Zero Degree Calorimeters Research Articles

Probing configuration of α clusters with spectator particles in relativistic heavy-ion collisions

We propose to use spectator particle yield ratios to probe the configuration of α clusters in 12C and 16O by their ultracentral collisions at RHIC and LHC energies. The idea is illustrated based on initial density distributions with various α-cluster configurations generated by a microscopic cluster model, and without α clusters from mean-field calculations. The multifragmentation of the spectator matter produces more spectator light nuclei including α clusters in collisions of nuclei with chain structure of α clusters, compared to those of nuclei with a more compact structure. The yield ratio of free spectator neutrons to spectator particles with mass-to-charge ratio A/Z=2 scaled by their masses can be practically measured by the zero-degree calorimeter (ZDC) at RHIC and LHC, serving as a clean probe free from modeling the complicated dynamics at midrapidities.

ALICE luminosity determination for Pb–Pb collisions at √s NN = 5.02 TeV

Luminosity determination within the ALICE experiment is based on the measurement, in van der Meer scans, of the cross sections for visible processes involving one or more detectors (visible cross sections). In 2015 and 2018, the Large Hadron Collider provided Pb–Pb collisions at a centre-of-mass energy per nucleon pair of √s NN = 5.02 TeV. Two visible cross sections, associated with particle detection in the Zero Degree Calorimeter (ZDC) and in the V0 detector, were measured in a van der Meer scan.This article describes the experimental set-up and the analysis procedure, and presents the measurement results. The analysis involves a comprehensive study of beam-related effects and an improved fitting procedure, compared to previous ALICE studies, for the extraction of the visible cross section. The resulting uncertainty of both the ZDC-based and the V0-based luminosity measurement for the full sample is 2.5%. The inelastic cross section for hadronic interactions in Pb–Pb collisions at √s NN = 5.02 TeV, obtained by efficiency correction of the V0-based visible cross section, was measured to be 7.67 ± 0.25 b, in agreement with predictions using the Glauber model.

Heavy flavor machine learning algorithms for fast data processing in sPHENIX

The sPHENIX experiment at RHIC utilizes the first new heavy ion detector since the switch on of the LHC experiments. It’s optimized for precision jet and heavy flavor physics measurements, and recorded its first collisions in spring 2023. sPHENIX uses a tracking system with streaming readout and barrel calorimetry to reconstruct the collision topology. Event plane detectors, minimum bias detectors and zero-degree calorimeters are used to characterize the event. The streaming readout detectors are capable of recording 10% of the minimum bias rate, in addition to triggered events, in p+p collisions which will enable unabated, precision b-hadron and heavy flavor jet measurements at RHIC. An AI-assisted hardware trigger demonstrator is under development to sample the remaining 90% of minimum-bias p+p collisions with an aim for further deployment at the EIC.

Centrality-dependent modification of hadron and jet production in electron-nucleus collisions

Centrality-dependent measurements of hadron and jet cross section attenuation in deep inelastic scattering on nuclei can shed new light on the physics of final-state interactions in nuclear matter, including the path-length dependence of the in-medium parton shower formation and evolution. Recent simulation studies have demonstrated the feasibility of experimental centrality determination in eA reactions at the electron-ion collider via neutron detection in the zero-degree calorimeter. Motivated by these results, we present the first theoretical calculation of the production rate modification for hadrons and jets in central and peripheral ePb collisions. We find that the variation in the suppression of inclusive jet cross section as a function of centrality is less than a factor of two. In more differential measurements, such as the distribution of hadrons versus the hadronization fraction zh, the difference can be enhanced up to an order of magnitude.

Classifier for centrality determination with zero-degree calorimeter at the cooling-storage-ring external-target experiment

Classifier for centrality determination with zero-degree calorimeter at the cooling-storage-ring external-target experiment

Neutron emission in ultraperipheral Pb-Pb collisions at sNN=5.02 TeV

In ultraperipheral collisions (UPCs) of relativistic nuclei without overlap of nuclear densities, the two nuclei are excited by the Lorentz-contracted Coulomb fields of their collision partners. In these UPCs, the typical nuclear excitation energy is below a few tens of MeV, and a small number of nucleons are emitted in electromagnetic dissociation (EMD) of primary nuclei, in contrast to complete nuclear fragmentation in hadronic interactions. The cross sections of emission of given numbers of neutrons in UPCs of $^{208}$Pb nuclei at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV were measured with the neutron zero degree calorimeters (ZDCs) of the ALICE detector at the LHC, exploiting a similar technique to that used in previous studies performed at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. In addition, the cross sections for the exclusive emission of one, two, three, four, and five forward neutrons in the EMD, not accompanied by the emission of forward protons, and thus mostly corresponding to the production of $^{207,206,205,204,203}$Pb, respectively, were measured for the first time. The predictions from the available models describe the measured cross sections well. These cross sections can be used for evaluating the impact of secondary nuclei on the LHC components, in particular, on superconducting magnets, and also provide useful input for the design of the Future Circular Collider (FCC-hh).

Readout Electronics for the Zero Degree Calorimeter at HIRFL-CEE Experiment

The CSR External-target Experiment (CEE) at the Heavy Ion Research Facility at Lanzhou (HIRFL) will be the first GeV large-scale nuclear physics experiment developed independently in China. The primary physics goal of the CEE is to study the nuclear equation of state, hyper nuclei, and radioactive ion beam physics. The Zero Degree Calorimeter (ZDC) of CEE measures the centrality and reaction plane of the nuclear-nuclear collision relative to the hadron background. It consists of 192 roughly trapezoidal Plastic Scintillator (PS) crystal blocks coupled with PMT (Photo Multiplier Tube) to convert charged particles into electrical signals. The readout electronics consists of 12 FEE (Front End Electronics), the sub-trigger module, and the sub-clock module. In addition, one HV (High Voltage) crate provides a high voltage power supply for the PMTs. According to the electrical test on the electronics, the RMS (Root Mean Square) noise is less than 0.4 mV, and the nonlinearity is less than 0.06%. The heavy-ion beam test shows that the ZDC can measure particles up to Z=7, which meets the physics requirements.

Exciting ions: A systematic treatment of ultraperipheral heavy ion collisions with nuclear breakup

We present an updated theoretical treatment of ultraperipheral collisions (UPCs) of heavy ions, within the SuperChic Monte Carlo generator. This in particular accounts for mutual ion excitation through additional photon exchanges between the colliding ions. This effect occurs frequently in UPCs, and indeed can be (and has been) measured in data through the use of zero degree calorimeter (ZDC) detectors installed in the far forward region. The theoretical approach presented here accounts for the non-trivial and non-negligible impact such ion dissociation has on the measured cross sections and distributions of the produced particles in the central detectors. This builds on previous work, whereby the survival factor probability of no additional inelastic ion-ion scattering due to the strong interaction, and its kinematic impact, are also accounted for within the same overall framework. We compare to data from ATLAS and CMS at the LHC, and STAR at RHIC, and find in general encouraging agreement for a range of observables and ZDC neutron tags, with some room for further improvement, suggesting the inclusion of higher order QED effects and/or tuning of the the $\gamma A \to A^*$ cross section may be desirable. Overall, this gives confidence in the approach considered here and for applications to new phenomena within and beyond the Standard Model.

ALICE Zero Degree Calorimeters. The new readout system in LHC Run 3

The Zero Degree Calorimeters (ZDC) were designed to provide the measurement of the event geometry and luminosity in heavy-ion operation. The readout system was redesigned in order to operate in continuous mode without dead time at 2.5 MHz event rate. The new acquisition chain is based on a commercial 12 bit digitizer with a sampling rate of about 1 GSps, assembled on an FPGA Mezzanine Card. The signals produced by the 26 ZDC channels are digitized, and samples are processed through an FPGA to extract information such as timing, baseline average estimation and luminosity.

Measuring deformed neutron skin with free spectator nucleons in relativistic heavy-ion collisions

The neutron skin in deformed nuclei is generally not uniformly distributed but has an angular distribution, depending on both the spin-dependent nuclear interaction and the nuclear symmetry energy. To extract the information of the deformed neutron skin, we have explored the possibility of using free spectator nucleons in central tip-tip and body-body collisions at top RHIC energy with four typical deformed nuclei. The density distributions of neutrons and protons are consistently obtained from the Skyrme-Hartree-Fock-Bogolyubov calculation, and the angular distribution of the neutron skin can be varied by adjusting the strength of the nuclear spin-orbit coupling. With the information of spectator nucleons obtained based on a Monte-Carlo Glauber model, the free spectator nucleons are generated from a multifragmentation process. By investigating the results from different systems and with different collision configurations, we found that although it is difficult to probe the deformed neutron skin in 96Zr and 238U by their collisions, it is promising to extract the polar angular distributions of the neutron skin in 96Ru and 197Au by comparing the yield ratios of free spectator neutrons to protons in their central tip-tip and body-body collisions. The proposed observables can be measured by dedicated zero-degree calorimeters in heavy-ion collision experiments that have been carried out in recent years by RHIC.

Joint ATLAS/CMS ZDC upgrade project for the High Luminosity LHC

The High Luminosity LHC (HL-LHC) provides the opportunity to study heavy ion, proton-nucleus, photon-nucleus and photon-photon collisions with unprecedented luminosities at the TeV scale. The LHC heavy ion community has mapped out an extensive range of physics measurements at the HLLHC that will push forward our understanding of both QCD, QED and even electroweak physics. The measurement of forward neutrons and photons in Zero Degree Calorimeters (ZDCs) is essential for event classification and triggering. In order to reach the required luminosities, the LHC interaction regions will be redesigned, necessitating the need to build new ZDCs that will be both narrower and much more radiation tolerant. This challenge motivated the formation of a joint project between ATLAS and CMS to build new ZDCs for Run 4, JZCaP. The ZDCs are based on radiation-hard fused silica rods that produce Cherenkov light. These rods have been developed by Heraeus Quartzglas in collaboration with JZCaP and the LHC BRAN and FLUKA groups. The Run 4 ZDCs (HL-ZDCs) are the first joint detector project between CMS and ATLAS. This talk will present the capabilities of the new ZDCs and recent R&D highlights.

Status of the LHCf experiment

A precise understanding of hadronic interactions is essential to interpreting the mass composition of ultra-high energy cosmic rays from the results of air shower experiments. The Large Hadron Collier forward (LHCf) experiment aims to measure forward neutral particles for validation of hadronic interaction models adopted in air shower simulations. We already published the production cross sections of forward photons and neutrons for proton-proton collisions at √s=13 TeV. Recently, we showed a preliminary result of the energy spectrum of forward η mesons for proton-proton collisions at √s=13 TeV. Moreover, in September 2022, we had another data-taking for proton-proton collisions at √s=13.6 TeV. In data taking, we planned to obtain a number of π0 and η candidates ten times larger for precise measurements and to perform the joint operation with ATLAS Roman pots and zero-degree calorimeters. Thanks to the joint operation with the ATLAS Roman pots, we can measure diffractive mass and neutral particles from diffractive dissociation simultaneously. Furthermore, energy resolution for neutrons is expected to be improved from 40% to 20% by combining the LHCf and the ATLAS zero-degree calorimeters. In this work, we report the status and prospects of the LHCf experiment.

Performance of the readout system of the ALICE Zero Degree Calorimeters in LHC Run 3

The ALICE Zero Degree Calorimeters (ZDC) provide information about event geometry in heavy-ion collisions through the detection of spectator nucleons and allow to estimate the delivered luminosity. They are also very useful in p–A collisions, allowing an unbiased estimation of collision centrality. The Run 3 operating conditions will involve a tenfold increase in instantaneous luminosity in heavy-ion collisions, with event rates that, taking into account the different processes, could reach 5 MHz in the ZDCs. The challenges posed by this demanding environment lead to a redesign of the readout system and to the transition to a continuous acquisition. The new system is based on 12 bit, 1 Gsps FMC digitizers that will continuously sample the 26 ZDC channels. Triggering, pedestal estimation and luminosity measurements will be performed on FPGA directly connected to the front-end. The new readout system and the performances foreseen in Run 3 are presented.

Multi-differential studies to explore strangeness enhancement in pp with ALICE at the LHC

The study of energy and multiplicity dependence of strange hadron production in proton-proton collisions provides a powerful tool to understand similarities and differences between small and large collision systems. In order to better understand the origin of strangeness enhancement in pp new multi-differential analyses have been performed. The first separates the contribution of soft and hard processes, such as jets, to strange hadron production through two-particle correlation techniques. The second exploits the concept of the effective energy available for particle production in the event, which is estimated by an anti-correlation with the energy deposited in ALICE's Zero Degree Calorimeters. The results indicate that strangeness production emerges from the growth of the underlying event and confirm it is related to the final state multiplicity.

Study of very forward energy and its correlation with particle production at midrapidity in pp and p-Pb collisions at the LHC

The energy deposited at very forward rapidities (very forward energy) is a powerful tool for characterising proton fragmentation in pp and p-Pb collisions. The correlation of very forward energy with particle production at midrapidity provides direct insights into the initial stages and the subsequent evolution of the collision. Furthermore, the correlation with the production of particles with large transverse momenta at midrapidity provides information complementary to the measurements of the underlying event, which are usually interpreted in the framework of models implementing centrality-dependent multiple parton interactions.Results about very forward energy, measured by the ALICE zero degree calorimeters (ZDCs), and its dependence on the activity measured at midrapidity in pp collisions at sqrt{s} = 13 TeV and in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 8.16 TeV are discussed. The measurements performed in pp collisions are compared with the expectations of three hadronic interaction event generators: PYTHIA 6 (Perugia 2011 tune), PYTHIA 8 (Monash tune), and EPOS LHC. These results provide new constraints on the validity of models in describing the beam remnants at very forward rapidities, where perturbative QCD cannot be used.

Studying the mechanisms for strange particle production with ALICE at LHC

The main goal of the ALICE experiment is to study the physics of strongly interacting matter, focusing on the properties of the quark-gluon plasma (QGP). The relative production of strange hadrons with respect to non-strange hadrons in heavy-ion collisions was historically considered as one of the signatures of QGP formation. However, the latest results in proton-proton (pp) and proton-lead (p-Pb) collisions have revealed an increasing trend in the yield ratio of strange hadrons to pions with the charged-particle multiplicity in the event, showing a smooth evolution across different collision systems and energies. We present the new studies which are performed with the aim of better understanding the production mechanisms for strange particles and hence the strangeness enhancement phenomenon in small collision systems. In one of the recent studies, the very forward energy transported by beam remnants (spectators) and detected by the Zero Degree Calorimeters (ZDC) is used to classify events. The contribution of the effective energy and the particle multiplicity on strangeness production is studied using a multi-differential approach in order to disentangle initial and final state effects. In the second study, the origin of strangeness enhancement with multiplicity in pp has been further investigated by separating the contribution of soft and hard processes, such as jets, to strange hadron production. Techniques involving full jet reconstruction or two-particle correlations have been exploited. The results indicate that the increased relative strangeness production emerges from the growth of the underlying event, being disconnected from initial state properties, and suggest that soft (out-of-jets) processes are the dominant contribution to strange hadron production.

Tackling the kaon structure function at EicC * *Supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34030301), the National Natural Science Foundation of China (12005266) and the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008)

Measuring the kaon structure beyond proton and pion structures is a prominent topic in hadron physics, as it is one way to understand the nature of the Nambu-Goldstone boson of QCD and observe the interplay between the EHM and HB mechanisms for hadron mass generation. In this study, we present a simulation of the leading Λ baryon tagged deep inelastic scattering experiment at EicC (Electron-ion collider in China), which is engaged to unveil the internal structure of kaon via the Sullivan process. According to our simulation results, the suggested experiment will cover the kinematical domain of and up to 50 GeV , with the acceptable statistical uncertainties. In the relatively low- region ( GeV ), the Monte-Carlo simulation shows a good statistical precision ( %) for the measurement of the kaon structure function . In the high- region (up to 50 GeV ), the statistical uncertainty of is also acceptable ( %) for the data at . To perform such an experiment at an electron-ion collider, a high-performance zero-degree calorimeter is suggested. The magnitude of the background process and the assumed detector capabilities are also discussed and illustrated in the paper.

Probing the Gluonic Structure of the Deuteron with J/ψ Photoproduction in d+Au Ultraperipheral Collisions.

Understanding gluon density distributions and how they are modified in nuclei are among the most important goals in nuclear physics. In recent years, diffractive vector meson production measured in ultraperipheral collisions (UPCs) at heavy-ion colliders has provided a new tool for probing the gluon density. In this Letter, we report the first measurement of J/ψ photoproduction off the deuteron in UPCs at the center-of-mass energy sqrt[s_{NN}]=200 GeV in d+Au collisions. The differential cross section as a function of momentum transfer -t is measured. In addition, data with a neutron tagged in the deuteron-going zero-degree calorimeter is investigated for the first time, which is found to be consistent with the expectation of incoherent diffractive scattering at low momentum transfer. Theoretical predictions based on the color glass condensate saturation model and the leading twist approximation nuclear shadowing model are compared with the data quantitatively. A better agreement with the saturation model has been observed. With the current measurement, the results are found to be directly sensitive to the gluon density distribution of the deuteron and the deuteron breakup process, which provides insights into the nuclear gluonic structure.

Investigating the origin of strangeness enhancement in small systems through multi-differential analyses

The main goal of the ALICE experiment is to study the physics of strongly interacting matter, including the properties of the quark-gluon plasma (QGP). The relative production of strange hadrons with respect to non-strange hadrons in heavy-ion collisions was historically considered as one of the signatures of QGP formation. However, measurements at the LHC in pp and p-Pb collisions have shown similar features to those observed in Pb-Pb, measuring an increase in the production of strange hadrons relative to pions with the charged-particle multiplicity in the event. In order to better understand the role of the event multiplicity to the observed enhancement in pp, two new complementary analyses have been performed. The first exploits the angular correlation between strange and high-pT hadrons in the event to classify in-jet and out-of-jet strangeness production. The second uses the concept of the effective energy available in the event for particle production which is estimated by an anti-correlation with the energy deposited in ALICE’s Zero Degree Calorimeters. The results suggest that strangeness enhancement emerges from the growth of the underlying event and is not connected to initial state properties.

Prototype design of readout electronics for Zero Degree Calorimeter in the HIRFL-CSR external-target experiment

Located at the center of the end of the CSR External-target Experiment (CEE), the Zero Degree Calorimeter (ZDC) is designed to rebuild the centrality and reaction plane of the nuclear-nuclear collision. To meet the target of ZDC to detect the energy distribution of colliding particles, a high-performance readout system prototype, which implements a Gaussian shaping algorithm, has been designed. The system consists of 4 channels; each channel mainly includes an I-V conversion circuit, a slow forming circuit, a threshold trigger circuit, and a digital signal processing unit based on a field-programmable gate array (FPGA).Performance studies indicate that the noise of each channel is less than 0.8 mV and the nonlinearity is better than 0.6%. Tests with a LED driver source indicate that the Gaussian shaping algorithm can improve the photon energy resolution from 7.481% to 6.196%. Tests with cosmic rays also produced expected results.