1 / 20

Study of W± Bosons at LHC Energies

This study focuses on the production of W± bosons in proton-proton collisions at 14 TeV at the LHC. The aim is to analyze the rapidity and transverse momentum distributions of W± bosons and their decay modes, particularly into muons. The results provide valuable insights into weak interactions and quark distribution functions.

caldwellb
Download Presentation

Study of W± Bosons at LHC Energies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Study of W± bosons @ LHC energiesZ Buthelezi, iThemba LABSfor the ALICE Collaboration

  2. Scope • Introduction • Motivation • Objectives • Status of W±→± production in pp collision @ 14 TeV • Remarks • Outlook

  3. Introduction • W± are intermediate vectorbosons, MW = 80.398± 0.25 GeV/c2, electric charge: ±1 e, spin = 1 • Carrier particles for weak interactions  can change generation of a particle (quark flavour change) • Best known for role in n beta decay to p, e and • First observed experimentally @ CERN in 1983 - Carlo Rubbia and Simon van der Meer (Nobel prize 1984)

  4. Introduction continues…. • In pp collisions W± are produced in initial hard collisions between quarks • Lowest order process: • Highest order processes: g and  initial & final state radiation

  5. Intro continues... W± decay modes: • leptonic: l + l(10.80 ± 0.09%),  + (< 8 x 10e-5 confidence level: 95%) • Electronic: e + e(10.75 ± 0.13%) • Muonic:  + (10.57 ± 0.15%) • Charm: c + X( 33.4 ± 2.6%), c +(31 ± 13%) • Light unflavored meson: +  (11.25 ± 0.2%) • Charmed meson: + (< 1.3 x 10e-3 confidence level: 95%)

  6. Motivation Background study: W production in pp, PbPb & pPb collisions @ LHC energies: W± detection in the Muon Spectrometer. Z Conesa del Valle et al. Scientific motivation: • Probe PDF in the Bjorken-x range: x (10-4 – 10-3)  -4.0 < y < -2.5 for Q2 ~ MW2 • Validate binary scaling, study nuclear modification of quark distribution function • W as reference for observing GQP induced effects on other probes, e.g. suppression of high pT heavy q Analysis: - Fast simulation (without ALICE detector configuration) - Rapidity (y) and pTdistributions for W→ (10.57 ± 0.15%) , W→cX→…→ ( 33.4 ± 2.6%) Ref: ALICE-INT-2006-021/01, arXiv:0712.0051v1 [hep-ph] 1 Dec 2007 and PhD thesis, 2007

  7. Objectives • ±pT ~ MW / 2 = 30 – 50 GeV/c • Full simulation (ALICE detector configuration) in whole rapidity range and in in the ALICE Muon Spectrometer Acceptance: 2 <  < 9   -4.0 < y < -2.5 • Reproduce y and pT distributions • Used dHLT to cut background

  8. Status of W → production in pp @ 14TeV 1. Simulation • PYTHIA version 6.2, AliRoot v4-15-01 • QCD process: 2 → 1 • Decay channel: W±→± +  • PDF: CTQ4L • Nevents = 500 000 • Total cross section

  9. 2. Analysis: • Differential cross section determined using eqtn by Frixione and Mangano (Ref. Hep-ph/0405130) • Muon Spectrometer Acceptance (AW) = y = 0.1, NObs = 500 000 events, (W)PYTHIA x BRW→ = 17.3 nb Note: Spectra normalised to NLO theoretical calculations: th(W)NLO x BRW→ = 20.9 nb (Ref: Lai et al, arXiv:hep-ph/9060399v2, 10 Aug 1996)

  10. 3. Results:A. W± rapidity distributions in pp @ ECMS = 14 TeV for whole rapidity range • More W+ than W-: W± are produced in  by charge conservation - W+ produced by and - W- produced and BUT there are more u than d in pp, i.e. Nu~ 2Nd NW+ > NW- • W+ peaks @ yhigh while W- peaks @ ymid: In ppu valence quarks carry, on average, high amount of the proton’s incident energy (momentum) than d valence quarks

  11. Predicted LO in pp → W + X @ LHC

  12. B. W±→rapidity distributions in pp @ ECMS = 14 TeV in whole rapidity range • More + than - because NW+ > NW- • +distribution is narrower than that of W+ while -distribution iswider than that of W- due - Polarization effects Parity conservation: we expect + to be emitted in valence q direction BUT …. →

  13. W- → -  Jz = -1 W+ → +  Jz = +1 Jz = -1 Polarization effects in W • - will be emitted in the valence q direction, i.e. P and J are conserved. • Due violation total J conservation  + will be produced in opposite direction of valence quark momentum  + could be produced @ mid rapidity & - @ high rapidity W

  14. C. Production cross section ratios in the whole rapidity range W+ / W- + / -

  15. Projection of ALICE Muon Spectrometer cuts in W+ and W- Rapidity distributions

  16. D. W→ pT distributions: Whole rapidity range • ± peaks @ pT = 30-40 GeV/c • m± Differential x-section is reduced by factor ~7 in the muon spectrometer acceptance range • Significant effect of muon spectrometer in the shape of pT distribution, i.e. peak has a pronounced structure to it. • m+ is produced @ a higher rate in the muon spectrometer than m- Muon+ Muon- ALICE Muon Spectrometer Acceptance: 2<<9

  17. E. Ratio of single m+ / m- yields as functions of pT • m+ / m- is higher in the muon spectrometer acceptance than in the whole rapidity range. • At pT < 40 GeV/c the m+ / m- is consistently below 1.5 in the whole rapidity range and @ pT > 40 GeV/c it increases from 1.5 up 3.4 • In the Muon spectrometer Acceptance the m+ / m- is constantly below 2 at pT up to 20 GeV/c and slowly increases to ~ 10 at pT > 30 GeV/c

  18. Remarks: • W+ generation is greatly favoured in pp collisions due to Nu > Nd. • Charge asymmetry on W • W parity violation has an important effect in the m+ and m- rapidity distributions • Single ± pT distribution is significantly reduced in the ALICE Muon Spectrometer Acceptance  need to double statistics for efficient dHLT analysis.

  19. Outlook 1. pp collisions • W→ c + X → …→  + Y • Generate pT distribution for different channels • dHLT analysis: cuts @ 2 GeV/c < pT < 20 GeV/c 2. Pb – Pb collisions @ 5.5 TeV • W→  +  • W→ c + X → …→  + Y

More Related