meson structure with dilepton production - indico...
TRANSCRIPT
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Meson Structure with Dilepton Production
Jen-Chieh Peng
University of Illinois at Urbana-Champaign
9th Workshop on “Hadron Physics in China and Opportunities Worldwide”
Nanjing University, July 24-28, 2017
In collaboration with Wen-Chen Chang and Stephane Platchkov
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
First Dimuon Experiment
29 GeV protonp U Xµ µ+ −+ → + +
Lederman et al. PRL 25 (1970) 1523
Experiment originally designed to search for neutral weak boson (Z0)
Missed the J/Ψ signal !
“Discovered” the Drell-Yan process
3
5
Exp P (GeV) targets Number of D-Y events
WA11 175 Be 500 (semi-exclusive)
WA39 40 W (H2) 3839 (all beam, M > 2 GeV)
NA3 150, 200, 280 Pt (H2) 21600, 4970, 20000 (535, 121, 741)
NA10 140, 194, 286 W (D2) ~84400, ~150000, ~45900 (3200, --, 7800)
E331/E444 225 C, Cu, W 500
E326 225 W
E615 80, 252 W 4060, ~50000
Experiments at CERN and Fermilab
Relatively pure beam Relatively large cross section due to contents in ud
π
π
−
−
•
•
6
Exp P (GeV) targets D-Y events
WA39 40 W (H2)
NA3 200 Pt (H2) 1750 (40)
E331/E444 225 C, Cu, W
Require beam particle identification to reject large proton content Smaller DY cross section due to contents in Very few DY data with beam
du π
π
+
+
•
•
•
7
Exp P (GeV) targets D-Y events
WA39 40 W (H2)
NA3 150, 200 Pt 688, 90
Exp P (GeV) targets D-Y events
WA39 40 W (H2)
NA3 200 Pt 170
Exp P (GeV) targets D-Y events
WA39 40 W (H2)
NA3 150, 200 Pt 275, 32
E537 125 W, Cu, Be 380
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Ratio of ( ) / ( ) Drell-Yan cross sectionsA p Aπ − + +
2
2 2
2
2
2
1 2 1
1 1
1 2
1
( / )( / )4 ( ) ( ) ( )4 ( ) ( )
( ) ( )( )
Black: valence
( )( ) ( )
( )
Red: s a e
N
N N
NDY
p NDY
N
p p
N
p N
d d
d
MdyRd dMdyu x u x d x x
u xu x d x
u x u xu
d x
x u x
π
π π
π
σσ
+
+=
++
2
2
Rapid rise in at large reflects the rise in valence/sea
( )ratio as increases )
:(
N
N
M
xu
xx
R
u
From E331/E444
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Ratios of ( ) / ( ) Drell-Yan cross sectionsC Cπ π+ −+ +
1 2 2 1
1
1 2 1 2
1 2 12 22 1
( ) ( ) ( ) ( )( )
( )( )
( )( ) ( ) ( )
( ) 5 ( ) 5 ( ) 104 ( ) ( ) 5 ( ) 5 ( ) 10 4
N N
N N
DY
DY
N N
N N
S x S x S x S
CRC
V x V x V x V x AV
x BS x S x S x S x Bx V x V x V x Aπ π
π π
π π
π π
σ πσ π
+
−
+=
++ + + +
=+ + + +
( ) ( ) ( ) ( ) ( )
Defining ( ) ( ) ( ) ( ) ( )
( ) [ ( ) ( )] / 2
Considering only the and f( ) [ ( ) ( )] /
la r2
vo s
V V V
p
p
N
V
N p
p
S x u x d x d x u x
S x u
V x u x d x d x u x
V x
x d x
u x d x
u d
π π π
π π
π
π
π
π π
+ +
+ +
−
− −
−= = =
= = = =
+
= +
=
=
From E331/E444
1 / 4 1R≤ ≤
Black: Valence; Red : Sea
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( ) versus ( ) Drell-Yan cross sectionsW p Wπ − + +
Valence quark -distributionin pion is broader than thatin antiproton (proton)
x
E537, 125 GeV
Drell-YanWπ − +
Drell-Yanp W+
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How to determine the valence quark distribution in pion?
11 2 2 1
1
2 1 2
1 2 1 22 2 1
( ) ( ) ( ) ( )( ) 4 ( ) ( ) 5 ( ) 5 ( ) 10
( ) ( ) ( ) 5 ( ) 5 ( ) 1( ) ( 0) ( ) ( )DY N N
DY
N
NN
N
NN
D S x S x S x S xS x S x S x S x
V x V x V x V xD V x V x V x V x
π π
π
π π
π ππ
σ π
σ π
−
+
+ ∝ + + +
+ ∝ + + +
1 2
Only ( ) ( ) 3 ( ) ( )
the valence-quark term remain!DY DY ND D V x V xπσ π σ π− ++ − + ∝
Only very low statistics data for ( ) are available!DY Dσ π + +
See Londergan et al., PL B361 (1995) 110
Compare ( ) with ( ) Drell-Yan cross sectionsD Dπ π− ++ +
12
1 2
Only( ) ( ) 4 ( ) ( ) the valence-quark term remain!
uDY DY K NK D K D V x V xσ σ− ++ − + ∝
1 2
( ) is more sensitive to kaon's sea-quark content than ( )(especially data at low and large (negative ) region!)
DY DY
F
K D K Dx x x
σ σ+ −+ +
1 2 2 2
1 2 1 2
1 1
12
( ) 4 ( ) ( ) 4 ( ) ( ) ( )( ) ( ) ( ) (
( )5 ( ) 10 2 ) ( )
N N
K K
u u sDY K N K
N N N
K
K
K D V x V x V x V xV x
S x s xS x S x S x S x s x
σ − + ∝ + ++ + +
2 2
1 1 2 1
1
2
1
2
( ) 4 ( ) ( )5 ( )
( ) ( )( ) ( ) ( ) ( )1 2 ( )0
u sDY K K
N
N N
K K N K N
S x s xS
K D V x V xVx S x S x S x s xx
σ + + ∝ ++ + +
See Londergan al., PL B380 (1996) 393
How to determine the valence quark distribution in kaon?
Compare ( ) with ( ) Drell-Yan cross sectionsK D K D− ++ +
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Attemps to extract the pion valence quark distribution
0.5 0.46( ) 0.72 (1 )F x x xπ = −
NA3, 200 GeV
E331, 225 GeVBNL, 22 GeV
WA11, 175 GeV
0.5 1.27( ) 0.90 (1 )F x x xπ = −
0.5 1.57( ) 2.43 (1 )F x x xπ = −0.45 1.17( ) (1 )F x Ax xπ = −
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Attemps to extract the pion valence quark distribution
NA3, 200 GeV
0.442 1.248( ) (1 )F x Ax xπ = −
E537, 125 GeV
E615, 252 GeV
0.6 1.26( ) (1 )F x Ax xπ = −
A global fit to all data is needed
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• OW-P (PRD 30, 943 (1984))– LO QCD– J/Ψ data from NA3 and WA39; D-Y data
from E537 and NA3
Four pion PDF sets available at LHAPDF library
16
• SMRS (PR D45, 2349 (1992))
– NLO QCD– NA10 and E615 D-Y data,
WA70 direct photon data
Four pion PDF sets available at LHAPDF library
Need new global fits to all existing data Need new experimental data
with pion and kaon beams
•
•
17
Kaon PDF from ( ) / ( ) Drell-Yan ratiosK D Dπ− −+ +
From NA3; 150 GeV, Pt target
1 2 1 1 2 1
1
2 2
2 2
1
1 11 2
( )( )
4 ( ) ( ) 4 ( ) ( ) 5 ( ) ( )4 ( ) ( ) 5 ( ) 5
( ) ( ) ( )( ) () ))( (
DY
DYu u s u
K N K K N K
N N
N p K
N
S x s x S
K DRD
V x V x V x V x V x V xV x V x V x V x V x
xS x S xπ π ππ
σσ π
−
−
+=
+
+ + ++ +
0.18 0.07(1 ) softer -valence in kaon than in pionR x u±− ⇒
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( Pt) / ( Pt) ratios for J/ productionK π− −+ + Ψ
Ratios for D-Y
Similar behavior at large for D-Y and J/ production?Fx Ψ
From NA3; 150 GeV, Pt target
Ratios for J/Ψ
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Comparison between data and CEM calculations
same pdf for and K π− −
The / ratios of J/ production at large might indicate
a softer in than in the pion, similar to the D-Y data?FK x
u Kπ
−
Ψ
( Pt) / ( Pt) ratios for J/ productionK π− −+ + Ψ
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
Dilepton data with meson beams at COMPASS
• Prospect of RF-separated kaon and antiproton beams in the future 21
See talks of M. Perdekamp and W.C. Chang
190 GeV π- beam
22
Three proton parton distributions describing transverse momentum and/or transverse spin
1) Transversity
2) Sivers function
3) Boer-Mulders function
Correlation between and q Ns S⊥ ⊥
Correlation between and q qs k⊥ ⊥
Correlation between and N qS k⊥ ⊥
Three transverse quantities:1) Nucleon transverse spin
2) Quark transverse spin 3) Quark transverse momentum
Three different correlations
N
q
q
S
s
k
⊥
⊥
⊥
⇒
23
One pion parton distribution describing transverse momentum and transverse spin
1) Boer-Mulders function
Correlation between and q qs k⊥ ⊥
Two transverse quantities:1) Quark transverse spin 2) Quark transverse momentum
One correlation
q
q
s
k
⊥
⊥
⇒
2424
It can be measured in Drell-Yan process
1 1
Boer-Mulders functions:
Drell-Yan does not require knowledge of the f
- Unpolar
ragmentation f
ized Drell-Yan:
unctions T-odd T
( ) ( )co
MDs ar
s
e predicted to change si
(2 ) DY q qd h x h xσ φ⊥ ⊥∝
•
• gn from DIS to DY (Boer-Mulders and Sivers f
Remains to be tested exunct
peri mentaions)
lly!
25
Boer-Mulders function h1┴
κ1=0.47, MC=2.3 GeV
221 12 2( , ) ( )T TkC HT
T HT C
M Mh x k c e f xk M
ααπ
−⊥ =+
1
1
1 represents a correlation between quark's and transverse spin in an unpolarized hadron (ana is a time-reversal odd, chiral-o
logous to Colldd TMD p
ins fuarton distributio
nction)n
T
h
h
h k⊥
⊥
⊥
•
•
•
1 1
1 1
can lead to an azimuthal dependence with h hf f
ν⊥ ⊥
∝
2 2
1 2 2 216( 4 )
T C
T C
Q MQ M
ν κ=+
Boer, PRD 60 (1999) 014012
ν>0 implies valence BM functions for pion and nucleon have same signs
Can one test the predicted sign-change from DIS to D-Y for pion’s B-M function?
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,1,
1) From NA10 pion Drell-Yan data, one deduces that the productof the pion valence quark B-M function and the proton valencequark B-M function is positive. Using -quark dominance,
( ) we have:
DYu
uh p⊥
, ,1, 1,
, ,1, 1,
,1,
Therefore, either ( )
or
a) ( ) 0; ( ) 0
b) ( )2) In polarized D
( ) < 0; ( ) < 0t
* (
he sin ( ) mo
) > 0
Y, du-
DYu
DY DYu u
DY DYu u
S
h p h
h p h
sign change
no sign c
h
hangepπ φ
π
π
π
φ
⊥ ⊥
⊥ ⊥
⊥
+
−>
−
>
−
,1, (being measured at COMPASS)
3) Need to mea
lation is sensitive
to the sign of (sure the sign of pion's B-M functi
)on in DIS
DYuh π⊥
HOW?
SIDIS on the meson cloud of proton at EIC
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TSIDIS (Tagged Semi-Inclusive DIS)
TSIDIS
underlying process:
1) An independent check of pion's PDF2) Could a D
llow valence-sea flavor sepaetected is most likely from (or ) s
rea in
Det
ati
ected
o
n
e p e n x
u
e e
d
x
π
π π
π
π
π− + − ±
− − ±
− +
+
′+ → + + +
′+ → + +
3) Pion B-M funis most likely
ction is extracfrom valenc
ted from cos2 modulatione (or ) in u d π
φ
+
Summary
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New territory for theory and experiment * Unique opportunity at COMPASS * Complementary to JLab/EIC tagged DIS p
Meson and Kaon parton distributions
Pion's TMD (Boer-Muldrogra
ers f nctms
u
•
•
∗
ion) Exclusive Drell-Yan with and bea
Test sign-change prediction for pion B-M function
Probe pion and kaon distribution amplitudes First measurement seems feasi
m
ble at
s
J-P
ARC
Kπ − −•
∗
∗∗