e835 at fnal annihilations pp charmonium spectroscopy in · › large (but not too much) density...

E835 at FNALCharmonium spectroscopy in pp annihilations

Claudia Patrignani – Universita and INFN Genova

FermilabFerraraGenova

NorthwesternU.MinnesotaUCI Irvine

Torino

C.Patrignani, Genova 1 2nd Panda Workshop, Frascati March 18-19,2004

Why pp ?

• All states can be formed, regardless of JPC

→ in e+e− all states (except 1−−) observed (or searched for) in cascade decays ofψ′

• Large hadronic non resonant background: σT OT

∼ 70 mb

B’s of charmonium to e.m. (or O.Z.I. suppressed) final states are 10−2 ÷ 10−4

(cc) → e+e−; (cc) → J/ψ + X → e+e− + X

(cc) → γγ; (cc) → nγs;

(cc) → φφ → K+K−K+K−; ...

σOBS

∼ nb ÷ pb−→ High luminosityC.Patrignani, Genova 2 2nd Panda Workshop, Frascati March 18-19,2004

Experimental technique

Charmonium states formed in pp annihilations:

σ(ECM ) =

∫

Gb(E) · σBW (E)dE

σBW ∝ BppBfin

• Resonance parameters from excita-tion curve

→ p beam and source characteristicsdetermine the quality of the mea-surement

→ The detector is used to recognize thegiven final states

• ... a search requiring a scan over alarge mass interval (> 10 MeV/c2

can be VERY time consuming


Antiproton Beam

8 · 1011p per stackaccumulation rate 4 · 1010p/hCompensation for dE/dx in the targetEfficient use of p Continuous beam

p accumulated at 8.9 GeV/c anddecelerated decreasing dipole current“fine scan” using stochastic cooling

Γ(Ecm) ≈ 500 ÷ 1000 keV∆Eabs

cm (χ2) ≈ 70 keV −→≈ 20 KeV

∆Erun/runcm (χ2) ≈ 80 ÷ 250 keV

P

PRODUCTION

(800 MeV)LINAC

MAIN INJECTOR(120 GeV)

BOOSTER(8.9 GeV)

TEVATRON

DEBUNCHER

ACCUMULATOR

E835 EXPERIMENT

TARGET


The H2 targetMolecular cluster H2 gas jet with variable density

⊗ Large (but not too much) density constant luminosity ←− pile-up⊗ Almost point-like interaction region ←− photons


The DetectorE835-I (OCT 96 - SEP 1997):

∫

Ldt ≈ 143pb−1

ANTIPROTONBEAM

CENTRAL CALORIMETER

CERENKOV

VETOCOUNTERS

CALORIMETERFORWARD

LUMINOSITYMONITOR

INTERACTIONPOINT

GASJET

2.63m

FREON 13

CO2INNER DETECTOR

H2SF

SC2

SILH2’SC1

H1

E835-II (JAN-NOV 2000):∫

Ldt ≈ 113pb−1

L = 1 ÷ 3 · 1031cm−2s−1 constant (variable jet density)

⊗ Select (already at trigger level) e+e− and γγ with large invariant mass

⊗ Must handle an asynchrounous interaction rate of ∼ 5 MHz

−→ E.M. calorimeter, threshold C, charged particle hodoscopes and tracking;timing information.

⊗ Final state reconstruction essential for background reduction

σ(E)

E=

6%√

E(GeV )+ 1.4% σ(θ) = 6 mrad σ(φ) = 10 mrad (neutrals);

σ(θ) ≈ 2 mrad σ(φ) ≈ 7 mrad (charged)C.Patrignani, Genova 6 2nd Panda Workshop, Frascati March 18-19,2004

Center of mass energy determinationEcm from antiproton velocity, measuring revolution frequency and orbit lenght

cβ = f(L0 + Li)

• f from Schottky noise spectrum: ∆f/f ∼ 10−7

• L0

(≈ 475 m) reference orbit length from knownψ′ mass: (absolute scale)∆(L0) = 0.7 mm since ∆Mψ′ ≈ 100 keV →27 keV∆Ecm: 30÷100 keV → 10 ÷ 27 keV

• Li run/run difference from ref. orbit∆Li ≈ 1 mm (Beam Position Monitors):∆Ei

cm: 50 ÷ 160 keV

∆Li may locally distort (“blur”) the excitation curvesource of systematic error on Γ (narrow resonances)Large ∆Li can be a limiting factor for the detection of narrow, low-cross sectionresonances.

Beam energy distribution from Schottky noise ∆pp = −

(

1γ2

t

− 1γ2

)−1∆ff

Typical center of mass energy distribution Γ(Ecm) (FWHM): 500 ÷ 1000 KeVη = 1

γ2t

− 1γ2 (measured to ≈ 10%) largest source of syst. error on total width


Luminosity measurement

From known pp elastic cross section at approx 90o

Count recoil protons in solid state detectors below the target

Syst. error on run/run luminosity measure-ment ≤ 1%negligible contribution to syst. error on totalwidth for narrow resonancesAbsolute luminosity error ± 2% from ppelastic cross section uncertaintysource of systematic error for peak cross-section (partial width) measurement

Channel Number

Cou

nts

10

10 2

10 3

0 100 200 300 400 500


Data taking summary by resonance

E835-I (1996/1997) E835-II (2000)


Main results:

• Direct measurement of mass and width of ηc, J/ψ[E760], χ0, χ1, χ2, ψ′[E760],

• Measurement of cross section for

– pp → J/ψ, ψ′ → e+e−

– pp → χcJ → J/ψγ → e+e−γ

– pp → ηc, χc0,2 → γγ

– pp → χc0 → π0π0, ηη exploiting the interference with the continuumhadronic cross section

to derive Γγγ , B(pp), and Γ(χ0 → J/ψγ)

• Measurement of ψ′ branching ratios

• χ1, χ2 and ψ′ angular distributions

• e.m. form factor of the proton in time-like region


Selection of e+e− and J/ψX → e+e− final states

• Online: Two energy deposits in CCAL with invarian mass>2.4 GeV/c2),Cerenkov signal in coincidence with hits in charged hodoscopes

• Offline: likelihood ratio electron vs background (Electron Weight).– Data as “training samples”.

– A pair of electron in final state

−→ test done on EW1·EW2

– Background mainly from π0 (conver-sions and Dalitz);

−→ Calorimeter granularity and detectionthreshold more relevant than energyresolution

−→ C for π± / e±

• All decay products reconstructed in the detector (“closed” events)

• Topology and/or kinematic to specific final states


“J/ψ inclusive” selectionInvariant mass e+e− at ψ′ formationenergy: events selected (dotted line)and events rejected (dark area) by EWcut(1996/1997 and 2000)

σobs(pp → J/ψX) (not corrected)


Proton e.m. form factors in time-like regionpp → e+e− differential cross section depends from the electric GE and magneticGM form factors of the proton:

dσ

d(cos θ∗)=

πα2(hc)2

8EP·[

|GM |2 (1 + cos2 θ∗) +4m2

pc4

s|GE |2 (1 − cos2 θ∗)

]

Select events with a pair of electrons in the detector, topologically andkinematically compatible with pp → e+e−

expected background < 100 fb;

Sample size and limited acceptance do not allow to extract |GM | and |GE | fromthe angular distribution.

|GM | measured in the hypotesis GE ∼ GM (a) and GE ∼ 0(b)

s L N σacc | cos θ∗|max 102 × |GM |(GeV2) (pb−1) (pb) (a) (b)

11.63±0.17 32.86 32 1.61+0.34+0.17−0.29−0.10

0.575 1.74+0.18+0.11−0.16−0.07

1.94+0.20+0.12−0.17−0.08

12.43±0.01 50.50 34 1.11+0.23+0.12−0.19−0.07

0.601 1.48+0.15+0.08−0.13−0.05

1.63+0.17+0.09−0.14−0.05

14.40±0.19 5.17 0 < 0.80 0.603 < 1.38 < 1.51

18.22±0.01 2.10 0 < 1.98 0.512 < 2.77 < 2.99


Form factors: other experiments and theory

In the approximation of “large” momentumtranfer:

q4|GM | ∝ α2s(q

2)

M. Andreotti et al. Phys. Lett B 559 (2003) 20.M. Ambrogiani et al. Phys. Rev. D 60 (1999) 032002.T. A. Armstrong et al.Phys. Rev. Lett. 70 (1993) 1212.


Direct measurement of mass and width of χcJχ0 E835-I χ1 E760 χ2 E760

χ0 E835-II χ1 E835-II χ2 E835-II

T. A. Armstrong et al. Nucl. Phys. B 373 (1992) 35.M. Ambrogiani et al. Phys. Rev. Lett. 83 (1999) 2902.S. Bagnasco et al. Phys. Lett. B 533 (2002) 237.


Results pp → χcJ → J/ψγ → γe+e−

χc0 E835-II E835-I AverageM [MeV/c2] 3515.4±0.4±0.2 3417.4+1.8

−1.9±0.2 3415.5±0.4± 0.07ΓTOT [MeV] 9.8±1.0±0.1 16.7+5.2

−3.7± 0.1 10.1±1.0B(pp)B(J/ψ + γ)[×107] 27.2±1.9±1.3 29.3+5.7

−4.7±1.5 27.6±2.5± 0.7χc1 E835-II (prelim) E760 Average

M [MeV/c2] 3510.64±0.10±0.07 3510.53±0.10± 0.07 3510.59±0.07± 0.07ΓTOT [MeV] 0.88 ± 0.09 0.88± 0.14 0.88±0.08

B(pp)Γ(J/ψ + γ)[eV] 18.8±0.7±0.6 21.8±2.7± 1.2 19.0±0.7± 1.2χc2 E835-II (prelim) E760 Average

M [MeV/c2] 3556.10±0.15±0.07 3556.15±0.11±0.07 3556.13±0.09±0.07ΓTOT [MeV] 1.93±0.22 1.98±0.18 1.96±0.14

B(pp)Γ(J/ψ + γ)[eV] 25.8±1.9±0.8 28.2±2.9±1.5 26.5±1.6±1.4

cc0 mass

3405 3410 3415 3420M(MeV/c2)

CBALL(86)E835(97)BES(99)CLEO2(01)E835(02)

cc1 mass

3506 3508 3510 3512M(MeV/c2)

MARK2(80)CB(82)R704(86)E760(92)BES(99)E835(03)

cc2 mass

3555 3560 3565M(MeV/c2)

MARK2(80)CB(82)R704(86)E760(92)BES(99)CLEO2(01)E835(03)

cc0 width

0 10 20G(MeV)

CBALL(86)E835(99)BES(99)E835(02) cc1 width

-1 0 1 2 3G(MeV)

E835(03)E760(92)

cc2 width

-1 0 1 2 3G(MeV)

CBALL(86)R704(86)E760(92)E835(03)

χc1,2 very stable after 10 years, upgraded detector and heavy changes in the p source.C.Patrignani, Genova 16 2nd Panda Workshop, Frascati March 18-19,2004

Fine splittingsLattice calculations are beginning to provide estimates close to the experimentalvalue although with large errors...good test ground

Measured(preliminary)

∆M12 = M(χc2) − M(χc1) (MeV/c2) 45.55±0.11∆M10 = M(χc1) − M(χc0) (MeV/c2) 95.2±0.4

ρ =∆M21

∆M100.478±0.002

Mc.o.g =M(χ0) + 3M(χ1) + 5M(χ2)

9(MeV/c2) 3525.31±0.07

More traditional approaches:

The spin-orbit and tensor term of cc Hamiltonian in terms of these splittings are

< hLS >=2∆M10 + 5∆M21

12= 34.84 ± 0.08MeV

< hT >=10∆M10 − 5∆M21

72= 10.06 ± 0.05MeV

If central part of the cc potential of the Cornell type ( V = − 34

αs

r + Kr)

αs = 30.18(MeV ) × m2 < r3 > K = 51.04(MeV ) × m2 < r >


Direct measurement of J/ψ and ψ′ widthsE760 has performed the first (and so far unique) direct measurement of total widthfor J/ψ e ψ′

Given a resonance of width ΓR, and a center of mass energy spread with almostgaussian distribution of variance σB

σmeaspeak = σpeak

√

π

8

ΓR

σBexp

Γ2R

8σ2B

erfc

[

ΓR√8σB

]

and if ΓB > ΓRσpeak

A' 0.94

ΓB

[

1 − 0.94ΓR

ΓB

]

With AA beam even for J/ψ ΓR

ΓB' 0.2 −→ direct measurement feasible provided

the error on σB is sufficiently small

∆p

p= −1

η

∆f

f

This requires a <10% error on ηC.Patrignani, Genova 18 2nd Panda Workshop, Frascati March 18-19,2004

Direct measurement of J/ψ e ψ′ width

Double Scan: The value of η determinesthe momentum difference between p onthe central orbit (frequency fc) andthose circulating on a “side” orbit atfrequency fc + ∆f .In a double scan the ∆p(∆f) is de-termined by measuring simultaneoulsythe cross section σ(fc) on the centralorbit and comparing it to the valueσside(fc+∆f) measured when the beamis displaced to a “side” orbit for whichthe revolution frequecy changes by ∆f

J/ψ ψ′

M [MeV/c2] 3096.87 ± 0.03 ± 0.03 3686.02 ± 0.09 ± 0.27ΓTOT [keV] 99 ± 12 ± 6 306± 36 ± 16

T. A. Armstrong et al. Phys. Rev. D 47 (1993) 772.


Angular distribution χc1,2

In the processpp → χc1,2

→ J/ψγ → e+e−

formation and subsequent radiative decay can be described by

• formation amplitudes B0, B1, B−1

→ helicity 0, 1 contribution to Γpp

• decay amplitudes a1, a2, a3

→ deviation from dipole approximation from E1-M2 and E1-E3 interference

• χc1angular distribution has just one parame-

ter: a2 (a1 > 0)

B0 = 0, B1 = −B−1 = 1/√

2

• For χc2there are 3 parameters: B0, a2, a3

(a1 > 0)

B1 = B−1

e+

e-

y

f /

q

q/

gcc

p-


pp → χc1,2→ J/ψγ → e+e− (E835-I)

0

50

100

150

200

250

300

350

400

-1 0 1cosq*

even

ts/b

in

0

50

100

150

200

250

300

350

0 0.5 1cosq/

0

50

100

150

200

250

300

350

0 p/2 pf /(rad)

cc1 ≈ 2100 events

a2 = 0.02± 0.032± 0.004

M. Ambrogiani et al. Phys. Rev. D65 (2002) 052002.T. A. Armstrong et al. Phys. Rev. D48 (1993) 3037. (E760 just χ2)

≈ 6000 events

a2 = −0.093+0.039−0.041±0.006

a3 = 0.020+0.055−0.044 ± 0.009

B20 = 0.13 ± 0.08 ± 0.01

0

100

200

300

400

500

600

700

800

900

-1 0 1cosq*

even

ts/b

in

0

100

200

300

400

500

600

700

800

0 0.5 1cosq/

0

100

200

300

400

500

600

700

800

0 p/2 pf /(rad)

cc2


Comparison with other experiments and theory

E835

E760

Crystal Ball

E835

Crystal Ball

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1a2

c1c2

Exerimentally:

a2(χ1)

a2(χ2)= −0.10 ± 0.31

Potential model prediction:

a2(χ1)

a2(χ2)=

√5Eγ(χ1)

3Eγ(χ2)= 0.676

indepedent from mc e µc

Γpp(χc0) can have only helicity 0 contribution.

B20 =

Γpp(χ2, Jz = 0)

Γpp(χ2)= 0.13± 0.008± 0.001 −→ Γpp(χ0)

Γpp(χ2, Jz = 0)≈ 130????


ψ′ sample

E835 collected (in the two runs) an integrated luminosity of ≈ 25 pb−1 at the ψ′

forming ≈ 3M ψ′

E835-II sample

We reconstruct:

≈ 36000 ψ′ → J/ψ X → e+e− X

≈ 7500 ψ′ → e+e−

events with purity > 98%Not a 4π detector: efficiency requiresknowledge of angular distribution


Angular distributions

The angular distributions for ψ′ → J/ψ X → e+e− X depend on ψ′ helicityformation amplitudes

pp → J/ψ → ππ → e+e−ππ:

dN

d cos θd cos θ′dφ′= (1 + λ cos2 θ)(1 + cos2 θ′) + (λ + 1 − 2λ cos2 θ)(1 − cos2 θ′)

+ λ sin2 θ′ sin2 θ cos 2φ′ − 4λ sin θ cos θ sin θ′ cos θ′ cos φ′

pp → J/ψ → π0(η) → e+e−π0(η):

dN

d cos θd cos θ′dφ′= (1 + cos2 θ′)(1 + λ cos2 θ) − λ cos(2φ′)(1 − cosθ)(1 − cos2 θ′)

• θ is the angle between the J/ψ and the p in CM

• θ′ angle between the electron and the J/ψ direction in J/ψ rest frame

• φ′ angle between the p − J/ψ plane and the e+e− plane in J/ψ rest frame.

λ =C2

1 − C20

C21 + C2

0

is the ratio of helicity 0 and 1 formation amplitudes


Angular distributions (continued)pp → γ1χJ → γ1γ2J/ψ → γ1γ2e

+e−:

W (θp, φp, θγγ , θe, φe) =

1∑

m,m′=−1

%(m,m′)(θp, φp)∑

µ=±1

Bm+µBm′+µ

1∑

n,n′=−1

ε(n,n′) ∗(θe, φe)∑

ν=±1

An+νAn′+ν

dJk+µ,n+ν(θγγ)dJ

k′+µ,n′+ν(θγγ)

where%(m,m′)(θp, φp) =

∑1λ=−1 C2

λD1m,λ(θp, φp)D1∗

m′,λ(θp, φp);

ε(n,n′) ∗(θe, φe) =∑

χ=±1 D1∗n,χ(θe, φe)D1

n′,χ(θe, φe)and

• θp, φp: azimuthal and polar angle of the antiproton in the ψ′ CM

• θγγ : azimuthal angle of γ1 in χc reference frame

• θe, φe azimuthal and polar angle of the positron in J/ψ reference frame.

Bi and Ai are the multipole decay amplitudes for the radiative decaysC.Patrignani, Genova 25 2nd Panda Workshop, Frascati March 18-19,2004

Measurement of angular distributionpp → ψ′ → e+e−

dN

d cos θ∗∝ 1 + λ cos θ∗2

E835-I (2579 ev) E835-II (4822 ev)

Combining the two data sets λ = 0.67+0.15−0.14 ± 0.04 from which |C0

C1| = 0.44+0.12

−0.11

E760 measured λ = 0.69 ± 0.26 based on a sample of 2687 inclusive eventspp → ψ′ → e+e−, J/ψ X → e+e−X (under the assumption of S = 0 dipion recoil)


Branching ratios for ψ′ → e+e−, ψ′ → J/ψππ,ψ′ → J/ψη ψ′ → J/ψπ0,ψ′ → χcγ → J/ψγγ

• Events fully reconstructed• Normalized to the number of ob-

served ψ′ → J/ψX−→ Direct measurement of

B(ψ′ → A)

B(ψ′ → J/ψX)

• The sum of events observed in eachdecay mode when corrected by accep-tance and efficiency, accounts for thenumber of ψ′ → J/ψX observed


ψ′ → χcγ → J/ψγγ, ψ′ → J/ψη, and ψ′ → J/ψπ0

The number of ψ′ → χcγ → J/ψγγ, ψ′ → J/ψη, and ψ′ → J/ψπ0 from a fit to theDalitz plot ψ′ → J/ψγγ

New measurement ofB(ψ′ → χcγ)B(χc → J/ψγ)

B(J/ψ X)with a sample size comparable toCrystall Ball

E835 C. BallJ/ψγγ 2363 2234J/ψη 478±24 386χ0γ 38±13 17χ1γ 967±36 943χ2γ 563±28 479

J/ψπ0(res+n.r.) 153±16 -J/ψπ0(res ) 78±17 23

The number of J/ψπ0 events has a large contribution from non resonantpp → J/ψπ0, which is well measured on data taken for η′

c search.

Angular distribution uncertainties beeing reduced by our own measurement of χc

multipole amplitudes and ψ′ formation amplitudesC.Patrignani, Genova 28 2nd Panda Workshop, Frascati March 18-19,2004

ψ′ → e+e−, ψ′ → J/ψππ and ψ′ → J/ψη

B(mode)

B(J/ψ X)(%)

Decay Mode E760 E835-I E835-II (PREL)≈ 2400 ev ≈ 13800 ev ≈ 31500 ev

e+e− 1.44±0.08±0.02 1.28±0.03±0.02 1.21±0.06±0.02J/ψπ+π− 49.6±3.7 – 51.8±2.7J/ψπ0π0 32.3±3.3 32.8±1.3±0.8 29.9±3.3J/ψη 6.1±1.5 7.2±0.9 5.3±0.8

E835-I and E835-IIVERY PRELIMINARY

J/ψη 5.6±0.5χ0γ → J/ψγγ 0.23±0.08χ1γ → J/ψγγ 5.40±0.38χ2γ → J/ψγγ 3.30±0.28J/ψπ0 0.41±0.09∑

J/ψ X excl. modes 99±3M. Ambrogiani et al. Phys. Rev. D 62 (2000) 032004.T. A. Armstrong et al. Phys. Rev. D 55 (1997) 1153.


Comparison with other experimentsUsing B(ψ′ → J/ψX) = 0.579 ± 0.019 (PDG03 web update)

Channel B(mode)(%) B(mode)(%) B(mode)(%) B(mode)(%)E835 BES-II Crystal Ball Crystal Ball

(preliminary) hep-ex/0403023 (exclusive) (inclusive)J/ψη 3.24±0.29 2.98±0.09±0.23 2.55±0.29 -J/ψπo 0.24±0.05 0.143±0.014±0.013 0.11±0.03 -χ2γ → J/ψγγ 1.91±0.16 1.62±0.04±0.12 1.47 ±0.14 0.99±0.13χ1γ → J/ψγγ 3.13±0.22 2.81±0.05 ±0.23 2.78 ±0.30 2.56±0.23χ0γ → J/ψγγ 0.13±0.05 - 0.069±0.019 -

But we can also compare to (indirect) determination of the radiative B’s

From E835 χ0 → π0π0 and χ0 → J/ψγ scans (using BES for B(χc0 → ππ)

B(χc0 → J/ψγ) = 1.34 ± 0.23 ± 0.09 ± 0.19%

Taking preliminary CLEO-C values for ψ′ → χcJγ (LP03,Skwarnicki talk):B(χJ → J/ψγ) = (9.75 ± 0.14 ± 1.7)%) [J=2]; (9.64 ± 0.11 ± 0.69)%) [J=1];(9.83 ± 0.13 ± 0.87)% [J=0]our values would imply

B(χ2 → J/ψγ) = (19.6 ± 1.6 ± 3.4)%) PDG03: (20.2±1.9)%B(χ1 → J/ψγ) = (32.5 ± 2.3 ± 2.4)%) PDG03: (31.6±2.7)%

B(χ0 → J/ψγ) = (1.35 ± 0.46 ± 0.12)% PDG03: (1.11±0.18)%C.Patrignani, Genova 30 2nd Panda Workshop, Frascati March 18-19,2004

pp → χc0 → π0π0 and ηη

• Non resonant cross section À reso-nant (by ≈ ×50)

• First measurement in pp of a de-cay mode to LH non O.Z.I. sup-

pressed

• Which channels can Panda ex-

plore?

−→ ηc → pp? direct measurement

of Γpp, Γγγ and indirect con-

straint on B(J/ψ → γηc)−→ χc0,2

→ V V, PP ?


Differential cross section pp → χc0 → π0π0

dσ

dz(x, z) =

∣

∣

∣

−AR

x + i+ AI eiδI

∣

∣

∣

2

+∣

∣

∣ANI eiδNI

∣

∣

∣

2

x =ECM−Mχ0

Γχ0/2 and z ≡ | cos θ∗|

AR → Resonant amplitude,AI = AI(x, z) → interferingpart of non resonant amplitude(λ=0),ANI = ANI(x, z) → non in-terfering part of non resonantamplitude (λ=1)

λ = λp − λp initial state helicityof pp .


χc0 → π0π0 and ηηIntegrated cross section as a function of Ecm

(square resonant amplitude enlarged for plotting purposes)

B.R.(χc0 → pp)× B.R.(χc0 → π0π0) = (5.09 ± 0.81(sta) ± 0.25(sys))× 10−7

M.Andreotti et al. Phys. Rev. Lett. 91 (2003) 091081; hep-ex/0308055

B.R.(χc0 → pp)× B.R.(χc0 → ηη) = (4.0 ± 1.2)× 10−7; (preliminary)C.Patrignani, Genova 33 2nd Panda Workshop, Frascati March 18-19,2004

χc0 radiative transition

From our own measurements (taking into account common systematics) we obtainthe following ratio of χc0 branching ratios

B(χc0 → J/ψγ)

B(χc0 → π0π0)= 5.34 ± 0.93 ± 0.34

Taking B(χc → π0π0)= 12B(χc → π+π−) = (2.5 ± 0.35)10−3 (BES) our

measurement translates into

B(χc0 → J/ψγ) = 1.34 ± 0.23 ± 0.09 ± 0.19%

which can further be translated into an E1 partial width

Γ(χc0 → J/ψγ) = 131 ± 26 ± 8 ± 18 KeV

that is in excellent agreement with the E3γ scaling of Γ(χc1,2 → J/ψγ)

Γ(n3PJ → n′3S1 γ) ∝ E3γ |Eif |2 where Eif =

∫

r3Ri(r)Rf (r)dr

which would predict respectively 137±23 keV and 137±18 keV


Selection of (cc) → γγ final states

• Online: Two energy deposits in CCAL with large invariant mass , veto onscintillators’ coincidences

• Offline: Topology (no extra cluster “on time”), πo veto ( invariant mass of γcandidates and clusters without timing info) and kinematic fit

• Background mainly from pp → πoπo,pp → πoγ where low energy γ(’s) are notdetected (“feed-down”)– Background cross section mostly for-

ward peaked−→ select events in central cos θ∗ region−→ Excellent angular resolution for pho-

tons thanks to point-like source−→ Calorimeter granularity and detection

threshold more relevant than energyresolution.

−→ Simply detecting low energy photonswith poor energy resolution can dras-tically reduce the background.


pp → ηc(11S0) → γγ

M. Ambrogiani et al. Phys. Lett. B 566 (2003)45.

2980 3000 3020MARK2(80)CBALL(86)MARK3(86)R704(87)DM2(91)E760(95)DELPHI(98)BES(00)CLEO2(00)BES(03)E835(03)BELLE(03)BABAR(prel)

0 20 40 60CBALL(86)MARK3(86)R704(87)E760(95)BES(00)CLEO(00)BES(03)E835(03)BELLE(03)BABAR(prel)

M = 2984.1±2.1 ± 1.0 MeV/c2 Γ=20.4+7.7−6.7 ± 2.0 MeV Γγγ=3.8+1.1

−1.0+1.9−1.0 keV

Poor consistency among mass and width measurements.Even worse with new preliminary measurements from BaBar and CleoC.Patrignani, Genova 36 2nd Panda Workshop, Frascati March 18-19,2004

pp → χc0 → γγ• incoherent background from π0π0 and π0γ (feeddown calculated by MC):forward peaked → | cos θ∗| < 0.4• can interfere with non resonant pp → γγ: visible for | cos θ∗| > 0.2from γγ → pp by CLEO/VENUS ∼ 10 pb for | cos θ∗| = 0.6(compatible with our data after feedown subtraction)

B(χc0 → pp)× B(χc0 → γγ) = (6.52 ± 1.18(sta) +0.48−0.72(sys))× 10−8

B(χc0 → γγ)

B(χc0 → J/ψγ)= (2.2 ± 0.4+0.1

−0.2) 10−2[E835 − II] (1.45 ± 0.74) 10−2 [E835 − I]

M. Andreotti et al. Phys. Lett. B 584 (2004) 16. M. Ambrogiani et al., Phys. Rev. D 62 (2000) 052002.


Γ(χc0 → γγ)

Using B(χc0 → pp) = (2.2±0.5)× 10−4 from PDG2002 and ΓE835χc0

=9.8±1.0 MeV:

Γγγ = (2.90 ± 0.59(sta + sys) ± 0.66(br) ± 0.3(Γ)) keV

Alternatively, from our measurement of

B(χc0 → γγ)

B(χc0 → π0π0)

taking our value for the total width and again B(χc → π0π0) = (2.5 ± 0.35)10−3

(BES) we could obtain

Γ(χc0 → γγ) = 3.1 ± 0.8 ± 0.5 KeV

PQCD(with first order radiative correction)

Γγγ

Γgg=

8α2

9α2S

× (1 + 0.2αS/π)

(1 + 9.5αS/π)

. (Γ(χc0 → gg) ' ΓTOT (χc0), αS = 0.28) predicts

Γγγ,PQCD = 3.26 ± 0.33 keV


χc2 → γγ

E760 and E835-I measured respectively:

B(χc2 → γγ) × B(χc2 → J/ψγ) = (1.60 ± 0.42) 10−8

B(χc2 → γγ)

B(χc2 → J/ψγ)= (0.99 ± 0.18) 10−3

E835-I Γγγ after 2002 PDG global fit(Belle measurement was not in-cluded)

-1 0 1 2Γγγ(keV)

E760(93)CLEO2(94)OPAL(98)L3(99)E835(00)BELLE(02)

M. Ambrogiani et al., Phys. Rev. D 62 (2000) 052002.T. A. Armstrong et al. Phys. Rev. Lett. 70 (1993) 2988


Search for ηc(2S)Search for pp → ηc(2S) → γγ set upper limits on B(pp)B(γγ) in the whole massinterval between χ2 and ψ′

thus setting the charged veto. Calculation of the probabilityof conversion in the 0.14 mm stainless steel beam pipe, av-eraged over the angular distribution of the gg events, gives avalue Pconv50.01160.001.

Pcont is the probability that a random event contaminatesa good event, causing it to be rejected.3 This can happen atthe trigger level if the overlapping event sets the chargedveto, or in the off-line analysis if ~a! the second event occurswithin ;10 ns of a real gg event and contributes one ormore in-time clusters in CCAL, or if ~b! one time-undetermined cluster from the overlapping event forms thep0 mass when combined with a photon from the gg event.

e2 is predominantly the efficiency of the kinematic fit,4

but also incorporates small localized inefficiencies not ac-counted for in e1 and originating from a few dead CCALchannels.

Pcont and e2 are determined together for each data pointby Monte Carlo techniques. The Monte Carlo program simu-lates the CCAL response to pp→gg events starting from theenergy deposited in each counter, taking account of passivematerial and dead channels ~typically 4 out of 1280!. Theeffect of accidental events is incorporated by superimposing~actual! data taken with a random gate on the simulatedevents. The combined events are subject to the standard clus-tering algorithms and analysis cuts, and the quantity (12Pcont)3e2 is given by the fraction which survive.

The factor (12Pcont) varies linearly from ;0.88 at L

;1.531031 cm22 s21 to ;0.81 at L;2.531031 cm22 s21,the luminosity range for these data; e2 is typically 90%.Given that we use actual data events to simulate the contami-nation, we estimate less than 1% systematic error in (12Pcont). The uncertainty of e2 was determined from asample of real J/c→e1e - events. These events can be se-lected with high efficiency and free of background withoutusing the kinematical fit, thus permitting a direct measure-ment of e2 to be compared with the Monte Carlo calculation.We found e2MC

2e2exp50.00260.025.

The overall efficiency for each data point is calculatedusing Eq. ~2!. Its values are reported in Table I. They have anestimated relative error at most ;3%, calculated by addingin quadrature the contributions from the maximal errors onPcont and e2, and the error on Pconv .

Since the two photon decay of the hc8 is isotropic, thegeometrical acceptance is equal to the ucos u*u cutoff valuea50.4.

IV. RESULTS

A. E835 experiment

The cross section measurements for candidate gg eventswithin the acceptance region (cos u*,0.40) obtained from

data taken at various center of mass energies between 3526and 3686 MeV are shown as open circles in Fig. 3. Datataken at 3556.2 MeV, where a xc2→gg signal was observed@15#, have been excluded, since they are not used in thispaper. Cross sections have been corrected for analysis andtrigger inefficiencies. No resonance signal is seen in the plot.The full circles refer to our previous experiment E760 andwill be discussed in Sec. IV B.

The background to the resonance search consists of a con-tinuum two photon production ~expected to be very small5!and a fraction of p0p0 and p0g events that survive the eventselection. These processes are expected to produce a back-ground with smooth energy dependence. We describe thebackground with the form

sbkgd~s !5AS 3556.2 MeV

AsD B

~3!

and use high integrated luminosity data points at ;3526 and3686 MeV ~46.6 pb21 and 8 pb21, respectively! to help con-strain the background level throughout the search region.

3Since the p beam has no time structure, this probability followsPoisson statistics and is determined by the interaction rate.

4The inefficiency is almost twice that expected from the theoreti-cal x2 distribution, due to non-Gaussian tails of the error distribu-tions.

5In spite of the small cross section, possible interference of thenonresonant continuum pp→gg with the hc8 may distort the lineshape of the resonance. This effect was not considered in this analy-sis since neither the gg cross section nor its partial amplitudes areknown. We do not expect interference to alter the results of thisanalysis.

FIG. 3. Cross section for pp→gg candidates vs center of massenergy: open and full circles for E835 and E760, respectively. Thefact that the background levels in the two experiments differ isaccounted for in the analysis ~see the text!. The dashed line shows,superimposed on the E835 best fit background, an estimate of thesignal expected for an hc8 candidate with an assumed width of 8MeV. The uncertainty on the estimated peak cross section is 40%ignoring the theoretical uncertainty ~see the text!. The signal isdrawn at the mass of the crystal ball hc8 candidate with the uncer-tainty in its mass indicated by the overlaying horizontal segment.

SEARCH FOR THE hc8 (2 1S0) CHARMONIUM RESONANCE PHYSICAL REVIEW D 64 052003

052003-5

We obtain upper limits to the product Br(hc8→ pp)3Br(hc8→gg) anywhere in the search range as follows.

A maximum likelihood analysis of the data in the interval3526,As,3686 MeV, which includes the backgroundpoints at 3526 and 3686 MeV, was performed by fitting to asuperposition of a Breit-Wigner resonance and a smoothbackground parametrized according to Eq. ~3!.

The likelihood function to be maximized, L, is written asthe product of N ~5number of data points in the energy scan!Poisson functions, each giving, for the ith data point, theprobability that ni events be observed if n i are expected,

L5)i51

N n ini e2n i

n i !, ~4!

where

n i5F E L dt GiS aE f i~As ! speak

3

G2

4~As2Mc2!21G2

dAs1sbkgd~s !D ~egg! i , ~5!

speak5

4p~\c !2~2J11 !

s24m2c43Br~hc8→ pp !3Br~hc8→gg !.

~6!

The integral gives the convolution of the resonance Breit-Wigner with the ~Gaussian! center of mass energy distribu-tion function f i(As), *L dt is the integrated luminosity ofeach data point, a is the geometrical acceptance, M and Gare the resonance mass and width, egg is the efficiency givenby formula ~2!, and m is the proton mass.

Repeated fits were performed, over a grid of fixed valuesof the resonance mass and width, covering the range 3575 to3660 MeV/c2 with three hypothetical values of the reso-nance width, 5, 10, and 15 MeV, in steps of 0.5, 1.0, and 1.0MeV, respectively. Free parameters in the fits were the reso-nance branching ratio product BR[Br(hc8→ pp)3Br(hc8

→gg)3108, and the background parameters A and B.Several methods exist to produce limits when the signal

being sought is small compared to the background and theparameter being measured has physical bounds @16#. In Ap-pendix A we present a comparison of the upper limits ob-tained applying different methods to analyze this experiment.

In this section we present the method of Feldman andCousins @17# applied assuming the best fit value to be Gauss-ian distributed with standard deviation equal to the parabolicerror.6 We calculate the 90% C.L. upper limit interpolatingTable X of Ref. @17#.

Since the upper limits tend to be underestimated whenthere are downwards fluctuations of the background, follow-ing the authors’ suggestion we evaluated the sensitivity of

our experiment @17#. The sensitivity is defined as the meanupper limit that would be obtained in repeated experimentsunder the same conditions with the same expected back-ground but no true signal. The calculation of the experimentsensitivity is discussed in Appendix B.

The limits on Br(hc8→ pp)3Br(hc8→gg) and the sensi-tivity of the experiment are presented in Fig. 4; shown asopen ~full! circles are the lower ~upper! limits of the 90%confidence intervals. The curve represents the sensitivity ofthis experiment and the band displays the standard deviationrange of upper limits obtained from repeated experiments inthe absence of a resonance; upper limits below the sensitivityof the experiment, such as those occurring at As near 3610,3630, and 3655 MeV are not significant and are interpretedas downwards fluctuations of the background. Notice the en-ergy behavior of both the upper limit and the sensitivity,much smoother for G510,15 MeV than for G55 MeV. Thisis because the spacing in energy of the data points ~;5 MeV!is too large for a G55 MeV resonance search, giving rise tolocal minima just at the scan points ~indicated by arrows!.

We have examined the effect of the choice of the back-ground form by comparing the upper limits obtained usingour standard form and using forms linear ~2 parameter! andquadratic ~3 parameter! in As . We find that our results areindependent of the way the background is parametrized.Likewise we found that the systematic errors on the inte-grated luminosity and on the efficiency egg have negligibleeffect on our results.

6A Monte Carlo simulation of repeated experiments has shownthis assumption to be realistic, see Appendix B.

FIG. 4. 90% confidence intervals for the product of the pp andthe gg branching ratios vs As . Full circles for upper limits; opencircles for lower limits ~not shown when zero!. The resonance widthwas fixed at ~a! 5 MeV, ~b! 10 MeV, and ~c! 15 MeV. The line in theshaded band is the experiment sensitivity ~see the text!. Arrowsindicate the energies where data points were taken; arrow lengthsare proportional to integrated luminosities. An estimate of Br(hc8

→ pp)3Br(hc8→gg) is shown as the small open square. We havedrawn it at the crystal ball hc8 candidate mass, with the horizontalerror bar reflecting the uncertainty in the candidate’s mass.

M. AMBROGIANI et al. PHYSICAL REVIEW D 64 052003

052003-6

Dashed line shows expected signal for ΓTOT =8 MeV and “plausible” B(pp)B(γγ).

Result difficult to interpret because of large uncertainties (> 40%) on B(pp)B(γγ)predictions and because only a fraction of data had been collected at what we(now) know to be the correct mass value...

With high luminosity at the appropriate mass detect E1 ηc(2S) → γhc → γJ/ψπ0

and M1 ηc(2S) → γJ/ψ ? M. Ambrogiani et al. Phys. Rev. D 64 (2001) 052003.


ψ′ and χc branching ratios: an exampleThe values of Γ, B(χc → pp), B(χc → 4π), B(χc → 2π), B(ψ′ → γχc) B(χc → γγ)and B(χc → J/ψγ) (7 quantities) are measured in 11 different combinations:

e+e−: (BES/CLEO-c) B(ψ′ → γχc), B(ψ′ → γχc)B(χc → pp),B(ψ′ → γχc)B(χc → J/ψγ), B(ψ′ → γχc)B(χc → 4π) andB(ψ′ → γχc)B(χc → 2π)

pp: (E835) Γ, ΓB(χc → pp)B(χc → J/ψγ), B(χc→2π)B(χc→J/ψγ) and B(χc→γγ)

B(χc→J/ψγ)

γγ: (LEP,CLEO,B factories) ΓB(χc → γγ)B(χc → J/ψγ) andΓB(χc → γγ)B(χc → 4π)

−→ Those measurements indirectly constrain B(ψ′ → χcγ) and B(χc → J/ψγ)• The new fit in PDG since 2002 exploits these constraints (and avoids hiddencorrelations)Those constraints make a real difference! In some cases the error is drastically

reduced, but in some cases also the central value changed significantly...B(χ0 → γJ/ψ) = (0.66 ± 0.18)% [2000] −→ (1.11 ± 0.18)% [2003]The precision on partial width of radiative decays is now ≈ 10%...These constraints arise because different techniques measure different combinationsof the same set of branching ratios: pp → ηc → φφ (or to any other hadronic decaymode detected in γγ or e+e− experiments) could help constraint J/ψ and ψ′ M1transitions...C.Patrignani, Genova 41 2nd Panda Workshop, Frascati March 18-19,2004

Conclusions

• E835 (and E760) have measured directly the masses and widths of ηc, J/ψ,χcJ , and ψ′

• Total widths of χc states have been measured to ≈ 10%

• The measurement of product of branching ratios for χ e ψ′ provide, togetherwith new measurements in γγ, an (indirect) significant constraint to theradiative decay B’s, first measured in e+e− experiments

−→ global refitting of all ψ′ and χc branching ratio based on directly measuredproducts/ratios of B’s lead to substantial changes

• The observation of pp → χ0 → π0π0 and ηη through the interference with thecontinuum suggest new possibilities for future pp experiments

• The splitting of χc states has been measured to <0.5 MeV

• Total width measurements allow to calculate radiative decay widths of ψ′ andχc to ≈ 10%


Extra Slides


Update on hc

E760 performed a scan in the region of χc center of gravity, observing a structurein pp → J/ψπ0 interpreted as the hc

MR = 3526.2 ± 0.15 ± 0.2 MeVΓR < 1.1 MeV (90%CL)

(1.8 ± 0.4) · 10−7 < B(pp)B(J/ψπ0) <(2.5 ± 0.6) · 10−7

B(J/ψππ)B(J/ψπ0) ≤ 0.18 (90%CL)

The probability that the continuumpp → J/ψπ0 statistical fluctuationwould have produced such a structureanywere in the scanned region is 1/400.The number of J/ψ X candidates iscompatible with the number of exclu-sive events fully reconstructed.T. A. Armstrong et al., Phys. Rev. Lett. 69 (1992) 2337.


hc status of the analysis

E835-I and E835-II collected data for > 90 pb−1 of which ≈ 70 pb−1 within 1 MeVfrom the mass value determined by E760.

Not an independent search, the goal was to confirm or exclude E760 result

Unfortunately most of E835-I data had been collected while some of the BeamPosition Monitors were not properly working.

The center of mass energy cannot be determined with the precision that would bedesirable to scan a narrow resonance

The analysis is ongoing for the following channels

• J/ψπ0

• J/ψππ

• ηcγ → 3γ

• ηcγ → φφγ (only E835-II)


e835 at fnal annihilations pp charmonium spectroscopy in · › large (but not too much) density...

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