Investigation of Hyperon Investigation of Hyperon Polarization and Analysis of Polarization and Analysis of
bb
Decay Channel in ATLASDecay Channel in ATLAS
August 11, 2005
Sarah Lumpkins(University of Oklahoma)
Advisors: Dr. Eduard De La Cruz Burelo
Dr. Homer Neal(University of Michigan)
2
• OutlineOutline– Motivation for polarization studies– Quark-Quark scattering model– Momentum scaling of proton and
polarization data– Hyperon production systematics
Project 1: Investigation of Hyperon Polarization Systematics
3
Motivation for Polarization Studies
• Data has existed for ~30 years
• Presently, no theoretical model can account for all data
• Studies this summer are focused on hyperons
– Unexpected high polarization!
- Unexplained plateau in data after pt > 1 GeV/c
Inclusive 0 production – linear relationship with polarization up to ~1 GeV/c and then plateaus
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Quark-Quark Scattering Model
Polarization in p-p elastic scattering as a function of transverse scattering
momentum squared
•Goal: Want to find a way to compare Proton & Scattering:
PP->PP
PP-> X
•Find scaling factors such that:
P = w Pp
PT = k PTp
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Predictions From a Simple Model
• In both p-p and collisions, scattering occurs in discrete interactions of 1, 2, 3… quarks (Quark-Quark scattering model)
• Polarization of final proton or is sum of the polarization of each discrete interaction
• Transverse momentum generated is the sum of the transverse momentum of each quark in the interaction
• According to this model, the scaling parameters needed to compare proton and scattering are:
P = 2 Pp
PT = 2/3 PTp
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Momentum Scaling: Experimental
• My task: find parameters that relate 0 and P-P data by:
– Finding linear fits for both data sets
– Extracting w and k values that fit 0 data onto PP data such that:
y2=w*y1, x2=k*x1
Y = polarization
x = transverse momentum
y1=ax1+b
y2=cx2+d
P-P
0
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Results of Calculations
•Pt relation between 0 and P-P data is ~ same for different values of beam energy
•Polarization parameter increases for increasing beam energy
•A more accurate analysis would involve comparing P-P and data at the same beam energies, so more data is needed
Fit Parameters that Correlate Lambda & P-P Data
0
1
2
3
4
0 100 200 300 400
Beam Energy (GeV)
P_
T a
nd
Po
lari
zati
on
P
ara
me
ters
WvalsPolarization
KvalsP_t
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…Results Continued• Since there does not exist p-p and data at comparable beam
energies, scaling was done for:– P-P data at 300 GeV/c, data at 400 GeV/c
• ROOT fits gave w = 2.69 + 1.07, k = .711 + .32– Thedata was scaled and placed on top of the P-P data as shown:
W(pol) = 2.69
K(pt) = .711
-Red = P-P data
- Blue = scaled data
•P-P data appears to line up with data
•However, with the current data it is difficult to draw final conclusions due to the large errors
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Hyperon Production Systematics
• Project goal: conduct a more general survey of all existing hyperon polarization data and try to find commonalities between the data
• Questions this survey will probe is:– Why the has essentially 0
polarization– Why the particles are the only
hyperons with positive polarization– Why the data reaches a plateau
after the first kinematic region
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Hyperon Polarization Data
0
+
0
-
P-P
-
0
-
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• Motivation
Project 2: Analysis of b
+ Decay Channel For ATLAS b Studies
• Due to their large mass, b particles have not been produced in large enough amounts for polarization measurements to be made-
• Mass of 0 (uds) = 1.116 GeV, Mass s-quark = .150 GeV
• Mass of b (udb) = 5.624 GeV, Mass b-quark = 4.5 GeV
• ATLAS should produce ~75,000 b’s – enough for polarization analysis!!
• polarization data of b is important because:
• It will increase data pool of hyperon polarization
• Its comparison with 0 data can help determine whether quark mass is a factor in hyperon polarization
• The first measurements of b+ properties will be measured in ATLAS
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Goal of this Project
• Determine the degree of background associated with b
+ signal
• It will be important to distinguish primary b production from b decay products for accurate polarization studies
• Use PYTHIA to analyze one decay channel that produces unwantedb particles
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My Contribution
• Use PYTHIA to generate ~4000 b+ events
• In the reaction P+P -> b+ + X, I edited an existing C++ file
to store properties of X if X includes:– Final state particles (does not decay)– Charged particles– Includes: Kaons, protons, pions, muons, electrons
• Use ROOT to analyze properties of these particles, including:
– Pt
– Angular distributions
• Identify cuts to reduce background of b+ during reconstruction
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Reconstruction of b+
• In ATLAS events generating b+, b signal will be
reconstructed first• Need to combine b with to look for b
+
• Challenge:– With every b
+, event, we have a “real” and ~40 background – How to choose the right ?– When plotting cosine of angle between real & “fake” , we see that
to choose the right in a event, we have to look for this amongst particles very close to the b (cosine > .97)
Real Pions
Background Pions
Cos(angle) > ~.97
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•Apply cuts to reduce background of “fake” in reconstructing b+
•Cos(angle) between b & > .97
•Pt > 500 GeV/c
•Pseudorapidity () < 2.7
•From plots, even without cuts, background under the signal will be small
•This means ATLAS should see a clear b+ signal!!!
Background of b+ Signal
S/N = 27.8
No Cuts
Background
S/N = 26Cuts applied
Background
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Conclusions• Project 1
– Still need to look at hyperon properties to try and develop production models
– Need more data for experimentally extracting momentum / polarization scale factors for P-P and data
• Project 2– Should be a clear b
+ signal in ATLAS
– Further analysis needs to be done to find additional background in b
+ signal associated with background in b reconstruction
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Acknowledgements
• My advisors– Dr. Eduard De La Cruz Burelo – Dr. Homer Neal
• University of Michigan– Dr. Krisch– Jeremy Herr
• Ford Motor Company
• National Science Foundation• CERN
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…Results Continued