future d g measurements at star

Future DG Measurements at STAR

Renee Fatemi University of Kentucky

RHIC Spin Meeting, LBNL, November 21st 2009


Discussion Outline

Where we started.Where we are now.Where should we go next?When have we gone far enough?


“Pre-RHIC” and “Mid-RHIC” D & DG in DSSV Framework

DeFlorian, Sassot, Stratmann and Vogelsang, Phys.Rev.Lett. 101:072001, 2008DeFlorian, Sassot, Stratmann and Vogelsang, Phys.Rev.D 80:034030, 2009

Q2 =10 GeV


STAR DG DATAInclusive Jets

Inclusive neutral pions

Inclusive charged pions

DG data covers only one decade in X compared to the 3 decades for D.

Need to lower/raise X reach.

Quark-gluon scattering in forward regions provide access to low x gluons.

Move to higher center of mass scattering energies while measuring same kinematic range

DG data (to date) integrates over X range while DIS/SIDIS accesses X directly.

Need to reduce integration bins in X.

Correlation data – di-jets and photon-jets.

RANGE

X mapping


X Mapping Techniques

Increased sensitivity to XBJ in Run 9 via Di-jets @ 200 GeV

LO and NLO track fairly closely

West BEMC + EEMC provides access to lowest x values!

EBEMC+EEMC harder to measure due to smaller partonic aLL. But can access same kinematics in E+W BEMC. RHIC Spin Meeting, LBNL, November 21st

2009

EBEMC+EBEMC

EBEMC+EEMC

WBEMC+WBEMCWBEMC+EEMC

EBEMC+WBEMC

2exp 43

21ηη

sMx,x


Framework 2009 Dijet ALL prepared

Dijet X-sec from 2005 New preliminary result shown at DNP in October Corresponds with West-West BEMC x range Good agreement with NLO


Photon-jets @ 200 GeV in Run9

Very clean and sensitive to partonic XBJ.

Relatively rare and difficult to measure.

LOTS of development on algorithms and simulations. Plot shows STAR sensitivity for :

pT,γ > 10 GeV/c 1.09 < ηγ < 2 (EEMC) √s = 200 GeV 50 pb-1 @ 60% pol.

DOES NOT INCLUDE: Efficiency and background effects


Charged and Neutral pion channels @ 200 GeV

Continue to look at

inclusive channels with

increased precision.

While moving toward jet-hadron correlation measurements.

NLO calculations show a strong correlation between the real x and z values and LO estimates from jet – hadron measurements.

de Florian Phys. Rev. D79:114014, 2009


Run 6 Inclusive Jets @ 200 GeV

Leading systematics, such as trigger + reconstruction bias, are reduced as constraints on DG increase.

The stats from

requested Run 9 @ 200 GeV

The stats from

received Run9 200

GeV

xT = 2 pT / √s


Extending X reach


Moving to higher CM Energies

Higher √s WILL provide access to lower x gluons BUT this does NOT automatically translate into increased sensitivity to DG at low x.

The sub-process fractions are stable WRT to XT and the low “x” region is still dominated by gluon-gluon scattering.

DG is not large so we must enhance our sensitivity by using the larger valence quark analyzing power.

Optimize for qG scattering! Gluon goes forward and quark stays at mid-rapidity.

Di-jet Projections for 300 pb-1 @ 500 GeV

Lower x reach Brings smaller ALL Assumes 30 pb-1 at

70% polarization

EB+EB

EB+EE

WB+WB

WB+EE

EB+WB

Inclusive Jet Projections for 100 pb-1 @ 500 GeV


What does this xT range correspond to? Very small ALL and errors! DSSV error ~0.0025 in this region so error bars bigger than this loose their utility quickly….

Stat Uncerts

only


How far should we go?

EMC Collaboration Nucl. Phys. B328, 1 (1989)

1) Current situation very different compared to D. Apparent 2 decades ago from the EMC data that g1

p was saturating.

2) Measuring a small DG gives little indication about rest of integral.

3) What mechanisms limit sea quark polarization at low/high x? These mechanisms must also limit gluon polarization at low/high x.

4) How do you construct a reasonable functional form from the mechanisms in 3)?

… as far as we can!… until integral saturates?… range covered by D?


How do we sensible draw conclusions about the unmeasured part of the integral?


Summary STAR’s inclusive measurements have had a strong impact on the determination DG.

If our goal is to measure DG as precisely as we have measured DS then we have to change our tactics.

Get a better grasp on functional form via correlation measurements. Dijets, jet-hadron correlations and photon-jets will allow more direct map from pT to x.

Expand x range by 1 higher precision inclusive measurements at

higher roots2 play the eta game – using polarized q to access

low x gluons.


Dijet Kinematics

Inclusive jet projection for 500 GeV Run 11

Assume 100 pb-1 sampled at an average polarization of 50% JP2+AJP take-all threshold at 13 GeV (same as Run 9)

~250 Hz at C-AD projected max possible lumi ~120 Hz at C-AD projected final average lumi

Above figure assumes a JP1 trigger at 7.3 GeV with <ps> = 30 ~100 Hz at C-AD projected final average lumi

If an additional ~100 Hz is tolerable, a better choice would be: ~100 Hz with JP thr ~ 5.5 GeV (i.e., Run 9 pp200 JP1 thr) ~100 Hz with JP thr ~ 9 GeV (split diff with take-all level)

future d g measurements at star

Documents

nlo rhic spin meeting

pionsrhic spin meeting

gevrhic spin meeting

x range

real x

low x gluons

low x region

westwest bemc x