Recent Results on the Measurement of Fragmentation Functions in e + e - Annihilation

Transcription

1 Recent Results on the Measurement of Fragmentation Functions in e + e - Annihilation 1 ANSELM VOSSEN Evolution Workshop, Santa Fe, 2014 Motivation Belle (BaBar) Results p/k Cross-sections Kaon Collins Fragmentation Function New Di-hadron asymmetries Outlook: SuperKEKB, Belle II

2 Why Study Fragmentation Functions? q D h q ( z, Q 2 ) 2 hadron () FFs needed for Semi-inclusive measurements Spin averaged for a LL, x-sections etc Transverse spin dependent for transverse spin structure FFs non-perturbative QCD objects Confinement Quarks with QCD vacuum Compare to Nucleon Structure, study related issues like Evolution dξ 2π eipξ P ψ i (0)a h + a h ψ j (ξ) P e ipξ dξ 2π 0 ψ i(ξ)a + h a h ψ j (0) 0

3 Where to Study? e + e - cleanest way to access FFs hadronic jet 3 π e - e + γ* q q D h q ( z, Q 2 ) B factories Hadron close in energy to SIDIS (100 GeV 2 vs 2-3 GeV 2 ) Large integrated lumi!, high z reach h

4 Measurements of Fragmentation Functions in e+eat Belle and Babar B-Factories: asym. e+ (3.5/3.1 GeV) e- (8/9 GeV) collider: - s = GeV, e+e-à Υ(4S)à B anti-b - s = GeV, e+e-à qqbar (u,d,s,c) continuum ideal detector for high precision measurements: - Azimuthally symmetric acceptance, high res. Tracking, PID Available data (Belle, Babar similar): ~1.8 *109 events at GeV, ~220 *106 events at GeV 4/18

5 Cross-Section for identified Pions and Kaons 5 Initial State Radiation Exclude events where CME/2 changes by more than 0.5% Large at low z, correct based on MC PID Correct for acceptance, ττ, 2γ, decay in flight, } < 10% Smearing Corrections

6 PID Corrections from Data 6 ToF forward geometry acceptance limit fill matrix of PID probabilities for each single bin from real data calibration- need large statistics [P]ij (plab, cosθ lab ) = ~ p( e -> ~ ~ e) p( µ -> e) p( π -> ~ e ) p( K -> ~ e ) p( p -> e ) ~ ~ ~ p( e -> µ) p( µ -> µ) p( π -> µ ) ~ p( e -> π) ~ p( e -> K) ~ p( e -> p) ~ p( µ -> π) ~ p( µ -> K) ~ p( µ -> p) ~ p( π -> π ) ~ p( π -> K ) ~ p( π -> p ) ~ p( K -> µ ) ~ p( K -> π ) ~ p( K -> K ) ~ p( K -> p ) ~ p( p -> µ ) ~ p( p -> π ) ~ p( p -> K ) ~ p( p -> p ) scatter plot: e, µ, π, K and p tracks from 4e+05 events e.g. D* D 0 ToF backward geometry acceptance limit K - π + slow π + fast Misidentification πà K up to 15%, Kà π up to 20% M

7 Cross sections 7 Phys. Rev. Lett. 111, (2013)

8 Some Tension between Belle/BaBar 8 DSS@IIFF13 Possible Reasons ISR treatments Decays (small contribution)

9 Collins Fragmentation Function for Kaons see F. DIS 14 9 s! q q h 1 k T ϕ C

10 There are two methods with two or one soft scale φ1+φ2 method: hadron azimuthal angles with respect to the qq - axis proxy 10 φ0 method: hadron 1 azimuthal angle with respect to hadron 2 D. Boer Nucl.Phys.B806:23,2009 R 12 U/L = N(ϕ 1 +ϕ 2 ) N 12 R 0 U/L = N(2ϕ 0 ) N 0

11 Use of Double Ratios 11 Likesign A 0 Amplitude of sin(2φ 0 ) fit Unlike } z A 0 Use of Double Ratios False asymmetries due to Acceptance and QCD radiation Charge independent Fit to R 0 U R 0 L z

12 Double Ratios for π/k pairs 12 ππ => non-zero asymmetries, increase with z1, z2 πk => asymmetries compatible with zero KK => non-zero asymmetries, increase with z1,z2 similar size of pion-pion

13 P T0 Dependence 13 ππ => non-zero asymmetries, increase with z1, z2 πk => asymmetries compatible with zero KK => non-zero asymmetries, increase with z1,z2 similar size of pion-pion BaBar

14 Significant Charm to contribution to UDS 14 ππ couples (likesign) πk couples (likesign) ~80% uds ~50% uds KK couples (likesign) ~45% uds ~70% uds πk couples (unlikesign)

15 Test of Kinematic Dependence 15 linear in sin 2 Θ/(1+cos 2 Θ), go to 0 for sin 2 Θ/(1+cos 2 Θ) 0 A 0 dependence different from A 12 No intersect with 0

16 Di-Hadron Fragmentation s! q q R r h 2 h 1 16 φ RS R r ϕ R2 -π P! h1!! P P! h 1 + Ph 2 h2 π-ϕ R1

17 Di-Hadron Asymmetries 17 Di-hadron Cross Section from Boer,Jakob,Radici[PRD 67,(2003)]: Expansion of Fragmentation Matrix Δ: encoding possible correlations in fragmentation (k: P h1 +P h2 ) Measure Cos(φ R1 + φ R2 ), Cos(2(φ R1 -φ R2 )) Modulations!

18 Di-hadron Cross Section from Boer,Jakob,Radici[PRD 67,(2003)] Δ: Fragmentation Matrix, encoding possible correlations in fragmentation 18 k: P h1 +P h2 Spin independent part from Boer,Jakob,Radici[PRD 67,(2003)]

19 Cross Section 19 Δ: Fragmentation Matrix, encoding possible correlations in fragmentation Correlation of transverse spin with Di-hadron plane

20 Di-hadron Cross Section from Boer,Jakob,Radici[PRD 67,(2003)] 20 Δ: Fragmentation Matrix, encoding possible correlations in fragmentation Helicity dependent correlation of Intrinsic transverse momentum with k: P h1 +P h2 Di-hadron plane Measure Cos(φ R1 + φ R2 ), Cos(2(φ R1 -φ R2 )) Modulations and additional Cos(φ R1 - φ R2 ) (handedness, non pqcd related)

21 Study of A cos(ϕ1-ϕ2) and A cos(2(ϕ1-ϕ2)) Asymmetries in Belle MC Belle uses Pythia+Evtgen (implements decay tables) After detector asymmetries of the order of 1% (0.5%) are left. Pythia w/o detector is consistent with shows similar effect Possible culprits: gluon radiation, weak decays, detector effects 21

22 New: Use Jet Reconstruction at Belle Robust vs. final state radiation We use anti-kt algorithm implemented in fastjet Cone radius R=0.55 Min energy per jet 2.75 GeVà suppress weak decays Only allow events with 2 jets passing energy cut (dijet events) Only particles that form the jet are used in the asymmetry calculation Thrust cut of 0.8< T<

23 Mixed event subtracted flattens acceptance related false asymmetries 23 Remaining asymmetries in MC+their stat error used to estimate systematics

24 Asymmetries for Cos(2(φ R1 -φ R2 )) (G 1 ) small 24 Work in progress Work in progress

25 Asymmetries in Data persists for Cos(φ R1 -φ R2 ) 25 Work in progress Work in progress Systematics driven by MC

26 KEKB/Belleà SuperKEKB, Upgrade Aim: super-high luminosity ~10 36 cm -2 s -1 (~40x KEK/Belle) Upgrades of Accelerator (Microbeams + Higher Currents) and Detector (Vtx,PID, higher rates, modern DAQ) Significant US contribution 26 First data in

27 SuperKEKB luminosity profile We are here Integrated luminosity (ab -1 ) Goals of Belle II/SuperKEKB We will reach 50 ab -1 in months/year 20 days/month Peak luminosity (cm -2 s -1 ) Commissioning starts in late Shutdown for upgrade Year 27 Y. Ohnishi

28 28

29 Belle II Detector (in comparison with Belle) SVD: 4 DSSD lyrs g 2 DEPFET lyrs + 4 DSSD lyrs CDC: small cell, long lever arm ACC+TOF g TOP+A- RICH ECL: waveform Parameters sampling are preliminary (+pure CsI for end- caps) KLM: RPC g Scintillator +MPPC(end- caps) 29

30 Improve Charm Discrimination with SVD&PXD 30 Belle σ[µm] Belle II pβsin(θ) 3/2 [GeV/c]

31 PID improvement with itop Compare with ~85% efficiency for Belle 31 2 GeV/2 3 GeV/2 4 GeV/2 Only itop, no de/dx

32 SuperKEKB Schedule CY2010 CY2011 CY2012 CY CY2014 CY2015 CY2016 US-FY2010 US-FY2011 US-FY2012 US-FY2013 US-FY2014 US-FY2015 US-FY2016 Disassemble KEKB/Belle Beam pipe Manufacturing Coating and baking Installation Magnets Field mapping Manufacturing Installation Alignment RF system Manufacturing and installation Belle-II detector Installation Commissioning without Belle-II Belle-II roll-in Physics run Prototype test and detailed design Manufacturing Cosmic ray test Quartz bar production

33 Analysis Underway Di-Hadron Asymmetries Outlook Neutral Meson Collins Fragmentation Function Jet-Jet asymmetries from gluon radiation Analysis started Di-Hadron Cross-sections 33 Belle II

34 Backup 34

35 35 Integrated luminosity (ab -1 ) 50 ab -1 in ~5 years Peak luminosity (cm -2 s -1 )

36 Fragmentation contributions 36 Assuming charm contribute only as a dilution

37 Fragmentation For pion-pion couples: contributions 37 For pion-kaon couples: For Kaon-Kaon couples: Not so easy! A full phenomenological study needed!

38 Belle detector today ready for upgrade 38

39 Results: A 12 vs. (p t1,p t2 ); A 0 vs. p t0 BABAR preliminary BABAR preliminary FIRST MEASUREMENT of Collins asymmetries vs. p t in e + e - annihilation at Q 2 ~110 nonzero A UL and A UC (GeV/c) 2 only modest dependence on (p t1,p t2 ); A UC < A UL ; complementary information on H, fav 1 and H, dis 1 A 0 < A 12, but interesting structure in p t 39

40 ππ versus sin 2 Θ/(1+cos 2 Θ) 40 fit form: p0 + p1 sin 2 Θ/(1+cos 2 Θ) p0 forced to 0

41 πk versus sin 2 Θ/(1+cos 2 Θ) 41 linear in sin 2 Θ/(1+cos 2 Θ), go to 0 for sin 2 Θ/(1+cos 2 Θ) 0 fit form: p0 + p1 sin 2 Θ/(1+cos 2 Θ) p0 forced to 0

42 KK versus sin 2 Θ/(1+cos 2 Θ) 42 linear in sin 2 Θ/(1+cos 2 Θ), go to 0 for sin 2 Θ/(1+cos 2 Θ) 0 fit form: p0 + p1 sin 2 Θ/(1+cos 2 Θ) p0 forced to 0

43 43

44 uds-charm-bottom-tau contributions 44 ππ couples Published ππ studied a charm enhanced data and found charm contribute only as dilution => charm contribution corrected out

45 itop: an imaging time-of-propagation detector Space constrained by exis1ng 45 calorimeters Quartz radiator + mirror + expansion block + MCP- PMT 1.2m 1.5T e - 8.0GeV 2.6m 3.5GeV e + Backward Forward

46 46

47 47

48 Belle at KEKB 48