1 / 16

Diffractive ρ ° production at COMPASS

This paper presents the analysis and preliminary results of the diffractive ρ° production at COMPASS experiment, focusing on the spin density matrix elements and their implications for GPD studies. The weak violation of SCHC and the double spin longitudinal asymmetry for ρ° production are also discussed.

dalea
Download Presentation

Diffractive ρ ° production at COMPASS

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. Diffractive ρ° production at COMPASS Nicole d’Hose, CEA-Saclay On behalf of the COMPASS collaboration Physics motivations COMPASS experiment Ongoing analysis Preliminary results Prospects for the future DIS 2005, Madison, USA, April 27-May 1, 2005

  2. μN μ’N’ρ * π+π- Q 2 W N’ N t Description of the diffractive ρ° production Regge theory, pQCD calculations (for σL ), … At low energy W < 5 GeV: exchange of 2 quarks or of Reggeon ρ,ω (JP=1-), a2, f2 (JP=2+), a3, f3 (JP=3-), … At higher energy : exchange of 2 gluons or of Pomeron COMPASS: 10-2<Q2<10 GeV2, <W>=10GeV, t small Experimental observations (NMC, E665, ZEUS, H1, HERMES): the helicity of γ* is approximatively retained by theρ° meson  SCHC the exchange object has natural parity P=(-1)J NPE

  3. Spin properties of the production amplitudes Angular Distribution of the production and decay ofρπ+π- Spin density matrix elements bilinear combinations of the helicity amplitudesA( γ*(λγ)ρ(λρ) ) Tλρλγ λγ=  1, 0 λρ=  1, 0 if NPE T- λρ -λγ= (-1)λρ-λγTλρλγ 9helicity amplitudes reduce to five5 independent amplitudes : A(L L), A(TT) >>A(T L) >A(L T) >A(T -T) i.e. T00,T11 >>T01>T10>T-11 SCHC>> single helicity flip > double helicity flip SCHNC

  4. μ COMPASSexperiment trigger-hodoscopes ~ 250 physicists from 28 institutes DW45 straws SM2 dipole Muon-filter2,MW2 HCAL1 RICH_1 Gem_11 SM1 dipole ECAL2,HCAL2 MWPC Gems Scifi Polarised Target 6LiD Muon-filter1,MW1 straws,MWPC,Gems,SciFi Veto Gems,SciFi,DCs,straws Silicon First results @ DIS2005: ΔG/G : C. Bernet Longitudinalspin depdt g1d : J. Hannappel Transversity : 1) Collins and Sivers asym: P. Pagano 2) 2 hadrons correlation: R. Joosten SciFi Micromegas,DC,SciFi 160 GeV from CERN SPS

  5. Selection of the sample * Q 2 • Topology : • 1 incoming μ and 1 scattered μ • only 2 hadrons of opposite charge • vertex in the 6LiD polarized target • Kinematical conditions: • ν > 30 GeV • Eμ’ > 20 GeV • Q² > 0.01 GeV² Focus on Incoherent Exclusive ρ0 production... W N’ N t

  6. Background proc. rejected : 6LiD Incoherent exclusive ρ0 production Assuming both hadron are p 0.5 < Mpp< 1 GeV Mpp Exclusivity of the reaction Emiss=(M²X-M²N) /2MN -2.5 < Emiss < 2.5 GeV Emiss Incoherent production 0.15 < pt²< 0.5 GeV² scattering off a quasi-free nucleon pt²

  7. Kinematical domain of the final sample after event selection • 2002 : this analysis • ~ 700,000 evts (whole range) • ~ 20,000 evts (Q²>1GeV²) • 2003 and 2004: • - trigger coverage improved • enlarged acceptance at high Q² • (up to 20 GeV) • - ~ 4 times more statistics 10-4 1 10 10-3 10-2 10-1 Q2 [GeV2] W [GeV]

  8. ρ° angular distributions W(cosθ, φ, Φ) depends on theSpin density matrix elements 23 (15) observables with polarized (unpolarized) beam φ This analysis: only one-dimensional angular distribution We will use also: ψ= φ - Φ

  9. 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² Angular distributions 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 φ Preliminary : - Corrected for Acceptance, smearing and efficiency (MC:DIPSI gen) - Background not subtracted Statistical error only, limited by MC

  10. 04 00 Measurement of r 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 Distribution : Spin density matrix elements: Tλρλγare helicity amplitudes meson photon

  11. 2002 2003 + 2004 Determination of Rρ° =sL/sT If SCHC holds : only T00≠0 T11≠0 Then : Impact on GPD study: easy determination of sL factorisation only valid for sL

  12. Measurement of r 1 1-1 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 Distribution, if SCHC holds: with if in addition, NPE holds:

  13. Measurement of r and Im r 04 1-1 3 1-1 φ Distribution : beam polarisation weak violation Spin density matrices: If SCHC holds

  14. Conclusions and perspectives Incoherent exclusive ρ° production under investigation: - high statistics from photo-production to the hard regime - larger acceptance at high Q2 in 2003 and 2004 (up to 20 GeV2) Preliminary results on a few Spin Density Matrix Elements: - only statistical errors are shown (dominated by MC) - systematics to be evaluated (background contamination) -SDME in agreement with other experiments - weak violation of SCHC observed Double spin longitudinal asymmetry for ρ° production (NPE control) Spin asymmetries for transversally polarised target (GPD study) Exclusive production off and J/Y also observed and will be studied

  15. r0 mass distribution Söding parametrization: No acceptance corrections yet ! (subtracted)

More Related