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