Embed Size (px)
Citation preview
ANSELM VOSSEN
Recent Results on the Measurement of Fragmentation Functions in e+e- Annihilation
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
1
Why Study Fragmentation Functions?
� FFs needed for Semi-inclusive measurements ¡ Spin averaged for aLL, 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
q
hadron ()
),( 2QzDhq
eipξ dξ2π
0 ψi (ξ )ah+ahψ j (0) 0∫dξ
2πeipξ P ψi (0)ah
+ahψ j (ξ ) P∫
2
Where to Study?
� e+e- cleanest way to access FFs
� B factories ¡ close in energy to SIDIS (100 GeV2 vs
2-3 GeV2) ¡ Large integrated lumi!, high z reach
h
h
q
q γ*
Hadron
e-
e+
hadronic jet
),( 2QzDhq
π
3
• B-Factories: asym. e+ (3.5/3.1 GeV) e- (8/9 GeV) collider: -√s = 10.58 GeV, e+e-àΥ(4S)àB anti-B -√s = 10.52 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 10.58 GeV, ~220 *106 events at 10.52 GeV
4/18
Measurements of Fragmentation Functions in e+e- at Belle and Babar
Cross-Section for identified Pions and Kaons
• Correct for acceptance, • ττ, 2γ, • decay in flight,
} < 10%
• Initial State Radiation • Exclude events where CME/2
changes by more than 0.5% • Large at low z, correct based on MC
• Smearing Corrections
PID
5
PID Corrections from Data
6
¡ Misidentification πàK up to 15%, Kàπ up to 20% M
fill matrix of PID probabilities for each single bin from real data calibration- need large statistics
[P]ij (plab, cosθlab) =
scatter plot: e, µ, π, K and p tracks from 4e+05 events
ToF forward geometry acceptance limit
ToF backward geometry acceptance limit
p( e -> µ) p( π -> µ )
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 )
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~
~ p( e -> π)
p( e -> K)
p( e -> p)
p( µ -> µ) ~
~
~
~
p( µ -> π)
p( µ -> K)
p( µ -> p)
p( e -> e) p( π -> e ) p( K -> e ) p( p -> e ) ~ ~ ~
~
p( µ -> e) ~
e.g. D* D0
π+slow
K-
π+fast
Cross sections 7
Phys. Rev. Lett. 111, 062002 (2013)
Some Tension between Belle/BaBar
� Possible Reasons ¡ ISR treatments ¡ Decays (small contribution)
DSS@IIFF13
8
“Collins” Fragmentation Function for Kaons
� see F. Giordano @ DIS 14
ϕC
q
qs!
kT
1h
9
There are two methods with two or one soft scale 10
𝜙0 method: hadron 1 azimuthal angle with respect to hadron 2
𝜙1+𝜙2 method: hadron azimuthal angles with respect to the qq axis proxy -
D. Boer Nucl.Phys.B806:23,2009
R12U /L =
N(ϕ1 +ϕ2 )N12
R0U /L =
N(2ϕ0 )N0
Use of Double Ratios
A0 Amplitude of sin(2φ0) fit
R0U
R0LFit to
A0
� False asymmetries due to Acceptance and QCD radiation
� Charge independent
} z
z
Use of “Double Ratios”
Likesign
Unlike
11
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
PT0 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
Significant Charm to contribution to UDS 14
KK couples (likesign)
𝜋𝜋 couples (likesign)
𝜋K couples (likesign)
𝜋K couples (unlikesign)
~80% uds ~50% uds
~70% uds
~45% uds
Test of Kinematic Dependence
linear in sin2𝜭/(1+cos2𝜭), go to 0 for sin2𝜭/(1+cos2𝜭) ➛0
� A0 dependence different from A12
� No intersect with 0
15
Di-Hadron Fragmentation
RSφ
q
qs!
Rr
Rr
1h2h
ϕR2-π
π-ϕR1
1hP!
2hP!
2h1h PP!!
+
16
Di-Hadron Asymmetries
� Di-hadron Cross Section from Boer,Jakob,Radici[PRD 67,(2003)]: Expansion of Fragmentation Matrix Δ: encoding possible correlations in fragmentation (k: Ph1+Ph2)
Measure Cos(φR1+ φR2), Cos(2(φR1-φR2)) Modulations!
17
� Δ: Fragmentation Matrix, encoding possible correlations in fragmentation
� k: Ph1+Ph2
from Boer,Jakob,Radici[PRD 67,(2003)]
Spin independent part
Di-hadron Cross Section from Boer,Jakob,Radici[PRD 67,(2003)]
18
Cross Section
� Δ: Fragmentation Matrix, encoding possible correlations in fragmentation
Correlation of transverse spin with Di-hadron plane
19
� Δ: Fragmentation Matrix, encoding possible correlations in fragmentation
� k: Ph1+Ph2
Helicity dependent correlation of Intrinsic transverse momentum with Di-hadron plane
Di-hadron Cross Section from Boer,Jakob,Radici[PRD 67,(2003)]
Measure Cos(φR1+ φR2), Cos(2(φR1-φR2)) Modulations and additional Cos(φR1- φR2) (handedness, non pQCD related)
20
Study of Acos(ϕ1-ϕ2) and Acos(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
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< 0.95
22
� Mixed event subtracted flattens acceptance related false asymmetries
� Remaining asymmetries in MC+their stat error used to estimate systematics
23
Asymmetries for Cos(2(φR1-φR2)) (G1⊥) small
Work in progress Work in progress
24
Asymmetries in Data persists for Cos(φR1-φR2)
� Systematics driven by MC…
Work in progress Work in progress
25
KEKB/BelleàSuperKEKB, Upgrade 26
� Aim: super-high luminosity ~1036 cm-2s-1 (~40x KEK/Belle) � Upgrades of Accelerator (Microbeams + Higher Currents) and Detector
(Vtx,PID, higher rates, modern DAQ) � Significant US contribution
http://belle2.kek.jp First data in 2016
27
Inte
grat
ed lu
min
osity
(a
b-1)
Peak
lum
inos
ity
(cm
-2s-1
)
Year
Goals of Belle II/SuperKEKB
We will reach 50 ab-1 in 2021
9 months/year 20 days/month
Commissioning starts in late 2014.
Shutdown for upgrade
Y. Ohnishi
We are here
SuperKEKB luminosity profile
28
29 Parameters are preliminary
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 sampling (+pure CsI for end-‐caps) KLM: RPC g Scintillator +MPPC(end-‐caps)
Belle II Detector (in comparison with Belle)
Improve Charm Discrimination with SVD&PXD
σ[µ
m]
pβsin(θ)3/2 [GeV/c]
Belle II
Belle
30
PID improvement with iTOP
� Compare with ~85% efficiency for Belle
Only iTOP, no dE/dx 2 GeV/2
4 GeV/2 3 GeV/2
31
SuperKEKB Schedule
CY2010 CY2011 CY2012 CY2013 CY2014 CY2015 CY2016
Disassemble KEKB/Belle
Beam pipe Manufacturing
Coating and baking Installation
Magnets
Installation
Field mapping
Alignment RF system
Manufacturing and installation
Belle-II detector
Commissioning without Belle-II
Belle-II roll-in
Physics run
Cosmic ray test
Installation
Manufacturing Prototype test and detailed design
US-FY2010 US-FY2011 US-FY2012 US-FY2013 US-FY2014 US-FY2015 US-FY2016
Quartz bar production
Manufacturing
32
Outlook
� Analysis Underway ¡ Di-Hadron Asymmetries ¡ Neutral Meson Collins Fragmentation Function ¡ Jet-Jet asymmetries from gluon radiation
� Analysis started ¡ Di-Hadron Cross-sections
� Belle II
33
Backup 34
Inte
grat
ed lu
min
osity
(ab-1
)Pe
ak lu
min
osity
(c
m-2
s-1)
50 ab-1 in ~5 years
35
36
Assuming charm contribute only as a dilution
Fragmentation contributions
37 For pion-pion couples:
For pion-Kaon couples:
For Kaon-Kaon couples:
Not so easy! A full phenomenological study needed!
Fragmentation contributions
Belle detector today – ready for upgrade 38
FIRST MEASUREMENT of Collins asymmetries vs. pt in e+e- annihilation at Q2~110 (GeV/c)2
• nonzero AUL and AUC ⇒ only modest dependence on (pt1,pt2); ⇒ AUC < AUL; complementary information on H1
⊥, fav and H1⊥, dis
⇒ A0 < A12, but interesting structure in pt
BABAR preliminary BABAR
preliminary
Results: A12 vs. (pt1,pt2); A0 vs. pt0
39
versus sin2𝜭/(1+cos2𝜭) 40
𝜋𝜋
p0 forced to 0
fit form: p0 + p1 sin2𝜭/(1+cos2𝜭)
41 𝜋K versus sin2𝜭/(1+cos2𝜭)
linear in sin2𝜭/(1+cos2𝜭), go to 0 for sin2𝜭/(1+cos2𝜭) ➛0
p0 forced to 0
fit form: p0 + p1 sin2𝜭/(1+cos2𝜭)
42 KK versus sin2𝜭/(1+cos2𝜭)
linear in sin2𝜭/(1+cos2𝜭), go to 0 for sin2𝜭/(1+cos2𝜭) ➛0
p0 forced to 0
fit form: p0 + p1 sin2𝜭/(1+cos2𝜭)
43
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
iTOP: an imaging time-of-propagation detector
2.6m
1.2m
e-
8.0GeV e+
3.5GeV
1.5T
Forward Backward
Space constrained by exis1ng calorimeters Quartz radiator + mirror + expansion block + MCP-‐PMT
45
46
47
48
Belle at KEKB
