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Measurement of the EMC Effect in the Deuteron K Old Dominion University ODU Digital Commons Physics Faculty Publications Physics 2015 Measurement of the EMC Effect in the Deuteron K. A. Griffioen J. Arrington M. E. Christy R. Ent N. Kalantarians See next page for additional authors Follow this and additional works at: https://digitalcommons.odu.edu/physics_fac_pubs Part of the Elementary Particles and Fields and String Theory Commons, and the Nuclear Commons Repository Citation Griffioen, K. A.; Arrington, J.; Christy, M. E.; Ent, R.; Kalantarians, N.; Keppel, C. E.; and Kuhn, S E., "Measurement of the EMC Effect in the Deuteron" (2015). Physics Faculty Publications. 225. https://digitalcommons.odu.edu/physics_fac_pubs/225 Original Publication Citation Griffioen, K. A., Arrington, J., Christy, M. E., Ent, R., Kalantarians, N., Keppel, C. E., . Zhang, J. (2015). Measurement of the EMC effect in the deuteron. Physical Review C, 92(1), 015211. doi:10.1103/PhysRevC.92.015211 This Article is brought to you for free and open access by the Physics at ODU Digital Commons. It has been accepted for inclusion in Physics Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contact [email protected]. Authors K. A. Griffioen, J. Arrington, M. E. Christy, R. Ent, N. Kalantarians, C. E. Keppel, and S E. Kuhn This article is available at ODU Digital Commons: https://digitalcommons.odu.edu/physics_fac_pubs/225 PHYSICAL REVIEW C 92, 015211 (2015) Measurement of the EMC effect in the deuteron K. A. Griffioen,1 J. Arrington,2 M. E. Christy,3 R. Ent,4 N. Kalantarians,3 C. E. Keppel,4 S. E. Kuhn,5 W. Melnitchouk,4 G. Niculescu,6 I. Niculescu,6 S. Tkachenko,7 and J. Zhang7 1College of William and Mary, Williamsburg, Virginia 23187, USA 2Argonne National Laboratory, Argonne, Illinois 60439, USA 3Hampton University, Hampton, Virginia 23668, USA 4Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA 5Old Dominion University, Norfolk, Virginia 23529, USA 6James Madison University, Harrisonburg, Virginia 22807, USA 7University of Virginia, Charlottesville, Virginia 22901, USA (Received 3 June 2015; revised manuscript received 29 June 2015; published 21 July 2015) Rd = F d / F n + F p F n/F d We determined the structure function ratio EMC 2 ( 2 2 ) from recently published 2 2 data taken by the BONuS experiment using CLAS at Jefferson Lab. This ratio deviates from unity, with a slope dRd /dx =− . ± . x W> . EMC 0 10 0 05 in the range of Bjorken from 0.35 to 0.7, for invariant mass 1 4 GeV and Q2 > 1 GeV2. The observed EMC effect for these kinematics is consistent with conventional nuclear physics models that include off-shell corrections, as well as with empirical analyses that find the EMC effect proportional to the probability of short-range nucleon-nucleon correlations. DOI: 10.1103/PhysRevC.92.015211 PACS number(s): 21.45.Bc, 25.30.Fj, 24.85.+p, 13.60.Hb I. INTRODUCTION proton), but the deuteron too may exhibit an EMC effect. Several data-driven, model-dependent attempts [7,13,26]have In the early 1980s the European Muon Collaboration d d n p been made to determine R = F /(F + F ), in which (EMC) discovered that deep-inelastic scattering from atomic EMC 2 2 2 F n(p) nuclei is not simply the incoherent sum of scattering from 2 is the free neutron (proton) structure function. However, the constituent nucleons [1]. Their data suggested that quarks the lack of knowledge about the free neutron’s structure has with longitudinal momentum fraction x in the range 0.35 to clouded these efforts. Theoretical estimates of the deuteron EMC ratio have also been made [27–39], often with the goal 0.7 were suppressed in bound nucleons, and their observations p of isolating F n/F . were quickly confirmed at SLAC [2,3]. The deep-inelastic 2 2 d A R F x A A clean measurement of EMC is greatly needed. The structure function 2 ( ) for a nucleus with nucleons was compared to the equivalent quantity F d (x) for the deuteron, deuteron is weakly bound (by 2.2 MeV), and the nucleons d 2 pn such that RA = (F A/A)/(F /2). At intermediate x, RA are governed only by the interaction. Therefore, a precise EMC 2 2 EMC Rd is less than unity, and this deviation grows with A.Overthe measurement of EMC can shed light on the cause of the following three decades, subsequent dedicated measurements EMC effect. Because the deuteron has a weak mean field / / [4–8] confirmed the EMC effect with ever-increasing precision (1 MeV nucleon binding versus 8 MeV nucleon for heavier for a wide range of nuclei. Drell-Yan data from Fermilab [9], nuclei), but a substantial contribution from high-momentum pn however, which were largely sensitive to sea quarks, showed no pairs, it is a good test case. modifications of the antiquark sea for 0.1 <x<0.3, contrary to models predicting antiquark enhancement. Despite many theoretical papers on the EMC effect, no universally accepted II. DATA ANALYSIS explanation has emerged. For reviews, see Refs. [10–12]. Rd A new extraction of EMC with smaller uncertainties on The precise, new measurements from Jefferson Lab on light F n 2 is now possible thanks to the high-quality data from nuclei [8] have generated a renewed interest in understanding the BONuS experiment [40–42] using CLAS at Jefferson |dRA /dx| . <x< . the EMC effect. The slopes EMC for 0 35 0 7 Lab with electron beams up to 5.26 GeV. BONuS was increase with A; however, the 9Be slope is anomalously large, x F n/F p designed to measure the high- structure function ratio 2 2 suggesting perhaps that the EMC effect is dependent on local F n using a model-independent extraction of 2 that relies on density and that 9Be might be acting like two tightly bound the spectator tagging technique. The experiment used a α particles and a neutron. A recent analysis [13] suggests 7-atm gaseous deuterium target surrounded by a radial time dRA /dx that EMC is proportional to the probability of finding projection chamber capable of detecting recoil protons in short-range correlations in nuclei [14–19]. Recent work on this the range 70–200 MeV/c [40]. By selecting backward-going subject [20–25] concludes that although binding and Fermi and low-momentum spectators, final-state pn interactions and motion effects contribute, some modification of the bound off-shell effects were minimized, respectively [42]. Detection nucleon’s structure appears to be required to explain the EMC of the spectator proton ensured that the electron scattered effect. Whether this is caused by the nuclear mean field, short- from the neutron. The initial-state kinematics of the neutron range correlations, or both is still open to debate. were then calculated from the spectator momentum. This EMC ratios are usually taken with respect to the deuteron, F n/F d technique enabled the extraction of 2 2 over a wide range which is the best proxy for an isoscalar nucleon (neutron plus of x for 4-momentum transfer squared Q2 between 0.7 and 0556-2813/2015/92(1)/015211(5) 015211-1 ©2015 American Physical Society K. A. GRIFFIOEN et al. PHYSICAL REVIEW C 92, 015211 (2015) 4.5 GeV2, which covers the resonance region and part of certainties. To explore the region x>0.45 we pushed our the deep-inelastic region. For the present analysis we have analysis into the resonance region (1.4 <W<2.0GeV). Q2 RA used the published data from the 4.22- and 5.26-GeV beam Available data, albeit at slightly higher , suggest that EMC energies with Q2 1GeV2 and invariant final-state mass in the resonance region is similar to that in the deep-inelastic W> . Rd scattering region at the same x [47]. Therefore, we expect 1 4 GeV to determine EMC. The primary data from BONuS are the ratios F n/F d that an average over many different Q2 values washes out any 2 2 Rd x obtained from measuring tagged neutron event rates in CLAS resonance structure and that duality ensures EMC at fixed , and dividing them by the untagged deuteron rates recorded averaged over W, approaches the deep-inelastic limit. These simultaneously at the same kinematics [42]. Consequently, assumptions were tested and confirmed within statistical and detector acceptance and other systematic effects largely cancel, systematic uncertainties by looking for a Q2 dependence of F n Rd within each x bin and by considering variations in Rd and the accuracy of this ratio is far better than that of 2 alone. EMC EMC The overall normalization of the BONuS data, which takes among four kinematic cases: into account the spectator proton detection efficiency, was 2 p (1) W>1.4 GeV and Q2 > 1GeV , initially chosen [41]tomakeF n/F at x = 0.3 agree with the 2 2 (2) W>1.8 GeV and Q2 > 1GeV2, CTEQ–Jefferson Lab (CJ) [43] global fit for this point. There (3) W>2.0 GeV and Q2 > 1GeV2, and is a 3% normalization uncertainty associated with this choice. (4) W>2.0 GeV and Q2 > 2GeV2. For the final BONuS results [42], which include the resonance χ 2 F n/F d W region, the normalization minimized the of the full data The 2 2 data were sorted into 20-MeV-wide bins set with respect to the most recent update [44]oftheChristy and into logarithmic Q2 bins (13 per decade) with edges at and Bosted (CB) fits [45,46]. In this case, the convolution 0.92, 1.10, 1.31, 1.56, 1.87, 2.23, 2,66, 3.17, 3.79, 4.52, and model of Refs.
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