RHIC AND THE HELICITY DISTRIBUTIONS OF THE QUARKS AND GLUONS E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012
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Transcript RHIC AND THE HELICITY DISTRIBUTIONS OF THE QUARKS AND GLUONS E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012
RHIC
AND
THE HELICITY DISTRIBUTIONS OF
THE QUARKS AND GLUONS
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
1
RHIC@BNL Today
Jet/C-Polarimeters
12:00 o’clock
RHIC
PHENIX
8:00 o’clock
LINAC
NSRL
EBIS
Booster
AGS
ANDY
2:00 o’clock
RF
Beams: √s=<500 GeV pp; 50-60% polarization
4:00 o’clock
Lumi: ~10 pb-1/week
STAR
6:00 o’clock
STAR
ERL Test Facility
Tandems
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
2
RHIC polarized protons – luminosity and
polarization
• <P> increased from 37% to
46% at 250 GeV in Run-11
still significant effort needed to
reach goal of 70%
also for 100GeV Beams
• Building blocks for pp design
luminosity at 250 GeV
demonstrated in Run-9 and
Run-11
need to be put together
plans to go beyond
• Expect no significant
increase in luminosity at
100 GeV before electron
lenses
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
3
Predictive power of pQCD
P1
q(x1)
x1P1
Hard Scattering Process
sˆ
P2
x2P2
X
g(x2)
“Hard” (high-energy) probes have predictable rates given:
Partonic hard scattering rates (calculable in pQCD)
Parton distribution functions (need experimental input)
Fragmentation functions (need experimental input)
DIS
E.C. Aschenauer
?
pQCD
Universal
nonperturbative
functions
e+e-
INT-Workshop, Orbital Angular Momentum in QCD, 2012
4
Underlying processes in pp
Mid-rapidity pp p0/jetX dominated by gggg and gqgq
Forward-rapidity pp p0/jet X dominated by gqgq
s ++ - s +- Dfa Dfb
ALL = ++
µ
aˆ LL
+s +s
fa fb
=3.3, s=200 GeV
qq qq
gq gq
gg gg
E.C. Aschenauer
kinematics is unknown
Scale: pT
parton kinematics needs to be
unfolded in theo. calculation
INT-Workshop, Orbital Angular Momentum in QCD, 2012
5
The Gluon Polarization
RHIC: many sub-processes with a
dominant gluon contribution
high-pT jet, pion, heavy quark, …
T
in NLO
h
e
o
r
e
t
i
c
a
l
unpolarised cross sections nicely reproduced in NLO pQCD
P
E.C. Aschenauer
r in QCD, 2012
INT-Workshop, Orbital Angular Momentum
6
Does QCD work: Cross Sections
s=62 GeV (PRD79, 012003)
s=200 GeV (PRD76, 051106)
s=500 GeV (Preliminary)
PRL 97, 152302
Data compared to NLO pQCD calculations:
s=62 GeV calculations may need inclusion of NLL (effects of threshold logarithms)
s=200 and 500 GeV: NLO agrees with data within ~30%
Input to qcd fits of gluon fragmentation functions DSS
√s=200 GeV Jet Cross Sections agree with data in ~20%
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
7
Current
knowledge
on DIS
Dg and polarized pp
Δg from
inclusive
DIS
Scaling violations of g1
(Q2-dependence) give indirect access
to the gluon distribution via DGLAP
EIC
RHIC polarized pp collisions at midrapidity
directly involve gluons
evolution.
Rule out large DG for 0.05 < x < 0.2
DIS
RHIC
constrained x-range still very limited
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
8
Much more data
Direct photon
Phys. Rev. D 79, 012003 : √s = 62.4 GeV
Increased √s allows to go to lower x
low pt low x ?Scale uncertainty?
Different final states select between
gg and qg scattering
sign of Dg
Future measurements will include
di-hadron at forward rapidity
constrain x and to go to lower x
E.C. Aschenauer
η ALL : Phys. Rev. D 83, 032001
2-2.5 GeV/c
4-5 GeV/c
9-12 GeV/c
2-2.5 GeV/c
4-5 GeV/c
9-12 GeV/c
INT-Workshop, Orbital Angular Momentum in QCD, 2012
9
Reconstructing Jets at STAR
MC Jets
GEANT
PYTHIA
Particle
Detector
Data Jets
e,n,g,
p,p,etc
q
E.C. Aschenauer
g
The large acceptance of the
STAR detector makes it well
suited for jet measurements:
TPC provides excellent
charged-particle tracking and
pT information over broad range
in η
Extensive EM calorimetry over
full 2π in azimuth and for -1 <
η < 2
Sophisticated multi-level
trigger on EMC information at
tower and patch scale
Use midpoint cone algorithm
many more have been used
Dominated by qg sign of DG
INT-Workshop, Orbital Angular Momentum in QCD, 2012
10
Correlation Measurements: ΔG
STAR
Inclusive ALL measurements at
fixed pT average over a broad
range of xgluon
Reconstructing correlated probes
(eg. di-jet, γ-jet) provides
information on initial state
partonic kinematics at LO
x1 =
x2 =
1
s
1
s
(p
(p
T3
M=
eh + pT 4 eh
3
T3
4
e - h + pT 4 e - h
3
)
4
This allows for constraints on
the shape of Δg(x)
)
x1x2 s
x1
h 3 + h 4 = ln
x2
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
11
STAR
E.C. Aschenauer
Much more data
INT-Workshop, Orbital Angular Momentum in QCD, 2012
12
Inclusive Results: p0,p+,p- ALL
STAR
In Run 6, STAR measured p0 ALL in three different pseudorapidity ranges
Mid-rapidity results excludes maximal Δg model, consistent with EEMC result
qg scattering dominates at high η with large x quarks and small x gluons
•
In Run 5, STAR measured ALL
for inclusive charged pions
• ALL(π+) - ALL(π-) is sensitive
to the sign of ΔG
• Trigger using neutral jet patch
Introduces significant
trigger bias (charged pions
often subleading particles
in jets)
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
13
DG: Path Forward
Limitations in current data:
Limited x-range covered
Weak sensitivity to the shape of DG(x)
Improve precision of current measurements
Get more data
Extend xg-range
Move to forward rapidities
Constrain kinematics: map DG vs xg
More exclusive channels: pp g + jet and pp jet + jet
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
14
Forward Calorimetry: PHENIX MPC
Muon Piston Calorimeter (MPC): PbWO4
3.1 < || < 3.9
2p azimuth
Gives access to lower: x10-3
Fully available from 2008
PHENIX pp p0 X : projections ||<0.35
MPC p0 500 GeV
300 pb-1 P=0.55
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
15
STAR Expected
Future Inclusive Jet Sensitivity
Plan to measure inclusive jet ALL in 500 GeV collisions
during 2012 and 2013 RHIC runs
• Sensitive to smaller xg at higher beam energy
• Smaller asymmetries expected, so control of
systematics important
Future running at 200 GeV expected to significantly reduce
uncertainties relative to 2009 data as well
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
16
STAR
Projected Di-jet Sensitivity @ 500 GeV
Projected Stat. Uncertainty: 50% Pol 390 pb-1
Higher energies give
access to lower xg
Expect ALL to be
smaller than 200 GeV
Mjj [GeV]
Mjj [GeV]
Projections shown are
purely statistical
Forward jets in EEMC
region sensitive to even
lower xg
Mjj [GeV]
E.C. Aschenauer
Mjj [GeV]
INT-Workshop, Orbital Angular Momentum in QCD, 2012
17
Marco
Heavy Flavor
Very Very difficult:
Need to shrink uncertainties at
least by x50 (x2500 in lumi!!!)
Correlations may give larger
asymmetries, but will have even
smaller stat. power.
Both experiments have / or will
have -vertex detectors
Heavy Flavor
•
•
•
Production dominated by
gluon gluon fusion
Measured via e+e-, +-, e,
eX, X
Need more P4L
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
18
Relative Luminosity
Biggest systematic uncertainty
Need to control R to < 10-4 for low x measurements
Beam-Beam Counters (BBC)
++
L++ L-- N BBC
R = +- = -+ = +L
L
N BBC
PHENIX:
Δη = ±(3.1 to 3.9), Δφ = 2π
STAR:
Δη = ±(3.3 to 5.5)
Cross checked with ZDC:
<2.5 mrad (>6)
Different physics signal, different kinematic region
ALL of BBC relative to ZDC is ~0
Results-200 GeV i.e. for PHENIX, STAR very similar
2005: R ~ (25)10-4 ALL ~ (13)10-4
2006: R ~ (7.5)10-4 ALL ~ (8.2)10-4
2009: R ~ (14)10-4 ALL ~ (8.2)10-4
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
19
Dq: W Production Basics
Since W is maximally parity violating
W’s couple only to one parton helicity
large Δu and Δd result in large asymmetries.
u
No Fragmentation !
d
Similar expression for W- to get Δ
E.C. Aschenauer
and Δd…
INT-Workshop, Orbital Angular Momentum in QCD, 2012
20
expectations for ALe in pp collisions
de Florian, Vogelsang
t large
strong sensitivity to
E.C. Aschenauer
u large
t large
u large
limited sensitivity to
INT-Workshop, Orbital Angular Momentum in QCD, 2012
21
Central region: W e from Run9
Triggered by energy in EMCal
Momentum from energy in EMCal
Charge from tracking in B field
STAR: |e|<1
PHENIX: |e|<0.35
e+
eL=12 pb-1
L=8.6 pb-1
e+
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
e22
Measured Cross Sections
Reconstruction efficiency
determined from MC
Acceptance from NLO
calculation with PDF
uncertainty folded in
Good agreement between
experiment and theory over
wide kinematic range
arXiv:1112.2980
s Wtot( Z) × BR ( W ( Z ) ® en ( ee )) =
E.C. Aschenauer
NWobs( Z) - NWbkgd
( Z)
L × e Wtot( Z) × AW ( Z)
INT-Workshop, Orbital Angular Momentum in QCD, 2012
23 23
W Cross Section Ratio: RW
STAR
Ratio of W+ to W- cross sections
sensitive to unpolarized sea quark
flavor asymmetry
Complementary to fixed-target DY
and LHC collider measurements
arXiv:1112.2980
PRL 80, 3715 (1998)
obs
bkgd
tot
s W+ NW+
- NW+
e W+
u(x1 )d (x2 ) + d (x1 )u(x2 )
RW =
= obs
× tot =
bkgd
s W- NW- - NW- e W- u(x1 )d(x2 ) + d(x1 )u(x2 )
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
24 24
ALW: First proof of principle Run-09
P=0.39
L=8.6/12 pb-1 in PHENIX/STAR
PHENIX: PRL106, 062001 (2011)
STAR:
PRL106, 062002 (2011)
STAR
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
25
Future STAR W Measurements
Forward GEM Tracker
upgrade
6 light-weight triple-GEM
η=1
disks using industrially
produced GEM foils
Partial Installation for 2012
η=2
FGT
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
26 26
PHENIX: Forward -Arm upgrade
MuID Trigger existing:
Selecting momentum
> 2 GeV
E.C. Aschenauer
MuTRG (fully installed):
Fast selection of high
momentum tracks
RPC 1 & 3 (installed):
Provide timing and rough
position information
INT-Workshop, Orbital Angular Momentum in QCD, 2012
27
PHENIX Forward Arm: W
trigger eff.
First data collected in 2011:
L~15 pb-1 P~0.52
Data being analyzed
Raw yields with different triggers and cuts
trigger rejection
Expected W yield
More challenging than We at ~0
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
28
W l : Projections
PHENIX: W
PHENIX: We
STAR: We
S/B = 5
Lumi: 300 pb-1 &
60% polarisation
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
29
Dq from Hyperon Spin Transfer
STAR
PRD 80 111102 (2009)
Future:
Can improve statistics at ||<1 significantly
Go to more forward rapidities
W.Zhou, PRD81,057501,2010
2005 Data at √s=200 GeV
Caveat:
many theoretical models, but
L is product of hyperon decays
--> Impact on Dq ????
E.C. Aschenauer
√s=500 GeV at 2.5<<3.5
INT-Workshop, Orbital Angular Momentum in QCD, 2012
30
ALW: Future Possibilities
Can we increase p-beam energy?
325 GeV: factor 2 in sW
access to lower x for Dg(x)
ALW: pp @ 500 GeV
ALW: He3-p @ 432 GeV
Increased beam-energy and polarized He-3 beam full flavor separation
phase 2 of pp2pp@STAR can separate scattering on n or p
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
31
Critical √s of W cross section
s w (650GeV)
~2
s w (500GeV)
Main issues:
Quench performance of magnets (DX, arc dipoles and quads, IR quads)
Crossing angles at IPs and luminosity
estimated # of training quenches
Polarization
Current feed-throughs
Power supplies and transformers
polarised He-Beams
Dump kicker (strength, pre-fires)
had a aat
workshop
to discuss possibilities
Reliability generallyreduced
higher energies
https://indico.bnl.gov/conferenceDisplay.py?confId=405
Report: W. MacKay
BNL C-A/AP/422
no show stoppers, but need additional snakes in RHIC
Conclusion:
many ideas to increase luminosity of RHIC
techniquely
challenging,
CEC magnets
10% increase to275
GeV feasible
with i.e.
current
about 20 DX, 10 other training quenches, more cooling at some current leads
Requires some hardware upgrades (power supplies)
Effect on polarization still needs study
Energies >275 GeV require too many training quenches
hundreds of arc dipole training quenches alone for 325 GeV
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
32
What can be done in polarized pp
constraining Jg
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
33
From pp to gp
Get quasi-real photon from one proton
Ensure dominance of g from one identified proton
by selecting very small t1, while t2 of “typical hadronic size”
small t1 large impact parameter b (UPC)
Final state lepton pair timelike compton scattering
timelike Compton scattering: detailed access to GPDs
including Eq;g if have transv. target pol.
Challenging to suppress all backgrounds
Final state lepton pair not from g* but from J/ψ
Done already in AuAu
Estimates for J/ψ (hep-ph/0310223)
transverse target spin asymmetry calculable with GPDs
AUT (t ,t) ~
t0 - t Im(E * H)
mp
|H|
M J2 /Y
t=
s
information on helicity-flip distribution E for gluons
golden measurement for eRHIC
Work in collaboration with Jakub Wagner, Dieter Mueller, Markus Diehl
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
34
phot on-phot on
ples are nuclear
air and meson
. T he exchange
i, yielding large
al st at es t o low
riment al signahe first observauct ion, AuAu →
ccompanied by
Au ρ0 . Ult ralaborat ory for
o fixed-t arget ρ0
meson exchange, as indicat ed by t he rise of t he ρ product ion cross sect ion wit h increasing energy in lept onnucleon scat t ering [6]. In addit ion t o coherent ρ0 product ion, t he exchange of virt ual phot ons may excit e t he nuclei. T hese processes are assumed t o fact orize for heavyion collisions, which is just ified by t he similar case of
two-phot on int eract ions in relat ivist ic ion collisions accompanied by nuclear breakup, where it was shown t hat
t he non-fact orisable diagrams are small [7]. T he process
AuAu → Au Au ρ0 is shown in Fig. 1b. In lowest order,
mut ual nuclear excit at ion of heavy ions occurs by t he exchange of two phot ons [8, 9]. Because of t he Coulomb
What is feasible
Thomas Ullrich and Tobias Toll have written an MC for exclusive
VM / DVCS production in ep & eA
Modified to UPC in AA
a)
Au
→ AuAuρ (c.f.
s¨acker-Williams
e vect or meson
by one nucleus
scat t ers elast inuclei are not
olely of t he two
uct s [5]. In t he
#*
0
!
P
Au
b)
Au
Au
#*
²
!
²
P
Au
Au
²
²
Au*
#*
#*
Au*
a: elastic scattering
b: nucleus breaks up by emitting neutrons
ZDC
FIG. 1: Diagram for (a) exclusive ρ0 product ion in ult raperipheral heavy ion collisions, and (b) ρ0 product ion wit h
nuclear excit at ion. T he dashed lines indicat e fact orizat ion.
Also modified for UPC in pp
AuAu Au+Au+r
First simulations underway
cross sections agrees with
hep-ph/0310223 s ~ 6.2 nb
STAR has good acceptance for J/psi
Roman-Pots to tag exclusivity
SATRE still needs to be
tracked through the
STAR-MC to get
resolution effects included
Good agreement
Need to do full rate estimate
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
35
UPC in polarized pp collisions
STAR
Phase-I (installed): for low t-coverage
Phase-II (proposed): for high t-coverage
No special b* running needed any more
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
36
NYC,BNL and RHIC are beautiful
Summary
and the GIANTS
won the Superbowl
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
37
BACKUP
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
38
How do the partons form the spin of protons
Is the proton looking like this?
DG
SqDq
q
Lg SqLq
f1T
SqL
q
SqDq
DG
f1T
q
Lg
“Helicity sum rule”
gluon
spin
1 = P, 1 | J z | P, 1 = 1S z + S z + Lz + Lz
q
g å q
g
2
2 QCD 2 å
q 2
q
total u+d+s
quark spin
E.C. Aschenauer
Where do we stand
solving the “spin puzzle” ?
angular
momentum
INT-Workshop, Orbital Angular Momentum in QCD, 2012
39
Probing the Proton Structure
EM interaction
Photon
Sensitive to electric charge2
Insensitive to color charge
Strong interaction
Gluon
Sensitive to color charge
Insensitive to flavor
Weak interaction
Weak Boson
Sensitive to weak charge ~ flavor
Insensitive to color
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
40
What We Measure
Two-spin helicity asymmetry:
ALL
versus
1 N++/L++ N+/L+
P1P2 N++/L++ + N+/L+
Can be large in pQCD hard scatter.
Stat. Unc. ~ (P12P22 L dt )1/2
One-spin helicity asym. AL violates parity
if non-vanishing, but can be large in weak
processes like W prod’n.
Single-spin transverse asym.
N/L N/L
AN 1
P1 N/L + N/L
versus
E.C. Aschenauer
where () are defined with
respect to reaction plane, is
suppressed by chiral symmetry in
pQCD hard scatter, but can occur
via non-pert. aspects of initial and
final-state spin dynamics.
Stat. Unc. ~ (P12 L dt )1/2
INT-Workshop, Orbital Angular Momentum in QCD, 2012
41
Inclusive Jet Cross Section
pT [GeV/c]
pT [GeV/c]
• Data well described by NLO pQCD when including hadronization
and underlying event corrections from PYTHIA
• Hadronization and UE corrections more significant at low jet pT
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
42 42
Inclusive Jet Asymmetry at s=200 GeV
STAR: Large acceptance
Jets have been primary probe
Not subject to uncertainties on
fragmentation functions, but need to
handle complexities of jet
reconstruction
ALL systematics
(x 10 -3)
Reconstruction
+ Trigger Bias
[-1,+3]
(pT dep)
p
+
e
p
Non-longitudinal ~ 0.03
Polarization
p
(pT dep)
Relative
Luminosity
0.94
Backgrounds
1st bin ~
0.5
Else ~ 0.1
pT systematic
6.7%
Helicity asymmetry measurement
GRSV curves and data with cone radius R= 0.7 and -0.7 < < 0.9
E.C. Aschenauer
STAR
INT-Workshop, Orbital Angular Momentum in QCD, 2012
4343
Studying Gluon Polarization at RHIC
s ++ - s +- Dfa Dfb
ALL = ++
µ
aˆ LL
+s +s
fa fb
Partonic fractions in jet
production at 200 GeV
0
10
E.C. Aschenauer
20
30 pT(GeV)
INT-Workshop, Orbital Angular Momentum in QCD, 2012
44
Correlation pT – x and √s
2-2.5 GeV/c
4-5 GeV/c
9-12 GeV/c
low pT low x
scale uncertainty
high √s low x
forward rapidity low x
2-2.5 GeV/c
4-5 GeV/c
9-12 GeV/c
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
45
Star: Forward Physics program
add electromagnetic calorimetry at forward rapidity
access low and high x
TPC:
TPC:
BEC:
BEC:
-1.0
-1.0
-1.0
-1.0
<
<
<
<
<
< 1.0
1.0
<
< 1.0
1.0
E.C. Aschenauer
2003: FPD: 3.3 < < 4.1
2008: FMS: 2.5 < < 4.1
INT-Workshop, Orbital Angular Momentum in QCD, 2012
46
STAR Forward Pion
Detectors Permit
Study of Hadron
Prod’n @ High
Rapidity
Pb-glass arrays
S
N
High-energy p0 in this
region are predominantly
high-z fragments from
asymmetric q-g scattering
@ moderate pT
<z>
<xq>
NLO pQCD
Jaeger,Stratmann,Vogelsang,Kretzer
<xg>
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
47
How to disentangle Sivers and Transversity
Sivers:
AN for direct photons
AN for jets
AN for dijets
AN for Ws
AN for heavy flavour gluon Sivers
Transversity:
AN for angular modulation of p in around jet axis
Interference fragmentation function
proton spin
parton
kTx
x
y
z
BUT
Processes Universality vs non-universality:
Semi-Inclusive deep inelastic scattering ✔
Drell-Yan ✔
✔ Watch out for sign flips !
e+/e- annihilation ✔
p + p h1 + h2 + X ! !
TMD PDF is not just non-universal,
arXiv:1102.4569
it is ill-defined at the operator level !
work has started to fix this problems
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
48
2009 Inclusive Jet ALL
Separate into two η bins which sample different partonic kinematics
Models predict a ~20% reduction in ALL from |η|<0.5 to 0.5<|η|<1
Data falls between DSSV and GRSV-STD in both ranges
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
49 49
Charged pions opposite jets
ALL
ALL
Trigger and reconstruct a jet, then look
for a charged pion on the opposite side
Correlation measurement significantly
increases the sensitivity of ALL(π+)
Full NLO calculations for this observable:
de Florian, arXiv:0904.4402
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
50 50
W → e + ν Candidate
Event
• Isolated track pointing to isolated
EM deposit in calorimeter
• Large “missing energy” opposite
electron candidate
Di-jet Background Event
• Several tracks pointing to EM
deposit in calorimeter spread
over a few towers
• Vector pt sum is balanced by
opposite jet, “missing energy” is
small
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
51 51
W/Z Algorithm Description
Match high pT track to BEMC
cluster
Isolation Ratios
Signed-Pt Balance
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
52 52
Background Estimation
Sources:
EWK: W -> τ , Z -> e+e-
QCD: Data-driven
Good Data/MC agreement
E.C. Aschenauer
INT-Workshop, Orbital Angular Momentum in QCD, 2012
53 53
RHIC: AL for W bosons
RHIC: can detect only decay leptons;
lepton rapidity most suited observable
de Florian, Vogelsang, arXiv:1003.4533
• strong correlation with x1,2
allows for flavor separation for 0.07 < x < 0.04
Δχ2 = 2% uncertainty bands
of DSSV analysis
E.C. Aschenauer
Δχ2 = 2% uncertainty bands
with RHIC data
INT-Workshop, Orbital Angular Momentum in QCD, 2012
54