arXiv subjects

M. J. Tannenbaum

Publications and source records attributed to M. J. Tannenbaum.

At least 19 recordsLinked to original sources

arXiv2018

Improved Comparison of Measurements and Calculations of $\hat{q}L$ via transverse momentum broadening in Relativistic Heavy Ion Collisions using di-hadron correlations

The renewed interest in analyzing RHIC data on di-hadron correlations as probes of final state transverse momentum broadening as shown at Quark Matter 2018[1] by theoretical calculations[6] compared to experimental measurements[4,5] led me to review the quoted theoretical calculations and experimental measurements because the theoretical calculation[6] does not show the PHENIX measurements[4] as published. The above references were checked and fits were performed to the published measurements[4,7] to determine $\hat{q}L$ from the measured azimuthal broadening to compare with the theoretical calculation[6]. The new results will be presented in addition to some corrections to the previous work[3]. The measured values of $\hat{q}L$ show the interesting effect of being consistent with zero for larger values of associated $p_{Ta}\geq3$ GeV/c which is shown to be related to well known measurements of the ratio of the Au+Au to p+p associated $p_{Ta}$ distributions for a given trigger $p_{Tt}$ called $I_{AA}$[23,25]. Di-jets rather than di-hadrons are proposed as an improved azimuthal broadening measurement to determine $\hat{q}L$ and possibly $\hat{q}$.

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arXiv2018

Highlights from BNL and RHIC 2017

Highlights of news from Brookhaven National Laboratory (BNL) and results from the Relativistic Heavy Ion Collider (RHIC) in the period July 2016-2017 are presented. 2017 was the 70th birthday of Brookhaven National Laboratory which was built starting in 1947 on Camp Upton, a military base in 1917 for World War I and in September 1944 for World War II. Highlights in 70 years of research at BNL are presented, which include 6 Nobel Prizes as well as other important discoveries and inventions. RHIC is the world's only polarized proton collider and a review of the establishment of the Riken BNL Research Center with research focus on spiin physics at RHIC is presented. Discoveries at RHIC in Jet Quenching and the Quark Gluon Plasma are reviewed as well as new ideas on flow in small systems including a measurement of the vorticity of the QGP via polarization of $Λ$ hyperons. An attempt at measuring the transport coefficient $\hat{q}$ of the Quark Gluon Plasma from azimuthal broadening of high $p_T$ di-hadron pairs is presented.

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arXiv2018

How hadron collider experiments contributed to the development of QCD: from hard-scattering to the perfect liquid

A revolution in elementary particle physics occurred during the period from the ICHEP1968 to the ICHEP1982 with the advent of the parton model from discoveries in Deeply Inelastic electron-proton Scattering at SLAC, neutrino experiments, hard-scattering observed in p$+$p collisions at the CERN ISR, the development of QCD, the discovery of the J/$Ψ$ at BNL and SLAC and the clear observation of high transverse momentum jets at the CERN SPS $\bar{p}+p$ collider. These and other discoveries in this period led to the acceptance of QCD as the theory of the strong interactions. The desire to understand nuclear physics at high density such as in neutron stars led to the application of QCD to this problem and to the prediction of a Quark-Gluon Plasma (QGP) in nuclei at high energy density and temperatures. This eventually led to the construction of the Relativistic Heavy Ion Collider (RHIC) at BNL to observe superdense nuclear matter in the laboratory. This article discusses how experimental methods and results which confirmed QCD at the first hadron collider, the CERN ISR, played an important role in experiments at the first heavy ion collider, RHIC, leading to the discovery of the QGP as a perfect liquid as well as discoveries at RHIC and the LHC which continue to the present day.

hep-ex↗

arXiv2018

Measurement of $\hat{q}$ in RHI collisions using di-hadron correlations

In the BDMPSZ model, the energy loss of an outgoing parton in a medium $-dE/dx$ is the transport coefficient $\hat{q}$ times $L$ the length traveled. This results in jet quenching, which is well established. However BDMPSZ also predicts an azimuthal broadening of di-jets also proportional to $\hat{q}L$ which has so far not been observed. The broadening should produce a larger $k_T$ in A$+$A than in p$+$p collisions. This presentation introduces the observation that the $k_T$ measured in p$+$p collisions for di-hadrons with $p_{Tt}$ and $p_{Ta}$ must be reduced to compensate for the energy loss of both the trigger and away parent partons when comparing to the $k_T$ measured with the same di-hadron $p_{Tt}$ and $p_{Ta}$ in A$+$A collisions. This idea is applied to a recent STAR di-hadron measurement in Au$+$Au at $\sqrt{s_{NN}}$=200 GeV, [Phys. Lett. B760 (2016) 689], with result $<{\hat{q}L}>=2.1\pm 0.6$ GeV$^2$. This is more precise but in agreement with a theoretical calculation of $<{\hat{q}L}>=14^{+42}_{-14}$ GeV$^2$ using the same data. Assuming a length $<{L}>\approx 7$ fm for central Au$+$Au collisions the present result gives $\hat{q}\approx 0.30\pm 0.09$ GeV$^2$/fm, in fair agreement with the JET collaboration result from single hadron suppression of $\hat{q}\approx 1.2\pm 0.3$ GeV$^2$/fm at an initial time $τ_0=0.6$ fm/c in Au$+$Au collisions at $\sqrt{s_{NN}}=200$ GeV. There are several interesting details to be discussed: for a given $p_{Tt}$ the $<{\hat{q}L}>$ seems to decrease then vanish with increasing $p_{Ta}$; the di-jet spends a much longer time in the medium ($\approx 7$ fm/c) then $τ_0=0.6$ fm/c which likely affects the value of $\hat{q}$ that would be observed.

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arXiv2018

Constituent quarks and systematic errors in mid-rapidity charged multiplicity $dN_{\rm ch}/dη$ distributions

Centrality definition in A$+$A collisions at colliders such as RHIC and LHC suffers from a correlated systematic uncertainty caused by the efficiency of detecting a p$+$p collision ($50\pm 5\%$ for PHENIX at RHIC). In A$+$A collisions where centrality is measured by the number of nucleon collisions, $N_{\rm coll}$, or the number of nucleon participants, $N_{\rm part}$, or the number of constituent quark participants, $N_{\rm qp}$, the error in the efficiency of the primary interaction trigger (Beam-Beam Counters) for a p$+$p collision leads to a correlated systematic uncertainty in $N_{\rm part}$, $N_{\rm coll}$ or $N_{\rm qp}$ which reduces binomially as the A$+$A collisions become more central. If this is not correctly accounted for in projections of A$+$A to p$+$p collisions, then mistaken conclusions can result. A recent example is presented in whether the mid-rapidity charged multiplicity per constituent quark participant $({dN_{\rm ch}/dη})/{N_{\rm qp}}$ in Au$+$Au at RHIC was the same as the value in p$+$p collisions.

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arXiv2017

Measurement of $\hat{q}$ in Relativistic Heavy Ion Collisions using di-hadron correlations

The azimuthal width of the di-hadron correlations in p$+$p collisons, beyond the fragmentation transverse momentum, $j_T$, is dominated by $k_T$, the so-called intrinsic transverse momentum of a parton in a nucleon, which can be measured. The predicted azimuthal broadening in A$+$A collisions should produce a larger $k_T$ than in p$+$p collisions. The present work introduces the observation that the $k_T$ measured in p$+$p collisions for di-hadrons with $p_{Tt}$ and $p_{Ta}$ must be reduced to compensate for the energy loss of both the trigger and away parent partons when comparing to the $k_T$ measured with the same di-hadron $p_{Tt}$ and $p_{Ta}$ in Au$+$Au collisions. This idea is applied to a recent STAR di-hadron measurement, with result $\langle{\hat{q}L}\rangle=2.1\pm 0.6$ GeV$^2$. This is more precise but in agreement with a theoretical calulation of $\langle{\hat{q}L}\rangle=14^{+42}_{-14}$ GeV$^2$ using the same data. Assuming a length $\langle{L}\rangle\approx 7$ fm for central Au$+$Au collisions the present result gives $\hat{q}=0.30\pm 0.09$ GeV$^2$/fm, in fair agreement with the JET collaboration result of $\hat{q}\approx 1.2\pm 0.3$ GeV$^2$/fm at initial time $τ_0=0.6$ fm/c in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

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arXiv2017

Highlights from BNL and RHIC 2016

Highlights of news from Brookhaven National Laboratory (BNL) and results from the Relativistic Heavy Ion Collider (RHIC) in the period July 2015-2016 are presented. Transverse single spin asymmetries from polarized p+p collisions are presented for $π^0$ and jets as a function of Feynman $x_F$. An energy scan to study the $\sqrt{s}$ dependence of collectivity and flow for small systems was performed as well as a high luminosity Au$+$Au run. The failure of a quench protection diode resulted in a pause in the run to replace it, but otherwise performance of RHIC was the best ever. Experimental results discussed are an elegant measurement from STAR of the force between anti-protons using HBT correlations, flow in U+U collisions, an improved method of generating constituent quarks by PHENIX and new Number of Quark Participants (NQP) scaling of $E_T$ distributions in p$+$p,d$+$Au and Au$+$Au which worked well. New hard-scattering results as a function of $\sqrt{s}$ in Au$+$Au central collisions are presented. Also, measurements of the di-hadron acoplanarity for $π^0 +h$ and $γ+h$ in p+p collisions at $\sqrt{s}=500$ GeV are presented in terms of the out-of-plane transverse momentum $p_{\rm out}$ which differ from the prediction of the TMD framework of parton transverse momentum dynamics.

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arXiv2016

Waiting for the W and the Higgs

The search for the left-handed $W^{\pm}$ bosons, the proposed quanta of the weak interaction, and the Higgs boson, which spontaneously breaks the symmetry of unification of electromagnetic and weak interactions, has driven elementary-particle physics research from the time that I entered college to the present and has led to many unexpected and exciting discoveries which revolutionized our view of subnuclear physics over that period. In this article I describe how these searches and discoveries have intertwined with my own career.

physics.hist-ph↗

arXiv2016

Tests of constituent-quark generation methods which maintain both the nucleon center of mass and the desired radial distribution in Monte Carlo Glauber models

Several methods of generating three constituent-quarks in a nucleon are evaluated which explicitly maintain the nucleon's center of mass and desired radial distribution and can be used within Monte Carlo Glauber frameworks. The geometric models provided by each method are used to generate distributions over the number of constituent-quark participants ($N_{qp}$) in $p+p$, $d+$Au and Au$+$Au collisions. The results are compared with each other and to a previous result of $N_{qp}$ calculations, without this explicit constraint, used in measurements of $\sqrt{s_{_{NN}}}$=200 GeV $p+p$, $d+$Au and Au$+$Au collisions at RHIC.

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arXiv2016

Highlights from BNL and RHIC 2015

Highlights of news from Brookhaven National Laboratory (BNL) and results from the Relativistic Heavy Ion Collider (RHIC) in the period July 2014-June 2015 are presented. The news this year was mostly very positive. The major event at BNL was the startup and dedication of the new NSLS II, "the World's brightest Synchrotron Light Source". The operation of RHIC was outstanding with a polarized p+p run at $\sqrt{s}=200$ GeV with integrated luminosity that exceeded the sum of all previous p+p integrated luminosity at this $\sqrt{s}$. For the first time at RHIC asymmetric p+Au and p+Al runs were made but the p+Al run caused damage in the PHENIX forward detectors from quenches that were inadequately shielded for this first p+A run. This was also the 10th anniversary of the 2005 announcement of the Perfect Liquid Quark Gluon Plasma at RHIC and a review is presented of the discoveries leading to this claim. A new result on net-charge fluctuations (with no particle identification) from PHENIX based on previous scans over beam energy to look for a QCD critical point is discussed which combined with Lattice QCD calculations and smaller errors on the higher cumulants than previous measurements led to calculations of the baryon chemical potential and freezeout temperature in agreement with the best accepted analysis from baryon/anti-baryon ratio measurements.

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arXiv2015

Is $\hat{q}$ a physical quantity or just a parameter? and other unanswered questions in High-$p_T$ Physics

The many different theoretical studies of energy loss of a quark or gluon traversing a medium have one thing in common: the transport coefficient of a gluon in the medium, $\hat{q}$, which is defined as the mean 4-momentum transfer$^2$, $\left $, by a gluon to the medium per gluon mean free path, $λ_{\rm mfp}$. In the original BDMPSZ formalism, the energy loss of an outgoing parton, $-dE/dx$, per unit length ($x$) of a medium with total length $L$, due to coherent gluon bremsstrahlung, is proportional to the $\left< q^2\right>$ and takes the form: ${-dE/dx }\simeq α_s \left<{q^2(L)}\right>=α_s\, μ^2\, L/λ_{\rm mfp} =α_s\, \hat{q}\, L\ $ , where $μ$, is the mean momentum transfer per collision. Thus, the total energy loss in the medium goes like $L^2$. Additionally, the accumulated momentum$^2$, $\left<{k_{\perp}^2}\right>$, transverse to a gluon traversing a length $L$ in the medium is well approximated by $\left<{k_{\perp}^2}\right>\approx\left<{q^2(L)}\right>=\hat{q}\, L$. A simple estimate shows that the $\left<{k_{\perp}^2}\right>\approx\hat{q}\,L$ should be observable at RHIC at $\sqrt{s_{NN}}=200$ GeV via the broadening of di-hadron azimuthal correlations resulting in an azimuthal width $\sim\sqrt{2}$ larger in Au$+$Au than in $p+p$ collisions . Measurements relevant to this issue will be discussed as well as recent STAR jet results presented at QM2014. Other topics to be discussed include the danger of using forward energy to define centrality in $p(d)+$A collisions for high $p_T$ measurements, the danger of not using comparison $p+p$ data at the same $\sqrt{s}$ in the same detector for $R_{AA}$ or lately for $R_{pA}$ measurements.

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arXiv2015

Highlights from BNL and RHIC 2014

Highlights of news from Brookhaven National Laboratory (BNL) and results from the Relativistic Heavy Ion Collider (RHIC) in the period July 2013-June 2014 are presented. It was a busy year for news, most notably a U. S. Government shutdown for 16 days beginning October 1, 2013 due to the lack of an approved budget for FY2014. Even with this unusual government activity, the $\sqrt{s_{NN}}=200$ GeV Au+Au Run14 at RHIC was the best ever with integrated luminosity exceeding the sum of all previous runs. Additionally there was a brief He$^3$+Au run to continue the study of collective flow in small systems which was reinforced by new results presented on identified particle flow in d+Au. The other scientific highlights are also mostly concerned with ``soft (low $p_T$)'' physics complemented by the first preliminary results of reconstructed jets from hard-scattered partons in Au+Au collisions at RHIC . The measurements of transverse energy ($E_T$) spectra in p-p, d+Au and Au+Au collisions, which demonstrated last year that constituent quarks are the fundamental elements of particle production in all 3 systems, led to the conclusion that the two-component ansatz which has been used to represent $E_T$ distributions as a function of centrality is simply a proxy for the number of constituent quark participants as well as to an explanation of the surprising elliptical flow results from U+U collisions. An extensive discussion of the latest measurements in Au+Au of net-charge and net-proton distributions represented by Cumulants of the distributions and plans for a Beam Energy Scan at RHIC to look for a QCD critical point is presented and compared to the claim implied by a press release during the 2011 ISSP.

nucl-ex↗

arXiv2014

Transverse Energy ($E_T$) distributions at mid-rapidity in $p$$+$$p$, $d$$+$Au and Au$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV and implications for particle production models

Measurements of the midrapidity transverse energy distribution $d{\rm E}_T/dη$ are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au Collisions at $\sqrt{s_{_{NN}}}$=62.4--200 GeV. The ${\rm E}_T$ distributions are compared with the number of participants, $N_{\rm part}$, the number of constituent-quark participants, $N_{qp}$, and the number of color-strings (Additive Quark Model-AQM) calculated from a Glauber model. For Au$+$Au, $\langle d{\rm E}_T/dη/(0.5 N_{\rm part})\rangle$ increases with $N_{\rm part}$, while $\langle d{\rm E}_T/dη/N_{qp}\rangle$ is approximately constant vs. centrality for $\sqrt{s_{_{NN}}} \geq 62.4$ GeV. This indicates that the two component ansatz, $d{\rm E}_T^{\rm AA}/dη=(d{\rm E}_T^{\rm pp}/dη)\ [(1-x)\, N_{\rm part}/2 + x\, N_{\rm coll}]$, which has been used to represent ${\rm E}_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in ${\rm E}_T$ distributions. The $d{\rm E}_T/dη$ distributions of $d$$+$Au, and Au$+$Au are calculated from the measured $p$$+$$p$ ${\rm E}_T$ distribution using two models (AQM and $N_{qp}$) that both reproduce the Au$+$Au data. For the asymmetric $d$$+$Au system, the $N_{qp}$ model reproduces the data while the AQM does not.

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arXiv2014

Highlights from BNL-RHIC 2011-2013

Highlights from Brookhaven National Laboratory (BNL) and experiments at the BNL Relativistic Heavy Ion Collider (RHIC) are presented for the years 2011--2013. This review is a combination of lectures which discussed the latest results each year at a three year celebration of the 50th anniversary of the International School of Subnuclear Physics in Erice, Sicily, Italy. Since the first collisions in the year 2000, RHIC has provided nucleus-nucleus and polarized proton-proton collisions over a range of nucleon-nucleon c.m. energies from 7.7 to 510 GeV with nuclei from deuterium to uranium, most often gold. The objective was the discovery of the Quark Gluon Plasma, which was achieved, and the measurement of its properties, which were much different than expected, namely a `perfect fluid' of quarks and gluons with their color charges exposed rather than a gas. Topics including quenching of light and heavy quarks at large transverse momentum, thermal photons, search for a QCD critical point as well as measurements of collective flow, two-particle correlations and $J/Ψ$ suppression are presented. During this period, results from the first and subsequent heavy ion measurements at the Large Hadron Collider (LHC) at CERN became available. These confirmed and extended the RHIC discoveries and have led to ideas for new and improved measurements.

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arXiv2014

How do quarks and gluons lose energy in the QGP?

At RHIC, a suppression, $R_{AA}\approx 0.2$ relative to binary-scaling, for $π^0$ with $5\leq p_T\leq 20$ GeV/c was discovered in central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV, and surprisingly also for single-electrons from the decay of heavy quarks. Both these results have been confirmed in Pb+Pb collisions at the LHC at $\sqrt{s_{NN}}=2.76$ TeV. In this $p_T$ range, the LHC results for pions nearly overlap the RHIC results but the flatter spectrum at LHC implies that the energy loss in the medium must be $\sim 40$% larger than at RHIC. At LHC, the unique and beautiful measurement of the fractional transverse momentum imbalance $1-\langle{\hat{p}_{T_2}/\hat{p}_{T_1}}\rangle$ of di-jets in Pb+Pb collisions relative to p-p collisions, shows $\approx 15\%$ for jets with $120\leq\hat{p}_{T_1}\leq 360$ GeV/c. This is a much smaller fractional jet imbalance than the $\approx 45\%$ derived from two-particle correlations of di-jet fragments at RHIC corresponding to jet $\hat{p}_T\approx 10-20$ GeV/c. This presents a challenge to both theory and experiment for improved understanding. There are many other such unresolved issues, for instance, the absence of evidence for a $\hat{q}$ effect by observation of momentum transferred to the medium by outgoing partons. An implied hard scattering component for the soft physics multiplicity distributions in A+A collisions based on a popular formula, ${dN_{\rm ch}^{AA}/dη}= [(1-x) \langle{N_{\rm part}}\rangle {dN_{\rm ch}^{pp}/dη}/2 + x\, \langle{N_{\rm coll}}\rangle {dN_{\rm ch}^{pp}/dη}]$, seems to be an unphysical way to understand the deviation from $N_{\rm part}$ scaling. Based on recent p-p and d+A measurements, a more physical way is presented along with several other stimulating results and ideas from recent d+Au (p+Pb) measurements.

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arXiv2014

Latest Results from BNL and RHIC--2013

A selection of results from the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) from 2012 to 2013 is presented together with a few newsworthy developments in this period. The move of the g-2 magnet from BNL to Fermilab for the "fifth muon g-2 experiment" inspired a brief discussion of the original g-2 experiments at CERN. Highlights of the past year include a change in the measurement of the suppression of large transverse momentum ($p_T$) particles in the Quark Gluon Plasma to a measure of the fractional shift in the observed $p_T$ spectrum from the expected A+A spectrum for independent collisions as an estimate of the energy loss in the medium. The p+Pb run at LHC in early 2013 spurred new or improved measurements in d+Au at RHIC which included the observation of elliptical flow in d+Au collisions and measurements of transverse energy ($E_T$) spectra in p-p, d+Au and Au+Au collisions at 200 GeV nucleon-nucleon c.m. energy which demonstrated that constituent quarks are the fundamental element of particle production in all 3 systems. Measurements of identified hadrons in d+Au show a huge Cronin effect for protons but no effect for mesons. An important step for the future was the acquisition by BNL of the superconducting solenoid used in the BABAR experiment at SLAC for use in future experiments at RHIC and possibly eRHIC, starting with an upgrade of the PHENIX experiment called sPHENIX.

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arXiv2013

Highlights from BNL-RHIC-2012

Recent highlights from Brookhaven National Laboratory and the Relativistic Heavy Ion Collider (RHIC) are reviewed and discussed in the context of the discovery of the strongly interacting Quark Gluon Plasma (sQGP) at RHIC in 2005 as confirmed by results from the CERN-LHC Pb+Pb program. Outstanding RHIC machine operation in 2012 with 3-dimensional stochastic cooling and a new EBIS ion source enabled measurements with Cu+Au, U+U, for which multiplicity distributions are shown, as well as with polarized p-p collisions. Differences of the physics and goals of p-p versus A+A are discussed leading to a review of RHIC results on pi0 suppression in Au+Au collisions and comparison to LHC Pb+Pb results in the same range 5 30 GeV. Improved measurements of direct photon production and correlation with charged particles at RHIC are shown, including the absence of a low pT (thermal) photon enhancement in d+Au collisions. Attempts to understand the apparent equality of the energy loss of light and heavy quarks in the QGP by means of direct measurements of charm and beauty particles at both RHIC and LHC are discussed.

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arXiv2012

Highlights from BNL-RHIC

Recent highlights from Brookhaven National Laboratory and the Relativistic Heavy Ion Collider (RHIC) are reviewed and discussed. Topics include: Discovery of the strongly interacting Quark Gluon Plasma (sQGP) in 2005; RHIC machine operation in 2011 as well as latest achievements from the superconducting Magnet Division and the National Synchrotron Light Source II project. Highlights from QGP physics at RHIC include: comparison of new measurements of charged multiplicity in A+A collisions by ALICE at the LHC to previous RHIC measurements; Observation of the anti-alpha particle by the STAR experiment; Collective Flow, including the Triangular Flow discovery and the latest results on v3; the RHIC beam energy scan in search of the QCD critical point. The pioneering use at RHIC of hard-scattering as a probe of the sQGP will also be reviewed and the latest results presented including: jet-quenching via suppression of high pT particles and two particle correlations; new results on fragmentation functions using gamma-hadron correlations in p-p and Au+Au collisions; comparison of jet imbalance in A+A relative to p-p collisions measured by PHENIX using pizero-hadron correlations to CMS measurements with reconstructed jets; first measurement by PHENIX of anisotropic flow of direct photons in the thermal range 1< pT < 3 GeV/c, with v2 as large as that of pions; a review of the equality of the suppression of inclusive pi0 (from light quarks and gluons) and direct-single electrons (from the decay of heavy quarks) in the transverse momentum range 4< pT < 9 GeV/c, at RHIC (now also seen with reconstructed charm mesons by ALICE at the LHC) which disfavors a radiative explanation of suppression and leads to a fundamental question of whether the Higgs boson gives mass to fermions.

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