M. Medinnis, DESY Hamburg

Search for Pentaquarks in 920 GeV Proton-Nucleus Collisions with HERA-B

M. Medinnis, DESYFor the HERA-B Collaboration

ICHEP, BeijingSession on Hadron Spectroscopy and Exotics

M. Medinnis, DESY

HERA Experiments

N

S

W E

c0

+ ?

+ + - -

c0

+

M. Medinnis, DESY

Experimental situation• According to a recent count*:

– 12 reports of a narrow resonance (NR) in nK+ or pK0

s near 1530 MeV/c2 (+).

– 8 reports this year of negative results on searches for +.

– H1 reports a NR decaying into D*p (0c ) but

Zeus reports non-observation.– NA49 reports a NR decaying into -- (--).

*J. Pochodzalla, hep-ex/0406077

The existence of pentaquarks is not established.If they exist, the production mechanism is unclear.

M. Medinnis, DESY

HERA-B contribution

Search for:

+(1540) p K0s p +-

--(1862) - - 0 - - p - - -

At mid-rapidity in pA collisions at 920 GeV,

using a large, clean (pileup 10%) minimum bias sample: 200 million interactions

(A = C, Ti, W)

M. Medinnis, DESY

HERA-B Detector

WireTargets

Maintracker

RICH

VertexDetector

920 GeV incident protons

ECAL

MAGNET

x

z

M. Medinnis, DESY

RICH/ECAL Particle ID

• For K0s, reconstruction:

no particle ID requirements

• Otherwise: (where L likelihood)– Pions: (weak) LRICH(e,, ) > .01,

LECAL(e) < 0.9

– Kaons: (strong) LRICH(K) > 0.95

mis-id < 2%, p range: 12 – 55 GeV/c– Protons: (strong) LRICH(p) > 0.95

mis-id < 1%, p range: 22 – 55 GeV/c

M. Medinnis, DESY

K0s

V0 Selection

DCA < 0.7mm, Mild lifetime cut: ptc > .05

GeV/ccm, K/ ambiguities are rejected

~

M. Medinnis, DESY

- and (1520) Signals- (1520)

- recon: |mp-m| < 3, Cascade topology, z > 2.5cm

M. Medinnis, DESY

1.4 1.475 1.55 1.625 1.7

pK0s mass (GeV/c2) for -0.3< rapidity <

0.3

UL(95%): Carbon

pK0s mass, Upper Limit

mass=3.9 MeV/c2 @+

With N A0.7, UL(95%)Bd/dy|y=0 =3.7 b/N @ 1530GeV/c2

sensitivity

event mixing

M. Medinnis, DESY

1.4 1.8 2.2 2.6 Mass GeV/c2

Co

un

ts /

7.5

Me

V/c

2

Mass

1.4 1.6 1.8 2 2.2Mass GeV/c2

Co

un

ts /

3 M

eV

/c2

HERA-B NA49

--

-+

+-

++

(p + C)

C. Alt et al. PRL 92, 042003

20

10

10

6

M. Medinnis, DESY

Combined Plot, UL(95%)

Co

un

ts /

3 M

eV/c

2B

d/

dy

b/C

HERA-B NA49

Rapidity: -0.7 < y < 0.7

mass = 6.6 GeV/c2 @ 1862 MeV/c2

Assuming N A0.7,UL(95%) Bd/dy|y=0

= 2.5 b/N@ m(--) =1862 GeV/c2

--

M. Medinnis, DESY

Signal Statistics

Signal C Target All targets MeV/c2

NA49

K0s 2.2M 4.9M 4.9

440k / 210k 1.1M / 520k 1.6

(1520) 1.3k / 760 3.5k / 2.1k 2.3

- 4.7k / 3.4k 12k / 8.2k 2.6 1.6k / 550

(1530)0 610 / 380 1.4k / 940 2.9 (150*)

Particle / anti-particle, : mass resolution

*H.G.Fischer, S.Wenig hep-ex0401014

M. Medinnis, DESY

Summary I: + p K0s

Reaction sGeV

+

+ .

(1520)Source

pA, y0

42 <0.92 <2.7 HERA-B

pp, y=0 18 2.3 M. Bleicher et al.

pp 20/40 6.3/5.0 F.M. Liu et al.

pp 17 4.7 57 F. Becattini et al.

AA 20 3-10 50-200 J. Letessier et al.

AA 40 3-7 44-140 J. Letessier et al.

UL(95%) Bd/dy|y=0 = 3.7 b/N @ mpKs=1530 MeV

See hep-ex/0408048 for more details

Production ratios and comparison to predictions

(%) (%)

B(+ p K0s) 0.25

M. Medinnis, DESY

Summary II: --(1862) - -

Reaction sGeV

--

- -- .

(1530)0

Source

pA, y0

42 <3/B <4/B HERA-B

pp 20/40 2.5/3.6 F.M. Liu et al.

AA 20 0.4 --1 J. Letessier et al.

AA 40 0.4 -- 1 J. Letessier et al.

pp 17 18/B J. Kadija* (NA49)

See hep-ex/0408048 for more details

UL(95%) Bd/dy|y=0 = 2.5 b/N

*N(0) from hep-ex/0401014, --/ 0 eff ratio = HERA-B

(%) (%)

Production ratios and comparison to predictions, NA49