Constraining D g with p 0 ALL: Experimental issues

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Constraining D g with p 0 ALL: Experimental issues. Kieran Boyle Stony Brook University December 4, 2006. Tell them what you will tell them. Outline. The Concept p + p  p 0 + X The Equation A LL The Measurement Luminosity How do you define a collision Relative Luminosity

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### Constraining Dg with p0 ALL:Experimental issues

Kieran Boyle

Stony Brook University

December 4, 2006

Tell them what you will tell them

Outline

• The Concept
• p + p p0 + X
• The Equation
• ALL
• The Measurement
• Luminosity
• How do you define a collision
• Relative Luminosity
• Why do we need it
• What can go wrong
• Polarization
• Total Polarization
• Quick and Dirty (CNI)
• Slow and accurate (Hpol jet)
• Local Polarimetry (Which way is Pol. Pointing?)
• p0 yields
• How to reconstruct
• p0 background reduction
• The Results
• The “Theoretical” inputsWhat does the data say about Dg

2

Tell Them: The concept
• One lesson we all surely learned at ECT:
• How can we get Dg?

with DS ~25%, Dg not well constrained, DL ?

l, k’

(SI)DIS:

Clean but mostly colorblind

l, k

h

Dq

Dg

Hard Scattering Process

p0

P+P:

Dirty but colorful

Dg2

DgDq

Dq2

3

p+p  Dg ?
• Theorist says:
• is hard to calculate (LO, NLO, etc.) but with lots of effort it’s done
• So theorist tell experimentalist to “simply” measure:

-

Ds =

4

where , is rapidity

p+p  Dg ?
• Experimentalist replies:

bias Trigger bias

From experimental data

geom Geometrical acceptance

From MC

reco Reconstruction efficiency (cut efficiencies)

From MC or/and experimental data

smear Smearing effect (due to finite resolutions):

From MC

Each efficiency has a systematic uncertainty (~1-10%), which makes measuring a (small) difference difficult

where

5

p+p  Dg ?
• Compromise
• If Df = Dq, then we have this from pDIS
• So roughly, we have

From ep (&pp)

(HERA mostly)

From e+e-

pQCD NLO

+- =

+

=

++

+

6

But why is ALL any better?
• We can write

and that e can give large systematics

• So then

ALL =

Assume f++ = f+-

i.e. helicity independent

7

BRAHMS & PP2PP (p)

PHENIX (p)

STAR (p)

Does f++ = f+- ?
• Only if efficiencies don’t change between ++ and +- measurementdetector stability between Polarization flips.
• Examples:
• SMC: Solid or liquid targetflip takes 1 hour, so do it every 8 hours
• Hermes: gas targetflip on the order of seconds(s)
• RHIC: Polarized bunchflip every bunch=every 106ns

RHIC CNI (pC) Polarimeters

Absolute Polarimeter

(H jet)

RHIC allows a great reduction in systematics

Spin Rotators

Siberian Snakes

Partial Siberian Snake

LINAC

BOOSTER

Pol. Proton Source

AGS

AGS Internal Polarimeter

200 MeV Polarimeter

Rf Dipoles

8

How Do We Actually Measure ALL?
• The ingredients:
• Luminosity (L):
• How do we measure it?

 Relative Luminosity (R)

• How do we define a collision\event?
• Measurement
• Systematic uncertainty
• Polarization (P)
• Magnitude
• Direction (Is it really longitudinal?)
• p0 yield (N)
• How do we get p0’s?

9

From Astrid Morreale

LUMINOSITY

Luminosity is the number of particles per unit area per unit time times the

Opacity of the target, usually expressed in either the cgs units cm-2 s-1 or b-1 s-1.

The integrated luminosity is the integral of the luminosity with respect to time.

The luminosity is an important value to characterize the performance of an accelerator.

Where

• L is the Luminosity.
• N is the number of interactions.
• ρ is the number density of a particle beam, e.g. within a bunch.
• σ is the total cross section.
• dΩ is the differential solid angle.
• is the differential cross section
• For an intersecting storage ring collider:
• f is the revolution frequency
• n is the number of bunches in one beam in the storage ring.
• Ni is the number of particles in each beam
• A is the cross section of the beam.

}

n, A, N1, N2 all have uncertainty:

stat. and systematic

Can we reduce uncertainty?
• Well Luminosity can be written as
• With this definition, we can use the same trick:

What are you saying?!?

Assume s++ = s+- for ppX

i.e. helicity independent

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BBC

How do you define an event?

Calculate

c*(T1-T2)/2

c=spd of light

We call this Minimum Bias (minbias) trigger

2.887m

0.6m

14

8

But Why Use Relative Luminosity?
• Consider a game of pool (billiards)
• There is no physical asymmetry in whether a collision can occur (If they get close enough they collide in both a and b).
• However, we will see an asymmetry as there is more likelihood of collision on table a.

a) High Luminosity “Bunch”

a) Low Luminosity “Bunch”

b) Low Luminosity Bunch

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Relative Luminosity
• Calculate Relative Luminosity using BBC defined collisions.
• Due to a feature of RHIC, one spin pattern has 3 less bunches that the other, and so we end up with two “structures” in Relative Luminosity (one with ++ with more bunches, the other with +- with more bunches).
• Statistical uncertainty <0.00001

A fill is defined as from beam injection to beam dump, ~7-8 hours long.

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But does s++ = s+-
• Not always (otherwise there is no point measuring ALL)
• Consider two different luminosity detectors (here, the BBC and ZDC)
• Assume each has some asymmetry in what they measure (ABBC and AZDC)
• Look at ratio
• Fit this with

where ALL is the asymmetry in the ratio.

• We find ALL consistent with zero, which implies:
• ALL|BBC = ALL|ZDC
• Now the physics measured by BBC (charged hadrons with 3<|h|<4) and ZDC (neutrons with |h|>6) are different. So it is unlikely for them to be non zero and equal.
• Take uncertainty on ALL|BBC to be uncertainty in ALL of p0 from R.

17

Polarization—Magnitude

(I am not an expert on this)

Forward scattered proton

slow, low statistics but absolute

Quick, high statistics, relative

proton target

BRAHMS & PP2PP (p)

RHIC proton beam

recoil proton measure!

Carbon target

PHENIX (p)

90º in Lab frame

STAR (p)

Recoil carbon

Polarized proton

Polarimetry at RHIC

RHIC CNI (pC) Polarimeters

Absolute Polarimeter

(H jet)

Spin Rotators

Siberian Snakes

Partial Siberian Snake

LINAC

BOOSTER

Pol. Proton Source

AGS

AGS Internal Polarimeter

200 MeV Polarimeter

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Rf Dipoles

and Carbon proton

Single spin asymmetry

Double spin asymmetry

Physics topics of pp elastic scattering in the CNI region
• Described using Helicity Amplitudes 1~ 5
• Interaction matrix M; Nuclear + Coulomb force
• Nuclear and Coulombforces become similar in size at –t~10-3 (GeV/c)2.
• They interfere with each other Coulomb Nuclear Interference

spin non–flip

double spin flip

spin non–flip

double spin flip

single spin flip

Well known

Unpolarized pp elastic scattering experiment

 Very small

No one photon exchange contribution to ANN.  Sensitive to 5had and 2had !

20

Ultra thin Carbon ribbon Target

(3.5mg/cm2)

6

1

3s Mass cut

15cm

carbon

2

5

non-relativistic kinematics

Time of Flight (ns)

MC ~ 11.17 GeV

sM ~ 1.5 GeV

Si strip detectors

(TOF, EC)

3

4

prompts

alpha

Thin dead layer for low energy

carbon spectroscopy

Invariant Mass

2mm pitch 12 strips

Energy (keV)

10mm

p+ implants

~150 nm depth

With alternating spin pattern (+,-,+,-)

square-root formula

72 strips in total

CNI Detector setup
• Particle ID (banana cut)
• Clear separation from backgrounds using TOF measurement

So we know Pbeam if we know AN

21

Forward scattered proton

JET target

FWHM ~6.5mm

RHIC 24, 100GeV/c proton beam ~1mm

Recoil particle

JET

80cm

left

Si detectors

Measuring AN: Two in One

proton beam

proton target

Recoil proton

goal

scaling uncertainty

right

22

BRAHMS & PP2PP (p)

PHENIX (p)

STAR (p)

Transverse

Longitudinal

(Transverse)

Use Spin Rotators

Spin rotators are partial siberian snakes, and can rotate the polarization direction to many different orientations.

RHIC CNI (pC) Polarimeters

Absolute Polarimeter

(H jet)

Spin Rotators

Siberian Snakes

Partial Siberian Snake

LINAC

BOOSTER

Pol. Proton Source

AGS

AGS Internal Polarimeter

200 MeV Polarimeter

Rf Dipoles

24

ZDC

Run 5

charged

particles

neutron

But How Longitudinal is Longitudinal?
• We have to check if we have or
• Take a look at transverse spin asymmetries:
• Charged/Neutral pion in forward (large xF) direction is seen, so why not use that? (STAR actually does something like this)
• PHENIX cannot measure

forward pions (before

J. Koster et al. built MPC)

• A. Bazilevsky et al.

(hep-ex/0610030) found a

very forward neutron

asymmetry at RHIC.

• When beam is

longitudinal,

asymmetry0

by parity

25

p

p

Charged

particles

Neutral

particles

Neutral

particles

How do you measure forward neutrons?
• Using 3 ZDC units, we can measure the majority of the neutron shower, and remove photon showers by excluding events which do not deposit energy in each unit.

Yellow

Blue

26

Raw asymmetry

SMD

Raw asymmetry

YELLOW

BLUE

f

f

Raw asymmetry

Raw asymmetry

YELLOW

BLUE

f

f

X

Y

How do you measure AN for neutrons?
• To measure asymmetry, we need position. For this, we use a Shower Maximum Detector (SMD)
• Detector consists of a grid of horizontal and vertical scintilator strips.
• Get X,Y position and calculate f position.

X

Y

27

LR

c2/NDF = 82.5/97

p0 = -0.00423±0.00057

c2/NDF = 88.1/97

p0 = -0.00323±0.00059

UD

XF>0

XF>0

UD

c2/NDF = 119.3/97

p0 = -0.00056±0.00063

c2/NDF = 81.7/97

p0 = -0.00026±0.00056

LR

XF<0

XF<0

Measured Asymmetry During Longitudinal Running

<PT/P>=

10.25±2.05(%)

<PL/P> =

99.48±0.12±0.02(%)

<PT/P>=

14.47±2.20(%)

<PL/P> =

98.94±0.21±0.04(%)

28

Fill Number

Fill Number

Remaining Transverse ComponentATT
• Here
• ATT
• azimuthally independent double transverse spin asymmetry.
• ALL background (e<0.01).
• expected to be small, but previously unmeasured.
• In Run5, PHENIX took a short transverse run specifically to measure ATT.
• Consistent with zero.
• Possible systematic contribution to ALL <0.07dALL.

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g

g

p0

p

p

X

p0
• Why measure p0?
• Very abundant in p+p collisions
• Decay is 99.9% p0gg
• PHENIX is designed for very good photon and electron measurements
• p0 are easy to measure with our limited acceptance
• Kinematics
• Two clusters with energy E1 and E2
• Then

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CARTOON

#

Combinatorial background

Mgg

p0

h

g-g Invariant Mass Spectrum
• We actually take all clusters that resemble photons, and calculate an invarient mass

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h

g

Apply Some Cuts to the Data
• Shower Shape:
• Calculate c2 based on energy distribution. Remove clusters with less than 2% of being a photon.
• Calibrated with test beam data
• Time of Flight (ToF)
• Can accurately measure collision time and detection time.
• Remove slow (low E) hadrons.
• Charge Veto
• Some hadronic clusters survive shower shape and ToF.
• Use detector of charged particles about 20 cm in front of EMCal to remove some remaining charged hadrons

33

p0 Cross Section
• Consistent with previous PHENIX results.
• NLO pQCD Theory is consistent with data over nine orders of magnitude.
• As theory agrees well with our data, we can use it to interpret our results in terms of Dg

35

Calculating p0 ALL
• Calculate ALL(p0+BG) and ALL(BG) separately.
• Get background ratio (wBG) from fit of all data.
• Subtract ALL(BG) from ALL(p0+BG):

ALL(p0+BG) = wp0· ALL(p0) + wBG · ALL(BG)

p0+BG region :

±25 MeV around

p0peak

BG region :

two 50 MeV regions

around peak

37

### The Result and (Possible) Interpretation

Run6 p0 ALL (200 GeV)
• Run6 Data set from filtered data requiring a high pT photon
• Data below 5 GeV limited statistics due to filter, so must wait full production.
• GRSV curves are parameterizations using different input parameters for Dg, at an input scale of Q2=0.4 GeV

GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 63 (2001) 094005.

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• Confidence levels from a simple c2 test between our data and the four curves plotted.
• Theoretical uncertainties are not taken into account (for now).

Range is from varying ALL by polarization scale uncertainty

* At input scale: Q2 = .4 GeV2

• Run 6 rules out maximal gluon scenarios.
• Expect clearer statement when lower pT data from Run6 is available; possibly will allow differentiation between STD and Dg=0.

40

x

p0 Does a Lot to Constrain Dg

So if Dg>0, p0 provides a

powerful constraint of Dg.

AAC

Or Not?

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Conclusions (What I told you)
• Experimentalist measure ALL to reduce systematic uncertainties.
• Each element for measuring in ALL has been described.
• Systematic uncertainties have been considered
• Results for p0 ALL from 2005 and (partial) 2006 have been shown.
• Simple c2 interpretation on the results clearly exclude Dg=g, and also exclude Dg=-g.
• 2006 low pT will add to the current constraint on Dg.
• AAC found that 2005 give a significant constraint on Dg if we assume Dg>0.

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