# Presentation: 460651

## Particle production and spectroscopy in ep collisions

- Roberval Walsh (McGill University)
*On behalf of H1 and ZEUS Collaborations*

***Low-x meeting***
*June 28 - July 1, 2006, Lisbon, Portugal*

## Outline

- Introduction
- Charm fragmentation: ratios, fractions & functions
- Strange production: K0S,  production, ratios...
- Search for pentaquarks_x0013_
- Summary

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation ratios and fractions

- Are the charm fragmentation characteristics universal?

- Are u- & d-quarks produced equally?

- What are the fractions of c-quarks hadronising in a charm hadron?

- Is the fraction of  D mesons produced in a vector state in accordance with spin counting (=0.75)?

- What is s-quark production suppression?

**Charm hadrons cross sections needed to extract the ratios and fractions.**

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm hadrons reconstruction in DIS

_**Event selection**_
** ****1.5 < Q****2**** < 1000 GeV****2**
** ****0.02 < y < 0.7**
** ****p****T****(D,********c****) > 3 GeV**
** ****|********(D,********c****)| < 1.6**
** **L** = 81.7 (65.0) pb****-1**, 1998-2000 (1998-1999, for D+ and c due to trigger availability)

- Charm mesons D0, D*±, D±, Ds± and the c± baryons are reconstructed in deep inelastic scattering at HERA with the **ZEUS** detector from the following decay modes:

** ****D****0**** ******** K****- ********+**
** ****D*****+ ******** D****0 ********+**** ******** K****- ********+ ********+**
** ****D****+ ****_x0016_******** K****- ********+ ********+**
** ****D****s****+ ****_x0016_******** ******** ********+ ******** K****- ****K****+ ********+**
** ********c****+ ******** K****- ****p**** ********+**
**(+ c.c.)**

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm hadrons reconstruction in DIS

- D0 and D* signals are splited in independent samples:
-  D0 not coming from D* (D0(untag))
-  D0 from D* (D0(tag))
-  “Additional” D*

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm hadrons reconstruction in DIS

- Clear signals from D+ and Ds+, but not for c.

**D****s****+**

******c****+**

**D****+**

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation ratios

**ZEUS preliminary results**

*(Large systematic error from D**0**(untag) signal extraction procedure, this has consequences in the other measurements.)*

*Measured P**V**d** is smaller than spin-counting prediction P**V**d**=0.75*

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation fractions

- Rates fromc0,± and c0 are estimated from non-charm  and  states to be 14±5% of c rate.

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation fractions

**ZEUS preliminary results**

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation functions (H1)

- Event selection
-  D*+  D0+  K-++
-   2 < Q2 < 100 GeV2; 0.05 < y < 0.7
-  pT (D*) > 1.5 GeV; |(D*)| < 1.5

- Hemisphere method:
- In p-frame cc pair is balanced in pT

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation functions (H1)

- Peterson = 0.018 + 0.004- 0.003

- Kartvelishvili = 5.9 + 0.7 - 0.6

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation functions (ZEUS)

- Event selection
-  D*+  D0+  K-++
-   Q2 < 1 GeV2; 130 < W < 280GeV
-  pT (D*) > 2 GeV; |(D*)| < 1.5
-  ETjet > 9 GeV; |jet| < 2.4

- Jet method: Energy of c-quark is approximated by the energy of the D* jet

- Peterson = 0.064 ± 0.006 +0.011-0.008

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Charm fragmentation functions

- ZEUS and H1 comparison with other experiments

-  Different extraction methods and different scales involved, reasonable agreement between charm fragmentation function from different processes.

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Strange production at HERA

- Strangeness is largely produced at HERA providing a rich environment to study the fragmentation process by investigating production rates, relative yields, polarizations...

- Clean background and high statistics

- Measurements performed in the following phase spaces:
-  Photoproduction, at least 2 jets
-  DIS 5 < Q2 < 25 GeV2
-  DIS Q2 > 25 GeV2
- For the three sets:
-  0.6 < pT(K0s,) < 2.5_x0013_ GeV
-  |(K0s,)| < 1.2

- Reconstruction of K0s and 

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## K0s production

- DIS(5 < Q2 < 25 GeV2)

-  In general, Ariadne describes reasonably well the data (s=0.3).
-  But for lower pT, s=0.22 describes better the data.
-  Lepto does not reproduce the data.
-  Pythia also fails to reproduce the data in PHP.

- DIS(Q2 > 25 GeV2)

- Q2 (GeV2)

- Photoproduction

- LAB

- LAB

- pTLAB (GeV)

- pTLAB (GeV)

- pTLAB (GeV)

- LAB

- xOBS

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

##  and  production

-  Similar situation as in the K0s analysis.
-  Adjusting a single parameter, s, is not sufficient enough to describe the data simultaneously.

**__**

- Photoproduction

- DIS(5 < Q2 < 25 GeV2)

- DIS(Q2 > 25 GeV2)

- Q2 (GeV2)

- LAB

- LAB

- pTLAB (GeV)

- pTLAB (GeV)

- pTLAB (GeV)

- LAB

- xOBS

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

##  to  asymmetry

****** ****to ******** asymmetry**

-  Results consistent with no asymmetry.
-  Production of both baryons should follow the same mechanism.
-  Influence from the initial proton should be small.

**__**

- Photoproduction

- Q2 (GeV2)

- LAB

- pTLAB (GeV)

- xOBS

- LAB

- pTLAB (GeV)

- xBJ

- DIS (Q2 > 25 GeV2)

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Baryon to meson ratio

**Baryon to meson ratio**

-  Ariadne predicts R well in DIS, whereas in PHP Pythia underestimates R.
-  R ~ 0.4 for both direct PHP and low Q2 DIS
-  R increases up to ~0.7 for lower values of x, where resolved PHP is dominant.

**R between ~0.3-0.4**

**R up to ~0.7!**

- Photoproduction

- xOBS

- LAB

- pTLAB (GeV)

- Q2 (GeV2)

- xBJ

- xBJ

- DIS(5 < Q2 < 25 GeV2)

- DIS(Q2 > 25 GeV2)

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Search for strange pentaquarks (ZEUS)

**Search for strange pentaquarks (ZEUS)**

- _Search for __****_**+**  K0sp - clear signal observed
-  Q2 > 20 GeV2, 0.04 < y < 0.95
-  pT(K0sp) > 0.5 GeV, |(K0sp)| < 1.5
-  p(p) < 1.5 GeV, p selection with dE/dx
-  221±48 events
-  M(+) = 1521.5±1.5+2.8-1.7 MeV
-  width = 6.1±1.6 MeV

- Cross sections (ZEUS preliminary)
- (epe+XeK0spX)=		**125 ± 27 ****+36****-28 ****pb**
- (+)/() = **4.2 ± 0.9 ****+1.2****-0.9 ****%**

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Search for strange pentaquarks (H1)

- _Search for __****_**+**  K0sp - NO signal observed by H1
-  5 < Q2 < 100 GeV2, 0.1 < y < 0.6
-  pT(K0sp) > 0.5 GeV, |(K0sp)| < 1.5

**ZEUS signal**

**ZEUS signal**

**ZEUS signal**

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Search for strange pentaquarks (H1)

**Search for strange pentaquarks (H1)**

- _Search for __****_**+**  K0sp
- Applying an upper cut in the momentum of the proton for comparison with ZEUS
-  p(p) < 1.5 GeV
-  20 < Q2 < 100 GeV2
-  notice different y ranges
-  0.1 < y < 0.6 (H1)
-  0.04 < y < 0.95 (ZEUS)

**ZEUS signal**

- No + signal obeserved!
- Cross section upper limit @ 95% CL:
- 	(M=1.52 GeV) < 72 pb

- (ZEUS preliminary)(epe+XeK0spX) = 125 ± 27 +36-28pb

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Search for strange pentaquarks (ZEUS)

**Search for strange pentaquarks (ZEUS)**

- _Search for __****_**--**  - -

- No -- signal observed!
- Upper limit @ 95% CL:
- 	N(--)/N(0(1530)) < 0.29

- Signal observed by NA49:mass = 1862 MeVwidth < 18 MeV
- Searches from other experiments give negative results

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Search for charm pentaquarks (H1)

**Search for charm pentaquarks (H1)**

- _Search for __****_**c**  D*p
-  DIS: 1 < Q2 < 100 GeV2; 0.05 < y < 0.7
-  p: Q2 < 1 GeV2; 0.2 < y < 0.8
-  D* reconstructed from the decay mode: D*+  D0+  K-++
-  protons selected using dE/dx measurements

-  Mass = 3099 ± 3 ± 5 MeV
-  Width = 12 ± 3 MeV
-  50.6±11.2 events(5.4: background fluctuation probability of 4x10-8 (poissonian) converted to gaussian sigmas)

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Search for charm pentaquarks (H1)

**Search for charm pentaquarks (H1)**

- _Search for __****_**c**  D*p
-  Acceptance corrected ratio D*p/D* for1 < Q2 < 100 GeV2 (preliminary)**R****cor****(D*p/D*) = 1.59 ± 0.33 ****+0.33****-0.45****%**** **
-  Differential cross sections in DIS
-  D*p suppressed close to the central rapidity regions compared to inclusive D*.
-  D*p fragmentation function is hard as expected for a charm hadron of such mass. Hadronization function of D* from D*p is softer than inclusive D*.

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Search for charm pentaquarks (ZEUS)

**Search for charm pentaquarks (ZEUS)**

- _Search for __****_**c**  D*p
-  p and DIS
-  D* reconstructed from the decay modes: D*+  D0+  K-++ and K-++-+

- p & DIS

- DIS

- “H1 selection criteria”

**No signal observed!**

- Shaded histogram is MC signal normalized to 1% of the inclusive D*

**R****cor****(D*p/D*) < 0.59 % @95% CL**(DIS, K2 mode)

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Summary

- The charm fragmentation ratios and fractions were measured in deep inelastic scattering at HERA and results are consistent with universality.
- Charm fragmentation functions are measured. Reasonable agreement from different processes.
- K0s, ,  production at HERA
- Differential cross sections were measured in DIS and PHP. Data is reasonably well reproduced by Ariadne in DIS, where as Pythia fails to reproduce PHP.
-  to  production consistent with no asymmetry in the given phase space.
- Baryon to meson production ratio show an enhancement in resolved PHP. This is not predicted by Pythia.

**__**

**__**

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh

## Summary

- Strange pentaquark searches
- Narrow state K0sp observed by ZEUS at 1520 MeV.(epe+XeK0spX) = 125 ± 27 +36-28pbNot seen by H1.
- ZEUS does not observe --  --, seen by NA49.
- Charm pentaquark searches
- Narrow state D*p observed by H1 at 3099 MeV.Rcor(D*p/D*) = 1.59 ± 0.33 +0.33-0.45% (in DIS)Not seen by ZEUS.

- Low-x meeting, June 28 - July 1, 2006, Lisbon, Portugal

- R. Walsh