Transcript STUDY OF D* NATURAL LINE WIDTH

Capstone Presentation
Department of Physics
09 June 2010
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Study of elementary building blocks of matter
◦ Interactions of particles
◦ Forces that hold particles together and act on
particles
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What gives particles their mass?
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Why an imbalance between matter and antimatter
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Physicists want to find limits of The Standard Model of
Fundamental Particles and Interactions and see what
is beyond
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
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Set up to analyze collisions between electrons and their equal/opposite
antiparticles, positrons
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To understand differences between matter and antimatter
PEP-II Storage Rings of Accelerator
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
Graphics provided by BABAR Collaboration
www.slac.stanford.edu/BFROOT
BABAR Detector
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Decay being studied (for D*+ natural line width):
D*+
D0 πs+
D0
K- π+
πs+
π+
D0
Signal Side
e
+
These particles
reach layers of
the detector
K-
D*+
e-
Tag Side
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
4
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Previous studies
◦ ACCMOR 1:
 90% CL upper limit to Γ of 131 keV
 Poor statistics
◦ CLEO 2:
 1st measurement Γ = [96 ± 4 (stat) ± 22 (syst)] keV
 Good resolution, poor statistics
1. S. Barlag, et al. Measurement of the mass and width of the charmed meson D*+ (2010), Phys. Let. B 279, 4 (1992); 480-484
2. A Anastassov, et. al. First Measurement of Γ(D*+) , Phys. Rev. Lett. 87, 25 (2001)
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
5
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For high quality tracks, good track resolution and to
remove background:
◦ Slow Pion DCH Hits
◦ Kaon DCH Hits
◦ Pion DCH Hits
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> 12
> 20
> 20
Make requirements on number of hits to have well
measured tracks:
◦ Pion
◦ Kaon
◦ Slow Pion
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
SVT OK
SVT OK
SVT OK
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To eliminate electron mis-identification from
D*0 → D0 π 0
π 0 → γ γ , γ e+ e◦ πs , veto on IsGammaConversion
◦ πs , veto on IsDalitzConversion
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Overall general cut, to eliminate e◦ -3 < πs Pull for dE/dx (DCH) < 2
◦ -3 < πs Pull for dE/dx (SVT)
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
< 2
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3 Ranges of K- π + mass
Normalized to Highest Bin
1.8495 - 1.8595
1.8595 - 1.8695
1.8695 - 1.8795
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
8
MONTE CARLO (MC)
We use a Monte Carlo
simulation to determine the
resolution function.
Signal (peak)
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Sum of 3 Gaussians with
independent means
(central values) and
widths
Background (red dotted line)
Pull Distribution (σ)
is modeled with:
is modeled with:
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Threshold function
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
We look at pull distributions centered around
zero to check for systematic variation
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REAL DATA BW Convo with [(Res Fct) x (1+ε)]
REAL DATA (RD)
Δ m signal (peak)
is modeled with:
Pull Distribution (σ)
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Non-relativistic Breit-Wigner
convolved with resolution
function extracted from MC
and includes:
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Offset parameters
 Allows for differences in mean
(central) values in MC and RD
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Parameter ε
 Scales overall MC resolution
function
Background (red dotted line)
is modeled with:
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010

Threshold function
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ε
Gaussian
Width & Mean
Fixed
Offset
Free to float
ε
Free to float
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
11
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Using this non-relativistic Breit-Wigner
model for the line shape, we find the D*+
natural line width to be:
Γ = [101 ± 1 ] keV
Systematic error is still being investigated
◦ This measurement will constrain models used to describe
interactions of charm mesons
◦ Providing a model with correct Breit-Wigner tails will permit
better Monte Carlo simulations of D*+ in the future.
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
12
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We will:
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Try different Breit-Wigner shapes
Study variation of results as a function of such
variables as:
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Lab momentum of the sample
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Track quality
Evaluate cause of systematic variation observed in
pull distribution plots
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
13
Advisors
Mike Sokoloff
Brian Meadows
Post Doctorates
Mikhail Dubrovin
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
Graduate Students
Rolf Andreassen
Zach Huard
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BACK-UP SLIDES
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
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Quarks
Up (u)
charm (c)
top (t)
Down (d)
Strange (s)
Bottom (b)
Leptons Electron
neutrino (Υe)
electron (e)
Force
Carriers
Photon (γ)
Gluon (g)
Muon
Tau neutrino
neutrino (Υμ) (Υτ)
Z boson
mu (μ)
W boson
Tau (τ)
•The strong force is responsible for quarks “sticking” together to form protons, neutrons and related particles.
•The electromagnetic force binds electrons to atomic nuclei (clusters of protons and neutrons) to form atoms.
•The weak force facilitates the decay of heavy particles into smaller siblings.
•The gravitational force acts between massive objects. Although it plays no role at the microscopic level, it is the
dominant force in our everyday life and throughout the universe.
•The gluon mediates the strong force; it “glues” quarks together.
•The photon carries the electromagnetic force; it also transmits light.
•The W and Z bosons represent the weak force; they introduce different types of decays
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
16
Graphics provided by BABAR Collaboration
www.slac.stanford.edu/BFROOT
17
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Silicon Vertex Detector:
Provides precise position information on charged tracks
Drift Chamber:
Provides main momentum measurements for charged particles; helps with particle ID
through dE/dx measurements
CSF Calorimeter
A calorimeter is a device that measures the energy and position of a particle by absorbing it.
Detector of Internally Reflected Cerenkov radiation: DIRC
A Cerenkov detector is a particle identification device. It uses the Cerenkov angle of a
charged track to determine the track velocity.
The primary task of the DIRC is to distinguish between charged pions and charged kaons at
high momentum. (At low momentum, pion/kaon separation is based on dE/dx
measurements in the SVT and DCH.)
Instrumented Flux Return: IRF
The IFR is BaBar's outermost subdetector. It is used to detect muons and long-lived neutral
hadrons.
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
Descriptions provided by BABAR Collaboration
www.slac.stanford.edu/BFROOT
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Bitmask
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>2 hits in r/phi-view (at least 1 hit in layer 1-3)
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>2 hits in z-view (at least 1 hit in layer 1-3)
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>6 hits total (r/phi + z view)
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
19
FIXED
ALLOWED TO FLOAT
means for Gaussians (Resolution)
BW width (Convolution)
sigmas (Resolution)
slope
signl_num (Resolution)
Epsilon
ΔM
Offset
Pion mass
sigEvents (Convolution)
bckgd_frct (Convolution)
Gaussian
Width & Mean
Fixed
Get from MC
Offset
Free to float
Allow RD average to differ from MC
ε
Free to float
Allow for resolution difference
between MC and RD
Carol Fabby
Capstone Presentation
University of Cincinnati
09 June 2010
20
Short Answer
The lifetime of a D*+ is so quick we can’t resolve it, but we can find the width and
from that we can find the lifetime: τ = 1/ Γ
Longer Answer
The underlying mechanics are revealed at / hinted by the lifetime. For example: Φ
which is a ssbar state
[See diagram]
This is a strong decay
Φ → K -K +
(1.02 GeV)→ (0.99 GeV) in terms of mass
So only a small amount of energy goes to the kinematics of K -K+.
On the other hand there is a light mode
Φ→ π+ π- π0 (1.02 GeV)→(0.415 GeV)
Much more energy (phase space) for this mode
[See diagram]
But if you can ‘cut’ the gluon lines in a diagram the ‘fast’ 3π decay mode is
suppressed and the 2K mode is slower, since it needs specific kinematics to happen.
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On the other hand there is a light mode
Φ→ π+ π- π0 (1.02 GeV)→(0.415 GeV)
Much more energy (phase space) for this mode
But if you can ‘cut’ the gluon lines in a diagram the ‘fast’ 3π decay
mode is suppressed and the 2K mode is slower, since it needs
specific kinematics to happen.
Carol Fabby
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