Investigation of Hyperon Polarization and Analysis of S + b Decay Channel in ATLAS

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