The H1 Collaboration reports the first measurement of the 1-jettiness event shape observable $\tau_1^b$ in neutral-current deep-inelastic electron-proton scattering (DIS). The observable $\tau_1^b$ is equivalent to a thrust observable defined in the Breit frame. The data sample was collected at the HERA $ep$ collider in the years 2003-2007 with center-of-mass energy of $\sqrt{s}=319\,\text{GeV}$, corresponding to an integrated luminosity of $351.1\,\text{pb}^{-1}$. Triple differential cross sections are provided as a function of $\tau_1^b$, event virtuality $Q^2$, and inelasticity $y$, in the kinematic region $Q^2>150\,\text{GeV}^{2}$. Single differential cross section are provided as a function of $\tau_1^b$ in a limited kinematic range. Double differential cross sections are measured, in contrast, integrated over $\tau_1^b$ and represent the inclusive neutral-current DIS cross section measured as a function of $Q^2$ and $y$. The data are compared to a variety of predictions and include classical and modern Monte Carlo event generators, predictions in fixed-order perturbative QCD where calculations up to $\mathcal{O}(\alpha_s^3)$ are available for $\tau_1^b$ or inclusive DIS, and resummed predictions at next-to-leading logarithmic accuracy matched to fixed order predictions at $\mathcal{O}(\alpha_s^2)$. These comparisons reveal sensitivity of the 1-jettiness observable to QCD parton shower and resummation effects, as well as the modeling of hadronization and fragmentation. Within their range of validity, the fixed-order predictions provide a good description of the data. Monte Carlo event generators are predictive over the full measured range and hence their underlying models and parameters can be constrained by comparing to the presented data.

The Breit frame provides a natural frame to analyze lepton–proton scattering events. In this reference frame, the parton model hard interactions between a quark and an exchanged boson defines the coordinate system such that the struck quark is back-scattered along the virtual photon momentum direction. In Quantum Chromodynamics (QCD), higher order perturbative or non-perturbative effects can change this picture drastically. As Bjorken-x decreases below one half, a rather peculiar event signature is predicted with increasing probability, where no radiation is present in one of the two Breit-frame hemispheres and all emissions are to be found in the other hemisphere. At higher orders in α _s or in the presence of soft QCD effects, predictions of the rate of these events are far from trivial, and that motivates measurements with real data. We report on the first observation of the empty current hemisphere events in electron–proton collisions at the HERA collider using data recorded with the H1 detector at a center-of-mass energy of 319 GeV. The fraction of inclusive neutral-current DIS events with an empty hemisphere is found to be 0.0112 ± 3.9%_stat± 4.5%_syst± 1.6%_mod in the selected kinematic region of 150

AbstractThe H1 Collaboration at HERA reports the first measurement of groomed event shape observables in deep inelastic electron-proton scattering (DIS) at $$\sqrt{s} =319~$$ s = 319 GeV, using data recorded between the years 2003 and 2007 with an integrated luminosity of 351 $$\textrm{pb}^{-1}$$ pb - 1 . Event shapes provide incisive probes of perturbative and non-perturbative QCD. Grooming techniques have been used for jet measurements in hadronic collisions; this paper presents the first application of grooming to DIS data. The analysis is carried out in the Breit frame, utilizing the novel Centauro jet clustering algorithm that is designed for DIS event topologies. Events are required to have squared momentum-transfer $$Q^2 > 150$$ Q 2 > 150 GeV$$^2$$ 2 and inelasticity $$ 0.2< y < 0.7$$ 0.2 < y < 0.7 . We report measurements of the production cross section of groomed event 1-jettiness and groomed invariant mass for several choices of grooming parameter. Monte Carlo model calculations and analytic calculations based on Soft Collinear Effective Theory are compared to the measurements.

The radiation pattern within high energy quark- and gluon-initiated jets (jet substructure) is used extensively as a precision probe of the strong force as well as an environment for optimizing event generators with numerous applications in high energy particle and nuclear physics. Looking at electron-proton collisions is of particular interest as many of the complications present at hadron colliders are absent. A detailed study of modern jet substructure observables, jet angularities, in electron-proton collisions is presented using data recorded using the H1 detector at HERA. The measurement is unbinned and multi-dimensional, using machine learning to correct for detector effects. All of the available reconstructed object information of the respective jets is interpreted by a graph neural network, achieving superior precision on a selected set of jet angularities. Training these networks was enabled by the use of a large number of GPUs in the Perlmutter supercomputer at Berkeley Lab. The particle jets are reconstructed in the laboratory frame, using the k_T jet clustering algorithm. Results are reported at high transverse momentum transfer Q^2>150 GeV^2, and inelasticity 0.2 < y < 0.7. The analysis is also performed in sub-regions of Q^2, thus probing scale dependencies of the substructure variables. The data are compared with a variety of predictions and point towards possible improvements of such models.

A bstract A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35 . 6 fb −1 collected at $$ \sqrt{s}=13 $$ s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕ γ and ρ γ of 4 . 8 × 10 −4 and 8 . 8 × 10 −4 , respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0 . 9 × 10 −6 and 25 × 10 −6 for ϕ γ and ρ γ, respectively.

A search for leptoquarks decaying into the bτ final state is performed using Run 2 proton-proton collision data from the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1 at √(s) = 13 TeV recorded by the ATLAS detector. The benchmark models considered in this search are vector leptoquarks with electric charge of 2/3e and scalar leptoquarks with an electric charge of 4/3e. No significant excess above the Standard Model prediction is observed, and 95

The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H → ZZ* → 4ℓ and H → γγ decay channels. The results are based on a dataset of 139 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider. The measured total Higgs boson production cross-section is 55.5_-3.8^+4.0 pb, consistent with the Standard Model prediction of 55.6 ± 2.5 pb. All results from the two decay channels are compatible with each other, and their combination agrees with the Standard Model predictions. A combined statistical interpretation of the measured fiducial cross-sections as a function of the Higgs boson transverse momentum is performed in order to probe the Yukawa couplings to the bottom and charm quarks. A similar interpretation is performed by including also the constraints from the measurements of Higgs boson production in association with a W or Z boson in the H → bb and cc decay channels.

AbstractThe HERAPDF2.0 ensemble of parton distribution functions (PDFs) was introduced in 2015. The final stage is presented, a next-to-next-to-leading-order (NNLO) analysis of the HERA data on inclusive deep inelastic ep scattering together with jet data as published by the H1 and ZEUS collaborations. A perturbative QCD fit, simultaneously of $$\alpha _s(M_Z^2)$$ α s ( M Z 2 ) and the PDFs, was performed with the result $$\alpha _s(M_Z^2)= 0.1156 \pm 0.0011~\mathrm{(exp)}~ ^{+0.0001}_{-0.0002}~ \mathrm{(model}$$ α s ( M Z 2 ) = 0.1156 ± 0.0011 ( exp ) - 0.0002 + 0.0001 ( model $$\mathrm{+ parameterisation)}~ \pm 0.0029~\mathrm{(scale)}$$ + parameterisation ) ± 0.0029 ( scale ) . The PDF sets of HERAPDF2.0Jets NNLO were determined with separate fits using two fixed values of $$\alpha _s(M_Z^2)$$ α s ( M Z 2 ) , $$\alpha _s(M_Z^2)=0.1155$$ α s ( M Z 2 ) = 0.1155 and 0.118, since the latter value was already chosen for the published HERAPDF2.0 NNLO analysis based on HERA inclusive DIS data only. The different sets of PDFs are presented, evaluated and compared. The consistency of the PDFs determined with and without the jet data demonstrates the consistency of HERA inclusive and jet-production cross-section data. The inclusion of the jet data reduced the uncertainty on the gluon PDF. Predictions based on the PDFs of HERAPDF2.0Jets NNLO give an excellent description of the jet-production data used as input.

The first measurement of lepton-jet momentum imbalance and azimuthal correlation in lepton-proton scattering at high momentum transfer is presented. These data, taken with the H1 detector at HERA, are corrected for detector effects using an unbinned machine learning algorithm (multifold), which considers eight observables simultaneously in this first application. The unfolded cross sections are compared with calculations performed within the context of collinear or transverse-momentum-dependent factorization in quantum chromodynamics as well as Monte Carlo event generators.

This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The s=13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb−1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.

The determination of the strong coupling constant alpha(s)(m(Z)) from H1 inclusive and dijet cross section data [1] exploits perturbative QCD predictions in next-tonext-to-leading order (NNLO) [2-4]. An implementation error in the NNLO predictions was found [4] which changes the numerical values of the predictions and the resulting values of the fits. Using the corrected NNLO predictions together with inclusive jet and dijet data, the strong coupling constant is determined to be alpha(s)(m(Z)) = 0.1166 (19)(exp) (24)th. Complementarily, alpha(s)(m(Z)) is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The value alpha(s)(m(Z)) = 0.1147 (25)(tot) obtained is consistent with the determination from jet data alone. Corrected figures and numerical results are provided and the discussion is adapted accordingly.

The first measurement of longitudinal decorrelations of harmonic flow amplitudes v_{n} for n=2-4 in Xe+Xe collisions at sqrt[s_{NN}]=5.44  TeV is obtained using 3  μb^{-1} of data with the ATLAS detector at the LHC. The decorrelation signal for v_{3} and v_{4} is found to be nearly independent of collision centrality and transverse momentum (p_{T}) requirements on final-state particles, but for v_{2} a strong centrality and p_{T} dependence is seen. When compared with the results from Pb+Pb collisions at sqrt[s_{NN}]=5.02  TeV, the longitudinal decorrelation signal in midcentral Xe+Xe collisions is found to be larger for v_{2}, but smaller for v_{3}. Current hydrodynamic models reproduce the ratios of the v_{n} measured in Xe+Xe collisions to those in Pb+Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe+Xe and Pb+Pb. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions.

AbstractThe determination of the strong coupling constant $$\alpha _{\mathrm{s}} (m_{\mathrm{Z}})$$ α s ( m Z ) from H1 inclusive and dijet cross section data [1] exploits perturbative QCD predictions in next-to-next-to-leading order (NNLO) [2–4]. An implementation error in the NNLO predictions was found [4] which changes the numerical values of the predictions and the resulting values of the fits. Using the corrected NNLO predictions together with inclusive jet and dijet data, the strong coupling constant is determined to be $$\alpha _{\mathrm{s}} (m_{\mathrm{Z}}) =0.1166\,(19)_{\mathrm{exp}}\,(24)_{\mathrm{th}}$$ α s ( m Z ) = 0.1166 ( 19 ) exp ( 24 ) th . Complementarily, $$\alpha _{\mathrm{s}} (m_{\mathrm{Z}})$$ α s ( m Z ) is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The value $$\alpha _{\mathrm{s}} (m_{\mathrm{Z}}) =0.1147\,(25)_{\mathrm{tot}}$$ α s ( m Z ) = 0.1147 ( 25 ) tot obtained is consistent with the determination from jet data alone. Corrected figures and numerical results are provided and the discussion is adapted accordingly.

Exclusive photoproduction of rho 0(770) mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross sections for the reaction gamma p -> pi+pi -Y. Reactions where the proton stays intact (mY=mp) are statistically separated from those where the proton dissociates to a low-mass hadronic system (mpGeV). The double-differential cross sections are measured as a function of the invariant mass m pi pi of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon-proton collision energy W gamma p. The phase space restrictions are 0.5 <= m pi pi <= 2.2GeV, |t|<= 1.5GeV2, and 20 <= W gamma p <= 80GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the m pi pi dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the rho 0(770) meson mass and width at m rho =770.8-2.7+2.6(tot.)MeV and Gamma rho =151.3-3.6+2.7(tot.)MeV, respectively. The model is used to extract the rho 0(770) contribution to the pi+pi- cross sections and measure it as a function of t and W gamma p. In a Regge asymptotic limit in which one Regge trajectory alpha (t) dominates, the intercept alpha (t=0)=1.0654-0.0067+0.0098(tot.) and the slope alpha ' (t=0)=0.233-0.074+0.067(tot.)GeV-2 of the t dependence are extracted for the case mY=mp.

Exclusive photoproduction of $${{\\rho ^0}} (770)$$\n mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross sections for the reaction $$\\gamma p \\rightarrow \\pi ^{+}\\pi ^{-}Y$$\n . Reactions where the proton stays intact (\n $${{{m_Y}} {=}m_p}$$\n ) are statistically separated from those where the proton dissociates to a low-mass hadronic system (\n $$m_p{\u003c}{{m_Y}} {\u003c}10~{{\\text {GeV}}} $$\n ). The double-differential cross sections are measured as a function of the invariant mass $$m_{\\pi \\pi }$$\n of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon–proton collision energy $${{W_{\\gamma p}}} $$\n . The phase space restrictions are $$0.5\\le m_{\\pi \\pi } \\le 2.2~{{\\text {GeV}}} $$\n , $$\\vert t\\vert \\le 1.5~{{\\text {GeV}^2}} $$\n , and $$20 \\le W_{\\gamma p} \\le 80~{{\\text {GeV}}} $$\n . Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the $${m_{\\pi \\pi }}$$\n dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the $${{\\rho ^0}} (770)$$\n meson mass and width at $$m_\\rho = 770.8{}^{+2.6}_{-2.7}~({\\text {tot.}})~{{\\text {MeV}}} $$\n and $$\\Gamma _\\rho = 151.3 {}^{+2.7}_{-3.6}~({\\text {tot.}})~{{\\text {MeV}}} $$\n , respectively. The model is used to extract the $${{\\rho ^0}} (770)$$\n contribution to the $$\\pi ^{+}\\pi ^{-}$$\n cross sections and measure it as a function of t and $${W_{\\gamma p}}$$\n . In a Regge asymptotic limit in which one Regge trajectory $$\\alpha (t)$$\n dominates, the intercept $$\\alpha (t{=}0) = 1.0654\\ {}^{+0.0098}_{-0.0067}~({\\text {tot.}})$$\n and the slope $$\\alpha ^\\prime (t{=}0) = 0.233 {}^{+0.067 }_{-0.074 }~({\\text {tot.}}) ~{{\\text {GeV}^{-2}}} $$\n of the t dependence are extracted for the case $$m_Y{=}m_p$$\n .

Exclusive photoproduction of ρ ^0 (770) mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross sections for the reaction γ p →π ^+π ^-Y . Reactions where the proton stays intact ( m_Y=m_p ) are statistically separated from those where the proton dissociates to a low-mass hadronic system ( m_p<m_Y<10 GeV ). The double-differential cross sections are measured as a function of the invariant mass m_ππ of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon–proton collision energy W_γ p . The phase space restrictions are 0.5≤ m_ππ≤ 2.2 GeV , | t|≤ 1.5 GeV^2 , and 20 ≤ W_γ p≤ 80 GeV . Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the m_ππ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the ρ ^0 (770) meson mass and width at m_ρ = 770.8^+2.6_-2.7 (tot.) MeV and Γ _ρ = 151.3 ^+2.7_-3.6 (tot.) MeV , respectively. The model is used to extract the ρ ^0 (770) contribution to the π ^+π ^- cross sections and measure it as a function of t and W_γ p . In a Regge asymptotic limit in which one Regge trajectory α (t) dominates, the intercept α (t=0) = 1.0654 ^+0.0098_-0.0067 (tot.) and the slope α ^' (t=0) = 0.233 ^+0.067 _-0.074 (tot.) GeV^-2 of the t dependence are extracted for the case m_Y=m_p .

AbstractExclusive photoproduction of $${{\rho ^0}} (770)$$ ρ 0 ( 770 ) mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross sections for the reaction $$\gamma p \rightarrow \pi ^{+}\pi ^{-}Y$$ γ p → π + π - Y . Reactions where the proton stays intact ($${{{m_Y}} {=}m_p}$$ m Y = m p ) are statistically separated from those where the proton dissociates to a low-mass hadronic system ($$m_p{<}{{m_Y}} {<}10~{{\text {GeV}}} $$ m p < m Y < 10 GeV ). The double-differential cross sections are measured as a function of the invariant mass $$m_{\pi \pi }$$ m π π of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon–proton collision energy $${{W_{\gamma p}}} $$ W γ p . The phase space restrictions are $$0.5\le m_{\pi \pi } \le 2.2~{{\text {GeV}}} $$ 0.5 ≤ m π π ≤ 2.2 GeV , $$\vert t\vert \le 1.5~{{\text {GeV}^2}} $$ | t | ≤ 1.5 GeV 2 , and $$20 \le W_{\gamma p} \le 80~{{\text {GeV}}} $$ 20 ≤ W γ p ≤ 80 GeV . Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the $${m_{\pi \pi }}$$ m π π dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the $${{\rho ^0}} (770)$$ ρ 0 ( 770 ) meson mass and width at $$m_\rho = 770.8{}^{+2.6}_{-2.7}~({\text {tot.}})~{{\text {MeV}}} $$ m ρ = 770.8 - 2.7 + 2.6 ( tot. ) MeV and $$\Gamma _\rho = 151.3 {}^{+2.7}_{-3.6}~({\text {tot.}})~{{\text {MeV}}} $$ Γ ρ = 151.3 - 3.6 + 2.7 ( tot. ) MeV , respectively. The model is used to extract the $${{\rho ^0}} (770)$$ ρ 0 ( 770 ) contribution to the $$\pi ^{+}\pi ^{-}$$ π + π - cross sections and measure it as a function of t and $${W_{\gamma p}}$$ W γ p . In a Regge asymptotic limit in which one Regge trajectory $$\alpha (t)$$ α ( t ) dominates, the intercept $$\alpha (t{=}0) = 1.0654\ {}^{+0.0098}_{-0.0067}~({\text {tot.}})$$ α ( t = 0 ) = 1.0654 - 0.0067 + 0.0098 ( tot. ) and the slope $$\alpha ^\prime (t{=}0) = 0.233 {}^{+0.067 }_{-0.074 }~({\text {tot.}}) ~{{\text {GeV}^{-2}}} $$ α ′ ( t = 0 ) = 0.233 - 0.074 + 0.067 ( tot. ) GeV - 2 of the t dependence are extracted for the case $$m_Y{=}m_p$$ m Y = m p .

This paper presents a search for direct top squark pair production in events with missing transverse momentum plus either a pair of jets consistent with Standard Model Higgs boson decay into b-quarks or a same-flavour opposite-sign dilepton pair with an invariant mass consistent with a Z boson. The analysis is performed using the proton–proton collision data at \n$$\\sqrt{s}=13$$\n\n TeV collected with the ATLAS detector during the LHC Run-2, corresponding to an integrated luminosity of 139 fb\n$$^{-1}$$\n\n. No excess is observed in the data above the Standard Model predictions. The results are interpreted in simplified models featuring direct production of pairs of either the lighter top squark (\n$$\\tilde{t}_1$$\n\n) or the heavier top squark (\n$$\\tilde{t}_2$$\n\n), excluding at 95% confidence level \n$$\\tilde{t}_1$$\n\n and \n$$\\tilde{t}_2$$\n\n masses up to about 1220 and 875 GeV, respectively.

The production cross-sections for W +/- and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb-1 collected at a centre-ofmass energy v s = 2.76 TeV. The deca ...