e.c. aschenauer why run top-energy p+p in run-16 2 transverse momentum dependent parton distribution...
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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
Why run top-energy p+p in run-16
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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
Why run top-energy p+p in run-16
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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
Why run top-energy p+p in run-16
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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)
Why run top-energy p+p in run-16
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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
Why run top-energy p+p in run-16
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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 run top-energy p+p in run-16
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
Why to run transvers pp in run-1611
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 to run transvers pp in run-1612
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
Why run top-energy p+p in run-16
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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
Why run top-energy p+p in run-16