1 / 71

Recent results from the OPERA experiment

Recent results from the OPERA experiment. Maximiliano Sioli (Bologna University and INFN) on behalf of the OPERA Collaboration SLAC Experimental Seminar - June 22, 2010. The OPERA Collaboration. Belgium IIHE Brussels Bulgaria Sofia Croatia IRB Zagreb

faunia
Télécharger la présentation

Recent results from the OPERA experiment

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Recent results from theOPERA experiment Maximiliano Sioli (Bologna University and INFN) on behalf of the OPERA Collaboration SLAC Experimental Seminar - June 22, 2010

  2. The OPERA Collaboration BelgiumIIHE Brussels BulgariaSofia CroatiaIRB Zagreb FranceLAPP Annecy, IPNL Lyon, IRES Strasbourg GermanyHamburg, Münster, Rostock IsraelTechnion Haifa ItalyBari, Bologna, LNF Frascati, L’Aquila, LNGS, Naples, Padova, Rome La Sapienza, Salerno JapanAichi, Kobe, Nagoya, Toho, Utsunomiya Korea Jinju RussiaINR Moscow, NPI Moscow, ITEP Moscow, SINP MSU Moscow, JINR Dubna, Obninsk SwitzerlandBern, Zurich TurkeyMETU Ankara M. Sioli - SLAC Experimental Seminar - June 22, 2010

  3. Outline Sub. to Physics Letters B (Acc 11/Jun/2010) arXiv:1006.1623 Published in EPJC 67 (2010) 25. arXiv:1003.1907 • Introduction • The OPERA experiment • The physics case • Detector description • Experimentalresults • Oscillationphysics  First nt candidate event • Non-Oscillationphysics  Atmosphericmuonchargeratio • Conclusions M. Sioli - SLAC Experimental Seminar - June 22, 2010

  4. Introduction • The OPERA experiment was mainly designed to unambiguously prove the oscillation phenomenon through direct nt appearance • Definitely close of the discovery phase of neutrino oscillations • The detector - although optimized for beam neutrino detection - can also be exploited for non-oscillation studies • Cosmic ray physics at the Gran Sasso Lab. M. Sioli - SLAC Experimental Seminar - June 22, 2010

  5. OPERAOscillation Project with Emulsion tRackingApparatus Long baseline neutrino oscillation experiment: search for tauneutrino appearance at Gran Sasso laboratory in a quasi-pure muonneutrinobeam produced at CERN (732 km) First direct observation of nm↔ ntoscillation M. Sioli - SLAC Experimental Seminar - June 22, 2010

  6. 732 km CNGSCERN Neutrino to Gran Sasso beam • Protons from SPS: 400 GeV/c • Cycle length: 6 s • 2 extractions separated by 50 ms • Pulse length: 10.5 ms • Beam intensity: 2.4 1013 proton/extr. M. Sioli - SLAC Experimental Seminar - June 22, 2010

  7. CNGSCERN Neutrino to Gran Sasso beam CNGS beam optimized for nt appearance, i.e. optimized for the maximal number of nt charged current interactions: nm flux spectrum above t threshold. Taken into account the nt CC cross section.  nm flux “off peak” w.r.t the maximum oscillation probability. “off peak” Limiting for nm ne searches 2 Δm L ® » 2 2 23 P( ) sin ( 2 θ ) sin ( 1 . 27 ) νm νt 23 E M. Sioli - SLAC Experimental Seminar - June 22, 2010

  8. CNGS PERFORMANCE 2010 5970 events collected until 23 May 2010 (within 1s in agreement with expectations) Improving features, high CNGS efficiency (97% in 2008-2009) 2010: close to nominal year; Multi Turn Extraction routinely running Aim at high-intensity runs in 2011 and 2012 2009 2008 Days M. Sioli - SLAC Experimental Seminar - June 22, 2010

  9. n Decay “kink” - m- nt nm h- nt n(po) e- nt ne p+ p- p- nt n(po) B. R. ~ 17% - nm nm oscillation t- B. R. ~ 50% n nt B. R. ~ 18% B. R. ~ 14% ~1 mm Detection of the nt appearance signal The challenge is to discriminate nt interactions fromninteractions: identify t leptons via their decay topology • Two conflicting requirements: •  Large mass ~O(kton) •  High granularity ~1mm resolution ECC concept adopted signal selection background rejection M. Sioli - SLAC Experimental Seminar - June 22, 2010

  10. 8.3 Kg 99.8 mm 125.1 mm Emulsion Cloud Chamber concept ECC = sequence of emulsion-lead layers  High resolution and large mass in a modular way. The brick is the target basic component: 57 nuclear emulsion films interleaved by 1 mm thick lead plates Emulsion Resolution: dx = 1 µm dq = 2 mrad Total number of bricks: ~150000 (1350 tons) M. Sioli - SLAC Experimental Seminar - June 22, 2010

  11. 15 tomographic views 44 mm 44 mm Track segment: aligned clusters Tracks in OPERA emulsions Automated emulsion scanning: based on the tomographic acquisition of emulsion layers. Field of view 390 μm × 310 μm Scanning speed: 20 cm2/h Passing-through tracks rejection Track segments found in 8 consecutive plates Vertex reconstruction in the brick M. Sioli - SLAC Experimental Seminar - June 22, 2010

  12. 10m 10m 20m OPERA general structure Target SuperModule (side view) n Target sections (6.7 m2): 29 brick walls (77500 bricks) 31 Target Tracker walls (TT) Brick selection Calorimetry Magnetic spectrometers (6×10 m2): 22 RPC planes 6 drift tube planes B = 1.55 T Total target mass = 1.35 ktons M. Sioli - SLAC Experimental Seminar - June 22, 2010

  13. The OPERA detector SM2 Bricks (lead + emulsions) and Target Tracker (plastic scintillators) High Precision Tracker(6 drift tube stations) Instrumented dipole magnet (22 RPC planes in total) Veto plane (RPC) M. Sioli - SLAC Experimental Seminar - June 22, 2010

  14. On-line analysis of electronic data Pb/Em. brick  8 cm p.h. 0 max Detector concept • The brick is the solution to the requirements of high granularity and large mass. • Need of electronic detectors in order to: • trigger for a neutrino interaction • locate the candidate brick • muon identification and momentum/charge measurement  hybrid detector needed Brick finding algorithm Selected brick is removed from the target and exposed to cosmic rays (alignment). Emulsions are developed and sent to scanning stations / labs M. Sioli - SLAC Experimental Seminar - June 22, 2010

  15. The first nt candidate

  16. ANALYSIS • OPERA nominal analysis flow applied to the hadronic kink candidates: • kink occurring within 2 lead plates downstream • kink angle larger than 20 mrad • daughter momentum higher than 2 GeV • decay Pt higher than 600 MeV, 300 MeV if ≥ 1 gamma pointing to the decay vertex • missing Pt at primary vertex lower than 1 GeV • Azimuthal angle between the resulting hadron momentum direction and the parent track direction larger than p/2 radians

  17. Invariant mass reconstruction • The event passes all cuts, with the presence of at least one gamma pointing to the secondary vertex, and is therefore a candidate to the t -> 1-hadron decay mode. • The presence of the charged prong and of two gammas pointing to the secondary vertex allows to attempt to the reconstruction of the r(770) invariant mass from the • -> p-p0ntdecay mode • According to the gammas assignment scheme shown before, we have then:

  18. We observe 1 event in the 1-prong hadron topology with a background expectation (assuming a conservative 50% error) of: 0.011±0.005 (syst) events 1-prong (hadron re-interaction) 0.007±0.003 (syst) events 1-prong (charm) 0.024±0.012 (syst) events 3-prongs, m and e decay channels Considering all decay modes the probability to observe 1 event due to background fluctuations is 4.3%. This corresponds to a statistical significance of 2.03 s on the measurement of a first t candidate event in OPERA. Considering the 1-prong channel only, the background fluctuation has a probability of 1.9%, for a significance of 2.35 s

  19. 1400 m OPERA as a cosmic ray detector Gran Sasso underground lab: 1400 m of rock (3800 m.w.e) shielding, cosmic ray flux reduced by a factor 106 w.r.t. surface, very reduced environmental radioactivity. • OPERA vs previous and current underground experiments:a deep underground detector with charge and momentum reconstruction and excellent timing capabilities (~10 ns). • Analyses under way: • Atmospheric neutrino induced muons • Coincidences among experiments (OPERA/LVD) • Atmospheric muon charge ratio  this talk M. Sioli - SLAC Experimental Seminar - June 22, 2010

  20. Atmospheric muon charge ratio • The atmospheric muon charge ratio Rm≡ Nm+/Nm-is being studied and measured since many decades • Depends on the chemical composition and energy spectrum of the primary cosmic rays • Depends on the hadronic interaction feautures • At high energy, depends on the prompt component • It provides the possibility to check HE hadronic interaction models (E>1TeV) in the fragmentation region, where no data exists • Since atmospheric muons are kinematically related to atmospheric neutrinos (same sources), Rmconstitus a benchmark for atmospheric n computations (background for neutrino telescopes) M. Sioli - SLAC Experimental Seminar - June 22, 2010

  21. The physics of CR TeV muons hadronic interaction: multiparticle productions(A,E), dN/dx(A,E)  extensive air shower Primary C.R. proton/nucleus:A, E, isotropic K (ordinary) meson decay:dNm/d cosq ~ 1/ cosq p m short-lifetime meson production and prompt decay (e.g. charmed mesons) Isotropic angular distribution transverse size of bundle  PT(A,E) m m TeV muon propagation in the rock:radiative processes and fluctuations detection:Nm(A,E), dNm/dr M. Sioli - SLAC Experimental Seminar - June 22, 2010

  22. Analytic predictions p (primary) air nucleus p • Naive prediction: • Since charged multiplicity grows with the energy, the extra-charge of the primary proton is diluited and Rm 1 in the HE limit (WRONG!) • A more elaborate model: • Suppose only primary protons with a spectrum dN/dE = N0E-(1+g) • Suppose only pions and neglect decays (HE limit) • Consider the inclusive cross-section for pions • The pion spectrum is then M. Sioli - SLAC Experimental Seminar - June 22, 2010

  23. Analytic predictions (cont’d) Feynman scaling Spectrum Weighted Moments • This expression can be simplified under the assumptionand becomes • Finally we have M. Sioli - SLAC Experimental Seminar - June 22, 2010

  24. Interpretation of the result • Interpretation of the result • The result is valid only in the fragmentation region, since in the central region Feynman scaling is strongly violated • But the steeply falling primary spectrum (g ~ 2.7) in the SWM suppresses the contribution of the central region in the secondary production  scaling holds (at least for E < 1 TeV);In other words: each pion is likely to have an energy close tothe one of the projectile (primary CR proton) and comes fromits fragmentation (valence quarks)  positive charge • Rm does not depend on Ep (or Em) nor on the target nature • Rm depends on the primary spectrum g M. Sioli - SLAC Experimental Seminar - June 22, 2010

  25. Neutrons in the primary flux Proton excess • Further refinements • Introducing the neutron component in the primary flux (in heavy nuclei) and considering the isospin symmetries: one obtains: M. Sioli - SLAC Experimental Seminar - June 22, 2010

  26. Kaon contribution q = 0o q = 60o ep eK ei = ei(q) is the “critical energy”, i.e. the energy above which interactions dominate over decays. Along the vertical (q = 0o) ei(0)= mich/ti (h = 6.5 km) ep = 115 GeV eK = 850 GeV eX > 107 GeV At higher energy (>100 GeV) the contribution of K becomes important In general, the contribution of eachcomponent to the muon flux Npar = (p, K, charmed, etc.) depends on the relative contributionof decays and interaction probabilities: where M. Sioli - SLAC Experimental Seminar - June 22, 2010

  27. Kaon contribution to Rm However, for kaons: Because of their strangeness (S = +1), K+ and K0 can be yielded in association with a leading barion Λ o Σ. On the other hand, the production of K−,K0 requires the creation of a sea-quark pair s − s together with the leading nucleon and this is a superior order process. This leads to a larger Rm ratio at high energy M. Sioli - SLAC Experimental Seminar - June 22, 2010

  28. General form for Rm q* q Earth POWERFUL HANDLE TO DISCRIMINATE MODELS The (magnetized) experiment with the largest Emcosq OPERA(2009): Emcosq ≈ 2000GeV Let us consider again the general form for the muon flux where we have explicited the ei(q) dependence on q where q* is the zenith angle at the production point The correct variable to describe the evolution of Rm istherefore Emcosq* The Rm evolution as a function of Emcosq* spans over the different sources Rm = wpRmp + wKRmK + wcharmRmcharm +… M. Sioli - SLAC Experimental Seminar - June 22, 2010

  29. Cosmic-event reconstruction • Cosmic-event tagging: • Outside the CNGS spill window • Dedicated pattern recognition and track finding/fitting: • Cosmic events are passing-through • Cosmic events comes from all directions • Cosmic events may have multiple parallel tracks (in OPERA 5% of the events are muon bundles) • Different reconstruction philosophy M. Sioli - SLAC Experimental Seminar - June 22, 2010

  30. Pattern recognition f q • Tracking philosophy • we know a priori which is the target: single tracks or bundle of tracks almost parallel (RMS is ~1 deg, mainly due to MCS in the overburden) • Hybrid strategy • global method (Hough Transform) to individuate the event direction • scan the Hough Space and select the slope corresponding to the maximum  used to set the qslice of the slice • local method (pivot points) on slices around the direction “resolutions” < 1 deg both for zenith and azimuth direction reconstruction M. Sioli - SLAC Experimental Seminar - June 22, 2010

  31. original coordinate plane Y 1 r 2 3 ypeak Z q Pattern recognition (cont’d) Real double muon event r y M. Sioli - SLAC Experimental Seminar - June 22, 2010

  32. Track finding and fitting f q Within each slice, build straight lines defined by all possible couples of external points (pivot points), then search for points aligned with the previous two according to pre-defined tolerances Fit the selected points and iterate the procedure to merge or reject extra points “resolutions” < 1 deg both for zenith and azimuth direction reconstruction Merge the tracks inthe XZ and YZ views 3D track M. Sioli - SLAC Experimental Seminar - June 22, 2010

  33. PT track reconstruction • 3D tracks are used to “guide”track finding and fitting in the PTsystem: • Find the line tangent to the drift circles with the best c2 • 250 mm position resolution • 0.15 (1) mrad angular resolution for doublets (singlets) for f = 0 • (improve for f > 0) Residuals ~250 mm M. Sioli - SLAC Experimental Seminar - June 22, 2010

  34. Momentum reconstruction B B l B ≡ Bd/l= effective magnetic field • In each side of the magnet arm we can reconstruct an independent angle fj, j=1,...,6. • Each fj can be reconstructed with one station (singlets) or two stations (doublets) • We compute Dfk = fi – fj , k=1,...,4, angle differences between adjacent station-pairs • 55% of Df’s comes from doublets • 9% from singlets • 36% are mixed M. Sioli - SLAC Experimental Seminar - June 22, 2010

  35. Charge reconstruction where • Charge is reconstructed according to the Df sign • If each track contributes to multiple Df angles, a weighted average is computed • weights = angular experimental errors M. Sioli - SLAC Experimental Seminar - June 22, 2010

  36. Maximum Detectable Momentum ~500 GeV/c Exact computation at all angles (MC) • Consider the magnetic field bending and the total deflection spoiling (detector + MCS) • Requiring DfB/sDf>1 we obtain (for f=0): • pmax(doublets) = 1.25 TeV • pmax(singlets) = 190 TeV • pmax(mixed) = 260 TeV M. Sioli - SLAC Experimental Seminar - June 22, 2010

  37. Charge mis-identification Cross-check with beam data Rm = (1.9 ± 0.9) % pm M. Sioli - SLAC Experimental Seminar - June 22, 2010

  38. Monte Carlo simulation • MC simulationusedfordifferentpurposes: • Calibrate and correct (unfold) experimental data • Estimate surfacemuonenergy and primary-cosmic-rayrelatedquantities • TwoMCsused: • Parametrizedgenerator - Fast butapproximate • Full Monte Carlo simulation - Slow butreliable M. Sioli - SLAC Experimental Seminar - June 22, 2010

  39. Monte Carlo simulation (MC1) Muon flux Generates multiple muon events at the level of the Underground Halls of the LNGS Laboratory • each primary type and its energy are sampled according to the composition model (MACRO-fit model) • the direction is sampled isotropically and the corresponding amount of rock overburden is computed (from Gran Sasso map) • given the primarytype, itsenergy, the direction and the rock, the probabilitytohavenmmuons at underground leveliscomputedusing tables obtained from a full MC simulation, the same used to derive the primary composition model  SELF-CONSISTENCY • Then the residual energy for each muon is computed from a parameterized function [PRD 44 (1991) 3543] • The lateral dispersion Rm of each muon w.r.t. the shower axis is again parameterized according to a full MC simulation • The muonchargeratioisintroducedbyhand (Rm = 1.4) M. Sioli - SLAC Experimental Seminar - June 22, 2010

  40. Monte Carlo simulation (MC2) g~2.7÷3 Ecut~3000 TeV Ecut E • Based on the FLUKA code • Full simulationchain: • Detailedgeometrydescription (atmosphere, mountain) • HE hadronicinteractions (h-N and N-N) handledby DPMJET • Primarycompositionmodelfrom APP 19 (2003) 193 • Predictiveof the atmospericmuonchargeratio • Usage: • Surfacemuonenergyestimation • Link between underground variables and primarycosmicrayparameter M. Sioli - SLAC Experimental Seminar - June 22, 2010

  41. Data pre-selection • Data taken during 2008 CNGS physics run: • from June 18th until November 10th2008 • The data acquisition was segmented in “extraction periods”of ~12 hours each. • Each “extraction” wasselected or rejected on the basis of: • Run stability • Global distributions (see figure) • Livetime: 113.4 days • Total number of events: 403069 M. Sioli - SLAC Experimental Seminar - June 22, 2010

  42. Data reduction A set of progressive cutsapplied in orderto isolate a clean data sample: • at leastonereconstructedDf angle (acceptance cut) • Removeeventswithlargenumberof PT hits (clean PT cut) • Removeeventswithbendingssmallerthan the experimentalresolution (deflection cut) c’) Removeeventswithverylargebendings(effectivefor pm<5 GeV/c) M. Sioli - SLAC Experimental Seminar - June 22, 2010

  43. Clean PT cut N’ = N - M(f) M = M(f) Removeeventswith a largenumberof PT tubesfired (d-rays, secondaryinteractions, electronic noiseetc)  can induce wrong matching M. Sioli - SLAC Experimental Seminar - June 22, 2010

  44. Deflection cut The robustness of the cut with respect to n was checked, i.e. the results do not depend on n, when n>2 Tracks with a bending below the experimental resolution are removed: Df/sDf > n, n=3 M. Sioli - SLAC Experimental Seminar - June 22, 2010

  45. Deflection cut: effects on Df and h The charge mis-identification h is stronglyreduced. Possible differences between MC and real h is a source of systematic uncertaintyon Rm will be reported later m- m+ m- m+ w/o deflection cut with deflection cut h ~ 3% M. Sioli - SLAC Experimental Seminar - June 22, 2010

  46. Data reduction - statistics M. Sioli - SLAC Experimental Seminar - June 22, 2010

  47. Quality cuts vs reconstructed pm No cuts Clean PT Df<100 mrad Df/sDf > 3 M. Sioli - SLAC Experimental Seminar - June 22, 2010

  48. Alignment of the PT system • Rm strongly depends on the alignment precision of the PT system • Two stages of correction: • Mechanical: gross corrections using a theodolite • Cosmic rays: finer corrections using HE muons(with and w/o magnetic field) • Mis-alignment may have different contributions: • Global: each PT station can be roto-translated as a whole w.r.t. the master reference frame • Accounted for with the present statistics • Local: each PT station may have distortions which vary from point-to-point • Not yet accounted for with the present statistics M. Sioli - SLAC Experimental Seminar - June 22, 2010

  49. Alignment of the PT system Phase1: Align two stations of a doublet treating them as rigid bodies - first shifts, in x, y and z - then rotation, in x, y and z Phase2: Align two doublets on both sides of an iron arm using CR data w/o magnetic field Phase3: Estimate bending effects M. Sioli - SLAC Experimental Seminar - June 22, 2010

  50. Underground muon charge ratio Rm = 1.377 ± 0.014 Rm computed separately for the three categories and then unfolded: Finally compute Rmunf as the weighted average of the 3 samples: M. Sioli - SLAC Experimental Seminar - June 22, 2010

More Related