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Lessons of physics at LEP

Anatoly Sokolov, IHEP Protvino

　 February 28, 2006 e+e- collisions from to , Novosibirsk

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OUTLINE

Kinematics of two-photon interactions Extraction of collision events at LEP and B-factories experiments

Two-photon event statistic for the low invariant mass range (W<4.5 GeV)

Study of some special two-photon reactions at LEP

Summary

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Two-photon collisions

Q2 = -q12 = 2 E1 E1 ( 1 - cos

1)

P2 = -q22 = 2 E2 E2 ( 1 - cos 2)

W 2 = ( i Ei ) 2 - ( i Pi )

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The final state can be:

1. Lepton pairs 2. A single resonant state 3. A non-resonant hadronic state

2 2TQ p

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The two-photon events can be classified as:

1. Non-tagged events (Q2 ~ P2 ~ 0)

Both scattered e are lost in the beam pipe Both photons are quasi-real. We can study: tot of collisions

Inclusive Charm and Beauty Production Single particle and Dijet production Resonances 2. Single-tagged events (Q2 >> P2 ~ 0)

Only one scattered electron is detected. One photon is highly virtual and the other is quasi-real Q2 is well measured We can study: Photon structure functions The photon-meson transition form factor

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The two-photon events can be classified as:

3. Double-tagged events (Q2, P2 >> 0)

Both scattered electrons are detected. Q2 and P2 are well measured.

W2

can be measured directly No unfolding We can study:

Cross section of collisions BFKL Pomeron Virtual photon structure function

The LEP Experiments The LEP Accelerator e+e- collisions at s 91 GeV (LEP I), s = 167-207 GeV (LEP II)

Integrated luminosity ~150 pb-1 /experiment (LEP I) , ~700 pb-1 /experiment (LEP II)

The dominant interactions

at LEP II are

two-photon processes

LEP II is the best place to study two-photon physics (high energy, high cross section, low background)

The KEKB/Belle Experiment

The KEKB Accelerator e+e collisions at s 10.6 GeV The world-highest luminosity 1.581034cm-2 s-1

and integrated luminosity ~500 fb-1

The Belle Detector Excellent energy/momentum resolutions and particle-separation capabilities

The cross sections observable there e+e(4S)BB --- 1.1 nb e+eqq (uds) --- 2.1 nb e+ecc --- 1.2 nb e+e --- 0.9 nb hadrons (W>0.8GeV) --- ~1 nb (within the acceptance)

visible

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Experiment see

GeV

Ldt

pb-1

nb

Nev

CLEO II 11 3000 1 3106

TPC/2 29 69 4 3105

PLUTO 35 45 5 2105

LEP I 91 150 * 4 10 9105

LEP II 198 700 * 4 15 1107

Belle 10.6 500 000 1 5108

LEP II advantages

• (e+e e+eh) rises with se+e

• bkg ~ 1/s

• hadrons events and background events are more separated

Disadvantages

• detector acceptance and trigger efficiency is reduced

(e+e e+ehadrons) for different experiments

Belle advantages

• high event statistic

• big detector acceptance

Disadvantages

• hadrons events and background events are less separated

Acceptance dependent

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Two-photon interaction kinematic (1)

Photon flux .)( hadreeee )( Reeee

LEP II s =200 GeV

<W >=8.6 GeV

LEP I

s =91 GeV

<W >=5.4 GeV

Belle, Babar

s =10.6 GeV

<W > =

= 1.8 GeV

u(d)u(d)

cc

bb

ss-

-

-

c

c0

b

W < 40 GeV

W < 90 Ge

V

W < 4.5 Ge

V

Belle, BaBar – resonances, low multiplicity states (W<4.5 GeV ~ )

LEP – high virtual photon study (W < 90 GeV ~ )

( , ) ( )( , )ee eeX Xs W WL s W

- -

/ 2ees

/ 2ees

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Two-photon interaction kinematic (2)

Detection efficiency of eventsBackground from e+e– annihilation events

LEP II

s =200 GeV

LEP I

s =91 GeV

Belle

s =10.6 GeV

Belle

s =10.6 GeV

Belle

s =10.6 GeV

LEP II

s =200 GeV

LEP I

s =91 GeV

LEP I , LEP II

0

ln2

Ws

y

)()(

2

)()(

4. X

XeeeeXeeY

XeeY

s

Wbkg

Low W (<4.5 GeV) (Belle) (LEP)

trigger eff.

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Resonance production in interactions

resonance hadrons

Measure the product of resonance two-photon width and

branching fractions (R ) B(R hadronic final state)

Internal (electromagnetic) structure of the resonance Tests of qq–meson models, perturbative/non-perturbative QCD Search for new resonance (C=+) states

Collision of two quasi-real photons (Q2<0.001GeV2)

with W =0.8 -4.5 GeVExclusive processes

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Low multuplicity hadronic states production in interactions

Tests of qq–meson models,perturbative/non-perturbative QCD

Collision of two quasi-real photons (Q2<0.001GeV2)

with W =0.8 - 4.5 GeVExclusive processes

Event Selection

Two-photon Exclusive event

pt-balance -- pt < 0.1 GeV/c in the e+e- CM frame

Exclusive requirement

bkg.

Charmonium signal at Belle

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Event statistic of exclusive two-photon interactions

/ K+ K-

Belle Ldt = 87.7 fb-1

N(+-) = 20 000 N(K+K-) = 9 700

N(+-)/fb = 230 N(K+K-)/fb = 110

DELPHI Ldt = 480 pb-1

N(+-) = 3 100 N(K+K-) = 220

N(+-)/fb = 6460 N(K+K-)/fb = 460

Test of models (S.J.Brodsky and G.P.Lepage; M.Diel, P.Kroll and C.Vogt)

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Event statistic of exclusive two-photon interactions

pp

Belle Ldt = 89 fb-1

N(pp) = 19 200 N(pp)/fb = 216

L3 Ldt = 667 pb-1

N(pp) = 990 N(pp)/fb = 1480

- - --

-

Test of models (three quarks; quark-diquark; handbag)

Also study of , 00,… reactions

- -

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Event statistic of two-photon resonance production

c K+K-+-

Belle Ldt = 280 fb-1

N(c2K2) = 1287 185 N(c)/fb = 4.5

L3 Ldt = 610 pb-1

N(c2K2) = 30 10 N(c)/fb = 50

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Resonances studied at LEP

M.N. Kienzle-Focacci, L3

~20-25%

~25-40%

~10-25%

stat

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4, 2K2, 4K. Results of G Br

Process Present G(eV) previous (PDG2004) direct indirect

Upper limits – 95%CL obtained by the 2 fits

Indirect:

Gindir(RX) = G(RA) Br(RX)/Br(RA)

RA - normalization process

G/Br(cKsK) ,G/Br(c0), G/Br(c2J)

- measured only in limited channels

S.Uehara

Belle (preliminary)

.stat

~15%

~12%

~11%

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Exclusive reactions 00 , +- (LEP) L3

non-tagged events (0 < Q2 < 0.02 GeV2) +single-tagged events (0.2 GeV2 < Q2 < 30 GeV2)

Ldt=850 pb-1 Nuntag(

+-+-) ~ 75000 Ntag( +

-+-) ~ 1900 Nuntag( +-

00) ~ 7500 Ntag( +-00) ~ 760

1.1 GeV < W < 3 GeV

2 2 2 2/ ~ 1/( ( )need dQ Q Q W

00 n = 2.9 0.14

+- n = 2.3 0.15

GVDM

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cross section

The relative magnitude of +- and 00 production changes in the vicinity of

Q21GeV2 different -pair productions mechanisms at low and high Q2.

The Q2 dependence of the process 00 is well reproduced by parametrisation based on GVDM model over the region Q2 > 0.2GeV2. +- data cannot be satisfactory described by such a parametrisation in the whole Q2 range.

preliminary

The discrepancy between the 00 cross section in the low Q2 range measured by PLUTO and L3.

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Inclusive J/J/ production in two-photon collisions (LEP II, DELPHI)

e+e- e+e- e+e-J/J/ X a sensitive tool for the gluon distribution in the photon

Main contribution

VDM “Resolved”

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Inclusive J/J/ production in two-photon collisions (LEP II, DELPHI)

Nch 4

3 GeV < Wvis < 35 GeV

ET(char) > 3 GeV

Ldt=617 pb-1 DELPHI

Nev = 274 000

+ 2 muons

(2 GeV/c < p < 20 GeV/c)

N(+-) 100

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Inclusive J/J/ production in two-photon collisions (LEP II, DELPHI)

Results of the fit:

M = 3.119 0.008 GeV = 0.035 0.007 GeV Nobs = 36 7

Fit by the form

Result: f = (74.0 22.0)%

2 2 2

Re

(1 )T T TDiffr solved

dN dN dNf f

dp dp dp

(e+e- e+e-J/J/ X) = (25.2 10.2) pb

(74 22)% of the observed J/J/ are due to “resolved” photons

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Open charm and beauty production in two-photon collisions

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D* tagging used for extracting the open charm cross section

Muon and electron spectra global fit gives the open c and b cross section

A naive increase of beauty QCD cross section gives an excess of charm

(e+e- e+e-cc)

1000 pb ( 10%)

(e+e- e+e-bb) 13 pb (

30%)

-

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Summary The possibility to extract -collisions at e+e- collider experiments increases logarithmically with . At LEP this possibility is only a few time higher than at B(c-,-)-factories.

The study of two-photon interactions at high energy e+e- collisions (LEP) has advantages because of the enlarged kinematical range of these reactions.

For the low invariant mass range (W<4.5(2) GeV) B(c-,-)-factories have advantages because of much higher luminosities than LEP.

Two-photon interactions at B(c-,-)-factories give a possibility for detail study of dynamic of hadron production at invariant mass range W<4.5(2) GeV.These interactions are a powerful tool for precision measurement of resonance parameters, search for new low-lying resonance states.

ees

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Summaryc , c0 , c2 in all the decay channels of , K+K and K+KK+K

are observed. c(2S) is not seen in any of these channels. f2f2, K*K*, are observed in these decays (some of these are new). Preliminary results for Br were obtained. (c)B(c …) are systematically smaller by about factor 3 in comparisons to previous experiments (although they are still not inconsistent). 　　　　　　　for c0 , c2 was measuredin the c0 , c2 , K+Kdecay modes.

Preliminary result for Br(c) was obtained (first measurement ). Helicity angle analysis of J/ → pp decay was performed.

Upper limit for the Br(B+ hc K+) BR(hc c) was obtained.

Evidence of a signal from the (4S) (1S) decay was observed. Preliminary result for the corresponding branching ratiowas obtained.

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Background

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Hadronic F2 : e+e e+ehadrons

F2 = F2 + F2

PL hadr

QPM VDM, non-perturbative QCD

Resolved , perturbative QCD

F2 : peaks at large x,

include cc, bb

PLF2 : main part at small x

hadr

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Hadronic F2 : Components

At high x Quark constituents are dominant

At low x Gluon constituents are dominant

The low x region is sensitive to the gluon density

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F2 : Kinematic region

The Q2 ranges from 1 GeV2 to 3000 GeV2

The x ranges down to 0.001 at low Q2

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F2,QCD : Wvis

Extract F2,QCD from differential cross section.

Due to detector acceptance and efficiency

Wvis < W Unfolding

Improve Wvis Use kinematics of etag

zp E p

2 2( )( ) | |tag tagine ee i

rec tiW p p p p

Use unfolding for xrec x

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The Present Study (s=10.5-10.6GeV, Ldt=280fb-1) c”4”c0 K

+K”2

K2”c2 K

+KK+K”4K”

c(2S) Event Selection

Two-photon Exclusive 4-prong event

pt-balance -- pt < 0.1 GeV/c in the e+e- CM frame

(Exclusive requirement)

/K separation - combined information from (CDC+ACC+TOF)

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Distributions of four-meson invariant masses

We observe c(2980)c0 (3415),

and c2(3555) in all the decay channels,

c(2S)(3650)is not significantly seen

in any of these channels.

c c0

c2

4 2K2

4K

misidentified (2S)

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c c0 　　　 c

2

Fits of the invariant-mass distributions

4

2K2

4K

Fit: background – 2nd-order polynomial charmonium – c,c0 --- finite and

fixed Mto MC

c2 --- assume is negligibly

small (~2MeV comparingtoM

Preliminary

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Study of two-meson resonances in their decays

Searches for resonance components decaying into , K, KK resonances

The intervals c – 50MeV, c0 – 50 MeV, c2 – 30MeV

0

f2(1270)

K*0(892) K+

K+K

f2’(1525) K+K

etc.

Sideband-subtraction technique

Watch distributions in “signal sideband”

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Resonance signals

Uppers: crosses: signal region, histo: sideband regionsLowers: signal – sideband=charmonium contribution

K*0 K in c2 2K2 KK in c0 4K

M(K) (GeV)

0 f2(1270)

in c 4

M() (GeV)

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Results of G Br (each decay mode)

Preliminary

Process Present G(eV) previous (PDG2004) direct indirect

Upper limits – 95%CL obtained by the 2 fits

Indirect:

Gindir(RX) = G(RA) Br(RX)/Br(RA)

RA - normalization process

G/Br(cKsK) ,G/Br(c0), G/Br(c2J)

- measured only in limited channels

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Charmonium c0, c2 seen (The first observations in these reactions)

(c0) = 2.62 0.23(stat.) 0.31(syst.) 0.24(Br) keV

(c2) = 0.44 0.07(stat.) 0.05(syst.) 0.05(Br) keV

(cJ) = NM2 (cJ)/ [4(2J+1) 2 L(McJ) Br( cJM+M-)

dt]ℒ

Charmonium production in / K+ K-

Belle PLB 615, 39 (2005) Based on Belle’s 87.7fb–1 data

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Primary event selection

There is exist a (ch+ch-)-pair with a M(ch+ch-)>9 GeV/c2

Standard Belle hadronic event selection criteria

N(tot) = 206700N()= 124500 (~60%)

Search for (4S)(1S)+- decay

Motivation: search for new bottomonium states, transitions.

Data sample: 357 fb-1, Υ(4s) 386106 BB – on-resonance

40 fb-1 – off-resonance

(1S)

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Event selection

X

M(>9 GeV/c2

(e+e- X )-events with M(e+e->9 GeV/c2 are put down by the Belle trigger

10.5 GeV < Evis < 12.5 GeV

cos < 0.95 reduce the bkg.

e+e- e+e- (1S), e+e-, e are identified as

N(X= 957

X

M(, GeV

M(fit)=9448.2 3.7 MeV

= 62.4 3.4 MeV

2/NDF=0.59

M((1S)(PDG)=9460.30 0.26 MeV

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Resonance decays in the (1S) state

on-resonance 9.4 GeV < M <9.52 GeV

Distribution of M=[M - M)

off-resonance

M, GeV M, GeV M21=M((2S)) –M((1S))

M31=M((3S)) –M((1S))

M41=M((4S)) –M((1S))M21=M((2S)) –M((1S))

M31=M((3S)) –M((1S))

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Peak parameters

M, GeV M, GeV M, GeV

1st peak (2S)(1S)+- 2nd peak (3S)(1S)+- 3d peak (4S)(1S)+-

M=562.0 0.1 MeV

= 2.1 0.2 MeV

2/NDF = 1.4

M(PDG) = 562.96

0.41 MeV

M=893.5 0.2 MeV

= 2.8 0.2 MeV

2/NDF = 1.8

M=1119.0 1.4 MeV

= 5.9 1.5 MeV

2/NDF = 0.5

M(PDG) = 894.9

0.56 MeV M(PDG) = 1120.

3.5 MeV

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Invariant mass of the system

M(, GeV M(, GeV

M(, GeV M(, GeV

1st peak (2S)(1S)+- 2nd peak (3S)(1S)+-

3d peak (4S)(1S)+-

Bkg.

Moxhay model

PR D39 (1989)3497

Yan model

PR D22 (1980) 1652

Yan model

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Branching fraction of the (4S) (1S) decay

Br((4S) (1S) ) =Nobs /[N tot Br((1S) )]

N tot = 386 106

Br((4S) (1S) + -) =

= (1.1 0.2(stat.) 0.4(syst.)) 10-4

= 0.035 Systematic - matrix element ~ 8% Belle hadronic event cut ~ 35%

Br((1S) ) = 0.0248

((4S) (1S) ) = (2.26 0.41 0.80) keV

((2S)) = 8.1 keV ((3S)) = 1.2 keV

Preliminary

Npeak = 48 Nbkg. = 10

N(4S) = 38 6.9(after bkg. subtraction)

3d peak (4S)(1S)+-

M, GeV

M=1119.0 1.4 MeV

= 5.9 1.5 MeV

2/NDF = 0.5

M(PDG) = 1120.

3.5 MeV

evidence of a signal(5.5)

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Open charm and beauty production in two-photon collisions

-

D* tagging used for extracting the open charm cross section

Muon and electron spectra global fit gives the open c and b cross section

A naive increase of beauty QCD cross section gives an excess of charm

(e+e- e+e-cc)

1000 pb ( 10%)

(e+e- e+e-bb) 13 pb (

30%)

-

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Open charm and beauty production in two-photon collisions

pT of the candidate with respect to the closest jet

2 distinct kinematical regions

Ldt=463 pb-1

Nev = 651 DELPHI Nbb = 118 26

(e+e- e+e-bb) = 14.9 3.3(stat.) 3.4(syst.) pb

-

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Inclusive J/J/ production in two-photon collisions (LEP II, DELPHI)

(Diffr.) = (1.79 0.07) %

(Res.) = (6.79 0.16) %The overall efficiency

.)(Re1

.)(1

sf

Diffrf

= (3.93 )%+2.18-1.03

(e+e- e+e-J/J/ X) = (25.2 10.2) pb

(74 22)% of the observed J/J/ are due to “resolved” photons