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Forum: Charmonium
Date: 01 Mar, 2014
From: Haiping Peng <Haiping Peng>

Dear all,
   Since Hypernews forum is delay due to the email problem, I post the message from Changzheng following what he have sent by email yesterday, Sorry for inconvenience

Cheers Haiping

For the charmonium topic, I think the search for D-wave spin-singlet eta_c2 can be a mode to show the photon detection ability.

One decay chain for this search is e+e- --> pi+pi-h_c(2P) [not observed yet] h_c(2P)--> gamma eta_c2 eta_c2-->gamma h_c h_c-->gamma eta_c eta_c-->KsK+pi-+c.c., K_s --> pi+pi-

As the h_c(2P) mass is unknown, we may take the calculation 
by Ted Barnes  (PRD 72, 054026 (2005)), 
   M=3934 MeV, width ~ 90 MeV
[another option is the mass is less than DD* threshold, and
the width will be very narrow, seems to me less probable]
the mass of the eta_c2 should be close to that of psi_2 state,
namely the X(3823). We may assume
   M=3823 MeV, width ~ 1 MeV

I only listed one mode for eta_c decays, in princile we can add more.

We donot know where is the best energy point to take data, I think we can start at the peak of psi(4415).

A simpler mode for the eta_c2 search is

psi(4415)-->gamma eta_c2 eta_c2-->gamma h_c h_c-->gamma eta_c eta_c-->KsK+pi-+c.c., K_s --> pi+pi-

[This decay chain may start from other charmonium or charmoniumlike states, such as psi(4160), Y(4260), Y(4360), and so on.]

Maybe this is a bit easier to simulate and analyze. We may expect some results for the March workshop.

Best regards,

Changzheng

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