BESIII status and preliminary results Xiaoyan SHEN (Representing BES Collaboration) Institute of High Energy Physics, Beijing XLVIII International Winter Meeting on Nuclear Physics Jan , 2010, Bormio, Italy

Outline Introduction Status of BESIII Preliminary results from BESIII Prospects

3 Linac Storage ring BES BSRF Beijing Electron Positron Collider (BEPC) at IHEP

4 BES 1-2.3GeV e+ e- collisions produce charmonium states （ J/  ，  (2S) ，  cJ and  (3770) etc.), charm mesons and  lepton. beam energy: 1.0 – 2.3(2.5) GeV Physics goal 4 （ BEPC/BES ）

We are unique now in  -charm region  In transition region between pQCD and non-pQCD. 5 The Y’s are here! From PDG Physics at BEPC/BES

6 BESI: run from BESII: run from L ~ 5  / cm 2  s at J/  E beam ~ 1 – 2.5 GeV BESII data samples DataBESIICLEOc J/  58 M--  (3668) 14 M27 M  (3770) 33 pb -1  580 pb -1

In the 1990s, there was discussion of the future. The conclusion was to continue tau-charm physics with a major upgrade of the accelerator and detector (BEPCII/BESIII). Officially approved in The physics window is precision charm physics and the search for new physics.  High statistics: high luminosity machine + high quality detector.  Small systematic error: high quality detector. BEPCII/BESIII

BEPCII Storage Ring: BEPCII Storage Ring: Double-ring Beam energy: GeV Luminosity: 1×10 33 cm -2 s -1 Optimum energy: 1.89 GeV Energy spread: 5.16 ×10 -4 No. of bunches: 93 Bunch length: 1.5 cm Total current: 0.91 A SR mode: 2.5 GeV

11  Study of Light hadron spectroscopy  search for non-qq or non-qqq states  meson spectroscopy  baryon spectroscopy  Study of the production and decay mechanisms of charmonium states: J/ ,  (2S),  C (1S),  C{0,1,2},  C (2S), h C ( 1 P 1 ),  (3770), etc. New Charmonium states above open charm threshold.  Precise measurement of R values,  mass,...  Precise measurement of CKM matrix  Search for DDbar mixing, CP violation, etc.. Physics Topics at BES arXiv:

New forms of hadrons  Hadrons consist of 2 or 3 quarks ： Naive Quark Model ：  QCD predicts the new forms of hadrons: Multi-quark states ： Number of quarks > ＝ 4 Hybrids ： qqg ， qqqg … Glueballs ： gg ， ggg … Meson （ q q ） Baryon （ q q q ）

13 Study of the spectroscopy – a way of understanding the internal structure glueball spectrum from LQCD Y. Chen et al., PRD 73 (2006) Motivation:  Establish spectrum of light hadrons  Search for non-conventional hadrons  Understand how hadrons are formed Why at a  -charm collider ?  Gluon rich  Clean environment, J PC filter Many results in BESII: ~ 50 publications Much more from BESIII:  100 statistics,  10  resolution

14 Study of Light hadron spectroscopy  Study of Light hadron spectroscopy  search for non-qqbar or non-qqq states  meson spectroscopy  baryon spectroscopy  Study of the production and decay mechanisms of charmonium states: J/ ,  (2S),  C (1S),  C{0,1,2},  C (2S), h C ( 1 P 1 ),  (3770), etc. New Charmonium states above open charm threshold.  Precise measurement of R values  Precise measurement of CKM matrix  Search for DDbar mixing, CP violation, etc.. Physics Topics at BES arXiv:

Charmonium physics What to study ?  Production, decays, transition, spectrum For what ?  A lab for pQCD and non-pQCD  Calibrate LQCD  How quarks form a hadron ? Why at a tau-charm collider ?  A clean environment  Tagging possible  Abundantly produced Examples of interesting/long standing issues:  puzzle Missing states ? Mixing states ? New states above open charm thre.(X,Y,Z,…)

16  Study of Light hadron spectroscopy  search for non-qqbar or non-qqq states  meson spectroscopy  baryon spectroscopy  Study of the production and decay mechanisms of charmonium states: J/ ,  (2S),  C (1S),  C{0,1,2},  C (2S), h C ( 1 P 1 ),  (3770), etc. New Charmonium states above open charm threshold.  Precise measurement of R values  Precise measurement of CKM matrix  Search for DDbar mixing, CP violation, etc.. Physics Topics at BES arXiv:

17 R : one of the most important and fundamental quantities in particle physics. R measurement Why precise R important? Essential for precise tests of SM.  the global fit of Higgs mass  anomalous  magnetic moment from g-2

18  Study of Light hadron spectroscopy  search for non-qqbar or non-qqq states  meson spectroscopy  baryon spectroscopy  Study of the production and decay mechanisms of charmonium states: J/ ,  (2S),  C (1S),  C{0,1,2},  C (2S), h C ( 1 P 1 ),  (3770), etc. New Charmonium states above open charm threshold.  Precise measurement of R values  Precise measurement of CKM matrix  Search for DDbar mixing, CP violation, etc.. Physics Topics at BES arXiv:

Precise measurement of CKM elements -- Test EW theory Precise measurement of CKM elements -- Test EW theory CKM matrix Three generations of quark? Unitary matrix?  5% precision  10% precision Expect precision < 2% at BESIIIImprove the precision at BESIII Precision measurement of CKM matrix elements --a precise test to SM model New physics beyond SM? Precision measurement of CKM matrix elements --a precise test to SM model New physics beyond SM? 19 CKM matrix elements are fundamental SM parameters that describe the mixing of quark fields due to weak interaction.

Decay constants vs LQCD 2.3  difference for f Ds. Real ? BESIII may resolve this issue, reach the precision of LQCD. fDfD f Ds

CP violation is regarded as the origin of asymmetry of the matter and anti-matter. CP violation predicted by theoretical models is not big enough to describe the asymmetry. CP violation is observed in K and B decays, but has never been in charm sector. CP violation and mixing 0 0 e + e -   (3770)  D 0 D 0 At BESIII, the sensitivity of the mixing rate: 1.5  mixing : a good place to search for CP violation In SM, the mixing is very small. 21

Mar. 2008: first full cosmic-ray event April 30, 2008: Move the BESIII to IP July 19, 2008: First e + e - collision event in BESIII Nov. 2008: ~ 14M  (2S) events collected April 14, 2009: ~100M  (2S) events collected May 30, 2009: ~42 pb -1 at continuum collected (3.65 GeV) July 28, 2009: ~200M J/  events collected Aug. – Dec., 2009: summer maintenance, SR run Jan. 12, 2009: started data taking at 3770 MeV Peak Nov. 2008: 1.2  cm -2 s -1 Peak May 2009: 3.2  cm -2 s -1 BESIII commissioning and data taking milestones

First collision event on July 19, 2008 e + e -   (3770)  D 0 D 0

Reso. 135  m σ P =11.0 MeV/c MDC performance & data/MC

Double-layer TOF Barrel Double Layer Z (cm) Time Resolution (ps) Time Resolution （ ps ） Design Target BhabhaDimu Barrel Single Layer 100~ Barrel Double Layer 80~ Endcap110~

EMC (CsI(Tl)) Barrel energy resolution energy resolution for Bhabha events Position resolution for Bhabha 4.4 mm energy deposit for e+e-  

EM transitions: inclusive photon spectrum  c2  c1  co  c1,2   J/  cc BESIII preliminary

June 12 – Jul. 28 Mar. 6 – April 14May 24 – June 2  100 M  (2S) data  200 M J/  data  45 pb -1 data at 3.65 GeV Data accumulated at BESIII

J/  ’’ World J/  and  ’ data samples

Preliminary BESIII results Confirm BESII results  threshold enhancement  ppbar, , X(1835), … New improved measurements  h c,  c,  cJ,, … New observations   cJ decays  h c decays  Light hadrons, … Only a few approved results will be shown here. Papers to be published starting from this year

h c at CLEOc

h c at BESIII

Observation of h c : E1-tagged  (2S)   0 h c,h c   c Select E1-photon to tag h c A fit of D-Gaussian signal+ sideband bkg. yield: M(h c ) Inc = ±0.16±0.10 MeV  (h c ) Inc = 0.89±0.57±0.23 MeV (First measurement) Br(  ’    h c )×Br(h c   c ) Inc =(4.69±0.48(stat)) ×10 -4 (  (h c ) floated) =(4.69±0.29(stat)) ×10 -4 (  (h c ) fixed at  (  c1 )) background subtracted Systematic errors under study CLEO’s results (arXiv v1) : M(h c ) Inc = ±0.23±0.15 MeV Br(  ’    h c )×Br(h c   h c ) Inc =(4.22±0.44±0.52) ×10 -4 (  (h c ) fixed at  (  c1 ) ~ 0.9MeV CLEOc: Combined E1-photon-tagged spectrum and exclusive analysis M(h c ) avg = ±0.19±0.12 MeV Br(  ’    h c )×Br(h c   h c ) avg =(4.19±0.32±0.45) ×10 -4 BESIII preliminary N(h c )= 2540±261  2 /d.o.f = 39.5/41.0

Observation of h c : Inclusive  (2S)   0 h c Select inclusive  0 A fit of D-Gaussian signal + 4 th Poly. bkg yield N(h c ) = 9233±935,  2 /d.o.f = 38.8/38.0 Combined inclusive and E1-photon-tagged spectrum Br(  ’    h c ) =(8.42±1.29(stat)) ×10 -4 (First measurement) Br(h c   c ) =(55.7±6.3(stat))% (First measurement) 35 background subtracted Inclusive   recoil mass spectrum Systematic errors under study BESIII preliminary

Study of  cJ at BESIII First measurement of  cJ   First measurement of  c1  ,  Precise measurement of  cJ   0  0, 

BR (10 -3 )  c0  c2 0000 BESIII3.25±0.03(stat)0.86±0.02(stat) PDG2. 43± ±0.08 CLEO-c2.94±0.07± ±0.03±0.08  BESIII3.1±0.1(stat)0.59±0.05(stat) PDG2.4±0.4<0.5 CLEO-c3.18±0.13± ±0.05±0.06 CLEO-c arxiv: Study of  (2S)→  0  0,  (  → ,  0 →  ) Interesting channels for glueball searches Based on  100M  (2S) BK study from 100M inclusive MC sample and 42pb -1 continuum sample Unbinned Maximum Likelihood fit:  Signal: PDF from MC signal  Background: 2 nd order Poly.  2S)   0  0 N  c ±175 N  c2 4149±82  2S)   N  c0 1541±56 N  c2 291±23

 cJ  

 cJ  

 cJ   Clear signal from doubly OZI suppressed decay  c0         (K + K - )  +  -  0 + 

mass threshold study in J/  and  ’ radiative decays Review of previous experimental results mass threshold study 

mass threshold study at BESII Observation of an anomalous enhancement near the threshold of mass spectrum M pp -2m p (GeV) theoretical speculation:  bound state (baryonium)  FSI effect  …… 43 BESII PRL 91 (2003)

No significant narrow strong enhancement near threshold (~2  if fitted with X(1860)) M pp (GeV) The narrow threshold enhancement is not observed in those channels 44 mass spectrum in other channels

mass spectrum and Dalitz plot at BESIII  Narrow threshold enhancement is evident in mass spectrum.  There is no obvious N* state. 45

Mass spectrum fitting result M pp -2m p (GeV) BESII M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL)  10  25 M=1865±5 MeV/c 2  < 33 MeV/c 2 (90% CL) PRL 91 (2003) BESIII preliminary

invariant mass spectrum at BESIII Significant narrow threshold enhancement exists 47

Fit result M pp -2m p (GeV) BESII BESIII preliminary M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL)  10  25

threshold mass spectrum in  ’ radiative decay M pp (GeV) BESII BESIII preliminary PRL 99 (2007) No significant narrow threshold enhancement No significant narrow strong enhancement near threshold (~2  if fitted with X(1860)) FSI interpretation of the narrow and strong threshold enhancement is disfavored.

Mass spectrum of from  Significant peak at M ~ 1835MeV  Statistic significance of X(1835) is about 18 σ BESIII preliminary

Mass spectrum of from  Significant peak at M ~ 1835MeV  Statistic significance of X(1835) is about 9 σ BESIII preliminary

Hadron 09 Mass spectrum fit BESII BESIII preliminary ??? Whether there are two new resonances, further careful study is needed.

Prospects: a bright future BESIII has resumed data taking after summer shutdown. ~4-5 months until next summer at 3770 MeV Expecting new and exciting results from new data

Backup slides

Drift chamber To measure the momentum of charged particles by their curvature in the magnetic field 7000 Signal wires: 25  m gold-plated tungsten Field wires: 110  m Al Gas: He + C 3 H 8 (60/40) Momentum Babar: ~ 110  m BELLE: ~ 130  m CLEO: ~ 110  m BESIII: ~ 130  m

BESIII CsI(Tl) crystal calorimeter To measure the energy of electromagnetic particles Barrel: 5280 crystals ， Endcap: 960 crystals Crystal: (5.2x 5.2 – 6.4 x 6.4) x 28cm 3 Readout: Photodiodes, 1cm  2cm, Energy range ： 20MeV – 2 GeV position resolution: 6 1GeV Tilt angle: theta ~ 1-3 o, phi ~ 1.5 o BELLE: CLEO: BESIII:

PID: TOF system Barrel: 2*88 BC408, 2.4 m long, 5cm thick Endcap ： 2* 48 BC 408 PMT: Hamamatzu R5942 Detectors length( cm) resolution BESIII ps CLEOII ps OBELIX ps BELLE25590~100 ps CDFII ps HARP ps

 system : RPC 9 layer, 2000 m 2 Special bakelite plate w/o lineseed oil 4cm strips, channels Noise less than 0.1 Hz/cm 2

61 Main parameters achieved in collision mode parametersdesignAchieved BERBPR Energy (GeV)1.89 Beam curr. (mA) Bunch curr. (mA)9.8>10 Bunch number93 RF voltage1.5   x * /  y * (m) 1.0/0.015~1.0/0.016 Inj. Rate (mA/min) 200 e   50 e + >200>50 Lum. (10 33 cm -2 s -1 )10.30

62 Statistics at BESIII at designed peak Luminosity (assuming 10 7 s data taking time each year) Physics Energy (GeV) Peak Luminosity (10 33 cm –2 s –1 ) Events/yearExisting data J/  × ×10 6 (BESII)  3.67(?) ×  ’ × ×10 6 (CLEOc) 14 ×10 6 (BESII) D ×10 6 5×10 6 (CLEOc) Ds ×10 6 4×10 3 (BESI) Ds × ×10 6 (CLEOc) R scan (?) A review (Yellow Book):  - charm physics at BES3 arXiv: