1. Quark Flavor Asymmetry in the nucleon sea and EMC studies at the SeaQuest Experiment
Arun Tadepalli
Advisor: Prof. Ron Gilman
Rutgers University
(on behalf of the SeaQuest E906 collaboration)

2. Outline of the talk/ Energy budget of the Universe
Dark energy
68.3%
26.8%
4.9%
Standard model matter
Dark matter
Nucleons and Nuclear structure
Dark forces & Hidden sector
Quark flavor asymmetry and EMC effect
Dark photons
Spectrometer
Current status & results

3. Tools used in probing the nucleus
space
space
At SeaQuest, we use the Drell-Yan process which has unique sensitivity to the antiquark structure of the nucleon
time
time
DEEP INELASTIC SCATTERING
Lepton scatters from hadron
Exchange of virtual photon
Higher states of the hadron
Doesn’t differentiate between quark and antiquark
DRELL YAN PROCESS
Quark from hadron annihilates with antiquark from another hadron
Virtual photon is created
Decays into a lepton + antilepton
Unique sensitivity to the anti-quark distributions

4. Leading Order Drell Yan cross-section formula
*Ignoring higher order processes in αs
space
time
Drell-Yan cross section
Charge weighted summation over all quark flavors
Fine structure constant
PDF of a quark of flavor i in the beam
Center of mass energy squared
PDF of anti quarks of flavor i in the target
momentum fraction of quark in the beam
momentum fraction of antiquark in the target

5. Accessing the anti-quark distributions
Detector acceptance chosen to study the antiquark distributions
of the target
xtarget
xbeam
Detector acceptance chooses xtarget and xbeam
Fixed target high xF ( xbeam – xtarget )
Valence beam quarks at high-x.
Sea target quarks at low/intermediate-x.
Ratio of cross sections of p-p and p-d reactions is the key to probing the sea structure

6. SeaQuest physics goals
What is the origin of the nucleon sea?
What about TMDs?
Do we know what causes the EMC effect?
Do partons lose energy in cold nuclear matter?
Did you just say dark photons??
Is J/ψ and ψ’ suppression in cold nuclear matter the same?
What happens to the dbar/ubar ratio at xbj ≈ 0.3?

7. Fermilab E906/SeaQuest Collaboration
Abilene Christian University
Ryan Castillo, Michael Daugherity, Donald Isenhower, Noah Kitts, Lacey Medlock, Noah Shutty, Rusty Towell, Shon Watson, Ziao Jai Xi
Academia Sinica
Wen-Chen Chang, Shiu Shiuan-Hao
Argonne National Laboratory
John Arrington, Don Geesaman*, Kawtar Hafidi,
Roy Holt, Harold Jackson, Michelle Mesquita de Medeiros, Bardia Nadim, Paul E. Reimer*
University of Colorado
Ed Kinney, Po-Ju Lin
Fermi National Accelerator Laboratory
Chuck Brown, Dave Christian, Gabriele Garzoglio, Su-Yin (Grass) Wang, Jin-Yuan Wu
University of Illinois
Bryan Dannowitz, Markus Diefenthaler, Bryan Kerns, Hao Li, Naomi C.R Makins, Dhyaanesh Mullagur R. Evan McClellan, Jen-Chieh Peng, Shivangi Prasad, Mae Hwee Teo,
Mariusz Witek, Yangqiu Yin
KEK
Shin'ya Sawada
Los Alamos National Laboratory
Gerry Garvey, Xiaodong Jiang, Andreas Klein, David Kleinjan, Mike Leitch, Kun Liu, Ming Liu, Pat McGaughey
Mississippi State University
Lamiaa El Fassi
University of Maryland
Betsy Beise, Andrew (Yen-Chu) Chen
University of Michigan
Christine Aidala, McKenzie Barber, Catherine Culkin, Vera Loggins, Wolfgang Lorenzon, Bryan Ramson, Richard Raymond, Josh Rubin, Matt Wood
National Kaohsiung Normal University
Rurngsheng Guo
RIKEN
Yuji Goto
Rutgers, The State University of New Jersey
Ron Gilman, Ron Ransome, Arun Tadepalli
Tokyo Tech
Shou Miyaska, Kei Nagai, Kenichi Nakano, Shigeki Obata, Toshi-Aki Shibata
Yamagata University
Yuya Kudo, Yoshiyuki Miyachi, Shumpei Nara
*Co-Spokespersons

8. The SeaQuest Spectrometer
3500 wires
550 prop tubes
350 hodo paddles

9. For anti-quark flavor asymmetry studies
Targets
For anti-quark flavor asymmetry studies
For EMC studies

10. hit
Accept this path
hit

11. hit
Reject this path
hit

12. Signal is a coincidence of μ+ & μ- paths
hit
Signal is a coincidence of μ+ & μ- paths
hit

13. Timeline of SeaQuest Light Cone 2018 WIN I REST REST REST II III
March 2012 I
REST
Nov 2013
REST
Nov 2014
REST II
III
IV & V & VI
DAQ upgrade
Main injector upgrades
Stable operation of all detector sub systems
Dark photon road sets included into the trigger system
New St3- installed
Improved duty factor
Continue data taking
Installation of new St 1 drift chamber
Scheduled accelerator maintenance
Commissioning run
All detector subsystems work
Issues and upgrades addressed

14. Event selection and reconstruction
E906 preliminary
Invariant mass spectrum for FY 2015 data
30% of anticipated data
Data agrees well with Monte Carlo (spectrometer works as expected)
Data with Mass > 4.2 GeV are mostly dimuons coming from the Drell-Yan process
J/y Monte Carlo
y’ Monte Carlo
Drell-Yan Monte Carlo
Random Background
Combined MC and bg

15. How is the nucleon sea generated?
Connected-sea partons?
Chiral Quark Soliton model?
Meson Cloud model?
Delicate balance of all competing mechanisms?
Statistical parton distribution functions?
Instanton model?
Hybrid model?

16. Initial guess at the nucleon sea structure
Nucleon sea naively assumed to be flavor symmetric
Gluons don’t couple to flavor
Masses of u and d quarks are small and similar, compared to proton mass and probing energies
Perturbative contributions calculated to be small
quark antiquark pair
gluon splits
recombine into a gluon
D. A. Ross and C. T. Sachrajda, Nucl. Phys. B149, 497 (1979)

17. Surprising results from previous experiments
Experiments have shown a flavor asymmetry in the sea
NMC (1991):
NA51 (1994):
NuSea/E866 (1998):
Drop in the ratio above xB = 0.2
A model that captures the correct non-perturbative physics that generates the nucleon sea will account for the observed flavor asymmetry!

18. Role of SeaQuest
SeaQuest will explore the unexplored with higher statistical precision compared to E866
J/ψ background scales as s
DY cross-section scales as 1/s
Knowledge of parton distributions used as crucial input in collider experiments is data driven
Recently Lattice QCD can calculate sea quark asymmetry, but with modest precision
SeaQuest will map out the xBjorken dependence and confront competing theoretical models that explain the origin of the sea!
SeaQuest extends this knowledge ✓

19. - preliminary results ~30% of the anticipated data
Ratio of cross-sections of LD2 and LH2
SeaQuest data points (red dots) slightly above E866 data points (black dots) due to difference in PDFs at different beam energies
We are studying:
Rate dependence, which has kinematic dependence in the high-x region
Backgrounds, which have a kinematic dependence in the high-x region

20. - preliminary results Leading order analysis
Nuclear corrections for Deuterium not applied
Excellent agreement with E866 in 0.1 < x < 0.25 region
Interesting difference between E866 is seen in the high-x region
Kinematic effects of rate dependence and background in the high-x region being studied

21. EMC effect in DIS EMC Slope
Quark distributions in the nuclei differ from quark distributions in the nucleon
In 1983, the EMC collaboration found per nucleon structure functions F2 (x,Q2) in heavy nuclei different from deuterium
Exact physics reason for EMC effect still being debated
EMC Slope
Aubert JJ, et. al. EMC Collaboration. Phys. Lett. B (1983)
Shadowing region 0 < x < 0.06
Anti-shadowing region 0.06 < x < 0.3
EMC region 0.3 < x < 0.8
Fermi motion region 0.8 < x < 1

22. EMC effect in Drell Yan process
E772 data
Little nuclear dependence in the shadowing region
EMC effect in Drell-Yan process limited by statistical uncertainty
Significant drop not observed in anti-shadowing region like in DIS but limited by statistical uncertainty
Alde et. al. E772 Collaboration. Phys. Rev. Lett (1990)
More precise measurements needed in the anti-shadowing and EMC region

23. Preview results
B. Dannowitz dissertation
Ratios of Drell-Yan cross sections for C/D, Fe/D, W/D shown
Contains < 10% of expected statistics
Already competitive with existing data

24. Current status of analyses
Beam offsets and other data quality issues discovered and implemented in simulations and data track reconstruction
Kinematic effects of rate dependence and background in the high-x region being studied
Collaboration discussing the best model for background
The contribution of randoms becomes significant with assumptions in background modeling
Background
Proton beam
Rate dependence
1.6 cm
Beam dump
target
Beam offsets and data quality

25. Summary and future outlook
Nucleons are dynamical quantum systems with rich inner sub-structure
Drell-Yan process has unique sensitivity to the antiquark distributions of the target nucleus
SeaQuest addresses important issues in nucleon and nuclear structure
Data from FY2015 was analyzed and preliminary results presented
Good agreement between E866 and SeaQuest data in 0.15 < xB < 0.25 region. Difference seen in xB ~ 0.3 and is under investigation
Successful data taking finished in 2017
Major analysis results underway to study:
Analysis cuts optimizing Drell-Yan events from the target
Rate dependence corrections
Modeling of background
Release preliminary results!
Stay tuned!

26. THANK YOU

27. Reconstructed dimuons
Analysis procedure
Triggered events
Data quality
Tracking recommended cuts
Reconstructed dimuons
Protons on target normalization
Empty target correction
Rate dependence correction

28. Pion cloud model
In a hadronic model for the proton, it has several components
CG = 1/√3 u u d u = u u + u u d d d π0 p π0 p p
CG = √(2/3) d u u u u + u + u u
CG = 1/√2 π- π+ n
Higher energy configuration, more off shell, suppressed  more than
Δ++

29. Pauli blocking
Attempts to explain the suppression of a certain kind of quark antiquark pair
Presence of an additional u valence quark suppresses as compared to
Not fully blocked as newly created u quark can exist with other u quarks with a different color

30. Calculation of the Gottfried integral IG
Step 1: Difference of structure functions
Proton and neutron are isospin particles
Step 2: Perform an integral in x
Step 3: Difference of structure functions
Integral would be 1/3 if the sea is flavor symmetric

31. Q2 evolution of pdfs
Slide taken from Bryan Kerns, APS, 2016

32. Analysis procedure – extraction of
PDF input is chosen (CT10lo in this case)
A value of is chosen to begin
The cross section ratio is estimated for this chosen value and compared with data in xtarget bins
The difference is adjusted to extract the ratio in an iterative way