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Introduction

Introduction. Delta resonances (also known as P 33 ) represent excited states of nucleons, and as such were always objects of great interest in particle physics. The study of these baryons is important for better understanding of various phenomena

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Introduction

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  1. Introduction • Delta resonances (also known as P33) represent excited states of nucleons, and as such were always objects of great interest in particle physics. The study of these baryons is important for better understanding of various phenomena • Delta’s represent isospin quadruplet within baryonic decuplet for spin S=3/2 (with all three quarks having the same spin alignment) • Members are: • Δ++ (uuu) J=3/2 • Δ+ (uud) J=1/2 • Δ0 (udd) J=-1/2 • Δ- (ddd) J=-3/2

  2. Delta++ • The idea for Delta++ search comes from desire for better understanding of pion production in nucleus-nucleus interactions • Δ++ is a typical Breit-Wigner resonance centered around 1232MeV with width of around 120MeV. It decays via strong interaction into proton and pi plus and has mean lifetime of the order of 10-24s.

  3. Methods • Extremely short lifetime means it is not possible to distinguish the point of decay from vertex of primary interaction • Our approach (event mixing method): • Invariant mass spectra were created by selecting all positive particles that come from primary vertex assuming that one is a proton and other a pion and vice-versa • Background was created by combining these particles with uncorrelated positive particles from previous event • The same was done using dE/dx data for identification of particles and results were compared (v2r4 version of software was used throughout)

  4. Runs used for analisys • p on LH158GeV: run-009971, run-009973, run-009974, run-009977, run-009978, run-, 09979, run-009981, run-009983, run-009985, run-009987, run-009988 • p on LH80GeV: run-010132, run-010133, run-010134, run-010135, run-010136, run-010137, run-010138, run-010139, run-010140, run-010141, run-010142, run-010143, run-010144, run-010145, run-010146, run-010147, run-010148 • p on LH31GeV: run-008947, run-008961, run-008992, run-009004, run-009009, run-009036, run-009040, run-009041, run-009043, run-009044, run-009049, run-009050, run-009051, run-009069, run-009070, run-009080, run-009081, run-009082, run-009083, run-, 09084, run-009085, run-009086, run-009087, run-009088, run-009089, run-009092, run-009093, run-009094, run-009095, run-009096, run-009097, run-009098, run-009099, run-009104, run-009105, run-009106, run-009107, run-009108, run-009109, run-009112, run-, 09113, run-009114, run-009118, run-009119, run-009120, run-009121, run-009125, run-009126, run-009127, run-009128, run-009133, run-009134, run-009135 • MC data for p on LH158GeV (downloaded from afs) • MC data for p on LH80GeV (produced locally in Belgrade)

  5. Statistics • Only “good” events were selected for analysis based on following criteria (for real data only): • The beam was good (based on BPDVertexIflag) • Primary Vertex reconstructed • Primary Vertex Iflag is OK • Primary Vertex was inside target (cut on Z coordinate of reconstructed vertex) • The following are number of events used in analysis

  6. Results – pp158GeV • pp158GeV - preliminary results: • Nature of the structure • on 1.34GeV?

  7. Results – pp158GeV • Isolating particles of interest by creating symmetric invariant mass spectra Invariant mass for p-p pairs Invariant mass for pi-pi pairs

  8. Results – pp158GeV • Difference between correlated particles (same event) and uncorrelated particles for selected intervals • Based on this a cut was introduced:

  9. Results – pp158GeV • After the cut • Structure is almost completely removed . This could be • illustrated by following calculation Signal+Background Signal

  10. Results – pp31GeV • pp 31 – preliminary results • Additional problem is • structure bellow 1.1 GeV

  11. New Cut • After introduction of the new cut (NPoint/NMaxPoint >0.5 - suggested at the last Evo meeting) pp 158GeV pp 31GeV

  12. PID by dE/dx – pp 158GeV • Rudimentary identification of particles using dE/dx was attempted. Two different methods were used for selection of protons and pions among positive primary particles and event mixing method was applied: • Selecting regions on dE/dxvslogP graph which give larger probabilities that particle is proton or a pion • Using T49Prob class and comparing calculated dE/dx with measured one

  13. PID by dE/dx – pp 158GeV • First method: • Region for assumed protons: • Region for assumed pions:

  14. PID by dE/dx – pp 158GeV • Signal – first method

  15. PID by dE/dx – pp 158GeV • Second method: assumed protons and pions • and signal

  16. MC Data • pp 158GeV MC data • The nature of 1230MeV(!) structure?

  17. Thank You

  18. Additional Slides • pp 31GeV - PID from dE/dx

  19. Additional Slides • Total event momentum

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