Ivan Vitev. Next generation nuclear physics with JLab12 and EIC Miami, FL, February 10 13, 2016

Transcription

1 Ivan Vitev Next generation nuclear physics with JLab12 and EIC Miami, FL, February 10 13, 2016

2 EIC, design and kinematics suitable for jet physics. Qualitative expectation, comparison between heavy ion collisions and SIDIS/ jet production in DIS. SCET and formal developments Hadron production and attenuation in semi- inclusive DIS. Energy loss and hadron absorption. QCD evolution techniques to in- medium modification of fragmentation functions Reconstructed jets at the EIC, jet cross sections. Jet substructure observables in DIS, jet shapes and jet fragmentation functions Event shapes at the EIC. Thrust and N- jettiness, extraction of the strong coupling constant. Polarized reactions at EIC Summary of EIC physics that can be addressed with jets

3 I. Background and comparison

4 BNL design JLab design 5-10 GeV electron ring (upgradable to GeV) GeV proton/ion 3-10 GeV electron ring GeV proton/ion NSAC long range plan (2015)

5 Let s take an example that covers both designs Energies 5 x 50 GeV ( x=0.1, Q 2 =20 GeV) ν = 100 GeV The important quantity is the energy of the struck quark (patron) in the rest frame of the nucleus, ν ( x=0.3, Q 2 =5 GeV) ν = 8 GeV BNL web site

6 Medium- induced parton shower modification is evaluated in the rest frame of the medium A E J = ν E TJ ν in the range (5 GeV 200 GeV) QGP p T / E T in the range (5 GeV 200 GeV) EIC will cover jet energy ranges where the bulk of the jet quenching phenomena are at RHIC and LHC. Note that we are interested in ν

7 The stopping power of matter is fundamental probe of the matter properties, in QED known to 1-2% Stopping power of Cu for muons B. Zakharov, (1996) R. Baier et al., (1997) M. Gyulassy et al., (2000) X. Guo et al., (2001) P. Arnold et al., (2003) The nature of the QCD theory gives rise to novel phenomena, such as the non- Abelian LPM effect Parametric high energy behavior k + dn n g m ~ cos ω dk + d 2 k ( k...n ) Δz k=2 k ( ) cos ( m ω ( k...n) Δz ) k=1 k m=1( ) ΔE E µ 2 L 2 ln E / Q 0 λ g E For processes that involve hard scattering there is cancellation of the medium- induced bremsstrahlung at very high energies

8 A scenario where the parton shower forms in the strong background gluon field of the nucleus EIC (Energy ν) IV., 2007 We expect parton energy loss, or more generally, the redistribution of the energy between vacuum and medium induced showers, to be factor of 2 (RHIC)- 3 (LHC) smaller than in the QGP but not orders of magnitude smaller. From this point of view, lower energy is good

9 Jet physics presents a multi- scale problem, EFT treatment SCET (Soft Collinear Effective Theory) C. Bauer et al. (2001) D. Pirol et al. (2004) QGP ~ E J CNM ~ k, q ~ T, gt,... ~ ˆq, Q s,... Glauber gluons to mediate physical interactions with the QCD medium ~ Λ QCD A. Idilbi et al. (2008) Ovanesyan et al. (2011)

10 n at LO, G. Ovanesyan et al. (2012) In- medium splitting functions beyond the soft gluon approximation Implemented in DGLAP evolution equations dn(tot.) dxd 2 k = dn(vac.) dxd 2 k + dn(med.) dxd 2 k As in vacuum, a total of 4 splitting functions A,B transverse propagators, Ωs interference phases

11 Properties Implemented in DGLAP evolution equations dn(tot.) dxd 2 k = dn(vac.) dxd 2 k + dn(med.) dxd 2 k Proven gauge invariance and factorization from H Being implemented in jet substructure Soft gluon emission the only well defined energy loss limit dn x 8 dx >< M. Gyulassy et al. (2012) >: q! qg g! gg 9 >= >; = s 2 ( C F [1 + O(x)] C A [1 + O(x)] ) Z Z d z g(z) d 2 k? d 2 q? 1 2k? q? apple1 k? 2 (k? q? ) 2 cos (k? q? ) 2 xp + 0 el z. d medium el d 2 q? Only 2 medium- induced splittings survive There is no flavor (q, g) mixing Results can be interpreted as energy loss

12 II. Semi- inclusive DIS, e- loss and hadronization

13 Energy loss- based approach compared to Hermes data X. Wang et al. (2002) F. Arleo et al. (2003) A wide range of ˆq obtained from < 0.1 GeV 2 /fm to 0.7 GeV 2 /fm

14 N. Chang et al. (2014) Using E- loss initial conditions Energy loss initial conditions followed by DGLAP evolution. Up to a small scale Q0 A quite small ˆq = 0.02 GeV 2 / fm. Again factor of 10 discrepancy in the transport properties of cold nuclear matter

15 One way to further constrain is the transverse momentum broadening or two particle momentum imbalance EIC reaction Dijet imbalance Dihadron imbalance Can directly constrain the transport properties of large nuclei A. Schafer et al. (2012) H. Xing et al. (2012) Transverse momentum broadening, Cronin effect and scale dependence of the broadening. At present some discrepancy in SIDIS and DY broadening. EIC et higher Q 2 and energy will provide definitive answers

16 Based on DGLAP evolution with with SCET G medium- induced splitting kernels (LHC example) R AA (p T ) ALICE charged hadron R AA, 0-5% ALICE charged hadron R AA, 5-10% Theory: SCET G medium evolution, g=1.9+/-0.1 N part = 350, with cold nuclear matter energy loss Z. Kang et al. (2014) With larger Q 2 and jet energy ν, this will be implemented for the EIC. But is important to be able to look at lower ν for largest effects R AA (p T ) p T [GeV] ATLAS charged hadron R AA η <02, 0-5% Central Pb+Pb, s 1/2 =2760 GeV ATLAS charged hadron R AA η <0.25, 0 5% Theory: SCET G medium evolution, g=2.0+/-0.1 N part = 350, without cold nuclear matter energy loss Central Pb+Pb, s 1/2 =2760 GeV p T [GeV]

17 Really depends what you analyze and where you put the effects nds R. Sassot et al. (2010) Electron Ion Collider will at least eliminate the IS interactions, much cleaner

18 For example the the RHIC pion data is included in some global analyses. Cronin effect sits at pt = GeV at all energies π + Predictions for LHC FF π+ pa /FFπ+ pp s=200gev y < 0.4 anti-k T R= < p jet < 15 GeV K. Kovarik et al. (2015) z Electron Ion Collider will at least eliminate the IS interactions, much cleaner. Has to be tested at low and high energies

19 Includes hadron but also pre- hadron formation and absorption A. Accardi et al., 2003 B. Kopeliovich et al., 2003 Δy + = 1 (0.2 GeV. fm) 2z(1 z) p+ = Δp k 2 + (1 z)m 2 2 h z(1 z)m q A. Accardi et al., 2005

20 III. Jet production at the EIC and jet substructure

21 The jet shape Narrow jets S. Ellis et al. (1993) S. Ellis et al. (1993) r Wide jets The transverse energy density inside a jet A lot of advances in understanding jet substructure come from SCET, motivated by boosted heavy particle decay Akers et al. (1994) Breitweig et al. (1999) Abe et al. (1993)

22 Convolution of had, beam, jet and soft functions C. Bauer et al. PRD (2001) D. Pirol et al. PRD (2004) Under very specific restrictions can be written as a product p T,y E r r J 1 Measured jet energy function R J 2 Λ

23 We use SCET resummation techniques and SCET G. (RG evolution) We start form the natural scales that eliminate all large logarithms in the fixed order calculation and evolve to a common scale [resumming ln(r/r)] µ µ jr E J R µ jr E J r To resum the jet shape to NLL accuracy

24 Recent renewed interest in this area was sparked in traditional QCD resummation ψ (r) NLL cone NLL anti- k 5.0 T LO CMS data R= r H- n. Li et al. (2011) The algorithm dependence of the jet shapes (anti)k T vs cone is included Significant improvement over fixed order calculation Examples for Tevatron, LHC Y.- T. Chien et al. (2014)

25 The key physics that jets in QCD matter probe is the modification of the partion shower (broader and softer) R AA s NN 2.76 TeV R 0.4, Η 2 centrality centrality 0 10 g 2.0 ± ATLAS p T Y.- T. Chien et al. (2015) The in- medium parton splitting allow to generalize the concept of jet energy loss beyond the soft gluon approximation

26 k k = p + 0 tan θ x(1 x) 2 = p + 0 tan θ 1 2 x = p + 0 tan θ 2 2 (1 x) θ 2 θ1 x, k One can evaluate the jet energy functions from the splitting functions r θ r θ 1 = r R θ = R 0 1 r R R r θ 2 = r First quantitative pqcd/scet description of jet shapes in QCD matter R p + 0 x Ρ r PbPb Ρ r pp s NN 2.76 TeV R 0.3, 0.3 Η 2 p T 100 GeV centrality 0 10 CNM only CNM R AA All effects CMS r

27 At EIC, in the kinematic region of interest there is a dominance of quark initiated jets. Excellent for jet substructure studies r We can mimic this in hadronic collisions by photon tagging Ρ r PbPb Ρ r pp s NN 5.10 TeV R 0.3, 0.3 Η 2 p T 100 GeV centrality 0 10 photon jet inclusive jet 0.5 γ Y.- T. Chien et al. (2015) Larger broadening of narrower quark jets r

28 Jet fragmentation functions probe the longitudinal jet substructure M. Procura et al. (2010) d h dy i dp Ti dz = H(y i,p Ti,µ) G h (z,µ)j 1 2(µ) J N (µ)s n1 n 2 n N (,µ)+o Q d = H(y i,p Ti,µ)J dy i dp 1 (µ) J N (µ)s n1 n 2 n N (,µ)+o + O(R) Ti Q Definition Gi h (,R,z,µ)= X Z 1 dx j z x J ij (,R,x,µ) Dj h ( z x,µ)+o d h. d F 1 (z,p Ti )= = Gh (z,µ) 1 dy i dp Ti dz dy i dp Ti J 1 (µ) 2 QCD 2 tan 2 (R/2)! + O(R) A ratio of a fragmenting jet function and unmeasured jet function, resummed to NLL accuracy Y. T. Chien et al. (2015)

29 ) T F(z, p ± h p+p s = 2.76 TeV anti-k T ATLAS R=0.4 y < 1.6 CMS R= < y < 2 [210,260] ) T F(z, p ± D* p+p s = 7 TeV anti-k T R=0.6 y < < p < 30 GeV T ATLAS PYTHIA 30 < p < 40 GeV T theory gluon-enhanced 9 10 [160,210] [110,160] 10 [80,110] 10 [60,80] 10 [45,60] [100,300] < p T 60 < p T < 50 GeV < 70 GeV 50 < p T 25 < p T < 60 GeV < 70 GeV z z z Very good comparison to data for z not too small and light hadrons. Both MC and pqcd /SCET fail for heavy flavor T. Kauffman et al. (2015) Y.- T. Chien et al. (2015)

30 [30, 40] [20, 30] 10 2 F(z, pt) [10, 20] EIC, s=100gev z The behavior of the jet fragmentation functions is similar to the one at pp colliders Expected modification is softening of the fragmentation functions, but also depletion due to suppression of gluon jets

31 IV. Event shapes at the EIC and α s

32 Thrust, jet broadening, angularities, N- jettiness τ=1- T R. Abatte et al. (2010) Extraction of α s Although the treatment of thrust is the most complete, there is discrepancy with the PDG average. Large (but universal) non- perturbative effects Ω

33 Generalization of thrust with N+1 collinear directions I. Stewart et al. (2010) Z. Kang et al. (2012) D. Kang et al. (2013) 1- jettines considered to avoid certain complications (NGL) C. Lee et al. in preparation

34 EIC opens unique possibilities to study jet/hadron production in cold dense QCD matter and provides ideal kinematics Jet and hadron production at the EIC will pinpoint the transport properties of large nuclei, the stopping power nuclear matter, and can test the strong gluon field paradigm Hadron production and attenuation in semi- inclusive DIS will shed light on the process of hadronization and the nature of color neutralization and confinement Jet substructue observables can provide a detailed picture of in- medium parton shower (longitudinal and transverse structure) in the background of strong color fields Event shape observables can be used for precise extraction of the strong coupling constant

35 DOF in FT DOF in EFT E Q Full Theory Effective Theory Simple but powerful idea to concentrate on the significant degrees of freedom [DOF]. Manifest power counting Q power counting DOF in FT DOF in EFT Chiral Perturbation Theory (ChPT) ΛQCD p/λqcd q, g K,π Heavy Quark Effective Theory (HQET) mb ΛQCD/mb ψ,a hv,as Soft Collinear Effective Theory (SCET) Q p /Q ψ,a ξn, An, As

36 Gluon splitting functions factorize form the hard scattering cross section only for spin averaged processes Altarelli- Parisi splitting G. Altarelli et al. (1978) Note that a collinear Wilson line appears in the R ξ gauge Single Born diagrams

37 For the purpose of this talk I will assume jet and hadron measurement capabilities, E T /p T, rapidity, momentum fraction z, in addition to DIS invariants H1 p Tracking, calorimetry, lepton and heavy flavor identification ZEUS P. Neuman et al. (2014) See talk E. Aschenauer

38 For e+p results for 2 and 3 jets are known to NLO Direct production Mirkes et al. (1996) Catani et al. (1997) Nagy et al. (2001) Photo production Gordon et al. (1992) Harris et al. (1997) Inclusive jet production Abramovitz et al, 2010 Provides excellent test for QCD formalisms. Compare and connect the collinear and k T factorization formalisms Generally smaller hadronization corrections