1. STAR Heavy Flavor and Spin Program --Lessons learned and other opportunities
Huan Zhong Huang
(黄焕中)
Department of Physics and Astronomy
University of California Los Angeles
Workshop on Heavy Flavor Production in High Energy Nuclear Collisions
June 17-18,
Priscilla Kurnadi, Ph.D. 2010

2. Outline Spin and Heavy Flavor Probes Gluon Spin
Results – Reality and Limitations
Transverse Spin Opportunities
Outlook
11/23/2018

3. Proton Structure Proton spin
Naïve picture: from valence quarks, e.g u(+)u(+)d(-) = p(+)
In reality, not so simple:
Parton contribution to proton spin:
Quark, gluon distribution inside proton given by probability density function as a function of momentum fraction x
Parton distribution functions from Deep Inelastic Scattering (DIS) experiments
Polarized parton distribution functions (PDFs):
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4. Double spin asymmetry
LO pQCD
Model-dependent ALL predictions rely on experimental data (PDF, FF) and pQCD calculations (partonic , aLL)
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5. Ignorance is a blessing
Pre-RHIC Spin data Period
Integrated (down to pTmin) charm ALL
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6. pQCD for HQ production at RHIC
Inclusive NPE from HQ semi-leptonic decays
Run05, 08
Phys. Rev. D 83 (2011)
pT (GeV/c)
pQCD Works for Heavy Quark Production at RHIC !
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7. Works for Charm and Bottom Separately too !
STAR used NPE-hadron correlations
to statistically separate Charm and
Bottom decay electrons.
pQCD describes experimental data
well !
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8. Longitudinal Double Spin Asymmetry
Spin-dependent cross sections
Relative luminosity btw bunch crossings w/ different spin configs
Average polarization over entire dataset
Spin-dependent non-photonic electron yield
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9. ALL NPE ALLMeasurement Statistically limited Systematics: polarization
STAR Preliminary
Statistically limited
Systematics:
polarization
STAR Preliminary
STAR Data: Prior 2008
-- major photonic electron background
-- limited data sample size
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10. Major Improvement in STAR Electron Data Quality since 2008
NPE/PE
Run
Gamma conversion only happens in material
0.5
STAR inner trackers were removed in
Run 2008~2011, much less material budget
photonic electron yield is significantly
lower than previous runs.
Best shot for non-photonic electrons:
Much higher signal to background ratio +
Less sensitive to the accuracy
of background removal efficiency in simulation
Run 2010
0.5
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11. STAR Data Quality and Quantity
A factor of Ten increase
in STAR data sample
Improved beam
polarization !
See
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12. Nature is also less kind on DG
Inclusive Jet
STAR
de Florian et al., PRL 101, (2008)
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13. 2009 Inclusive Jet ALL
2009 results are a factor of 3 or greater more precise than 2006
Data falls between predictions from DSSV and GRSV-STD
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14. Even Less Kind to NPE Probes
STAR Jet ALL Favors
between DSSV and GRSV(std)
Riedl, Schafer and Stratmann PRD 80, (2009)
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15. A Clever Observable Helps
May not enough
Need calculations for STAR acceptance
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16. Try New Direction – Transverse Spin
arXiv: v1
TSSA – Transverse Single-Spin
Asymmetry (AN)
E704
Right
Left
A long standing physics issue:
-- quark transversity
-- Sivers effect and/or Collins fragmentation
-- Higher twist calculations
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17. Particle Formation Dynamics
0 cross section in good agreement with PQCD calculation.
/ 0 cross section ratio similar to that observed where jet fragmentation is dominant.
AN () > AN(0 ) for XF > 0.55
What is the physics origin for
the possible dependence
p0h?
Extend to Vector Mesons – r/w and J/y
Extend to heavy quark mesons – NPE from
heavy quark semi-leptonic decays
Extend to direct photons/jets
AN from polarized p+A collisions to
probe CGC state in A
-- Kovchegov and Sievert hep-ph/
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18. STAR HFT Upgrade HFT SSD IST Inner Field Cage PXL PIXEL Magnet
Detector
Radius
(cm)
Hit Resolution
R/ - Z (m - m)
Radiation length
SSD 22
20 / 740
1% X0
IST 14
170 / 1800
<1.5 %X0
PIXEL 8
12/ 12
~0.4 %X0
2.5
12 / 12
~0.4% X0
TPC Volume
Magnet
Return Iron
Solenoid
Outer Field Cage
Inner Field Cage
EAST
WEST
FGT
PIXEL
two layers
18.4x18.4 m pixel pitch
10 sector, delivering ultimate pointing resolution that allows for direct topological identification of charm.
new monolithic active pixel sensors (MAPS) technology
SSD
existing single layer detector, double side strips (electronic upgrade)
IST one layer of silicon strips along beam direction, guiding tracks from the SSD through PIXEL detector. - proven strip technology
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19. STAR MTD Upgrade MRPC based Detector Modules
Schedule: Run 12 – 10%; Run 13 – 43%; Run 14 – 80%
Completion – Mar 2014.
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20. STAR forward instrumentation upgrade
proton
nucleus
~ 2016
FMS
FHC
~ 6 GEM disks
Tracking: 2.5 < η < 4
W powder HCal
Preshower
1/2” Pb radiator
Shower “max”
RICH
Baryon/meson separation
Forward instrumentation optimized for p+A and transverse spin physics
Charged-particle tracking
e/h and γ/π0 discrimination
Baryon/meson separation
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21. Outlook The likely small DG makes it difficult to make precision
ALL for heavy quarks from gluon fusion channel !
It may be worthwhile to measure ALL for high pT
electrons and e-m pairs to confirm small DG.
Probing transverse spin dynamics with heavy quarks –
unexplored territory !
STAR HFT/MTD upgrades and future Forward
Instrumentation upgrades will greatly enhance STAR
capability of HQ measurements for both heavy ion
and polarized p+p and p+A collisions.
11/23/2018