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 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?

3. 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”

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  [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)

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 ps can be used to extract |Vcb| = ± = 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
= 0.10 ± 0.02
Vcb

6. 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 = ± ps-1 (WA)  |Vtd| = ± 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 / 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)

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 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) 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 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)

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

13. 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

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 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)

19. 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

20. e – m separation e candidate 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%

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’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

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 appearance Experiments 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 Observatory concerning 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-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

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 ± 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

27. 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

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 ~ 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

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 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