Towards matching High Energy Factorization to Parton Shower

Transcription

1 Supported by Narodowe Centrum Nauki (NCN) with Sonata BIS grant NCN Towards matching High Energy Factorization to Parton Shower Krzysztof Kutak Based on ongoing project with: M. Bury, H. Jung, S. Sapeta, M. Serino, A. van Hameren

2 High Energy Factorization originally derived for gg QQ rapidities and pt of produced jets hard scale e.g. sum of pt of jets, used in DGLAP too Assumption: parton densities do not talk to one another transversal momentum of incoming gluon longitudinal momentum of incoming gluon In this framework of x of comparable values Decreasing longitudinal momentum fractions of off-shell partons BFKL like Decreasing longitudianl momentum fractions of off-shell partons BFKL like Gribov, Levin, Ryskin '81 Ciafaloni, Catani, Hautman '93 Does not take into account MPI as formulated in DGLAP i.e. emissions from independent chains Helicity based method for any process KK, Kotko, van Hameren '13 Further formal advancements by Serino, van Hameren '15 2

3 hybrid High Energy Factorization There is certain class of processes where one can assume that partons in one of hadrons are just collinear with hadron and in other are not Strongly decreasing transversal momentum of DGLAP like partons Strongly decreasing Longitudinal momentum fractions of off-shell partons 3

4 Hybrid factorization and dijets High energy factorization and forward jets Deak, Jung, K.K, Hautmann '09 conjecture P1 obtained from CGC after neglecting all nonlinearities g*g gg Iancu,Laidet qg* qg Van Hameren, Kotko, Kutak, Marquet, Petreska, Sapeta resummation of logs of x logs of hard scale P2 knowing well parton densities at large x one can get information about low x physics 4

5 Off-shell matrix elements old method pa pa Decomposition of polarization sum eikonal line Polarization sum for on-shell gluons Polarization of off-shell gluon Effective action based approach Lipatov 95, Lipatov, Vyazovsky 2000 New gauge link based derivation Kotko'14 5

6 Off-shell matrix elements modern method One consider embedding off-shell amplitude in on-shell and introduces eikonal lines Kotko, KK, van Hameren 2013, KK, Salwa, van Hameren

7 Off-shell matrix elements Kotko, KK, van Hameren 2013, KK, Salwa, van Hameren 2013 Agrees with: Effective action based approach Lipatov 95, Lipatov, Vyazovsky 2000 Gauge link based derivation Kotko'14 7

8 UPDF - Kimber Martin Ryskin Watt The relevance in low x physics at linear level recognized by: Catani, Ciafaloni, Fiorani,Marchesini; Kimber,Martin,Ryskin; Collins, Jung Survival probability of the gap without emissions and hard scale k Survival probability of the gap without emissions Kimber, Martin, Ryskin, Watt procedure : 8

9 Mimber Martin Ryskin Watt - updf We have now program to obtain TMD PDFS using KMRW procedure both at LO and NLO accuracy. The program has been written by PhD student Marcin Bury Integrating the gluon we get Back collinear PDF 9

10 Inclusive-forward jet 10

11 Performance of TMD - gluon single inclusive pt jet spectra 3.2 < y < 4.7 Bury, Deak, K.K, Sapeta '16 11

12 HEF vs. PYTHIA - single inclusive jet in CASTOR- x F spectra K.Kutak, H. van Haevermaet, P. van Mechelen Measures asymmetry in the longitudinal direction cross section ratio compare jets with different pt. For xf values below 0.3 one compares the jet cross section at 7 TeV in the saturation/regularization domain to the jet cross section at 13 TeV at larger pt, hence the sharp increase of the ratio. This effect is smoothed out by hadronization. The cross section ratio predicted by PYTHIA with all effects included is therefore again flat as a function of xf 12

13 Forward-forward di-jets 13

14 HEF vs. PYTHIA: effect of FSR - forward-forward dijets Bury, Deak, K.K, Sapeta '16 HEF framework with DLC2016 compatible with ISR in PYTHIA at moderate and large 14 Angles. Wide angle soft emissions lower cross section for hard jets

15 Monte Carlo tools Matrix elements part KaTie (A. van Hameren) complete Monte Carlo program for tree-level calculations any process within the Standard Model any initial-state partons on-shell or off-shell employs numerical Dyson-Schwinger recursion to calculate helicity amplitudes automatic phase space optimization Shower part CASCADE (H. Jung) kt factorization based Monte Carlo, program doing ISR and FSR. Can generate events using CCFM or KMRW pdfs. Uses PYTHIA for hadronization and FSR. Shower for quarks and gluons 15

16 Central-central di-jets 16

17 Forward-forward dijets HEF vs. Pythia P1 X P2 X Wide angle soft emissions lower cross section for hard jets 17

18 Angular ordered parton shower 18

19 Azimuthal angle decorelations - angular scale choice 19

20 Azimuthal angle decorelations pt ordering 20

21 4 inclusive central jets

22 4 jets pt spectra angular scale choice

23 Possibly contributing sub-processes K.K, Maciula, Serino, Szczurek, van Hameren '16 DPS SPS

24 Interesting four jet angle related observable Azimuthal angle between the sum of the two hardest jets and sum of the two softest jets. This variable has no distribution at LO in collinear factorization: pairs would have to be back-to-back 24

25 DPS contribution to 4 jets in HEF Pure tree level Kutak, Maciula, Serino, Szczurek, van Hameren 2016 Jets equally hard or harder than those from ME can come from the PS. The predictions without PS roughly agrees with data Once we include PS and remnant we recover a similar result as in collinear case Be careful. Possible MPI already in HEF. The result is strongly PDF sensitive 25

26 Outlook More extensive comparison to already accumulated data for p+p, and p+a using KaTie + CASCADE Corrections of higher orders to ME Ongoing development for A+A one needs to combine HEF with some framework for modeling medium (talk by Michal Deak) Parton densities from system of evolution equations for TMD PDFs 26