Exploration of hadronization through heavy flavor production at the future Electron-Ion Collider
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Search for Higgs boson production at high transverse momentum in the WW decay channel in proton-proton collisions at $\sqrt{s}=13$ TeV
A search for Higgs boson (H) production at high transverse momentum (p T ) in the WW decay channel is presented. The analysis uses proton-proton collisions at $\sqrt{s}=13$ TeV recorded by the CMS experiment in 2016–2018, corresponding to an integrated luminosity of 138 fb −1 . The visible decay products of the Higgs boson are reconstructed as a single large-radius jet with one isolated lepton or none (1ℓ and 0ℓ, respectively; ℓ = e, μ). The H-candidate jets are identified using an advanced transformer-based algorithm and are calibrated with the Lund jet plane reweighting technique. The 1ℓ channel is further split into gluon fusion, vector boson fusion, and associated production with hadronically decaying vector boson categories, while the 0ℓ channel considers all production processes inclusively. The measured cross section times the H → WW branching fraction relative to the standard model expectation is $\mu =-{0.19}_{-0.46}^{+0.48}$, indicating no evidence of a signal above the background. This measurement represents the first dedicated study of highly Lorentz-boosted H → WW decays, complementing earlier searches for high-p T Higgs boson in other decay channels.
Hadron-Hadron Scattering↗
Search for bottom-type vectorlike quark pair production in dileptonic and fully hadronic final states in proton-proton collisions at s = 13 TeV
A search is described for the production of a pair of bottom-type vectorlike quarks ( B VLQs) with mass greater than 1000 GeV. Each B VLQ decays into a b quark and a Higgs boson, a b quark and a Z boson, or a t quark and a W boson. This analysis considers both fully hadronic final states and those containing a charged lepton pair from a Z boson decay. The products of the H → b b boson decay and of the hadronic Z or W boson decays can be resolved as two distinct jets or merged into a single jet, so the final states are classified by the number of reconstructed jets. The analysis uses data corresponding to an integrated luminosity of 138 fb - 1 collected in proton-proton collisions at s = 13 TeV with the CMS detector at the LHC from 2016 to 2018. No excess over the expected background is observed. Lower limits are set on the B VLQ mass at the 95% confidence level. These depend on the B VLQ branching fractions and are 1570 and 1540 GeV for 100% B → b H and 100% B → b Z , respectively. In most cases, the mass limits obtained exceed previous limits by at least 100 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Quark flavor balancing in nuclear collisions
The notion of charge balance function, originally designed to study the evolution of charge production in heavy-ion collisions, is extended to consider quark flavor balancing. This extension is considered based on simulations performed with the PYTHIA 8 event generator in the context of pp collisions at √𝑠 = 13.6, 7, and 2.76 TeV but can be trivially applied to any other scenario and implemented in measurements of correlated particle production in pp, pA, and AA collisions at colliders. Correlation of selected flavor balancing pairs is examined as a function of the produced charged particle multiplicity. One finds that the amplitude of the correlations increases monotonically with the number of balanced flavors and the actual flavor content of correlated particles.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Studying 𝜋 + 𝜋 − photoproduction beyond Pomeron exchange
Forward photoproduction of 𝜋 + 𝜋 − pairs with invariant mass of the order of 𝑚 𝜌 ∼770 MeV is traditionally attributed to Pomeron exchange. Based on a detailed analysis of the CEBAF Large Acceptance Spectrometer photoproduction data collected at photon energies below 4 GeV, it is shown from a study of the angular moments that the dynamics of two-pion photoproduction for |𝑡| ≳ 0.5 GeV 2 cannot be explained by Pomeron exchange alone. This motivates the development of a new theoretical model of two-pion photoproduction which incorporates both two-pion and pion-nucleon resonant contributions. After fitting free parameters, the model provides an excellent description of the low moments of the angular distribution measured at CLAS and enables an assessment of the relative contributions of particular production mechanisms and an interpretation of the various features of the data in terms of these mechanisms.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Enhanced Deuteron Coalescence Probability in Jets
The transverse-momentum ($p_T$) spectra and coalescence parameters $B_2$ of (anti)deuterons are measured in p-p collisions at $\sqrt{s}=13$ $\text{TeV}$ for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest $p_T$ in the event ($p^{lead}_T > 5 GeV/c$) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the $B^{Jet}_2$ is not reproduced by the models, which instead give a decreasing trend.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Transverse Λ polarization in e + e – processes within a TMD factorization approach and the polarizing fragmentation function
We perform a re-analysis of Belle data for the transverse Λ and Λ¯ polarization in e + e – annihilation processes within a transverse momentum dependent (TMD) factorization approach. We consider two data sets, one referring to the associated production of Λ’s with a light unpolarized hadron in an almost back-to-back configuration, and one for the inclusive Λ production, with the reconstruction of the thrust axis. We adopt the Collins-Soper-Sterman framework and employ the recent formulation on the factorization of single-inclusive hadron production. This extends a previous phenomenological study carried out in a more simplified TMD approach, leading to a new extraction of the polarizing fragmentation function (FF). While confirming several features of the previous analysis, here we include the proper QCD scale dependence of this TMD FF and carefully exploit the role of its nonperturbative component. Here, the compatibility, within a unique TMD factorization scheme, of double and single-inclusive hadron production is discussed in detail. Moreover, we consider another data set for inclusive Λ production, at much larger energies, from the OPAL Collaboration, in order to test the consistency of the entire approach. Finally, we elaborate on some fundamental issues like the role of SU(2) isospin symmetry and the heavy quark contributions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of beauty production via non-prompt charm hadrons in p–Pb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV
The production cross sections of D 0 , D + , and Λ$^{+}_{c}$ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity in proton–lead (p–Pb) collisions at the center-of-mass energy per nucleon pair of $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV. Nuclear modification factors (R pPb ) of non-prompt D 0 , D + , and Λ$^{+}_{c}$ are calculated as a function of the transverse momentum (p T ) to investigate the modification of the momentum spectra measured in p–Pb collisions with respect to those measured in proton–proton (pp) collisions at the same energy. The R pPb measurements are compatible with unity and with the measurements in the prompt charm sector, and do not show a significant p T dependence. The p T -integrated cross sections and p T -integrated R pPb of non-prompt D 0 and D + mesons are also computed by extrapolating the visible cross sections down to p T = 0. The non-prompt D-meson R pPb integrated over p T is compatible with unity and with model calculations implementing modification of the parton distribution functions of nucleons bound in nuclei with respect to free nucleons. The non-prompt Λ$^{+}_{c}$/D 0 and D + /D 0 production ratios are computed to investigate hadronisation mechanisms of beauty quarks into mesons and baryons. The measured ratios as a function of p T display a similar trend to that measured for charm hadrons in the same collision system.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurements of Lund subjet multiplicities in 13 TeV proton-proton collisions with the ATLAS detector
This Letter presents a differential cross-section measurement of Lund subjet multiplicities, suitable for testing current and future parton shower Monte Carlo algorithms. This measurement is made in dijet events in 140 fb -1 of $\sqrt{s}$ =13 TeV proton–proton collision data collected with the ATLAS detector at CERN's Large Hadron Collider. The data are unfolded to account for acceptance and detector-related effects, and are then compared with several Monte Carlo models and to recent resummed analytical calculations. The experimental precision achieved in the measurement allows tests of higher-order effects in QCD predictions. Most predictions fail to accurately describe the measured data, particularly at large values of jet transverse momentum accessible at the Large Hadron Collider, indicating the measurement's utility as an input to future parton shower developments and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Inclusive and multiplicity dependent production of electrons from heavy-flavour hadron decays in pp and p-Pb collisions
Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at $\sqrt{s}$ = 13 TeV at midrapidity with the ALICE detector are presented down to a transverse momentum (p T ) of 0.2 GeV/c and up to p T = 35 GeV/c, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p-Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the p T range 0.5 < p T < 26 GeV/c at $\sqrt{s_{NN}}$= 8.16 TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p-Pb collisions grow faster than linear with the self-normalised multiplicity. A strong p T dependence is observed in pp collisions, where the yield of high-p T electrons increases faster as a function of multiplicity than the one of low-p T electrons. The measurement in p-Pb collisions shows no p T dependence within uncertainties. The self-normalised yields in pp and p-Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Collinear expansion for color singlet cross sections
We demonstrate how to efficiently expand cross sections for color-singlet production at hadron colliders around the kinematic limit of all final state radiation being collinear to one of the incoming hadrons. This expansion is systematically improvable and applicable to a large class of physical observables. We demonstrate the viability of this technique by obtaining the first two terms in the collinear expansion of the rapidity distribution of the gluon fusion Higgs boson production cross section at next-to-next-to leading order (NNLO) in QCD perturbation theory. Furthermore, we illustrate how this technique is used to extract universal building blocks of scattering cross section like the N-jettiness and transverse momentum beam function at NNLO.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Polarized fragmenting jet functions in inclusive and exclusive jet production
Abstract In this work, we present a complete theoretical framework for analyzing the distribution of polarized hadrons within jets, with and without measuring the transverse momentum relative to the standard jet axis. Using soft-collinear effective theory (SCET), we derive the factorization and provide the theoretical calculation of both semi-inclusive and exclusive fragmenting jet functions (FJFs) under longitudinal and transverse polarization. With the polarized FJFs, one gains access to a variety of new observables that can be used for extracting both collinear and transverse momentum dependent parton distribution functions (PDFs) and fragmentation functions (FFs). As examples, we provide numerical results for the spin asymmetry$$ {A}_{TU,T}^{\cos \left({\phi}_S-{\hat{\phi}}_{S_h}\right)} $$ A TU , T cos ϕ S − ϕ ̂ S h from polarized semi-inclusive hadron-in-jet production in polarizedppcollisions at RHIC kinematics, where a transversely polarized quark would lead to the transverse spin of the final-state hadron inside the jet and is thus sensitive to the transversity fragmentation functions. Similarly, another spin asymmetry,$$ {A}_{TU,L}^{\cos \left({\phi}_q-{\phi}_S\right)} $$ A TU , L cos ϕ q − ϕ S from polarized exclusive hadron-in-jet production in polarizedepcollisions at EIC kinematics would allow us to access the helicity fragmentation functions. These observables demonstrate promising potential in investigating transverse momentum dependent PDFs and FFs and are worthwhile for further measurements.
Physics↗
Measurements of multijet event isotropies using optimal transport with the ATLAS detector
A measurement of novel event shapes quantifying the isotropy of collider events is performed in 140 fb -1 of proton-proton collisions with $\sqrt{s}$ = 13 TeV centre-of-mass energy recorded with the ATLAS detector at CERN’s Large Hadron Collider. These event shapes are defined as the Wasserstein distance between collider events and isotropic reference geometries. This distance is evaluated by solving optimal transport problems, using the ‘Energy-Mover’s Distance’. Isotropic references with cylindrical and circular symmetries are studied, to probe the symmetries of interest at hadron colliders. The novel event-shape observables defined in this way are infrared- and collinear-safe, have improved dynamic range and have greater sensitivity to isotropic radiation patterns than other event shapes. The measured event-shape variables are corrected for detector effects, and presented in inclusive bins of jet multiplicity and the scalar sum of the two leading jets’ transverse momenta. The measured distributions are provided as inputs to future Monte Carlo tuning campaigns and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Prospects for exotic h → 4 τ decays in single and di-Higgs boson production at the LHC and future hadron colliders
We study the prospects for observing exotic decays of the Standard Model Higgs boson h into light beyond the Standard Model scalars a with mass m a ≲ m h / 2 in the single Higgs and Higgs pair production channels at the high luminosity run of the Large Hadron Collider (HL-LHC). Discovery prospects for single Higgs production in the gluon-gluon fusion and vector boson fusion modes with the Higgs boson decaying via the exotic mode h → a a → 4 τ are analyzed at the HL-LHC. The projected sensitivity for exotic Higgs decays in the nonresonant Higgs pair production channel p p → h h → ( h → b b ¯ ) ( h → a a → 4 τ ) → 2 b 4 τ at the HL-LHC and a future s = 100 TeV hadron collider (FCC-hh) are also estimated. Furthermore, we study HL-LHC’s potential reach for the Higgs-strahlung process in the 2 b 4 τ channel, taking into account the contamination from nonresonant Higgs pair production. Finally, the potential reach for resonant Higgs pair production in the 2 b 4 τ channel at the HL-LHC is also explored for several choices of { m H , m a } . Our studies suggest that significant improvements over existing bounds are achievable in several production channels, motivating new dedicated searches for h → a a → 4 τ at the HL-LHC and future colliders. Published by the American Physical Society 2024
Astronomy & Astrophysics↗
Polarized 𝐽/𝜓 production in semi-inclusive DIS at large 𝑄 2 : Comparing quark fragmentation and photon-gluon fusion
We compare the relative importance of different mechanisms for polarized 𝐽/𝜓 production in semi-inclusive deep inelastic scattering processes at large 𝑄 2 . The transverse momentum dependent (TMD) factorization framework and nonrelativistic quantum chromodynamics are used to study the leading contributions from light quark fragmentation to polarized 𝐽/𝜓, and compared to direct production via photon-gluon fusion, which can proceed through color-singlet as well as color-octet mechanisms. We identify kinematic regimes where light quark fragmentation dominates, allowing for the extraction of the 3 𝑆$^{[8]}_{1}$ matrix element, as well as regimes where photon gluon fusion dominates, suggesting that the gluon TMD parton distribution function can be probed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
The structure of quark mass corrections in the gg → HH amplitude at high-energy
The leading and next-to-leading order QCD predictions for Higgs boson pair production at hadron colliders suffer from a significant mass renormalisation scheme uncertainty related to the choice of the top-quark mass. The functional dependence of the result on the value of the intermediate quark mass can be understood in the high-energy limit using the Method of Regions and the tools of Soft-Collinear Effective Theory. In this work, we study the origin of the sizeable logarithmic mass corrections in the gg → HH amplitudes at leading and next-to-leading power in the limit s, |t|, |u| ≫ ${m}_t^2$ ≫ ${m}_H^2$. We argue that the mass corrections follow a predictable factorised pattern that can be exploited to simplify their computation. We present results for the leading power leading logarithmic corrections, our analysis leads to a significant reduction in the theoretical uncertainty of the double Higgs production amplitudes at scattering energies ≳ 1 TeV due to the top-quark mass scheme.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of spin-density matrix elements in ρ ( 770 ) production with a linearly polarized photon beam at E γ = 8.2 – 8.8 GeV
The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized 8.5GeV photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson rho(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. Here we confirm a high degree of s-channel helicity conservation at small squared four-momentum transfer t and are able to extract the t-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full t range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced rho(770) differ by two units are negligible for -t<0.5GeV 2 /c 2 .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the B + /B 0 production ratio in e + e - collisions at the $\Upsilon$ (4S) resonance using B → J/Ψ($\ell\ell$)K decays at Belle
We measure the ratio of branching fractions for the $\Upsilon$ (4S) decays to B + B - and B 0 $\bar{B}$ 0 using B + → J/Ψ($\ell\ell$)K + and B 0 → J/Ψ($\ell\ell$)K 0 samples, where J/Ψ($\ell\ell$) stands for J/Ψ → $\ell$ + $\ell$ - ($\ell$ = e or μ), with 711 fb -1 of data collected at the $\Upsilon$ (4S) resonance with the Belle detector. We find the decay rate ratio of $\Upsilon$ (4S) → B + B - over $\Upsilon$ (4S) → B 0 $\bar{B}$ 0 to be 1.065 ± 0.012 ± 0.019 ± 0.047, which is the most precise measurement to date. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainty is due to the assumption of isospin symmetry in B → J/Ψ($\ell\ell$) K.
79 ASTRONOMY AND ASTROPHYSICS↗