1 / 20

Hall B Collaboration Meeting

?. D eeply V irtual C ompton S cattering off 4 He eg6 @ CLAS.JLab. Yohann Perrin, Eric Voutier. Laboratoire de Physique Subatomique et de Cosmologie Grenoble, France. Physics motivations Experimental setup 4 He(e, e’p g ) 3 H cross check 4 He(e, e’ 4 He g ) analysis

ken
Télécharger la présentation

Hall B Collaboration Meeting

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. ? Deeply Virtual Compton Scattering off 4He eg6 @ CLAS.JLab Yohann Perrin, Eric Voutier Laboratoire de Physique Subatomique et de Cosmologie Grenoble, France • Physics motivations • Experimental setup • 4He(e,e’pg)3H cross check • 4He(e,e’4Heg) analysis • Physics background channels • Conclusion eg6 group (E07-009, E08-024) Hall B Collaboration Meeting Newport News, February 22-25, 2012

  2. Binding (t=-0.1 GeV2) Nuclear modifications (t=-0.1 GeV2) RA RA(t=0) . J. Gomez et al., PRD 49 (1994) 4348 x Physics Motivations Coherent Nuclear DVCS S. Scopetta, PRC 70 (2004) 015204 ; 79 (2009) 025207 S. Liuti, K.Taneja, PRC 72 (2005) 032201 ; 034902 • Nuclear DVCS probes the partonic structure of nuclei and offers the opportunity to investigate the role of the transverse degrees of freedom in the modifications of the nuclear parton distributions, as compared to free nucleons. Generalized EMC Ratio The ratio of beam-spin asymmetries on the nucleus and on the nucleon is predicted to be more sensitive to peculiar features of the EMCeffect modeling. Newport News, February 22-25, 2012

  3. 4He(e,e’g 4He) 4He(e,e’gp)3H • t = 0.000 GeV2 • t = 0.095 GeV2 • t = 0.329 GeV2 • t = 0.000 GeV2 • t = 0.100 GeV2 • t = 0.207 GeV2 Physics Motivations Incoherent Nuclear DVCS S. Liuti, K.Taneja, PRC 72 (2005) 032201 ; 034902 V. Guzey, PRC 78 (2008) 025211 V. Guzey, A.W. Thomas, K. Tsushima, PLB 673 (2009) 9 ; PRC 79 (2009) 055205 • The role of the transverse degrees of freedom in the EMC effect are pedicted to be more prominent in incoherent DVCS than in coherent DVCS. • Similarly to conventional (e,e’p) physics, the concept of bound nucleon GPDs can be adressed via incoherent DVCS. Newport News, February 22-25, 2012

  4. Physics Motivations Spinless Nucleus A. Belitsky, D. Müller, A. Kirchner, A. Schäfer, PR D64 (2001) 116002 V. Guzey, M. Strikman, PRC 68 (2003) 015204 • At leading order of the coupling constant, the partonic structure of spin 0 nuclei is characterized by one twist-2 (HA) and two twist-3 quark GPDs (+ gluon ones). • Because of the simple GPD structure of spin 0 nuclei, the twist-2 beam spin asymmetry (BSA) allows for a model-independent simultaneous extraction of the real and the imaginary parts of the twist-2 Compton form factor. Spatial Distribution of Strong Forces NuclearD-term accessible via the real part of the DVCS amplitude. M. Polyakov, PLB 555 (2003) 57 Momentum fraction of the target carried by the quark Newport News, February 22-25, 2012

  5. Experimental Setup E07-009 & E08-024 • The standard CLAS detector package is supplemented with a radial time projection chamber (RTPC), a forward electromagnetic calorimeter (IC), and a solenoidal magnet for Møller shielding. Radial Time Projection Chamber Solenoidal Magnet Inner Calorimeter Newport News, February 22-25, 2012

  6. Experimental Setup CLAS (e,p) The CLAS is used in a conventional way for electron and protondetection and identification. S. Dhamija, L. El Fassi, R. Paremuzyan, C. Salgado, C. Smith, B. Toryaev, M. Ungaro Newport News, February 22-25, 2012

  7. Experimental Setup IC (g) • The invariant mass of 2g-events in IC is used for the calorimeter calibration, taking into account the interaction vertex as given by CLAS. • The final resolution is 7.1% at the pion mass. F.-X. Girod Newport News, February 22-25, 2012

  8. Experimental Setup RTPC (4He) • Ad hoc cuts for the identification of a particles are defined for 24 (q,j) sectors with respect to the (adc,pRTPC) topology determined with elastic scattering data. Elastic Data dE/dx N. Baltzell, R. Dupré, R. Paremuzyan, Y. Perrin Newport News, February 22-25, 2012

  9. 4He(e,’e’pg)3H Cross Check Basic Event Selection • A preliminar analysis of the incoherent channel was attempted to check detector calibration, data quality, and analysis algorithm. • Electron : 1 and only 1 negative track in CLAS + (EC+CC ) pion rejection cut + target windows rejection • Proton: 1 and only 1 positive track in CLAS • Photon : 1 and only 1 cluster in IC + no neutral particle in EC Physics cuts are developped with the guidance of the PWIA picture, assuming that the interaction takes place on a quasi-free on-shell nucleon, leading to kinematical and angular correlations between the reaction products. Newport News, February 22-25, 2012

  10. 4He(e,’e’pg)3H Cross Check 3 level of physics cuts : reconstructed q’ out-of-plane angle missing mass Newport News, February 22-25, 2012

  11. 4He(e,’e’pg)3H Cross Check Helicity Signal A strong helicity signal is observed for incoherent DVCS candidate events which phase covers a large kinematical domain, similar to the CLAS p-DVCS experiment. The physics analysis will be conducted by N. Baltzell, C. Moody, O. Nusair (ANL) Newport News, February 22-25, 2012

  12. 4He(e,’e’ 4Heg) Analysis Basic Event Selection • Electron : 1 and only 1 negative track in CLAS + (EC+CC ) pion rejection cut + target windows rejection • Photon : 1 and only 1 cluster in IC + no neutral particle in EC • Helium : 1 and only 1 good positive track in the RTPC + good stoping power The correlation between the z-vertex locations as reconstructed by CLAS and the RTPC provides an additionnal basic mask to experimental data. Newport News, February 22-25, 2012

  13. 4He(e,’e’ 4Heg) Analysis Physics Event Selection • Kinematics of the coherent DVCS reaction allows to reconstruct the expected photon energy from the electron kinematics and the angle of the detected photon. • The out-of-plane angles between the leptonic and hadronic planes as reconstructed from the real photon (CLAS+IC) and the recoil helium (CLAS+RTPC) should be identical. • The momentum of the missing particle of the final state (e4HegX) should be nul. Newport News, February 22-25, 2012

  14. 4He(e,’e’ 4Heg) Analysis Newport News, February 22-25, 2012

  15. 4He(e,’e’ 4Heg) Analysis The missing mass spectra of final state (e4Heg) is consistent with a coherent DVCS reaction. The final t-distribution of selected events behaves as may be expected from the fast decrease of helium elastic form factor. Newport News, February 22-25, 2012

  16. 4He(e,’e’ 4Heg) Analysis Helicity Signal A clear helicity signal is observed for coherent DVCS candidate events, and confirmed by the out-of-plane angle distribution of events integrated over (t, Q2, xB). Newport News, February 22-25, 2012

  17. 4He(e,’e’ 4Heg) Analysis DVCS Phase Space xB≤ 0.3 -t≤ 1 GeV2 Q2 ≥ 1 GeV2 The candidate experimental phase space for coherent DVCS is limited and statistics does not allow for a multi-dimensionalanalysis as was performed in the CLAS p-DVCS experiment. Newport News, February 22-25, 2012

  18. 4He(e,’e’ 4Heg) Analysis DVCS Asymmetries 0 < -t < 0.15 0.15 < -t < 0.3 0.5 < -t < 1.0 0.3 < -t < 0.5 Large t data are irrelevant Newport News, February 22-25, 2012

  19. Physics Background Channels Coherent DVCS Assesment • Pion Contamination • Helium 3 Contamination • Tritium Contamination Newport News, February 22-25, 2012

  20. Conclusion & Outlook Summary Newport News, February 22-25, 2012

More Related