e.c. aschenauer why run top-energy p+p in run-16 2 transverse momentum dependent parton distribution...

WHY RUN TOP-ENERGY P+P IN RUN-16

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WHY ARE TMDs INTERESTING

E.C. AschenauerWhy run top-energy p+p in run-16

Transverse momentum dependent parton distribution functions initial state effects

important in calculating cross-sections in a range of processes provide a way to image the proton in transverse and longitudinal

momentum space (2+1d) provide access to spin-orbit correlations provide constrains to quark-gluon-quark correlations are important to describe the gluon distribution at low-x CGC the most popular explanation for the large AN seen in transverse

p+p

of special interest: The Sivers function, it describes the correlation of the parton transverse momentum with the transverse spin of the nucleon.

Transverse momentum dependent fragmentation functions final state effects

describe a correlation of the transverse spin of a fragmenting quark and the transverse momentum of a hadron

Collins FF

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INITIAL STATE: TMDs VS. TWIST-3

QLQCD QT/PT <<<<QT/PT

Collinear/twist-3

Q,QT>>LQCD

pT~Q

Transversemomentumdependent

Q>>QT>=LQCD

Q>>pT

Intermediate QT

Q>>QT/pT>>LQCD

Sivers fct.Efremov, Teryaev;

Qiu, Sterman

Need 2 scalesQ2 and pt

Remember pp:most observables one scale

Exception:DY, W/Z-production

Need only 1 scaleQ2 or pt

But should be of reasonable size

should be applicable to most pp observables

AN(p0/g/jet)

E.C. Aschenauer

related through

Why run top-energy p+p in run-16

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HOW TO STUDY TMDs IN P+P

E.C. Aschenauer

Initial State Final State AN as function of rapidity, ET, pT and xF for inclusive jets, direct photons

AN for heavy flavour gluon

AN as a function of rapidity, pT for W+/-, Z0, DY

AUT as a function of the azimuthal dependence of the correlated hadron pair on the spin of the parent quark (transversity x interference FF)

Azimuthal dependences of hadrons within a jet (transversity x Collins FF)

AN as function of rapidity, pT and xF for inclusive identified hadrons (transversity x Twist-3 FF)TMD, TWIST-3, Collinear


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VISUALIZE COLOR INTERACTIONS IN QCD

DIS: gq-scatteringattractive FSI

pp: qqbar-anhilation

repulsive ISIQCD:

SiversDIS = - SiversDY or SiversW or SiversZ0

Measure non-universality of sivers-function

E.C. Aschenauer

All three observables can be addressedthrough a 500 GeV Run

AN(direct photon) measures the sign change in the Twist-3 formalism

Critical test of fa

ctorization in QCD

no sign change need to rethink

QCD factorization


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much stronger thenany other knownevolution effects

needs input fromdata to constrainnon-perturbative

part in TMD evolution

current data extremely limitedfurther constraints

cannot come from fixedtarget SIDIS

too small lever arm in Q2 & pt

NOTE:the same evolution applies

to TMD FFs, i.e. Collinsand to e+e-,

SIDIS eRHIC

SURPRISE: TMD EVOLUTION

E.C. Aschenauer

Z. Kang: original paper arXiv:1401.5078Z.-B. Kang & J.-W. Qui arXiv:0903.3629

before evolutionafter evolution

÷ ~10

4 < Q < 9 GeV0 < qT 1 GeV

DY500 GeV

200 GeV

Z.-B. Kang & J.-W. Qui Phys.Rev.D81:054020,2010

÷ ~4

Z. Kang et al. arXiv:1401.5078before evolution

after evolution


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WHAT ELSE CAN WE LEARN

E.C. Aschenauer

What is the sea-quark Sivers fct.? W’s ideal rapidity dependence of AN separates quarks from antiquarks no constraint from existing SIDIS data

Z. Kang AN (W+/-,Z0) accounting for sea quark uncertainties through positivity boundsall plots after evolution (arXiv:1401.5078)


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WHERE DO WE STAND

E.C. Aschenauer

proof of principle analysis by STAR (S. Fazio for the collaboration, DIS-2014)Need to reconstruct W kinematics as lepton asymmetry cannot be resolved due to resolution effects

Apply analysis technique developed at the Tevatron and used at LHCi.e. CDF PRD 70, 032004 (2004)Philosophy: W l+ n as n is not seen reconstruct W through lepton and recoil


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STAR: ANW

E.C. Aschenauer

Analysis Strategy to fully reconstruct Ws:Follow the analysis steps of the AL W candidate selection via high pt leptonData set: 2011 transverse 500 GeV data (25 pb-1)

In transverse plane:

Recoil reconstructed using tracks and towers:

Part of the recoil not within STAR acceptance

correction through MC (Pythia) MC-correction


Why to run transvers pp in run-1610

W Rapidity reconstruction: W longitudinal momentum (along z) can

be calculated from the invariant mass: Neutrino longitudinal momentum

component from quadratic equation

STAR: ANW

E.C. Aschenauer

GOOD data/MC agreement

Systematics determined through a MC challenge methodinput asymmetries from arXiv:1401.5078 and reconstruct it back

Measuring the sign change through DY

STAR is investigating in detail if sensitive

DY measurements are possible

using several forward-upgrade scenarios

The biggest challenge is

QCD-background suppression of 106-107

106-107

QCD

DY


WHAT CAN WE DO IN RUN-16

E.C. Aschenauer

Assumptions: integrated delivered luminosity of 400 pb-1

7 weeks transversely polarized p+p at 510 GeV electron lenses are operational and dynamic b-squeeze is used throughout the fill

smoothed lumi-decay during fills reduced pileup effects in TPC high W reconstruction efficiency

Will provide data to constrain TMD evolution sea-quark Sivers fct

test sign-change if TMD evolution ÷ ~5 or less


WHY NOW?

E.C. Aschenauer

HP13 is being pursued also by others, notably COMPASS

knowledge about TMD evolution influences many other projects/plans physics of RHIC forward upgrades

pp/pA-LoI flavor separation of transversity and Sivers fct. AN for DY

TMD physics of an EIC STAR will not benefit from a luminosity increase for these

measurements TPC is pile-up limited luminosity numbers in the pp/pA LoI charge correspond to ~5

multiple interactions per bunch needs LHC technologies/techniques

no new SIDIS input to constrain non-perturbative component in TMD-evolution before EIC

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Note:similar capabilities with PHENIX MPC-EX

COMPLEMENTARY CHANNEL

E.C. Aschenauer

AN for direct photon production:

STAR FMS-PreShower:

3 layer preshower in front of the FMS, distinguish photons, electrons/positrons and charged hadrons installed for RUN-15

sensitive to sign change, but in TWIST-3 formalism not sensitive to TMD evolution no sensitivity to sea-quarks; mainly uv and dv at high x collinear objects but more complicated evolutions than DGLAP indirect constraint on Sivers fct.

Not a replacement for a AN(W+/-, Z0, DY) measurementbut an important complementary piece in the puzzle


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SUMMARY

E.C. Aschenauer

AN(W+/-,Z0) AN(DY) AN(g)

sensitive to sign change through TMDs

yes yes no

sensitive to sign change through Twist-3 Tq,F(x,x)

no no yes

sensitive to TMDevolution

yes yes no

sensitive to sea-quark Sivers fct.

yes yes no

need detector upgrades

no yesat minimum: FMS

postshower

yesinstalled for run-15

biggest experimental challenge

integrated luminosity

background suppression &

integrated luminosity

need to still proove analysis on data

AN(W+/-,Z0) clean and proven probe sensitive to all questions in a timely way without the need for upgrades


e.c. aschenauer why run top-energy p+p in run-16 2 transverse momentum dependent parton distribution...

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