New articles on High Energy Physics - Experiment

[1] 2407.14669

Measurement of azimuthal modulations in SIDIS off proton target at COMPASS

The azimuthal angle ($\phi_h$) distribution of hadrons produced in deep inelastic scattering serves as a powerful tool for probing the nucleon structure in terms of transverse momentum dependent parton distribution functions and fragmentation functions. For an unpolarized nucleon, three azimuthal modulations arise: $\cos\phi_h$ related to the Cahn effect, $\cos2\phi_h$ linked to the Boer--Mulders function, and $\sin\phi_h$ known as beam-spin asymmetry, each revealing insights into combinations of twist-two or higher-twist distribution and fragmentation functions. The COMPASS collaboration at CERN collected semi-inclusive deep inelastic scattering events in 2016 and 2017 using a longitudinally polarized 160 GeV/$c$ muon beam scattering off a liquid hydrogen target. Data from 2016 corresponding to about 1/3 of the full sample have been analyzed to measure the azimuthal modulations of charged hadrons. For the first time, the results were corrected for QED radiative effects using the DJANGOH MC generator.

[2] 2407.14704

Reactor-based Search for Axion-Like Particles using CsI(Tl) Detector

Null results for WIMP dark matter have led to increased interest in exploring other dark matter candidates, such as Axions and Axion-Like Particles (ALPs), which also helps in answering the strong CP problem. This experiment achieved a sub-100 DRU (differential-rate-unit, expressed in counts/keV/kg/day) background in the MeV region of interest by employing a combination of active and passive veto techniques. Such a low background facilitates the search for ALPs with axion-photon coupling $g_{a\gamma \gamma} > 10^{-6}$ and axion-electron coupling $10^{-8}< g_{aee} < 10^{-4}$ in the 1 keV to 10 MeV mass range. This indicates that the experiment has the capability to constrain the unexplored cosmological triangle in the ALP-photon parameter space for ALPs in the MeV mass range.

[3] 2407.15140

Measurement of the $e^+e^-\to K_SK_L$ cross section near the $φ(1020)$ resonance with the SND detector

The cross section for the $e^+e^-\to K_SK_L$ process is measured in the center-of-mass energy range from 1000 MeV to 1100 MeV in the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measurement is carried out in the $K_S\to 2\pi^0$ decay mode. Data with an integrated luminosity of 20 pb$^{-1}$ recorded in 2018 at 18 energy points are used in the analysis. The systematic uncertainty in the measured cross section at the maximum of the $\phi$ resonance is 0.9%. The mass, width of the $\phi$ meson, and the product of the branching fractions $B(\phi\to K_SK_L)B(\phi\to e^+e^-)$ are determined from the fit to the cross-section energy dependence.

[4] 2407.15172

Search for flavor-changing neutral current interactions of the top quark mediated by a Higgs boson in proton-proton collisions at 13 TeV

A search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on proton-proton collision data collected in 2016-2018 at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and corresponding to an integrated luminosity of 138 fb$^{-1}$. Events containing a pair of leptons with the same-sign electric charge and at least one jet are considered. The results are used to constrain the branching fraction ($\mathcal{B}$) of the top quark decaying to a Higgs boson and an up (u) or charm (c) quark. No significant excess above the estimated background was found. The observed (expected) upper limits at 95% confidence level are found to be 0.072% (0.059%) for $\mathcal{B}$(t $\to$ Hu) and 0.043% (0.062%) for $\mathcal{B}$(t $\to$ Hc). These results are combined with two other searches performed by the CMS Collaboration for flavor-changing neutral current interactions of top quarks and Higgs bosons in final states with a pair of photons or of bottom quarks. The resulting observed (expected) upper limits at 95% confidence level are 0.019% (0.027%) for $\mathcal{B}$(t $\to$ Hu) and 0.037% (0.035%) for $\mathcal{B}$(t $\to$ Hc). These results constitute the most stringent limits on these branching fractions to date.

[5] 2407.15308

Cross section of the process $e^+e^-\to n\bar{n}$ near the threshold

The $e^+e^-\to n\bar{n}$ cross section was measured at center of mass (c.m.) energies from the threshold to 1908 MeV. The experiment to measure the cross section has been carried out at the VEPP-2000 $e^+e^-$ collider in 13 energy points. The SND detector is used to detect the produced neutron-antineutrons ($n\bar{n}$) events. A special time measurement system on the calorimeter was used to select the time-delayed $n\bar{n}$ events. The measured $e^+e^-\to n\bar{n}$ cross section is 0.4--0.6 nb. The neutron effective timelike form factor in the energy range under study varies from 0.3 to 0.6.

[6] 2407.15550

Search for the associated production of charm quarks and a Higgs boson decaying into a photon pair with the ATLAS detector

A search for the production of a Higgs boson and one or more charm quarks, in which the Higgs boson decays into a photon pair, is presented. This search uses $\sqrt{s}=13$ TeV proton-proton collision data with an integrated luminosity of 140 fb$^{-1}$ recorded by the ATLAS detector at the Large Hadron Collider. The analysis relies on the identification of charm-quark-containing jets, and adopts an approach based on Gaussian process regression to model the non-resonant di-photon background. The observed (expected, assuming the Standard Model signal) upper limit at the 95% confidence level on the cross-section for producing a Higgs boson and at least one charm quark is found to be 10.4 pb (8.6 pb). The observed (expected) measured cross-section for this process is $5.2 \pm 3.0 ~\text{pb}$ ($2.9 \pm 2.8 ~\text{pb}$).

[7] 2407.15594

Measurement of single top-quark production in association with a $W$ boson in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

The inclusive cross-section for the production of a single top quark in association with a $W$ boson is measured using 140 fb$^{-1}$ of proton$-$proton collision data collected with the ATLAS detector at $\sqrt{s} = 13$ TeV. Events containing two charged leptons and at least one jet identified as originating from a $b$-quark are selected. A multivariate discriminant is constructed to separate the $tW$ signal from the $t\bar{t}$ background. The cross-section is extracted using a profile likelihood fit to the signal and control regions and it is measured to be $\sigma_{tW} = 75^{+15}_{-14}$ pb, in good agreement with the Standard Model prediction. The measured cross-section is used to extract a value for the left-handed form factor at the $Wtb$ vertex times the CKM matrix element $|f_\text{LV}V_{tb}|$ of $0.97 \pm 0.10$.

[8] 2407.15627

A precise measurement of the jet energy scale derived from single-particle measurements and in situ techniques in proton-proton collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector

The jet energy calibration and its uncertainties are derived from measurements of the calorimeter response to single particles in both data and Monte Carlo simulation using proton-proton collisions at $\sqrt{s} = 13$ TeV collected with the ATLAS detector during Run 2 at the Large Hadron Collider. The jet calibration uncertainty for anti-k$_t$ jets with a jet radius parameter of $R = 0.4$ and in the central jet rapidity region is about 2.5% for transverse momenta ($p_T$) of 20 GeV, about 0.5% for $p_T = 300$ GeV and 0.7% for $p_T = 4$ TeV. Excellent agreement is found with earlier determinations obtained from $p_T$-balance based in situ methods ($Z/\gamma$+jets). The combination of these two independent methods results in the most precise jet energy measurement achieved so far with the ATLAS detector with a relative uncertainty of 0.3% at $p_T = 300$ GeV and 0.6% at $4$ TeV. The jet energy calibration is also derived with the single-particle calorimeter response measurements separately for quark- and gluon-induced jets and furthermore for jets with $R$ varying from 0.2 to 1.0 retaining the correlations between these measurements. Differences between inclusive jets and jets from boosted top-quark decays, with and without grooming the soft jet constituents, are also studied.

[9] 2407.14548

Triply charm and bottom tetraquarks in a constituent quark model

Recently, the singly, doubly and fully charmed tetraquark candidates, $T_{c\bar{s}}(2900)$, $T^+_{cc}(3875)$ and $X(6900)$ are experimentally reported by the LHCb collaboration. Hence, it is quite necessary to implement a theoretical investigation on the triply heavy tetrquarks. In this study, the S-wave triply charm and bottom tetraquarks, $\bar{Q}Q\bar{q}Q$ $(q=u,\,d,\,s;\,Q=c,\,b)$, with spin-parity $J^P=0^+$, $1^+$ and $2^+$, isospin $I=0$ and $\frac{1}{2}$ are systematically studied in a constituent quark model. Particularly, a complete S-wave tetraquark configurations, which include the meson-meson, diquark-antidiquark and K-type arrangements of quarks, along with all allowed color structures, are comprehensively considered. A high accuracy and efficient computational approach, the Gaussian expansion method (GEM), in cooperation with a powerful complex-scaling method (CSM), which is quite ingenious in dealing with the bound and resonant state of a multiquark system simultaneously, are adopted in solving the complex scaled Schr\"odinger equation. This theoretical framework has already been successfully applied in various tetra- and penta-quark systems. Bound state of triply heavy tetraquark system is unavailable in our study, nevertheless, in a fully coupled-channel calculation by the CSM, several narrow resonances are found in each $I(J^P)$ quantum states of the charm and bottom sector. In particular, triply charm and bottom tetraquark resonances are obtained in $5.59-5.94$ GeV and $15.31-15.67$ GeV, respectively. Compositeness of exotic states, such as the inner quark distance, magnetic moment and dominant component, are also analyzed. These exotic hadrons in triply heavy sector are expected to be confirmed in future high energy experiments.

[10] 2407.14585

Strong CP and Flavor in Multi-Higgs Theories

We introduce a class of multi-Higgs doublet extensions of the Standard Model that solves the strong CP problem with profound consequences for the flavor sector. The Yukawa matrices are constrained to have many zero entries by a "Higgs-Flavor" symmetry, $G_{\rm HF}$, that acts on Higgs and quark fields. The violation of both CP and $G_{\rm HF}$ occurs in the Higgs mass matrix so that, for certain choices of $G_{\rm HF}$ charges, the strong CP parameter $\bar{\theta}$ is zero at tree-level. Radiative corrections to $\bar{\theta}$ are computed in this class of theories. They vanish in realistic two-Higgs doublet models with $G_{\rm HF} = \mathbb{Z}_3$. We also construct realistic three-Higgs models with $G_{\rm HF} = \rm U(1)$, where the one-loop results for $\bar{\theta}$ are model-dependent. Requiring $\bar{\theta}< 10^{-10}$ has important implications for the flavor problem by constraining the Yukawa coupling and Higgs mass matrices. Contributions to $\bar{\theta}$ from higher-dimension operators are computed at 1-loop and can also be sufficiently small, although the hierarchy problem of this class of theories is worse than in the Standard Model.

[11] 2407.14648

Exotic Particles at the DUNE Near Detector from Charged Pion Scattering

Fixed-target proton-beam experiments produce a multitude of charged pions that rescatter in the beam dump. These charged pion scattering events can be an additional irreducible source of exotic particles which couple to photons or hadrons. We analyze the sensitivity of the DUNE Near Detector complex to millicharged particles (MCPs) and heavy axion-like particles (ALPs) with low-energy couplings to gluons. Using the framework of chiral perturbation theory, we demonstrate regimes of parameter space where the charged pion production channel dominates over previously-considered production mechanisms for both MCPs and ALPs, thereby improving the sensitivity of DUNE to these new particles compared to previous studies.

[12] 2407.14673

Constraints on light dark sector particles from lifetime difference of heavy neutral mesons

Heavy meson decays with missing energy in the final state offer interesting avenues to search for light invisible new physics such as dark matter (DM). In this context, we show that such NP interactions also affect lifetime difference in neutral meson-antimeson mixing. We consider general dimension-six effective quark interactions involving a pair of DM particles and calculate their contributions to lifetime difference in beauty and charm meson systems. We use the latest data on mixing observables to constrain the relevant effective operators. We find that lifetime differences provide novel and complementary flavor constraints compared to those obtained from heavy meson decays.

[13] 2407.14716

Improved constraint on Higgs boson self-couplings with quartic and cubic power dependence in the cross section

Precise information on the Higgs boson self-couplings provides the foundation for unveiling the electroweak symmetry breaking mechanism. Due to the scarcity of Higgs boson pair events at the LHC, only loose limits have been obtained. This is based on the assumption that the cross section is a quadratic function of the trilinear Higgs self-coupling in the $\kappa$ framework. However, if higher-order corrections of virtual Higgs bosons are included, the function form would dramatically change. In particular, new quartic and cubic power dependence on the trilinear Higgs self-coupling would appear. To get this new function form, we have performed a specialized renormalization procedure suitable for tracking all the Higgs self-couplings in each calculation step. Moreover, we introduce renormalization of the scaling parameter in the $\kappa$ framework to ensure the cancellation of all ultraviolet divergences. With the new function forms of the cross sections in both the gluon-gluon fusion and vector boson fusion channels, the upper limit of $\kappa_{\lambda_3}=\lambda_{\rm 3H}/\lambda_{\rm 3H}^{\rm SM}$ by the ATLAS (CMS) collaboration is reduced from 6.6 (6.49) to 5.4 (5.37). However, it is still hard to extract a meaningful constraint on the quartic Higgs self-coupling $\lambda_{\rm 4H}$ from Higgs boson pair production data. We also present the invariant mass distributions of the Higgs boson pair at different values of $\kappa_{\lambda}$, which could help to set optimal cuts in the experimental analysis.

[14] 2407.14821

Energy Dependence of Polarized $\mathbf{γγ\rightarrow e^{+}e^{-}}$ in Peripheral Au+Au Collisions at RHIC

We report the differential yields at mid-rapidity of the Breit-Wheeler process ($\gamma\gamma\rightarrow e^{+}e^{-}$) in peripheral Au+Au collisions at $\sqrt{s_{_{\rm{NN}}}} = $ 54.4 GeV and 200 GeV with the STAR experiment at RHIC, as a function of energy $\sqrt{s_{_{\rm{NN}}}}$, $e^{+}e^{-}$ transverse momentum $p_{\rm T}$, $p_{\rm T}^{2}$, invariant mass $M_{ee}$ and azimuthal angle. In the invariant mass range of 0.4 $<$ $M_{ee}$ $<$ 2.6 GeV/$c^{2}$ at low transverse momentum ($p_{\rm T}$ $ < $0.15 GeV/$c$), the yields increase while the pair $\sqrt{\langle p_{\rm T}^{2} \rangle}$ decreases with increasing $\sqrt{s_{_{\rm{NN}}}}$, a feature is correctly predicted by the QED calculation. The energy dependencies of the measured quantities are sensitive to the nuclear form factor, infrared divergence and photon polarization. The data are compiled and used to extract the charge radius of the Au nucleus.

[15] 2407.14859

Enhancing High-Energy Particle Physics Collision Analysis through Graph Data Attribution Techniques

The experiments at the Large Hadron Collider at CERN generate vast amounts of complex data from high-energy particle collisions. This data presents significant challenges due to its volume and complex reconstruction, necessitating the use of advanced analysis techniques for analysis. Recent advancements in deep learning, particularly Graph Neural Networks, have shown promising results in addressing the challenges but remain computationally expensive. The study presented in this paper uses a simulated particle collision dataset to integrate influence analysis inside the graph classification pipeline aiming at improving the accuracy and efficiency of collision event prediction tasks. By using a Graph Neural Network for initial training, we applied a gradient-based data influence method to identify influential training samples and then we refined the dataset by removing non-contributory elements: the model trained on this new reduced dataset can achieve good performances at a reduced computational cost. The method is completely agnostic to the specific influence method: different influence modalities can be easily integrated into our methodology. Moreover, by analyzing the discarded elements we can provide further insights about the event classification task. The novelty of integrating data attribution techniques together with Graph Neural Networks in high-energy physics tasks can offer a robust solution for managing large-scale data problems, capturing critical patterns, and maximizing accuracy across several high-data demand domains.

[16] 2407.14961

Heavy four-quark mesons $bc\overline{b}\overline{c}$: Scalar particle

Parameters of the heavy four-quark scalar meson $T_{\mathrm{2bc}}=bc \overline{b}\overline{c}$ are calculated by means of the sum rule method. This structure is considered as a diquark-antidiquark state built of scalar diquark and antidiquark components. The mass and current coupling of $T_{ \mathrm{2bc}}$ are evaluated in the context of the two-point sum rule approach. The full width of this tetraquark is estimated by taking into account two types of its possible strong decay channels. First class includes dissociation of $T_{\mathrm{2bc}}$ to mesons $\eta_c\eta_{b}$, $ B_{c}^{+}B_{c}^{-}$, $B_{c}^{\ast +}B_{c}^{\ast -}$ and $ B_{c}^{+}(1^3P_{0})B_{c}^{\ast-}$. Another type of processes are generated by annihilations $\overline{b}b \to \overline{q}q$ of constituent $b$-quarks which produces the final-state charmed meson pairs $D^{+}D^{-}$, $D^{0} \overline{D}^{0}$, $D^{*+}D^{*-}$, and $D^{*0}\overline{D}^{*0}$. Partial width all of these decays are found using the three-point sum rule method which is required to calculate strong couplings at corresponding meson-meson-tetraquark vertices. Predictions obtained for the mass $m=(12697 \pm 90)~\mathrm{MeV}$ and width $\Gamma[T_{\mathrm{2bc}}]=(142.4 \pm 16.9)~ \mathrm{MeV}$ of the state $T_{\mathrm{2bc}}$ are compared with alternative results, and are useful for further experimental investigations of fully heavy resonances.

[17] 2407.15065

Anisotropic flow fluctuation as a possible signature of clustered nuclear geometry in O-O collisions at the Large Hadron Collider

Nuclei having $4n$ number of nucleons are theorized to possess clusters of $\alpha$ particles ($^4$He nucleus). The Oxygen nucleus ($^{16}$O) is a doubly magic nucleus, where the presence of an $\alpha$-clustered nuclear structure grants additional nuclear stability. In this study, we exploit the anisotropic flow coefficients to discern the effects of an $\alpha$-clustered nuclear geometry w.r.t. a Woods-Saxon nuclear distribution in O--O collisions at $\sqrt{s_{\rm NN}}=7$ TeV using a hybrid of IP-Glasma + MUSIC + iSS + UrQMD models. In addition, we use the multi-particle cumulants method to measure anisotropic flow coefficients, such as elliptic flow ($v_{2}$) and triangular flow ($v_{3}$), as a function of collision centrality. Anisotropic flow fluctuations, which are expected to be larger in small collision systems, are also studied for the first time in O--O collisions. It is found that an $\alpha$-clustered nuclear distribution gives rise to an enhanced value of $v_{2}$ and $v_3$ towards the highest multiplicity classes. Consequently, a rise in $v_3/v_2$ is also observed for the (0-10)\% centrality class. Further, for $\alpha$-clustered O--O collisions, fluctuations of $v_{2}$ are larger for the most central collisions, which decrease towards the mid-central collisions. In contrast, for a Woods-Saxon $^{16}$O nucleus, $v_{2}$ fluctuations show an opposite behavior with centrality. This study, when confronted with experimental data may reveal the importance of nuclear density profile on the discussed observables.

[18] 2407.15443

GRASIAN: Shaping and characterization of the cold hydrogen and deuterium beams for the forthcoming first demonstration of gravitational quantum states of atoms

A low energy particle confined by a horizontal reflective surface and gravity settles in gravitationally bound quantum states. These gravitational quantum states (GQS) were so far only observed with neutrons. However, the existence of GQS is predicted also for atoms. The GRASIAN collaboration pursues the first observation of GQS of atoms, using a cryogenic hydrogen beam. This endeavor is motivated by the higher densities, which can be expected from hydrogen compared to neutrons, the easier access, the fact, that GQS were never observed with atoms and the accessibility to hypothetical short range interactions. In addition to enabling gravitational quantum spectroscopy, such a cryogenic hydrogen beam with very low vertical velocity components - a few cm s$^{-1}$, can be used for precision optical and microwave spectroscopy. In this article, we report on our methods developed to reduce background and to detect atoms with a low horizontal velocity, which are needed for such an experiment. Our recent measurement results on the collimation of the hydrogen beam to 2 mm, the reduction of background and improvement of signal-to-noise and finally our first detection of atoms with velocities < 72 m s$^{-1}$ are presented. Furthermore, we show calculations, estimating the feasibility of the planned experiment and simulations which confirm that we can select vertical velocity components in the order of cm s$^{-1}$.

[19] 2407.15583

Application of a plasma-based energy booster in operational free-electron lasers

Plasma-based accelerators are a promising approach for reducing the size and cost of future particle accelerators, making them a viable technology for constructing and upgrading X-ray free-electron lasers (FELs). Adding an energy booster stage to the linear accelerator of an operational X-ray FEL is recognised as a realistic near-term application of plasma accelerators, with a significant impact on the scientific reach of these facilities. Here, we discuss potential use cases of such a plasma-based energy booster and apply particle-in-cell simulations to estimate its ability to enhance the performance of existing X-ray FEL facilities.