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

1. Investigation of Hyperon Polarization and Analysis of S+b Decay 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. Project 1: Investigation of Hyperon Polarization Systematics • Outline • Motivation for polarization studies • Quark-Quark scattering model • Momentum scaling of proton and L polarization data • Hyperon production systematics

3. Motivation for PolarizationStudies • Data has existed for ~30 years • Presently, no theoretical model can account for all data • Studies this summer are focused on L hyperons – Unexpected high polarization! - Unexplained plateau in data after pt > 1 GeV/c Inclusive L0 production – linear relationship with polarization up to ~1 GeV/c and then plateaus

4. Quark-Quark Scattering Model • Goal: Want to find a way to compare Proton & L Scattering: • PP->PP • PP-> L X • Find scaling factors such that: • PL = w Pp • PTL = k PTp Polarization in p-p elastic scattering as a function of transverse scattering momentum squared

5. Predictions From a Simple Model • In both p-p and L collisions, scattering occurs in discrete interactions of 1, 2, 3… quarks (Quark-Quark scattering model) • Polarization of final proton or L 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 L scattering are: PL = 2 Pp PTL = 2/3 PTp

6. Momentum Scaling: Experimental y1=ax1+b • My task: find parameters that relate L0 and P-P data by: • Finding linear fits for both data sets • Extracting w and k values that fit L0 data onto PP data such that: y2=w*y1, x2=k*x1 Y = polarization x = transverse momentum P-P y2=cx2+d L0

7. Results of Calculations • Pt relation between L0 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 L data at the same beam energies, so more data is needed

8. …Results Continued • Since there does not exist p-p and L data at comparable beam energies, scaling was done for: • P-P data at 300 GeV/c, L data at 400 GeV/c • ROOT fits gave w = 2.69 + 1.07, k = .711 + .32 • The L data was scaled and placed on top of the P-P data as shown: W(pol) = 2.69 K(pt) = .711 • P-P data appears to line up with L data • However, with the current data it is difficult to draw final conclusions due to the large errors • Red = P-P data • Blue = scaled L data

9. 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 W-has essentially 0 polarization • Why the S particles are the only hyperons with positive polarization • Why the L data reaches a plateau after the first kinematic region

10. Hyperon Polarization Data P-P L0 S+ X- X0 W- S- S0

11. Project 2: Analysis of Sb+ Decay Channel For ATLAS Lb Studies • Motivation • Due to their large mass, Lb particles have not been produced in large enough amounts for polarization measurements to be made- • Mass of L0 (uds) = 1.116 GeV, Mass s-quark = .150 GeV • Mass of Lb (udb) = 5.624 GeV, Mass b-quark = 4.5 GeV • ATLAS should produce ~75,000 Lb’s – enough for polarization analysis!! • polarization data of Lb is important because: • It will increase data pool of hyperon polarization • Its comparison with L0 data can help determine whether quark mass is a factor in hyperon polarization • The first measurements of Sb+ properties will be measured in ATLAS

12. Goal of this Project • Determine the degree of background associated with Sb+ signal • It will be important to distinguish primary Lb production from Lb decay products for accurate polarization studies • Use PYTHIA to analyze one decay channel that produces unwanted Lb particles

13. My Contribution • Use PYTHIA to generate ~4000 Sb+ events • In the reactionP+P -> Sb+ + 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 Sb+ during reconstruction

14. Reconstruction of Sb+ • In ATLAS events generating Sb+, Lb signal will be reconstructed first • Need to combine Lb with p to look for Sb+ • Challenge: • With every Sb+, event, we have a “real” p and ~40 background p • How to choose the right p? • When plotting cosine of angle between real & “fake” p, we see that to choose the right p in a event, we have to look for this p amongst particles very close to the Lb(cosine > .97) Real Pions Background Pions Cos(angle) > ~.97

15. Background of Sb+ Signal • Apply cuts to reduce background of “fake” p in reconstructing Sb+ • Cos(angle) between Lb & p > .97 • Pt > 500 GeV/c • Pseudorapidity (h) < 2.7 • From plots, even without cuts, background under the signal will be small • This means ATLAS should see a clear Sb+ signal!!! S/N = 26 Cuts applied S/N = 27.8 No Cuts Background Background

16. 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 L data • Project 2 • Should be a clear Sb+ signal in ATLAS • Further analysis needs to be done to find additional background in Sb+ signal associated with background in Lb reconstruction

17. 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

18. …Results Continued