I R F U DRELL-YAN at COMPASS Stephane Platchkov I nstitut de R echerche sur les lois F ondamentales de l’ U nivers CEA/IRFU, Saclay, France GDR Nucléon Ecole Polytechnique, December 15-17, 2014

I R F U Looked for W... Rapid fall-off: ~M µµ -4, - missed the J/Ψ! Explanation: 1970 by Drell and Yan: Model based on the newly invented partons (Feynman, 1968) Some history S. PlatchkovGDR Dec.15, PRL 25 (1970), 316, 902. E=30 GeV 1970

I R F U Main features of the “Parton annihilation model”  Drell-Yan cross section:  Features (parton model): Cross section depends on τ = M 2 /s Convolution of quark and antiquark PDFs Can be used to determine PDFs in , K, p Transverse momentum of µµ pair is small No fragmentation process  Confirmed in QCD Assumptions: factorization S. PlatchkovGDR Dec.15, Ito et al. PRD 23(1981)604. (from Kenyon, RPP, 1982) FERMILAB: non-DY contribution E=400 GeV Tung-Mow Yan (SLAC, 1998): “The process has been so well understood that it has become a powerful tool for precision measurements and new physics”

I R F U Nucleon structure studies – different probes S. PlatchkovGDR Dec.15, Drell-Yan TMD (x,k T )GPD (x,b T )PDF (x) from Bacchetta

I R F U Unpolarized DIS vs unpolarized Drell-Yan S. PlatchkovGDR Dec.15, McCaughey, Moss, Peng ARNPS ) 217. DIS Drell-Yan

I R F U Sivers: correlation between the quark transverse momentum and the nucleon transverse spin (polarized nucleon) Boer-Mulders: correlation between the quark transverse spin and transverse momentum (unpolarized nucleon) Transverse -Momentum Dependent (TMD) PDFs S. PlatchkovGDR Dec.15, worm- gear

I R F U  Full formalism for two hadrons  Access 4 TMDs – asymmetry modulations (pion beam): DY (polarized) cross section expansion S. PlatchkovGDR Dec.15, Arnold, Metz and Schlegel, Phys. Rev. D79 (2009) Boer-Mulders Sivers Pretzelosity Transversity Worm-Gear

I R F U TMDs in Drell-Yan and SIDIS  Complementary probes SIDIS DRELL-YAN  Assumptions Factorizaton Universality: (unlike PDFs) TMDs can be process dependent Opposite sign in SIDIS and DY processes: S. PlatchkovGDR Dec.15, Collins, Soper, Sterman, Adv. Ser. High En. Phys. 5, 1988.

I R F U Sivers asymmetry (SIDIS)  Compass and Hermes data on a proton target pions kaons S. PlatchkovGDR Dec.15, HERMES: PRL 103 (2009) COMPASS: PLB 692 (2010) 240 PLB 717 (2012) preliminary

I R F U Sivers TMD - as determined from SIDIS S. PlatchkovGDR Dec.15, Anselmino et al., Eur.Phys.J.A39 (2009) 89.

I R F U. COMPASS setup advantages Beam energy: 100 – 200 GeV Transversely polarized NH 3 / 6 LiD targets Large angular acceptance CERN beams Negative (pion, kaon, p ) or positive hadron beams With a negative pion beam: u /u annihilation Dominated by valence u quarks (x ≥ 0.1) Polarized Drell-Yan measurements S. PlatchkovGDR Dec.15, Drell and Yan, PRL 25 (1970), 316, 902.

I R F U COMPASS – a fixed target experiment  A very versatile setup Several beams available: µ +, µ -, h+, h -, e - => Several physics goals S. PlatchkovGDR Dec.15, m Energy: 100 – 200 GeV Intensity: up to 10 9 /spill Large acceptance, PID detectors Several particles in the final state Large (1.2 m) polarized target

I R F U COMPASS Drell-Yan setup S. PlatchkovGDR Dec.15, Small cross sections – high intensity h beam (~10 9 /spill of 10 sec) Possible use of thin nuclear targets (inside the absorber) pion beam 190 GeV Hadron absorber: Tungsten, Alumina and Stainless steel Nominal COMPASS setup (minor modifications) Dimuon trigger system Polarized Target

I R F U Drell-Yan acceptances (two muons) S. PlatchkovGDR Dec.15, COMPASS (2014)E615 (1989) ~4% ~40%

I R F U Polarized Drell-Yan – expected results S. PlatchkovGDR Dec.15, SiversBoer-Mulders PretzelosityTransversity 140 days of data pions/spill 2 x 55 cm NH 3 target 4 < M µµ < 9 GeV 2000 DY events/day in the mass region 4 < M µµ < 9 GeV/c 2

I R F U  Test setup (3 days in 2009) 190 GeV negative pion beam, I ≤ 1.5x10 7 /s (instead of 10 8 /s) “poor-man” hadron absorber ( concrete and steel) two polyethylene target cells preliminary DY trigger  Results Count rate confirmed Mass resolution as expected Good vertex resolution Low background at high masses Drell-Yan – test data taking S. PlatchkovGDR Dec.15, Drell-Yan region

I R F U In addition... there is also good physics without polarization... S. PlatchkovGDR Dec.15,

I R F U Targets for Drell-Yan 2014 and 2015 S. PlatchkovGDR Dec.15,

I R F U Angular distributions for Drell-Yan S. PlatchkovGDR Dec.15, θ and ϕ : polar and azimuthal angles of the µ+ in the dilepton rest frame Cross section: Parton model (naive DY):  = 1, µ = 0, ν = 0 pQCD : 1 –  2ν = 0 Lam-Tung, 1978 Valid at O(α 1 s ) NNLO corrections small Brandenburg et al., PRL 73 (1994) 939.

I R F U Lam-Tung relation: S. PlatchkovGDR Dec.15, NA10, Z. Phys. 37 (1988) GeV/c 194 GeV/c 286 GeV/c λ µ ν

I R F U Lam-Tung relation S. PlatchkovGDR Dec.15, CERN: NA10, Z. Phys. 37 (1988) – λ – 2ν p T (GeV/c) see Peng and Qiu, PPNP, 76 (2014) 43 FERMILAB: E615, PRD 39 (1989) GeV/c

I R F U Positive/negative hadron beams content S. PlatchkovGDR Dec.15, %24%1.5% 2.5% 96.5% 1%

I R F U COMPASS estimates (Takahiro Sawada, AS/Taipei) S. PlatchkovGDR Dec.15,

I R F U Ratio of K - and π - induced DY cross sections S. PlatchkovGDR Dec.15, NA3 experiment, CERN 1980 Ratio proportional to: u K (x)/ u π (x) u (x) distributions in K and π COMPASS, assuming 140 days data taking

I R F U Flavour-dependent EMC effect Cloët, Benz, Thomas, PRL 102 (2009): “For N≠Z nuclei the u and d quarks have distinct nuclear modifications” Dutta et al., PhysRev C83 (2011): Assuming SU(2): S. PlatchkovGDR Dec.15, With a flavour-dependent EMC effect u A (x) d A (x) Without flavour-dependence

I R F U Predictions for COMPASS with a 160 GeV pion beam Flavour-dependent EMC in COMPASS S. PlatchkovGDR Dec.15, from Dutta et al., Phys.Rev. C83 (2011) Already in 2015 Need data taking with a π+ beam With flavour dependence Without flavour dependence

I R F U Estimated number of DY events S. PlatchkovGDR Dec.15, Beam hadron dependence study: π -, K -, p Target hadron dependence study: NH 3, AL, W

I R F U 28 Planned Polarized Drell-Yan Experiments (Lorenzon, 2014) experimentparticlesenergyx b or x t Luminositytimeline COMPASS (CERN)  ± + p ↑ 160 GeV  s = 17.4 GeV x t = 0.2 – 0.32 x cm -2 s , 2018* PAX (GSI) p ↑ + p bar collider  s = 14 GeV x b = 0.1 – 0.92 x cm -2 s -1 >2017 PANDA (GSI) p bar + p ↑ 15 GeV  s = 5.5 GeV x t = 0.2 – 0.42 x cm -2 s -1 >2016 NICA (JINR) p ↑ + p collider  s = 20 GeV x b = 0.1 – 0.81 x cm -2 s -1 >2018 PHENIX (RHIC) p ↑ + p collider  s = 500 GeV x b = 0.05 – 0.12 x cm -2 s -1 >2018 RHIC internal target phase-1 p ↑ + p 250 GeV  s = 22 GeV x b = 0.25 – 0.42 x cm -2 s -1 >2018 RHIC internal target phase-1 p ↑ + p 250 GeV  s = 22 GeV x b = 0.25 – 0.46 x cm -2 s -1 >2018 SeaQuest (unpol.) (FNAL) p + p 120 GeV  s = 15 GeV x b = 0.35 – 0.85 x t = 0.1 – x cm -2 s Pol tgt DY ‡ (E1039) (FNAL) p + p ↑ 120 GeV  s = 15 GeV x t = 0.1 – x cm -2 s Pol beam DY § (E1027) (FNAL) p ↑ + p 120 GeV  s = 15 GeV x b = 0.35 – x cm -2 s ‡ 8 cm NH 3 target § L= 1 x cm -2 s -1 (LH 2 tgt limited) / L= 2 x cm -2 s -1 (10% of MI beam limited) S. PlatchkovGDR Dec.15, 2014

I R F U Summary: DY in COMPASS An ideal place for DY studies Only laboratory today with antiquark beams beam dependence: using K - and p beams target dependence: NH 3, Al, W targets Address several outstanding physics issues Test of QCD factorization theorems (Sivers, BM sign-change) Determine the BM function of the pion Better understanding of the violation of the Lam-Tung sum rule Flavor-dependence of the EMC effect? Comparison between u(x) PDFs in kaons and pions Long term Possibility for a RF separated K - and p beams Aim at 1 to 2 orders of magnitude improvement for K - and p 29 S. PlatchkovGDR Dec.15, 2014

I R F U Thank you! 30 S. PlatchkovGDR Dec.15, 2014

I R F U Estimated number of DY events S. PlatchkovGDR Dec.15, from T. Sawada 4 < M µµ < 9 GeV/c 2 ;  /k/ p = 96.5/2.5/1.0% 140 days of data taking Corrected for exp. efficiencies

I R F U 32 Next-to-Leading order DY contributions S. PlatchkovGDR Dec.15, 2014 Next-to-leading order diagrams complicate the picture These diagrams are responsible for 50% of the measured cross section

I R F U COMPASS Drell-Yan setup S. PlatchkovGDR Dec.15, Upgrade of the spectrometer Beam telescope (Sci-Fi) Thick hadron absorber/beam dump Vertex detector Polarized target moved 2.2 m upstream

I R F U Lam-Tung relation and BM function  Possible explanation (among others): cos2φ modulation Boer ( PRD60, 1999, ): the cos2 dependence could be due to the BM function. (BM function: correlation between k T and s T in an unpolarized nucleon ) S. PlatchkovGDR Dec.15, ν Data: NA10, 194 GeV/c

I R F U Drell-Yan: parameter ν vs p T S. PlatchkovGDR Dec.15, E866 (2007) : p + p E866 (2009) : p + d NA10 (1988) : π - + W Fits with parametrizations from Boer, PRD60 (99) from Peng and Qiu, PPNP, 2014 pion beam proton beam

I R F U Drell-Yan acceptances (COMPASS vs NA10) S. PlatchkovGDR Dec.15, NA10 COMPASS 5% 38%

I R F U Drell-Yan experiments (from Grosse-Perdekamp, SPIN 2014) S. PlatchkovGDR Dec.15,

I R F U Expected statistical accuracy  Assumptions: I beam = 10 8 p/s, L = 2.3x10 33, P=90%, f = 0.22, t = 140 days, spill length = 10 s, every 34 s ► ~ 2000 DY events/day in the mass region 4 < M µµ < 9 GeV/c 2 J/Ψ cross section: about 50 times larger S. PlatchkovGDR Dec.15, Boer-Mulders Sivers Pretzelosity Transversity