Status report of the DIRAC experiment (PS 212)

SPS Committee, April 5, 2011.

L.Nemenov

CERN Geneva, Switzerland

Kyoto University Kyoto, Japan

Bern University Bern, Switzerland

KEK Tsukuba, Japan

Santiago de Compostela University Santiago de Compostela, Spain

University of Messina Messina, Italy

IHEP Protvino, Russia

INFN-Laboratori Nazionali di Frascati Frascati, Italy

SINP of Moscow State University Moscow, Russia

JINR Dubna, Russia

Nuclear Physics Institute ASCR Rez, Czech Republic

IFIN-HH Bucharest, Romania

Institute of Physics ASCR Prague, Czech Republic

Tokyo Metropolitan University Tokyo, Japan

Czech Technical University Prague, Czech Republic

DIRAC collaborationDIRAC collaboration

Zurich University Zurich, SwitzerlandKyoto Sangyou University

Kyoto, Japan

3

1. Status of 2008–2010 data process on K+π− and K−π+ atoms.

2. Schedule of data analysis of K+π− and K−π+ atoms in 2011.

3. Status of the publication about π+π− atom lifetime measurement on 2001-2003 data

4. Status of 2008–2010 data process on π+π− atoms.

5. Multiple-scattering measurement during 2011 run.

6. Long-lived π+π− atoms and data taking in 2011 for their observation.

7. K+K− and πμ Coulomb pairs.

ContentContent

Modifided parts MDC - microdrift gas chambers, SFD - scintillating fiber detector, IH – ionization hodoscope. DC - drift chambers , VH – vertical hodoscopes, HH – horizontal hodoscopes, Ch – nitrogen Cherenkov , PSh - preshower detectors , Mu - muon detectors

4

Upgraded DIRAC setup

DIRAC setupDIRAC setup

Extrapolation to the targetExtrapolation to the target

target

DC

Y X

target

SFD

X-plane

The area where hits are

expecting

SFD

magnet

6

ππ++KK−− e experimental data 2008, 2009 xperimental data 2008, 2009

Experimental distribution of π+K− pairs with low background (points with error bar) are fitted with a sum of “atomic pairs” (red line), “Coulomb pairs” (blue line), “non-Coulomb pairs” (magenta line). A sum of “Coulomb” and “non-Coulomb” pairs is presented with black line. The cut on QT<4 MeV/c.

7

KK++ππ−− e experimental dataxperimental data 2008, 2009 2008, 2009

Experimental distribution of K+π− pairs with low background (points with error bar) are fitted with a sum of “atomic pairs” (red line), “Coulomb pairs” (blue line), “non-Coulomb pairs” (magenta line). A sum of “Coulomb” and “non-Coulomb” pairs is presented with black line. The cut on QT<4 MeV/c.

8

ππ++KK−− e experimental dataxperimental data 2009 2009

Comparison of the reconstructed π+K − events with low background and 2 SFD planes (red line) and events with medium background and 3 SFD planes (black line). The number of reconstructed events increased by 1.22.

9

KK++ππ−− e experimental dataxperimental data 2009 2009

Comparison of the reconstructed K+π− events with low background and 2 SFD planes (magenta line) and events with medium background and 3 SFD planes (blue line).The number of reconstructed events increased by 1.34.

10

All All ππKK e experimental dataxperimental data

π+K−

Year NA nA

2008 44 ± 13 23 ± 19

2009 66 ± 16 39 ± 23

2010 190% from 2008

K+π−

Year NA nA

2008

2009

66 ± 18 44 ± 26

150% from 2008

190% from 20082010

Sum of π+K− and K+π−*

NA nA

Ready

Expexted

176 ± 28 106 ± 39

170% from analyzed data

Numbers of generated πK atoms (NA) and numbers of “atomic pairs” (nA) found for data samples of 2008, 2009 and expected for 2010 for data with the low background.

* The expected number for events with the medium background will be higher by factor of 1.3

11

All All ππKK e experimental dataxperimental data

Expected ratio of signal to error for data with the the low background.

There is 40% of data with a higher background which implication is under investigation

4.5A

A

N

n

Accounting of events with medium background increase number of reconstructed events by factor 1.3 and the ratio becomes

5.2A

A

N

n

12

Schedule of data analysis of Schedule of data analysis of ππKK atoms in 2011 atoms in 2011

I. End of June 2011 1. Preparation of ntuples for 2008, 2009 and 2010 data.2. Preliminary results on atomic pairs extraction using 2008, 2009 data with low back-ground and two dimension spectra analysis. II End of October 2011 1. Search for πK atomic pairs using two dimension spectra and all statistic with low level background 2. Presentation of preliminary results on the analysis of statistic with low and medium level of back-ground.

13

ππ++ππ−− e experimental dataxperimental data 2008, 20092008, 2009

14

ππ++ππ−− datadata

Statistic for measurement of |a0-a2| scattering length difference and expected precision

Year nA δstat (%) δsyst

(%)

δsyst (%) MS δtot (%)

2001-2003 21000 3.1 3.0 2.5 4.3

2008

2009

2010

4800

7100

9000

2008-2010* exp.21000

(27000)

3.1

(2.7)

3.0

(2.1)

2.5

(1.25)

4.3

(3.4)

2001-2003 2008-2010

42000

(48000)

2.2

(2.0)

3.0

(2.1)

2.5

(1.25)

3.7

(2.9)

* There is 40% of data with a higher background which implication is under investigation

Results: lifetime & scattering lengthResults: lifetime & scattering length

DIRAC data

1ss

value stat syst theo* tot

|a0 – a2|

value stat syst theo* tot

Reference

2001 PL B 619 (2005) 50

2001-03 CERN-PH-EP-2011-028 (preprint)

91.2 49.062.0

264.0

0.0200.033

15.3 28.026.0

2533.0

0.01110.0106

NA48 K-decaya0 – a2

value stat syst theo tot

Reference

2009 K3 EPJ C64 (2009) 589

2010 Ke4 & K3 EPJ C70 (2010) 6350015.00020.02639.0

* theoretical uncertainty included in systematic error

45.038.0

19.049.0

20.019.0

20.018.0

017.0020.0

022.0009.0

0072.00077.0

0078.00080.0

0088.00029.00048.02571.0

Multiple-scattering measurement

16

- 4 planes DC- scatterer- 2 planes DC

Multiple-scattering measurement

17

Observation of long-lived π+π− atoms

em vac strnl nl nl nlE E E E

0 0

0 0 22strn nE A a a

0 0

2

0 2

1W R a a

2 2 0.59 0.0120 20 21 20 21

s p str em em vac vacE E E E E E eV

A2π decay dominated by annihilation process:

A2π lifetime depends on the ππ scattering length difference |a0 – a2|

Energy shift contributions

Strong interaction contribution

18

…opens future possibility to measure the energy splitting E(ns-np).

191919

For pA = 4.5 GeV/c ( = 16.1)

1s = 2.9 × 10 15 s , 1s = 1.4 × 10 3 cm2s = 2.3 × 10 14 s , 2s = 1.1 × 10 2 cm2p = 1.17 × 10 11 s , 2p = 5.7 cm, 3p 19 cm,

4p 43 cm

The A2π decay in the p-state is forbidden by angular momentum conservation. So the lifetime of the A2π atom in the 2p state (τ2p=1.17 ·10-11 s) is determined by the 2p–1s radiative transition with a subsequent annihilation in 1s state (τ1s=3 ·10-15 s): π+ + π- π0 + π0

The lifetime of the np-states is about 103 larger than the ns-states, so it is possible to measure the energy difference of these levels by exerting an electric field (Stark effect) on the atom and tracking the field dependence of the decay probability.The influence of an magnetic field on the A2π atom lifetime opens the possibility to measure the splitting between 2s and 2p levels.

Observation method

20

Production yields of A2π long-lived states

Probability of A2π breakup (Br) and production yields of the long-lived states 2p, 3p, 4p, 5p, 6p (m=0) as a function of the target thickness, for Beryllium (Z=4) target.

The A2π ground state lifetime is assumed to be 3.0·10-15s and the atom momentum 4.5 GeV/c.

21

Production yields of A2π long-lived states

Target material characteristics for production of long-lived atomic

states

- target thickness, chosen to provide maximum production yield of long-

lived states

- A2π breakup probability

- Σ (l ≥ 1): total yield of long-lived states including states with n ≤ 7

- 2p0, 3p0, 4p0, production yield of p-states with magnetic quantum number

m = 0

- Σ (l =1, m = 0): sum of the p-states up to n = 7

22

Part of the atoms, which were created in the Be target and then broken up in the Pt foil, as a function of the distance between Be target and Pt foil for all metastable states (n >1, l >0) and for some individual states with l=1. The foil thickness is 2μ.

Simulation of all π+π- pairs at experimental conditions

Tokyo Metropolitan University & Kyoto University

Neodymium magnetic piece=70x60x5mm3: Gap=60mm; BL=0.01Tm 　　　　　　　　　　　　　　　　　　 Time of delivery to CERN: before 4 May 2011

yz

x

150mm

90mm

60mm

24

Arrangement of Beryllium target, permanent magnet and Platinum foil.

25

Simulation of long-lived A2π observation

Simulated distribution of π+ π- pairs over QY with criteria: QX <1 MeV/c, QL < 1MeV/c. Additional magnet is implemented. “Atomic pairs” from long-lived atoms (light area) above background produced in Beryllium target (hatched area)

26

Simulation of long-lived A2π observation

Simulated distribution of π+π- pairs over QL, with criterion QT < 1 MeV/c. “Experimental” data (points with error bars) are fitted by a sum of “atomic pairs” from long-lived states, “Coulomb pairs” and “non-Coulomb pairs”. The background sum is shown by the solid line.

The number of atomic pairs are found to be

281 48longAn

atomic pairs from long-lived states

Coulomb pairs

non-Coulomb pairs

281 48longAn

27

Q and F for BeQ and F for Be 222LYX QQQQ

2

2

2

2

2

2

LYX Q

L

Q

Y

Q

X QQQF

0.5 /XQ MeV c

0.56 /LQ MeV c

0.32 /YQ MeV c

Qx

QL

Qy Q<1MeV/c

F<2

Simulation of long-lived A2π observation

28

Simulation of long-lived A2π observation

Simulated distribution of π+π- pairs over F, with criterion QT < 2 MeV/c. “Experimental” data (points with error bars) are fitted by a sum of “atomic pairs” from long-lived states, “Coulomb pairs”, “non-Coulomb pairs”. The background sum is shown by the solid line.

n =327 37 ; 8.8A

long AA

n

n

2 2 2

F= 0.50 0.32 0.56

X Y LQ Q Q

where 0.50, 0.32 and 0.56 Mev/c are RMS’s of the atomic pairs distribution over correspondingcomponents of the relative momentum Q. Now,

327 37longAn

Coulomb pairs

non-Coulomb pairs

atomic pairs from long-lived states

Long-lived π+π− atoms

29

The observation of ππ atom long-lived states opens the future possibility to measure the energy difference between ns and np states E(ns-np) and the value of ππ scattering lengths |2a0+a2|.

If a resonance method can be applied for the E(ns-np) measurement, then the precision of ππ scattering length measurement can be improved by one order of magnitude relative to the precision of other methods.

30

Thank you for your attention

31

≡ relative distance between + and mesons in A2 atom

r

≡ laboratory magnetic field

≡ electric field in the CM system of an A2 atom

F

BLab

Lab LabF B B

Atom beams are influenced by external magnetic field and the relativistic Lorentz factor γ

F

LabB

p

A

+

r

A2 ,v

c

z

L.Nemenov, V.Ovsiannikov, Phys.Lett. B514 (2001)

Measurements of the Lamb shift using external magnetic and electric fields

32

2p 2p

2 2

2p

2s

1 1201

4

eff

where: 2

2

22 2p s

F

E E

BLab = 2 Tesla

2p

2p

20 , 0.025 1.3

40 , 0.05 2.25

eff

eff

2(0) p

t

A AN N e

(0) eff

t

A AN N e

The dependence of A2π life time eff for 2p-states of the electric field F strength

3333

Resonant enhancement of the annihilation rate of AResonant enhancement of the annihilation rate of A22

L.Nemenov, V.Ovsiannikov, E.Tchaplyguine, Nucl. Phys. (2002)

Ap

Ap ,Lab LLaabbB

In CM System:2 2, cos , p s

Lab LLaabb

E Et

at resonance: res Lab resLab

In Lab. System:0 2

,Lab LabLab

lT

c T

l0

3434

Resonant enhancementResonant enhancement

35

Charged secondaryCharged secondaryCharged secondaryCharged secondary

Proton beamProton beamProton beamProton beam

p

ResonatorsResonatorsResonatorsResonators

γres1 γres2 γres3 γres4

0

Pt foilPt foilPt foilPt foil

0

0 0

0

0

+

-A*

2 A* A*K

Resonant methodResonant method

36

The production yield strongly increases for smaller Q

pnucleus

+

-

Strong interaction

For small Q there are Coulomb pairs :

pp, pK, K+K-, πµ C-pairs

pp, pK, K+K-, πµ atoms

Coulomb pairs and atomsCoulomb pairs and atoms

+ +

-

+

- -

+

-

+

-

Yield of dimeson atoms per one proton-Ni interaction, detectable by DIRAC upgrade setup at L=5.7º

24 GeV 450 GeV

EpA2π AK+π− Aπ+K− A2π AK+π− Aπ+K−

WA 1.1·10-9 0.52·10-10 0.29·10-10 0.13·10-7 0.10·10-8 0.71·10-9

WAN 1. 1. 1. 12. 19. 24.

WA /Wπ3.4·10-8 16.·10-10 9.·10-10 1.3·10-7 1.·10-8 7.1·10-9

WAN

/WπN

1. 1. 1. 3.8 6.2 8.

A multiplier due to different spill duration ~4

Total gain 1. 1. 1. 15. 25. 32.

DIRAC prospects at SPS CERN

38

Target Ni 98 m

A2π

p

24 GeV/c

p

24 GeV/c

π+

π−

π−π+

p

24 GeV/c π−

π+

π+

π0

π+

,,,…

η, η’,…

(NC)

(NA)Atomic pairs(nA)

p π−

π+

24 GeV/c

p

Coulomb correlatedpairs

Non-Coulomb pairs

Accidental pairs

Interaction point

Interaction point

Method of Method of AA2π2π observation and measurement observation and measurement

3939

Upgraded DIRAC experimental setupUpgraded DIRAC experimental setup