Transcript STAR Heavy Flavor and Spin Program -

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, 2012 @UIC
Priscilla Kurnadi, Ph.D. 2010
Outline
1) Spin and Heavy Flavor Probes Gluon Spin
2) Results – Reality and Limitations
3) Transverse Spin Opportunities
4) Outlook
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Proton Structure

• Quark, gluon distribution inside proton
given by probability density function as
a function of momentum fraction x
Proton spin


Naïve picture: from valence quarks,
e.g u(+)u(+)d(-) = p(+)
In reality, not so simple:
– Parton distribution functions from Deep
Inelastic Scattering (DIS) experiments
• Polarized parton distribution functions
(PDFs):
1
S    G  Lq , g
2

q( x, Q 2 )  q  ( x, Q 2 )  q  ( x, Q 2 )
Parton contribution to proton spin:


1
1
( x, Q 2 )   q( x, Q 2 )  q ( x, Q 2 ) dx
0
2
1
G ( x, Q 2 )   g ( x, Q 2 )dx
g ( x, Q 2 )  g  ( x, Q 2 )  g  ( x, Q 2 )
0
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Double spin asymmetry
LO pQCD
ALL 



f a  f b   f a f b  fX  a LL  D hf
f a  f b   f a fb  fX  D hf
• Model-dependent ALL predictions rely on
experimental data (PDF, FF) and pQCD
calculations (partonic , aLL)
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Ignorance is a blessing
Pre-RHIC Spin data Period
Integrated (down to pTmin) charm ALL
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pQCD for HQ production at RHIC
Inclusive NPE from HQ semi-leptonic decays
Run05, 08
Phys. Rev. D 83 (2011) 052006
2
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pT (GeV/c)
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pQCD Works for Heavy Quark Production at RHIC !
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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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Longitudinal Double Spin Asymmetry
    
1 N   RN
ALL 

     PB PY N   RN
Spin-dependent
cross sections
Average polarization
over entire dataset
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Spin-dependent
non-photonic
electron yield
Relative
luminosity btw
bunch crossings
w/ different spin
configs
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NPE ALLMeasurement
STAR Preliminary
ALL
• Statistically limited
• Systematics:
– polarization
STAR Preliminary
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STAR Data: Prior 2008
-- major photonic electron background
-- limited data sample size
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Major Improvement in STAR Electron
Data Quality since 2008
   material  e  e


Gamma conversion only happens in material
NPE/PE Run 2005
.
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
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Run 2010
0.5
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STAR Data Quality and Quantity
A factor of Ten increase
in STAR data sample
Improved beam
polarization !
See http://www.phy.bnl.gov/cnipol/fills/
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Nature is also less kind on G
Inclusive Jet
de Florian et al., PRL 101, 072001 (2008)
STAR
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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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Even Less Kind to NPE Probes
STAR Jet ALL Favors
between DSSV and GRSV(std)
Riedl, Schafer and Stratmann PRD 80, 114020 (2009)
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A Clever Observable Helps
May not enough
Need calculations for STAR acceptance
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Try New Direction – Transverse Spin
TSSA – Transverse Single-Spin
Asymmetry (AN)
1  L  R
AN 
P  L  R
arXiv:1205.6826v1
E704
1991-1992
Left
Right
A long standing physics issue:
-- quark transversity
-- Sivers effect and/or Collins fragmentation
-- Higher twist calculations
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Particle Formation Dynamics
What is the physics origin for
the possible dependence
p0h?
• p0 cross section in good agreement with
PQCD calculation.
• h/ p0 cross section ratio similar to that
observed where jet fragmentation is dominant.
• AN (h) > AN(p0 ) for XF > 0.55
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/1201.5890
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STAR HFT Upgrade
Radius
Detector
(cm)
HFT
Inner Field Cage
Hit Resolution
R/ - Z (m m)
Radiation
length
SSD
IST
SSD
22
20 / 740
1% X0
IST
14
170 / 1800
<1.5 %X0
8
12/ 12
~0.4 %X0
PXL
PIXEL
2.5
12 / 12
~0.4% X0
PIXEL
•
•
•
Outer Field Cage
•
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
TPC
• existing single layer detector, double side
strips (electronic upgrade)
Volume
IST one layer of silicon strips along beam direction, guiding tracks from the SSD through
PIXEL detector. - proven strip technology
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STAR MTD Upgrade
MRPC based Detector Modules
Schedule: Run 12 – 10%; Run 13 – 43%; Run 14 – 80%
Completion – Mar 2014.
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STAR forward instrumentation upgrade
proton
nucleus
~ 2016
~ 6 GEM disks
Tracking: 2.5 < η < 4
FMS
FHC
W powder HCal
RICH
Baryon/meson
separation
Preshower
1/2” Pb radiator
Shower “max”
• 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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Outlook
1) The likely small G 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- pairs to confirm small G.
2) Probing transverse spin dynamics with heavy quarks –
unexplored territory !
3) 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.
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