E906/SeaQuest at FNAL:
Measurement of Flavor Asymmetry of Antiquarks in the Nucleons
Wen-Chen Chang 章文箴
Institute of Physics, Academia Sinica 中央研究院 物理研究所
•Introduction
•Observation of flavor asymmetry of sea quark.
•Interpretation of origin.
•E906/SeaQuest experiment at FNAL.
•Status and prospect.
Inelastic Electron Scattering
Q2 :Four-momentum transfer
x : Bjorken variable (=Q2/2Mn)
n : Energy transfer
M : Nucleon mass
W : Final state hadronic mass
2
Unpolarized Parton Distributions (CTEQ6)
u valence
gluon (x 0.05)
sea
(x 0.05)
d
3
Is
u  d in the proton?
=
Gottfried Sum Rule
1
SG   [( F2p ( x)  F2n ( x)) / x] dx
0
1 2 1
   (u p ( x)  d p ( x)) dx
3 3 0
1

(if u p  d p )
3
4
Experimental Measurement of Gottfried Sum
New Muon Collaboration (NMC), Phys. Rev. D50 (1994) R1
SG = 0.235 ± 0.026
( Significantly lower than 1/3 ! )
5
The Drell-Yan Process
Phys. Rev. Lett. 25, 316–320 (1970)
d 2
4 2 1

ei2 [qi ( xbeam )qi ( xt arg et )  qi ( xbeam )qi ( xt arg et )]

dxbeamdxt arg et 9 xbeam xt arg et s i
6
x-dependence of Sea Quarks
Detector Acceptance: xbeam >> xtarget
xtarget
xbeam
d 2
4 2 1
2

e

i [ qi ( xbeam ) qi ( xt arg et )  qi ( xbeam ) qi ( xt arg et )]
dxbeamdxt arg et 9 xbeam xt arg et s i
 pd
|x
pp
2
beam
 x t arg et
1  d ( xt arg et ) 
 1 

2  u ( xt arg et ) 
7
Light Antiquark Flavor Asymmetry: Brief History
 Naïve Assumption:
 NMC (Gottfried Sum Rule)
 NA51 (Drell-Yan, 1994)
NA 51 Drell-Yan
confirms

d(x) > 
u(x)
8
Light Antiquark Flavor Asymmetry: Brief History
 Naïve Assumption:
 NMC (Gottfried Sum Rule)
 NA51 (Drell-Yan, 1994)
 E866/NuSea (Drell-Yan, 1998)
9

 Valence quark effect?
Origin of u(x)d(x):
• Pauli blocking
 is more suppressed than gdd in the proton
– guu
since p=uud (Field and Feynman 1977)
– pQCD calculation (Ross Sachrajda)
– Bag model calculation (Signal, Thomas, Schreiber)
• Chiral quark-soliton model (Diakonov, Pobylitsa,
Polyakov)
• Instanton model (Dorokhov, Kochelev)
• Statistical model (Bourrely, Buccella, Soffer; Bhalerao)
• Balance model (Zhang, Ma)
The valence quarks affect the Dirac vacuum and the quark-antiquark sea.
10


Origin of u(x)d(x): Valence quark + Non-perturbative effect?
• Meson cloud in the nucleons (Thomas, Kumano):
Sullivan process in DIS.
• Chiral quark model (Eichten, Hinchliffe, Quigg;
Wakamatsu): Goldstone bosons couple to valence quarks.

The pion cloud is a source of anti-quarks in the protons and it lead to d>u.
11
Proton Structure: Remove perturbative sea

There is a gluon splitting component
which is symmetric

– Symmetric sea via pair production from
gluons subtracts off
– No Gluon contribution at 1st order in s
– Nonperturbative models are motivated
by the observed difference

A proton with 3 valence quarks plus
glue cannot be right at any scale!!
Greater deviation at large-x
12
Advantages of 120 GeV Main Injector
The (very successful) past:
The future:
Fermilab E866/NuSea
Fermilab E906
 Data in 1996-1997
 1H, 2H, and nuclear targets
 800 GeV proton beam
 Cross section scales as 1/s
– 7x that of 800 GeV beam
 Backgrounds, primarily from J/
decays scale as s
– 7x Luminosity for same detector
rate as 800 GeV beam
 Data taking planned in 2010
 1H, 2H, and nuclear targets
 120 GeV proton Beam
Tevatron
800 GeV
Main
Injector
120 GeV
50x statistics!!
13
Extracting d-bar/-ubar From Drell-Yan Scattering
Ratio of Drell-Yan cross sections
(in leading order—E866 data analysis
confirmed in NLO)
 Global NLO PDF fits which
include E866 cross section ratios
agree with E866 results
 Fermilab E906/Drell-Yan will
extend these measurements and
reduce statistical uncertainty.
 E906 expects systematic
uncertainty to remain at approx.
1% in cross section ratio.
14
Physics at the LHC is sensitive to
the anti-quark distribution
Tevatron: W production is dominated by a LO process
with two valence quarks.
LHC: The LO contribution must involve a sea quark;
and the NLO contribution from a gluon is significant.
Timeline of E906
 2002: E906 Approved by Fermilab PAC
 2006: E906 funded by DOE Nuclear Physics
 2008: With addition of Japan and Taiwan groups, Stage-II
approval by Fermilab Director. MOU between Fermilab and
E906 Collaboration finalized.
 2009-2010: Construction and installation of spectrometer and
readout electronics.
16
E-906/SeaQuest Collaboration
Abilene Christian University
Brandon Bowen
Brianna Edlund
Tyler Hague
Donald Isenhower
Ben Miller
Tim Sipos
Rusty Towell
Shon Watson
Academia Sinica 中研院
Wen-Chen Chang 章文箴
Yen-Chu Chen 陳彥竹
Jia-Ye Chen 陳家益
Shiuan-Hal Shiu 許軒豪
Da-Shung Su 蘇大順
Argonne National Laboratory
John Arrington
Kevin Bailey
Don Geesaman*
Kawtar Hafidi
Roy Holt
Harold Jackson
Tom O'Connor
David Potterveld
Paul E. Reimer*
Josh Rubin
University of Colorado
Ed Kinney
Po-Ju Lin
Fermi National Accelerator
Laboratory
Chuck Brown
David Christian
University of Illinois
Bryan Dannowitz
Bryan Kerns
Naomi C.R Makins
R. Evan McClellan
Jen-Chieh Peng
KEK
Shin'ya Sawada
Kyoto University
KenIchi Imai
Tomo Nagae
Ling-Tung University 嶺東大學
Ting-Hua Chang 張定華
Los Alamos National Laboratory
Christine Aidala
Gerry Garvey
Mike Leitch
Han Liu
Ming Xiong Liu
Pat McGaughey
Andrew Puckett
University of Maryland
Betsy Beise
Kaz Nakahara
University of Michigan
Chiranjib Dutta
Wolfgang Lorenzon
Richard Raymond
Michael Steward
National Kaohsiung Normal University 高師大
Rurngsheng Guo 郭榮升
Su-Yin Wang 王素音
Hsi-Hung Yao 姚錫泓
University of New Mexico
Imran Younus
RIKEN
Yoshinori Fukao
Yuji Goto
Atsushi Taketani
Rutgers University
Lamiaa El Fassi
Ron Gilman
Ron Ransome
Yawei Zhang
Texas A & M University
Carl Gagliardi
Robert Tribble
Thomas Jefferson National Accelerator Facility
Dave Gaskell
Patricia Solvignon
Tokyo Institute of Technology
Shou Miyaska
Ken-ichi Nakano
Florian Sanftl
Toshi-Aki Shibata
Shintaro Takeuchi
Yamagata University
Yoshiyuki Miyachi
*Co-Spokespersons
Liquid H2, d2, and
solid targets
Solid iron magnet
 Reuse SM3 magnet coils
 Sufficient Field with reasonable coils
 Beam dumped within magnet
Hadron Absorber
E906 Spectrometer
Experimental Challenge:
 Higher probability of muonic decay for
the produced hadrons.
 Larger multiple scattering for the muon
traveling through hadron absorber and
solid magnet.
 Worse duty factor for beam structure.
 Higher singles rates.
18
NM4/KTeV Hall (before installation)
19
NM4/KTeV Hall (after installation)
HODO 1
KMAG
HODO 2
HODO 3
HODO 4
20
Beam Pipe & Target Moving Table
Focusing Magnet
Hodoscope 1 & 2
Hodoscope 3 & 4
Station 1: MWPC (uncompleted)
KTeV Magnet
Station 2: Drift Chamber
Station 3-: Drift Chamber
Station 3+ : Drift Chamber
Station 4 :Proportional Tubes
Readout Electronics
(IPAS’s works done by 蘇大順、陳家益、王素音、張定華、章文箴).
PreAmp by FNAL
PreAmp by IPAS
TDC /Latch by IPAS
Dimuon Online Trigger
• Online trigger system is
composed of 5 CAEN
V1495 FPGA modules.
• Without deadtime, the
decision of a di-muon
trigger or a single-muon
trigger can be made
within 200 ns, based on
the input of 400 channels
of the four hodoscopes
(work done by 許軒豪、張定華).
Data Acquisition System: CODA
• The DAQ system for E906 is
based on “CODA”, a DAQ
framework originally developed
by the JLAB.
• We successfully deploy the
CODA as our DAQ system,
and incorporate our VME
modules into a multi-crate
readout system and the slow
control system.
• The need of DAQ for chamber
testing and data-taking is fully
supported and welldocumented (works done by 王
素音、陳彥竹).
Offline Analysis
• The official raw data will
be stored as the mySQL
tables.
• For the convenience of
analysis, we construct the
framework for converting
mySQL tables into ROOT
ntuples and PAW ntuples
(works done by 姚錫泓、郭榮升
).
• GEANT4-based MonteCarlo simulation of E906
has been successfully
exercised.
Timeline of E906
 2002: E906 Approved by Fermilab PAC
 2006: E906 funded by DOE Nuclear Physics
 2008: With addition of Japan and Taiwan groups, Stage-II
approval by Fermilab Director. MOU between Fermilab and
E906 Collaboration finalized.
 2009-2010: Construction and installation of spectrometer and
readout electronics.
 There is a delay of 6 months in the commissioning, originally
schedule in Sep, 2010. The Commission run will start in Feb,
2011 and physics run is expected in the summer of 2011!
 Scheduled to run in 2011 and 2013 for 2 years of data
collection.
35
Possible Future Programs
• FNAL: polarized
target and pionic
Drell-Yan.
• Apparatus available
for future programs at,
e.g. J-PARC and
RHIC.
J-PRAC 50 GeV
36
BACKUP SLIDES
37
Experiment Run Schedule
http://www.fnal.gov/directorate/program_planning/schedule/index.html
38
Partonic Energy Loss
 An understanding of partonic energy loss in
both cold and hot nuclear matter is paramount
to elucidating RHIC data.
 Pre-interaction parton moves through cold
nuclear matter and looses energy.
 Apparent (reconstructed) kinematic values (x1
or xF) is shifted
 Fit shift in x1 relative to deuterium
 Models:
– Galvin and Milana
– Brodsky and Hoyer
– Baier et al.
39
Parton Energy Loss
 Energy loss / 1/s
– larger at 120 GeV
 Ability to distinguish
between models
 Measurements rather
than upper limits
 E906 will have
sufficient statistical
precision to allow
events within the
shadowing region, x2 <
0.1, to be removed
from the data sample
E906 expected uncertainties
Shadowing region removed
LW10504
40
EMC effect of antiquark distribution?
 The binding of nucleons in a
nucleus is expected to be
governed by the exchange of
virtual “Nuclear” mesons.
 No antiquark enhancement seen
in Drell-Yan (Fermilab E772)
data.
 Contemporary models predict
large effects to antiquark
distributions as x increases.
 Models must explain both DISEMC effect and Drell-Yan
x2
41
Drell-Yan Decay Angular Distributions
Θ and Φ are the decay polar
and azimuthal angles of the
μ+ in the dilepton rest-frame
Collins-Soper frame
A general expression for Drell-Yan decay angular distributions:
n
 1  d   3  

2
2

1


cos



sin
2

cos


sin

cos
2

 
  

d

2
 
  4  

Lam-Tung relation: 1    2n Phys. Rev. D 18, 2447–2461
 Reflect the spin-1/2 nature of quarks
(analog of the Callan-Gross relation in DIS)
 Insensitive to QCD - corrections
42
Azimuthal cos2Φ Distribution in p+p and p+d Drell-Yan
E866 Collab., Lingyan Zhu et al.,
PRL 99 (2007) 082301; PRL 102 (2009) 182001
Smallνis observed
for p+d and p+p D-Y
With Boer-Mulders function h1┴:
ν(π-Wµ+µ-X)~ [valence h1┴(π)] * [valence h1┴(p)]
ν(pdµ+µ-X) ~ [valence h1┴(p)] * [sea h1┴(p)]
43
Sea-quark BM functions are much smaller than valence quarks