The Lambda and Lambda-bar polarizations in muon neutrino charged current interactions have been m... more The Lambda and Lambda-bar polarizations in muon neutrino charged current interactions have been measured in the NOMAD experiment. The event sample (8087 reconstructed Lambda's and 649 Lambda-bar's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. For the Lambda hyperons we observe negative polarization along the W-boson direction which is enhanced in the target fragmentation region: Px(xF < 0) = -0.21 +- 0.04 (stat) +- 0.02 (sys). In the current fragmentation region we find Px(xF > 0) = -0.09 +- 0.06 (stat) +- 0.03(sys). A significant transverse polarization (in the direction orthogonal to the Lambda production plane) has been observed for the first time in a neutrino experiment: Py = -0.22 +- 0.03 (stat) +- 0.01 (sys). The dependence of the absolute value of Py on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement wit...
Measurement of Lambda0 and bar Lambda 0 Polarization in nu mu CC Interactions in NOMAD
Acta Physica Polonica B - ACTA PHYS POL B, 2002
The Lambda 0 and bar Lambda 0 polarizations in nu mu charged current interactions have been measu... more The Lambda 0 and bar Lambda 0 polarizations in nu mu charged current interactions have been measured in the NOMAD experiment. The event sample (8087 reconstructed Lambda 0's and 649 bar Lambda 0's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. For the Lambda 0 hyperons we observe negative polarization along the W-boson direction which is enhanced in the target fragmentation region: Px (xF < 0) = -0.21 ± 0.04 (stat) ± 0.02 (syst). In the current fragmentation region we find Px (xF > 0) = -0.09 ± 0.06 (stat) ± 0.03 (syst). A significant transverse polarization (in the direction orthogonal to the Lambda 0 production plane) has been observed for the first time in a neutrino experiment: Py = -0.22 ± 0.03 (stat) ± 0.01 (syst). The dependence of the absolute value of Py on the Lambda 0 transverse momentum with respect to the hadronic jet direction is in qualitative agreeme...
Recently completed precision measurements and other ongoing analyses by NOMAD experiment are revi... more Recently completed precision measurements and other ongoing analyses by NOMAD experiment are reviewed
The main areas of research are neutrino physics, spin physics, fragmentation and fracture functio... more The main areas of research are neutrino physics, spin physics, fragmentation and fracture functions, astrophysics, cosmic rays, cosmology.
This lecture presented at the BaikaL Summer School on Physics of Elementary Particles and Astroph... more This lecture presented at the BaikaL Summer School on Physics of Elementary Particles and Astrophysics in 2011 reviewes recent hot results in neutrino physics.
The Λ 0 polarization in ν µ charged current interactions has been measured in the NOMAD experimen... more The Λ 0 polarization in ν µ charged current interactions has been measured in the NOMAD experiment. The event sample (8087 reconstructed Λ 0 's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. We observe negative polarization along the W-boson direction which is enhanced in the target fragmentation region: P x (x F < 0) = −0.21 ± 0.04(stat) ± 0.02(sys). In the current fragmentation region we find P x (x F > 0) = −0.09 ± 0.06(stat) ± 0.03(sys). These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization (in the direction orthogonal to the Λ 0 production plane) has been observed for the first time in a neutrino experiment: P y = −0.22 ± 0.03(stat)± 0.01(sys). The dependence of the absolute value of P y on the Λ 0 transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments.
In this paper we discuss some aspects of the theory of wave packets. We consider a popular non-co... more In this paper we discuss some aspects of the theory of wave packets. We consider a popular non-covariant Gaussian model used in various applications and show that it predicts too slow a longitudinal dispersion rate for relativistic particles. We revise this approach by considering a covariant model of Gaussian wave packets, and examine our results by inspecting a wave packet of arbitrary form. A general formula for the time dependence of the dispersion of a wave packet of arbitrary form is found. Finally, we give a transparent interpretation of the disappearance of the wave function over time due to the dispersion a feature often considered undesirable, but which is unavoidable for wave packets. We find, starting from simple examples, proceeding with their generalizations and finally by considering the continuity equation, that the integral over time of both the flux and probability densities are asymptotically proportional to the factor 1/|x| 2 in the rest frame of the wave packet, just as in the case of an ensemble of classical particles.
We discuss a possibility that the so-called reactor antineutrino anomaly can be, at least in part... more We discuss a possibility that the so-called reactor antineutrino anomaly can be, at least in part, explained by applying a quantum field-theoretical approach to neutrino oscillations, which in particular predicts a small deviation from the classical inverse-square law at short but macroscopic distances between the neutrino source and detector. An extensive statistical analysis of the reactor data is performed to examine this speculation.
We consider models for the spin transfers to Λ andΛ hyperons produced in lepton-nucleon deep-inel... more We consider models for the spin transfers to Λ andΛ hyperons produced in lepton-nucleon deep-inelastic scattering. We make predictions for longitudinal Λ andΛ spin transfers for the COMPASS experiment and for HERA, and for the spin transfer to Λ hyperons produced at JLAB. We demonstrate that accurate measurements of the spin transfers to Λ andΛ hyperons with COMPASS kinematics have the potential to probe the intrinsic strangeness in the nucleon. We show that a measurement ofΛ polarization could provide a clean probe of the spin transfer froms quarks and provides a new possibility to measure the antistrange quark distribution function. COMPASS data in a domain of x that has not been studied previously will provide valuable extra information to fix models for the nucleon spin structure. The spin transfer toΛ hyperons, which could be measured by the COMPASS experiment, would provide a new tool to distinguish between the SU(6) and Burkardt-Jaffe (BJ) models for baryon spin structure. In the case of the HERA electron-proton collider experiments with longitudinally-polarized electrons, the separation between the target and current fragmentation mechanisms is more clear. It provides a complementary probe of the strange quark distribution and helps distinguish between the SU(6) and BJ models for the Λ andΛ spin structure. Finally, we show that the spin transfer to Λ hyperons measured in a JLAB experiment would be dominated by the spin transfer of the intrinsic polarized strangeness in the remnant nucleon, providing an independent way to check our model predictions.
A multiple production study of neutral strange particles in ν µ charged current interactions has ... more A multiple production study of neutral strange particles in ν µ charged current interactions has been performed using the full data sample from the NOMAD experiment. This analysis allows one to investigate the mechanisms of strange particle production in neutrino interactions. In this study we have tried to build a model for the production of strange particles, which would allow us to describe our measured rates of neutral strange particles, as well as the rates of the single-, double-and triple-V 0 production:
The Daya Bay reactor neutrino experiment has observed the disappearance of electron antineutrinos... more The Daya Bay reactor neutrino experiment has observed the disappearance of electron antineutrinos from nuclear reactors at ∼kilometer baselines. The relative measurement of theν e rate and spectrum between near and far detectors allows for a precision measurement of the oscillation parameters sin 2 2θ 13 and |Δm 2 ee |. Two new antineutrino detectors (ADs) were installed in summer 2012, bringing the experiment to the final 8-AD configuration. With 621 days of data, Daya Bay has measured sin 2 2θ 13 = 0.084 ± 0.005 and |Δm 2 ee | = 2.44 +0.10 −0.11 × 10 −3 eV 2. This is the most precise measurement of sin 2 2θ 13 to date and the most precise measurement of |Δm 2 ee | in this channel. Several other analyses are also performed, including an independent measurement of sin 2 2θ 13 usingν e samples tagged by neutron capture on hydrogen, a search for light sterile neutrinos, and a measurement of the absolute reactor antineutrino flux.
Neutrino velocity anomalies: a resolution without a revolution
We argue that the neutrino advance of time observed in MINOS and OPERA experiments can be explain... more We argue that the neutrino advance of time observed in MINOS and OPERA experiments can be explained in the framework of the standard relativistic quantum theory as a manifestation of the large effective transverse size of the eigenmass neutrino wavepackets. Note: After eliminating the errors, dedicated upgrades of the CNGS timing system and of the OPERA detector, and so on, the OPERA collaboration has disconfirmed their earlier result, showing no significant deviation of the muon neutrino velocity from the speed of light. Similar measurements (with similar conclusions) were performed by the ICARUS, Borexino and LVD collaborations... So the problem is dead. But the idea about macroscopically large neutrino wavepackets is still alive and can be applied to other topics.
We discuss a process of hadronization of light quarks into charged pions in e + e − annihilations... more We discuss a process of hadronization of light quarks into charged pions in e + e − annihilations and in deep inelastic scattering of charged leptons and neutrino off nucleons. We write the corresponding semi-inclusive cross sections of pions production in terms of quark fragmentation functions and fracture functions. We suggest a new method of measurements of fragmentation and fracture functions based on analysis of semi-inclusive data.
We propose a model for the longitudinal polarization of Lambda baryons produced in deep-inelastic... more We propose a model for the longitudinal polarization of Lambda baryons produced in deep-inelastic lepton scattering at any xF, based on static SU(6) quark-diquark wave functions and polarized intrinsic strangeness in the nucleon associated with individual valence quarks. Free parameters of the model are fixed by fitting the NOMAD data on the longitudinal polarization of Lambda hyperons in neutrino interactions. Our model correctly reproduces the observed dependences of Lambda polarization on the kinematic variables. Within the context of our model, the NOMAD data imply that the intrinsic strangeness associated with a valence quark has anticorrelated polarization. We also compare our model predictions with results from the HERMES and E665 experiments using charged leptons. Predictions of our model for the COMPASS experiment are also presented.
A first result of the search for ν μ → ν e oscillations in the OPERA experiment, located at the G... more A first result of the search for ν μ → ν e oscillations in the OPERA experiment, located at the Gran Sasso Underground Laboratory, is presented. The experiment looked for the appearance of ν e in the CNGS neutrino beam using the data collected in 2008 and 2009. Data are compatible with the non-oscillation hypothesis in the three-flavour mixing model. A further analysis of the same data constrains the non-standard oscillation parameters θ new and $ \varDelta m_{\mathrm{new}}^2 $ suggested by the LSND and MiniBooNE experiments. For large $ \varDelta m_{\mathrm{new}}^2 $ values (>0.1 eV2), the OPERA 90% C.L. upper limit on sin2(2θ new) based on a Bayesian statistical method reaches the value 7.2 × 10−3.
We present a search for neutrino-induced events containing a single, exclusive photon using data ... more We present a search for neutrino-induced events containing a single, exclusive photon using data from the NOMAD experiment at the CERN SPS where the average energy of the neutrino flux is 25 GeV. The search is motivated by an excess of electron-like events in the 200-475 MeV energy region as reported by the Mini-BOONE experiment. In NOMAD, photons are identified via their conversion to e + e − in an active target embedded in a magnetic field. The background to the single photon signal is dominated by the asymmetric decay of neutral pions produced either in a coherent neutrino-nucleus interaction, or in a neutrino-nucleon neutral current deep inelastic scattering, or in an interaction occurring outside the fiducial volume. All three backgrounds are determined in situ using control data samples prior to opening the 'signal-box'. In the signal region, we observe 155 events with a predicted background of 129.2 ± 8.5 ± 3.3. We interpret this as null evidence for excess of single photon events, and set a limit. Assuming that the hypothetical single photon has a momentum distribution similar to that of a photon from the coherent π 0 decay, the measurement yields an upper limit on single photon events, < 4.0 × 10 −4 per ν µ charged current event. Narrowing the search to events where the photon is approximately collinear with the incident neutrino, we observe 78 events with a predicted background of 76.6 ± 4.9 ± 1.9 yielding a more stringent upper limit, < 1.6 × 10 −4 per ν µ charged current event.
Results of a detailed study of strange particle production in neutrino neutral current interactio... more Results of a detailed study of strange particle production in neutrino neutral current interactions are presented using the data from the NOMAD experiment. Integral yields of neutral strange particles (K 0 s , Λ,Λ) have been measured. Decays of resonances and heavy hyperons with an identified K 0 s or Λ in the final state have been analyzed. Clear signals corresponding to K ⋆± and Σ(1385) ± have been observed. First results on the measurements of the Λ polarization in neutral current interactions have been obtained.
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