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 d g with p 0 all experimental issues

Constraining Dg with p0 ALL:Experimental issues

Kieran Boyle

Stony Brook University

December 4, 2006


Tell them what you will tell them

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

Tell Them: The concept

  • One lesson we all surely learned at ECT:

  • How can we get Dg?

withDS ~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 d g

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


P p d g1

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 d g2

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 a ll any better

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


Does f f

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 a ll

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


Luminosity

Luminosity


Constraining d g with p 0 all experimental issues

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

    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

    12


    Relative luminosity

    Relative Luminosity


    How do you define an event

    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


    But why use relative luminosity

    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

    15


    Relative luminosity1

    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.

    16


    But does s s

    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

    Polarization—Magnitude

    (I am not an expert on this)


    Polarimetry at rhic

    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

    19

    Rf Dipoles


    Physics topics of pp elastic scattering in the cni region

    and Carbon proton

    Hiromi Okada, Spin2006

    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


    Cni detector setup

    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


    Measuring a n two in one

    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


    Polarization direction

    Polarization—Direction


    Use spin rotators

    BRAHMS & PP2PP (p)

    PHENIX (p)

    STAR (p)

    Transverse

    Longitudinal

    Radial

    (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


    But how longitudinal is longitudinal

    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


    How do you measure forward neutrons

    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


    How do you measure a n for neutrons

    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


    Measured asymmetry during longitudinal running

    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 a tt

    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.

    29


    P 0 yield

    p0 Yield


    Constraining d g with p 0 all experimental issues

    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

    31


    G g invariant mass spectrum

    CARTOON

    #

    Combinatorial background

    Mgg

    p0

    h

    g-g Invariant Mass Spectrum

    • We actually take all clusters that resemble photons, and calculate an invarient mass

    32


    Apply some cuts to the data

    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


    G g invariant mass spectrum1

    g-g Invariant Mass Spectrum

    34


    P 0 cross section

    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


    The asymmetry

    The Asymmetry


    Calculating p 0 a ll

    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

    The Result and (Possible) Interpretation


    Run6 p 0 a ll 200 gev

    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.

    39


    What about d g

    What about Dg?

    • 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


    P 0 does a lot to constrain d g

    x

    p0 Does a Lot to Constrain Dg

    So if Dg>0, p0 provides a

    powerful constraint of Dg.

    AAC

    Or Not?

    41


    Conclusions what i told you

    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.

    42


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