february 10, 2011wwnd: winter park, colorado1 upsilon production and upsilon + hadron correlations...

February 10, 2011 WWND: Winter Park, Colorado 1

Upsilon Production and

Upsilon + Hadron Correlations

Matthew Cervantes for the STAR Collaboration

Texas A&M University, Cyclotron Institute


• Physics Motivation

* Study quarkonium suppression as a signature of QGP

* Study the prompt production mechanism of heavy quarkonium

• Experiment

* Accelerator: Relativistic Heavy Ion Collider (RHIC)

* Detector: Solenoidal Tracker at RHIC (STAR)

* STAR Upsilon trigger

• Upsilon

* STAR Upsilon results

* Upsilon + Hadron correlation

• Summary and Outlook

Outline


QGP and Heavy Quarkonia• In a QGP the high energy density of the medium

“deconfines” the J/ and bound states. Deconfinement could lead to suppression of measured J/ and yields in data.

• At RHIC, J/ may be regenerated (i.e. “regeneration” of cc)

• At RHIC, the collision energy is NOT high enough to allow copious production of bottom anti-bottom quarks. is not expected to undergo regeneration (bb << cc).

• Measurements of J/ and at STAR will help us understand the properties of the QGP.

• Establish base line measurements in p+p collisions (e.g. base line for the melting of the (1S, 2S, 3S) states in a QGP).

• Collisions in p+p can also be used to study the prompt production mechanism of heavy quarkonium.

-

-


STAR data (Cu+Cu) of J/ at high-pT shows a lack of suppression. May indicate that J/ cannot exist in a colored state on a long enough timescale to be affected by the medium. (STAR Collaboration, Phys. Rev. C 80, 041902(R) (2009))

Historically, not fully described by models, the Color Singlet Model (CSM) and the Color Octet Model (COM).

Prompt production of Heavy Quarkonium

CSM: Historically the calculations under-predicted the production cross section, but recent development with higher-order corrections (Lansberg J.P., arXiv:0811.4005v1) can describe data better.

COM: Success in explaining the pT spectra of quarkonia. Polarization prediction disagrees with experimental data. (e.g CDF Collaboration, Phys. Rev. Lett. 99 (2007) 132001)

J/

(2S)

Looking for new ways to study the prompt production mechanism of heavy quarkonium at STAR experiment.

J/ is the only hadron that does not exibit high-pT suppression at RHIC.

Lack of J/ suppression at high-pT suggests production is not dominated via a color channel.


STAR

• Circumference (3.834 km)

• Species (pp, dAu, CuCu, AuAu)

• Energy (200, 500) GeV


Large geometrical acceptance (-1 < < 1 and = 2 increased ability to study heavier (larger opening angle) vector mesons such as e+e-

STAR Detector for measurement

• Time Projection Chamber (TPC)

• Acceptance: || < 1.4 , 0 < < 2

• Tracking => momentum• e ID: ionization energy loss

dE/dx• Barrel Electromagnetic Calorimeter

(BEMC)• Acceptance: || < 1 , 0 < < 2• e ID : p/E• High-energy tower trigger• Good efficiency => essential for

luminosity limited measurement


charged tracks

STAR trigger: BEMC L0+L2

• L0 (hardware)– High energy tower

• ET > 4.3 GeV

• L2 (software)– High energy tower cluster

pair• E1 > 4.5 and E2 > 3.0 GeV

– Loose cut on cos(θ)• θ is the 3D opening angle

– Cut on Mee= √[2E1E2(1-cos(θ))]

Large acceptance BEMC L0+L2 trigger: Great di-electron trigger for luminosity limited

measurements

e+

e-

Event Display: One d+Au 200 GeV event as seen by the TPC in STAR


Upsilon invariant mass: p+p (2006)

PhysRevD.82.012004

Ph

ysR

evD

.82.0

12004


STAR p+p cross section theory/world data

* STAR data point agrees with CEM at NLO (Phys. Rept. 462, 125 (2008))

* CSM underestimates STAR data by 2 (PRD 81, 051502 (2010))

* STAR data consistent with world data trend


Upsilon invariant mass: d+Au (2008)

• Signal + Background unlike-sign electron pairs• Background like-sign electron pairs• (1S+2S+3S) total yield: integrated from 7 to 11 GeV from background-

subtracted mee distribution– Raw Yield: 172 +/- 20 (stat.)– Strong signal (8σ significance) Nucl.Phys. A830: 235c-238c (2009)

H. Liu, QM 2009 No inner silicon detectors (SVT + SSD), reduced material in 2008

Integrated luminosity of 32 nb-

1 ~ 12.5 pb-1 (p+p equivalent)


Nuclear modification factor

)(20.0)(28.078.0 sysstatRdA


signal region: Mass window of 8.0 to 10.5 (11.5) GeV used

in making the association of Upsilon candidates to hadrons.

Upsilon invariant mass : p+p (2009)

p+p 2009

(2S+3S)

(1S) ~ 9.46 GeV/c2

(2S) ~ 10.02 GeV/c2

(3S) ~ 10.36 GeV/c2

Relative to 2006 p+p:

* Less material budget

* Integrated luminosity ~ 3x higher

Relative to 2006 p+p:

* Increased luminosity provides

smaller error in the baseline

S/B region higher than the 2006 p+p measurement:

(S/B) ~ 5.76


- The prompt quarkonium production mechanism in hadronic collisions include direct production via gluon fusion and CSM and COM transitions.- Multiple soft gluon emission expected with an during the prompt production in COM.

CSM COM

Associated Hadronic Activity

Possible indication of prompt production via COM: an increase in the hadronic activity found in the vicinity of a promptly produced .


Hadronic activity directly around the heavy quarkonium has been suggested as an experimental observable to measure the radiation emitted off the colored heavy quark pair during production. (Kraan, A. C., arXiv:0807.3123v1 [hep-ex] 19 Jul 2008)

Upsilon + Hadron Correlations

* Sum of the hadronic pT within defined radius (R) of the was previous method by A.C. Kraan:

R = sqrt [() 2 + ()2 ]

* Observation of this effect in simulation (PYTHIA).

* We search for the increase in hadronic activity coming from the radiated gluons using the similar but alternative method of “azimuthal correlations”.

– correlation measurement

LHC-like energies


• Physics Goal: Investigate prompt production mechanism by looking for an increase in the hadronic activity on the near-side peak.

* Gluon emission on near-side indicative of COM?

• STAR detector configuration for d+Au (2008) and p+p (2009) provides an almost background-free Upsilon. High S/B provides a clean opportunity to perform the Azimuthal correlation.

• Analysis: Run 8 d+Au 200 GeV collisions (~ 32 nb-1 integ. lum.)

• Analysis: Run 9 p+p 200 GeV collisions (~ 20 pb-1 integ. lum.)

+ h correlation: physics goal


Run 8 d+Au data (left) Run 9 p+p data (right)

In d+Au data, correlation is not significant relative to the underlying-event.

In p+p data, PYTHIA has a similar underlying-event.

*RAW: - correlation is not corrected for efficiency and acceptance.

- correlation (*RAW): Data vs. PYTHIA


STAR Upsilon results:

p+p at √s=200 GeV:

d+Au at √s=200 GeV:

p+p at √s=200 GeV (2009 integrated luminosity ~20 pb-1):

Heavy Quarkonium prompt production mechanism:

* + h correlation being studied as a way to investigate heavy prompt production

* spin-alignment studies also being studied in parallel with the + h correlation

Summary and Outlook

Bee×(dσ/dy)ϒ+ϒ’+ϒ”y=0 = 114±38+23-24pb

(σDY+σbb)|y|<0.5,8<m<7 GeV/c2 = 38±24 pb

Bee×(dσ/dy)ϒ+ϒ’+ϒ”y=0 = 35±4(stat)±5(syst)nb

RdAu= 0.78±0.28(stat)±0.20(syst)

** Reduced material ** Reduced uncertainty for RdAu ** Possible separation of ϒstates


Summary and Outlook (cont.)

A large area of muon telescope detector (MTD) at mid-rapidity, allows

for the detection of:

1) di-muon pairs from QGP thermal radiation, quarkonia, light vector

mesons, possible correlations of quarks and gluons as resonances in

QGP, and Drell-Yan production

2) single muons from the semi- leptonic decays of heavy flavor hadrons

3) advantages over electrons: no conversion, much less Dalitz decay

contribution, less affected by radiative losses in the detector materials, trigger capability in Au+Au

4) trigger capability for low to high-pT J/ in central Au+Au collsions,

excellent mass resolution, separate different upsilon states e-muon

correlation to distinguish heavy flavor production from initial lepton

pair production

STAR-MTD Physics Motivation

The prototype of MTD works at STAR from Run 7 to Run 10:

The results published are at L. Ruan et al., Journal of Physics G: Nucl. Part. Phys. 36 (2009)095001; 0904.3774; Y. Sun et al., NIMA 593 (2008) 430.


Backup…


is the angle between the direction of the e+ momentum, measured in the ’s rest frame with respect to the ’s direction of motion, i.e. the polarization axis.

Upsilon Spin-Alignment

i.e. boost the to its rest frame, then boost e+ and e- into the rest frame, and then measure (e+ direction w.r.t. direction of motion)

= (T - 2L)/(T + 2L)

e

e

= -1, 0, +1 reflects longitudinal, zero, or transverse polarization.

= 1

= 0

= -1

1 +

c

os

2

Parameterize the measurement to quantify the polarization.


- Spin-alignment (“polarization”) of the during the prompt production for CSM vs. COM.

CSM:

COM:

Prompt production: Observable II

Octet quarkonia

inherits thetransverse polarization of the gluon.

No strong correlation between the initial

gluon polarization and final state.

J/ (2S

)

J/ (2S

)


Upsilon Spin-Alignment (pT > 0 GeV/c)Corrections

from embedding needed before the fit can be performed and anything about the polarization value can be stated.

p+p 2009

= 1

= 0

= -1

1 +

c

os

2

february 10, 2011wwnd: winter park, colorado1 upsilon production and upsilon + hadron correlations...

Documents

winter park

star slide

e e star detector

star upsilon trigger

p p equivalent slide

rhic star

star upsilon results

star data point