# Presentation: 657128

## Charmonium, open charm and beauty   production at HERA-B

**P****IETRO**** ****F****ACCIOLI****,  *****for the *****HERA-B *****Collaboration***
***Università di Bologna and INFN***

***Charmonium, open charm and beauty   production at HERA-B***

***June 14, 2006***
***Asilomar Conference Grounds,***
***Pacific Grove, California***

## HERA-B detector and physics topics
results and comparison with previous experiments

- results and comparison with previous experiments

***outline***

***heavier states and feeddown to J/******ψ***
***ψ*****′****/*****ψ*** and kinematics
- fraction of **J/*****ψ***’s from ***χ******c***

***J/******ψ****** production***
*p*T and *x*F distributions,  *A*-dependence

***new*****: *****decay angular distributions***

- fraction of **J/*****ψ***’s from ***b*** decays

***charm***
- inclusive *D*0, *D*+, *D**+ and ratios
*A*-dependence

*highest*
* **energy*
*among*
*fixed-target*
* **experiments*

*often unclear*
*experimental*
* **picture,*
*especially*
*for p-A*
* **collisions*

*test production models (pQCD + initial/final state interactions in nuclei)*

***largest***
***χ*****c**** *****statistics***
*analyzed in*
*hadron*
* **collisions*

*first data at* ***negative x*****F**

*observation of*
***low-p******T***** ****/*****|x*****F****|**
** *****effects***

## the HERA-B detector

- 0 m

- 20 m

**target wires**
**(C, Ti, W)**

**Magnet**

**Tracking**

_***good PID    ***_**(*****e******±*****, *****μ******±*****, *****π*****, *****K*****, *****p*****)**

**√****s = 41.6 GeV**
***A***** = 12 ÷ 184**

_***large acceptance***_
**(15-220 mrad)**

_***high resolution***_

- (top view)

**electrons**

_***fixed nuclear target***_

***the HERA-B detector***

***+ photon reconstruction***

**ECAL**

**MUON**

**RICH**

**920 GeV/*****c***** protons**

**Vertex Detector**

## physics at HERA-B

**J/*****ψ***,  ***χ*****c**, ***ψ******′***,               with *A*-dependence
***D*****o**** ********* ******μ******μ***** **(FCNC)
**inclusive *****b*** production
*********,     ************,    ******ρ******/******ω***

**dilepton trigger:**** ****~ 150·10****6**** events**

***ψ******′***

**J/*****ψ***

***ρ***/***ω***

******

******(1S)**

******(2-3S)**

*two independent channels* (***e******e***** + *****μ******μ***)

***physics at HERA-B***

***K*****s**,** *****K********,*** *****Λ**,** ********,** ****Ξ****+-**
- pentaquarks
***D*****o**,** *****D*****+**,** *****D******+**,** *****D******s***
**J/*****ψ***

**~ 210·10****6**** minimum bias events**

**‘****hard photon’ trigger:**** ****~ 35·10****6**** events**

**direct**
***γ******,***** *****π****** *****o****, *****η***
- production
- with four
- different
- nuclei

***e******e***

***μ******μ***

***μ******μ***

## ee

***J/******ψ****** and ******ψ′****** signals***

**entries/(25 MeV/*****c*****2****)**

***m*****(*****μ******μ*****)** [GeV/*c*2]

**10****3**

**10****4**

**2.8            3.2            3.6           4.0**

***m*****(*****e******e*****)** [GeV/*c*2]

**entries/(30 MeV/*****c*****2****)**

**10****3**

**10****4**

**2.5           3.0          3.5          4.0**

***~ *****120**** ****000 ****J/*****ψ***
*** ******~ *****2**** ****200 *****ψ′****** ***
***σ*****J/*****ψ****** ~ *****64 MeV**

***e******e***

***full dilepton data sample***** (3 target materials)**

**J/*****ψ***

***ψ′***

***μ******μ***

**J/*****ψ***

***ψ′***

***~ *****170**** ****000 ****J/*****ψ***
*** ******~ *****3**** ****000 *****ψ′****** ***
***σ*****J/*****ψ****** ~ *****44 MeV**

## J/ψ production kinematics: pT distribution

***preliminary data*** (_di-electron channel_). Compatible results from the di-muon data, not shown here.

- comparison with
*p*-*A* results
- at similar energy
- (√s = 38.8 GeV)

## xF distribution

***Preliminary data*** (***e******e***), compared with *p*-*A* results at 38.8 GeV

**first data centred at *****negative***** *****x*****F**

## xF

*x*F

- E866	38.8 GeV	Be/Fe/W
- E789	38.8 GeV	Be/C/Cu/W
- E772	38.8 GeV	H2/C/Ca/Fe/W
- NA50	29.1 GeV	Be/Al/Cu/Ag/W
- NA3	22.9 GeV	H2/Pt

******

- - R. Vogt, PRC 61 (2000) 035203, NP A700 (2002) 539
-  K.G. Boreskov & A.B. Kaidalov, JETPL **77 **(2003) 599

- B&K

- Vogt: final state absorption

- Models (with variants):

**HERA-B *****preliminary***
- (di-muon channel,
- carbon+tungsten
- double-wire runs)
- errors statistical only

## 1)

**J/****ψ**** direction** in the hadron (p-n) **CM frame**

**beam direction** in the J/ψ rest frame

- bisector between **beam and (–)target directions** in the J/ψ rest frame

- Collins-Soper (“**CS**”)

- Gottfried-Jackson (“GJ”)

- “**BEAM**”

- helicity “**HCM**”

**E615, E672-706, E771, E537, etc.**

**E866, NA3, etc.**

**CDF, NA60, etc.**

**Il Nuovo Cimento Vol. XXXIII, N. 2 (1964)**

**Phys. Rev. D16, 2219 (1977)**

**target direction** in the J/ψ rest frame = (-)J/ψ** **direction in the lab frame

**reformulated as**

- 2)

- 3)

## parametrization

- example:

- example:

***parametrization***

## φ ~ 

*********φ****** ******~ *********

- BEAM

- CS

- HB	41.6 GeV	*p*-C/Ti/W
- NA3	22.9 GeV	*p*-Pt/*p*-H2
- E615	21.8 GeV	π±-W
- 		*p**-*W**/**π**W
- E537	15.4 GeV 	*p**-*Be**/**π**Be
- 		*p**-*Cu**/**π**Cu

- /
- /
- /

- /

*********φ***

- HCM

## meaning of θφ 

***meaning of ************θφ****** ***

- The “natural” polarization frame has ********* ******θφ*** equal to zero: in such frame the decay distribution is symmetric and  is described by only two parameters.

- polar axis

- production plane

******** *****θφ***** ≠ 0** means that the axes of the current frame are not principal axes of symmetry for the angular distribution.
- But it is always possible to define a reference frame with this property: the angular distribution can always be diagonalized to a form with ** *θφ* = 0

## θφ in the three  frames

- BEAM   CS   HCM

- preliminary,

- The three frames actually see the decay kinematics from different perspectives
-                                            CS the best frame?

- (statistically ~100% correlated)

## >

*********θ****** and the hierarchy of  frames ***

- BEAM (arb. norm.)

- HCM
- (arb. norm.)

- CS

- preliminary

*dN*/*d*(cos*θ*)  1 + ***λ******θ*** cos2*θ*

**|***********θ*****|**

**|***********θ*****|**

**|***********θ*****|**

**>**

**>**

- HCM   BEAM   CS

*********θ***

## interpretation

- The data are consistent (for example) with a polarization
- generated **in the** **CS frame**

***interpretation***

- polarization generated in the CS frame

- ... and translated into the HCM frame

*********θ***

- points = data,
- lines = Toy MC

- generation in the HCM frame

- CS

- HCM  CS

*********θ***

- The CS frame is the best approximation of the “natural” polarization frame
-  physics: origin of J/*ψ* polarization

- No hypothesis of generation in the HCM fr. can reproduce the data in the CS fr.

- case 1

- case 2

## experimental situation: CS frame

- J/*ψ* significantly polarized at low momentum (low *p*T _*and*_ |*x*F|)

*********θ***

## BEAM frame

*********θ***

## HCM frame

- polarization almost completely smeared out, except for *p*T very close to zero

*********θ***

## ψ′-to-J/ψ production ratio

*p*-*A* results consistent within a 4% variation:
- no apparent dependence on production energy and kinematics (different *x*F/*y, *cos*θ* windows)
- slight dependence on the target nucleus: NA38/50/51 (+ E866)

- Analysis finished. Combined results (*e*+*e*- + *μ*+*μ*-):

## ψ′ kinematics

***ψ′****** kinematics***

- measured relative to the J/*ψ* distributions: *B′σ*(*ψ′*)/*Bσ*(J/*ψ*) as a function of *x*F. *p*T , cos*θ*

**HERA-B **(full stat, *e*+*e*-/*μ*+*μ*- avg.)

**E771** (38.8 GeV)

**NA50 **(29.1 GeV)

**E789 **(38.8 GeV)

***B′******σ***(***ψ′***)***/B******σ***(**J/*****ψ***)

## χc production

**fraction of J/*****ψ*****’s from *****χ******c***:
**kinematical distributions**
***A*****-dependence**

***χ******c****** production***

- selection:

- from the 2000 data, with
**370 ± 74 ** ***χ*****c****’s** (*μ**μ* + *e**e*):
*R*(******c**)** = 0.32 ± 0.06 ± 0.04**
- [Phys. Lett. B 561, 61 (2003)]

**new data: 40** **bigger *****χ*****c**** statistics**
- (the largest analyzed in a hadronic experiment)

***preliminary***
- 2002/2003 data
- (di-muon sample)

## R(χc)

***preliminary*** evaluation (2002/2003 data):

- based on 1300 *χ*c’s
- reconstructed in the di-muon channel
- (less than 10% of the total statistics)

**(21 ± 5)%** of the produced J/*ψ*’s come from *χ*c decays

## J/ψ’s  from  b decays

***pA***** ******** *****bb****** X***

***b***** ******** ****J/*****ψ***** *****Y***** ******** *****e*****+*****e*****-****/********+********-**** *****Y***

- detached J/*ψ*’s

***m*******

- - extrapolation to full xF range
- - normalization by total J/*ψ* cross sect.
- - correction by BR of *b*  J/*ψ*

***m******ee***

## indirect and direct J/ψ production

- E771

- E789

- ISR

- E672/706

- NA50

- E595  E288

- E705

- UA6

- E444

- E331

- NA3

- NA3

- E331

***indirect and direct J/ψ production***

**(21 ± 5)%**

**(7.0****±0.4)****%**

**(0.065****±0.011)****%**

- (to be improved!)

- extracted from MB data

**(72 ± 5)% of the J/*****ψ*****’s**
**are produced directly**** **

- Using partial/preliminary HERA-B results:

- curve: NLO NRQCD fit of all data
- (Maltoni *et al.*, hep-ph/0601203)

***p*****-*****p***

***p*****-*****A***

## open charm: reconstructed signals

***open charm: reconstructed signals***

**194 ± 20**

**preliminary**

**preliminary**

**preliminary**

**92 ± 11**

***D***±

***D****±

***m*****(*****K******π******π*****)-*****m*****(*****K******π*****) [GeV/c****2****]**

**entries/(0.5 MeV/c****2****)**

**49 ± 10**

## D cross sections

***D*****0**: unclear situation at **high √s**
- E789 result clearly disfavoured
**energy dependence** well described in each case by the function
- reflecting the behaviour of **proton PDFs** (Lourenço & Wöhri)

*comparison **with p-p/p-A results*

## cross section ratios: experiments vs. isospin symmetry

***cross section ratios: experiments vs. isospin symmetry***

*u*  *d*

- 3 polar. states

- PDG averages for *D**0, *D**±  *D*0, *D*± feeddown BRs

***violated***
*by a factor of*
**1.87 ± 0.25**

**isospin symmetry**

**experiments**

## A-dependence

***α*****AVG.****(*****x*****F****~0) =**** ****1.01 ± 0.03**

- experimental situation (***p-A***):

- mass spectra
- by target material
- (e.g. for ***D*****0**):

**entries/(10 MeV/c****2****)**

***K******π***** inv. mass (GeV/c****2****)**

**C**

**Ti**

**W**

**70 ± 11**

**19 ± 6**

**103 ± 14**

- consistent with
- no suppression

***α*****(*****D*****0****)= 0.92±0.08**
***α*****(*****D*****±****)= 1.02±0.09**
***α*****(*****D************±****)= 1.05±0.14**

## summary

***J/******ψ****** ******production *****in *****p*****-*****A***** collisions at √*****s***** = 41.6 GeV *****...***

***... ******and its components:***

- high statistics, clean signals, two decay channels
- wide kinematical coverage
*p*T up to 5.5 GeV/*c*
- negative* x*F
- A-dependence:
- flat suppression
- down to *x*F ~ -0.35

*ψ′*-to-J/*ψ* ratio
- fraction of J/*ψ’s* from* **χ**c*
- fraction of J/*ψ’s* from* b*

**300000 J/*****ψ***’s

**15000 *****χ******c***’s

**5000***** ******ψ*****′**’s

**80 J/*****ψ***’**s from b**

***J/******ψ****** decay ******angular distributions***

*D*0, *D*±, *D**± inclusive production cross sections and ratios
*A*-dependence consistent with *α* = 1

***open charm***

- longitudinal polarization rapidly increasing in magnitude with decreasing *p*T and |*x*F|
- strong hierarchy of frames: the direction of the original interaction (CS frame) is better than the J/*ψ* “flight” direction (HCM) as a reference for the observation of the “true” decay distribution