Columbia University Christine Aidala September 2005 Transverse Spin at Results and Prospects Transversity 2005, Como

Columbia UniversityChristine Aidala

September 2005

Transverse Spin at

Results and Prospects

Transversity 2005, Como

C. Aidala, Transversity 2005, September 2005

2

RHIC’s Experiments

Transverse spin only (No rotators)

Longitudinal or transverse spin

Longitudinal or transverse spin

Also pp2pp, pC, and polarized H jet polarimeters studying polarized elastic

scattering


3

AGSLINACBOOSTER

Polarized Source

Spin Rotators

200 MeV Polarimeter

AGS Internal Polarimeter

Rf Dipole

RHIC pC Polarimeters Absolute Polarimeter (H jet)

PHENIX

PHOBOS BRAHMS & PP2PP

STAR

AGS pC Polarimeter

Partial Snake

Siberian Snakes

Siberian Snakes

Helical Partial SnakeStrong Snake

Spin Flipper

RHIC as a Polarized p-p Collider

Various equipment to maintain and measure beam polarization through acceleration and storage


4

The PHENIX Collaboration 13 Countries; 62 Institutions; 550 Participants as of 3/05


5

The PHENIX Detector2 central spectrometers- Track charged particles and detect electromagnetic processes

2 forward spectrometers- Identify and track muons

2 global detectors- Determine when there’s a collision

Philosophy: High rate capability & granularity Good mass resolution and particle ID Sacrifice acceptance


6

PHENIX Detector (cont.) Central arms

Photons, electrons, identified charged hadrons

|| < 0.35 = 180 degrees

Forward muon armsTrack and identify muons

1.2 < || < 2.4

Beam-beam counters Charged particles

3.0 < || < 3.9

Zero-degree calorimetersNeutrons

4.7 < || < 5.6


7

Spin Running at PHENIX So Far

• 2001-2– Transversely polarized p+p

collisions– Average polarization of ~15%– Integrated luminosity 150 nb-1

– Figure of merit (P2L) 3.38 nb-1

• 2003– Longitudinally polarized p+p

collisions achieved– Average polarization of ~27%– Integrated luminosity 220 nb-1


• 2004– 5 weeks commissioning, 4 days

data-taking– Average polarization ~40%– Integrated luminosity 75 nb-1


• 2005– Average polarization ~48%– Integrated longitudinal lumi

3.59 pb-1

– Figure of merit (P4L) ~1.9 pb-1

– Integ. transverse lumi 0.163 pb-1

– Figure of merit (P2L) 0.038 pb-1


8

ATT

Proton Spin Structure at PHENIX

Prompt Photon LLA (gq X)

Transverse Spinu u d d , , ,

u u d d

Flavor decomposition

L lA (u d W ) T

,

A p p ( , ) X

I nterference fragmentation:

NSingle Asymmetries A

GGluon Polarization

Production LLA (gg,gq X) W Production

L lA (u d W )

Heavy Flavors LLA (gg cc,bb X)


9

Current Context for Transverse Measurements at PHENIX

• STAR and BRAHMS measurements at 200 GeV– Non-zero asymmetries for forward pions

• Coverage: STAR xF > 0.2, BRAHMS xF > 0.15

– Potential contributions from multiple mechanisms

– AN consistent with zero for backward pions and forward protons

• HERMES and COMPASS Sivers and Collins results• BELLE measurement of non-zero Collins FF for pions

– Input for further interpretation of observed and future asymmetries!


10

AN

xF*100

Transverse single-spin asymmetries for +, -, and proton production at BRAHMS

Preliminary

xF < 0

Raw asym

PreliminaryRaw asym

pT (GeV/c)

protons


11

AN of Mid-rapidity Neutral Pions and Charged Hadrons: Final Results

hep-ex/0507073Submitted to PRL

|| < 0.35

AN for both charged hadrons and neutral pions at mid-rapidity consistent with zero to within a few percent.


12

• NLO pQCD consistent with data within theoretical uncertainties.

• PDF: CTEQ5M

• Fragmentation functions:• Kniehl-Kramer-Potter (KKP)Kniehl-Kramer-Potter (KKP)

• Kretzer

• Spectrum constrains D(gluon ) fragmentation function

• Factorization applicable, with small scale dependence

hep-ex/0507073

|| < 0.35

Mid-rapidity Cross Section Measurements

9.6% normalization error not shown

PRL 91, 241803 (2003)

|| < 0.35

0


13

Mid-rapidity Partonic Processes

• Particle production at mid-rapidity at these transverse momentum values mostly from gluon scattering– AN results should constrain

gluon Sivers (U. d’Alesio’s discussion)

• Future measurements reaching higher pT dominated by quark scattering, thus more sensitive to transversity + Collins

0

Fraction

's producedLarge asymmetries observed due to

valence quarks?


14

Other (So Far Unpolarized) Mid-rapidity Measurements

Direct ’s

(Published for pT < 7 GeV/cas Phys. Rev.

D71:071102, 2005)

PHENIX Preliminary

— Fit to data


15

Mid-rapidity Cross Sections (cont.)

Non-photonic electrons


16

Forward-Backward Neutrons and Charged Particles

• Zero-degree calorimeters (ZDC)– Hadronic calorimeters– Neutrons, 4.7 < || < 5.6

• Beam-beam counters (BBC)– Quartz Cherenkov detectors– Charged particles, 3.0 < || < 3.9


17

Forward neutrons (ZDC) at 200 and 410 GeV: AN ~ -11%

Backward neutrons (ZDC): AN consistent with zero

Neutron Asymmetry vs.

(Raw

Asy

mm

etry

) / (

bea

m

pol

.)

Vertical polarization

Radial polarization


18

• Inclusive forward charged particles (BBC): AN consistent with zero

• Forward charged (BBC) in forward-neutron-tagged (ZDC) events:

• Backward charged (BBC) in forward-neutron-tagged (ZDC) events: 210)10.055.028.2(

210)22.050.050.4(

Forward-Backward Neutrons and Charged Particles (cont.)

p

N*(*) n+X

Y

Diffractive-like process?

AN(X) < 0, AN(Y) > 0

p


19

Upcoming Transverse Spin Measurements at PHENIX

• 2005 data– Similar transverse statistics to 2001-02, but ~3x

higher polarization

– Improved mid-rapidity measurements of 0, h+/- AN

– More detailed study of forward and backward neutrons at 200 and 410 GeV

– Forward and backward stopped hadrons (mostly pi and K)

– AN of forward and backward muons


20

2005 Expected Muon Measurements

• Single inclusive muons from 2005 data– Mostly pion and kaon decays

– pT 0.5-5.0 GeV/c

– xF 0.02-0.11 GeV/c• More data in the future will allow access to higher xF

– 1.2 < || < 2.4– Eventually separate into prompt muons (heavy flavor)

and muons from light meson decays• Decay muons have enhanced K/ ratio, K/ ~ 1


21

Upcoming Transverse Spin Measurements at PHENIX (cont.)

• 2006 or 2007: Expect long spin run at RHIC– PHENIX anticipates 5-20(?) pb-1 transverse data, 60-70% polarization

• Depends on machine performance • 2006 Beam-Use Proposal under development this month

• studies• AN of mid-rapidity single electrons—open charm• Forward-backward single muon studies to higher xF

• Forward-backward J/ AN (note forward cross section already published)

• ATT measurements possible (but not yet for DY)

• Back-to-back jets to probe Sivers– Because of PHENIX central arm acceptance, better to run with radial than

vertical polarization


22

Jet Asymmetry Due to Sivers

• Non-zero Sivers function implies spin-dependence in kT distributions of partons within proton

• Would lead to an asymmetry in of back-to-back jets

• Trigger doesn’t have to be a jet or leading particle, but does have to be a good jet proxy– Studies being done for high-pT photon + away-

side charged hadron

0

2

h

Boer and Vogelsang, Phys.Rev.D69:094025,2004

anti-alignedaligned

Run03 -charged dn/d

(Schematic)


23

Di-Hadrons vs. Di-Jets

updownunpolarized

away side parton AN

di-hadrondi-jet

• Don’t reconstruct jets fully—use di-hadron correlations to measure jet . • Smears out di-hadron AN relative to the di-jet AN, with smearing function g (assumed here to be a gaussian, with jT=0.35).

'))('()'())()((

'))('()'()())()(()(

dxdxxxxgxNxN

dxdxxxxgxAxNxNA

dijetdijet

dijetNdijetdijetdihad

N

Broadens and slightly lowers asymmetry, but still measurable


24

PHENIX Detector Upgrades(longitudinal)

Also: silicon endcaps covering muon arm acceptance (1.2 < || < 2.4) - forward-backward charm and B physics hadron-blind detector for 2 electron coverage at mid-rapidity - open charm, electronic decays of J/, , . . .

Transverse spin possibilities with planned upgrades not yet fully explored!


25

Summary• Final 2002 PHENIX results for mid-rapidity 0

and charged hadron asymmetries now available (hep-ex/0507073)– consistent with zero within a few percent

• PHENIX forward neutron asymmetry of -11% observed at 200 and 400 GeV– Backward neutron asymmetry consistent with zero

• Significant non-zero results for forward and backward charged particles in events with a forward neutron


26

Summary (cont.)• Muon arm results expected from 2005 data• Di-jet Sivers measurement expected 2006 or 2007• Forward upgrades will improve access to kinematic

region where large asymmetries have been observed • Mid-rapidity upgrades will improve jet measurements

• Present RHIC results at forward, backward, and mid-rapidity suggest large SSA’s a valence quark effect?– Significance of BRAHMS zero proton asymmetries?

• Some overlapping, some complementary coverage and capabilities of PHENIX with other experiments should allow upcoming measurements to gradually put together a cohesive picture of proton transverse spin structure


27

Extra Slides


28

Single Transverse Collision

Hard Scattering Process

2 2x P

1 1x P

s

qgqg

)(0

zDq

X

q(x1)

g(x2)

1P

2P

left

right


29

Unpolarized Results from Run03 p+p

anti-alignedaligned

•Asymmetry

•numerator is difference between aligned and anti-aligned dist’s, where aligned means trigger jet and spin in same direction•denominator is simply unpolarized distribution

•On left are some theoretical guesses on expected magnitude of AN from Siver’s•On right are gamma-charged hadron dist’s from Run03 p+p

•2.25 GeV gamma’s as jet trigger, 0.6-4.0 GeV charged hadrons to map out jet shape•Dotted lines are schematic effect on away side dist due to Siver’s Fn (not to scale)

NA

Run03 -charged dn/dBoer and Vogelsang, PRD69:094025,2004


30

Obtaining the (Spin-Dependent) 0 Yields• 18M events used • Central spectrometer

arms || < 0.35– 0 via 0 – Electromagnetic

calorimeter (EMCal)• Lead scintillator calorimeter

(PbSc)

• Lead glass calorimeter (PbGl)

0 width ~10-15 MeV/c2


31

EMCal-RICH Trigger• 2x2 tower non-overlapping energy sum

• Threshold ~ 0.8 GeV

• Also used in conjunction with RICH to form an electron trigger

2x2 Trigger in 2001-2002 run.

Min. Bias range

~14 GeV/c

0 trigger efficiency

0 5 10PT (GeV/c)

0.78 0.03+_

Min. Bias range

~14 GeV/c

0 trigger efficiency

0 5 10PT (GeV/c)

0.78 0.03+_


32

Handling Background in the 0 Asymmetry

Invariant mass (GeV/c2)

- 50-MeV/c2 windows around the 0 peak (60-110 and 170-220 MeV/c2)- 250-450 MeV/c2 (between 0 and )

• Eliminate as much background as possible using EMCal cluster shower shape cut and charged veto• Calculate asymmetry of (signal + background) in the 0 mass window• Calculate the asymmetry of two different background regions as an estimate of the asymmetry of the background under the peak• Subtract the asymmetries

r

rAAA

bkgN

bkgN

N

1

0

0


33

Obtaining Charged Hadron Yields

• 13M events used• Event vertex from

BBC’s• Track reconstruction

from – vertex

– drift chamber

– pad chambers

BBC

PC1 PC1

PC3PC3

DCDC


34

Background in h+/h- Sample• Note that tracking detectors in

PHENIX are outside the magnetic field

• Assume track originates at event vertex, then measure momentum based on deflection angle observed at drift chamber

• Low-momentum tracks that don’t originate from the vertex may be misreconstructed with higher momentum – Conversion electrons– Decay products from long-lived

particles (K+-, K0L)


35

Background in h+/h- Sample (cont.)

• RICH veto to eliminate electrons– Electron threshold 0.017 GeV/c– Pion threshold 4.7 GeV/c– < 1% electron contamination in final sample

• Estimate decay background from long-lived particles from tracks with reconstructed pT > 9 GeV/c but that didn’t produce a hit in the RICH– < 5% in final sample


36

AN of Neutral Pions and Charged Hadrons: Systematic Checks

• Independent results from two polarized beams

• Independent results from two detector arms (luminosity formula)

• Comparison of square-root and luminosity formulas

• Fill-by-fill stability of asymmetry

• Effects of background on 0 asymmetry– Integrate over different ranges of photon-pair invariant

mass

– Measure and subtract asymmetry of two different background invariant-mass regions


37

Forward Neutron Asymmetry at RHIC

• Large and negative (-11%)

• Observed at 200 and 410 GeV

• ~Zero for backward neutrons

• Why large asymmetry for forward neutrons but not forward protons?? (But admittedly not same kinematics)

AN = 0.110±0.015

preliminary


38

BBC Asymmetry• Forward neutron, forward BBC, left-right

- 9!• Forward neutron, backward BBC, left-right

- No significant asymmetry in backward ZDC

tagged data or in top-bottom asymmetry. Systematic error doesn’t include AN

CNI error.

210)22.050.050.4(

210)10.055.028.2(

K.Tanida

p

N*(*) n+X

Y

• Diffractive-like process

AN(X) < 0, AN(Y) > 0

pp

n

X

p

• kick-out/recoil picture

AN(X) > 0, AN(Y)??


39

Converter subtraction methodWe defined as • P : the yield of the photonic component• N : the yield of the non-photonic component• A : All electron yield in the non-converter data set• C : All electron yield in the converter data set• Rsim : the ratio of the photonic electron in converter to non-converter data set

• The following relation holds between those variables C = Rsim * P + N A = P + N

• Therefore P and N can be determined as P = ( C – A ) / ( Rsim – 1) N = ( Rsim * A – C ) / ( Rsim – 1)

** All parameter have pt dependence.

Documents

Columbia University Christine Aidala September 2005 Transverse Spin at Results and Prospects Transversity 2005, Como