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)

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

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

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

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

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?

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

The SeaQuest Spectrometer 3500 wires 550 prop tubes 350 hodo paddles

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

hit Accept this path hit

hit Reject this path hit

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

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

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

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?

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)

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!

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 ✓

- 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

- 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

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 123.275 (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

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. 64.2479 (1990) More precise measurements needed in the anti-shadowing and EMC region

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

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

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!

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

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++

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

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

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

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