Belgium (Brussels, Louvain-la-Neuve), CERN, Germany (Berlin, Münster), Israel (Haifa), Italy (Bari, Cagliari, Ferrara, Naples, Rome, Salerno), Japan (Toho, Kinki, Aichi, Kobe, Nagoya, Osaka, Utsunomiya),Korea (Gyeongsang), The Netherlands (Amsterdam), Russia (Moscow), Turkey (Adana, Ankara, Istanbul) CHORUS « Phase I » and beyond

  -,h - , (  o ’s)   path vertex kink MOTIVATION: (1993, proposal) Topological identification of   interactions for the discovery of    and e   oscillations in the cosmological region of  m 2 ~ 50 eV 2 (2000) the SK results!...And NEW CMB expts (COBE - MAXIMA -BOOMERANG) +LSS+BBN models indicate  m <4eV (  m 2 <16 eV 2 ) at 90%CL...STILL HDM is unresolved! -54  m -36  m -21  m 0  m Red frame: ~30x40  m 2 beam A HIGH SENSITIVITY  APPEARANCE EXPERIMENT

Muon spectrometer Muon spectrometer Air core spectrometer and emulsion tracker Air core spectrometer and emulsion tracker Veto plane  - -  - - Calorimeter Chorus Detector (94-97) Neutrino target Active nuclear emulsion target Scintillating fiber tracker Hadrons Sign and momentum air-core magnet spectrometer  p/p = p(GeV/c)  upgrade: ET, HC Showers energy, missing P t lead&fibers “spaghetti” calorimeter  E/E=32%/  E (hadrons)  E/E=14%/  E (electrons)  hadr ~60 GeV Muon ID, sign and momentum iron-core muon spectrometer  p/p~10%-15% (p<70 GeV) Target

CHORUS PHASE I strategy First experiment applying AUTOMATIC emulsion scanning procedures!

shift each frame (angle is GIVEN) sum up sliced emulsion image A track to be recognized Recognized track AUTOMATIC SCANNING: The Track Selector (TS)

Predictions, Scanback and Vertex location tan   Once the track is found inside the target, large plate-to-plate scanback efficiency; it allows vertex location by disappearance of the scanback track in two consecutive plates.

scanback track   Offline selection Offline selection  small impact parameter between parent and daughter  kink point is in the vertex plate  parent particle not found in plate n- 1  - kink detection in “phase I” Principle Principle: decay topologies will look like vertices; But the Parent track (  ) can be detected by a larger angular scan at the vertex plate (many angles tried) Impact parameter Despite a relatively low kink finding efficiency, the kink detection can be accomplished by the TRACK SELECTOR algorithm

Manual scanning on kink candidates Low momentum BG track 80.0% Parent = daughter no angle difference (distortion) 4.0% Backward going track: nuclear fragment 12.0% Hadron 2ry interaction2.5% Decay (kink) 1.5% 5% of located events

Final PHASE I DataFlow 164 Kevents searched for a kink. Corresponding to about 8K  -equivalent* (reduced by post-scanning analysis, see later)  -equivalent: events expected in the hypothesis    Emulsion triggers 2,305 K Events with 1 negative muon and vertex predicted in emulsion 713,351 P muon < 30GeV/c and angular cuts 477,625 Events scanned  Vertices located and kink search Events with vtx predicted in emul.335,398 1 negative track with P[-20,-1] GeV/c and angular cuts 122,412 Events scanned  Vertices located and kink search 20,081

CHORUS Background~White Kinks Definition: 1-prong nuclear interactions with no heavily ionizing tracks or other evidence for nuclear breakup in the  hadronic decays. Poor previous knowledge of WK (P,P t ). Difficult to extrapolate (sensitive to the operative definition of “whitness”) Direct background evaluation from the 26 WK found in 243m of hadron tracks measured in Chorus FAR from the vertex plate  WK measurement in the signal-free region MC development to tune the cuts against the WK background –Fluka to model the hadron interactions in emulsion –Cuts to reproduce the minimum observable activity (the white- gray transition) in the Chorus emulsions

Background measurement We measured WK (P t > 250MeV  c) = 21.3  7 m. This corresponds, for example, to 2.8  0.8 WK expected in the signal region < 3 plates from the vertex position. P t kink (GeV)  kink (rad) WK  h

Post-scanning WK Reduction  (rad)  t cut L decay cut  =0.83  t cut:  opposite to the shower in the transverse plane L decay cut:  flight length shorter and correlated with P had Flight length (cm) Hadron momentum (GeV) L 90% L 80% L 70% L 3plates WK  h WK

 BG expt  N obser v Sensitivity x 10 4  N observ BG tot Charm antineut Charm neutrino WK L decay effic Sensitivity maximization  t cut Cuts optimisation by the a-priori criteria of maximizing the sensitivity, independently from data (corresponding to 7018  -equivalent). A posteriori, DATA behave as expected in the hypothesis of NO signal. L 3plates

0.6eV 2 Today a serious “linguistic” problem, i.e. how to speak the same language. different philosophies, different results, different interpretations: is there A BEST? CHORUS approach: we try to publish all numbers that allow You to reproduce our curves or recompute ANY statistical quantity you understand/like. CHORUS limit and sensitivity (continuous red line) speaks the same language of CDHS,CHARM II,CCFR,E531 (T. Junk, NIM A434 (1999) 435) The dotted red line limit in the Unified Approach is also reported; it speaks the same language of the NOMAD curve ( 2000); the corresponding sensitivity is the solid red line curve. LIMITOLOGY

Limit Computation , , A systematic error of 17% is included in the evaluation of N  =2.4 (T.Junk).

Measurement of backgrounds High sensitivity oscillation search P(    )<3.4x10 90%C.L. Technology/techniques evolution Phase I results summary NU96 JPS96 LP97 PRL98 NU98 MOR99 SPSC99 NU2000 SPSC96 months sensitivity

PRINCIPLES:  MULTI-TRACK predictions (and scanback) without kinematical cuts.  FULL VERTEX emulsion data taking (on located vertices)  OFFLINE Emulsion Analysis CHORUS NOW :PHASE II New EMULSION data-taking and analysis for Increased sensitivity oscillation search Charm physics (~5Kevents) on V cd,  c branching ratios, D s branching ratios, etc. Phase II Emulsion data-taking started March 2000

Ultra Track Selector (HW based) Current performance: 3 Hz (for all tracks with  z < 400 mrad) Faster Hardware processing of images: from digitization to grain finding and data storage After 16 images are stored: PARALLEL angular scan for every possible angle: HW summation by FPGA technology (Field programmable Gated Arrays) to find tracks while the microscope moves to the next position

SYSAL/CERN Microscopes (SW based) Mpixel digital camera to analyze a large emulsion volume per view DSP (Digital Signal Processor) cards for flexible data treatment (grain finding) Advanced dedicated optics  Enlarged Field Of View=0.5 mm Reduced Depth of Field=1.2  m 450 nm illumination Computer Farms for software data-processing.

NetScan Data Taking Readout of ALL tracks (  <0.4 rad ) at the surface of each plates around a primary interaction => reconstruct vertex topology CHORUS N2 decay Current scanning volume: 1.5x1.5x6.3 mm 3 /event Line extrapolated to next plate decay daughters Still NOT ALL of the information ~15% of straight tracks

OFFLINE Emulsion Analysis 1.5 mm All track segments 8 plates overlapped 6.3 mm  2 segments connected Not passing through 1) Reduction of ~ 10K track segments (each event, a “two-years” history!) by use of emulsion+electronic data AND 2) Subsequent Physics analysis

new prediction/scanback procedure allows us to increase by >80 Kevents the current “located” sample of ~164 Kevents (scanback started) Vertex data-taking has started: 26 Kevents in the Central Database, current speed ~10 Kevents/month; “next year”: 20X improvement! Post-scanning analyses are starting on the first data: Selection of track segments and trackers matching; Post-scanning electronic reconstruction of emulsion tracks; Special topology selections and improved kink finding procedures; Physics analyses; PHASE II Status

 Final PHASE I results on     and  e   oscillation.  PHASE II Emulsion data-taking has started, and will take - new results on charm physics; - improved oscillation search results in the cosmological region; - improved emulsion scanning technologies and techniques. Outlook