Transcript 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:
1. Flavour physics
2. Neutrino physics
• 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
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
• 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
• 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]
+ O(l4)
• 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
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
= 0.10 ± 0.02
Vcb
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)
BaBar
(dileptons)
 |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
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)
• Long-standing debate over
statistical approach:
Bayesian or Frequentist
h
• Recent workshop at CERN
compared competing approaches
• When fed with same input
likelihoods, outputs are very
similar
• Remaining small differences
due to differing interpretation
h
of theoretical errors
• Can be used to predict
(indirectly) substantial
CP violation in B0 decays
Bayesian
(68, 95, 99, 99.9)% CL
r
Frequentist
r
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
p
• 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)
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)
in time
out of time
• Use of accurate timing information important to reject background
• Startup of B-factories amazingly successful!
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
± 2s
± 1s
• Direct measurement of sin 2b currently in perfect agreement with
expectation from Standard Model CKM fit
How to go further?
1. 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
2. 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)
3. 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
• 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
• 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
• 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
• 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
• Two major sources of neutrinos:
1. Solar: from nuclear fusion processes in sun
All ne (at least when produced), E < 20 MeV
2. 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
• 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 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%
m candidate
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
Dm2 = 2.5 10-3 eV2
sin2 2q = 1.0
m
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
• 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
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
12 m
PMs
Observed n reactions
1. Elastic Scattering: nx+e-  nx+ealready seen by Super-Kamiokande
gives strong directional sensitivity
(peaked towards sun)
2. Charged Current: ne+d  p + p +einvolves only ne
3. 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
• Threshold for n detection E > 5 MeV  sensitive to n from process
8B  8Be* + e+ + n in sun
e
• 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
• 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
108 TeV
• 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
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
• E > 100 TeV to suppress atmospheric n background
 10 – 1000 events/year in 1 km2 detector
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
• 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
• 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
• 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