Physics with RICH detectors

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Information about Physics with RICH detectors

Published on November 15, 2007

Author: Arundel0


Physics with RICH detectors:  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 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 Flavour physics Neutrino physics Contributing experiments:  Contributing experiments Flavour physics BaBar (SLAC), CLEO (Cornell), HERA-B (DESY), LHCb (CERN), CKM, SELEX and BTeV (Fermilab) Neutrino physics Super-Kamiokande (Kamioka), SNO (Sudbury), ANTARES (Toulon), NESTOR (Pylos), Baikal (Lake Baikal), AMANDA (South Pole) Hadron structure HERMES (DESY), COMPASS (CERN), PR93015 (Jefferson Lab) Heavy Ions HADES (GSI), STAR and PHENIX (Brookhaven), ALICE (CERN) Space physics AMS 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? 1. Quark mixing:  1. Quark mixing Weak eigenstates of quarks are “rotated” combination of flavour states CKM matrix elements give couplings between quarks Unitary transformation relationships between elements: S VijVik* = 0 (j  k) One has terms of similar magnitude Vud Vub* + Vcd Vcb* + Vtd Vtb* = 0  relationship in complex plane “Unitarity Triangle” Unitarity Triangle:  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 SM h  0  CP violation Rescale unitarity triangle by Vcd Vcb* Sides can be measured with B decays Angles probed by CP violation + O(l4) Measurement of sides:  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 ps can be used to extract |Vcb| = 0.041 ± 0.001 = Al2 and hence A = 0.84 Vub measured from charmless b decays eg DELPHI select sample enriched in b  u transitions using a K/p veto from their RICH, and hadronic mass m < 1.6 GeV: Vub Vcb = 0.10 ± 0.02 B0 – B0 mixing:  B0 – B0 mixing Vtd does not directly involve b quark, but accessible through loops B0 – 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) Current status:  Current status Despite heroic efforts at LEP / SLD B0s 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) Fit for (r, h):  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 h r Bayesian Frequentist (68, 95, 99, 99.9)% CL h r HERA-B:  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 target Very 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) 12 7 Beam momentum (GeV) p B-factories:  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 CP violation:  CP violation CP asymmetries arise from phase of CKM matrix elements eg (CP eigenstate) decay “via mixing” with different phase Depends on phase of B0 oscillation arg(Vtd)  angle b Unambiguously seen by BaBar sin 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) Comparison with CKM fit:  Comparison with CKM fit Direct measurement of sin 2b currently in perfect agreement with expectation from Standard Model CKM fit ± 1s ± 2s How to go further?:  How to go further? Reduce hadronic uncertainties CLEO [T.Skwarnicki] has long been at the forefront of b physics Now overtaken by the B-factories Proposed 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 decays CKM [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 experiments Hadron colliders give enormous b production rate (~1012 bb pairs/year at LHCb!) All b-hadron species produced  many CP measurements possible, over-constrain triangle LHCb:  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 LHCb RICH layout:  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 Performance:  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 BTeV:  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) 2. Neutrino physics:  2. Neutrino physics Two major sources of neutrinos: Solar: from nuclear fusion processes in sun All ne (at least when produced), E < 20 MeV Atmospheric: from interaction of cosmic rays with atmosphere ne and nm produced from decay chain, E ~ O(GeV) p + A  p X, p  m nm , m  e nm ne ( 2 nm for each ne) If neutrinos have mass, expect similar mixing formalism as quarks Oscillation probability = sin22q sin2(1.27 Dm2 L/En) Super-Kamiokande:  Super-Kamiokande Cylindrical water Cherenkov detector 1 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 e – m separation:  e – m separation m candidate 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 Evidence for nm oscillation:  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: Dm2 = 2.5 10-3 eV2 sin2 2q = 1.0 e m AQUA-RICH:  AQUA-RICH Super-Kamiokande doesn’t really qualify as a RICH, as light 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 Long-baseline experiments :  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 appearance Experiments OPERA (emulsion) and ICARUS (Liquid-Ar TPC) Concept for RICH-based detection of t appearance [C. Hansen] However, d-ray background (not included here) is severe Offset ring from t SNO:  SNO Spectacular new results from Sudbury Neutrino Observatory concerning solar neutrinos Spherical acrylic vessel holding 1000 tons of heavy water D20 2km underground Observed by 10,000 8” PMs 12 m D20 PMs Observed n reactions:  Observed n reactions Elastic Scattering: nx+e-  nx+e- already seen by Super-Kamiokande gives strong directional sensitivity (peaked towards sun) Charged Current: ne+d  p + p +e- involves only ne Neutral Current: nx+d  p + n + nx involves all active neutrinos ne, nm or nt  By comparing their rates can separately measure flux of ne and sum of all n from sun Evidence for ne oscillation:  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 prediction as 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 Neutrino astronomy:  Neutrino astronomy Cosmic ray spectrum extends up to 108 TeV Highest energy cosmics are difficult to explain: 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 Cosmic n sources:  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 ~ 109 M GRB: O(1s) duration, identified with galaxies at large redshift – most energetic events in universe: E ~ M c2 modelled as coalescence of binary system e acceleration in such sources  g (synchrotron radiation) Expect protons are also accelerated  hadronic interactions  n High energy n flux:  High energy n flux E > 100 TeV to suppress atmospheric n background  10 – 1000 events/year in 1 km2 detector Neutrino telescopes:  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 AMANDA:  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” Undersea experiments :  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! Conclusions:  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

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