star decadal plan 1 carl gagliardi texas a&m university

STAR Decadal Plan 1

STAR Decadal Plan

Carl GagliardiTexas A&M University

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

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

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

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

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?

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)

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

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)

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


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%


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


• 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


• 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


• 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?


• 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


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


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


• 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


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


• 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


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


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


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


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


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


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


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)


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

star decadal plan 1 carl gagliardi texas a&m university

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