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STAR Decadal Plan 1
STAR Decadal Plan
Carl GagliardiTexas A&M University
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STAR Decadal Plan 2
The charge• A brief summary of the detector upgrades already (or soon to be)
in progress … This can even be summarized in tabular form, and should be consistent with the latest RHIC Midterm Plan.
• The compelling science goals you foresee for RHIC A+A, p+p, and d+A collisions that can only be carried out with additional upgrades (or replacements) of detector subsystems or machine capabilities (e.g., further luminosity or diamond size improvements).
• Prioritized, or at least time-ordered, lists of the major (above $2M total project cost) and more modest (below $2M total project cost) new detector upgrades
• Any plans or interest your Collaboration has in adapting your detector or detector subsystems (or detector R&D) to study electron-nucleon and electron-ion collisions with an eventual eRHIC upgrade.
• The envisioned evolution of your Collaboration through the decade
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STAR Decadal Plan 3
Remarkable discoveries at RHICThe first six years
• A+A collisions– Jet quenching– Perfect liquid– Number of constituent quark scaling– Heavy-quark suppression
• Polarized p+p collisions– Large transverse spin asymmetries in the pQCD regime
• d+A collisions– Possible indications of gluon saturation at small x
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STAR Decadal Plan 4
The discoveries continue
• A+A collisions– First ever observation of an anti-hypernucleus– Azimuthal charged-particle correlations that may arise from local
strong parity violation– Even b-quark production is suppressed in central Au+Au
collisions
• Polarized p+p collisions– Most precise constraints to date on the polarization of the gluons
• Global analysis that combines DIS, SIDIS, and RHIC data• Contribution to proton spin from gluons with 0.05 < x < 0.2 is small
• d+A collisions– Dramatic broadening of forward π0-π0 correlations in central d+Au
• Clearest indication to date that the onset of gluon saturation is accessible at RHIC
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STAR Decadal Plan 5
New research areas
• STAR and RHIC continue to perform very well under extreme conditions– Au+Au collisions at 7.7 GeV
– Charge-sign separation to pT ~ 50 GeV
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STAR Decadal Plan 6
Key unanswered questions
• What is the nature of QCD matter at the extremes?– What are the properties of the strongly-coupled system
produced at RHIC, and how does it thermalize?– Where is the QCD critical point and the associated first-order
phase transition line?– Are the interactions of energetic partons with QCD matter
characterized by weak or strong coupling? What is the detailed mechanism for partonic energy loss?
– Can we strengthen current evidence for novel symmetries in QCD matter and open new avenues?
– What other exotic particles are produced at RHIC?
• What is the partonic structure of nucleons and nuclei?– What is the partonic spin structure of the proton?– What are the dynamical origins of spin-dependent interactions in
hadronic collisions?– What is the nature of the initial state in nuclear collisions?
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STAR Decadal Plan 7
Tracking: TPC Particle ID: TOF
Full azimuthal particle identification over a broad range in pseudorapidity
STAR: a beautiful detector
Recent upgrades:DAQ1000TOF
have already begun to position STAR for the coming decade
Electromagnetic Calorimetry:
BEMC+EEMC+FMS(-1 ≤ ≤ 4)
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STAR Decadal Plan 8
How to answer these questions• Hot QCD matter: high luminosity RHIC II (fb-1 equivalent)
– Heavy Flavor Tracker: precision charm and beauty– Muon Telescope Detector: e+μ and μ+μ at mid-rapidity– Trigger and DAQ upgrades to make full use of luminosity
• Phase structure of QCD matter: energy scan– Electron cooling if lowest beam energies most promising
• Near-term upgrades for p+p collisions– Forward GEM Tracker: flavor-separated anti-quark polarizations– Forward Hadron Calorimeter: strange quark polarization– Roman Pots phase II: search for glueballs
• Nucleon spin and cold QCD matter: high precision p+p and p+A, followed by e+p and e+A– Major upgrade of capabilities in forward direction– Devote the beam time needed to do p+A, rather than d+A– Existing mid-rapidity detectors well suited for portions of the
initial e+p and e+A program
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STAR Decadal Plan 9
Tracking: TPC
Forward Gem Tracker(2011)
Particle ID: TOF
Full azimuthal particle identification over a broad range in pseudorapidity
Evolution of STAR
Additionalupgrades:Muon Telescope
Detector Trigger and DAQForward Upgrades
Heavy Flavor Tracker (2013)
Electromagnetic Calorimetry:
BEMC+EEMC+FMS(-1 ≤ ≤ 4)
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STAR Decadal Plan 10
Local strong parity violation
• Transitions between domains with different topological charge may induce parity violation in the dense matter– Similar transitions (at much higher energies) might have produced the
matter-antimatter asymmetry in the early universe• Magnetic field in A+A plays a key role: chiral magnetic effect• Crucial to verify if parity violation is the correct explanation
– Beam-energy dependence– Compare collisions of isobaric systems– U+U collisions: collisions with more v2 and less B field than Au+Au
STAR, PRL 103, 251601
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STAR Decadal Plan 11
Anti-quark and gluon polarization with 500 GeV p+p
• W measurement will significantly reduce uncertainties on anti-quark polarizations– FGT essential for the forward W’s
• Inclusive jet and di-jet ALL will extend our knowledge of gluon polarization to smaller x
Assumes 600 pb-1 delivered @ P = 50%
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STAR Decadal Plan 12
Accessing strange polarization with Λ
• STAR has performed initial Λ DLL measurements at mid-rapidity– Provides access to strange quark polarization– Most interesting with quite high pT Λ (trigger and stat limited)
• Similar measurements at forward rapidity are very promising– Requires the Forward Hadron Calorimeter
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STAR Decadal Plan 13
• Does charm flow hydrodynamically?
– Heavy Flavor Tracker: unique access to low-pT fully reconstructed charm
• Are charmed hadrons produced via coalescence?– Heavy Flavor Tracker: unique access to charm baryons
– Would force a significant reinterpretation of non-photonic electron RAA
• Muon Telescope Detector: does J/Ψ flow?
Properties of sQGP: charm
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STAR Decadal Plan 14
• Precise measurements with TOF, DAQ upgrade
• Correlated charm in A+A– Decorrelation? Order of
magnitude uncertainty• Address with:
– HFT: D0, displacement– MTD: e-μ correlations
Properties of sQGP: dileptons
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STAR Decadal Plan 15
• Muon Telescope Detector: dissociation of Υ, separated by state– At RHIC: small contribution from coalescence, so interpretation clean– No contribution of Bremsstrahlung tails, unlike electron channel
Properties of sQGP: Upsilon
Υ
RHICWhat states of quarkonia is the energy density of matter at RHIC sufficient to dissociate?What is the energy density?
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STAR Decadal Plan 16
• Is the mechanism predominantly collisional or radiational?– Detailed, fully kinematically constrained measurements via gamma-
hadron and full jet reconstruction– Pathlength dependence, especially with U+U
• Does the mechanism depend on the parton type?– Gluons: particle identification, especially baryons– Light quarks: gamma-hadron– Heavy quarks: Heavy Flavor Tracker and Muon Telescope Detector
• Does the energy loss depend on the parton energy and/or velocity?– High precision jet measurements up to 50 GeV– Vary velocity by comparing light quarks, charm, and beauty
Mechanism of partonic energy loss
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STAR Decadal Plan 17
Jets: proven capabilities in p+pB.I. Abelev et al. (STAR Coll.), Phys.Rev.Lett. 97, 252001, 2006 SPIN-2010: Matt Walker/Tai Sakuma, for the collaboration
• Jets well understood in STAR, experimentally and theoretically
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STAR Decadal Plan 18
To date: jets and γ-hadron in A+ATriggered: ~0.3 nb-1 Untriggered: ~0.01 nb-1
• Beginning results from Run 7 indicative, but far from final word
• Huge increase in significance with trigger upgrades+luminosity
• Complementary to LHC– RHIC: quarks; LHC: gluons– Best place to do jets <~ 50 GeV
Phys. Rev. C 82, 034909
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STAR Decadal Plan 19
• Sufficient statistical reach out to ~50 GeV for precision measurements– Large unbiased datasets– Trigger upgrades to lessen
bias with walking jet patches
• Smearing of high momentum charged hadrons under control– Corrections: need to calibrate
level of smearing– Hard cutoff in hadrons: small
loss of jets that fragment hard– Dominant uncertainty
fluctuations in the underlying event
Jet capabilities in A+A
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STAR Decadal Plan 20
Velocity dependence
• QED: different momenta, different mechanisms• Just beginning the exploration of this space in QCD
“Passage of Particles through Matter”, Particle Data Book
b c light partons
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STAR Decadal Plan 21
• What is the velocity dependence of energy loss?– Key tools: heavy quarks with precise kinematic reconstruction– Key technology: Heavy Flavor Tracker and Muon Telescope Detector
Velocity dependence via heavy quarks
STAR Preliminary
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STAR Decadal Plan 22
Cold QCD matter
• Hint that RHIC provides unique access to onset of saturation • Compelling and necessary further measurements in future
– Kinematic constraints: large rapidity photons, Drell-Yan in p+A• Same observables very important for our understanding of
transverse spin asymmetries in p+p• Beyond p+p and p+A: the Electron Ion Collider
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STAR Decadal Plan 23
Sivers effect sign change
• In SIDIS, knock a colored quark out of a color-neutral nucleon– Quark was bound to the rest of the nucleon before the interaction– Final-state interaction that produces the interference is attractive
• In Drell-Yan, a quark in one hadron annihilates with an anti-quark of the same flavor and opposite color from the other hadron– The rest of the “other hadron” has the same color charge as the
incident quark– Initial-state interaction that produces the interference is repulsive
• Leads to opposite signs for the Sivers effects in the two cases– A key test of the TMD approach
• Similar sign change occurs for direct photon production within the Twist-3 approach
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STAR Decadal Plan 24
Other closely related measurements
• AN for W production
– Only measure the electron (or muon)– Can preserve significant sensitivity if measure just above the
Jacobian peak with good pT resolution
• Not clear whether we can achieve sufficient resolution or not
• AN for Z production
– Very easy to interpret– Very small cross section !!!– Not clear if this is practical or not
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STAR Decadal Plan 25
MRPC ToF BarrelMRPC ToF Barrel
BBC
FPD
FMS
EMC BarrelEMC End Cap
DAQ1000DAQ1000
COMPLETE
Ongoing R&D
TPC
computing
STAR as of 2014
HFTHFT FGTFGT
MTDMTD
Roman Pots Phase 2
Trigger and DAQ Upgrades
FHC
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STAR Decadal Plan 26
STAR forward upgrade
nucleus electron
proton nucleus
To fully investigate the proton spin and cold QCD matter,STAR will move forward
• Positive η: γ and Drell Yan – High precision tracking– e/h and γ/π0 discrimination– Baryon/meson via RICH(?)– Optimized for p+A and p+p– High momentum scale
• Negative η: eRHIC– Optimized for low energy
electrons (1~5 GeV)– Triggering, tracking, ID for
-2.5 <~ η < -1– Can we ID hadrons, too?– R&D necessary for optimal
technology choice
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STAR Decadal Plan 27
STAR and eRHIC Phase 1
• Current detector matches quite well to kinematics of eRHIC– Particle ID, sufficent pT resolution, etc. at mid-rapidity
• High Q2 electron scattering• Quark jets from low x events
• A spin example: Explore strange quark polarization at low x– Existing DIS and SIDIS results appear inconsistent
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STAR Decadal Plan 28
Energy loss in cold QCD matter
• Complementary probe of mechanism of energy loss• HERMES: mixture of hadronic absorption and partonic loss
– Hadrons can form partially inside the medium • eRHIC: light quarks form far outside medium• Heavy quarks: unexplored to date. Low β: short formation time
Lc up to few 100 fm
RAπ Hermes, Nucl. Phys.B 780, 1 (2007)
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STAR Decadal Plan 29
Conclusions
• RHIC and STAR have been extraordinarily successful in their first decade of operations
• The STAR Collaboration has identified compelling physics opportunities for the coming decade
• The STAR Collaboration has identified the detector upgrades required to address these opportunities
• The path forward:– Early in the decade: physics with low mass in the central region– Mid decade: physics of the HFT and MTD– Later in the decade: physics in the forward region
• End of the decade: early phase of eRHIC