dependence of light-quark sea in the seaquest experiment · seaquest data collection completed july...
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Status of the measurement of the flavordependence of light-quark sea in the
SeaQuest experiment
XXVII International Workshop on Deep InelasticScattering and Related Subjects
April 8th-12th 2019
Jason DoveUniversity of Illinois at Urbana-ChampaignRepresenting the SeaQuest Collaboration
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Jason Dove DIS 2019 2
Outline
● The Drell-Yan process
● Flavor asymmetry of the nucleon sea
● SeaQuest experiment
● Status of D2/H2 cross section ratio (new!)
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Jason Dove DIS 2019 3
Drell-Yan process
● Related to DIS via crossingsymmetry
● Provides informationcomplementary to DIS
● Directly probes antiquarks
Deep InelasticScattering
Drell-Yan
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Jason Dove DIS 2019 4
Drell-Yan process
● Related to DIS via crossingsymmetry
● Provides informationcomplementary to DIS
● Directly probes antiquarks
Deep InelasticScattering
Drell-Yan
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Jason Dove DIS 2019 5
Observation of flavor asymmetry of nucleon sea
●
● Significant deviation of from 1
● Asymmetry has a strongdependence on x
● Can x dependence be explained?
Using 800 GeV proton beam
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Jason Dove DIS 2019 6
Possible explanations● Pion Cloud model
● Chiral Quark model
● Statistical Model
● Rise at low x wellexplained
● None explain drop athigh x
● Need more accuratemeasurement at high x
Meson Cloud Model with physical pion mass and floating pion mass (dashed)
J. Alwall and G. Ingelman. PRD, 71:094015, 2005.
Bourrely, Soffer, Buccella. Eur. Phys. J. C 23, 487–501 (2002)
Statistical model
Dashed line: global fit to data
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Jason Dove DIS 2019 7
● 120 GeV protonbeam
● Completely newdetector apparatus
● ~10x instantaneousintensity
Tevatron
800 GeV
Main Injector120 GeV
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Jason Dove DIS 2019 8
Fermilab E906/SeaQuestCollaboration
● Abilene Christian University
● Academia Sinica
● Argonne National Laboratory
● University of Colorado
● Fermi National Accelerator Laboratory
● University of Illinois
● KEK
● Los Alamos National Laboratory
● Mississippi State University
● University of Maryland
● University of Michigan
● National Kaohsiung Normal University
● RIKEN
● Rutgers, The State University of NewJersey
● Tokyo Tech
● Yamagata University
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Jason Dove DIS 2019 9
E906 Apparatus● 120 GeV proton beam on LH
2,
LD2 targets
● New beamline
● New apparatus
● Forward spectrometer (xF > 0)
● Focusing magnet to bendtracks to spectrometer
● Spectrometer magnet tomeasure momentum of tracks
Target
104 cm
500 cm
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Jason Dove DIS 2019 10
Timeline
● After extensive efforts from 2012,data collection finished in July2017
● Analysis based on run2 and run3data
Firstprotonbeam
2012 2013 2014 2015 2016 2017 2018
MI upgrade run2
Newchambers
run3 run4 run5 run6
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Jason Dove DIS 2019 11
Dimuon mass distribution afterevent selection
● Analysis cuts designed toselect dimuons originatingfrom the target
● Able to resolve and
● By applying a cut of mass> 4.2 GeV we caneffectively removeand
Drell-Yan
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Jason Dove DIS 2019 12
Accidental background
● To get high statistics we run at high intensity ~1e12protons/ second
● Accidental events: from coincidence of two singlemuons such as from pion or kaon decay
● Signal event rate: proportional to intensity linearly
● Accidental event rate: proportional to intensity squaredor higher
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Jason Dove DIS 2019 13
D2/H
2 cross section ratio from intensity
extrapolation method● By extrapolating the
normalized D2/H2 D-Y
yields ratio to zerointensity, all forms ofrate dependence can beremoved
● The intercept gives theD2/H2 cross section ratio
Proton Intensity
D2/H
2
D2/H
2 Drell-Yan yield ratio
vs proton intensity
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Splitting the data into x2
bins
xBeam
xTarget
xTarg
et (x
2)
xBeam (x1)
0 0.5 1
0 0.5 1
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15
D2/H
2 cross section ratio from intensity
extrapolation method
● The intercept gives the D2/H2 cross section ratio
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Jason Dove DIS 2019 16
Systematics● Extrapolation functional fit
● Negligible
– Choice of intensity binning and range
– Target contamination
– Empty flask subtraction
– Target length
– Beam intensity
– tail contamination
– Event selection cuts
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Jason Dove DIS 2019 17
Drell-Yan cross section ratio
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Jason Dove DIS 2019 18
Cross check withthe mass fit
● Performing a component fitto the mass spectrum
● Use Monte Carlo for signalevents
● Use mixed single trackevents for accidentalbackground
● Compute D-Y cross sectionfor individual targets
● Preliminary D-Y resultsshow consistent D2/H2 ratios
LD2
Preliminary
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Jason Dove DIS 2019 19
Summary● SeaQuest data collection completed July 2017
● New extraction of D-Y D2/H2 as a function of x from 0.1 to 0.45
● New cross section ratio result includes removal of accidentalbackground
● Independent mass-fit method shows consistent D2/H2 ratio
● Extraction of ratio from D2/H2 ratio is underway
● Inclusion of data from after 2016 is underway
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Jason Dove DIS 2019 20
Backup slides
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Jason Dove DIS 2019 21
Fit functional form
● For each x2 bin I, the fit function is of the form
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Jason Dove DIS 2019 22
PDFs
● Q between 4.2 and 8.7 GeV
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Jason Dove DIS 2019 23
E906 vsE866
● E866 and E906have different
– Beam energy (800vs 120 GeV)
– Acceptance
– x1 distributions
● E886 systematics<1% and not shown