Measurement of W ± γ differential cross sections in proton-proton collisions at s = 13 TeV and effective field theory constraints
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Einstein-Podolsky-Rosen Paradox and Quantum Entanglement at Subnucleonic Scales
Not Available
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Heavy Neutral Leptons via Axionlike Particles at Neutrino Facilities
Heavy neutral leptons (HNLs) are often among the hypothetical ingredients behind nonzero neutrino masses. If sufficiently light, they can be produced and detected in fixed-target-like experiments. We show that if the HNLs belong to a richer—but rather generic—dark sector, their production mechanism can deviate dramatically from expectations associated with the standard-model weak interactions. In more detail, we postulate that the dark sector contains an axionlike particle (ALP) that naturally decays into HNLs. Since ALPs mix with the pseudoscalar hadrons, the HNL flux might be predominantly associated with the production of neutral mesons (e.g., π 0 , η ) as opposed to charge hadrons (e.g., π ± , K ± ). In this case, the physics responsible for HNL production and decay are not directly related and experiments like DUNE might be sensitive to HNLs that are too weakly coupled to the standard model to be produced via weak interactions, as is generically the case of HNLs that play a direct role in the type-I seesaw mechanism. Published by the American Physical Society 2024
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
The case for an EIC Theory Alliance: Theoretical Challenges of the EIC
We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spectroscopy and tests of fundamental symmetries. We review the present status and future challenges in EIC theory that have to be addressed in order to realize this ambitious and impactful physics program, including how to engage a diverse and inclusive workforce. In order to address these many-fold challenges, we propose a coordinated effort involving theory groups with differing expertise is needed. We discuss the scientific goals and scope of such an EIC Theory Alliance.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
LHCb: Recent Results and Future Plans
In this overview contribution we introduce the most recent results in high-multiplicity $pp$ and heavy ion collisions obtained by the LHCb experiment, detector developments and plans for the future heavy ion program. Some of the highlights include the study of double charm production, nuclear modification of B-hadrons, quarkonia and Z-bosons in pPb and the suppression of prompt X(3872) hadrons in high multiplicity $pp$ events. On the detector side, we bring to attention the preparation for the upcoming Run III in LHC and the fixed target program.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Studying the hadron structure with PANDA and CLAS using machine learning techniques
The hadron spectroscopy and structure are currently very active fields of research to study the non-perturbative regime of quantum chronodynamics. The first one studies the complex structure of excited hadrons by looking at their decay products, while the latter uses lepton scattering on nucleons. Both methods require reconstruction algorithms with great efficiency and good particle identification and background rejection rates. This work aims to provide these by either improving the existing methods or developing new ones. The first part of this document presents a feasibility study of a predicted hybrid charmonium state for the PANDA experiment. Lattice QCD calculations predict the ground state hybrid charmonium to be a spin exotic with quantum numbers of JP C = 1?+ at a mass of around 4.3 GeV with a width to be around 20 MeV. A machine learning based data analysis scheme is proposed to further improve the signal efficiency and the background reduction, alongside with improvements of the analysis software (PandaRoot), that are vital for this study. These improvements include a reworked clustering algorithm for the electromagnetic calorimeter (EMC) and an optimized monte carlo matching for neutral particles. The second part of this document is about studying the proton structure. A multidimensional study of the structure function ratio Fsin(?)LU /FUU has been performed for K±, based on the measurement of beam-spin asymmetries. It uses the high statistics data recorded with the CLAS12 spectrometer at Jefferson Laboratory. Fsin(?)LU is a twist-3 quantity that provides information about the quark gluon correlations in the proton. This document will present for the first time a simultaneous analysis of two kaon channels over a large kinematic range of z, xB , PT and Q2 with virtualities Q2 ranging from 1 GeV2 up to 8 GeV2 using machine learning techniques for improved particle identification.
Kripko, Aron↗
Search for electroweak production of supersymmetric particles in final states with two τ -leptons in $\sqrt{s}$ = 13 TeV pp collisions with the ATLAS detector
Three searches for the direct production of τ-sleptons or charginos and neutralinos in final states with at least two hadronically decaying τ-leptons are presented. For chargino and neutralino production, decays via intermediate τ-sleptons or W and h bosons are considered. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 139 fb -1 , recorded with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed and supersymmetric particle mass limits at 95% confidence level are obtained in simplified models. For direct production of $\sim\atop{\chi}$ $^+_1$ $\sim\atop{\chi}$ $^-_1$, chargino masses are excluded up to 970 GeV, while $\sim\atop{\chi}$ $^±_1$ and $\sim\atop{\chi}$ $^0_2$ masses up to 1160 GeV (330 GeV) are excluded for $\sim\atop{\chi}$ $^±_1$ $\sim\atop{\chi}$ $^0_2$ / $\sim\atop{\chi}$ $^+_1$ $\sim\atop{\chi}$ $^-_1$ production with subsequent decays via τ-sleptons (W and h bosons). Masses of τ-sleptons up to 500 GeV are excluded for mass degenerate $\sim\atop{\tau}$ L,R scenarios and up to 425 GeV for $\sim\atop{\tau}$ L-only scenarios. Sensitivity to $\sim\atop{\tau}$ R -only scenarios from the ATLAS experiment is presented here for the first time, with $\sim\atop{\tau}$ R masses excluded up to 350 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Nonprompt direct-photon production in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV
The measurement of the direct-photon spectrum from Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV is presented by the PHENIX Collaboration using the external-photon-conversion technique for 0%–93% central collisions in a transverse-momentum (𝑝 𝑇 ) range of 0.8–10 GeV/𝑐. An excess of direct photons, above prompt-photon production from hard-scattering processes, is observed for 𝑝 𝑇 < 6 GeV/𝑐. Nonprompt direct photons are measured by subtracting the prompt component, which is estimated as 𝑁 coll -scaled direct photons from 𝑝 + 𝑝 collisions at 200 GeV, from the direct-photon spectrum. Results are obtained for 0.8 < 𝑝 𝑇 < 6.0 GeV/𝑐 and suggest that the spectrum has an increasing inverse slope from ≈0.2 to 0.4 GeV/𝑐 with increasing 𝑝 𝑇 , which indicates a possible sensitivity of the measurement to photons from earlier stages of the evolution of the collision. In addition, like the direct-photon production, the 𝑝 𝑇 -integrated nonprompt direct-photon yields also follow a power-law scaling behavior as a function of collision-system size. Finally, the exponent, 𝛼, for the nonprompt component is found to be consistent with 1.1 with no apparent 𝑝 𝑇 dependence.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Measurement of the top-quark Yukawa coupling from $t\overline{t}$ production in the lepton+jets final state using pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
The top-quark Yukawa coupling is extracted from the distribution of the top-quark pair ($t\overline{t}$) invariant mass in proton-proton collisions using 140 fb −1 of data at $\sqrt{s}=13$ TeV collected in 2015–2018 by the ATLAS experiment at the Large Hadron Collider. In the region near the production threshold, the $t\overline{t}$ invariant mass spectrum is sensitive to electroweak virtual corrections, including contributions from Higgs boson exchange, thereby providing sensitivity to the top-quark Yukawa coupling. This is the first measurement in ATLAS that aims to obtain this coupling exploiting this approach. The $t\overline{t}$ system is reconstructed in the single-lepton final state, requiring exactly one isolated electron or muon and at least four jets with at least two identified as originating from b-quarks. The measured Yukawa coupling is found to be in good agreement with the Standard Model prediction. An upper limit on the top-quark Yukawa coupling strength of Y t < 2.1 relative to the Standard Model prediction is observed at 95% confidence level, consistent with the expected sensitivity.
Hadron-Hadron Scattering↗
Scattering and stopping of hadrons in nuclear matter
It was observed, in the 180 litre xenon bubble chamber, that when hadrons with kinetic energy higher than the pion production threshold fall on a layer of nuclear matter - on an atomic nucleus in other words - in many cases they can pass through it without causing particles production but they are deflected through some deflection angles; if the energy is lower than a few GeV and the nuclear matter layer is thick enough, the hadrons can be stopped in it. The amount of the deflection at a given incident hadron energy varies with the way the hadron strikes the atomic nucleus; the probability of the occurrence of stopping depends on the incident hadron identity and energy, and on the way the hadron passed through the nucleus, as well.
Strugalski, Z.↗
Measurement of the total and differential Higgs boson production cross-sections at $ \sqrt{s} $ = 13 TeV with the ATLAS detector by combining the H → ZZ* → 4ℓ and H → γγ decay channels
The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H → ZZ* → 4ℓ and H → γγ decay channels. The results are based on a dataset of 139 fb –1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider. The measured total Higgs boson production cross-section is $55.5$$^{+4.0}_{–3.8}$ pb, consistent with the Standard Model prediction of 55.6 ± 2.5 pb. All results from the two decay channels are compatible with each other, and their combination agrees with the Standard Model predictions. A combined statistical interpretation of the measured fiducial cross-sections as a function of the Higgs boson transverse momentum is performed in order to probe the Yukawa couplings to the bottom and charm quarks. A similar interpretation is performed by including also the constraints from the measurements of Higgs boson production in association with a W or Z boson in the H → bb¯ and cc¯ decay channels.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Multiplicity and pseudo-rapidity density distributions of charged particles produced in pp, pA and AA collisions at RHIC & LHC energies
Multiplicity and pseudorapidity (η) density (d N ch /dη) distributions of charged hadrons provide key information towards understanding the particle production mechanisms and initial conditions of high-energy heavy-ion collisions. However, detector constraints limit the η-range across which charged particle measurements can be carried out. Extrapolating the measured distributions to large η-range by parameterizing measured distributions and by using calculations from event generators, we characterize the production of charged particles over the full kinematic range. In the present study, we use three different ansätze to obtain quantitative descriptions of the shape of pseudorapidity distributions of charged hadrons produced in pp, p–A, and A–A collisions for beam energies ( s NN ) ranging from a few GeV to a few TeV corresponding to RHIC and LHC energies. We study the limiting fragmentation behavior in these collisions and report evidence for participant-scaling violations in high-energy collisions at the TeV scale. We additionally examine measured pseudorapidity distributions to constrain models describing initial conditions of particle production. We predict the centrality dependence of charged particle multiplicity distributions at FAIR and NICA energies and give an estimation of charged particle multiplicity at η = 0 for the proposed HE-LHC and FCC energies.
Physics↗
Exploring J/ψ Production Mechanism at the Future Electron-Ion Collider
We propose to use transverse momentum p T distribution of J/ψ production at the future Electron Ion Collider (EIC) to explore the production mechanism of heavy quarkonia in high energy collisions. We apply QCD and QED collinear factorization to the production of a $c\bar{c}$ pair at high p T , and non-relativistic QCD factorization to the hadronization of the pair to a J/ψ. We evaluate J/ψ p T -distribution at both leading and next-to-leading order in strong coupling, and show that production rates for various color-spin channels of a $c\bar{c}$ pair in electron-hadron collisions are very different from that in hadron-hadron collisions, which provides a strong discriminative power to determine various transition rates for the pair to become a J/ψ. We predict that the J/ψ produced in electron-hadron collisions is likely unpolarized, and the production is an ideal probe for gluon distribution of colliding hadron (or nucleus). We find that the J/ψ production is dominated by the color-octet channel, providing an excellent probe to explore the gluon medium in large nuclei at the EIC.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of inclusive electrons from open heavy-flavor hadron decays in p + p collisions at s = 200 GeV with the STAR detector
We report a new measurement of the production cross section for inclusive electrons from open heavy-flavor hadron decays as a function of transverse momentum (p T ) at midrapidity (|y| < 0.7) in p + p collisions at √s = 200 GeV. Overall, the result is presented for 2.5 < P T < 10 GeV/c with an improved precision above 6 GeV/c with respect to the previous measurements, providing more constraints on perturbative QCD calculations. Moreover, this measurement also provides a high-precision reference for measurements of nuclear modification factors for inclusive electrons from open-charm and -bottom hadron decays in heavy-ion collisions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Accessing subnuclear fluctuations and saturation with multiplicity dependent J/ψ production in p+p and p+Pb collisions
We study the production of J/ψ vector mesons as a function of charged hadron multiplicity in p+p and p+Pb collisions at LHC energies. We employ the color glass condensate framework, using running coupling Balitsky-Kovchegov evolved dipole amplitudes, to compute gluon and cc¯-pair production. We use fragmentation functions to obtain charged hadrons, and explore two different hadronization schemes for the J/ψ: non-relativistic quantum chromodynamics and the improved color evaporation model. In our framework, event-by-event multiplicity fluctuations of both hadrons and J/ψ are driven by geometric and saturation scale normalization fluctuations. Studying the correlation between J/ψ and hadron multiplicity, we show that the characteristic difference between forward and backward rapidity in p+Pb collisions is a result of different degrees of saturation probed at different rapidities. We demonstrate that experimental data on heavy-flavor production as a function of event activity provide stringent constraints on the fluctuating proton structure
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Quantum simulations of hadron dynamics in the Schwinger model using 112 qubits
Hadron wave packets are prepared and time evolved in the Schwinger model using 112 qubits of IBM’s 133-qubit Heron quantum computer ibm_torino. The initialization of the hadron wave packet is performed in two steps. First, the vacuum is prepared across the whole lattice using the recently developed SC-ADAPT-VQE algorithm and workflow. SC-ADAPT-VQE is then extended to the preparation of localized states, and used to establish a hadron wave packet on top of the vacuum. This is done by adaptively constructing low-depth circuits that maximize the overlap with an adiabatically prepared hadron wave packet. Due to the localized nature of the wavepacket, these circuits can be determined on a sequence of small lattices using classical computers, and then robustly scaled to prepare wave packets on large lattices for simulations using quantum computers. Time evolution is implemented with a second-order Trotterization. To reduce both the required qubit connectivity and circuit depth, an approximate quasilocal interaction is introduced. This approximation is made possible by the emergence of confinement at long distances, and converges exponentially with increasing distance of the interactions. Using multiple error-mitigation strategies, up to 14 Trotter steps of time evolution are performed, employing 13,858 two-qubit gates (with a CNOT depth of 370). The propagation of hadrons is clearly identified, with results that compare favorably with Matrix Product State simulations. Finally, prospects for a near-term quantum advantage in simulations of hadron scattering are discussed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for long-lived charged particles using large specific ionisation loss and time of flight in 140 fb −1 of pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector
This paper presents a search for massive, charged, long-lived particles with the ATLAS detector at the Large Hadron Collider using an integrated luminosity of 140 fb −1 of proton-proton collisions at $\sqrt{s}$ = 13 TeV. These particles are expected to move significantly slower than the speed of light. In this paper, two signal regions provide complementary sensitivity. In one region, events are selected with at least one charged-particle track with high transverse momentum, large specific ionisation measured in the pixel detector, and time of flight to the hadronic calorimeter inconsistent with the speed of light. In the other region, events are selected with at least two tracks of opposite charge which both have a high transverse momentum and an anomalously large specific ionisation. The search is sensitive to particles with lifetimes greater than about 3 ns with masses ranging from 200 GeV to 3 TeV. The results are interpreted to set constraints on the supersymmetric pair production of long-lived R-hadrons, charginos and staus, with mass limits extending beyond those from previous searches in broad ranges of lifetime.
beyond Standard Model↗
Search for single production of a vectorlike T quark decaying into a Higgs boson and top quark with fully hadronic final states using the ATLAS detector
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗