1

Forward Physics• Origins of STAR Forward Meson Spectrometer

• Original physics goals for FMS and overview of implementation

• Run-8 FMS results, to date

• Outlook

L.C. Bland

STAR Review of FMS

1 September 2009

2

STAR

• Large acceptance near midrapidity

• Windows to large rapidity

3

Transverse Single-Spin Asymmetries (AN)

Probing for (1) orbital motion within transversely polarized protons;

(2) Evidence of transversely polarized quarks in polarized protons.

4

Origins of FMS

5

Run-2 Prototype FPDE

X STRIP Y STRIP

Eto

wer

YX

Prototype calorimeter located 750 cm (zvert) east of STAR interaction region

Typical single event:

PRL 92 (2004) 171801

6

Forward Production

• Measured large- cross sections consistent with pQCD calculations

• Large transverse single-spin effects observed for s = 200 GeV pp collisions

STAR collaborationPRL 92, 171801 (2004)

7

The STAR Forward Detector

Shower Maximum DetectorHorizontal and Vertical PlanesEach made of 48 strips of plastic scintillator with a wavelength shifting optical fiber through the center of eachMultianode PMTs

Pre-Shower Detector7 vertical lead-glass crystals with PMT+base.

Lead Glass Calorimeter7x7 matrix of 3.8cm x 3.8cm lead-glass crystals with PMT+base.

0 Rebecca Lamb, RPI undergraduate

(BNL/SULI program 1/03 – 5/03)

Lead-glass detectors built by IHEP, Protvino group for FNAL E-704 experiment.

8

STAR Forward p+p Cross SectionsSTAR Forward p+p Cross Sections

C~5 / B~6

PRL 97 (2006) 152302 D.A. Morozov, hep-ex/0512011

• Forward cross sections agree with NLO pQCD

• Cross sections used in DSS global analyses of fragmentation functions PRD 76 (074033) 2007

9

• PYTHIA 5.7 prediction agrees well with the inclusive 0 cross section at 3-4• Dominant sources of large xF production from:

● q + g q + g (22) + X

● q + g q + g + g (23) + X

g+g andq+g q+g+g

q+g

Soft processes

PYTHIA: a guide to the physicsForward Inclusive Cross-Section: Subprocesses involved:

q

gg

q g

STAR FPD

xF

hep-ex/0403012

10

Run-3 Results from FPDdAu/pp comparisons

PRL 97 (2006) 152302

• d+Au+X cross section suppressed relative to shadowing expectations

• d+Au+h± correlations are suppressed relative to p+p

Qualitatively consistent with color glass condensate model of gluon saturation

11

Runs 3-6 FPD Resultsp+p+X analyzing power

PRL 101, 222001 (2008)

Theory (blue): M. Boglione, U. D’Alesio, F. Murgia, PRD 77 (2008) 051502

Theory (red): C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, PRD 74 (2006) 114013

• AN(xF) consistent with Sivers function from semi-inclusive DIS (arXiv:0906.3918)

• AN(pT) does not decrease like (pT)-1, as expected by theory

1Brookhaven National Laboratory2University of California- Berkeley3Pennsylvania State University4IHEP, Protvino5Stony Brook University6Texas A&M University7Utrecht, the Netherlands

8Zagreb University

STAR Forward Meson SpectrometerF.Bieser2, L.Bland1, E. Braidot7, R.Brown1, H.Crawford2, A.Derevshchikov4, J.Drachenberg6, J.Engelage2, L.Eun3, M.Evans3, D.Fein3, C.Gagliardi6, A. Gordon1, S.Hepplemann3, E.Judd2, V.Kravtsov4, J. Langdon5, Yu.Matulenko4, A.Meschanin4, C.Miller5, N. Mineav4, A. Mischke7, D.Morozov4, M.Ng2, L.Nogach4, S.Nurushev4, A.Ogawa1, H. Okada1, J. Palmatier3, T.Peitzmann7, S. Perez5, C.Perkins2, M.Planinic8, N.Poljak8, G.Rakness1,3, J. Tatarowicz3, A.Vasiliev4, N.Zachariou5

These people built the Forward Meson Spectrometer (FMS) and/or its components

13

Three Highlighted Objectives In STAR Forward Meson Spectrometer Proposal

[hep-ex/0502040]

1. A d(p)+Aud(p)+Au+X+X measurement of the parton model gluon density distributions xg(x) in gold gold nucleinuclei for 0.001< 0.001< xx <0.1 <0.1. For 0.01<x<0.1, this measurement tests the universality of the gluon distribution.

2. Characterization of correlated pion cross sections as a function of Q2 (pT

2) to search for the onset of gluon saturation effects associated with macroscopic gluon fields. macroscopic gluon fields. (again d-Au)(again d-Au)

3. Measurements with transversely polarized transversely polarized protonsprotons that are expected to resolve the origin resolve the origin of the large transverse spin asymmetriesof the large transverse spin asymmetries in reactions for forward forward production. production. (polarized (polarized pp)pp)

DOE milestone

14

Guzey, Strikman and Vogelsang Guzey, Strikman and Vogelsang Phys. Lett. B603 (2004) 173Phys. Lett. B603 (2004) 173

PYTHIA Simulation PYTHIA Simulation

• constrain x value of gluon probed by high-x quark by detection of second hadron serving as jet surrogate.

• span broad pseudorapidity range (-1<<+4) for second hadron span broad range of xgluon

• provide sensitivity to higher pT for forward reduce 23 (inelastic) parton process contributions thereby reducing uncorrelated background in correlation.

15

• Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<<4 approaching full acceptance detector

FPD in far position

• 50 larger acceptance than run-3 FPD west-south module used for dAu

Run-8 Results from STAR Forward Meson Spectrometer

(FMS)

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FMS Detector ElementsLead Glass From FNAL E831

804 cells of 5.8cm5.8cm60cmSchott F2 lead glass

Loaded On a Rental Truck for Trip To BNL

See talk by A. Gordon

17

FMS High VoltageXP2972 (from E864) + Nanometrics CW bases powered by I2C controlled DAC (L. Eun)

FEU84 (from FNAL-E704 / IHEP) + PSU CW base (L. Eun)

XP2202 + resistive divider bases, powered by four LRS 1440 HV systems (A. Gordon)

5 Zener diodes per base

18

QT Readout / DSM Trigger

Front-end electronics and trigger (C. Perkins)

19

Software, Monitoring and Calibration Overview

• Event reconstruction from FPD extended to FMS (see L. Nogach and E. Braidot talks)

• Online monitoring mostly done from trigger data as written by L2 (see talk by A. Ogawa)

• LED system is the method to monitor FMS gain (see talks by A. Gordon and A. Ogawa)

• Calibrations are from reconstruction. Cell-by-cell calibrations partially fed back to HV settings (see talk by L. Nogach)

20

FMS Results

21

Run 8 FMS Inclusive 0 Results

Octant subdivision of FMS for inclusive spin sorting. arXiv:0901.2828

Nikola Poljak – SPIN08

• Azimuthal dependence as expected• AN comparable to prior

measurements

x

y

P

22

Negative xF

J. Drachenberg– SPIN08 arXiv:0901.2763Akio Ogawa – CIPANP 09

Positive xF

RHIC Run 8 with East FPD/FMSpT Dependence

Indication of Positive AN persists up to pT ~5 GeVNeeds more transverse spin running

Negative xF consistent with zero

23

First Look at “Jet-like” Events in the FMSEvent selection:

• “Jet shape” in data matches simulation well• Reconstructed Mass doesn’t match as well• High-Tower Trigger used in Run 8 biases Jets

• >15 detectors with energy > 0.4GeV in the event (no single pions in the event)• cone radius = 0.5 (eta-phi space)• “Jet-like” pT > 1 GeV/c ; xF > 0.2• 2 perimeter fiducial volume cut (small/large cells)

“Jet-shape” distribution of energy within jet-like objects in the FMS as a function of distance from the jet axis.

Nikola Poljak – SPIN08 (arXiv:0901.2828)

24

•Comparison to dAu •Spin-1 meson AN

High xF Vector MesonsRHIC Run 8 with FMS

Background only MCRun8 FMS dataFit is gaussian + P3

μ=0.784±0.008 GeV σ=0.087±0.009 GeV Scale=1339±135 Events

3 photon events to look for0BR

•PT(triplet)>2.5 GeV/c •E(triplet)>30 GeV•PT(photon cluster)>1.5 GeV/c •PT(π0)>1 GeV/c

Significant (10) 0 signal seen in the data.

A Gordon– Moriond09 (arXiv:0906.2332)

Triple Photons : 0

Next :

25

FMS Minbias Simulations and Association Analysis

• Fast J/ψ generator + full GEANT simulations

• Reconstructed quantities match generated quantities quite well

• Simulation : – PYTHIA 6.222 + full GEANT simulations– 9.2 nb-1 Integrated Luminosity

• Full simulation models Mpair data very well

• Data : – Plot includes < 1% of full data set

C.Perkins, QM09 (arXiv:0907.4396)

26

Fit with Gaussian + Offset

Gaussian Fit Parameters:– μ = 3.080 ± 0.020 GeV/c2

– σ = 0.082 ± 0.026 GeV/c2

– χ2/d.o.f. = 20.83/26– Significance from fit

• 4.5 σ

Forward p+p J/ψ – 2-Cluster Analysis

Cuts Applied:– E_pair > 60.0 GeV– Zγγ < 0.7– Isolation Radius:

Reconstructed 2-cluster invariant mass / (~ 6 pb-1 Sampled Luminosity)

– 0.4

– pT_cluster > 1.0 GeV/c

C.Perkins, QM09 (arXiv:0907.4396)

• high-xF J/ may have implications for intrinsic charm at large Bjorken-x in proton

• use to benchmark simulations for future transverse-spin Drell-Yan experiment

27

STAR Detector• Large rapidity coverage for electromagnetic calorimetry (-

1<<+4) spanning full azimuth azimuthal correlations

• Run-8 was the first run for the Forward Meson Spectrometer (FMS)

28

Azimuthal Correlations with Large E. Braidot (for STAR), Quark Matter 2009 (arXiv:0907.3473)

Unc

orre

cted

Coi

ncid

ence

P

roba

bilit

y (r

adia

n-1)

p+p+h±+X, s=200 GeV

requirements:

pT,>2.5 GeV/c

2.8<<3.8

h± requirements:

1.5<pT,h<pT,

h<0.9

• clear back-to-back peak observed, as expected for partonic 22 processes

• fixed and large trigger, with variable h map out Bjorken-x dependence

• of greatest interest for forward direct- trigger

29

Azimuthal Correlations (3)

++X

+h±+X

Un

corr

ect

ed C

oin

cid

ence

Pro

bab

ilit

y (r

adia

n-1)

-lead

p+p d+Au

“GSV” Selection “GSV” Selection

2.5 GeV/c<pT(=3)

1.5 GeV/c<pT(||<0.9)<pT

(=3)

dAu – pp = 0.09±0.04

“GSV” selection leads to clear back-to-back peak with similar pp/dAu widths as expected by pQCD

E. Braidot, QM09

E. Braidot (for STAR), Quark Matter 2009 (arXiv:0907.3473)

30

Azimuthal Correlations (3)

++X

+h±+X

Un

corr

ect

ed C

oin

cid

ence

Pro

bab

ilit

y (r

adia

n-1)

-lead

p+p d+Au

“lower-pT” Selection “GSV” Selection

2.5 GeV/c<pT(=3)

1.5 GeV/c<pT(||<0.9)<pT

(=3)

dAu – pp = 0.09±0.04

“lower-pT” Selection

2.0 GeV/c<pT(=3)

1.0 GeV/c<pT(||<0.9)<pT

(=3)

dAu – pp = 0.19±0.03

Evidence of pT dependent azimuthal broadening of signal

E. Braidot, QM09

E. Braidot (for STAR), Quark Matter 2009 (arXiv:0907.3473)

31

Forward 0 – Forward 0 Azimuthal Correlations

• Possible back-to-back di-jet/di-hadron Sivers measurement• Possible near-side hadron correlation for Collins fragmentation function/Interference fragmentation function + Transversity • Low-x / gluon saturation study – accessing lowest xBj

gluon

Akio Ogawa- CIPANP 09

32

SummaryFMS Results to Date

• Inclusive analyzing power results consistent with modular FPD results

• Forward + mid-rapidity h±/ azimuthal correlations are observed. The dAu results are consistent with pT dependent azimuthal broadening.

• Lowest Bjorken-x values are probed when forward pairs are observed. Clear near-side and away-side peaks are observed for p+p++X

• Large-rapidity production observed in p+p collisions at s=200 GeV

• Large-rapidity J/ production observed in p+p collisions at s=200 GeV

33

Run-8 Analysis Outlook

• Determine normalization for two-particle correlations

• Extract forward pair azimuthal correlations from dAu

• Clustering: towards +jet or jet+jet

• Pursue spin dependence of forward pairs and

34

Future Plans for FMS

• Extend p+p correlations to ~6, including spin dependence (Run 9, underway)

• Extend xF-pT map for forward J/ via multi-cluster triggered slow events (Run 9)

• Forward direct photons and spin dependence (see upgrades talk)

• Measure analyzing power for forward jets (see upgrades talk)

• Forward (see upgrades talk)