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arXiv2018

The Soreq Applied Research Accelerator Facility (SARAF) - Overview, Research Programs and Future Plans

The Soreq Applied Research Accelerator Facility (SARAF) is under construction in the Soreq Nuclear Research Center at Yavne, Israel. When completed at the beginning of the next decade, SARAF will be a user facility for basic and applied nuclear physics, based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. Phase I of SARAF (SARAF-I, 4 MeV, 2 mA CW protons, 5 MeV 1 mA CW deuterons) is already in operation, generating scientific results in several fields of interest. The main ongoing program at SARAF-I is the production of 30 keV neutrons and measurement of Maxwellian Averaged Cross Sections (MACS), important for the astrophysical s-process. The world leading Maxwellian epithermal neutron yield at SARAF-I ($5\times 10^{10}$ epithermal neutrons/sec), generated by a novel Liquid-Lithium Target (LiLiT), enables improved precision of known MACSs, and new measurements of low-abundance and radioactive isotopes. Research plans for SARAF-II span several disciplines: Precision studies of beyond-Standard-Model effects by trapping light exotic radioisotopes, such as $^6$He, $^8$Li and $^{18,19,23}$Ne, in unprecedented amounts (including meaningful studies already at SARAF-I); extended nuclear astrophysics research with higher energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the rapid (r-) process; nuclear structure of exotic isotopes; high energy neutron cross sections for basic nuclear physics and material science research, including neutron induced radiation damage; neutron based imaging and therapy; and novel radiopharmaceuticals development and production. In this paper we present a technical overview of SARAF-I and II, including a description of the accelerator and its irradiation targets; a survey of existing research programs at SARAF-I; and the research potential at the completed facility (SARAF-II).

physics.ins-det↗

arXiv2018

The impact of $\mathbf{K^+Λ}$ photoproduction on the resonance spectrum

The Jülich-Bonn coupled-channel framework is extended to $K^+Λ$ photoproduction. The spectrum of nucleon and $Δ$ resonances is extracted from simultaneous fits to several pion-induced reactions in addition to pion, eta and $K^+Λ$ photoproduction off the proton. More than 40,000 data points up to a center-of-mass energy of E$\sim$2.3 GeV including recently measured double-polarization observables are analyzed. The influence of the $γp\to K^+Λ$ channel on the extracted resonance parameters and the appearance of states not seen in other channels is investigated. The Jülich-Bonn model includes effective three-body channels and guarantees unitarity and analyticity, which is a prerequisite for a reliable determination of the resonance spectrum in terms of poles and residues.

nucl-th↗

arXiv2013

A method for studying initial geometry fluctuations via event plane correlations in heavy ion collisions

A method is proposed to measure the relative azimuthal angle distributions involving two or more event planes of different order in heavy ion collisions using a Fourier analysis technique. The analysis procedure is demonstrated for correlations involving two and three event planes (Phi_n, Phi_m and Phi_h). The Fourier coefficients of these distributions are found to coincide with previously proposed correlators, such as cos(6Phi_2-6Phi_3) and cos(Phi_1+2Phi_2-3Phi_3) etc, hence the method provides a natural framework for studying these correlators at the same time. Using a Monte Carlo Glauber model to simulate Au+Au collisions with fluctuating initial geometry, we are able to identify several new two- or three-plane correlators that have sizable magnitudes and should be measured experimentally.

nucl-th↗

arXiv2012

Study on initial geometry fluctuations via participant plane correlations in heavy ion collisions: part II

Further investigation of the participant plane correlations within a Glauber model framework is presented, focusing on correlations between three or four participant planes of different order. A strong correlation is observed for $\cos(2Φ_{2}^*+3Φ_{3}^*-5Φ_{5}^*)$ which is a reflection of the elliptic shape of the overlap region. The correlation between the corresponding experimental reaction plane angles can be easily measured. Strong correlations of similar geometric origin are also observed for $\cos(2Φ_{2}^*+4Φ_{4}^*-6Φ_{6}^*)$, $\cos(2Φ_2^*-3Φ_3^*-4Φ_4^*+5Φ_5^*)$, $\cos(6Φ_2^*+3Φ_3^*-4Φ_4^*-5Φ_5^*)$, $\cos(Φ_1^*-2Φ_2^*-3Φ_3^*+4Φ_4^*)$, $\cos(Φ_1^*+6Φ_2^*-3Φ_3^*-4Φ_4^*)$, and $\cos(Φ_1^*+2Φ_2^*+3Φ_3^*-6Φ_6^*)$, which are also measurable. Experimental measurements of the corresponding reaction plane correlators in heavy ion collisions at RHIC and the LHC may improve our understanding of the physics underlying the measured higher order flow harmonics.

nucl-ex↗

arXiv2013

Pulse shape discrimination for GERDA Phase I data

The GERDA experiment located at the LNGS searches for neutrinoless double beta (0νββ) decay of ^{76}Ge using germanium diodes as source and detector. In Phase I of the experiment eight semi-coaxial and five BEGe type detectors have been deployed. The latter type is used in this field of research for the first time. All detectors are made from material with enriched ^{76}Ge fraction. The experimental sensitivity can be improved by analyzing the pulse shape of the detector signals with the aim to reject background events. This paper documents the algorithms developed before the data of Phase I were unblinded. The double escape peak (DEP) and Compton edge events of 2.615 MeV γ rays from ^{208}Tl decays as well as 2νββ decays of ^{76}Ge are used as proxies for 0νββ decay. For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.92$\pm$0.02 of signal-like events while about 80% of the background events at Q_{ββ}=2039 keV are rejected. For semi-coaxial detectors three analyses are developed. The one based on an artificial neural network is used for the search of 0νββ decay. It retains 90% of DEP events and rejects about half of the events around Q_{ββ}. The 2νββ events have an efficiency of 0.85\pm0.02 and the one for 0νββ decays is estimated to be 0.90^{+0.05}_{-0.09}. A second analysis uses a likelihood approach trained on Compton edge events. The third approach uses two pulse shape parameters. The latter two methods confirm the classification of the neural network since about 90% of the data events rejected by the neural network are also removed by both of them. In general, the selection efficiency extracted from DEP events agrees well with those determined from Compton edge events or from 2νββ decays.

physics.ins-det↗

arXiv2014

Charmonium and $e^+e^-$ pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\rm NN}}$=2.76 TeV

The ALICE Collaboration at the LHC has measured the J/$ψ$ and $ψ^{'}$ photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 $μ\rm{b}^{-1}$. The cross section for coherent and incoherent J/$ψ$ production in the rapidity interval $-0.9<y<0.9$, are $\mathrm{d}σ_{{\rm J}/ψ}^{\rm coh}/\mathrm{d}y = 2.38^{+0.34}_{-0.24}\big(\mathrm{sta+sys}\big)$mb. and $\mathrm{d}σ_{{\rm J}/ψ}^{\rm inc}/\mathrm{d}y = 0.98^{+0.19}_{-0.17}\big(\mathrm{sta+sys}\big)$mb, respectively. The results are compared to theoretical models for J/$ψ$ production and the coherent cross section is found to be in good agreement with those models incorporating moderate nuclear gluon shadowing, such as EPS09 parametrization. In addition the cross section for the process $γγ\rightarrow e^+ e^-$ has been measured and found to be in agreement with models implementing QED at leading order.

nucl-ex↗

arXiv2014

Measurement of negatively charged pion spectra in inelastic p+p interactions at $p_{lab}$ = 20, 31, 40, 80 and 158 GeV/c

We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/c ($\sqrt{s} = $ 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus-nucleus and proton-nucleus collisions.

hep-ex↗

arXiv2014

Studies of dijet transverse momentum balance and pseudorapidity distributions in pPb collisions at sqrt(s[NN]) = 5.02 TeV

Dijet production has been measured in pPb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. A data sample corresponding to an integrated luminosity of 35 inverse nanobarns was collected using the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet transverse momentum balance, azimuthal angle correlations, and pseudorapidity distributions are studied as a function of the transverse energy in the forward calorimeters (ETHFfour). For pPb collisions, the dijet transverse momentum ratio and the width of the distribution of dijet azimuthal angle difference are comparable to the same quantities obtained from a simulated pp reference and insensitive to ETHFfour. In contrast, the mean value of the dijet pseudorapidity is found to change monotonically with increasing ETHFfour, indicating a correlation between the energy emitted at large pseudorapidity and the longitudinal motion of the dijet frame. The pseudorapidity distribution of the dijet system in minimum bias pPb collisions is compared with next-to-leading-order perturbative QCD predictions obtained from both nucleon and nuclear parton distribution functions, and the data more closely match the latter.

nucl-ex↗

arXiv2014

Initial performance of the CUORE-0 experiment

CUORE-0 is a cryogenic detector that uses an array of tellurium dioxide bolometers to search for neutrinoless double-beta decay of ^{130}Te. We present the first data analysis with 7.1 kg y of total TeO_2 exposure focusing on background measurements and energy resolution. The background rates in the neutrinoless double-beta decay region of interest (2.47 to 2.57 MeV) and in the α background-dominated region (2.70 to 3.90 MeV) have been measured to be 0.071 \pm 0.011 and 0.019 \pm 0.002 counts/keV/kg/y, respectively. The latter result represents a factor of 6 improvement from a predecessor experiment, Cuoricino. The results verify our understanding of the background sources in CUORE-0, which is the basis of extrapolations to the full CUORE detector. The obtained energy resolution (full width at half maximum) in the region of interest is 5.7 keV. Based on the measured background rate and energy resolution in the region of interest, CUORE-0 half-life sensitivity is expected to surpass the observed lower bound of Cuoricino with one year of live time.

physics.ins-det↗

arXiv2018

Measurement of longitudinal flow de-correlations in Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 2.76$ and 5.02 TeV with the ATLAS detector

Measurements of longitudinal flow decorrelations are presented for charged particles in the pseudorapidity range $|η|<2.4$ using 7 $μ$b$^{-1}$ and 470 $μ$b$^{-1}$ of Pb+Pb collisions at $\sqrt{s_{\textrm{NN}}}=2.76$ and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients $v_n$ measured in two separated $η$ intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the $η$ separation between the intervals. The slopes for this flow decorrelation are found to be larger at 2.76 TeV than 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the $k^{\textrm{th}}$-moment of the $v_n$ are found to be proportional to $k$ for $v_3$, but not for $v_2$. The decorrelation effect is separated into contributions from the magnitude of $v_n$ and the event-plane orientation changing with $η$. These two contributions are found to be comparable. The longitudinal flow correlations are also measured between $v_n$ of different order in $n$. The longitudinal fluctuations of $v_2$ and $v_3$ are found to be independent of each other, while the longitudinal fluctuations of $v_4$ and $v_5$ are found to be driven by the nonlinear contribution from $v_2^2$ and $v_2v_3$, respectively.

nucl-ex↗

arXiv2018

Prompt and non-prompt J/$ψ$ production and nuclear modification at mid-rapidity in p-Pb collisions at ${\bf \sqrt{{\it s}_{\text{NN}}}= 5.02}$ TeV

A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{\rm NN}}=5.02$ TeV is presented. The semi-inclusive decay channel of beauty hadrons into J/$ψ$ is considered, where the J/$ψ$ mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/$c$. The ${\rm {b\overline{b}}}$ production cross section at mid-rapidity, ${\rm d}σ_{\rm {b\overline{b}}}/{\rm d} y$, and the total cross section extrapolated over full phase space, $σ_{\rm {b\overline{b}}}$, are obtained. This measurement is combined with results on inclusive J/$ψ$ production to determine the prompt J/$ψ$ cross sections. The results in p-Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor $R_{\rm pPb}$, and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. $R_{\rm pPb}$ is found to be smaller than unity at low $p_{\rm T}$ for both J/$ψ$ coming from beauty hadron decays and prompt J/$ψ$.

nucl-ex↗

arXiv2018

Generalized Lomb-Scargle analysis of $\rm{^{90}Sr/^{90}Y}$ decay rate measurements from the Physikalisch-Technische Bundesanstalt

We apply the generalized Lomb-Scargle (LS) periodogram to independently confirm the claim by Sturrock et al (arXiv:1605.03088) of oscillation at a frequency of 11/year in the decay rates of $\rm{^{90}Sr/^{90}Y}$ from measurements at the Physikalisch Technische Bundesanstalt (PTB), which however has been disputed by Kossert and Nahle (arXiv:1407.2493). For this analysis, we made two different {\it ansatze} for the errors. For each peak in the LS periodogram, we evaluate the statistical significance using non-parametric bootstrap resampling. We find using both of these error models evidence for ~11/year periodicity in the $\rm{^{90}Sr/^{90}Y}$ data for two of the three samples, but at a lower significance than that claimed by Sturrock et al.

astro-ph.HE↗

arXiv2021

Extraction of the specific shear viscosity of quark-gluon plasma from two-particle transverse momentum correlations

The specific shear viscosity, $η/s$, of the quark-gluon plasma formed in ultrarelativistic heavy-ion collisions at RHIC and LHC is estimated based on the progressive longitudinal broadening of transverse momentum two-particle correlators, $G_2$, reported as a function of collision centrality by the STAR and ALICE experiments. Estimates are computed as a function of collision centrality using the Gavin ansatz which relates the $G_2$ longitudinal broadening to the specific shear viscosity. Freeze out times required for the use of the ansatz are computed using a linear fit of freeze out times reported as a function of the cubic root of the charged particle pseudorapidity density $({\rm d}N_{\rm ch}/{\rm d}η)^{1/3}$. Estimates of $η/s$ based on ALICE data exhibit little to no dependence on collision centrality at LHC energy, while estimates obtained from STAR data hint that $η/s$ might be a function of collision centrality at top RHIC energy.

nucl-ex↗

arXiv2021

A method to remove lower order contributions in multi-particle femtoscopic correlation functions

In recent years the femtoscopy technique has been used by the ALICE Collaboration in small colliding systems at the LHC to investigate the strong-interaction of hadron pairs in the low-energy regime. The extension of this technique to the study of many-body correlations aims to deliver in the next years the first experimental measurements of the genuine many-hadron interactions, provided that the contributions due to the lower order terms are properly accounted for. In this paper we present a method that allows to determine the residual lower order contributions to the three-body correlation functions, based on the cumulant decomposition approach and on kinematic transformations. A procedure to simulate genuine three-body correlations in three-baryon correlation functions is also developed. A qualitative study of the produced correlation signal is performed by varying the strength of the adopted three-body interaction model and comparisons with the expectations for the lower order contributions to the correlation function are shown. The method can be also applied to evaluate the combinatorial background in the two-body correlation functions, providing an improved statistical accuracy with respect to the standard techniques. The example of the contribution by the pK$^+$K$^-$ channel to the recently measured p$ϕ$ correlation is discussed.

nucl-th↗

arXiv2008

Highlights and Perspectives of the JLab Spin Physics Program

Nucleon spin structure has been an active and exciting subject of interest for the last three decades. Recent precision spin-structure data from Jefferson Lab have significantly advanced our knowledge of nucleon structure in the valence quark (high-x) region and improved our understanding of higher-twist effects, spin sum rules and quark-hadron duality. First, results of spin sum rules and polarizabilities in the low to intermediate Q^2 region are presented. Comparison with theoretical calculations are discussed. Surprising disagreements of Chiral Perturbation Theory calculations with experimental results on the generalized spin polarizability, δ_{LT}, were found. Then, precision measurements of the spin asymmetry in the high-x region are presented. They provide crucial input for global fits to world data to extract polarized parton distribution functions. The up and down quark spin distributions in the nucleon were extracted. The results for Δd/d disagree with the leading-order pQCD prediction assuming hadron helicity conservation. Results of precision measurements of the g_2 structure function to study higher-twist effects are presented. The data indicate a significant higher-twist (twist-3 or higher) effect. The second moment of the spin structure functions and the twist-3 matrix element d_2 results were extracted. The high Q^2 result was compared with a Lattice QCD calculation. Results on the resonance spin-structure functions in the intermediate Q^2 range are presented, which, in combination with DIS data, enable a detailed study of quark-hadron duality in spin-structure functions. Finally, an experiment to study neutron transversity and transverse spin asymmetries is discussed. A future plan with the 12 GeV energy upgrade at JLab is briefly outlined.

nucl-ex↗

arXiv2013

Review of Recent Results from the RHIC Beam Energy Scan

We review recent results from the RHIC beam energy scan (BES) program, aimed to study the Quantum Chromodynamics (QCD) phase diagram. The main goals are to search for the possible phase boundary, softening of equation of state or first order phase transition, and possible critical point. Phase-I of the BES program has recently concluded with data collection for Au+Au collisions at center-of-mass energies ($\sqrt{s_{NN}}$) of 7.7, 11.5, 19.6, 27, and 39 GeV. Several interesting results are observed for these lower energies where the net-baryon density is high at the mid-rapidity. These results indicate that the matter formed at lower energies (7.7 and 11.5 GeV) is hadron dominated and might not have undergone a phase transition. In addition, the centrality dependence of freeze-out parameters is observed for the first time at lower energies, slope of directed flow for (net)-protons measured versus rapidity shows an interesting behavior at lower energies, and higher moments of net-proton show deviation from Skellam expectations at lower energies. An outlook for the future BES Phase-II program is presented and efforts for the detailed study of QCD phase diagram are discussed.

nucl-ex↗

arXiv2013

Study of some characteristics of protons using interactions of light nuclei

Behavior of some average characteristics of protons are studied in protons and deuterons induced interactions with carbon nuclei at 4.2 A GeV/c. The emitted particles are divided in two groups depending on their polar angle in the lab. frame using half angle technique. Results of the experimental data are compared with Dubna version of cascade model. Analysis of the results show that the incone protons are leading particles.

nucl-ex↗

arXiv2013

Results on neutrinoless double beta decay from GERDA Phase I

The GERmanium Detector Array, GERDA, is designed to search for neutrinoless double beta (0$νββ$) decay of $^{76}$Ge and it is installed in the Laboratori Nazionali del Gran Sasso (LNGS) of INFN, Italy. In this review, the detection principle and detector setup of GERDA are described. Also, the main physics results by GERDA Phase I, are discussed. They include the measurement of the half-life of 2$νββ$ decay, the background decomposition of the energy spectrum and the techniques for the discrimination of the background, based on the pulse shape of the signal. In the last part of this paper, the estimation of a limit on the half-life of 0$νββ$ ($T^{0ν}_{1/2} >2.1\cdot 10^{25}$ yr at 90% C.L.) and the comparison with previous results are discussed. GERDA data from Phase I strongly disfavour the recent claim of 0$νββ$ discovery, based on data from the Heidelberg-Moscow experiment.

hep-ex↗