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Heavy quarkonium production and polarization

Heavy quarkonium production and polarization Puzzles, Challenges and Opportunities in the LHC Era CTEQ-LPC workshop, 17-18 Nov. 2011. z CS. Carlos Louren ço (CERN) and Pietro Faccioli (LIP-Lisbon) in collaboration with:

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Heavy quarkonium production and polarization

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  1. Heavy quarkonium production and polarization Puzzles, Challenges and Opportunities in the LHC EraCTEQ-LPC workshop, 17-18 Nov. 2011 zCS Carlos Lourenço (CERN) and Pietro Faccioli (LIP-Lisbon) in collaboration with: João Seixas (LIP-Lisbon)Hermine Wöhri (CERN) Valentin Knünz (HEPHY-Vienna) λθ = –1 λφ = 0 λθ = –1 λφ = 0 zHX zCS λθ = –1/3 λφ = –1/3 zHX Bibliography: FLSW, JHEP 10, 004 (2008) FLSW, PRL 102, 151802 (2009) FLSW, EPJC 69, 657 (2010) FLS, PRL 105, 061601 (2010) FLS, PRD 81, 111502(R) (2010) FLSW, PRD 83, 096001 (2011) FLSW, PRD 83, 056008 (2011) V. Knünz, Diploma thesis, Vienna University of Technology, 2011 λθ = +1 λφ = –1 zCS

  2. Too many models… not enough data? Much remains to be understood in quarkonium productiondespite all the measurements made in the last 30 yearsand the vast progress in the theory sector Differential production cross sections are not able to significantly discriminatewhich model gives the best description of Nature: all models survive this test NRQCD CSM CDF CSM@LO NRQCD (CSM + COM) pT[GeV/c]

  3. Not enough models… too good data? Quarkonium polarization is the best available probe of the different quarkonium production mechanisms: NRQCD, CSM@NLO, etc But it seems that polarization is too powerful as “model killer”: no model survives the confrontation with the CDF J/y data λθ pbar-p 1.96 TeVhelicity frame NRQCD :prompt J/ψ Braaten, Kniehl & Lee, PRD62, 094005 (2000) CDF : promptJ/ψ CDF Coll., PRL 99, 132001 (2007) Colour-singlet @NLO : directJ/ψ Gong & Wang, PRL 100, 232001 (2008) Artoisenet et al., PRL 101, 152001 (2008)

  4. Are the data really so good? • The CDF prompt-J/y polarization measurement is not a clear probe of charmonium production; without the azimuthal anisotropy, lf, the J/y polarization is unknown • We can easily list three very different physical polarization scenarios that describe equally well the CDF data: • Scenario 1: lf = 0 in the helicity frame (implicitly assumed by CDF) • Scenario 2: lf = 0 in the Collins-Soper frame • Scenario 3: Superposition of two processes fully transverse in different frames • These scenarios can be “confirmed”or falsified by improved analyses, which: • measure the full dimuon angular distribution, not just the cos(q) projection • provide results in several frames: Collins-Soper, helicity, perpendicular helicity Scenario 1 Natural polarization in HX frame CS helicity

  5. Scenario 2: lf = 0 in the Collins-Soper frame E866 : lq ~ const = +1 in the CS framefor the Y(2S)+Y(3S) states, implying lf = 0 1 . 5 Drell-Yan 1 . 0 E866 (CS) (2S+3S) 0 . 5 CDF (HX) E866 (CS) 0 . 0 pCu, 0 < xF < 0.6, √s = 38.8 GeV HERA-B (CS) - 0 . 5 0 1 2 pT [GeV/c] CS λφ = 0 Natural polarization in CS frame All translated to the CS frame as function of p

  6. Scenario 3: two fully transverse processes Two processes giving fully transversely polarized J/y mesons, one in the CS frame and the other in the helicity frame, with pT-dependent relative fractions The third, very different but equally perfect, description of the CDF data ! We must measure (and calculate) the azimuthal anisotropy lf to avoid ambiguities of interpretation Fully transverse J/y mesons in the helicity frame = 30% → 15% in the Collins-Soper frame = 70% → 85%

  7. Summary of the three scenarios; in the helicity frame Significantly different azimuthal anisotropies; & frame-invariant polarizations CDF |y| < 0.6

  8. Predictions for LHCb Significantly different polar & azimuthal anisotropies; & frame-invariant polarizations LHCb 3 < |y| < 3.5

  9. Brand new CDF results on Upsilon polarizations Very nice conceptual and experimental progress !!! But observed polarization is very weak, almost non-existent… Y(1S)

  10. Hidden variables The J/y and Y(1S) measurements are not easy to interpret because of the huge impact of the feed-down decays from P states The prompt J/y polarization measured by CDF might very well be in agreement with the direct J/y polarization prediction of the CSM…if we account for the cc feed-down in the scenario h(cc1) = 0 and h(cc2) = ±2

  11. The importance of being P Strong and opposite polarizations of direct and indirect S states can average to weak observable inclusive polarizations, if the feed-down fractions are high example: from fully longitudinal direct J/yto several prompt polarizations, lq Jz(χc2) 0 ±1 ±2 Jz(χc1) Jz(J/ψdir) = 0 0 ±1 J/ψ’sfrom χc1 dominate over J/ψ’sfrom χc2 same number of J/ψ’sfrom χc1 andJ/ψ’s from χc2 J/ψ’sfrom χc2 dominate over J/ψ’sfrom χc1 (plots valid for p > 4 GeV/c)

  12. We do not know enough about the P states… J/ψ in CDF data (1S) in CDF data directly produced directly produced (2S) +(3S) ψ(2S) non-prompt (b-hadrons) χb1(2P) +χb2(2P) χc2 χb1(1P)+χb2(1P) χc1 CDF cb(1P) cb(1P) cb(2P) cb(2P) ? A challenge and opportunity for LHC experiments

  13. From the J/y puzzle to the Y(3S) puzzle The Y(3S) state is much “cleaner” to study; no feed-down complications NLO NRQCDGong, Wang & Zhang, PRD83, 114021 (2011) Y(1S) Large uncertainty caused by cb feed-down lq Y(3S)

  14. From the J/y puzzle to the Y(3S) puzzle The Y(3S) state is much “cleaner” to study; no feed-down complications NLO NRQCDGong, Wang & Zhang, PRD83, 114021 (2011) Y(1S) Large uncertainty caused by cb feed-down lq No evidence for significant polarization – Even up to pT of 40 GeV/c – Even for the Y(3S) Matthew Jones, CDF, at HCP, Nov. 17, 2011 Y(3S) Despite its large uncertainties, the Y(3S) lack of polarization is puzzling… A challenge and opportunity for LHC experiments

  15. Summary and outlook So much done… and so much to do Many opportunities (and challenges) for the LHC experiments 

  16. Backup slides; further reading

  17. Frame (in)dependence and azimuthal anisotropy zCS • The observed polarization depends on the frame • zCSzHX • for mid rap. / high pT • i.e. pT >> |pL| λθ = –1 λφ = 0 zCS 2) The azimuthal anisotropy is not a detail Two very different physical cases, indistinguishable if λφ is not measured (integration over φ) λθ = –1/3 λφ = –1/3 zHX zHX 3) The shape of the distribution is frame-invariant → it can be characterized by a frame-independent parameter, e.g λθ = +1 λφ = –1 λθ = +1 λφ = 0 zCS

  18. J = 1 states are intrinsically polarized Single elementary subprocess: |y〉 = a-1 |1,-1〉 + a0 |1,0〉 + a+1 |1,+1〉 • There is no combination of a0, a+1 and a-1 such that λθ = λφ = λθφ = 0 • The angular distribution is never intrinsically isotropic • Polarization is a distinctive property of quarkonium • Only a “fortunate” mixture of subprocesses(or randomization effects) can lead to a cancellationof all three observed anisotropy parameters • To measure zero polarization would be exceptionally “interesting” (and puzzling)

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