The SeaQuest E906 Experiment Arun Tadepalli Rutgers University

Frontiers and Careers in Nuclear and Introduction Nucleus

p n ò Nuclei are made up of nucleons ( and )

ò Nucleons are made up of and gluons

ò A Goal of nuclear physics u

ò Nucleon structure u ò Behavior of the various d constituents of the nucleon

2 How to probe the nucleus?

Incident Scattered ò Scattering experiments beam particles ò Beam of known energy and momentum ò Incident on object (target) Exchange of a virtual ò Change in kinematical particle quantities and cross sections recorded using detectors target ò Experimental fit to data to extract parameters (structure Example of deep inelastic scattering functions, parton distribution functions, radius etc..) 3 Simple Parton model of the Nucleon (1968)

Richard Feynman ò Nucleon consists of partons Structure Functions extracted (quarks and gluons) from deep inelastic scattering

ò Partons carry a fraction x of the Summation Bj over all nucleon’s longitudinal flavors momentum in the infinite http://www.jimandellen.org/ Parton gmuhome/RFeynman.jpg momentum frame Bjorken distribution scaling functions ò Nucleon structure can be given variable x as an incoherent sum of the interactions of the various “free partons”

ò Nucleon structure depends on the Bjorken scaling variable xBj and also the probing energy (Q2)

4 http://www.aip.org/history/acap/images/ bios/bjorkenj.jpg Proton structure

Different colors ò Proton is a composite object of quarks made up of: Protons interacting via ò Quarks exchange of gluons ò Valence quarks (2u, d) dominate at high x ( x ≥ 0.35 ) ò Sea quarks mostly u u , dd, ss dominate at low x ( x ≤ 0.2 ) ò Gluons – color force carriers ò Proton structure reconstructed in terms of Parton Distribution Functions (PDFs) Virtual quark antiquark pairs

5 DIS and Drell-Yan process space space time time DEEP INELASTIC SCATTERING DRELL YAN PROCESS

• Lepton scatters from • Quark from one hadron annihilates with antiquark from another hadron • Exchange of a virtual photon • Virtual photon is created • Higher states of the hadron • Decays into a lepton antilepton • Doesn’t differentiate between quark and antiquark • Unique sensitivity to the anti quark sea

6 Drell Yan process

Charge Fine weighted PDF of a Drell-Yan summation quarks of cross section structure constant over all quark flavor i in the flavors beam 2 2 d σ 4πα 2 = Σεi [qbeam (xbeam ) qt arg (xt arg ) + qt arg (xt arg )qbeam (xbeam )] dxt argdxbeam 9sxt arg xbeam i

Center of PDF of anti mass momentum momentum fraction of quarks of energy fraction of flavor i in the squared quark in the antiquark in beam target the target 7 Drell-Yan cross section

Leading order cross section

• Simplest picture

• Ignoring higher order processes in αs

2 2 d σ 4πα 2 = Σεi [qbeam (xbeam ) qt arg (xt arg ) + qt arg (xt arg )qbeam (xbeam )] dxt argdxbeam 9sxt arg xbeam i

Acceptance of Term negligible the spectrometer compared to the allows this term other term to dominate

8

SOME ISSUES IN NUCLEON STRUCTURE

9 Quark flavor asymmetry Nucleon sea generated by Gluon splitting: ò Naively assumed to be flavor symmetric as:

ò Up & down quark masses similar gluon quark recombine ò Strong force does not couple to splits antiquark into gluon flavor space pair

ò Violation of the Gottfried integral IG by: time ò NMC (1991) ò Flavor asymmetry also found by:

ò NA51(1994) ò NuSea/E866 (1998)

10 R. S. TOWELL et al. PHYSICAL REVIEW D 64 052002

¯ ¯ ¯ ¯ TABLE XI. The cross section ratio, d/u and dϪu values determined from the combination of all data sets for each x2 bin. The first uncertainty is statistical and the second uncertainty is systematic. The quantities extracted from the cross section ratio are given for Q2 ϭ54 GeV2/c2. The cross section ratio has a systematic uncertainty of less than 1% as shown in Table X. The average values for kinematic variables are also shown.

x2 range ͗pT͗͘M ␮ϩ␮Ϫ͘ 2 pd pp min-max ͗x2͗͘xF͘ (GeV/c)(GeV/c ) ␴ /2␴ ¯d/¯u ¯dϪ¯u

0.015–0.030 0.026 0.534 1.004 4.6 1.038Ϯ0.022 1.085Ϯ0.050Ϯ0.017 0.862Ϯ0.489Ϯ0.167 0.030–0.045 0.038 0.415 1.045 5.1 1.056Ϯ0.011 1.140Ϯ0.027Ϯ0.018 0.779Ϯ0.142Ϯ0.096 0.045–0.060 0.052 0.356 1.076 5.6 1.081Ϯ0.010 1.215Ϯ0.026Ϯ0.020 0.711Ϯ0.077Ϯ0.060 0.060–0.075 0.067 0.326 1.103 6.2 1.086Ϯ0.011 1.249Ϯ0.028Ϯ0.021 0.538Ϯ0.055Ϯ0.041 0.075–0.090 0.082 0.296 1.122 6.8 1.118Ϯ0.013 1.355Ϯ0.036Ϯ0.023 0.512Ϯ0.044Ϯ0.028 0.090–0.105 0.097 0.261 1.141 7.2 1.116Ϯ0.015 1.385Ϯ0.046Ϯ0.025 0.400Ϯ0.040Ϯ0.022 0.105–0.120 0.112 0.227 1.156 7.5 1.115Ϯ0.018 1.419Ϯ0.060Ϯ0.027 0.321Ϯ0.038Ϯ0.017 0.120–0.135 0.127 0.199 1.168 7.8 1.161Ϯ0.023 1.630Ϯ0.085Ϯ0.031 0.338Ϯ0.034Ϯ0.013 0.135–0.150 0.142 0.182 1.161 8.2 1.132Ϯ0.027 1.625Ϯ0.110Ϯ0.033 0.259Ϯ0.035Ϯ0.010 0.150–0.175 0.161 0.164 1.156 8.7 1.124Ϯ0.027 1.585Ϯ0.111Ϯ0.032 0.180Ϯ0.027Ϯ0.008 0.175–0.200 0.186 0.146 1.146 9.5 1.144Ϯ0.038 1.709Ϯ0.158Ϯ0.036 0.142Ϯ0.023Ϯ0.005 0.200–0.225 0.211 0.133 1.146 10.3 1.091Ϯ0.047 1.560Ϯ0.194Ϯ0.034 0.081Ϯ0.022Ϯ0.004 0.225–0.250 0.236 0.120 1.178 11.1 1.039Ϯ0.063 1.419Ϯ0.264Ϯ0.036 0.045Ϯ0.023Ϯ0.003 0.250–0.300 0.269 0.097 1.177 12.0 0.935Ϯ0.067 1.082Ϯ0.256Ϯ0.032 0.006Ϯ0.019Ϯ0.002 0.300–0.350 0.315 0.046 1.078 12.9 0.729Ϯ0.124 0.346Ϯ0.395Ϯ0.022 Ϫ0.040Ϯ0.036Ϯ0.002 proton. An extrapolation was made to account for the unmea- VII. CHARGE SYMMETRY AND SHADOWING sured region at low x. To extrapolate this integral from the The analysis presented here assumes that the parton dis- measured region, which is shown in Fig. 11, to the unmea- tributions of the nucleon obey charge symmetry: i.e., u (x) sured region, MRST and CTEQ5M were used to estimate the p ¯ ¯ contribution for 0рxр0.015 and it was assumed that the ϭdn(x), d p(x)ϭun(x), etc. This is consistent with the treat- contribution for xу0.35 was negligible. The uncertainty ment in previous experiments ͓1–4͔ and global fits ͓13–15͔. from this extrapolation was estimated to be 0.0041 which is The possibility that charge symmetry could be significantly half the difference betweenQuark the contributions flavor as given by asymmetry MRST and CTEQ5M.

NA51 found a considerable excess of d / u at x = 0.18

Parametric fits such as CTEQ4M, MRS(r2) based on NA51 data

The E866/NuSea experiment extended the measurements to a region up to x ≈ 0.35 and reported a drop in the ratio

Parametric fits such as CTEQ5M based on E866 data FIG. 10. ¯dϪ¯u as a function of x shown with statistical and systematic uncertainties. The E866 results, scaled to fixed Q2 J. Arrington et al., Proposal of E906 Experiment". ϭ54 GeV2/c2, are shown as the circles. Results from HERMES FIG. 9. ¯d(x)/¯u(x) versus x shown with statistical and system-11 (͗Q2͘ϭ2.3 GeV2/c2) are shown as squares. The error bars on the atic uncertainties. The combined result from all three mass settings E866 data points represent the statistical uncertainty. The inner er- is shown with various parametrizations. The E866 data and the ror bars on the HERMES data points represent the statistical uncer- parametrizations are at Q2ϭ54 GeV2/c2. The NA51 data point is tainty while the outer error bars represent the statistical and system- also shown. atic uncertainty added in quadrature.

052002-10 EMC effect

ò Quark distributions in the nuclei differ from quark distributions in the nucleon

ò In 1983, the EMC collaboration found per nucleon 2 structure functions F2 (x, Q ) in heavy nuclei different from deuterium

ò Underlying physics not understood completely

12 EMC effect in Deep Inelastic Scattering

Anti-shadowing region 0.06 < x < 0.3

Shadowing Fermi motion region region 0 < x < 0.06 0.8 < x < 1 D.F.Geesaman, K.Saito, and A.W.Thomas, Annu.Rev. Nucl. Part. Sci. 45, 337 (1995). EMC region 0.3 < x < 0.8

13 EMC effect in Drell Yan process

Little nuclear dependence in the shadowing region EMC effect Significant drop not seen in Drell- observed in anti- Yan process shadowing region like in DIS but limited by statistical uncertainty D.F. Geesaman, K. Saito, and A.W. Thomas, Annu.Rev. Nucl. Part. Sci. 45, 337 (1995).

• More precise measurements needed in the anti-shadowing region 14

ADDRESSING THE ISSUES

15 The SeaQuest E906 experiment

ò 120 GeV proton beam from the Main Injector at Fermilab ò Fixed target experiment ò Uses Drell-Yan process as a probe ò Optimized for detecting high rate di-muons ò Aimed at studying the antiquark distributions in the target nucleus

16 FERMILAB

Tevatron 800 GeV

Main Injector 120 GeV

17 The SeaQuest Spectrometer The SeaQuest E906 experiment

ò Extend the measurements to higher (x > 0.2)

ò Higher statistical precision compared to E866

ò Higher cross section scales as 1/s ò Lower background from J/ ψ as it scales as s ò Shed light on mechanisms that generate the nucleon sea

19 The SeaQuest E906 experiment

ò Will explore the anti- shadowing region

ò Will explore the EMC region

ò Will explore with higher precision compared to E772

20 Summary and outlook

ò Nucleons are dynamical quantum systems

ò Drell-Yan process has unique sensitivity to the antiquark distributions

ò SeaQuest experiment addresses issues in nucleon and nuclear structure by taking advantage of the Drell Yan process

ò Started taking data in Nov 2013

ò Many interesting topics explored by SeaQuest

ò Exciting time ahead!

21 Thank you!

22