Transcript Spontaneous Symmetry Breaking

08 June 2009
Experimental
measurement of a new
Asymmetry at Belle
Manmohan Dash
work done at Virginia Tech & Belle
by the generous support of
Professor Leo Piilonen.
“Experimental study of a new form
of asymmetry in the high energy
charm Physics at Belle”
Seminar given at Dept. of High Energy Physics,
Tata Institute of Fundamental Research, Mumbai, India
Gratitude
I am thankful
To Dr Gagan Mohanty for inviting me to
TIFR
To Professor Naba Mondal for kindly
arranging this seminar.
To the friendly people of TIFR for their
support in my stay at TIFR.
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Symmetry is central to
understanding of nature
The basic quest of any High Energy
Physics experiment is to explore the
physical realities at the most
fundamental level accessible to present
day particle accelerators.
The concepts of symmetry are central
to such an endeavor and our
knowledge.
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Violations of symmetry can be
measured experimentally
Experimentally we try to measure the
small deviations from symmetries and
this often lead to deeper consequences
in our understanding of nature.
My measurement is an experimental
investigation of asymmetry in neutral
charmed meson’s (D0, D-zero) decay.
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There “is” an asymmetry in the
decay of D0 to (KS/KL)0
I have performed a measurement at
KEK e+e- collider to determine the
asymmetry in the rates at which the
neutral charmed meson D0 decays into
its final states of KS00 and KL00
No other measurement is known yet to
determine this asymmetry.
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Its becoming clear that this
asymmetry does exist.
My signals are large and clear
especially for the notorious KL but the
measurement is still on the tenterhooks.
The size of the analyzed data sample
needs to be upgraded.
Final verdict on the asymmetry needs
very careful analysis.
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High Energy Accelerator
Research Organization
or KEK for [“Kō Enerugī Kasokuki Kenkyū Kikō”]
Presently I am a
member at Belle
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Accelerator-Collider-Detector
Belle detector
cavity
e+ source
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The Belle-Detector
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The Event View at Belle
Detector
Side view
End view
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The Belle “brouhaha”
Since summer of 2002, when I joined as a
graduate student researcher at Belle, Belle has
broken and established many records for
unprecedented amount of data and luminosity.
This has also resulted in hundreds of Physics
results coming out of Belle many of which
made international news. New particles,
resonances and “unknown” particle states
were discovered along with many important
asymmetry measurements.
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Further in this talk…
Elementary particles
An introduction to the concept of
symmetry and its violations
Introduction to this measurement, its
motivation
Details of approach
Results of this study
Future path
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Elementary Particles
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What’s an elementary
particle?
In the study of the structure and interaction of
“very very very very small” particles
“beyond” the nucleus if we can’t probe the
size of particles with the highest resolution
then we call them elementary.
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Examples of an elementary
particle?
Electrons are elementary. “Protons”
were thought to be elementary. It is
known that proton’s “mass and
charge” are spread over a length, in 3D space, whose radii is something like
10-15 meters. [1femto-meter]
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What is Resolution !!
it’s the smallest extent of something that we can
measure, beyond that it would be like a “point”
something whose extent we can’t measure.
Wavelength of beam
Resolution of an optical microscope
Angular Aperture of the light beam
Larger “angle” and smaller “wavelength” gives better
resolution, therefore ultraviolet is better than visible light.
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Resolution in particle physics
For elementary particles, which obey
Quantum Mechanics
[Laws of Physics for extremely small objects
where they exhibit both “wave” and “particle”
behavior]
Where q = “momentum” transferred to
the “particles” of the incident beam
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Proton is not an elementary
particle
From the equation just explained
“momentum” corresponding to an “energy”
of 10 GeV “gives us” a resolution of 10-16
meters, which is one-tenth the size of a
proton. So now we can make 10 marks on the
body of the proton, not just ONE.
“Ichi-ni-san-yon-go-roku-hachi-nana-kya-ju”
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Why High Energy in “High
Energy Physics”
We saw that with higher energy of incident
beam we are equipped better to probe the
smaller size and know what’s elementary
and what’s not.
There is yet another reason why Particle
Physics needs very high energies. There
are elementary particles which are hundreds
of times massive than extended particles
like protons. And to produce these particles
in the Lab in order to study them means
production of higher energies.
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How high is high energy ?
Total energy of a beam in accelerator
where 1 particle would have 1 TeV of
energy: “per” bunch of 1013 particles,
“per” second equals to energy of
30,000 light bulbs which again equals
to energy of a 15 tonne truck moving
at 30 miles per hour
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Symmetry and its Violations
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Concepts of symmetry
 Symmetry is important at quantum level. At a
classical level its not manifested very exactly.
At quantum level this is very precise and must
be dealt with the principles of Quantum
Mechanics.
 Examples of symmetry: All transformation
laws in Physics. Here the state vector is
conserved [unchanged] under the
transformation, hence the symmetry.
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Symmetry in the Physical
rotation
world Continuous:
of a circle
Continuous
Discrete
Discrete: rotation of a polygon
900
+900
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Symmetry leads to invariance
and vice versa
Invariance of
physical laws
Invariance of force:
infinitely long
electrically charged
wire: cylindrical
symmetry of the
electric force field
E
E
E
Rotation of a system
of charges =>
rotation of the
Electric force
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Examples of symmetry
operations
“Time”
Space transformations
Scaling, reflection, rotation etc
“Functions”
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Continuous symmetries
Space-time symmetries
Time translation
Spatial translation
t  t a
r  r a
Spatial rotation: Proper:square matrix
det =1, Improper:square matrix det =-1
Poincare transformation:distances in
Minkowski space-time are invariants

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Discrete symmetries
Time reversal:
t t
Upon reversing the
“sign” of time
some physical
laws/quantities are
unchanged

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Discrete symmetries
Spatial inversion
r r
Symmetries in Crystals
C,P,T symmetries are discrete, used in
Particle Physics

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CPT invariance
Hypothesis: Under C, P or T the universe is invariant
“charge conjugation” or particle-to-
antiparticle transformation
Mirror reflection or space parity
Time reversal
Individually C, P or T do not provide a good symmetry
Collectively CPT is supposed to be an
invariant in nature
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CP Violation, Super-symmetry
Violation of CP symmetry is in
consonance with amount of baryonic
matter in the universe which in turn is
necessary for existence of life.
Super-symmetry is an advancement to
Standard Model of Particle Physics and
assigns a super-partner to Bosons and
Fermions.
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Motivations/Introduction
“my measurement”
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Motivations
As mentioned in the early slides: There
“is” an asymmetry in D0 to (KS/KL)0,
which has been proposed in
phenomenological works.
Independent of that, this asymmetry can
be “measured” with recourse to the
present sensitivity of our detector at
Belle.
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
The signal channels
Explicitly, there is a natural asymmetry
in the Branching Fraction of
D  K L  andD  K S 
0
0
0
0
These decays are identified
experimentally (a.k.a. tagged) by their
parent decay
D *  D 0  
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Asymmetry because of
interference
The asymmetry arises supposedly
because of interference in the
amplitudes of the Cabibbo Favored (CF)
and Doubly Cabibbo suppressed (DCS)
modes of the D0 meson.
D K 
0
D K 
0
0
0
0
0
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Detector bias
Apart from this asymmetry the detector
can provide a bias in the measurement
of KL vis-à-vis KS. The complete KL info
is not available from the detector. A
“missing energy method” is used to
tackle this.
The KL reconstruction efficiency is
strongly momentum dependent
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Reconstruction efficiency
KL, Strong
momentum
dependence
KS efficiency “flat”
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Calibration channels
 We need to have calibration modes of the D0.
When the D0 decays via the K*- (or K*+)
resonance to the (KS and KL final states)
there is no natural asymmetry here. The
asymmetry is detector induced.
 Most systematics of the detector cancel out
due to same final state particles, (same
reconstruction efficiency).
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Details of approach of my
measurement
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The KL is partially
reconstructed
KL direction only
Improved direction
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K-Long missing energy is
recovered
Detector does not
give pKL, “quadratic
solutions” are obtained from
relativistic kinematics
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KS is reconstructed pretty well
“V for Vertex”
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Signal and calibration modes
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Event Selection
 To do this analysis an integrated luminosity of
32 fb-1 belle data was used. The corresponding
monte carlo used is roughly 3 times of this.
 The D* candidates were selected by choosing
their reconstructed scaled momentum xp
between 0.6 to 1.0
 this new variable is defined as xp =
p*/sqrt(Ebeam2 - M2) where p* is the cms
momentum.
 This rejects D* from B-decays and suppresses
Combinatorics.
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Event selection methods
 Apart from standard selection procedure for
Pions and KS, the daughter gammas of pi0 are
rejected if their energy is less than 50 MeV
 For the KS its pi-pi vertex should be separated
from the IP in the transverse plane by more than
500 micro-meters
 KS’s pi-pi tracks should not be separated by more
than 1 cm, at the KS vertex, along the beam axis
 Angle between assumed KS trajectory from IP to
vertex and the reconstructed one should be very
small, i.e. cosine(of this angle)>0.95
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Event Selection
KL in the KLM are contaminated by
unreconstructed charged particles
which are rejected by vetoing
associated energy in the ECL in the
range of 0.15 to 0.3 GeV which
corresponds to minimum ionization
energy
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Event Selection
 A large chunk of background is gotten rid of
by applying a selection on the K0 flight angle
wrt D0 boost as it peak towards forward
direction as shown in next slide. For signal
this angle is isotropic with a slight tilt to the
forward direction due to detector efficiency.
This happens when arbitrary soft pions as
opposed to our signal slow pion combines
with high momentum K and forms a good
signal.
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The sharp peak is caused by the
reverse situation when K is soft
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Event Selection
-
Invariant mass of K* (K0pi-) is required
to be within 50 MeV/c2 of nominal
K*(892) mass, also the pi+pi- pair in
these modes are required to be less
than 0.7 GeV/c2
This makes the signal and calibration
kinematically similar and reduces
contribution from K0Rho
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Modes studied in monte-carlo
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Results of my measurement
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Division of event structure
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Detailed analysis of event
structure
A clean
mode
Only 2 out of 6 divisions data samples which
corresponds to 4 modes are shown here
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
Peaking backgrounds were
found
These are of
many kinds,
some are
present
negligibly and
some are not so
 These will be
appropriately
scaled and
subtracted
 Some events
are still
unidentified
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Details of events in montecarlo
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“Data” events, calibration
channels
Note the large
background
D0->(KS
D0->(KL
clean
Results for signal modes not shown here
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Future path !!
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 Upgrade to bigger data sample
 Completion of identification of all event
sources
 Careful analysis of numbers/errors and
publication
 The most ambitious vision/wish: a hobnob
between theory, phenomenology and
experimental approach to bring a clearly
determined verdict on this form of asymmetry.
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