and particle production. A future measurement of hadron and photon measurement is discussed.

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