Publications

Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at sqrt[s]=13  TeV with the ATLAS Detector.

Physical review letters 124 (2020) 82301

The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at sqrt[s]=13  TeV using a data sample with an integrated luminosity of 150  pb^{-1} recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range |η|&lt;2.4. A significant nonzero elliptic anisotropy coefficient v_{2} is observed for muons from charm decays, while the v_{2} value for muons from bottom decays is consistent with zero within uncertainties.

Search for electron antineutrino appearance in a long-baseline muon antineutrino beam

arXiv Cornell University (2019)

K Abe, D Barrow, C Barry, M Batkiewicz-Kwasniak, A Beloshapkin, M Antonova, A Ariga, S Aoki, R Akutsu, A Ali, C Alt, L Anthony, C Andreopoulos, Y Asada, Y Ashida, ET Atkin, Y Awataguchi, M Barbi, S Ban, GJ Barker, G Barr, F Bench, V Berardi, A Cervera

Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the PMNS mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40{\sigma} and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.

Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector

PHYSICAL REVIEW D 101 (2020) 32009

G Aad, B Abbott, D Abbott, AA Abud, K Abeling, D Abhayasinghe, S Abidi, H Abramowicz, G Aielli, S Akatsuka, T Akesson, E Akilli, A Akimov, K Al Khoury, G Alberghi, J Albert, MJA Verzini, S Alderweireldt, M Aleksa, I Aleksandrov, C Alexa, D Alexandre, T Alexopoulos, A Alfonsi

© 2020 CERN. A search for the direct production of the supersymmetric partners of τ-leptons (staus) in final states with two hadronically decaying τ-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 139 fb-1, recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one τ-lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidence level for a massless lightest neutralino.

Measurement of the muon neutrino charged-current single $π^+$ production on hydrocarbon using the T2K off-axis near detector ND280

Physical Review D: Particles, Fields, Gravitation and Cosmology American Physical Society (2020)

We report the measurements of single and double differential cross section of muon neutrino charged-current interactions on carbon with a single positively charged pion in the final state at the T2K off-axis near detector using $5.56\times10^{20}$ protons on target. The analysis uses data control samples for the background subtraction and the cross section signal, defined as a single negatively charged muon and a single positively charged pion exiting from the target nucleus, is extracted using an unfolding method. The model dependent cross section, integrated over the T2K off-axis neutrino beam spectrum peaking at $0.6$~GeV, is measured to be $\sigma = (11.76 \pm 0.44 \text{(stat)} \pm 2.39 \text{(syst)}) \times 10^{-40} \text{cm}^2$~$\text{nucleon}^{-1}$. Various differential cross sections are measured, including the first measurement of the Adler angles for single charged pion production in neutrino interactions with heavy nuclei target.

Evidence for electroweak production of two jets in association with a Z gamma pair in pp collisions at root S=13 TeV with the ATLAS detector

PHYSICS LETTERS B 803 (2020) ARTN 135341

© 2020 The Author(s) Evidence for electroweak production of two jets in association with a Zγ pair in s=13 TeV proton–proton collisions at the Large Hadron Collider is presented. The analysis uses data collected by the ATLAS detector in 2015 and 2016 that corresponds to an integrated luminosity of 36.1fb−1. Events that contain a Z boson candidate decaying leptonically into either e+e− or μ+μ−, a photon, and two jets are selected. The electroweak component is measured with observed and expected significances of 4.1 standard deviations. The fiducial cross-section for electroweak production is measured to be σZγjj−EW=7.8±2.0fb, in good agreement with the Standard Model prediction.

Measurement of the azimuthal anisotropy of charged-particle production in Xe plus Xe collisions at root S-NN=5.44 TeV with the ATLAS detector

PHYSICAL REVIEW C 101 (2020) 24906

© 2020 CERN. This paper describes the measurements of flow harmonics v2-v6 in 3μb-1 of Xe+Xe collisions at sNN=5.44 TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and pT dependence of the vn obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured vn at high pT, especially in peripheral events. Comparisons of the measured vn with measurements in Pb+Pb collisions and p+Pb collisions at sNN=5.02 TeV are also presented. The vn values in Xe+Xe collisions are observed to be larger than those in Pb+Pb collisions for n=2, 3, and 4 in the most central events. However, with decreasing centrality or increasing harmonic order n, the vn values in Xe+Xe collisions become smaller than those in Pb+Pb collisions. The vn in Xe+Xe and Pb+Pb collisions are also compared as a function of the mean number of participating nucleons, (Npart), and the measured charged-particle multiplicity in the detector. The v3 values in Xe+Xe and Pb+Pb collisions are observed to be similar at the same (Npart) or multiplicity, but the other harmonics are significantly different. The ratios of the measured vn in Xe+Xe and Pb+Pb collisions, as a function of centrality, are also compared to theoretical calculations.

Measurement of differential cross sections for single diffractive dissociation in root s=8 TeV pp collisions using the ATLAS ALFA spectrometer

JOURNAL OF HIGH ENERGY PHYSICS 2020 (2020) ARTN 42

© 2020, The Author(s). A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s = 8 TeV is used to study inclusive single diffractive dissociation, pp → X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 &lt; log10ξ &lt; −1.6 and 0.016 &lt; |t| &lt; 0.43 GeV2, where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X. The data are consistent with an exponential t dependence, dσ/dt ∝ eBt with slope parameter B = 7.65 ± 0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09. [Figure not available: see fulltext.]

Z boson production in Pb+Pb collisions at s<inf>NN</inf>=5.02 TeV measured by the ATLAS experiment

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 802 (2020)

© 2020 The Author(s) The production yield of Z bosons is measured in the electron and muon decay channels in Pb+Pb collisions at sNN=5.02 TeV with the ATLAS detector. Data from the 2015 LHC run corresponding to an integrated luminosity of 0.49 nb−1 are used for the analysis. The Z boson yield, normalised by the total number of minimum-bias events and the mean nuclear thickness function, is measured as a function of dilepton rapidity and event centrality. The measurements in Pb+Pb collisions are compared with similar measurements made in proton–proton collisions at the same centre-of-mass energy. The nuclear modification factor is found to be consistent with unity for all centrality intervals. The results are compared with theoretical predictions obtained at next-to-leading order using nucleon and nuclear parton distribution functions. The normalised Z boson yields in Pb+Pb collisions lie 1–3σ above the predictions. The nuclear modification factor measured as a function of rapidity agrees with unity and is consistent with a next-to-leading-order QCD calculation including the isospin effect.

Nuclear binding energy and transverse momentum imbalance in neutrino-nucleus reaction

arxiv (2019)
Part of a series from Arxiv

F Akbar, DA Andrade, MV Ascencio, L Bellantoni, JL Bonilla, A Bodek, MF Carneiro, D Coplowe, A Filkins, H Gallagher, A Ghosh, R Gran, DA Harris, A Lozano, T Le, E Maher, WA Mann, S Manly, V Paolone, A Olivier, S Henry, S Jena, J Kleykamp, M Kordosky

Observables based on the final state kinematic imbalances are measured in the mesonless production of $\nu_\mu+A\rightarrow\mu^-+p+X$ in the MINERvA tracker. Components of the muon-proton momentum imbalances parallel ($\delta p_{Ty}$) and perpendicular($\delta p_{Tx}$) to the momentum transfer in the transverse plane are found to be sensitive to the nuclear effects such as Fermi motion, binding energy and non-QE contributions. The QE peak location in $\delta p_{Ty}$ is particularly sensitive to the binding energy. Differential cross sections are compared to predictions from different neutrino interaction models. None of the Fermi gas models simultaneously describe every feature of the QE peak width, location, and non-QE contribution to the signal process. Correcting the GENIE's binding energy implementation according to theory causes better agreement with data. Hints of proton left-right asymmetry is observed in $\delta p_{Tx}$. Better modelling of the binding energy can reduce bias in neutrino energy reconstruction and these observables can be applied in current and future experiments to better constrain nuclear effects.

Search for displaced vertices of oppositely charged leptons from decays of long-lived particles in pp collisions at root s=13 TeV with the ATLAS detector

PHYSICS LETTERS B 801 (2020) ARTN 135114

M Aaboud, G Aad, B Abbott, O Abdinov, B Abeloos, D Abhayasinghe, S Abidi, O AbouZeid, N Abraham, H Abramowicz, H Abreu, Y Abulaiti, B Acharya, S Adachi, L Adamczyk, J Adelman, M Adersberger, A Adiguzel, T Adye, A Affolder, Y Afik, C Agheorghiesei, J Aguilar-Saavedra, S Akatsuka, T Akesson

© 2019 The Author(s) A search for long-lived particles decaying into an oppositely charged lepton pair, μμ, ee, or eμ, is presented using 32.8fb−1 of pp collision data collected at s=13 TeV by the ATLAS detector at the LHC. Candidate leptons are required to form a vertex, within the inner tracking volume of ATLAS, displaced from the primary pp interaction region. No lepton pairs with an invariant mass greater than 12 GeV are observed, consistent with the background expectations derived from data. The detection efficiencies for generic resonances with lifetimes (cτ) of 100–1000 mm decaying into a dilepton pair with masses between 0.1–1.0 TeV are presented as a function of pT and decay radius of the resonances to allow the extraction of upper limits on the cross sections for theoretical models. The result is also interpreted in a supersymmetric model in which the lightest neutralino, produced via squark–antisquark production, decays into ℓ+ℓ′−ν (ℓ,ℓ′=e, μ) with a finite lifetime due to the presence of R-parity violating couplings. Cross-section limits are presented for specific squark and neutralino masses. For a 700 GeV squark, neutralinos with masses of 50–500 GeV and mean proper lifetimes corresponding to cτ values between 1 mm to 6 m are excluded. For a 1.6 TeV squark, cτ values between 3 mm to 1 m are excluded for 1.3 TeV neutralinos.

Search for non-resonant Higgs boson pair production in the bbl nu l nu final state with the ATLAS detector in pp collisions at root s=13 TeV

PHYSICS LETTERS B 801 (2020) ARTN 135145

M Aaboud, G Aad, B Abbott, O Abdinov, B Abeloos, D Abhayasinghe, S Abidi, O AbouZeid, N Abraham, H Abramowicz, H Abreu, Y Abulaiti, B Acharya, S Adachi, L Adamczyk, J Adelman, M Adersberger, A Adiguzel, T Adye, A Affolder, Y Afik, C Agheorghiesei, J Aguilar-Saavedra, S Akatsuka, T Akesson

© 2019 The Author(s) A search for non-resonant Higgs boson pair production, as predicted by the Standard Model, is presented, where one of the Higgs bosons decays via the H→bb channel and the other via one of the H→WW⁎/ZZ⁎/ττ channels. The analysis selection requires events to have at least two b-tagged jets and exactly two leptons (electrons or muons) with opposite electric charge in the final state. Candidate events consistent with Higgs boson pair production are selected using a multi-class neural network discriminant. The analysis uses 139 fb−1 of pp collision data recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. An observed (expected) upper limit of 1.2 (0.9−0.3+0.4) pb is set on the non-resonant Higgs boson pair production cross-section at 95% confidence level, which is equivalent to 40 (29−9+14) times the value predicted in the Standard Model.

Search for the Higgs boson decays H -> ee and H -> e mu in pp collisions at root s=13 TeV with the ATLAS detector

PHYSICS LETTERS B 801 (2020) ARTN 135148

M Aaboud, G Aad, B Abbott, S Akatsuka, T Akesson, E Akilli, A Akimov, G Alberghi, J Albert, P Albicocco, MJA Verzini, S Alderweireldt, M Aleksa, I Aleksandrov, C Alexa, T Alexopoulos, M Alhroob, B Ali, G Alimonti, J Alison, S Alkire, C Allaire, B Allbrooke, B Allen, P Allport

© 2019 The Author Searches for the Higgs boson decays H→ee and H→eμ are performed using data corresponding to an integrated luminosity of 139fb−1 collected with the ATLAS detector in pp collisions at s=13 TeV at the LHC. No significant signals are observed, in agreement with the Standard Model expectation. For a Higgs boson mass of 125 GeV, the observed (expected) upper limit at the 95% confidence level on the branching fraction B(H→ee) is 3.6×10−4 (3.5×10−4) and on B(H→eμ) is 6.2×10−5 (5.9×10−5). These results represent improvements by factors of about five and six on the previous best limits on B(H→ee) and B(H→eμ) respectively.

Search for Magnetic Monopoles and Stable High-Electric-Charge Objects in 13 Tev Proton-Proton Collisions with the ATLAS Detector.

Physical review letters 124 (2020) 031802-

A search for magnetic monopoles and high-electric-charge objects is presented using 34.4  fb^{-1} of 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015 and 2016. The considered signature is based upon high ionization in the transition radiation tracker of the inner detector associated with a pencil-shape energy deposit in the electromagnetic calorimeter. The data were collected by a dedicated trigger based on the tracker high-threshold hit capability. The results are interpreted in models of Drell-Yan pair production of stable particles with two spin hypotheses (0 and 1/2) and masses ranging from 200 to 4000 GeV. The search improves by approximately a factor of 5 the constraints on the direct production of magnetic monopoles carrying one or two Dirac magnetic charges and stable objects with electric charge in the range 20≤|z|≤60 and extends the charge range to 60<|z|≤100.

Constraint of the MINERνA medium energy neutrino flux using neutrino-electron elastic scattering

Physical Review D American Physical Society 100 (2019) 092001

E Valencia, D Jena, D Coplowe, X Lu

Tuning the GENIE pion production model with MINERvA data

Physical Review D American Physical Society 100 (2019) 072005

P Stowell, L Pickering, C Willkinson, F Akbar, C Wret, L Bellantoni, MV Ascencio, DA Andrade, M Betancourt, A Bercellie, A Bodek, A Bravar, H Budd, G Caceres, T Cai, MF Cameiro, J Chaves, H Da Motta, GA Diaz, L Fields, J Felix, A Filkins, R Fine, N Fiza

Faced with unresolved tensions between neutrino interaction measurements at few-GeV neutrino energies, current experiments are forced to accept large systematic uncertainties to cover discrepancies between their data and model predictions. The widely used pion production model in genie is compared to four MINERνA charged current pion production measurements using nuisance. Tunings, i.e., adjustments of model parameters, to help match genie to MINERνA and older bubble chamber data are presented. We find that scattering off nuclear targets as measured in MINERνA is not in good agreement with expectations based upon scattering off nucleon (hydrogen or deuterium) targets in existing bubble chamber data. An additional ad hoc correction for the low-Q2 region, where collective nuclear effects are expected to be large, is presented. While these tunings and corrections improve the agreement of genie with the data, the modeling is imperfect. The development of these tunings within the nuisance framework allows for straightforward extensions to other neutrino event generators and models, and allows omitting and including new datasets as they become available.

Cosmogenic neutron production at the Sudbury Neutrino Observatory

PHYSICAL REVIEW D 100 (2019) ARTN 112005

B Aharmim, S Ahmed, A Anthony, N Barros, P Doe, G Doucas, P-L Drouin, M Dunford, S Elliott, F Fleurot, R Ford, J Formaggio, N Gagnon, K Gilje, J Goon, K Graham, E Guillian, S Habib, R Hahn, A Hallin, E Hallman, P Harvey, R Hazama, W Heintzelman, J Heise

First measurement of inclusive muon neutrino charged current differential cross sections on argon at Eν∼0.8  GeV with the MicroBooNE detector

Physical Review Letters American Physical Society 123 (2019) 131801

M Bass, F Bay, A Bhat, F Cavanna, G Cerati, Y Chen, E Church, D Cianci, EO Cohen, GH Collin, JM Conrad, M Convery, L Cooper-Troendle, JI Crespo-Anadón, M Del Tutto, D Devitt, A Diaz, B Eberly, A Ereditato, L Escudero Sanchez, AP Furmanski, D Garcia-Gamez, D Goeldi, S Gollapinni, O Goodwin

We report the first measurement of the double-differential and total muon-neutrino charged-current inclusive cross sections on argon at a mean neutrino energy of 0.8 GeV. Data were collected using the MicroBooNE liquid argon time projection chamber located in the Fermilab Booster neutrino beam, and correspond to $1.6 \times 10^{20}$ protons on target of exposure. The measured differential cross sections are presented as a function of muon momentum, using multiple Coulomb scattering as a momentum measurement technique, and the muon angle with respect to the beam direction. We compare the measured cross sections to multiple neutrino event generators and find better agreement with those containing more complete physics at low $Q^2$. The total flux integrated cross section is measured to be $0.693 \pm 0.010 \, (\text{stat.}) \pm 0.165 \, (\text{syst.}) \times 10^{-38} \, \text{cm}^{2}$.

Commissioning and Operation of the Readout System for the SoLid Neutrino Detector

Journal of Instrumentation IOP Publishing (2019)

Y Abreu, Y Amhis, G Ban, W Beaumont, S Binet, M Bongrand, D Boursette, BC Castle, H Chanal, K Clark, B Coupé, P Crochet, D Cussans, AD Roeck, D Durand, M Fallot, L Ghys, L Giot, K Graves, B Guillon, D Henaff, B Hosseini, S Ihantola, S Jenzer, S Kalcheva, LN Kalousis, M Labare, G Lehaut, S Manley, L Manzanillas, J Mermans, I Michiels, S Monteil, C Moortgat, D Newbold, J Park, V Pestel, K Petridis, I Piñera, L Popescu, D Ryckbosch, N Ryder, D Saunders, M-H Schune, M Settimo, L Simard, A Vacheret, G Vandierendonck, SV Dyck, PV Mulders, NV Remortel, S Vercaemer, M Verstraeten, B Viaud, A Weber, F Yermia

The SoLid experiment aims to measure neutrino oscillation at a baseline of 6.4 m from the BR2 nuclear reactor in Belgium. Anti-neutrinos interact via inverse beta decay (IBD), resulting in a positron and neutron signal that are correlated in time and space. The detector operates in a surface building, with modest shielding, and relies on extremely efficient online rejection of backgrounds in order to identify these interactions. A novel detector design has been developed using 12800 5 cm cubes for high segmentation. Each cube is formed of a sandwich of two scintillators, PVT and 6LiF:ZnS(Ag), allowing the detection and identification of positrons and neutrons respectively. The active volume of the detector is an array of cubes measuring 80x80x250 cm (corresponding to a fiducial mass of 1.6 T), which is read out in layers using two dimensional arrays of wavelength shifting fibres and silicon photomultipliers, for a total of 3200 readout channels. Signals are recorded with 14 bit resolution, and at 40 MHz sampling frequency, for a total raw data rate of over 2 Tbit/s. In this paper, we describe a novel readout and trigger system built for the experiment, that satisfies requirements on: compactness, low power, high performance, and very low cost per channel. The system uses a combination of high price-performance FPGAs with a gigabit Ethernet based readout system, and its total power consumption is under 1 kW. The use of zero suppression techniques, combined with pulse shape discrimination trigger algorithms to detect neutrons, results in an online data reduction factor of around 10000. The neutron trigger is combined with a large per-channel history time buffer, allowing for unbiased positron detection. The system was commissioned in late 2017, with successful physics data taking established in early 2018.

Pion-proton correlation in neutrino interactions on nuclei

Physical Review D American Physical Society 100 (2019) 073010

T Cai, X Lu, D Ruterbories

In neutrino-nucleus interactions, a proton produced with a correlated pion might exhibit a left-right asymmetry relative to the lepton scattering plane even when the pion is absorbed. Absent in other proton production mechanisms, such an asymmetry measured in charged-current pionless production could reveal the details of the absorbed-pion events that are otherwise inaccessible. In this study, we demonstrate the idea of using final-state proton left-right asymmetries to quantify the absorbed-pion event fraction and underlying kinematics. This technique might provide critical information that helps constrain all underlying channels in neutrino-nucleus interactions in the GeV regime.

Measurement of neutrino and antineutrino neutral-current quasielastic-like interactions on oxygen by detecting nuclear de-excitation $γ$-rays

Physical Review D: Particles, Fields, Gravitation and Cosmology American Physical Society (2019)

Neutrino- and antineutrino-oxygen neutral-current quasielastic-like interactions are measured at Super-Kamiokande using nuclear de-excitation $\gamma$-rays to identify signal-like interactions in data from a $14.94 \ (16.35)\times 10^{20}$ protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are $\langle \sigma_{\nu {\rm -NCQE}} \rangle = 1.70 \pm 0.17 ({\rm stat.}) ^{+ {\rm 0.51}}_{- {\rm 0.38}} ({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}$ with a flux-averaged energy of 0.82 GeV and $\langle \sigma_{\bar{\nu} {\rm -NCQE}} \rangle = 0.98 \pm 0.16 ({\rm stat.}) ^{+ {\rm 0.26}}_{- {\rm 0.19}} ({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}$ with a flux-averaged energy of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are the most precise to date, and the antineutrino result is the first cross section measurement of this channel. They are compared with various theoretical predictions. The impact on evaluation of backgrounds to searches for supernova relic neutrinos at present and future water Cherenkov detectors is also discussed.