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Physics High Energy Physics (Experiment)

hep-ex Watch High Energy Physics (Experiment)

Wednesday 30 September

High Energy Physics (Experiment) · Cross-listed from physics.ins-det

Impact of Gain Layer Doping Concentration on the Performance of 4H-SiC LGADs

Tao Yang, Ben J. Sekely, Yashas Satapathy et al. (+12 more)

Gain layer doping concentration determines the electric field profile in a low gain avalanche detector (LGAD) and is therefore the primary design parameter. This work reports its influence on the charge collection and timing behavior of 4H-SiC LGADs. Two mesa-isolated devices with cold He ion implanted termination differ only in gain layer doping, $4\times10^{17}$~$cm^{-3}$ and $5\times10^{17}$~$cm^{-3}$, and are characterized together with a PIN diode from the same wafer using the ultraviolet transient current technique (UV-TCT). The 25% doping difference produces a gain difference of about two orders of magnitude at the same applied bias, representing a gain range of 3.7 to 216. Under UV-TCT excitation, the higher-doped device exhibits time-resolution minima within a gain range of about 20–80 across the investigated laser intensities, consistent with the transition from electronic-noise-dominated jitter to multiplication shot noise. The non-monotonic timing response is also observed under a $^{90}Sr$ beta source with a Si LGAD reference: the higher-doped device reaches 51.7 ps at 280 V and then degrades, while the lower-doped device requires more than 450 V. This measured gain window provides an experimental reference for further optimization of the gain-layer design.
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All authors Tao Yang, Ben J. Sekely, Yashas Satapathy, Abraham Tishelman-Charny, Greg Allion, Gil Atar, Philip Barletta, Gabriele Giacomini, Carl Haber, Steve Holland, John F. Muth, Spyridon Pavlidis, Chengxi Yang, Haichen Wang, Stefania Stucci

High Energy Physics (Experiment) · Cross-listed from hep-ph

Neutrino trident process at a muon collider

Reinaldo Francener and Victor P. Goncalves

A TeV-scale muon collider enables the production of a highly collimated high-energy neutrino flux by muon decay in the straight sections of the collider ring. Recent studies have demonstrated that these neutrinos can be used for high-precision measurements in neutrino physics with a dedicated far-forward neutrino detector. In this study, we investigate the potentiality of the muon collider to discover the rare neutrino trident process, which is characterized by the fusion between a weak boson from the neutrino and a photon from the Coulomb field of the nucleus target. Our results indicate large neutrino trident rates per year [$\mathcal{O}(10^3)$] in a baseline 10 kg neutrino detector for a configuration of different flavour pairs of charged leptons in the final state, which will allow high-precision tests of the Standard Model and searches for New Physics. As a first example, we investigate the impact of the a new gauge boson $Z'$, as predicted by the $L_\mu - L_\tau$ model, and derive the projected sensitivity to this new gauge boson. Our findings show that a neutrino detector at a muon collider will significantly extend the current excluded regions of the parameter space.
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High Energy Physics (Experiment)

Scaling Collider Event Generation with Residual-Quantized Tokens

Dan Godi, Dmitrii Kobylianskii and Eilam Gross

Full detector simulation and reconstruction of collider events are projected to become major bottlenecks at the High-Luminosity Large Hadron Collider, motivating the development of fast, ML-based surrogates. At the same time, LLMs have driven fast progress in generative discrete modeling: autoregressive transformers trained on tokenized data now represent the state of the art across a range of generative tasks. We extend the discrete modeling paradigm by introducing a particle-level generative model trained on residual-quantized full-event data. We demonstrate the ability of this model family to perform conditional generation from detector-stable particles; we study its scaling behavior across a range of dataset and model sizes, characterize the effects of repeated data exposure and demonstrate that token-level loss systematically predicts downstream physical fidelity. These results provide an empirical framework for scalable collider full-event generation based on residual-quantized representations.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

A massive right-handed sterile neutrino in three-body ${\bar B}\to D^*\ell^-{\bar N}_R$ decays - a Monte Carlo simulation study

Bhubanjyoti Bhattacharya, Thomas E. Browder, Lucien M. Cremaldi et al. (+6 more)

We investigate the differential decay distributions of $\bar{B}\to D^*\ell^-{\bar N}_R $, where $N_R$ is a heavy right-handed neutrino (RHN) and $\ell = e, \mu$. We employ a newly developed Monte Carlo event generator based on the EvtGen framework that can simulate beyond-the-Standard-Model processes. We validate the implementation of the model by comparing the Monte-Carlo results with analytical results for several kinematic variables such as $q^2$ and missing mass, as well as signatures in the angular distributions such as $A_{FB}$, $S_{3}$, $S_{5}$, etc. This MC Generator will enable new experimental searches for RHNs. We discuss the sensitivity of various observables to the presence of an RHN and the feasibility of an experimental analysis at Belle II.
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All authors Bhubanjyoti Bhattacharya, Thomas E. Browder, Lucien M. Cremaldi, Horacio Crotte Ledesma, Nilakshi Das, Alakabha Datta, Tejhas Kapoor, Kumar Pandey, Alexei Sibidanov

High Energy Physics (Experiment) · Cross-listed from hep-ph

Quantum Information in High-Energy Physics: a top subject

Yoav Afik and Juan Ramón Muñoz de Nova

As a work selected for the Frontiers of Science Award, we present in the Proceedings of the ICBS an overview of how the techniques from the field of Quantum Information (QI) can be implemented in High-Energy Physics (HEP), including also some novel insights. We focus on the paradigmatic case of the top quark, a drosophila of a relativistic qubit. We study the presence of entanglement, perhaps the most genuine feature of Quantum Mechanics, in top-antitop quark production in high-energy colliders such as the LHC. We also analyze our experimental proposal of a quantum tomography protocol for the top-antitop quark pair, eventually leading to the entanglement observations by the ATLAS and CMS collaborations, which constituted the highest-energy observations of entanglement ever. We discuss how the concepts and techniques developed in our work have effectively spawned an already vast and rich field of QI in HEP.
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High Energy Physics (Experiment) · Cross-listed from physics.ins-det

Performance and quality testing of CBM RICH front-end electronics

Pavish Subramani, Christian Pauly, Joerg Foertsch et al. (+2 more)

This note describes the laboratory setup at the University of Wuppertal and its use to measure charge sharing crosstalk, perform high rate and high occupancy tests of MAPMT-DIRICH readout elec- tronics using a realistic detector setup, and also includes the analysis of induced electronic noise characteristics of a new iteration of the DIRICH power module to be used in the CBM RICH readout chain.
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All authors Pavish Subramani, Christian Pauly, Joerg Foertsch, Dennis Pfeifer, Karl-Heinz Kampert

High Energy Physics (Experiment)

First double-differential cross-section measurements in proton multiplicity and kinematics for mesonless $\nu_{\mu}$ charged-current interactions on argon using the MicroBooNE detector

MicroBooNE collaboration: P. Abratenko, D. Andrade Aldana, J. Asaadi et al. (+186 more)

We present the first double-differential cross-section measurements of muon neutrino charged-current interactions on argon with no mesons and one or more protons ($N_{p} \geq 1$) in the final state as a function of proton multiplicity and kinematics. The analysis uses the full Booster Neutrino Beam dataset collected by the MicroBooNE detector at Fermi National Accelerator Laboratory, corresponding to a total of $1.30 \times 10^{21}$ protons on target. We measure cross sections as a function of the proton multiplicity, the momenta and muon-proton opening angles of the leading and subleading protons up to and including the fourth-leading proton, as well as the total available kinetic energy of the hadronic system. The treatment of the statistical and systematic uncertainties includes correlations between the different extracted distributions. The measured cross sections are compared to predictions from several event generators using different primary and final-state interaction models. The results reveal strong sensitivity to the modeling of final-state interactions, and none of the generators tested provides a fully adequate description of the data. Significant disagreement between data and predictions is observed in the proton multiplicity distributions, particularly at backward opening angles and for subleading proton kinematics.
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All authors MicroBooNE collaboration: P. Abratenko, D. Andrade Aldana, J. Asaadi, A. Ashkenazi, S. Balasubramanian, B. Baller, A. Barnard, G. Barr, D. Barrow, J. Barrow, V. Basque, J. Bateman, B. Behera, O. Benevides Rodrigues, S. Berkman, A. Bhat, M. Bhattacharya, V. Bhelande, A. Binau, M. Bishai, A. Blake, B. Bogart, T. Bolton, M.B. Brunetti, L. Camilleri, D. Caratelli, F. Cavanna, G. Cerati, A. Chappell, Y. Chen, J.M. Conrad, M. Convery, L. Cooper-Troendle, J.I. Crespo-Anadon, R. Cross, M. Del Tutto, S.R. Dennis, P. Detje, R. Diurba, Z. Djurcic, K. Duffy, S. Dytman, B. Eberly, P. Englezos, A. Ereditato, J.J. Evans, C. Fang, B.T. Fleming, W. Foreman, D. Franco, A.P. Furmanski, F. Gao, D. Garcia-Gamez, S. Gardiner, G. Ge, S. Gollapinni, E. Gramellini, P. Green, H. Greenlee, L. Gu, W. Gu, R. Guenette, L. Hagaman, M. D. Handley, O. Hen, A. Hergenhan, M. Harrison, S. Hawkins, C. Hilgenberg, G.A. Horton-Smith, A. Hussain, B. Irwin, M.S. Ismail, C. James, X. Ji, J.H. Jo, A. Johnson, R.A. Johnson, D. Kalra, G. Karagiorgi, W. Ketchum, A. Kelly, M. Kirby, T. Kobilarcik, K. Kumar, N. Lane, J.-Y. Li, Y. Li, K. Lin, B.R. Littlejohn, L. Liu, S. Liu, W.C. Louis, X. Luo, T. Mahmud, N. Majeed, C. Mariani, J. Marshall, D.A. Martinez Caicedo, F. Martinez Lopez, M. G. Manuel Alves, S. Martynenko, A. Mastbaum, I. Mawby, N. McConkey, B. McConnell, L. Mellet, J. Mendez, J. Micallef, T. Mohayai, A. Mogan, M. Mooney, A.F. Moor, C.D. Moore, L. Mora Lepin, M. A. Hernandez Morquecho, M.M. Moudgalya, S. Mulleria Babu, D. Naples, A. Navrer-Agasson, D. Nawarathne, N. Nayak, M. Nebot-Guinot, C. Nguyen, L. Nguyen, J. Nowak, N. Oza, O. Palamara, N. Pallat, V. Paolone, A. Papadopoulou, V. Papavassiliou, H. Parkinson, S.F. Pate, N. Patel, Z. Pavlovic, E. Piasetzky, K. Pletcher, I. Pophale, X. Qian, J.L. Raaf, V. Radeka, A. Rafique, M. Reggiani-Guzzo, J. Rodriguez Rondon, M. Ross-Lonergan, I. Safa, C. Sauer, D.W. Schmitz, A. Schukraft, W. Seligman, M.H. Shaevitz, R. Sharankova, L. Silva, E.L. Snider, S. Soldner-Rembold, J. Spitz, M. Stancari, J. St. John, T. Strauss, A.M. Szelc, K. Terao, C.Thorpe, D. Torbunov, D. Totani, M. Toups, A. Trettin, Y.-T. Tsai, J. Tyler, M.A. Uchida, T. Usher, B. Viren, M. L. Velazquez Fernandez, L. Wang, M. Weber, H. Wei, A.J. White, S. Wolbers, T. Wongjirad, K. Wresilo, W. Wu, E. Yandel, T. Yang, L.E. Yates, H.W. Yu, G.P. Zeller, J. Zennamo, C. Zhang, Y. Zhang

High Energy Physics (Experiment) · Cross-listed from hep-ph

Interpreting the High-Recoil LUX-ZEPLIN Event with Bino-/Singlino-like and Higgsino Dark Matter

Subhojit Roy, Pedro Schwaller and Carlos E. M. Wagner

The LUX-ZEPLIN (LZ) experiment has recently reported a nuclear-recoil candidate at $E_R\simeq248$ keV. We study two supersymmetric interpretations based on distinct neutralino couplings to the $Z$ boson. In the elastic case, a bino- or singlino-like neutralino scatters through a diagonal axial $Z$ coupling set by the Higgsino asymmetry $X=|N_{13}|^2-|N_{14}|^2$ rather than by the total Higgsino fraction. Since the spin-dependent blind spot does not coincide with the spin-independent one, Higgs-mediated scattering can be suppressed while retaining $X\sim10^{-2}$. In the MSSM this favors low $\tan\beta$, in tension with the observed Higgs mass for a few-TeV squark spectrum, a tension relieved by the tree-level quartic of the NMSSM. An explicit NMSSM benchmark with $m_\chi\simeq500$ GeV and $X\simeq0.007$, below current LZ limits, obtains its relic abundance from a singlet-like pseudoscalar resonance just above threshold, which also suppresses present-day annihilation. In the inelastic case, a pseudo-Dirac Higgsino scatters endothermically, with a splitting of a few hundred keV generated by gauginos at the PeV scale which can be lowered by opposite-sign bino-wino cancellation, or by weak singlino mixing; the minimal thermal realization is strongly constrained by solar-neutrino searches. The two mechanisms predict distinct recoil spectra away from the candidate.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

New Physics in $ b \to s \tau^+\tau^-$ Processes and Correlations with $R(D^{(*)})$ and $B\to K^{(*)}\nu\bar\nu$: An (SM)EFT Analysis

Guillermo Baltà, Andreas Crivellin, Joaquim Matias et al. (+1 more)

Tauonic flavour-changing neutral-current transitions ($b\to s\tau^+\tau^-$) are sensitive probes of New Physics connected to third-generation quarks and leptons. Motivated by the persistent anomalies in $R(D^{(*)})$ and the indications of enhanced $B^+\to K^{+}\nu\bar\nu$ rates, we revisit and update the predictions for $b\to s\tau^+\tau^-$ processes. Building upon a previous work on a data-driven approach to include the dominant $\psi(2S)$ resonances, we provide predictions for $B\to K^{(*)}\tau^+\tau^-$ ($B_s\to\phi\tau^+\tau^-$) over the full kinematic range. To include possible New Physics contributions within the Weak Effective Theory, we provide semi-analytic expressions for the corresponding branching ratios. We then perform a comprehensive dimension-6 SMEFT analysis of New Physics realised at the TeV scale. We identify regions of parameter space preferred by current data where the branching ratios of $b\to s\tau^+\tau^-$ processes can be enhanced by several orders of magnitude. While current experimental sensitivities remain far above the SM rates, the enhancements suggested by present flavour data imply that forthcoming limits from LHCb, CMS, and Belle~II will probe significant regions of the relevant SMEFT parameter space. Furthermore, we highlight that while different scenarios can lead to the same predictions for $B\to K^{(*)}\nu\bar\nu$ branching ratios, they can be disentangled by measuring $B\to K^{(*)}\tau^+\tau^-$, $B_s\to\tau^+\tau^-$ and $B_s\to\phi\tau^+\tau^-$.
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All authors Guillermo Baltà, Andreas Crivellin, Joaquim Matias, Martín Novoa-Brunet

High Energy Physics (Experiment) · Cross-listed from hep-ph

Production Shape Effects Beyond Rate Rescaling in Dark Photon Searches

X. Zhong, H.Y. Qiu and X.Q. Shen

Production model uncertainties in long-lived particle searches can affect both the inclusive yield and the kinematic distributions sampled by the experimental acceptance. We isolate the latter effect by comparing the modified Weizsäcker–Williams description with the effective quasireal approximation for dark photon production via proton bremsstrahlung after normalizing both spectra on a common physical domain. At fixed production yield within this domain, the resulting acceptance difference directly measures the departure from rate factorization. In the NA62 beam dump geometry, the central calculation gives a fractional acceptance shift $\delta_{\rm NF}>0.3$ at every numerically converged grid point within the displayed NA62 sensitivity overlap. This conclusion persists for effective QRA off-shell scales of 1.0, 1.5, and 2.0~GeV and under the aperture variations considered. Separately, the public NA62 full selection acceptances give a nonconstant dimuon acceptance ratio between the Mixing and Bremsstrahlung production categories, ranging from approximately 0.58 to 4.23, with a median absolute departure from unity of approximately 0.79 over the analyzed HEPData grid. This provides complementary evidence that the published full selection acceptance depends on the production category. More generally, the projection criterion provides a quantitative test of rate factorization. The normalized production shape variation must have negligible projection onto the acceptance response at the required accuracy. When this condition is not satisfied, production model dependence must be propagated through the acceptance calculation or treated as an acceptance uncertainty.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

PINNing the pion: conformal deep learning for $F_\pi(s)$ and the $(g-2)_\mu$ hadronic contribution

Mayank Goel, Subhadip Mitra and Monalisa Patra

Extracting the pion electromagnetic form factor $F_{\pi}(s)$ through phenomenological curve-fitting models introduces model dependence, unphysical artefacts, and kinematic inconsistencies. We introduce a Physics-Informed Neural Network (PINN) embedded in a conformal $z$-plane that constructs $F_{\pi}(s)$ directly from first principles across spacelike and timelike domains: charge normalisation and Schwarz reflection are enforced by construction, while Cauchy-Riemann analyticity, dispersion relations, Watson's theorem, and perturbative QCD asymptotics enter through the loss functional. Thus, the fundamental S-matrix principles dictate the form factor's behaviour while data act as constraints. Mapping the cut complex plane onto the unit disk bounds the Hessian norm and prevents Neural Tangent Kernel spectral starvation, two known failure modes of deep-learning optimisation. Besides $e^+e^-$ scattering data, we also incorporate $\tau$-decay data through a switch that isolates the pure isovector form factor natively, bypassing model-dependent isospin-breaking pre-corrections. The network organically yields an interior zero-free form factor, while the framework tests experimental tensions around the $\rho(770)$ peak against analyticity and dispersion constraints. We obtain model-independent estimates of the pion charge radius, $\langle r_{\pi}^2 \rangle = 0.435 \pm 0.008_{\text{stat}} \pm 0.007_{\text{cali}}$ fm$^2$, the second-sheet pole parameters, $m_{\rho}^{\text{pole}} = 761.72\pm 1.04$ MeV and $\Gamma_{\rho}^{\text{pole}} = 135.99 \pm 1.20$ MeV, and the two-pion contribution to the muon anomalous magnetic moment, $a_{\mu}^{\pi\pi} = (506.48 \pm 2.02_{\text{stat}} \pm 1.70_{\text{cali}}) \times 10^{-10}$.
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High Energy Physics (Experiment)

Non-parametric and continuous extraction of amplitudes in realistic electroweak penguin decays

Tingzhen Xiao, Anja Beck and Eluned Smith

A novel approach to extract decay amplitudes in $B\to V(\to M_1M_2)\ell^+\ell^-$ processes, where $V$ represents a meson with either $J = 0$ (S-wave) or $J = 1$ (P-wave), was recently proposed. In this method, the dependence of the amplitudes on the dihadron and dimuon invariant masses is extracted model-independently through a fit to the helicity angles and a subsequent calculation of sPlot weights. In this paper, we show that this method still performs well when applied to data with experimental realism, namely in the presence of detection efficiencies and background candidates, both of which can have non-factorising dependencies between the fitted helicity angles and extracted two-particle masses. We show that a non-factorising efficiency can be accommodated with a small change to the conventional calculation of the sPlot weights, and a non-factorising background by expanding the description of the background distribution into individually factorising terms. We illustrate the method using simulated $B\to K^+\pi^-\mu^+\mu^-$ data, containing both S- and P-wave contributions to the $K^+\pi^-$ system, mixed with non-factorising background candidates and generated with a realistic function for the detection efficiency. We also show that this method can be applied over a much larger dimuon invariant-mass range than studied previously. This work suggests that the method is suitable for application to real experimental data, where it could provide model-independent decay-amplitude shapes for direct comparison with theoretical predictions. A measurement using this technique can improve sensitivity to potential new-physics effects in $b\to s\ell\ell$ transitions, as well as the understanding of hadronic form factors, particularly in the S-wave system.
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High Energy Physics (Experiment)

Measurement of prompt and non-prompt ${\rm D}^{\rm *+}$-meson spin alignment in pp collisions at $\sqrt{s}$ = 13.6 TeV$

ALICE Collaboration

A precise measurement of prompt and non-prompt ${\rm D}^{\rm *+}$-meson spin alignment with respect to the helicity and production axes in proton-proton (pp) collisions at $\sqrt{s} = 13.6$ TeV is presented, using data collected with the ALICE experiment at the LHC. The spin alignment is quantified by measuring the diagonal spin density matrix element $\rho_{\rm 00}$ for ${\rm D}^{\rm *+}$ mesons at midrapidity ($|y|<0.8$). The measurement is performed in the transverse-momentum ($p_{\rm T}$) range $3<p_{\rm T}<100$ GeV/$c$ for prompt ${\rm D}^{\rm *+}$ mesons and $3<p_{\rm T}<30$ GeV/$c$ for non-prompt ${\rm D}^{\rm *+}$ mesons, respectively. The measured $\rho_{\rm 00}$ values for prompt ${\rm D}^{\rm *+}$ mesons are consistent with the unpolarised expectation of $1/3$ over the entire $p_{\rm T}$ range, indicating no evidence of spin alignment. In contrast, $\rho_{\rm 00}$ of non-prompt ${\rm D}^{\rm *+}$ mesons exhibit a deviation from $1/3$, consistent with expectations from weak beauty-hadron decays and well described by PYTHIA 8 simulations coupled with the EvtGen decay package. These results confirm and extend previous measurements, providing a precise baseline for future studies of ${\rm D}^{\rm *+}$ spin alignment in heavy-ion collisions.
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High Energy Physics (Experiment)

Measurement of the triple-differential cross section of Z+jet production in proton-proton collisions at $\sqrt{s}$ = 13 TeV

CMS Collaboration

A measurement is presented of the triple-differential production cross section of Z/$\gamma^*$($\to$ $\mu\mu$)+jet events using proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the CMS experiment at the CERN LHC. The data, collected in the years 2016$-$2018, correspond to an integrated luminosity of 138 fb$^{-1}$. The cross section is measured as a function of the transverse momentum of the muon pair, the boost in rapidity of the center-of-mass system of the muon pair and the leading jet with respect to the laboratory frame, and half of their absolute rapidity separation. This choice of observables ensures sensitivity to the scattering angle in the center-of-mass frame and the fractional momenta of the interacting partons. After unfolding for detector effects in all three dimensions simultaneously, the results are compared with predictions at next-to-next-to-leading order in perturbative quantum chromodynamics corrected for electroweak and nonperturbative effects. This measurement provides valuable information towards characterizing the partonic structure of the proton and determining the strong coupling.
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High Energy Physics (Experiment) · Cross-listed from gr-qc

Neutrino Oscillations without Mass: A Re-analysis of KamLAND Data following the Dirac Equation in Curved Spacetime

Golam Mortuza Hossain and Pushpit Kumar

The Dirac equation in stationary curved spacetime implies that describing two-flavor neutrino oscillations requires treating the invariant mass and conserved energy of each propagating state distinctly, as gravity affects energy differently than mass. By re-analysing the publicly released KamLAND dataset, we show that modeling flavor states of massless neutrinos as two-level quantum states with energy-dependent level splitting, analogous to modified Jaynes-Cummings models, results in a higher-likelihood fit to the observed data than the standard massive-neutrino paradigm.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Supermassive charged gravitinos and the Lux-Zeplin event

Krzysztof A. Meissner and Hermann Nicolai

The Lux-Zeplin collaboration recently reported one unusual event which was interpreted as first evidence for a WIMP (arXiv:2609.02823[hep-ex]). In this note we offer an alternative explanation of this event, following our earlier proposal that dark matter could consist of fractionally charged supermassive gravitinos. A main difference between the two interpretations is that one expects small cross sections and large flux rates for WIMPs, whereas it is the opposite for supermassive gravitinos, namely large (electromagnetic) cross sections and very low flux rates. The observed nuclear recoil energy of about 250 keV and the occurrence of one event in one year fit well with the estimates quoted in (K.A. Meissner, H.~Nicolai, Eur.Phys.J.C 84 (2024) 3, 269). A main characteristic of the new interpretation distinguishing it unequivocally from the WIMP hypothesis would be the sequential occurrence of two or more recoils within a few microseconds along the gravitino's straight trajectory, a prediction that remains to be checked. Such a measurement would also allow to overcome the `neutrino floor'. In this note we refine our previous estimates and propose some extra steps so as to enable the experiment to discriminate between the WIMP and gravitino hypotheses.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Exclusive production of $\pi^+ \pi^-$ pairs in diffractive $\gamma p$ and in $pp$ collisions within the tensor-pomeron approach

Piotr Lebiedowicz, Otto Nachtmann and Antoni Szczurek

We discuss exclusive production of $\pi^+ \pi^-$ pairs in diffractive $\gamma p$ and in $pp$ collisions at high energies, considering resonant ($\rho(770)$, $\omega$, $f_2(1270)$) and non-resonant (Drell-Söding) contributions within the tensor-pomeron approach. For the $\gamma p \to \pi^+ \pi^- p$ reaction, the model describes well the H1 data in the region $M_{\pi \pi} \lesssim 1.2$ GeV. We discuss the important role of the Drell-Söding mechanism in shaping the resonance line. We also predict differential cross sections for the $pp \to pp \pi^+ \pi^-$ reaction at $\sqrt{s} = 13$ TeV where at least one proton emits a virtual photon. These findings are relevant for the central exclusive production of $\pi^+ \pi^-$ pairs in the context of ALICE, ATLAS, CMS, and LHCb measurements in hadron-hadron collisions at the LHC, especially under experimental selections using only rapidity-gap conditions. Additionally, our results are also applicable to $\pi^+ \pi^-$ production in ultraperipheral $p$A/AA collisions at the LHC and to photo- and electroproduction of $\pi^+ \pi^-$ at future electron-proton/ion colliders (EIC, LHeC).
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High Energy Physics (Experiment) · Cross-listed from nucl-ex

Probing jet quenching via the correlation of groomed jet substructure observables in Pb$-$Pb and pp collisions

ALICE Collaboration

A measurement of the correlation between the splitting angle $\theta_{\rm g}$ and the momentum-sharing fraction $z_{\rm g}$ of the first hard splitting in a parton shower in pp collisions and 0$-$10% central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5 TeV with the ALICE detector is reported. Charged-particle jets are reconstructed using the anti-$k_{\rm T}$ algorithm with a jet resolution parameter $R$ = 0.2, in the transverse-momentum range $60 \leq p_{\rm T,ch\;jet} < 80$ GeV/$c$. The Soft Drop grooming algorithm is used to identify the first splitting in the parton shower. Jets observed in Pb$-$Pb collisions are narrower than in pp collisions. This effect is more pronounced for balanced than for unbalanced jets. No significant modification of the momentum-sharing fraction is observed for jets with small opening angles. In contrast, there is a hint that jets with a large opening angle may be less balanced in transverse momentum in Pb$-$Pb collisions compared to pp collisions. The correlations between $\theta_{\rm g}$ and $z_{\rm g}$ are well described in pp collisions by PYTHIA 8 and POWHEG while HERWIG shows too few jets with large opening angle. In Pb$-$Pb collisions the measurement is compared to a variety of models. The measurement is insensitive to the different implementations of medium response. Inclusion of elastic scatterings, as implemented in the HYBRID model is preferred to describe the unbalanced jets with large $\theta_{\rm g}$ in Pb$-$Pb collisions. The balanced jets, however, are less sensitive to elastic scatterings.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Central exclusive production of $\eta$ and $\eta'$ mesons in diffractive proton-proton collisions at the LHC

Piotr Lebiedowicz, Otto Nachtmann and Antoni Szczurek

We discuss central exclusive production (CEP) of $\eta$ and $\eta'(958)$ mesons in high-energy proton-proton collisions using the tensor-pomeron approach, incorporating absorption effects at the amplitude level. Model parameters are constrained using WA102 experimental data measured at $\sqrt{s} = 29.1$ GeV. We present cross sections and differential distributions for the LHC energy of $\sqrt{s} = 13$ TeV. For $pp \to pp \eta$, the upper limit of the total cross section is 2.5 $\mu$b for $|\eta_{M}| < 1$ and 5.6 $\mu$b for $2 < \eta_{M} < 5$. For $pp \to pp \eta'$, the predicted cross sections are 0.3–0.7 $\mu$b and 0.9–2.1 $\mu$b in the respective pseudorapidity regions. These results demonstrate the feasibility of studying diffractive flavour singlet pseudoscalar meson production to probe the nature of the pomeron at the LHC.
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High Energy Physics (Experiment) · Cross-listed from physics.ins-det

Measurement of the $^{39}$Ar specific activity in atmospheric argon with DArT at the Canfranc Underground Laboratory

P. Agnes, H. O. Back, S. Bharat et al. (+41 more)

We report the measurement of the $^{39}$Ar specific activity of atmospheric argon using DArT, a low-background single-phase liquid-argon detector read out by cryogenic silicon photomultipliers, at the Canfranc Underground Laboratory (LSC) in Spain. DArT was first filled with atmospheric argon and then with a sample of underground argon of known radioactivity from the DarkSide-50 experiment. The underground argon serves as a background reference in this measurement, making the result robust because we do not rely on background simulations. We measure the $^{39}$Ar specific activity with both a cut-and-count method and a binned maximum-likelihood fit, yielding consistent results. We obtain $a_{\text{AAr}}= 0.955 \pm 0.008~\text{Bq}/\text{kg}$. This result agrees with previous measurements from other experiments and provides the most precise determination of the $^{39}$Ar specific activity in atmospheric argon to date. It also validates DArT as a key component of the DArTInArDM experiment at LSC, which aims to measure the $^{39}$Ar activity of the argon extracted from deep underground wells in Colorado (USA) for the Darkside-20k and LEGEND-1000 experiments at Laboratori Nazionali del Gran Sasso in Italy.
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All authors P. Agnes, H. O. Back, S. Bharat, W. M. Bonivento, M. Boulay, M. Caboni, N. Canci, N. Cargioli, P. Castello, S. Cebrián, L. Consiglio, R. Crampton, D. Diaz Mairena, D. Franco, I. Fuente-Ortega, F. Gabriele, D. Gahan, C. Galbiati, P. Garcia Abia, T. Hessel, S. Horikawa, A. Ianni, G. Korga, M. Kuźniak, L. Luzzi, A. Marasciulli, M. Martínez, P. Organtini, A. Ortiz de Solórzano, R. Pavarani, P. Pegoraro, V. Pesudo Fortes, M. Razeti, O. U. Rehman, L. Romero, D. Sablone, E. Sánchez García, R. Santorelli, C. Seoane, J. Sosiak, S. Sulis, C. Tierney, S. Tullio, G. Vera Díaz

High Energy Physics (Experiment)

Projected Sensitivity to Atmospheric Neutrino Oscillations using a 1725 m$^{3}$ Liquid-Nitrogen Detector at CJPL

Xiao-Yu Peng, Shin-Ted Lin, Shu-Kui Liu et al. (+7 more)

In atmospheric neutrino analyses, the usable zenith-angle range is generally restricted to upward-going events to suppress the cosmic-ray muon background. Motivated by the exceptionally low underground muon background at the China Jinping Underground Laboratory (CJPL), we investigate whether extending the zenith-angle acceptance can improve the sensitivity of atmospheric neutrino oscillation measurements. An existing 1725 m$^{3}$ liquid-nitrogen volume is adopted as the basis of a simplified detector model, in which the accepted zenith-angle range is extended from $\cos\theta_{\mu}\in[-1,0]$ to $\cos\theta_{\mu}\in[-1,0.3]$, and the projected oscillation sensitivity is evaluated for a 10-year exposure. The atmospheric neutrino flux is estimated by interpolating standard flux predictions as a function of geomagnetic latitude. Neutrino interactions in the surrounding rock and the liquid-nitrogen volume are simulated for neutrino energies of $E\ge0.1$ GeV, followed by secondary-particle transport and geometry-based event selection. For the benchmark oscillation parameters $\Delta$m$^{2}_{32}$ = $2.4\times10^{-3}\ \mathrm{eV}^{2}$ and $\sin^{2}\theta_{23}=0.5$, the neutrino-induced muon flux from the surrounding rock is estimated to be $(3.65 \pm 1.00)\times10^{-13}$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$, corresponding to a muon yield of $(0.13 \pm 0.034)$ day$^{-1}$ in the 1725 m$^{3}$ liquid-nitrogen volume. Three-flavor neutrino oscillations are incorporated into a Poisson-likelihood $\chi^{2}$ analysis to evaluate the sensitivity to the oscillation parameters. Extending the usable zenith-angle range leads to a clear improvement in the projected oscillation sensitivity at the 90% confidence level over a 10-year exposure.
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All authors Xiao-Yu Peng, Shin-Ted Lin, Shu-Kui Liu, Hao-Yang Xing, Jing-Jun Zhu, Han-Yu Li, Bi-Jun Xiao, Li-Tao Yang, Qian Yue, Muhammed Deniz

High Energy Physics (Experiment)

Particle track reconstruction in high-density collider environments with an Evolving-Geometry Transformer

Chenxiu Ou, Yan Wang, Mingjiang Liang et al. (+3 more)

Charged particle track reconstruction at the High-Luminosity Large Hadron Collider is challenged by dense hit environments and combinatorial ambiguities. Existing graph-based and Transformer approaches commonly rely on static geometric neighbourhoods, which cannot adapt as track-level representations evolve. We propose the Evolving-Geometry Transformer (EGT), a graph Transformer that reconstructs the hit-connectivity graph at successive encoder layers and incorporates relative hit coordinates as learnable attention biases. Across five simulation benchmarks spanning linear, helical, and reduced TrackML events with up to 200–500 simultaneous trajectories, EGT achieves the highest FitAccuracy on three of five settings under the shared benchmark protocol, reaching 79.6% on the most complex setting and exceeding the strongest baseline by 1.6 percentage points. Replacing the evolving topology with a static graph reduces the perfect-track rate from 81% to 29%, while removing the geometric bias reduces it to 73%. Under synthetic background injection equal to the number of signal hits, FitAccuracy decreases by 3.4 percentage points. The neural-network forward pass requires 31~ms per event on an NVIDIA A100 GPU. These results indicate that iterative refinement of hit associations improves complete-track recovery when local geometry alone is insufficient to determine trajectory membership.
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All authors Chenxiu Ou, Yan Wang, Mingjiang Liang, Man-Hong Yung, Qin Zhang, Zhaofeng Su

Tuesday 29 September

High Energy Physics (Experiment) · Cross-listed from cs.LG

Beyond a Better Score: Long-Horizon Agentic ML Development and Evaluation Protocol for Physics Time Series

Yue Ma, Lucas Venetoulias, Akbota Assan et al. (+1 more)

Physics time-series data are central to fundamental discoveries involving dark matter, neutrinos, and gravitational waves. Machine learning has shown strong potential to recover weak scientific signals buried in complex noise. Recent LLM-agent systems further automate ML development, but existing approaches are often driven primarily by one or a few numerical scores. In pursuit of a better score, agents may exploit shortcuts, trigger mode collapse, or game the evaluation procedure, producing models that achieve high scores but are scientifically invalid. We introduce SIDERIUS, an LLM agent system designed to move beyond a better score toward scientifically valid, long-horizon ML development. SIDERIUS combines contract-defined composable capabilities for flexible orchestration and human-in-the-loop, a multi-layer scientific evaluation protocol that distinguishes valid models from unhealthy or gaming models, and resource-aware exploration for computationally expensive scientific ML. In our TIDMAD benchmark, SIDERIUS with a GPT-based orchestrator achieves the highest Valid-model proposal rate of 63.8% and the best valid denoising score of 2.744, compared with 1.6% and -0.647, respectively, for the same GPT model using the general-purpose Codex coding agent. We further benchmark SIDERIUS on three additional physics time-series datasets, demonstrating its reuse and performance across different tasks. Together, these results suggest that progress in agentic scientific ML should be measured beyond a better score, by how an agent explores and by whether the models it produces can be trusted as science.
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All authors Yue Ma, Lucas Venetoulias, Akbota Assan, Aobo Li

High Energy Physics (Experiment) · Cross-listed from nucl-th

Nuclear Deep Inelastic Scattering around $x=0.3$

S.A. Kulagin and R. Petti

Deep-inelastic scattering (DIS) data on nuclei, from deuterium to lead, indicate that nuclear effects on the partonic structure of bound nucleons are remarkably small around $x=0.3$, where valence-quark distributions peak. We present the results of a global analysis of DIS data on the cross-section ratios $\sigma^A/\sigma^{{}^2\text{H}}$ in the range $0.25 \leq x \leq 0.35$, revealing a remarkable cancellation of nuclear effects across the entire range of nuclear targets. We also discuss the interpretation of such an observation within a microscopic model of nuclear modifications of the structure functions.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

QCD corrections to light-quark dipole sensitivity via transverse spin asymmetries at the Electron-Ion Collider

Sally Dawson and Zhite Yu

We consider the effects of next-to-leading order (NLO) QCD corrections to transverse spin asymmetries (TSAs) in deep inelastic scattering at the future Electron-Ion Collider (EIC) with polarized electron and proton beams that depend on light quark dipole operators. The TSAs are robust under the inclusion of the NLO QCD effects and provide sensitivity to new physics that is complementary to limits extracted from the Drell-Yan measurements at the LHC and from neutron electric dipole moments. The major uncertainty on our results is from the poor existing determination of the transversity parton distribution function for the down quark. Interesting relations from parity and time reversal invariance, along with chiral symmetry, constrain the analytic form of the TSAs.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Constraints on Complex Electroweak WIMPs from Solar Capture

Juan P. Luengas, Maxim Pospelov and Harikrishnan Ramani

One of the most convincing realizations of particle dark matter is provided by models based on electroweak multiplets. The lightest neutral state of such a multiplet can be a stable Majorana fermion or a real scalar, and its phenomenology is governed by two parameters: the dark matter mass and the mass splitting $\{m_\chi,\delta\}$. The sub-MeV range for $\delta$ is particularly important as it allows for a large inelastic scattering cross section. In this paper, we analyze solar capture, energy loss, and annihilation of scalar and fermionic electroweak multiplet dark matter, generalizing earlier results for the Higgsino to other representations. We find that, while the case of a doublet is somewhat special, higher representations behave in a self-similar way. For the higher multiplets, IceCube results constrain the splitting to $\delta \gtrsim 350$ keV for all dark matter masses up to $100$ TeV. Assuming thermal freeze-out and a Standard Halo Model velocity distribution, this rules out most models of electroweak dark matter as a possible origin of the single high-recoil event reported by the LZ collaboration. We also show that a high-velocity tail in the dark matter distribution, such as that induced by the Large Magellanic Cloud, raises the splitting preferred by the LZ event above the solar bounds for many of the multiplets.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Searching for BSM Experimental Signatures with Large Lagrangian Models

Ibrahim Elsharkawy, Victoria Knapp-Perez, Wahid Bhimji et al. (+1 more)

The search for physics Beyond the Standard Model (BSM) is generally limited not by the supply of theory descriptions but by the lack of discriminating experimental observations. A case in point is dark matter, where the overwhelming gravitational evidence only goes so far in distinguishing between models within a vast theory space. Exploring the space of testable model signatures may help identify overlooked experimental observables and indicate the utility of future experiments. A challenge is designing a search through model signatures outside what is found in the literature. Our primary contribution is hAIthem, a framework that combines the self-guided exploration of reinforcement learning (RL) with the broad literature-derived knowledge of LLMs. We build an RL agent that learns to find which portions of a theory's high-dimensional parameter space are not excluded under some subset of constraints by playing a Battleship-style "game" against a suite of phenomenology tools. The agent is built as a Large Lagrangian Model (LLaM), an autoregressive transformer that reads a tokenized Lagrangian, is pretrained at scale (here on ~1 billion tokens from ~10,000 Lagrangians), and is fine-tuned in a live environment. The framework then constructs a decision tree that separates RL-found regions using observables computed with established tools, and passes the remaining degenerate regions to a set of LLM agents that compete to produce realistic signatures. In this proof of concept, RL-search outperforms an evolutionary-algorithm baseline, finding more viable regions with greater physical diversity. In a restricted space of single dark scalar multiplet models, we find that hAIthem proposes interesting combinations of previously studied observables, such as the application of a halo-independent kinematic ratio to paleo-detectors.
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All authors Ibrahim Elsharkawy, Victoria Knapp-Perez, Wahid Bhimji, Aishik Ghosh

High Energy Physics (Experiment)

Overview of the HL-LHC CMS outer tracker upgrade and lessons learned from 2S module production

F. Zhang

For operation at the High-Luminosity LHC, the CMS collaboration is developing a significantly enhanced silicon detector system with improved radiation hardness, higher granularity, and extended coverage up to a pseudorapidity of $|\eta|\approx$ 4. The Outer Tracker will be equipped with two types of modules (2S and PS) that will provide tracking information to the L1 trigger of the HL-LHC CMS detector, by rejecting signals from particles below a certain transverse momentum threshold. Hence, these modules must be assembled with high precision and have to pass strict requirements. In this note, an overview of 2S module production is presented, as well as representative examples of problems and experience acquired during module assembly and performance tests.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

The new LHCb beauty-strange state as the bottom partner of the $D_{s0}^*(2317)$: a LQCD constrained coupled-channel chiral analysis

Miguel Albaladejo, Pablo Encarnación, Albert Feijoo et al. (+1 more)

The LHCb Collaboration has observed a narrow state in the $\bar{B}_s^0\pi^0$ spectrum, about 74 MeV below the $B^-K^+$ threshold, which is the natural candidate for the bottom partner of the $D_{s0}^*(2317)$. Such a state had been predicted as a $\bar{B}K$ bound state by unitarized heavy-meson chiral perturbation theory with lattice-QCD input. We analyze the LHCb spectrum with these coupled-channel amplitudes, including isospin breaking through the physical meson masses, $\pi^0$-$\eta$ mixing, and $m_u\neq m_d$ in the chiral amplitudes, thereby allowing the $\bar{B}_{s0}^*$ to decay through its only open strong channel, $\bar{B}_s^0\pi^0$. With the parameters fixed by lattice QCD and no experimental input from the LHCb measurement, the predicted state lies within 1.1-1.7 standard deviations of the observed peak. Adjusting a single parameter, the spectrum is described as well as with the zero-width limit of the LHCb analysis. The new state thus emerges naturally from these amplitudes, with a large $\bar{B}K$ component and an isospin-violating width of tens of keV, and its $J^P=1^+$ heavy-quark spin partner is predicted with a precision comparable to that of the measured mass.
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All authors Miguel Albaladejo, Pablo Encarnación, Albert Feijoo, Juan M. Nieves

High Energy Physics (Experiment)

Search for $\boldsymbol{\pi_1(1600)}$ in a three-pion system at GlueX

Ilia Belov and Farah Afzal

The GlueX experiment in Hall D at Jefferson Lab enables studies of the light meson spectrum in $\gamma p$ interactions with a linearly polarized photon beam. GlueX aims in particular to search for hybrid mesons that have exotic quantum numbers and therefore cannot be classified as conventional hadrons. We present the search for the $\pi_1(1600)$ meson by means of a partial-wave analysis of the $\pi^{+}\pi^{-}\pi^{-}$ system produced off the $\Delta^{++}$-baryon. Data with the selected three-pion final state are fitted in bins of $m_{3\pi}$ as coherent sums of partial-wave amplitudes defined in the reflectivity basis. The properties of $a_{2}^{-}(1320)$ production are investigated through the extracted signal in the $\rho\,\pi^{-}$ $D$-waves. In this analysis, the overall $m_{3\pi}$ lineshape will be extracted for each of the model contributions. The main interest lies in establishing the existence of a resonant $1^{-+}$ contribution in the $\rho\,\pi^{-}$ $P$-wave configuration.
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