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Physics with RICH detectors. Focus on experiments contributing to this conference (currently taking data or in preparation) Even so, there is an enormous range of physics topics impossible to do them all justice

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Physics with RICH detectors


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    1. Physics with RICH detectors • Focus on experiments contributing to this conference (currently taking data or in preparation)Even so, there is an enormous range of physics topics impossible to do them all justice • Since the conference is dedicated to Tom Ypsilantis I will concentrate on two fields that he illuminated: • Both have seen breakthroughs since RICH98 • Flavour physics • Neutrino physics Overview talk for Session 9: “RICH pattern recognition and performance for physics” Roger Forty (CERN) 4th Workshop on RICH Detectors (5-10 June 2002) Pylos

    2. Contributing experiments • Flavour physicsBaBar (SLAC), CLEO (Cornell), HERA-B (DESY), LHCb (CERN), CKM, SELEX and BTeV (Fermilab) • Neutrino physicsSuper-Kamiokande (Kamioka), SNO (Sudbury), ANTARES (Toulon), NESTOR (Pylos), Baikal (Lake Baikal), AMANDA (South Pole) • Hadron structureHERMES (DESY), COMPASS (CERN), PR93015 (Jefferson Lab) • Heavy IonsHADES (GSI), STAR and PHENIX (Brookhaven), ALICE (CERN) • Space physicsAMS and EUSO (Space station) • One field notably absent: High pT physics (Higgs/Supersymmetry)CDF and D0 (Tevatron), ATLAS and CMS (LHC) Lepton ID and b-tagging more important for them than hadron ID?

    3. 1. Quark mixing • Weak eigenstates of quarks are “rotated” combination of flavour states • CKM matrix elements give couplings between quarks • Unitary transformationrelationships between elements:S VijVik* = 0 (j k) • One has terms of similar magnitudeVud Vub* + VcdVcb* + VtdVtb* = 0 relationship in complex plane“Unitarity Triangle”

    4. Unitarity Triangle • For 3 quark generations, 33 matrix has 4 independent parameters:3 angles and one phase  CP violation in the Standard Model • Parametrize expanding in powers of l = sin qC 0.22 [Wolfenstein] • Parameters (l, A, r, h) fundamental constants of the SMh  0  CP violation • Rescale unitarity triangle by Vcd Vcb*Sides can be measured with B decays Angles probed by CP violation + O(l4)

    5. Measurement of sides • Vcb can be extracted from the B lifetime and semileptonic BR: • Recent world average values (dominated by CLEO, LEP and SLD)B(b  cln) = 10.8 ± 0.2 %, tb = 1.56 ± 0.01 pscan be used to extract |Vcb| = 0.041 ± 0.001 = Al2 and henceA = 0.84 • Vub measured from charmless b decayseg DELPHI select sample enriched in b  u transitions using a K/p veto from their RICH, and hadronic mass m < 1.6 GeV: Vub = 0.10 ± 0.02 Vcb

    6. B0 – B0 mixing • Vtd does not directly involve b quark, but accessible through loopsB0 – B0 mixing:Oscillation frequency: • B0 oscillation now precisely measured:Dmd = 0.496 ± 0.015 ps-1 (WA) |Vtd| = 0.008± 0.002,error dominated by hadronic uncertainties • If B0s oscillations could be measured, much of hadronic uncertainty would cancel in ratio of oscillation frequencies BaBar (dileptons)

    7. Current status • Despite heroic efforts at LEP / SLDB0s oscillations still not seen (some indication at Dms ~ 18 ps-1) • Current limit Dms > 14.9 ps-1 • Summary of constraints on apex: • Includes constraint from CP violation in the K0 system, |eK| • Measurements consistent fit for apex (r, h)

    8. Fit for (r, h) • Long-standing debate over statistical approach: Bayesian or Frequentist • Recent workshop at CERN compared competing approaches • When fed with same input likelihoods, outputs are very similar • Remaining small differences due to differing interpretation of theoretical errors • Can be used to predict (indirectly) substantial CP violation in B0 decays Bayesian (68, 95, 99, 99.9)% CL h r Frequentist h r

    9. HERA-B • Originally conceived to search for CP violation in B0 J/y KS decays[M. Staric] • Uses halo of HERA proton beam (920 GeV), incident on a wire targetVery high rate (40 MHz design) and tiny signal/background ~ 10-10 • Problems with tracking detectors and trigger  overtaken by B-factories • Now detector is in good shape, physics goals redefined to use ~2106 J/y expected in coming year • Measure bb cross section and study J/y suppression with different targets sbb = 32 ±14±6 nb/nucleon (prelim) p 7 12 Beam momentum (GeV)

    10. B-factories • BaBar (SLAC) and Belle (KEK) designed to perform the direct measurement of CP violation in the B0 system • BaBar includes the DIRC [J.Schwiening] conic-section-imaging Cherenkov detector for particle ID (Belle has a threshold device) • Use of accurate timing information important to reject background • Startup of B-factories amazingly successful! in time out of time

    11. CP violation • CP asymmetries arise from phase of CKM matrix elementseg(CP eigenstate) decay “via mixing” with different phase Depends on phase of B0 oscillation arg(Vtd)  angle b • Unambiguously seen by BaBarsin 2b = 0.75 ± 0.09± 0.04(from 56 fb-1  60 M BB pairs!) • Consistent result from Belle:sin 2f1 = 0.82 ± 0.12± 0.05(from 42 fb-1)

    12. Comparison with CKM fit • Direct measurement of sin 2b currently in perfect agreement with expectation from Standard Model CKM fit ± 2s ± 1s

    13. How to go further? • Reduce hadronic uncertaintiesCLEO [T.Skwarnicki] has long been at the forefront of b physicsNow overtaken by the B-factoriesProposed to refocus the aims of the experiment to study the charm threshold region: CLEO-c Precision charm data will test the methods used to handle non-perturbative QCD  prospect of reducing uncertainties • Search for rare kaon decaysCKM [J. Engelfried] will search for K+p+nn (BRSM ~ 10-10!)  theoretically clean measurement of |Vtd| Use RICH detectors for K+ and p+ to measure decay kinematics(based on design used by SELEX to study charmed baryons) • Second-generation b physics experimentsHadron colliders give enormous b production rate (~1012 bb pairs/year at LHCb!) All b-hadron species produced  many CP measurements possible, over-constrain triangle

    14. LHCb • Dedicated b-physics experiment at the LHC, under construction to be ready on day 1 (2007) • Predominantly forward production fixed-target like geometry • 2 RICH detectors (1 < p < 100 GeV) • Original layout from Tom Ypsilantis

    15. LHCb RICH layout • Aerogel and C4F10 radiators combined in single device [S. Easo] • Typical event (from full simulation) illustrates high track density  careful handling of pattern-recognition required

    16. Performance • Global pattern recognition technique: simultaneous maximum-likelihood fit for all track mass-hypotheses • Performs well (full simulation): • Particle ID crucial to suppress background, eg of other 2-body decays in the search for B0p+ p- • ~ 5000 signal events/year in this channel

    17. BTeV • Dedicated b experiment proposed to run at the Tevatron[S. Blusk] • Compared to LHCb, 5 lower bb cross-section (due to lower energy)compensated by lower multiplicity + trigger on offset tracks at earliest level Liquid radiator rather than aerogel:  more p.e. but more X0 (and PMs)

    18. 2. Neutrino physics • Two major sources of neutrinos: • Solar: from nuclear fusion processes in sunAll ne (at least when produced), E < 20 MeV • Atmospheric: from interaction of cosmic rays with atmospherene and nm produced from decay chain, E ~ O(GeV) p + A  p X, pm nm , m enm ne ( 2 nm for each ne) • If neutrinos have mass, expect similar mixing formalism as quarksOscillation probability = sin22q sin2(1.27 Dm2L/En)

    19. Super-Kamiokande • Cylindrical water Cherenkov detector1 km underground • 50 kton pure water(22.5 kton fiducial) • 11,200 20” PMs • 1500 days of data taken • Accident on 12 November 2001 • ~60% of 20” PMs imploded (in few s) most likely due to shock wave after single tube broke • Plan to rebuild detector with remaining PMs in ~1 year, and replace broken PMs in ~4 years

    20. e – m separation • Clear separation (real data) of m- and e-like rings (showering) • PID parameter ~ log-likelihood difference for e and m hypotheses • Misid rate < 1% e candidate m candidate

    21. Evidence for nm oscillation • Deficit of m from atmospheric nm compared to simulation (with no oscillation )particularly in upward direction • e agree with simulation • Fitted parameters: e m Dm2 = 2.5 10-3 eV2 sin2 2q = 1.0

    22. AQUA-RICH • Super-Kamiokande doesn’treally qualify as a RICH, aslight is not focused • Tom Ypsilantis proposed a focused water Cherenkov:“Super-K with spectacles” • At its latest incarnation, 1 megaton of water inside a reflective spherical balloon • HPDs distributed on outer sphere looking inwards, and on inner sphere looking out • Potential advantages: localized ring images allow easier treatment of multi-ring events, and potential for momentum measurement from width of ring (via multiple scattering) However, no recent progress

    23. Long-baseline experiments • Important to check the atmospheric n results with n from accelerators • Already started by K2K: nm beam KEK – Super-Kamiokande (250 km)En = 1.3 GeV, below threshold for t production 56 events observed, compared to ~81 expected without oscillation probability of null oscillation scenario < 3% • CERN – Gran Sasso: (730 km) En = 17 GeV  search for t appearanceExperiments OPERA (emulsion) and ICARUS (Liquid-Ar TPC)Concept for RICH-based detection of t appearance[C. Hansen] Offset ring from t However, d-ray background (not included here) is severe

    24. SNO • Spectacular new results from Sudbury Neutrino Observatoryconcerning solar neutrinos • Spherical acrylic vessel holding 1000 tons of heavy water D20 2km underground • Observed by 10,000 8” PMs D20 PMs 12 m

    25. Observed n reactions • Elastic Scattering:nx+e- nx+e-already seen by Super-Kamiokandegives strong directional sensitivity (peaked towards sun) • Charged Current:ne+d  p + p+e-involves onlyne • Neutral Current:nx+d  p + n+nxinvolves all active neutrinos ne, nm or nt  By comparing their rates can separately measure flux of ne and sum of allnfrom sun

    26. Evidence for ne oscillation • Threshold for n detection E > 5 MeV  sensitive to n from process 8B 8Be* + e+ + ne in sun • Predicted ne flux = 5.1 ± 0.9 (in units of 106 cm-2 s-1) [J. Bahcall et al] • Measured ne flux = 1.76 ± 0.10 ie ~ 35% of predictionas seen in other experiments (the “solar neutrino problem”) • Flux of all neutrino flavours measured from the NC rate = 5.1 ± 0.6 in agreement with solar model prediction!  clear evidence (> 5s) that ne have oscillated to nm or nt • Looking at day/night variations and using all available data, preferred parameter region is strongly constrained

    27. Neutrino astronomy • Cosmic ray spectrum extends up to 108 TeV • Highest energy cosmics are difficult toexplain: size and B-field of our galaxy are insufficient for their acceleration • Thought to be produced by violent cosmic sources such as Active Galactic Nuclei and Gamma Ray Bursts • CR charged – don’t point to source • Universe opaque to high energy photons (due to material and interaction with CMBR) n astronomy: neutral, penetrating particles • Only astronomical n source observed to date (apart from sun): SN1987A 108 TeV

    28. Cosmic n sources • AGN: most powerful known objects in the Universe O(1040 W) modelled as due to matter accreting into black hole Candidate in Virgo:m ~ 109M • GRB: O(1s) duration, identified with galaxies at large redshift – most energetic events in universe: E ~ Mc2modelled as coalescence of binary system • e acceleration in such sources g (synchrotron radiation) Expect protons are also accelerated  hadronic interactions n

    29. High energy n flux • E > 100 TeV to suppress atmospheric n background  10 – 1000 events/year in 1 km2 detector

    30. Neutrino telescopes • Use water Cherenkov technique: water (or ice) acts as target, radiator and shielding • m angle follows n: Dq ~ 1/E (TeV), Em ~ En/2 • m reconstruction from timing (c = 22cm/ns in water) • Em from range ~5m/GeV (E < 100 GeV) or dE/dx (E > 1TeV) • B.Lubsandorzhiev • A.Hallgren • S.Tzamarias • G.Hallewell

    31. AMANDA • Based at the South Pole • Clear signals seen for upward-going m • Consistent with expectations from atmospheric n: • Extension proposed to 1 km2 array: “Ice-cube”

    32. Undersea experiments • Baikal has demonstrated feasibility of water-based array, but limited depth (and limited prospects for expansion) • Experiment in Northern Hemisphere complementary to AMANDA • ANTARES and NESTOR differ in their approach to deployment of optical-module strings: with submersible (ANTARES) or at surface using towers (NESTOR) • Interesting results expected in the coming years!

    33. Conclusions • Physics performed with RICH detectors is extremely diverse • RICH technique is the clear choice when hadron identification is required at high momenta, crucial for flavour physics Since RICH98, unambiguous observation of CP violation in the B0 system • Water Cherenkov technique opens the possibility of massive neutrino detectors with m – e separation Since RICH98, clear evidence for n oscillation, both nm (atmospheric) and ne (solar) • Many future experiments are planned using RICH detectors so we can expect further surprises! • Tom Ypsilantis initiated the field of RICH detection, and had a broad interest in many aspects of the physics—he is sorely missed