Proton-proton elastic scattering has been measured by the TOTEM experiment at the CERN Large Hadron Collider at root s = 7 TeV in special runs with the Roman Pot detectors placed as close to the outgoing beam as seven times the transverse beam size. The differential cross-section measurements are reported in the vertical bar t vertical bar-range of 0.36 to 2.5 GeV2. Extending the range of data to low t values from 0.02 to 0.33 GeV2, and utilizing the luminosity measurements of CMS, the total proton-proton cross section at root s = 7 TeV is measured to be (98.3 +/- 0.2(stat) +/- 2.8(syst)) mb.

TOTEM has measured the differential cross-section for elastic proton-proton scattering at the LHC energy of root s = 7 TeV analysing data from a short run with dedicated large-beta* optics. A single exponential fit with a slope B = (20.1 +/- 0.2(stat) +/- 0.3(syst)) GeV(-2) describes the range of the four-momentum transfer squared vertical bar t vertical bar from 0.02 to 0.33 GeV(2). After the extrapolation to vertical bar t vertical bar = 0, a total elastic scattering cross-section of (24.8 +/- 0.2(stat) +/- 1.2(syst)) mb was obtained. Applying the optical theorem and using the luminosity measurement from CMS, a total proton-proton cross-section of (98.3 +/- 0.2(stat) +/- 2.8(syst)) mb was deduced which is in good agreement with the expectation from the overall fit of previously measured data over a large range of center-of-mass energies. From the total and elastic pp cross-section measurements, an inelastic pp cross-section of (73.5 +/- 0.6(stat) (+1.8)(-1.3) (syst)) mb was inferred.

The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with a center-of-mass energy of root s = 7 TeV. By utilizing the very forward TOTEM tracking detectors T1 and T2, which extend up to vertical bar eta vertical bar = 6.5, a clean sample of double diffractive pp events was extracted. From these events, we determined the cross section sigma(DD) = (116 +/- 25) mu b for events where both diffractive systems have 4.7 < vertical bar eta vertical bar(min) < 6.5.

Precise knowledge of the beam optics at the LHC is crucial to fulfill the physics goals of the TOTEM experiment, where the kinematics of the scattered protons is reconstructed with near-beam telescopes—so-called Roman pots (RP). Before being detected, the protons' trajectories are influenced by the magnetic fields of the accelerator lattice. Thus precise understanding of the proton transport is of key importance for the experiment. A novel method of optics evaluation is proposed which exploits kinematical distributions of elastically scattered protons observed in the RPs. Theoretical predictions, as well as Monte Carlo studies, show that the residual uncertainty of the optics estimation method is smaller than $2.5$.

The TOTEM collaboration has measured the proton-proton total cross section at root s = 8 TeV using a luminosity-independent method. In LHC fills with dedicated beam optics, the Roman pots have been inserted very close to the beam allowing the detection of similar to 90% of the nuclear elastic scattering events. Simultaneously the inelastic scattering rate has been measured by the T1 and T2 telescopes. By applying the optical theorem, the total proton-proton cross section of (101.7 +/- 2.9) mb has been determined, well in agreement with the extrapolation from lower energies. This method also allows one to derive the luminosity-independent elastic and inelastic cross sections: sigma(el) = (27.1 +/- 1.4) mb; sigma(inel) = (74.7 +/- 1.7) mb.

The TOTEM experiment at the LHC has performed the first luminosity-independent determination of the total proton-proton cross-section at root s = 7 TeV. This technique is based on the optical theorem and requires simultaneous measurements of the inelastic rate - accomplished with the forward charged-particle telescopes T1 and T2 in the range 3.1 < vertical bar eta vertical bar < 6.5 - and of the elastic rate by detecting the outcoming protons with Roman Pot detectors. The data presented here were collected in a dedicated run in 2011 with special beam optics (beta* = 90m) and Roman Pots approaching the beam close enough to register elastic events with squared four-momentum transfers vertical bar t vertical bar as low as 5 . 10(-3) GeV2. The luminosity-independent results for the elastic, inelastic and total cross-sections are sigma(el) = (25.1 +/- 1.1) mb, sigma(inel) = (72.9 +/- 1.5) mb and sigma(tot) = (98.0 +/- 2.5) mb, respectively. At the same time this method yields the integrated luminosity, in agreement with measurements by CMS. TOTEM has also determined the total cross-section in two complementary ways, both using the CMS luminosity measurement as an input. The first method sums the elastic and inelastic cross-sections and thus does not depend on the rho parameter. The second applies the optical theorem to the elastic-scattering measurements only and therefore is free of the T1 and T2 measurement uncertainties. The methods, having very different systematic dependences, give results in excellent agreement. Moreover, the rho-independent measurement makes a first estimate for the rho parameter at root s = 7 TeV possible: vertical bar rho vertical bar = 0.145 +/- 0.091.

The TOTEM experiment at the LHC has measured the inelastic proton-proton cross-section at root s = 7 TeV in a beta* = 90 m run with low inelastic pile-up. The measurement was based on events with at least one charged particle in the T2 telescope acceptance of 5.3 < vertical bar eta vertical bar < 6.5 in pseudorapidity. Combined with data from the T1 telescope, covering 3.1 < vertical bar eta vertical bar < 4.7, the cross-section for inelastic events with at least one vertical bar eta vertical bar <= 6.5 final-state particle was determined to be (70.5 +/- 2.9) mb. This cross-section includes all central diffractive events of which maximally 0.25 mb is estimated to escape the detection of the telescopes. Based on models for low mass diffraction, the total inelastic cross-section was deduced to be (73.7 +/- 3.4) mb. An upper limit of 6.31 mb at 95% confidence level on the cross-section for events with diffractive masses below 3.4 GeV was obtained from the difference between the overall inelastic cross-section obtained by TOTEM using elastic scattering and the cross-section for inelastic events with at least one vertical bar eta vertical bar <= 6.5 final-state particle.

The T2K Collaboration reports evidence for electron neutrino appearance at the atmospheric mass splitting, vertical bar Delta m(32)(2)vertical bar approximate to 2.4 X 10(-3) eV(2). An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beam's origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of 3.3 +/- 0.4(syst) events is expected. The background-only hypothesis is rejected with a p value of 0.0009 (3.1 sigma), and a fit assuming nu(mu) -> nu(e) oscillations with sin (2)2 theta(23) = 1, delta(CP) = 0 and vertical bar Delta m(32)(2)vertical bar = 2.4 X 10(-3) eV(2) yields sin (2)2 theta(13) = 0.088(-0.039)(+0.049)(stat + syst).

We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43×1020 protons on target, we observe 31 fully-contained single μ-like ring events in Super-Kamiokande, compared with an expectation of 104±14 (syst) events without neutrino oscillations. The best-fit point for two-flavor νμ→ντ oscillations is sin⁡2(2θ23)=0.98 and |Δm322|=2.65×10-3  eV2. The boundary of the 90% confidence region includes the points (sin⁡2(2θ23),|Δm322|)=(1.0,3.1×10-3  eV2), (0.84, 2.65×10-3  eV2) and (1.0, 2.2×10-3  eV2).

At the LHC energy of root s = 7TeV, under various beam and background conditions, luminosities, and Roman Pot positions, TOTEM has measured the differential cross-section for proton-proton elastic scattering as a function of the four-momentum transfer squared t. The results of the different analyses are in excellent agreement demonstrating no sizeable dependence on the beam conditions. Due to the very close approach of the Roman Pot detectors to the beam center (approximate to 5 sigma(beam)) in a dedicated run with beta* = 90 m, vertical bar t vertical bar-values down to 5.10(-3) GeV2 were reached. The exponential slope of the differential elastic cross-section in this newly explored vertical bar t vertical bar-region remained unchanged and thus an exponential fit with only one constant B = (19.9+/-0.3) GeV-2 over the large vertical bar t vertical bar-range from 0.005 to 0.2 GeV2 describes the differential distribution well. The high precision of the measurement and the large fit range lead to an error on the slope parameter B which is remarkably small compared to previous experiments. It allows a precise extrapolation over the non-visible cross-section (only 9%) to t = 0. With the luminosity from CMS, the elastic cross-section was determined to be (25.4+/-1.1) mb, and using in addition the optical theorem, the total pp cross-section was derived to be (98.6 +/- 2.2) mb. For model comparisons the t-distributions are tabulated including the large vertical bar t vertical bar-range of the previous measurement (TOTEM Collaboration (ANTCHEV G. et al.), EPL, 95 (2011) 41001).

The TOTEM experiment has measured the charged-particle pseudorapidity density dN ch/dη in pp collisions at for 5.3<|η|<6.4 in events with at least one charged particle with transverse momentum above 40 MeV/c in this pseudorapidity range. This extends the analogous measurement performed by the other LHC experiments to the previously unexplored forward η region. The measurement refers to more than 99% of non-diffractive processes and to single and double diffractive processes with diffractive masses above ∼3.4 GeV/c 2, corresponding to about 95% of the total inelastic cross-section. The dN ch/dη has been found to decrease with |η|, from 3.84 ± 0.01(stat) ± 0.37(syst) at |η|=5.375 to 2.38±0.01(stat)±0.21(syst) at |η|=6.375. Several MC generators have been compared to data; none of them has been found to fully describe the measurement.

The T2K experiment observes indications of nu(mu) -> nu(mu) e appearance in data accumulated with 1.43 x 10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Delta m(23)(2)| = 2.4 x 10(-3) eV(2), sin(2)2 theta(23) = 1 and sin(2)2 theta(13) = 0, the expected number of such events is 1.5 +/- 0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7 x 10(-3), equivalent to 2.5 sigma significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2 theta(13) < 0.28(0.34) for delta(CP) = 0 and a normal (inverted) hierarchy.

The T2K off-axis near detector ND280 is used to make the first differential cross-section measurements of electron neutrino charged current interactions at energies ∼1  GeV as a function of electron momentum, electron scattering angle, and four-momentum transfer of the interaction. The total flux-averaged νe charged current cross section on carbon is measured to be ⟨σ⟩ϕ=1.11±0.10(stat)±0.18(syst)×10−38  cm2/nucleon. The differential and total cross-section measurements agree with the predictions of two leading neutrino interaction generators, NEUT and GENIE. The NEUT prediction is 1.23×10−38  cm2/nucleon and the GENIE prediction is 1.08×10−38  cm2/nucleon. The total νe charged current cross-section result is also in agreement with data from the Gargamelle experiment.

The physics programme of the TOTEM experiment requires the detection of very forward protons scattered by only a few microradians out of the LHC beams. For this purpose, stacks of planar Silicon detectors have been mounted in moveable near-beam telescopes (Roman Pots) located along the beamline on both sides of the interaction point. In order to maximise the proton acceptance close to the beams, the dead space at the detector edge had to be minimised. During the detector prototyping phase, different sensor technologies and designs have been explored. A reduction of the dead space to less than 50 mu m m has been accomplished with two novel silicon detector technologies: one with the Current Terminating Structure (CTS) design and one based on the 3D edge manufacturing. This paper describes performance studies on prototypes of these detectors, carried out in 2004 in a fixed-target muon beam at CERN's SPS accelerator. In particular, the efficiency and accuracy in the vicinity of the beam-facing edges are discussed.

The T2K Collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Super-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to 3.01 x 10(20) protons on target. In the absence of neutrino oscillations, 205 +/- 17 (syst) events are expected to be detected while only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum, assuming three neutrino flavors and normal mass hierarchy yields a best-fit mixing angle sin(2) (theta(23)) = 0.514 +/- 0.082 and mass splitting vertical bar Delta m(32)(2)vertical bar = 2.44(-0.15)(+0.17) x 10(-3) eV(2)/c(4). Our result corresponds to the maximal oscillation disappearance probability.

The TOTEM Experiment is designed to measure the total proton-proton cross-section with the luminosity-independent method and to study elastic and diffractive pp scattering at the LHC. To achieve optimum forward coverage for charged particles emitted by the pp collisions in the interaction point IP5, two tracking telescopes, T1 and T2, are installed on each side of the IP in the pseudorapidity region 3.1 <= |eta| <= 6.5, and special movable beam-pipe insertions - called Roman Pots (RPs) - are placed at distances of +/- 147m and +/- 220m from IP5. This article describes in detail the working of the TOTEM detector to produce physics results in the first three years of operation and data taking at the LHC.

-Proton-proton elastic scattering has been measured by the TOTEM experiment at the CERN Large Hadron Collider at root s = 7 TeV in dedicated runs with the Roman Pot detectors placed as close as seven times the transverse beam size (sigma(beam)) from the outgoing beams. After careful study of the accelerator optics and the detector alignment, |t|, the square of four-momentum transferred in the elastic scattering process, has been determined with an uncertainty of delta t = 0.1GeV root|t|. In this letter, first results of the differential cross-section are presented covering a |t|-range from 0.36 to 2.5GeV(2). The differential cross-section in the range 0.36 < |t| < 0.47 GeV(2) is described by an exponential with a slope parameter B = (23.6 +/- 0.5(stat) +/- 0.4(syst)) GeV(-2), followed by a significant diffractive minimum at |t| = (0.53 +/- 0.01(stat) +/- 0.01(syst)) GeV(2). For |t|-values larger than similar to 1.5GeV(2), the cross-section exhibits a power law behaviour with an exponent of -7.8 +/- 0.3(stat) +/- 0.1(syst). When compared to predictions based on the different available models, the data show a strong discriminative power despite th e small t-range covered. Copyright (C) EPLA, 2011

The TOTEM experiment is dedicated to the measurement of the total proton-proton cross-section with the luminosity-independent method and the study of elastic and diffractive scattering processes. Two tracking telescopes, T1 and T2, integrated in the CMS detector, cover the pseudo-rapidity region between 3.1 and 6.5 on both sides of the interaction point IPS. The Roman Pot (RP) stations are located at distances of +/- 147 m and +/- 220 m with respect to the interaction point to measure the very forward scattered protons at very small angles. During the LHC technical stop in winter 201012011, the TOTEM experiment was completed with the installation of the T1 telescope and the RP stations at +/- 147 m. In 2011, the LHC machine provided special optics with the large beta* = 90 m, allowing TOTEM to measure the elastic scattering differential cross-section, down to the four-momentum transfer squared vertical bar t vertical bar = 2 x 10(-2) GeV2. Using the optical theorem and extrapolation of the differential cross-section to t=0 (optical point), the total p-p cross-section at the LHC energy of root s = 7 TeV could be computed for the first time. Furthermore we measured with standard LHC beam optics and the energy of root s = 7 TeV the forward charged particle pseudorapidity density dn/d eta in the range of 5.3 < vertical bar eta vertical bar < 6.4. The status of the experiment, the performance of the detectors with emphasis on the RPs are described and the first physics results are presented. (C) 2012 Elsevier B.V. All rights reserved.

The T2K experiment has reported the first observation of the appearance of electron neutrinos in a muon neutrino beam. The main and irreducible background to the appearance signal comes from the presence in the neutrino beam of a small intrinsic component of electron neutrinos originating from muon and kaon decays. In T2K, this component is expected to represent 1.2% of the total neutrino flux. A measurement of this component using the near detector (ND280), located 280 m from the target, is presented. The charged current interactions of electron neutrinos are selected by combining the particle identification capabilities of both the time projection chambers and electromagnetic calorimeters of ND280. The measured ratio between the observed electron neutrino beam component and the prediction is 1.01 +/- 0.10 providing a direct confirmation of the neutrino fluxes and neutrino cross section modeling used for T2K neutrino oscillation analyses. Electron neutrinos coming from muons and kaons decay are also separately measured, resulting in a ratio with respect to the prediction of 0.68 +/- 0.30 and 1.10 +/- 0.14, respectively.

New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter θ23. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57×1020 protons on target, T2K has fit the energy-dependent νμ oscillation probability to determine oscillation parameters. The 68% confidence limit on sin2(θ23) is 0.514+0.055−0.056 (0.511±0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Δm232=(2.51±0.10)×10−3  eV2/c4 (inverted hierarchy: Δm213=(2.48±0.10)×10−3  eV2/c4). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations using an off-axismuon neutrino beam with a peak energy of about 0.6 GeV that originates at the Japan Proton Accelerator Research Complex accelerator facility. Interactions of the neutrinos are observed at near detectors placed at 280 m from the production target and at the far detector-Super-Kamiokande-located 295 km away. The flux prediction is an essential part of the successful prediction of neutrino interaction rates at the T2K detectors and is an important input to T2K neutrino oscillation and cross section measurements. A FLUKA and GEANT3-based simulation models the physical processes involved in the neutrino production, from the interaction of primary beam protons in the T2K target, to the decay of hadrons and muons that produce neutrinos. The simulation uses proton beam monitor measurements as inputs. The modeling of hadronic interactions is reweighted using thin target hadron production data, including recent charged pion and kaon measurements from the NA61/SHINE experiment. For the first T2K analyses the uncertainties on the flux prediction are evaluated to be below 15% near the flux peak. The uncertainty on the ratio of the flux predictions at the far and near detectors is less than 2% near the flux peak. DOI: 10.1103/PhysRevD.87.012001

The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of 7.3 sigma when compared to 4.92 +/- 0.55 expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles theta(12), theta(23), theta(13), a mass difference vertical bar Delta m(32)(2)vertical bar and a CP violating phase delta(CP). In this neutrino oscillation scenario, assuming vertical bar Delta m(32)(2)vertical bar = 2.4 x 10(-3) eV(2), sin theta(2)(23) = 0.5, and vertical bar Delta m(32)(2)vertical bar > 0 (vertical bar Delta m(32)(2)vertical bar < 0), a best- fit value of sin2 theta(2)(13) = 0.140(- 0.032)(+0.038) (0.170(-0.037)(+0.045)) is obtained at delta(CP) = 0. When combining the result with the current best knowledge of oscillation parameters including the world average value of theta(13) from reactor experiments, some values of delta(CP) are disfavored at the 90% C. L.

We report a measurement of the νμ inclusive charged current cross sections on iron and hydrocarbon in the Tokai-to-Kamioka (T2K) on-axis neutrino beam. The measured inclusive charged current cross sections on iron and hydrocarbon averaged over the T2K on-axis flux with a mean neutrino energy of 1.51 GeV are (1.444±0.002(stat)+0.189−0.157(syst))×10−38  cm2/nucleon and (1.379±0.009(stat)+0.178−0.147(syst))×10−38  cm2/nucleon, respectively, and their cross-section ratio is 1.047±0.007(stat)±0.035(syst). These results agree well with the predictions of the neutrino interaction model, and thus we checked the correct treatment of the nuclear effect for iron and hydrocarbon targets in the model within the measurement precisions.

T2K has performed the first measurement of nu(mu) inclusive charged current interactions on carbon at neutrino energies of similar to 1 GeV where the measurement is reported as a flux-averaged double differential cross section in muon momentum and angle. The flux is predicted by the beam Monte Carlo and external data, including the results from the NA61/SHINE experiment. The data used for this measurement were taken in 2010 and 2011, with a total of 10.8 x 10(19) protons-on-target. The analysis is performed on 4485 inclusive charged current interaction candidates selected in the most upstream fine-grained scintillator detector of the near detector. The flux-averaged total cross section is <sigma(CC)>(phi) = (6.91 +/- 0.13(stat) +/- 0.84(syst)) x 10(-39) cm(2)/nucleon for a mean neutrino energy of 0.85 GeV.

The next generation neutrino observatory proposed by the LBNO collaboration will address fundamental questions in particle and astroparticle physics. The experiment consists of a far detector, in its first stage a 20 kt LAr double phase TPC and a magnetised iron calorimeter, situated at 2300 km from CERN and a near detector based on a highpressure argon gas TPC. The long baseline provides a unique opportunity to study neutrino flavour oscillations over their 1st and 2nd oscillation maxima exploring the L/E behaviour, and distinguishing effects arising from δCP and matter. In this paper we have reevaluated the physics potential of this setup for determining the mass hierarchy (MH) and discovering CP-violation (CPV), using a conventional neutrino beam from the CERN SPS with a power of 750 kW. We use conservative assumptions on the knowledge of oscillation parameter priors and systematic uncertainties. The impact of each systematic error and the precision of oscillation prior is shown. We demonstrate that the first stage of LBNO can determine unambiguously the MH to > 5σ C.L. over the whole phase space. We show that the statistical treatment of the experiment is of very high importance, resulting in the conclusion that LBNO has ∼ 100% probability to determine the MH in at most 4-5 years of running. Since the knowledge of MH is indispensable to extract δCP from the data, the first LBNO phase can convincingly give evidence for CPV on the 3σ C.L. using today’s knowledge on oscillation parameters and realistic assumptions on the systematic uncertainties.

The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector located 295 km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator-bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker are used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/NOMAD dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system. (C) 2011 Elsevier B.V. All rights reserved.

Precise measurement of neutrino beam direction and intensity was achieved based on a new concept with modularized neutrino detectors. INGRID (Interactive Neutrino GRID) is an on-axis near detector for the T2K long baseline neutrino oscillation experiment. INGRID consists of 16 identical modules arranged in horizontal and vertical arrays around the beam center. The module has a sandwich structure of iron target plates and scintillator trackers. INGRID directly monitors the muon neutrino beam profile center and intensity using the number of observed neutrino events in each module. The neutrino beam direction is measured with accuracy better than 0.4 mrad from the measured profile center. The normalized event rate is measured with 4% precision. (C) 2012 Elsevier B.V. All rights reserved.

We report the first measurement of the neutrino-oxygen neutral-current quasielastic (NCQE) cross section. It is obtained by observing nuclear deexcitation γ rays which follow neutrino-oxygen interactions at the Super-Kamiokande water Cherenkov detector. We use T2K data corresponding to 3.01×1020 protons on target. By selecting only events during the T2K beam window and with well-reconstructed vertices in the fiducial volume, the large background rate from natural radioactivity is dramatically reduced. We observe 43 events in the 4–30 MeV reconstructed energy window, compared with an expectation of 51.0, which includes an estimated 16.2 background events. The background is primarily nonquasielastic neutral-current interactions and has only 1.2 events from natural radioactivity. The flux-averaged NCQE cross section we measure is 1.55×10−38  cm2 with a 68% confidence interval of (1.22,2.20)×10−38  cm2 at a median neutrino energy of 630 MeV, compared with the theoretical prediction of 2.01×10−38  cm2.

The T2K experiment is a long baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle theta(13) by observing nu(e) appearance in a nu(mu) beam. It also aims to make a precision measurement of the known oscillation parameters, Delta m(23)(2) and sin(2)2 theta(23), via nu(mu) disappearance studies. Other goals of the experiment include various neutrino cross-section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem. (C) 2011 Elsevier B.V. All rights reserved. RI Sobel, Henry/A-4369-2011; Stahl, Achim/E-8846-2011; Collazuol, Gianmaria/C-5670-2012; Kormos, Laura/D-1032-2012; De Rosa, Gianfranca/E-8737-2012; Sanchez, Federico/F-5809-2012; Yokoyama, Masashi/A-4458-2011; Berardi, Vincenzo/H-4550-2011; Takeuchi, Yasuo/A-4310-2011