Meson Structure with Dilepton Production

Transcription

1 Meson Structure with Dilepton Production Jen-Chieh Peng University of Illinois at Urbana-Champaign 9 th Workshop on Hadron Physics in China and Opportunities Worldwide Nanjing University, July 24-28, 2017 In collaboration with Wen-Chen Chang and Stephane Platchkov 1

2 Outline Overview of Drell-Yan experiments with meson beams What have we learned from these experiments What we would like to learn in the future Summary and outlook 2

3 First Dimuon Experiment p+ U µ + + µ + X 29 GeV proton Lederman et al. PRL 25 (1970) 1523 Experiment originally designed to search for neutral weak boson (Z 0 ) Missed the J/Ψ signal! Discovered the Drell-Yan process 3

4 The Drell-Yan Process 4

5 Experiments at CERN and Fermilab Exp P (GeV) targets Number of D-Y events WA Be 500 (semi-exclusive) WA39 40 W (H 2 ) 3839 (all beam, M > 2 GeV) NA3 150, 200, 280 Pt (H 2 ) 21600, 4970, (535, 121, 741) NA10 140, 194, 286 W (D 2 ) ~84400, ~150000, ~45900 (3200, --, 7800) E331/E C, Cu, W 500 E W E615 80, 252 W 4060, ~50000 Relatively pure beam Relatively large cross section due to ud contents in 5

6 Exp P (GeV) targets D-Y events WA39 40 W (H 2 ) NA3 200 Pt (H 2 ) 1750 (40) E331/E C, Cu, W Require beam particle identification to reject large proton content Smaller DY cross section due to du Very few DY data with + beam contents in + 6

7 Exp P (GeV) targets D-Y events WA39 40 W (H 2 ) NA3 150, 200 Pt 688, 90 Exp P (GeV) targets D-Y events WA39 40 W (H 2 ) NA3 200 Pt 170 Exp P (GeV) targets D-Y events WA39 40 W (H 2 ) NA3 150, 200 Pt 275, 32 E W, Cu, Be 380 7

8 Ratio of ( + A) / ( p+ A) Drell-Yan cross sections R = 2 + N ( d σ DY / dmdy) 2 p+ N ( d σ DY / dmdy) 4 u( x1) un ( x2) + d( x1) d N ( x2) 4 u ( x ) u ( x ) + d ( x ) d ( x ) p 1 N 2 p 1 N 2 From E331/E444 u ( x1) un ( x2) up( x1) un ( x2) Black: valence Rapid rise in R at large Red: sa e M reflects the rise in valence/sea un ( x2) ratio as x increases : u ( x ) N 2 8

9 + Ratios of ( + C) / ( + C) Drell-Yan cross sections Defining V V V V V ( x) = u ( x) = d ( x) = d ( x) = u ( x) S ( x) = u ( x) = d ( x) = d ( x) = u ( x) V N ( x) = [ u ( x) + d ( x)]/2 p S ( x) = [ u ( x) + d ( x)]/ 2 N + + p Considering only the u and d flavors p p + + From E331/E444 Black: Valence; Red: Sea R σ = σ DY DY + ( + C) ( + C) V( x1) VN( x2) + 5 S( x1) VN( x2) + 5 V( x1) SN( x2) + 10S( x1) SN( x2) A+ B = 4 V ( x ) V ( x ) + 5 S ( x ) V ( x ) + 5 V ( x ) S ( x ) + 10S ( x ) S ( x ) 4A+ B 1 N 2 1 N 2 1 N 2 1 N 2 1/4 R 1 9

10 ( + W) versus ( p+ W) Drell-Yan cross sections +W Drell-Yan Valence quark x-distribution in pion is broader than that in antiproton (proton) p+ W Drell-Yan E537, 125 GeV 10

11 How to determine the valence quark distribution in pion? + Compare ( + D) with ( + D) Drell-Yan cross sections σ σ ( + D) 4 V ( x ) V ( x ) + 5 S ( x ) V ( x ) + 5 V ( x ) S ( x ) + 10S ( x ) S ( x ) DY 1 N 2 1 N 2 1 DY N 2 + ( + D) V ( x ) V ( x ) + 5 S ( x ) V ( x ) + 5 V ( x ) S ( x ) + 10S ( x ) S ( x ) N 2 1 N 2 1 N 2 1 N 2 N σ ( + D) σ ( + D) 3 V ( x ) V ( x ) + DY DY 1 N 2 Only the valence-quark term remain! Only very low statistics data for σ ( + + D) are available! DY See Londergan et al., PL B361 (1995)

12 How to determine the valence quark distribution in kaon? + Compare ( K + D) with ( K + D) Drell-Yan cross sections σ ( K + D) 4 V ( x ) V ( x ) + 4 V ( x ) S ( x ) + V ( x ) s ( x ) u u s DY K 1 N 2 K 1 N 2 K 1 N S ( x ) V ( x ) + 10S ( x ) S ( x ) + 2 S ( x ) s ( x ) K 1 N 2 K 1 N 2 K 1 N 2 σ ( K + + D) 4 V ( x ) S ( x ) + V ( x ) s ( x ) u s DY K 1 N 2 K 1 N 2 σ + 5 S ( x ) V ( x ) + 10S ( x ) S ( x ) + 2 S ( x ) s ( x ) K 1 N 2 K 1 N 2 K 1 N ( K + D) σ ( K + D) 4 V ( x ) V ( x ) + u DY DY K 1 N 2 Only the valence-quark term remain! 2 σ DY ( K + + D) is more sensitive to kaon's sea-quark content than σ ( K + D) (especially data at low x and large x (negative x ) region!) 1 2 F DY See Londergan al., PL B380 (1996)

13 Attemps to extract the pion valence quark distribution BNL, 22 GeV E331, 225 GeV F ( x) = 0.72 x (1 x) F ( x) = 0.90 x (1 x) WA11, 175 GeV NA3, 200 GeV F ( x) = 2.43 x (1 x) F ( x) = Ax (1 x)

14 Attemps to extract the pion valence quark distribution E615, 252 GeV E537, 125 GeV NA3, 200 GeV F ( x) = Ax (1 x) F ( x) = Ax (1 x) A global fit to all data is needed 14

15 Four pion PDF sets available at LHAPDF library OW-P (PRD 30, 943 (1984)) LO QCD J/Ψ data from NA3 and WA39; D-Y data from E537 and NA3 15

16 Four pion PDF sets available at LHAPDF library SMRS (PR D45, 2349 (1992)) NLO QCD NA10 and E615 D-Y data, WA70 direct photon data Need new global fits to all existing data Need new experimental data with pion and kaon beams 16

17 Kaon PDF from ( K + D) / ( + D) Drell-Yan ratios From NA3; 150 GeV, Pt target R σ = σ DY DY ( K + D) ( + D) u u s u 4 VK( x1) VN( x2) + 4 VK( x1) SN( x2) + VK( x1) sp( x2) + 5 SK( x1) VN( x2) VK ( x1) 4 V ( x ) V ( x ) + 5 S ( x ) V ( x ) + 5V ( x ) S ( x ) V ( x ) 1 N 2 1 N 2 1 N 2 1 R x u 0.18± 0.07 (1 ) softer -valence in kaon than in pion 17

18 Comparison between data and theory 18

19 ( K + Pt) / ( + Pt) ratios for J/ Ψ production From NA3; 150 GeV, Pt target Ratios for D-Y Ratios for J/Ψ Similar behavior at large x for D-Y and J/ Ψ production? F 19

20 Comparison between data and CEM calculations ( K + Pt) / ( + Pt) ratios for J/ Ψ production same pdf for K and modified pdf for K Modified kaon PDF has the ubar valence quark distribution multiplied by (1-x) 0.18 and the strange quark distribution divided by (1-x) 0.18 The K / ratios of J/ Ψ production at large x F might indicate a softer u in K than in the pion, similar to the D-Y data? 20

21 Dilepton data with meson beams at COMPASS 190 GeV - beam See talks of M. Perdekamp and W.C. Chang Prospect of RF-separated kaon and antiproton beams in the future 21

22 Three proton parton distributions describing transverse momentum and/or transverse spin 1) Transversity Three transverse quantities: 1) Nucleon transverse spin N S 2) Quark transverse spin q s 3) Quark transverse momentum q k Three different correlations Correlation between 2) Sivers function Correlation between and 3) Boer-Mulders function Correlation between S s s q N q and and S k k N q q 22

23 One pion parton distribution describing transverse momentum and transverse spin Two transverse quantities: 1) Quark transverse spin q s 2) Quark transverse momentum q k One correlation 1) Boer-Mulders function Correlation between s q and k q 23

24 It can be measured in Drell-Yan process Boer-Mulders functions: - Unpolarized Drell-Yan: dσ h ( x ) h ( x )cos(2 φ) DY 1 q 1 q Drell-Yan does not require knowledge of the fragmentation functions T-odd TMDs are predicted to change sign from DIS to DY (Boer-Mulders and Sivers functions) Remains to be tested experimentally! 24

25 h 1 h 1 h 1 Boer-Mulders function h 1 represents a correlation between quark's k and transverse spin in an unpolarized hadron (analogous to Collins function) is a time-reversal odd, chiral-odd TMD parton distribution h 1 h 1 can lead to an azimuthal dependence with ν f f T 1 1 α M M 2 T h ( xk, ) = c e f( x) 2 T C H αt k 1 T H kt + MC ν = 16κ QM 2 2 T C ( QT + 4 MC) κ 1 =0.47, M C =2.3 GeV Boer, PRD 60 (1999) ν>0 implies valence BM functions for pion and 25 nucleon have same signs

26 Can one test the predicted sign-change from DIS to D-Y for pion s B-M function? 1) From NA10 pion Drell-Yan data, one deduces that the product of the pion valence quark B-M function and the proton valence quark B-M function is positive. Using u-quark dominance, we have: h, DY 1, u, DY 1, u Therefore, either a) h ( p) > 0; h ( ) > 0 ( sign change) or ( p) * h ( ) > 0, DY, DY 1, u 1, u b) h ( p) < 0; h ( ) < 0 ( no sign change), DY, DY 1, u 1, u 2) In polarized p D- Y, the sin ( φ + φ ) modulation is sensitive to the sign of h (, DY 1, u ) (being measured at COMPASS) 3) Need to measure the sign of pion's B-M function in DIS S HOW? 26

27 SIDIS on the meson cloud of proton at EIC TSIDIS (Tagged Semi-Inclusive DIS) TSIDIS ± e + p e + n+ + x underlying process: e + e + + 1) An independent check of pion's PDF 2) Could allow valence-sea flavor separation Detected is most likely from u (or d ) sea in Detected + ± x + + is most likely from valence u(or d) in 3) Pion B-M function is extracted from cos 2φ modulation + 27

28 28

29 T. Sawada, W. C. Chang, et al. 29

30 Summary Meson and Kaon parton distributions New territory for theory and experiment * Unique opportunity at COMPASS * Complementary to JLab/EIC tagged DIS programs Pion's TMD (Boer-Mulders function) Test sign-change prediction for pion B-M function Exclusive Drell-Yan with and K beams Probe pion and kaon distribution amplitudes First measurement seems feasible at J-PARC 30