Nonperturbative Transverse Momentum Effects in Dihadron and Direct Photon-Hadron Angular Correlations Joe Osborn for the PHENIX Collaboration University of Michigan QCD-N’16, July 12, 2016 Joe Osborn (UM) QCD-N 2016 12/07/16 1 / 21
Universality and Factorization in TMDs Drell-Yan SIDIS Sign change in Sivers TMD PDF predicted due to initial-state vs. final-state gluon exchange with proton remnants between DY and SIDIS: modified universality! What about p + p → h 1 h 2 where both initial- and final-state interactions are possible? Joe Osborn (UM) QCD-N 2016 12/07/16 2 / 21
TMD Factorization Breaking Rogers and Mulders paper predicts QCD factorization breaking in dihadron production from p + p collisions in a TMD framework (Phys. Rev. D 81,094006 (2010)) Back-to-back two particle angular correlations give ≥ 2 gluons exchanged with sensitivity to initial- and proton remnants leads to final-state transverse predicted breakdown momentum k T and j T Joe Osborn (UM) QCD-N 2016 12/07/16 3 / 21
Direct Photons and Dihadrons Direct photon-hadron and dihadron correlations both predicted to be sensitive to factorization breaking effects in PHENIX Assuming factorization, direct photon-hadrons probe three nonperturbative functions, while dihadrons probe four Direct photons offer one less avenue for gluon exchange in the final-state: fewer/different effects? Joe Osborn (UM) QCD-N 2016 12/07/16 4 / 21
Angular Correlation Observables Direct photon-hadron production Dihadron production p out = p assoc sin ∆ φ T Joe Osborn (UM) QCD-N 2016 12/07/16 5 / 21
PHENIX Detector PHENIX central arms ∆ φ ∼ π | η | < 0.35 Electromagnetic Calorimeter (PbSc/PbGl) provides isolated direct photon and π 0 → γγ detection Drift Chamber (DC) and New results from Pad Chambers (PC) 2012/2013 √ s =510 GeV provide nonidentified p + p runs charged hadron detection Joe Osborn (UM) QCD-N 2016 12/07/16 6 / 21
∆ φ Correlations for π 0 -h ± and Direct γ -h ± trig ⊗ trig ⊗ trig ⊗ 8<p <9 1<p assoc <2 GeV/c 8<p <9 3<p assoc <4 GeV/c 8<p <9 5<p assoc <10 GeV/c 0.2 T T T T 0.1 T T γ ± 0.5 Isolated Direct -h p+p at s =510 GeV π ± 0 -h η | |<0.35 Underlying Event 0 0 0 -1 0 1 2 3 4 -1 0 1 2 3 4 -1 0 1 2 3 4 trig ⊗ assoc trig ⊗ assoc trig ⊗ assoc 9<p <12 1<p <2 GeV/c 0.2 9<p <12 3<p <4 GeV/c 9<p <12 5<p <10 GeV/c 0.1 T T T T T T -1 0.5 [rad] PH ENIX preliminary φ dN ∆ d trig 1 N 0 0 0 -1 0 1 2 3 4 -1 0 1 2 3 4 -1 0 1 2 3 4 trig ⊗ assoc 0.2 trig ⊗ assoc trig ⊗ assoc 12<p <15 1<p <2 GeV/c 12<p <15 3<p <4 GeV/c 12<p <15 5<p <10 GeV/c 0.1 T T T T T T 0.5 0 0 0 -1 0 1 2 3 4 -1 0 1 2 3 4 -1 0 1 2 3 4 ∆ φ [rad] Two jet structure visible for π 0 -h ± , isolation cut on near side for direct γ -h ± Direct γ -h ± probes smaller jet energy due to emerging from hard scattering at LO Joe Osborn (UM) QCD-N 2016 12/07/16 7 / 21
� � p 2 out � Extracted from Fits to ∆ φ Correlations 5 5 [GeV/c] [GeV/c] assoc γ ± assoc 1<p <2 GeV/c Isolated Direct -h 1<p <2 GeV/c π ± 0 -h T T 4 4 assoc PH ENIX assoc PH ENIX 2<p <3 GeV/c 2<p <3 GeV/c 〉 〉 T T out preliminary preliminary out 2 assoc p assoc 2 3<p <4 GeV/c 3<p <4 GeV/c p T 〈 T 3 〈 3 η | |<0.35 η | |<0.35 p+p at s =510 GeV p+p at s =510 GeV 2 2 1 1 0 0 4 5 6 7 8 9 10 11 12 13 14 4 5 6 7 8 9 10 11 12 13 14 trig trig p [GeV/c] p [GeV/c] T T � � p 2 out � characterizes away-side jet width and decreases with hard scale p trig T Sensitive to perturbative and nonperturbative k T and j T Joe Osborn (UM) QCD-N 2016 12/07/16 8 / 21
p out Distributions -1 2 p out shows two 10 π ± [GeV/c] 0 -h p+p at s =510 GeV trig 4<p <5 GeV/c 10 T η | |<0.35 trig -1 distinct regions: 5<p <6 GeV/c (x10 ) T 1 π π Gaussian Fit Range: [-1.1,1.1] GeV/c 2 4 γ ± trig -2 ∆ φ -h 6<p <7 GeV/c (x10 ) < < T -1 3 3 trig -3 out 7<p <8 GeV/c (x10 ) 10 gaussian and power dN assoc T 0.7<p <10 GeV/c trig -4 dp 8<p <9 GeV/c (x10 ) -2 10 T T trig -5 9<p <12 GeV/c (x10 ) law trig T -3 10 PH ENIX trig -6 1 12<p <15 GeV/c (x10 ) N T preliminary -4 10 Gaussian fits clearly -5 10 -6 10 fail past ∼ 1.3 -7 10 -8 GeV/c 10 -9 10 Indicates transition -10 10 -11 10 -8 -6 -4 -2 0 2 4 6 8 from p [GeV/c] out nonperturbative to Note: Curves are Kaplan and perturbative k T and Gaussian fits, not calculations!! j T Joe Osborn (UM) QCD-N 2016 12/07/16 9 / 21
Gaussian Widths of p out Gaussian widths of p out distributions decrease 0.8 Gaussian Width [GeV/c] with hard scale p trig γ PHENIX Isolated Direct PH ENIX π T PHENIX 0 preliminary γ PYTHIA Perugia0 Isolated Direct Sensitive to only π PYTHIA Perugia0 0 0.7 π η | |<0.35 0 Linear Fit γ nonperturbative k T and p+p at s =510 GeV Isolated Direct Linear Fit assoc 0.7<p <10 GeV/c T j T in the nearly Fit Range: [-1.1,1.1] GeV/c 0.6 back-to-back region ∆ φ ∼ π 0.5 PYTHIA replicates slope 4 5 6 7 8 9 10 11 12 13 14 trig almost exactly, but shows p [GeV/c] T 15% difference in magnitude of widths Joe Osborn (UM) QCD-N 2016 12/07/16 10 / 21
Expectations from Collins-Soper-Sterman (CSS) Evolution Expectation from CSS 5 evolution is that any Gaussian Width [GeV/c] PYTHIA Perugia0 Simulation Drell-Yan Dilepton momentum width lep p >4 GeV/c T η | |<0.35 sensitive to 4 p+p at s =510 GeV nonperturbative k T grows with the hard scale 3 Broadening due to increased phase space 2 20 30 40 50 60 70 80 90 100 2 M [GeV/c ] for hard gluon radiation µ µ PYTHIA confirms Note that the CSS expectation from CSS evolution equation comes evolution for same directly out of the observable derivation for TMD factorization Joe Osborn (UM) QCD-N 2016 12/07/16 11 / 21
SIDIS and DY/Z Measurements Phys. Lett. B 633, 710 (2006) (DY/Z) DY/Z and SIDIS, where factorization is predicted to hold, have been shown to follow CSS evolution Phenomenological studies in both interactions show increasing momentum widths when sensitive to small k T scale Phys. Rev. D 89, 094002 (2014) (SIDIS) Joe Osborn (UM) QCD-N 2016 12/07/16 12 / 21
Conclusions Factorization breaking has been predicted in p + p → h + X collisions for observables sensitive to nonperturbative transverse momentum New measurements from PHENIX of nearly back-to-back dihadron and isolated direct photon-hadron correlations at √ s =510 GeV Angular correlations sensitive to initial-state k T and final-state j T show decreasing momentum widths with hard scale in p + p → h + X Literature shows that Drell-Yan/Z and SIDIS interactions, which CSS evolution describes, exhibit increasing momentum widths with hard scale Paper draft undergoing internal review process! Joe Osborn (UM) QCD-N 2016 12/07/16 13 / 21
Back Up Joe Osborn (UM) QCD-N 2016 12/07/16 14 / 21
Analysis Methods Correlated π 0 − h ± or Probability for a π 0 to decay to a isolated γ − h ± are collected photon which could not be tagged and corrected with: with 5 < p T < 7 GeV/c in PHENIX Charged hadron efficiency Acceptance correction Direct photons undergo additional statistical subtraction to remove decay photon background, estimated with Monte Carlo probability functions Isolation and tagging cuts 1 � � remove decay photon Y iso R iso γ Y iso inc − Y iso dir = dec R iso γ − 1 background and NLO fragmentation photons Joe Osborn (UM) QCD-N 2016 12/07/16 15 / 21
Measurement at √ s =510 GeV R iso γ R iso 2.2 measured for iso γ R p+p at s =510 GeV γ η | |<0.35 statistical subtraction of 2 PH ENIX isolated decay photon preliminary 1.8 contribution 1.6 R γ measured in PHENIX 1.4 and corrected by tagging 1.2 and isolation efficiencies 1 R iso > 1 indicates isolated 7 8 9 10 11 12 13 14 γ γ p [GeV/c] T direct photon production N iso R γ R iso inc = (1 − ǫ tag γ dec )(1 − ǫ niso N inc dec ) Joe Osborn (UM) QCD-N 2016 12/07/16 16 / 21
PYTHIA p out Distributions PYTHIA π 0 -h ± and isolated γ -h ± correlations analyzed similarly to data -1 γ ± π ± [GeV/c] -h 0 -h 3 PYTHIA Perugia0 Simulation 10 trig 4<p <5 GeV/c T trig -1 10 2 p+p at s =510 GeV 5<p <6 GeV/c (x10 ) T PYTHIA exhibits similar trig -2 6<p <7 GeV/c (x10 ) assoc 10 0.7<p <10 GeV/c T trig -3 T 7<p <8 GeV/c (x10 ) out π π T dN 2 4 trig 1 ∆ φ 8<p <9 GeV/c (x10 -4 ) < < T dp characteristics to data: 3 3 trig -5 9<p <12 GeV/c (x10 ) -1 10 η T | |<0.35 trig -6 trig 12<p <15 GeV/c (x10 ) T 1 10 -2 N nonperturbative -3 10 -4 10 transitioning to -5 10 -6 10 perturbative region -7 10 -8 10 -9 Initial and final state 10 -5 -4 -3 -2 -1 0 1 2 3 4 5 p [GeV/c] out interactions possible in PYTHIA: all particles are forced to color neutralize Joe Osborn (UM) QCD-N 2016 12/07/16 17 / 21
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